Biomass Fundamentals
Module 14: Lignin II:Specialty Applications
A capstone course for
BioSUCCEED:
Bioproducts Sustainability: a University Cooperative Center of Excellence in EDucation
The USDA Higher Education Challenge Grants program gratefully acknowledged for support
This course would not be possible without support from:
USDA
Higher Education Challenge (HEC) Grants Program
www.csrees.usda.gov/funding/rfas/hep_challenge.html
What is “lignin?”• The amorphous glue that
binds carbohydrate bundles• A complex, polydisperse
(weight average MW/Number average MW measure of distribution of individual MWs) polymer
• A source of endless discussion for the exact nature of its biosynthesis in plants (enzyme controlled vs. random radical coupling)
• C9 polypropylphenol derivative O
O
OHOCH3
O
O
H3CO H2COH OH3C
CH2OH
OCH3
O
OH3C
OH3C
O
OCHOH
CH2OH
OH
CH2OH OCH3
OCH3
OH3C
OH3COCH3
O
OH3C
OO
O
CHOH
CH2OH
O
CHOH
CH2OH
O
O
CH2OH
CHOH
CH2OH
O OH3C
OCH3 O
CHOH
CH2OH
O
OH
CHOH
CHOH
OCH2OH
CHOH
H2COHO
OH3C
OCH3
OCHOH
CH2OH
OH OH3C
OH
CH2OH
OCH3
OCH3 O
CHOH O
OCH3
CH2OH
OO
OCHOH
CH2OH
OH3C
CH2OH
CHOH
O
O
OH3C
HOCH2OH
CHOH
O
CH2OH
O
OH3C
CHOH
O
OCH3 OH
OO CH2OH
CH2OH
CHOH
Lignin Biosynthesis
Structures of Lignin Precursors
Flavonoids: Chemical Offshoots of Lignin Biosynthesis
• 15 carbon atom compounds (C6-C3-C6) – over 4000!
• Polyphenol• Phytochemicals (phenolic acids,
stilbenes, polyphenols)• Antioxidants• CV health: reduce agglomeration
of platelets in endothelia• Assist lignification of cell walls in
plants in response to injury• Antimicrobials
Biologically Active Isoflavonoid• Rotenone comes from
Derris root and Lonchocarpus species
• Insecticide• Fish poison• Topical treatment of
head lice, scabies, and ectoparasites
Rheological Properties of Lignin• Schematic illustration of
secondary cell wall of spruce tracheids
• Between ordered cellulose fibrils is the lignin-hemicellulose matrix
• Various vibrational studies (static & dynamic FT-IR) of lignin functional groups suggest lignin is ordered in plane with the plane of cell wall surface
• Distribution, however, is not ISOTROPIC in fiber wall
Rheological Properties of Lignin, Part Deux
• Monolignols couple/polymerize under environmental constraints along fiber axis to ordered polysaccharide matrix
• Polysaccharides templates*?• A high response in a 90° out-of-phase spectrum with lignin
peaks indicates a more viscoelastic behavior for lignin over carbohydrates – also can move freely in matrix unperturbed by carbohydrates
*
Lignin in Composite/Industrial Applications
• Lignosulfonates• Extrusion moldings• Fuel• Fertilizer/agricultural adjuvant• Potential raw material for fine chemical
production
Lignin as a Medical “Tissue”• Wood and bone possess unique structural
motifs that fulfill requirements of support & transport of nutrients
• Is it possible, therefore, to use wood as a implantable material?
• Can it be used, for example, as a femoral replacement?
Technical Hurdles to Address• Toxicity• Compatibility• Adsorption• Functionality• Mechanical Properties
What is Bone?• Ceramic-polymer composite• Calcium phosphate (hydroxyapatite) and collagen• The apatite has different metal ions that adjust
solubility and availability of mineral elements to rest of body
• Small apatite platelets crystallize in preferred locations on collagen
Ultrastructure of Bone
Attempts to Mimic Bone• MOE: *Hydroxyapatite + polyethylene – middle ear
implants, maxillofacial reconstruction, & bone repair; possesses MOE similar to bone
• Porosity: Porites (coral species) have similar pore size & interconnectivity; CaCO3 (aragonite in coral) hydroxyapatite by hydrothermal process
• Hierarchical Structure: tendon, muscle, WOOD, and bamboo
*
van Leeuwenhoek’s Famous Comment
When he first recognized the Haversian canals in bone in 1693, hemade reference to other hierarchical structures:
Structure & Function of Wood• Wood is a polymer of 20-30%
lignin and the virtual remainder carbohydrates
• Tracheid (osteocyte in bone) is “cell”
• Tracheids consists of 5-30 nm wide microfibrillar elements composes of cellulosic strands (2.5 nm diameter)
• Wood is porous and operates on negative pressure osmotic gradients in lumens and valves in pits – transport in bone is positive pressure from circulation of nutrients
Morphological Structure of Juniperus communis
A: annual rings; B: rays & pits; C: pirs in a ray connecting adjacent tracheid; D:Helical texture of spiraling cellulose strands outside a tracheid
Bone & Wood• Collagen is bone’s counterpart to wood’s
cellulose• Alternating fibrillar orientation in the
various lamellae in bone and wood imparts strength & toughness
• Pore networks differ only in size and connectivity
Material Property Chart for Orthopedics
Histological Section of Juniper Wood
A: cortical bone after 3 mos.
B: cortical bone after 6 mos.
C: trabecular bone after 6 mos.
D: Cortical bone after 1.5 years
E: cortical bone after 3 years
Conclusions from Medical Study• No infection, serendipitously due to wood oils• Boiling wood to remove excess oil and any
microorganisms lowered MOE, better mechanical fit to wood (see chart)
• Wood well tolerated by body – surrounded by bone
• Even bone growth into open pores and artificial microchannels (a priori machining) for improved integration