Thesis master 01 - 11.doc

7/23/2019 Thesis master 01 - 11.doc

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Functionalization of Carbohydrates

on the Macro-, Nano-, and Molecular Scale

by

Wei Chung Chen

A thesis submitted to McGill University in partialfulfillment of the requirements for the degree of

Doctor of Philosophy

Department of Chemistry

McGill University

Montreal, Quebec

Canada

Wei Chung Chen, !"# $eptember !"#


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Abstract

%he main ob&ective of the present thesis is to modify and to study carbohydrates in orderto ma'e use of their surface properties in bul', on the nano and molecular scale( %oachieve this goal, several strategies )ere e*plored( +n the case of bul' cellulose, the

silylationof )ood pulp by gasphase reaction )ith trichloromethylsilane -%CM$.produced a material that )e call Cellufoam( +n this silylationreaction, the hydro*yl -/0. groups of cellulose are silylated, )hich suppresses cellulose1s affinity for )ater(With a )ater drop contact angle of "#!2, the surface can be described assuperhydrophobic( 3y forcing )ater into Cellufoam1s fibre lumen and pressing the pulpinto a handsheet, the material )as sho)n to e*pand upon drying( %his is the result of theinterplay bet)een capillary force and the force of elastic rebound( After each cycle of useand re)etting, this drye*pansion property became less pronounced( %he reduction inperformance is e*plained by the e*posure of hydro*yl -/0. groups caused bymechanical damage after each cycle( /n the nanoscale, cellulose nanocrystals -C4C.)ere modified to stabili5e heterogeneous metalin)ater mi*tures( $ilver nanoparticles

-Ag46. )ere both synthesi5ed and stabili5ed by the use of cationic cellulose nanocrystals-cC4C.( +t )as sho)n that chloride and silver ions in solution can only yield silverchloride in the presence of C4C( 0o)ever, by using cC4C, )here each particle issmaller and e*poses more surface area, Ag46 )as produced due to the larger presence of7/0 groups( +n this )or', it )as determined that reducing ends -C8/. and 7/0 groupsare both capable of forming Ag46( %herefore, it can be proposed that reducing sugars arenot the only types of sugars )ith the ability to reduce metal ions( As a continuation of theAg46 study, sucrose, a nonreducing sugar, )as e*plored as a reducing agent andstabili5er for the gro)th of Ag46( A stable colloidal suspension )as formed )ithoutheating on the order of hours( 3y highresolution %9M, a coreshell structure )asobserved in )hich the core is single crystal silver and the shell is composed of sucrosebased on elemental analysis( +n comparison, arabinose and galactose also formed silvercolloidal suspensions, but these suspensions )ere less stable because their shells )eremuch thinner( %he greater stability of the sucrose Ag46 suspension also causes theformation of a silver mirror on the surface of the glass vial( Under the same condition,silver colloidal suspensions stabili5ed by reducing sugars succumbed to sedimentation( +nthis thesis, it is sho)n that carbohydrates in their various forms possess very differentproperties depending on their numerous functional groups( 3y silylation, cationi5ation,and the presence of aldehyde reducing ends, these materials can be madesuperhydrophobic, stabili5e metal nanoparticles, and form silver coreshell structures(

ii


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!su"!

:;ob&ectif principal de la pr


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Fore#ord

+n addition to the introduction and conclusion chapters, this thesis includes five papers(

Chapters , , E, and # each comprise one manuscript and appendi* ++is an abridged and

modified version of a manuscript( As of $eptember, !"#, three papers have been

published and t)o are currently under revie)F

Chapter F %e&ado A( Chen W(C( Alam M(4( van de Hen, %(G(M( $%&'()$uperhydrophobic foamli'e cellulose made of hydrophobi5ed cellulose fibres, Cellulose," -., "I#7"IE(

Chapter F Chen, W(C( %e&ado, A( Alam, M(4( van de Hen, %(G(M( $%&'*)0ydrophobic CelluloseF A Material %hat 9*pands Upon Drying, !"#, Cellulose, -E.,

"I#7"IE(Chapter EF Chen, W(C( Jang, 0( van de Hen, %(G(M( $%&'*)Cationic Cellulose4anocrystal Assisted Keduction of $ilver-+. to $ilver 4anoparticles, submitted to3iomacromolecules, Manuscript +DF bm!"#!"!E#)(

Chapter #F Chen, W(C( van de Hen, %(G(M( $%&'*)$ynthesis and $tabili5ation of $ilver4anoparticles With Carbohydrate $hells, submitted to Carbohydr( Kes(, Manuscript +DFCAKD"#!!#L

Appendi*F aushi', M( Chen, W(C( van de Hen, %(G(M( Moores, A($%&'()+magingCellulose 4anocrystals by %ransmission 9lectron $pectroscopy, 4ordic 6ulp and 6aperKes( N(, O -"., IIPE( -+nvited contribution to the special issue on 4anocellulose.

Contribution of Authors

All of the papers )ere coauthored by Dr( %heo van de Hen, the supervisor of this 6h(D(

pro&ect( All $9M and %9M microscopy found in this dissertation )ere performed )ith

the assistance of Dr( David:iu at the acility for 9lectron Microscopy Kesearch

-9MK.( %he full manuscript of the )or' sho)n in the Appendi* can be found in Madhu

aushi';s dissertation( /ther than the supervision and direction of Dr( van de Hen, all of

the )or' presented in this dissertation )as performed by the author(

iv


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Ac+no#ledge"ents

irstly, + )ould li'e to than' my supervisor, Dr( %heo van de Hen for his guidance in my

research over the past four and a half years( %his 6h(D( pro&ect )as great learning

e*perience than's to the valuable advice and dedication that he has given me( + especially

feel a need to ac'no)ledge Dr( van de Hen;s patience in sharing his 'no)ledge and

scientific e*pertise )ith me(

Although her name is not mentioned in the remainder of this dissertation, a ma&or

contributor to my )or' is anny, )ho has been )ith me for the entirety of my post

secondary education( Without her encouragement or support, this )or' )ould not have

been possible( + need to than' her a second time for translating my abstract to rench,

given her e*pertise as a translator(

+ )ould also li'e to than'F

Alvaro %e&ado, for his patience in )or'ing )ith me( 0is original )or' has helped us in

publishing t)o papers(

George Ki5is, from )hom + have learned all of my laboratory s'ills and from )hom +

have learned about improving my relationships )ith people at the )or'place(

All members of Dr( van de Hen;s group, past and presentF Amir A(, Amir $(, De5hi,

Goeun, 0an, evin, :eila, 4ur, and $alman(

Colleen and :ouis, for all of the help that they have provided me on this &ourney, )hich

are far too many to enumerate(

Chantal Marotte and other departmental staff( %heir help is very much appreciated(

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able of contentAbstract((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((iiK


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E((( 6reparation of cationic cellulose nanocrystals -cC4C.((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((#OE((E( Ag46 formation((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((#OE((#( Analysis((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((L!E(E( Kesults and discussion(((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((L"E(#( Mechanism((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((LLE(L( Conclusion(((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((LOE(I( Keferences(((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((I!3ridging section bet)een chapters E and #((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((IChapter #F(((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((I#("( Abstract((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((I#(( +ntroduction(((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((IE#(( Materials and methods(((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((I##(("( Materials(((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((I##((( Methods and characteri5ation techniques(((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((I##((( Ag46 formation((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((I##((E( Analysis((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((I##(E( Kesults and discussion(((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((IL#(#( Conclusion(((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((P#(L( Keferences(((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((PEL( Conclusions, contributions, and suggestions for future )or'((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((P#

L("( Conclusions and contributions to original 'no)ledge((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((P#L("("( $uperhydrophobic cellulose handsheets(((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((PLL("(( $uperhydrophobic cellulose handsheetF A material that e*pands upon drying((((((((((((((((((((((((((((((((((((PPL("(( Cationic cellulose nanocrystal assisted reduction of silver cations to silver nanoparticles(((((((((((((((((POL("(E( $ynthesis and stabili5ation of silver nanoparticles )ith carbohydrate shells(((((((((((((((((((((((((((((((((((((((O"L("(#( $uggestions for future )or'(((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((O3ridge to the appendi*((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((OEAppendi* +((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((O#A+"( UHH+$ spectroscopy((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((O#A+( Rray diffraction((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((OIA+( 9lectron diffraction(((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((("!!A+E( Rray photospectroscopy -R6$.(((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((("!"A+#( 9nergydispersive Rray photospectroscopy -9DR.((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((("!

A++L( Conductometric titration(((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((("!Appendi* ++F(((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((("!IA++"( Abstract((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((("!IA++( +ntroduction(((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((("!PA++( Materials and methods((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((""!A++("( Materials and equipment(((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((""!A++(( 6reparation of C4C for neverdried samples(((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((("""A++(( $amples preparation for %9M imaging((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((("""A++(E( $ynthesis of 6d nanoparticles onto C4Cs -6d46sSC4Cs.(((((((((((((((((((((((((((((((((((((((((((((((((((((((((""A++(#( :o) dose and high resolution transmission electron microscopy(((((((((((((((((((((((((((((((((((((((((((((((((""A++E( Kesults((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((""A++E("( /ptimi5ation of dispersion conditions for %9M imagingF p0 and grid type((((((((((((((((((((((((((((((((""A++E(( %he impact of C4C drying history on %9M imaging(((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((""L

A++E(( Comparison of %9M images of C4Cs under high resolution and lo) dose microscopy(((((((((((((""A++E(E( Morphology of modifiedTdecorated C4Cs )ith palladium nanoparticles((((((((((((((((((((((((((((((((((((""A++#( Discussion(((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((("A++L( Conclusions(((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((("#A++I( Keferences(((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((("L

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ist of figures

ig( "("( %he equilibrium structures of glucose, an aldohe*ose((((((((((((((((((((((((((((((((((#ig( "(( Wood fibres split into various component partsF nanofibrils -E"! nm.,

protofibrils -"!! m., microfibrils -#!"!! m., and )ood stem - m.( ( ((Lig( "(( Crosssection sho)ing the deformation of a fibre caused by nanofibril

coalescence sho)n )ith microfibrillation after refining((((((((((((((((((((((((((((((((((((Lig( "(E( %he amorphous regions of cellulose chains can undergo preferentialhydrolysis, )hich results in the isolation of cellulose nanocrystals -C4C.((((((""

ig( "(#( %he straight chain and the pyranose form of VDglucose )ith carbonpositions mar'ed(((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((("

ig( "(L( $chematic of a dead 9( coli bacterium )ith its cell )all and D4A damagedby silver granules formed from silver nanoparticles((((((((((((((((((((((((((((((((((((((((("#

ig( ("( $chematic illustration of t)o cellulose fibres crossing each otherperpendicularly )ith )ater and ethanol represented by blue areasF drying from)ater -top. causes shrin'age of the fibres due primarily to collapse of thelumen, )hile drying from ethanol -bottom. preserves the open11 fibre

structure(((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((ig( (( 9*perimental setup for the reaction of cellulose )ith %CM$( %he reactionvessel and %CM$ )ere preheated in a L#XC oven( A mesh bas'et containing thepulp sample )as introduced and held firmly in place by a rubber stopper insidethe vessel( %he sample )as reintroduced into the oven and the gasphase %CM$)as made to react )ith the sample((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((I

ig( (( -:eft. Wilhelmy balance setup and equation used, )here Y is the surfacetension -right. a table sho)ing the apparent foam density of )ood pulp driedfrom various solvents and their surface tension above the critical micelleconcentration -cmc.( $: -cmc 8 !(P )tZ., Do)fa* A" -cmc 8 !(!!I )tZ.,and %riton RE# -cmc 8 !(!"L )tZ.(((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((O

ig( (E( D images of individual fibres obtained )ith $'yscan ""I Micro C% RKay tomographyF a. after being dried from )ater and b. from a lo) surfacetension solvent -ethanol.( c. ibre si5e distribution of b06 fiber in )aterbefore drying obtained by using 0iKes fiber quality analy5er -QA.((((((((((((((!

ig( (#( $9M images of b06[cellulose fibers of a dried from )ater, b dried fromethanol, c crosssectional vie) dried from )ater and d crosssectional vie)dried from ethanol((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((!

ig( (L( A plot of the surface tension )ith respect to surfactant concentration in thiscase, %riton RE# is used and has a 'no)n surface tension of O m4Tm((((((((((("

ig( (I( $9M images of QO! nonbeaten cellulose fibers a. dried from )ater, b.dried from anionic surfactant, c. crosssectional vie) dried from )ater and d.crosssectional vie) dried from anionic surfactant(((((((((((((((((((((((((((((((((((((((((((

ig( (P( %CM$ adsorption as a function of reaction time also sho)n is the coverageassuming a surface area of "! mTg of 'raft pulp -Alince \ van de Hen, "OOI.

ig( (O( Water droplet on the surface of Cellufoam captured by a CCD camera(((((Eig( ("!( Unmodified hydrophilic -left. and %CM$hydrophobi5ed -right. cellulose

fibres in contact )ith a drop of )ater( 0ydrophilic fibers are dra)n into the)ater drop( /nly a sufficiently hydrophobic fiber remains at the )ater7 airinterface and sho)s 5ero engulfment((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((L

viii


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ig( ("( %he drye*pansion of sheets made from "!! Z soft)ood cellulose fibres( A)et handsheet is pressed and placed onto a glass slide( +mages of its crosssection )ere ta'en before drying -solid content of #! Z, left. and after drying-solid content of "!! Z, right.(((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((EL

ig( (( 9ach subsequent cycle results in progressively thic'er )et handsheets due

to flocculation that also causes a decrease in relative e*pansion )hen dry thecontact angle also decreases implying that the material becomes less and lesshydrophobic -the QO! pulp sample used in this figure is a different batch fromthe QO! sample of ig( (".(((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((EI

ig( (( %he drye*pansion of Cellufoam )hen drying during the first cycle -a. andsolid content of Cellufoam as a function of drying time -b.((((((((((((((((((((((((((((((EP

ig( (E( %he proposed mechanism for the e*pansion of Cellufoam upon drying theillustration of the lumen and fibre )all is not dra)n to scale and fibre crosssections are not necessarily tubular(((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((EP

ig( (#( %he relationship bet)een the tensile inde* and solids content for handsheetsmade from fibres of various lengths and curl indicesF hard)ood -06. is

mainly short fibres of lo) curl inde* and soft)ood -4D$6 and QO!. are longfibres of high curl inde*(((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((#!ig( E("( %he reaction scheme of C4C )ith QUA3 "#" -a quaternary ammonium

epo*ide. to produce cC4C and Ag46(((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((#Pig( E(( Conductometric titration curve of Ag4/)ith cC4C an equivalence point

at I(" m: -using a !(!" M standard., cC4C -#! m:, !(Z )T) suspension. )ascalculated to contain !(EI mmolTg of cationic charge groups(((((((((((((((((((((((((((L!

ig( E(( AM tapping mode image of unmodified C4C -left. and cC4C -right. theheight profile distribution of the t)o samples is plotted as t)o separatehistograms -bottom.(((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((L"

ig( E(E( %he particle si5e distribution of Ag46 from over "! %9M images -right. ane*ample of %9M imaging )here Ag46 is depicted as dar' spheres(((((((((((((((((L

ig( E(#( -:eft. %he RKD patterns ofF ". cationic )ood pulp and AgCl . C4C andAgCl . cC4C )ith Ag46 -Kight. %he ! reflection of Ag46 is sho)n forsample (((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((LE

ig( E(L( %he 9DR elemental analysis spectrum of silver nanoparticles vie)ed using%9M at !!'H the Ag pea's are prominent, but the Cl pea's are )ea' andslightly overlapped by secondary Ag pea's this technique is paired )ith R6$for a complete analysis((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((LL

ig( E(I( %he R6$ spectra of Ag46 -)ith point moving average. from cationiccellulose assisted reduction compared to a silver chloride standard -left andmiddle. the CC and C/ pea's are also compared before and after etching ofthe surface by using Ar] gas(((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((LL

ig( #("( %he UHH+$ spectra of # different carbohydrates )ith their most intensepea's sho)n at appro*imately E#! nm((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((II

ig( #(( %he reduction of silver cations to Ag46 using galactose -reducing sugar.proceeds on the order of minutes -A. and rapidly sediments after "! minutesthe reduction using sucrose -nonreducing sugar. proceeds on the order ofhours -3. and did not sediment((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((IP

i*


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ig( #(( A coreshell structure of Ag46 and carbohydrates is seen by high resolution%9M using galactose -A. and sucrose -C. a lo)resolution image of the samesystems reveal no coreshell structure )hen using galactose -3., though a faintshell can be seen in the case of sucrose -D. given the added thic'ness((((((((((((P!

ig( #(E( 0ighresolution %9M of Coreshell structures for higher molecular )eight

carbohydratesF agarose -A. and chitosan -3.(((((((((((((((((((((((((((((((((((((((((((((((((((((P"ig( #(#( %he 9DR spectra of Ag46 stabilised by various carbohydrates )ith theelectron beam aimed at the silver core -A. and the sugar shell -3.(((((((((((((((((((P"

ig( #(L( 9lectron diffraction pattern of the silver core -!. -A. and the amorphoussugar shell -3. the diffraction patterns for all samples )ere closely similarthese images )ere obtained using galactose stabilised Ag46(((((((((((((((((((((((((((P

ig( A+"( %he contribution of absorption and scattering to the e*tinction -left. theformation of a plasmonic dipole in spherical nanoparticles as determined bycomputation -right. the colours of the dipole -right. indicate the electric fieldenhancement )here the middle slice e*hibits ma*imal enhancement((((((((((((((OL

ig( A+( %he crystal spacing -d. as )ell as the ^ angle are illustrated(((((((((((((((((OP

ig( A+( %he top, middle, and lo)er ro)s represent the cubic -sc., the bodycentric cubic -bcc., and the facecentric cubic -fcc., respectively(((((((((((((((((((((OOig( A+E( A diagram illustrating the )or'ing principles of electron diffraction((("!"ig( A+#( %he )or'ing principle of R6$((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((("!"ig( A+L( 9DR )or's by e&ecting core electrons and detecting the Rrays emitted

by the transition of electrons from high energy levels to fill these electron holes((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((("!

ig( A+I 7 %he plot on the left sho)s the p0 versus titrant volume titration curvethe plot on the right sho)s the conductivity versus titration volume titrationcurve )here three distinct regions are represented by different slopes((((((((((("!E

ig( A+P 7 %he slope of the strong acid is al)ays steeper than that of the )ea' acidthe )ea' acid can have a positive or negative slope depending on its acidconstant e*cess base is characteri5ed by a significant rise in conductivity(((("!#

ig( A++"( 4everdried sample on carbon gridF -left. at p0 #L -right. at p0 (#""#ig( A++( 4everdried C4Cs at p0 #LF on formvar grid -left. silicon mono*ide

grid -right.((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((""#ig( A++( :ength and )idth distribution of C4Cs bundlesTrod of neverdried

C4Cs at p0 (# on different type of grids, based on the counting of !!particles on each type of grid(((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((""L

ig( A++E( %ypes of C4Cs at p0 #L, carbon gridF neverdried C4Cs -left. free5edried C4Cs -middle. spraydried C4Cs -right.(((((((((((((((((((((((((((((((((((((((((((((""P

ig( A++#( $praydried C4Cs -at p0 #L. onto a formvar grid -left., carbon grid-middle. and silicon mono*ide -right.(((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((""O

ig( A++L( ree5edried C4Cs -p0 #L and carbon grid.F high resolution %9M -top.and lo) dose %9M -bottom.((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((""O

ig( A++I( %9M image of modified C4Cs, 6d46sSC4Cs(((((((((((((((((((((((((((((((((("ig( A++P( 0istograms of C4Cs single rods length -top. and )idth -bottom.

measured on "!!! particles for neverdried particles on carbon grids at (# p0(((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((("E

*


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Chapter '

'.'. /eneral 01er1ie#

+n materials science, cellulose;s abundance, rene)ability, and biodegradability have given

researchers many reasons to study this natural biopolymer to e*ploit and to improve upon

its properties( With the everincreasing need for developing materials in a sustainable

manner, cellulose has often been considered for its properties in many industries( As a

highly abundant ra) material produced by plants, bacteria, and sealife, various forms of

carbohydrates and cellulose are readily available in many regions of the )orld( or this

reason, research groups have demonstrated interest in modifying and studyingcarbohydrates of different molecular )eightsin order to implement them for a )ide

variety of novel uses( As part of the Green ibre 4et)or', funding from 4atural $ciences

and 9ngineering Council of Canada -4$9KC. and the 6+nnovations industrial research

chair has allo)ed for this research pro&ect to be conducted(

'.'.'. hesis 0b2ecti1e

%he present thesis describesthe chemical modification of carbohydrates on the macro,

the nano, and the molecular scale to change its interaction either )ith )ater or in

heterogeneous systems( %he ob&ective of this )or' is to use saccharides to improve the

properties of various macro and nanosi5ed systems( /n the macroscale, the prevention of

lumen collapse in cellulose handsheets during de)etting )as studied( %he hornification

of )ood fibres is characteri5ed by dryshrin'age resulting in structural changes to fibres(

%his phenomenon )as prevented by ma'ing cellulose hydrophobic )ith

trichloromethylsilane -%CM$. in the gas phase( +n employing this chemical reaction, it

)as found that the material properties of the cellulose handsheet can be greatly altered(

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/n the nanoscale, cellulose )as usedto both reduce and to stabili5emetal nanoparticles

in a colloidal suspension( +n an aqueous mi*ture of silver cations -Ag]., cationic cellulose

nanocrystals-cC4C. can both reduce Ag]to silver nanoparticles -Ag46. and stabili5e

their formation thus achieving good si5e distribution( /n the molecular scale, silver

colloidal suspensions )ere again studied, but using various reducing and nonreducing

sugars of different molecular )eights( +t )as observed that a coreshell structure self

assembles )here the core issilver and the shell is made of carbohydrates(

'.'.%. he ayout of the hesis

%he introduction )ill be divided into five sections( %he first section is a brief introduction

to the structure of cellulose( %he follo)ing section deals )ith chemical modifications to

cellulose fibres to prevent hornification( %he third section focuses on cellulose

nanocrystals -C4C. and means of studying these nanometersi5ed organic nanoparticles(

%he fourth section is a scientific literature revie) of the reduction and stabili5ation of

silver cations to silver nanoparticles using carbohydrates( %he final section provides

detail on contributions for published )or'(

%his thesis consists of eight chapters( Chapter ", the introduction, is divided into four

sections, and provides fundamental information to help lay the foundation to the )or'

presented in this thesis( %he stability of macroscopic and nanoscopic systems are

e*plained in this chapter(

Chapter is the first of t)o pro&ects focused on chemically modifying cellulose pulp to

possess lo) density and superhydrophobicity( %his treatment solves the problem of

hornification and is publishedin &ournal titled CelluloseF A( %e&ado, W(C( Chen, Md 4(


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Alam, %(G M( van de Hen, $uperhydrophobic foamli'e cellulose made of hydrophobi5ed

cellulose fibres, Cellulose, %&'(, 21 (3), "I#7"IE(

Chapter is a continuation of the pro&ect in chapter ( +n this case, the superhydrophobicpulp is forced to upta'e )ater in vacuo and subsequently pressed into a handsheet( %his

handsheet, )hen dried, e*pands, )hich ma'es it the first reported material to possess dry

e*pansion properties( %he )or' presented is published in CelluloseF W(C( Chen, A(

%e&ado, Md 4( Alam, %(G(M( van de Hen, 0ydrophobic CelluloseF A Material %hat

9*pands Upon Drying, Cellulose, %&'*, 22 (4), "I#7"IE(

Chapter E is a study on the cationic modification of C4C to form a ne) type of

nanoparticle that is capable of reducing silver -+. to silver -!. as si5econtrolled silver

nanoparticles -Ag46.( %his )or' is submitted to3iomacromoleculesF W(C( Chen, 0(

Jang, %(G(M( van de Hen, Cationic Cellulose 4anocrystal Assisted Keduction of $ilver-+.

to $ilver 4anoparticles, %&'*, Manuscript +DF bm!"#!"!E#)

Chapter # is devoted to the use of reducing and nonreducing sugars to form and stabili5e

Ag46 in aqueous suspension( +n this )or', the use of nonreducing sugars to cause the

formation of coreshell Ag46 and the silver mirror resulting from colloidal stability are

discussed( %his )or' is submitted to Carbohydrate Kesearch &ournalF W(C( Chen, %(G(M(

van de Hen, $ynthesis and $tabili5ation of $ilver 4anoparticles With Carbohydrate

$hells, %&'*, Manuscript +DF CAKD"#!!#L(


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Chapter L is the final chapter of the thesis and contains the conclusion of the main body

of )or' from all previous chapters, contributions to the 'no)n scientific literature, and a

broad vie) for future developments in the field of biopolymeric research(

%here are t)o appendi* chapters( %he first one is a revie) of several instrumental and

analytical techniques used in previous chapters( %he second appendi* chapteris based on

)or' published in the 4ordic 6ulp and 6aper Kesearch NournalF M( aushi', W( C( Chen,

%( G( M( van de Hen, A( Moores, +maging Cellulose 4anocrystals by %ransmission

9lectron $pectroscopy,Nordic Pulp and Paper Res J, %&'(, O -"., IIPE( +n this chapter

and special issue on nanocellulose, the nanosi5ed biopolymeric particles C4C are

imaged using transmission electron microscopy -%9M. under different conditions(

'.%. 3ntroduction to Carbohydrates

Carbohydrates are naturally occurring compounds that comprise simple sugars called

monosaccharidesmore comple* sugars such as disaccharides and oligosaccharides, and

higher molecular )eight macromolecules and polymers called polysaccharides( %he

number of carbon atoms per sugar unit and the presence of aldehydes and 'etones

determine the class of the carbohydrate( +n this thesis, there is a heavy emphasis on

cellulose, )hich is a polymer of glucose units(%he simple sugar glucoseis an aldohe*ose

-presence of an aldehyde group and L carbons.( A stereoisomer of cellulose is starch

because both biopolymers are composed of glucose units lin'ed via the first and fourth

carbons( %he defining feature bet)een the t)o lies in the lin'age bet)een carbon " and E(

+n the case of cellulose, the "E bond is an equatorial _bond)hile for starch, the bond is

a*ial -Vbond.(

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6entoses and he*oses -# and Lmembered sugars. are capable of undergoing transitions

bet)een straight chain, furanose -#membered ring., and pyranose -Lmembered ring.

form( Depending on the sugar, steric effects )ill cause the equilibrium to favour a

specific structure over the others( or the purpose of this thesis, sugars are dra)n in the L

membered chair configuration because glucose is most sterically stable in this form(

ig( "("( %he equilibrium structures of glucose, an aldohe*ose

As mentioned previously, the basic building bloc' of cellulose is Dglucose, but more

precisely, these individual sugar bloc's are called Danhydroglucopyranose units -AGU.

-r`ssig, "OO.( rom the three hydro*yl -/0. groups present in each AGU, thefunctional groups atposition C and C are more reactive in etherification reactions than

at position CL because both behave as secondary alcohols( %he /0 group at position CL

is least reactive in etherification reactions -Wang et al(, !"E. ho)ever, in terms of

esterification reactivity, the order is reversedF CL C 8 C -Chen, !"E.( Cellulose

chains are bundled together into microfibrillated cellulose particles that can vary greatly

in si5e due to the polydispersity of the bundles( Under normal conditions, protofibrils, the

elementary fibrils, are made up of L cellulose chains -$ommerville, !!L Mut)il et al(,

!!P.( %hese protofibrils assemble into the tightly bound larger units called microfibrils,

)hich are then assembled into cellulose fibres -an et al(, !!P.(

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ig( "(( Wood fibres split into various component partsF nanofibrils -E"! nm.,protofibrils -"!! m., microfibrils -#!"!! m., and )ood stem - m.

%he macroscopic structure of cellulose fibres is composedof nanofibrils arranged into

many layers of lamellar structures along the cell )all -ahlen \ $almen, !!.( %he

relevance of the macroscopic structure to the )or' presented in this thesis lies in the fact

that voids and pores form bet)een nanofibrils, )hich allo)s )ater to permeate( Due to

)ea'force interactions such as hydrogen bonding, these interstitial spaces can constrict

and irreversibly close as nanofibrils coalesce(

ig( "(( Crosssection sho)ing the deformation of a fibre caused by nanofibrilcoalescence sho)n )ith microfibrillation after refining

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'.%.'. he Nanosctructure of Cellulose

3ased on evidence from imaging -AM, $9M, and electron tomography -Chunda)at et

al(, !"".., microfibril aggregates are assumed to be the fundamental cohesive unit of

)ood cell )alls -ernandes et al(, !"".( %hese units comprise crystalline and amorphous

regions, )hich )hen sub&ected to strong acid treatment, result in the isolation of the only

the crystalline parts( %hese shorter rodli'e particles are 'no)n in the scientific literature

as cellulose nanocrystals -C4C. -Kanby, "O#" /'e, !"!. and are also called cellulose

nano)his'ers or nanocrystalline cellulose -4CC.( Although this material is an organic

material and is therefore less electrondense, C4C can be imaged by %9M )ith relativelygood contrast( Another means of imaging C4C is by AM, )hich also provides the

height profile of the nanosi5ed rods( %he only dra)bac' of AM is the effect of shape

perturbation from the broadening phenomenon associated )ith the AM tip( %his causes

more bo*shaped C4C from sources such as valonia to appear round -0abibi et al(,

!"!.( 4ot only are the dimensions of C4C different depending on its source and

treatment conditions, but other properties also vary( A detailed account on the analysis of

C4C is presented in section "(E(

'.4. he Pre1ention of Da"age to 5ul+ Cellulose

Chemical modification of bul' cellulose is a practice )ith an e*tensive history( A lot of

)or' has been conducted to chemically modify the functional groups )ithin )ood pulp

in order to provide the final product )ith enhanced properties )here protection against

)ater damage is one type of enhancement under investigation )ithin the scope of this

)or'( %he large presence of hydro*yl -/0. groups )ithin the cellulose structure causes

this material to have an affinity for )ater it also signals that chemical modifications can

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be made at these sites( As far as paperbased products are concerned, irreversible damage

to the integrity of the fibre mat is often attributed to )etting( +n the scientific body of

)or' on this phenomenon, the term ;hornification; is used to describe the irreversible

coalescence of microfibrils caused by the hydrogen bonding of polysaccharide chains

-Nayme, "OEE.( $ubsequently, this coalescence also leads to lumen and pore collapse that

cellulose fibres undergo upon drying -0ubbe et al(, !!I.( +t is clear that fibres from

certain trees are more li'ely to succumb to hornification than others due to differences in

fibre dimensions and composition( 4evertheless, there are numerous studies on reducing

the ris' of hornification(

'.4.'. 6ornification and 6ydrogen-5onding

4umerous methods have been devised to prevent hornification( %he inactivation of

cellulose fibre surface is achieved by bloc'ing the formation of hydrogen bonds( +t has

been sho)n that solvent e*change, the use of e*tractives and fatty acids, and chemical

modification of the /0 groups can help prevent hornification -3rancato, !!P.( +n past

)or', as little as (Z substitution by methylation of the /0 groups is sufficient to

disrupt internal bonding( /ther )ays of achieving this )ould be silylation( +n the case of

substitution reactions, the goal is al)ays to hydrophobi5e to some e*tent cellulose;s

chemical structure( %he issue )ith chemical modification is the higher e*pense associated

)ith this strategy( +nstead of substitution, the treatment of )ood pulp )ith a )atersoluble

material can also prevent hornification( +n this case, the material )ould bond to the /0

groups thus obstructing contact bet)een cellulose microfibrils during drying( +t has been

found that the addition of sucrose andTor glycerol can perform this tas' at a loading

concentration of !Z( urthermore, the effectiveness is limited to " cycle because these

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bloc'ers are )ashed out during repulping( %herefore, although the use of bloc'ers is more

economically viable, they are ineffective in the case of paper recycling(

$tudying and understanding the phenomenon of hornification is of high significance tothe forest industry( Despite centuries of research on the topic of )ood pulp, no

economical industrial method can prevent irreversible damage to cellulose fibres due to

the effects of drying( %he consequence of this irreversible change is a reduction in the

quality of the cellulosebased material( %his is especially true in cases )here )ood pulp is

delignified because lignin and hemicellulose act as spacers for )ood fibres, )hich

prevents lumen and pore collapse and are part of the integral ma'eup of )ood(

Kemoving these constituents from )ood pulp generally results in a loss of strength

properties( $ignificant issues associated )ith hornification are the reduced accessibility to

the buried cellulose chains, the loss of strength, and fibre mat integrity(

'.4.%. 6ornification in this hesis

/f the numerous techniques to help prevent hornification, solvent e*change and chemical

modification )ere t)o methods used in con&unction to solve the problem in the )or'

presented -lemm et al(, "OOP.( 4evertheless, other means such as the use of additives

-4emati et al(, !"". and free5edrying -Kder \ $i*ta, !!E. have also been sho)n to

prevent hornification( +n all of the methods mentioned, the pore and lumen collapse is

assumed to be prevented based on the )ater retention volume -WKH.( +maging by means

of scanning electron microscopy and Rray tomography can also be used to determine the

crosssectional lumen structure(

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+n this thesis, t)o chapters of )or' are devoted to preventing lumen collapse )hen

drying cellulose fibre mats( %his has been achieved by performing solvent e*change and

chemical modification( Analysis )as performed by imaging using $9M and Rray

tomography( urthermore, contact angle goniometry )as performed to assess the

hydrophobicity and the crosssectional thic'ness of the fibre mat(

'.(. Cellulose Nanocrystals $CNC)

'.(.'. Sulphuric Acid 6ydrolysis of Cellulose

+t is 'no)n that sulphuric acid -0$/E. hydrolysis of cellulose is responsible for the

brea'do)n of fibres into rodli'e fragments -Koman \ Winter, !!E.( %he reason for

)hich hydrochloric acid -0Cl. is not used is e*plained by the colloidal stability of the

nanocrystalline particles in aqueous suspension( +f 0Cl )ere used instead of 0 $/E, then

aggregation occurs and results in the formation of microcrystalline cellulose -MCC.

-Ara'i et al(, "OOP.( %he sulfonate groups introduced onto the rodli'e fragments esterifya

lo) amount of surface hydro*yl -/0. groups( %his chemical reaction is responsible for

the colloidal stability of cellulose nanocrystals -C4C. -Kanby, "OEO.( %he amount of

sulfonate groups present can bedetermined by a potentiometric titration Gran plot( +t )as

found that higher reaction temperature, longer reaction times, and higher acid

concentration all lead to a higher amount of sulfonate groups esterified to the cellulose

nanorod surface( %he problem )ith these conditions lies in the possibility of degradation

and decomposition of the sample burning( +t )as found that, even lo)er temperature,

shorter reaction time, and lo)er sulphuric acid concentration, a sufficient presence of

sulfonate groups can be achieved( %his, in turn, leads to a stable suspension(

"!


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ig( "(E( %he amorphous regions of cellulose chains can undergo preferential hydrolysis,)hich results in the isolation of cellulose nanocrystals -C4C.

%he dimensions as )ell as the physical properties of C4C greatly depend upon the source

of the ra) material and the treatment that resulted in the isolation of the C4C product( +n

a published )or' from "OOP -Dong et al(, "OOP., the mean particle si5e of C4C )as

determined for samples at a )ide range of acid hydrolysis reaction time( +t )as found

that, using sulphuric acid to hydrolyse cellulose fibres, a shortening of the C4C length

occurred along )ith an increase in sulphur content( With a fi*ed acid concentration -LEZ

throughout the )or'., at a reaction temperature range of LXC to E#XC, an ivorycoloured

suspension of C4C )as observed depending on the reaction time( 0o)ever, increasing

the reaction temperature resulted in a dar'ening of the sample to the point of charring at

L#XC in only " hour( +n this same )or', a detailed histogram and t)o clear %9M images

demonstrating the si5e distribution of the C4C nanorods )ere sho)n for samples that

under)ent either ! minutes or E hours of acid hydrolysis at E#XC( +n agreement )ith the

theory proposed by the author, longer e*posure time to sulphuric acid resulting in shorter

C4C particles and more highly charged surfaces resulting in better dispersion(

%he %9M imaging )or' sho)n in many published papers involvesno negative staining

)ith heavy metals such as uranium salts( 0o)ever, )ith increasing analysis on C4C,

such staining techniques have gained popularity in this field of study( +t is important to

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note, though, that %9M imaging can often produce artifacts, especially from drying( %he

introduction of heavy metal salts can also obscure features in organicTinorganic systems

due to poor image contrast( %he details of these issues associated )ith %9M imaging of

C4C is further discussed in the appendi* of this thesis(

'.(.%. Che"ical Modification of Cellulose Nanocrystals

%he abundance of /0 groups for bul' cellulose is also observed in nanocellulose( After

all, the latter, )hen bundled up, is the structural building bloc' for the former( Given that

these /0 groups are reactive, chemical modifications can be carried out to alter the

properties of C4C( Amongst the hydro*yl groups per AGU, the reaction site at position

CL acts as a primary alcohol and is susceptible to many more types of reactions than at

sites C and C( +n this chapter, a scientific revie) serves tosummari5e the numerous

reactions studied in the past on C4C(

ig( "(#( %he straight chain and the pyranose form of VDglucose )ith carbon positionsmar'ed

or e*ample, )or' published in !!I -Dong \ Koman, !!I. demonstratedthe

fluorescent labelling of C4C using fluorescein#;isothiocyanate -+%C.( %his )or'

ma'es bioimaging possible )hen using C4C in fluorescence bioassay studies( $imilar to

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reactions )ith bul' cellulose, silylation is another important chemical modification to

C4C that renders the nanorods hydrophobic( %he use of al'yldimethylchlorosilanes

-AD. can ma'e the surface of cellulose hydrophobicat a higher degree of substitution,

though this has been found to disrupt the structural integrity of the nanoparticles(

Amongst the countless reactions that can be discussed in this section, cationi5ation )ill

be presented because this chemical modification has been e*tensively performed on

cellulose to stabili5e silver nanoparticles in Chapter E( Wor' performed in !!P -0asani

et al(, !!P. sho)ed that cationic ammonium groups can be tailored onto cellulose by

grafting epo*ypropyltrimethylammonium chloride onto C4C( UnmodifiedC4Cpossesses a slight negative charge due to the presence of sulfonate groupsand, by

reversing the charge to positive, a stable aqueous suspension is still observed, though

)ith gelling properties at a higher degree of substitution( %he degree of substitution is

measured by titration )ith silver nitrate -Ag4/. to measure the precipitation of chloride

anions )ith silver cations( +n the present thesis, it )as also assumed that silver chloride

-AgCl. nanoparticles )ould result from this titration( 0o)ever, further investigation

suggested that silver nanoparticlescan form instead(

'.(.4. Applications of Cellulose Nanocrystals

%here are numerous possible applications of C4C( A popular use is the incorporation of

this material in nanocomposite polymers( Given its tensile strength, C4C is a good

candidate for reinforcing polymeric matrices( +n the case of the aforementioned

lengthTdiameter aspect ratio, a higher value is characteristic of a better reinforcing filler(

+n a publication from !!E -$amir et al(, !!E., nano)his'ers of cellulose ranging from

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an aspect ratio of "! to LI sho)ed greater modulus increase for cellulose )ith higher

aspect ratios( %his helps to demonstrate the tunability of C4C for various applications(

'.*. Sil1er Nanoparticles

'.*.'. Properties of Sil1er Nanoparticles

%he study of metal nanoparticles is a very broad and active field in nanoscience and

technology lin'ing to carbohydrates such as simple sugars and cellulose for synthesis and

stabili5ation -see section "(#(.( Depending on si5e, shape, and surface morphology,

significant changes to the material;s electrical, chemical, optical, electronic, and thermal

properties can be greatly altered -Kaveendran et al(, !!.( 4oble metals such as silver

and gold nanoparticles are also effective in medicine and food pac'aging because of their

antimicrobial properties -$harma et al(, !!O.( +t has been demonstrated that silver

nanoparticles -Ag46. can hinder the gro)th ofE. coli, S. aureus, and a list of other

bacteria( A noble metal nanoparticle such as gold can be used in biosensors for the

detection of pathogens and be used for controlled drug delivery -Ayala et al(, !".(

Although it has been longestablished that silver has the ability to prevent bacterial

gro)th, convincing mechanistic evidence )as only published in a paper "# years ago

-eng et al(, !!!.( +n this )or', %9M images ofE. coliand S. aureussho)ed the upta'e

of Ag46 into the cell( %he small dar' nanoparticles of silver either adsorbed to the cell

)all of bacteria or permeated into the nucleus, thus condensing the D4A of the

bacterium( +t has been proposed in that paper that the penetration of silver ions from the

nanoparticles into the cell )all can react )ith the thiol groups of proteins found in D4A,

)hich causes the D4A to condense( %his mechanism leads to either damage or death of

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the microorganism( +n this same paper, it )as also found that 9( coli )as more susceptible

to Ag46 than S. aureusbecause the former is a Gramnegative bacterium )hile the latter

is Grampositive( %he peptidoglycan in the cell )all of Grampositive bacteria protects

against silver nanoparticles and prevents the penetration and entry of silver ions into the

cytoplasm(

ig( "(L( $chematic of a dead 9( coli bacterium )ith its cell )all and D4A damaged bysilver granules formed from silver nanoparticles

'.*.%. Synthesis and Stabilization of Sil1er Nanoparticles

+n the past, numerous methodologies for the synthesis and stabili5ation of Ag46 have

been published( %hey all produce similar results in )hich silver of a given shape no larger

than "!! nm isproduced( %his section )ill focus on the reduction of silver cations -Ag].

to silver metal -Ag!. as e*plained in the scientific literature( Moreover, because many of

these publications describe a reduction and stabili5ation mechanism that often differ andcontradict one another, a combination of the 'no)ledge gained from various )or' is

neededto try and understand )hat causes the formation of stable Ag46(

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26/139

+n Kaveendran;s !! publication -Kaveendran et al(, !!., it )as sho)n that starch can

reduce silver nitrate -Ag4/. to Ag46( %he synthesis )as carried out in argon gas at

E!XC for ! hours( %he nanoparticles )ere characteri5ed by UHH+$ spectroscopy, )hich

sho)s a broad pea' at E"O nm( %his signal is in a )avelength range associated )ith

Ag46( 3n nu"erous published #or+, analysis by 78-83S spectroscopy is considered

as a "easure of the absorption of light #ith respect to #a1elength, e9tinction due to

absorption and scatter "ust be considered. his is discussed in Appendi9 3.%he si5e

distribution of the nanoparticles )as measured by %9M and subsequent particle counting

and revealed a mean si5e of #( nm( %his )or' )as amongst the earlier e*plorations ofusing carbohydrates to synthesi5e Ag4p discussed in this thesis, )hich is )hy the

reaction conditions appear fairly harsh and the analytical techniques fairly limited( %he

nanosi5e metal particles that formed )ere a result of the high amount of hydro*yl -/0.

groups, )hich facilitates the comple*ation of silver ions to the molecular matri*( +n turn,

this prevents the aggregation of silver atoms, thus allo)ing for nanosi5ed silver to be

produced(

Kaveendran described the reducing sugar mechanism as a means of e*plaining ho) metal

ions can be reduced in the presence of carbohydrates this is a popular vie) in the present

day( 0o)ever, many other mechanisms have also been proposed to e*plain the reduction

mechanism( +n %ravan;s !!O publication -%ravan et al(, !!O., the reduction of silver

ions by using derivatives of chitosan )as e*plored( +t )as proposed in this )or' that a

polyol reduction mechanism is responsible for the reduction of silver ions( More

specifically, a primary alcohol is o*idi5ed to an aldehyde, follo)ed by the formation of a

cyclic hemiacetal, )hich is o*idi5ed to a lactone( /*idationcan provide electrons to

"L


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nearby metal ions, thereby forming metal nanoparticles( %he use of "C4MK and +K

spectroscopy helped identify the presence of lactone moieties and carbo*ylic acid groups(

Ag46 )as, again, characteri5ed by UHH+$ spectroscopy and %9M imaging( Kaman

spectroscopy )as also employed and sho)ed an enhanced $9K$ effect )hen Ag46 )as

present this suggests that there is a strong interaction bet)een carbohydrate surfaces and

silver nanoparticle surfaces( %his evidence corroborates the notion that the formation of

small Ag46 is achieved by the presence of sugar units( 0o)ever, the polyol reduction

mechanism differs from the reducing sugar mechanism proposed in the previous )or' by

Kaveendran(

Ayala;s !" publication in dealing )ith Ag46 and gold nanoparticles -Au46. sho)ed

that both reducing and nonreducing sugars can cause reduction of noble metal ions to the

metal nanoparticle form( %his )or' sho)s that metal reduction can occur even )ithout

reducing chain ends( %his )or' does not suggest that the reducing sugar mechanism is

)rong in fact, no mechanistic discussion )as included( +t can be assumed, based on

numerous publications, that no true agreement on the reduction mechanism has been

made( %he use of simple nonreducing sugars such as sucrose and fructose yielded more

prominent absorbance at E"O nm than reducing sugars such as maltose and and galactose(

+n this same paper, starch, comprising nonreducing sugar units, yielded a less prominent

absorbance signal at E"O nm than glucose, a reducing sugar( 0o)ever, starch is a high

molecular )eight polydisperse polymer made up of sugar units )hile glucose is a small

molecule monosaccharide(

"I


28/139

+n the present thesis, the reduction of Ag]ions to Ag46 is studied under conditions that

differ from the papers referenced( +n this case, an approach to modify cellulose ma'ing it

cationic )as employed as a novel means of synthesi5ing Ag46 -see chapter E.( /n the

other hand, the use of simple sugars )ith or )ithout reducing ends can also produce

varied results -see chapter #.( With the data obtained under specific conditions, a higher

level of understanding can be achieved to elucidate the mechanism of formation of Ag46(

'.:. Contributions

At the time of )riting this thesis, three papers have been published and t)o more have

been submitted( +n the chronological order of )riting, the first publication )as a

collaborative )or' )ith Dr( A( Moores from McGill University and graduate student M(

aushi'( %he paper titled +maging Cellulose 4anocrystals by %ransmission 9lectron

$pectroscopy )as published in the 4ordic 6ulp and 6aper Kesearch Nournal in !" -see

Appendi* ++.( %he author of the present thesis performed p0 dependent %9M imaging on

%9M grids coated )ith hydrophilic, neutral, and hydrophobic layers as )ell as

contributing to the )riting of the manuscript for the publication( %his allo)ed for a more

thorough understanding of the dispersion of C4C particles on %9M grids( %he second

publication )ith Dr( A( %e&ado, Dr( M(4( Alam, and Dr( %(G(M( van de Hen titled

$uperhydrophobic foamli'e cellulose made of hydrophobi5ed cellulose fibres )as

published in Cellulose in !"E -see chapter .( %he author of the present thesis performed

chemical modification of )ood pulp and analytical )or' to demonstrate the lo)density

and superhydrophobicity of the modified material as )ell as )riting the manuscript for

the publication in full( A( %e&ado is first author because he initiated the research and

provided the first samples for analysis( 0e also performed $9M and Rray tomography

"P


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analysis on the pulp samples( +n the third publication titled 0ydrophobic CelluloseF A

Material %hat 9*pands Upon Drying, e*perimental, analytical, and )ritten )or' )ere

contributed by the author of this thesis -see chapter .( Coauthors Dr( A( %e&ado and Dr(

M(4( Alam provided e*perimental results and Dr( %(G(M( van de Hen )as the principal

investigator( %he t)o manuscripts currently under revie) involve the use of cationic

cellulose nanocrystals -cC4C. to reduce and stabili5e silver nanoparticles -Ag46. -see

chapter E. and the use of various carbohydrates )ith or )ithout reducing ends to reduce

and stabili5e Ag46 -see chapter #.( +n both papers, the primary author is the author of this

thesis and the principal investigator is Dr( %(G(M( van de Hen(

'.;. eferences

Ara'i, N(, Wada, M(, uga, $(, /'ano, %( -'


30/139

ahlen, N(, $almen, :( $%&&%) /n the lamellar structure of the tracheid cell )all, 6lant3iol(, E -., OE#(

an, N(, :iu, N((, 0e, N(0( $%&&=) 0ierarchy of Wool ibers and ractal Dimensions, +nt N4onlin $ci 4um(, O -., OOL(

eng, Q(:(, Wu, N(, Chen, G(Q(, Cui, ((, im, %(4(, im, N(/( $%&&&) A mechanisticstudy of the antibacterial effect of silver ions on 9scherichia coli and $taphylococcusaureus, N 3iomed Mater Kes(, # -E., LLP(

ernandes, A(4(, %homas, :(0(, Altaner, C(M(, Callo), 6(, orsyth, H(%(, Apperley, D(C(,ennedy, C(N(, Narvish, M(C( $%&'')4anostructure of cellulose microfibrils in spruce)ood, 6roceedings of the 4ational Academy of $ciences of the United $tates of America,"!P -EI., 9""O#9"!(

0abibi, J(, :ucia, :(A(, Ko&as, /(N( $%&'&) Cellulose 4anocrystalsF Chemistry, $elf

Assembly, and Applications, Chem Kev, ""! -L., EIO#!!(0asani, M(, Cranston, 9(D(, Westman, G(, Gray, D(G( $%&&=)Cationic surfacefunctionali5ation of cellulose nanocrystals, $oft Matter, E, PEE(

0ubbe, M(A(, Henditti, K(A(, Ko&as, /(N( $%&&) 0o) fibers change in use, recycling,3ioKesources, -E., IOIPP(

Nayme, G( -'


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Kanby, 3(G( $'


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Chapter %>

$uperhydrophobic foamli'e cellulose made of hydrophobi5ed cellulose fibres

%.'. Abstract

Wood -'raft. pulp )as first dried into a lo)density foamli'e material by solvent

e*change )ith anhydrous ethanol( RKay tomography sho)ed that, )hile pulp fibres are

flat and resemble ribbons )hen dried from )ater, those dried from ethanol are quasi

tubular, inferring that capillary forces derived from a lo) surface tension solvent are not

strong enough to promote fibre lumen collapse, contrary to )hat happens in )ater( When

the resulting solidfoamli'e pulp )as then sub&ected to a vapour phase reaction )ithtrichloromethylsilane -%CM$. a silicon based polymeric coating )as created on the

surface of the fibres, and the totality of the hydro*yl groups -/0. on the e*ternal surface

of cellulose fibres and the internal surface of macroporesin the fibre )all became

silylated, )hereas the surface of the mesopores)as inaccessible to %CM$( %he novelty

lies in the ability to modify both the e*ternal surface and the internal micropore structure

of cellulose fibres from #! to "!! Z silane coverage, )hich results in a novel

superhydrophobic material, )ith an apparentcontact angle of appro*imately "#!X( %his is

the first time cellulose is rendered hydrophobicboth internally and e*ternally( We refer to

the resulting foam as Cellufoam(


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%.%. 3ntroduction

or the past many decades, environmental concerns have led to a greater emphasis on

rene)ability, biodegradability, and ecofriendliness -6ar' et al(, !!E.( A biopolymer that

meets the criteria as a green material is cellulose( As one of the most abundant natural

resources in the )orld, cellulose can be used in its native state or processed to afford

countless applications -Chen et al(, !!I.(

rom the point of vie) of advanced materials, cellulose1s hydrophilic character is unique

and can be modified for a number of different uses( +n the case of foams and building

materials, rendering )ood pulp hydrophobic has been greatly sought after and many

hydrophobi5ation techniques have been investigated( Most of those attempts failed to

provide a durable hydrophobic character to cellulose products, and the reasons for this are

discussed in this )or'(

ig( ("( $chematic illustration of t)o cellulose fibres crossing each other perpendicularly)ith )ater and ethanolrepresented by blue areasF drying from )ater -top. causesshrin'age of the fibres due primarily to collapse of the lumen, )hile drying from ethanol-bottom. preserves the open11 fibre structure(


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+t is 'no)n from the literature that as cellulose fibres dry, strong attractive capillary

forces related to the surface tension of )ater cause a collapse of the internal opening

called the lumen -%e&ado \ van de Hen, !"! 0uang et al(, !"" %e&ado \ van de Hen,

!""., especially for delignified fibres, and closes the pores present in the cell )all( %his

effect ma'es the interior portions of the fibres inaccessible to anything but )ater and to

some e*tent1 ions or molecules dissolved )ithin it( %his nonreversible fibre collapse is

typically referred to as hornification( +n order to obtain dry pulp )ithout fibre collapse,

the )ater content of neverdried pulp has to be substituted )ith a lo) surface tension

fluid -e(g( ethanol. by means of solvente*change -:i et al(, !" Uetani \ Jano, !".(+t is 'no)n that solvente*changed 'raft pulps maintain their internal porous structure,

)hich consists of mesopores)ith pore si5es of a fe) nanometers and surface areas in the

range !!7!! mTg and macropores)ith pore si5es of around I# nm and surface areas

of about "! mTg -Alince, "OI# Alince \ van de Hen, "OOI.( When solvente*changed

pulp is allo)ed to dry, the resulting product is a lo)density cellulose foamli'e material

-ig( (".( +n this )or', foamli'e pulp has been obtained by drying the original material

from, ethanol and several surfactant solutions in )ater &ust above critical micelle

concentration -cmc., all of them sho)ing surface tensions in the order of onethird that of

)ater(

Aside from the foamli'e material reported here, )hich relies on varying the surface

tension of the solvent before drying, aerogels have also been investigated for a long time

-Nin et al(, !"".( Cellulose aerogels avoid the problems related to fibre collapse and

aggregation upon )aterremoval by either free5edryingor supercritical drying(

E


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4evertheless, the resulting lo)density and highly porous solid is brittle and cannot be

made as easily as the material investigated in this study -Wu et al(, !".(

3ased on the combination of old 'no)ledge and recent findings, a ne) approach forcellulose hydrophobi5ation -surface polymeri5ation via a gasphase reaction over dried

but noncollapsed pulp. has been developed )hich, for the first time, results in totally

hydrophobic and durable cellulose fibres( %he macroporesin the fibre )all, around I# nm

in si5e, are sufficiently large for trichloromethylsilane -%CM$. gas molecules to freely

penetrate( rom the data sho)n belo), it appears that %CM$ does not penetrate the

mesopores, at least not on the time scale of the e*periments due to polymeri5ation of

%CM$ into silo*anes that obstruct the pores( As a consequence, vapour deposition

reaction )ith %CM$ allo)s the production of a superhydrophobic material )hich )e call

Cellufoam( +n the case of an aprotic solventbased reaction )ith %CM$, the results

sho)ed poor yield and )as not investigated further( Although the use of %CM$ to render

cellulose hydrophobic is not a novel reaction -:i et al( !!I, !!P Andresen et al(, !!L

ChingaCarrasco et al(, !"., its application on noncollapsed fibres is a simple and

novel approach that leads to remar'able ne) cellulose products, as )ill be sho)n in this

and upcoming papers( %he reaction bet)een cellulose and %CM$ also produces a by

product not often discussed, but that is detrimental to the overall quality of the

CellufoamF the production of hydrogen chloride gas, )hich readily adsorbs to pulp,

ma'ing its removal a challenge( %his issue has been resolved by blo)ing air onto the

product immediately follo)ing vapour deposition(

#


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%.4. ?9peri"ental Section

%.4.'. Materials

3eaten hard)ood 'raft pulp -b06. )as provided by 6+nnovations and soft)ood 'raft

pulp -QO!. )as provided by Domtar( %he %CM$ )as purchased from Aldrich( Anhydrous

ethanol )as purchased from Commercial Alcohols( $urfactants %riton R# and Do)fa*

A" )ere obtained from Do) Chemical( $ulfonated raft :ignin -$:. )as obtained

from Westvaco( 6aperma'ing machineries include the 3ritish $tandard Disintegrator

-4oram RKCC"#"., the 3ritish Automatic 6ress -4oram RKCC"E#. and the 3ritish

handsheet ma'er -4oram P!!L., all of )hich fulfil %A66+ standards(

%.4.%. Preparation of cellulose foa" using lo# surface tension sol1ent

A sample of neverdried )ood pulp -typically about "! g. )as placed in a plastic net of

#!! mpore si5e, )hich allo)ed e*cess )ater to drain( %he damp sample )as re

suspended in anhydrous ethanol and stirred for E h( %he ethanolsoa'ed sample )as

drained in the same net and resuspended again in anhydrous ethanol for E h )ith

constant stirring( %his process )as repeated three more times until the amount of )ater

remaining is negligible -typically !(# )tZ.( %he ethanol )as drained and the

ethanolsoa'ed pulp )as dried at I!XC in an oven for EP h( %he resulting material is

moulded by the shape of the drying vessel, cylindrical in the case of a bea'er, and has the

consistency of solid foam( A similar process )as repeated )here aqueous surfactant

solutions )ere used instead of ethanol( %he mi*ture of )ood pulp and this solution )as

sha'en to the point of foaming and, after draining and repeating a second time, the )et

pulp )as put into the oven at P!XC for another E h( %he resulting material )as, again,

moulded by the shape of the drying vessel &ust as before( %his part of the e*periment )as

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a proof of principle that demonstrated the feasibility of using surfactants instead of

ethanol( Chemical vapour deposition and all subsequent steps )ere performed using

ethanoldried pulp(

ig( (( 9*perimental setup for the reaction of cellulose )ith %CM$( %he reactionvessel and %CM$ )ere preheated in a L#XC oven( A mesh bas'et containing the pulpsample )as introduced and held firmly in place by a rubber stopper inside the vessel( %he

sample )as reintroduced into the oven and the gasphase %CM$ )as made to react )iththe sample

%.4.4. Che"ical 1apour deposition of trichloro"ethylsilane $CMS)

%he plastic net )as se)n into a cylindrical bas'et )ith thread and needle( %he cellulose

foam mass )as bro'en into smaller fragments and placed into the cylindrical bas'et that

)as subsequently hungfrom an 9rlenmeyer flas' top edge resulting in the sample being

suspended -ig( (.( :iquid %CM$ -" mmolT gcellulose. had been previously poured intothe flas', )hich )as then sealed )ith a glass stopper and placed into the oven at L#XC for

a period of ""# min( %he resulting superhydrophobic pulp )as first blo)n )ith air and

then rinsed )ith a generous amount of )ater to remove e*cess reagent and hydrogen

I


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chloride produced during the reaction( %he fragments of Cellufoam )ere redispersed in

ethanol and dried in the oven at P!XC for EP h to yield one single mass, )hich once more,

has been moulded by the shape of the drying vessel(

%.4.(. Analyses

%he si5e distribution analysis of individual fibres )as performed using the 0iKes fiber

quality analy5er -QA. -/p%est 9quipment +nc(.( %he contact angle goniometry

measurements )ere acquired using the Contact Angle $ystem /CA -Dataphysics.( %he

D images of individual fibres )ere obtained by Rray tomography using the ""I Micro

C% -$'yscan.( %he surface tension measurements )ere carried out using the $H $igma

I! %ensiometer -$H +nstruments.( %he surface morphology of fibres )as e*amined by

field emission high resolution scanning electron microscopy 9$9M -$ EI!! 0itachi,

%o'yo, Napan.( %he fibres )ere pressed onto a doublesided tape adhered to a sample

holder surface and sputtered )ith gold and palladium for min( +maging )as done )ith a

dispersive spectrometer( %he applied accelerating voltage and current )ere ! 'H and "!

A, respectively(

%.(. esults and Discussion

A cellulose fibre is 'no)n to collapse -i(e( shrin' by closing its lumen and pores. )hen it

is dried from a )ater suspension, acquiring a tough appearance and reducing its ability to

reabsorb )ater, in )hat has been traditionally called hornification11-Nayme, "OEE

Minor, "OOE.( %his behaviour has been avoided in the present )or' by using alternative

solvents of lo) surface tension and also decreasing the surface tension of )ater )ith

surfactants( As a result, foamli'e materials made entirely of cellulose fibres have been

P


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obtained, sho)ing an apparent density in the order of !(!L7!("! gTcm -ig( (. -"!!

times lo)er than )aterdried, depending on the procedure.( %he density )as determined

by measuring the volume of the cylindrical foam pulp and by )eighing the sample(

ig( (( -:eft. Wilhelmy balance setup and equation used, )here Y is the surface tension-right. a table sho)ing the apparent foam density of )ood pulp dried from varioussolvents and their surface tension above the critical micelle concentration -cmc.( $:-cmc 8 !(P )tZ., Do)fa* A" -cmc 8 !(!!I )tZ., and %riton RE# -cmc 8 !(!"L )tZ.

As sho)n by Rray tomography -ig( (E., )hen a sample of b06 )ood fibres dries

from )ater, its lumen is collapsed( %his is demonstrated by the narro) aspect ratio of the

fibre crosssection( When dried from ethanol, the fibre crosssection suggests an open

lumen structure, roughly the same as the dimensions of )et fibres in )ater measured by

QA -cf( ig( (Ec.( +t can be seen that, )hen dried from )ater, the fibres possess a

ribbonli'e shape but, )hen dried from ethanol, they possess a quasitubular shape( %his

can be e*plained by the fact that ethanol has a much lo)er surface tension value than

)ater -A5i5ian \ 0emmati, !! Ha5que5 et al(, "OO# Gunde et al(, "OO. and is unable

to collapse the lumen by capillary forces( +n an entangled net)or' of fibres, lumen

collapse leads to flat ribbons, )hich, )hen in contact )ith other ribbons, result in a larger

O


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binding area than noncollapsed fibres -van de Hen, !!P., leading to a more compact

structure( +n contrast, in the absence of lumen collapse, the structure is more open(

ig( (E( D images of individual fibres obtained )ith $'yscan ""I Micro C% RKaytomographyF a. after being dried from )ater and b. from a lo) surface tension solvent-ethanol.( c. ibre si5e distribution of b06 fiber in )ater before drying obtained by

using 0iKes fiber quality analy5er -QA.

ig( (#( $9M images of b06[cellulose fibers of a dried from )ater, b dried fromethanol, c crosssectional vie) dried from )ater and d crosssectional vie) dried fromethanol

!


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%o further support the Rray tomography data, $9M images -ig( (#. also suggest flatter

fibres that pac' more densely )hen dried in )ater compared to ethanoldried hand sheets(

%he lumen opening appears to be narro)er in $9M images due to pressing and metal

coating )hen sputtered )ith gold and palladium( 4evertheless, the crosssectional vie)

does point to an open lumen structure )hen dried from ethanol(

As sho)n in the table in ig( (, the surface tension of the surfactant solution is higher

than that of ethanol( 0o)ever, for cost considerations, !(!" Z surfactant solutions )ere

prepared to replace ethanol( During drying, the surface tension reaches the minimum -i(e(

&ust above the cmc. -ig( (L.( Using these replacements, the apparent density )as

lo)ered -!("! gTcm. to nearly the same value as ethanol -!(!L gTcm. -ig( (.(

0o)ever, drying from organic solvents still yield lo)er density cellufoam(

ig( (L( A plot of the surface tension )ith respect to surfactant concentration in thiscase, %riton RE# is used and has a 'no)n surface tension of O m4Tm

"


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When )ood pulp dries from a surfactant solution, again a foamli'e pulp is obtained(

$9M imaging -ig( (I. indicates that, indeed, the lumen is much narro)er and, in some

cases, nearly closed( %he reason for )hich the pulp displays such a lo)density is its

overall pac'ing( Although the individual fibres have partly collapsed lumens, the fibre

net)or' is much looser than )hen the pulp is dried from )ater( +t can be assumed that,

)ith surfactants, the surface tension is simply too high to prevent complete lumen

collapse(

ig( (I( $9M images of QO! nonbeaten cellulose fibers a. dried from )ater, b. driedfrom anionic surfactant, c. crosssectional vie) dried from )ater and d. crosssectionalvie) dried from anionic surfactant

%richloromethylsilane -%CM$. is a hygroscopic compound that almost instantly reacts

)ith air moisture and hydro*yl -/0. groups to form silo*ane and hydrogen chloride gas(

%he hydrogen chloride gas hydrolyses in the presence of moisture to afford concentrated

hydrochloric acid -%ripp \ 0air, "OO Artus \ $eeger, !".( Kemoval of 0Cl has been


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the challenging step in performing the proposed reaction( After several modifications to

the procedure, the best results )ere obtained from a timedependent chemical vapour

deposition follo)ed by blo)ing air to)ard the sample and lastly, rinsing the hydrophobic

pulp )ith a generous amount of deionised )ater( Without adequate removal of

hydrochloric acid, the )hite pulp burns in the presence of the strong acid and becomes

yello) in colour( A reaction time of " min )as deemed sufficient for achieving

superhydrophobicitybased solely on apparent contact angle measurements, because

increasing the e*posure time does not increase the contact angle( urthermore, )ith a

longer reaction time, polymeri5ation of silo*ane into a multilayer can congest the internalstructure of the fiber( An important feature of this process is that, although reaction times

of ""# min yield different degrees of silane coverage, a critical amount of coverage is

reached at &ust " min reaction time to achieve superhydrophobicity( Keaction times above

"# min result in yello)ing and disintegration of pulp( Despite the fact that full coverage

cannot be reached, partial coverage of the e*ternal surface and the internal micropore

surface has been achieved(

ig( (P( %CM$ adsorption as a function of reaction time also sho)n is the coverageassuming a surface area of "! mTg of 'raft pulp -Alince \ van de Hen, "OOI.


44/139

As sho)n in ig( (P, the percent of %CM$ coverage from #! to "!! Z of e*ternal

surface and the internal micropore surface of cellulose fibers( %o determine percent

coverage, it is assumed that %CM$ molecules cover an area of "!

-specific adsorptionof mgT m. and the combined surface area of the e*ternal surface and the macroporesis

about "! mTg for 'raft pulp -Alince \ van de Hen, "OOI.( 3y measuring the adsorption

of %CM$ as a function of reaction time -assuming that %CM$ is the only contributor to

the )eight gained., the reaction capacity should be appro*imately ! mgTm( +t is fair to

assume, in our )or', that after "# min of reaction, that full coverage of the macropores

has been achieved(

ig( (O( Water droplet on the surface of Cellufoam captured by a CCD camera

A material is classified as hydrophilic )hen its contact angle )ith a drop of )ater is

inferior to O!X and as hydrophobic )hen the contact angle is O!X -Chen et al( !"

Drelich et al( "OOL. in the latter case, superhydrophobicity is defined by a contact angle

"#!X -3lossey, !! :afuma \ Qu


45/139

)ater drops eventually get absorbed into the material( A replacement for commercial

plastics such as cellulose acetate, on the hand, has a contact angle of ##X -9rbil, "OOI.

along )ith reduced porosity( +n nature, certain plants and insects have evolved to produce

superhydrophobic coating at the surface of their anatomy( or e*ample, the +ndian cress

leaf -/tten \ 0erminghaus, !!E. has a contact angle of nearly "P!X, )hich is the

ma*imum degree of hydrophobicity( %he Cellufoam described in this )or' has a contact

angle of roughly "#!X at equilibrium, )hich mar's it as a superhydrophobic material

-ig( (O.( urthermore, the )ater drop evaporates before getting absorbed into the pores

of the material( %he aforementioned contact angle values are summari5ed in %able ("( +tis important to note that a thorough study of surface energy in relation to contact angle

)ould require the analysis of advancing and receding contact angles for )ater droplets at

an incline or by using the pendant drop test method( $urface energy analysis )as not

performed to ascertain the superhydrophobicity and stability of the material(

%able ("( Contact anglesof various materials

%he advantage of Cellufoam is the ease of production compared to other

superhydrophobic cellulosic materials in the literature( urthermore, only Cellufoam is

#


46/139

rendered hydrophobic both inside and out )ith respect to the fibres( /ga)a et al( -/ga)a

et al(, !!I. achieved "LX using ! bylayers of poly-diallyldimethylammonium

chloride. -6DDA.T%i/ Gonalves et al( -Gonalves et al(, !!P. achieved "EIX using

silica beads and "0,"0,0,0perfluorooctyl trietho*ysilane -/%$. -%able (".( %hese

are all fairly more comple* techniques compared to chemical vapour deposition )ith

%CM$ and, still, only the outer surfaces of these materials are rendered hydrophobic(

ig( ("!( Unmodified hydrophilic -left. and %CM$hydrophobi5ed -right. cellulosefibres in contact )ith a drop of )ater( 0ydrophilic fibers are dra)n into the )ater drop(/nly a sufficiently hydrophobic fiber remains at the )ater7 air interface and sho)s 5eroengulfment

4ot only does Cellufoam possess unprecedented properties in bul', its individual fibres

also possess qualities that have never been reported in the past( As sho)n by ig( ("!

-right., a fibre of the Cellufoam is sho)n to stic' to the surface of a )ater droplet( %his

)ould not have occurred )ith a natural fibre or )hen the hydrophobi5ation reaction is

performed after conforming a structure i(e( paper instead, partial )ater repellence and

partial engulfment )ould be e*pected in that case( As sho)n in ig( ("! -left., a native

cellulose fibre )ill instantly enter the )ater droplet due to its affinity for )ater(

L


47/139

%.*. Conclusion

+n this study, solvente*change has been used to dry )ood pulp fibres )ithout collapsing

the fibre lumens )hile minimi5ing the fibre7fibre pac'ing -preventing hornification.( %he

foamli'e material obtained has been successfully rendered superhydrophobic through a

vapour phase reaction )ith %CM$ )hich, combined, is a )hole ne) approach for

hydrophobi5ation of cellulose fibres on an individual scale and renders each cellulose

fibre hydrophobic inside -internal micropore. and outside -e*ternal surface. to reach a

ma*imum of "!! Z silane coverage( %he implication of such a material is significantF

lo)density insulation and pac'aging materials can be made this )ay and research intoma'ing Cellufoam flameretardant -Gates \ 0u, !"!. )ould allo) its introduction into

industries such as electronics, automotive and construction(

%.:. eferences

Alince, 3( $'


48/139

Chen, R(, 3urger, C(, Wan, (, hang, N(, Kong, :(, 0siao, 3($(, Chu, 3(, Cai, N(, hang,:( $%&&)$tructure study of cellulose fibers )etspun from environmentally friendly4a/0Turea aqueous solutions, 3iomacromolecules, P, "O"P"OL(

Chen 0(, Amirfa5li A(, %ang %( $%&'4)Modeling liquid bridge bet)een surfaces )ith

contact angle hysteresis, :angmuir, O, "!"O(ChingaCarrasco, G(, u5netsova, 4(, Garaeva, M(, :eirset, +(, Galiullina, G(, ostoch'o,A(, $yverud, ( $%&'%)3leached and unbleached MC nanobarriersF properties andhydrophobisation )ith he*amethyldisila5ane, N 4anoparticle Kes, "E, "P!(

Drelich, N(, Wilbur, N(:(, Miller, N(D(, Whitesides, G(M( $'


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:i, $(, hang, $(, Wang, R( $%&&=)abrication of superhydrophobic cellulosebasedmaterials through a solutionimmersion process, :angmuir, E, ##P###O!(

:i, ($(, :ively, K(6(, :ee, N($(, oros, W(N( $%&'4)Aminosilanefunctionali5ed hollo)fiber sorbents for postcombustion C/capture, +nd 9ng Chem Kes, #, POPPO#(

Minor, N(:( $'


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5ridging section bet#een Chapters % and 4

+n chapter , superhydrophobi5ation of cellulose )ood pulp )ith trichloromethylsilane

-%CM$. resulted in a foamli'e material of lo) density and an apparent )ater drop

contact angle of "#!X( %he lo) density material, called Cellufoam, resulted from never

dried pulp that has been dried from ethanol by the solvent e*change method in order to

prevent lumen and pore collapse that is caused by the coalescence of cellulose micro and

nanostructures( +t has been found that many lo) surface tension solvents can also be used

to replicate this )or'( or industrial consideration, surfactants can be used to reduce

costs( $canning electron microscopy and Rray tomography indicate that fibres remainedopen after drying from a lo) surface tension solvent, unli'e for )ater, )here fibres

appear to be completely collapsed( urther analysis )as performed by varying the

reaction time in order to achieve greater contact angle and to modify the nanostructure of

cellulose( 0o)ever, additional reaction time resulted in damage to the sample caused by

the formation of hydrochloric acid as a byproduct of the reaction(

+n chapter , the superhydrophobic material, Cellufoam, )as studied for its drying

behaviour and its )et )eb strength -WW$. in order to understand the contribution that

entanglement provides to handsheets( +n this )or', a ne) drying property of

superhydrophobic cellulose )as e*plored(

E!


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Chapter 4>

0ydrophobic celluloseF a material that e*pands upon drying

4.'. Abstract

A chemically modified hydrophobic cellulose material )as )etted by force in vacuo and

allo)ed to dry under ambient conditions( Most 'no)n materials shrin' upon drying and

s)ell upon )etting, a phenomenon 'no)n as dryshrin'age and thus are characteri5ed

by a dryshrin'age coefficient either equal or greater than 5ero( Different from

conventional materials, sheets of hydrophobic cellulose fibres e*pand upon drying, )hich

implies that they e*hibit drye*pansion( %his property is calculated as a negative dryshrin'age coefficient( We are una)are of any other material )ith this property( $uch

sheets can e*pand to over #!! Z in thic'ness upon drying in the first cycle of use( %his

property degrades )ith each cycle because more hydrophilic areas come in contact )ith

)ater as a result of mechanical damage to the material, thus ma'ing the sheets less

hydrophobic( With increasing solid content, a decrease in tensile strength is observed,

)hich is opposite to the conventional trend in )et )eb strength( A mechanism for the

drye*pansion of this material is being proposed(

E"


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4.%. 3ntroduction

When materials are placed in a )et environment, s)elling occurs the dimensions of the

material are altered so as to e*pand in at least one of its dimensions( As )ater is removed,

dryshrin'age occurs and is a measure of the decrease in volume as a function of

decreasing moisture content( %he dimensional change is quantified by a coefficient -_.

that is defined as the dimensional change -Z. divided by the change in moisture content

-Z. -Mar'lund and Harna, !!O.F

_ 8 dimensional change -volume Z. T moisture content-Z. -".

9quation " is used to describe t)o phenomena that are inherently lin'ed( 0ygroe*pansionand dryshrin'age share similarities in that both are properties governed by the

coefficient b -$ampson and Jamamoto

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