Unité de recherche de chimie industrielle organique et alimentaire 00UR/1201, Institut national des Sciences Appliquées et de Technologie INSAT, Centrerbain Nord B.P. N◦ 676/1080, Tunis, TunisiaEPCP IPREM, IUT des Pays de l’Adour, 371 rue du Ruisseau, BP 201, 40004 Mont de Marsan, France
a r t i c l e i n f o
rticle history:eceived 5 February 2013eceived in revised form 14 April 2013ccepted 30 April 2013
Alfa leaves, rush stems, palm leaflets and date palm wood are important renewable raw materials avail-able in Tunisia where they are commonly used in handcrafts (like basketwork and carpets for example).To add value to these plants by using them as a potential reinforcement in so called natural fiber com-posites a better understanding of their physico-chemical properties is needed. As an application, we havestudied the possibility of using alfa leaves, rush stems, palm leaflets as reinforcement in building mate-rials trying to replace commercial fibers. Thus, the effect of hygroscopic parameters were studied andshowed different behaviors depending on the raw material origin and morphology. Palm tree stipe ismore sensitive than other fibers concerning the impregnation yield and saturation degree. The chemicalcomposition was established. The contents of holocellulose and lignin were comparable to those foundwith fibers and wood (softwood and hardwood). Extractives in different solvents and ash contents are
iber-plaster composites relatively high. Extractives from fibers are similar in their values and correspond also to those of palmtree stipe, but they are higher than those of hardwood. About ash contents, the same observation wasfound.
Flexural strength of Tunisian fiber-plaster based composites show a maximum of resistance between4.8 and 5.6 MPa with a strengthening rate of 5% in comparison with commercial plant fiber that presentsa bending strength of 4.8 MPa for also a strengthening rate of 5%.
. Introduction
Natural fibers are a commonly available resource in differentountries on the world (Satyanarayana et al., 1986). Plant fibersould be extracted from leaves (banana, sisal, etc.), leaflets (palm,oconut, etc.), seeds (cotton), fruits (coir), trunk, stems (bagasse,emp, jute, rush, linen, etc.) and other grass fibers (Mwaikambo,006).
Fibers can be considered as naturally occurring compositesonstituted mainly of holocellulose (cellulose, hemicellulose) andignin with minor contents of sugars, starch, proteins, extractivesnd ash (John and Thomas, 2008; Rowell et al., 2000; Satyanarayanat al., 1990).
The performance of a plant fiber depends on several factorsncluding chemical composition and physical properties (Bledzkind Gassan, 1999; Rowell et al., 2000). Over the last few years, many
researchers have been involved in valorizing agricultural residuesand lignocellulosic fibers as reinforcement in polymeric compos-ite materials and cement matrices in substitution of those fromglass and carbon (Satyanarayana et al., 1986; Spinacé et al., 2009).They could offer several advantages, such as availability, recyclabil-ity, low cost, environmental and friendly character, no toxicity, noabrasion, biodegradability and mechanical performance (Bledzkiand Gassan, 1999; John and Thomas, 2008; Reddy and Yang, 2005).
Plaster is a cheap building material, which has been used sinceancient times. It has a lot of applications such as plaster board forinterior building system, fireproofing and decoration. The princi-pal disadvantages associated with plaster are its brittleness andweakness in tension. Therefore, it is relevant to reinforce plasterwith fibers to ameliorate its mechanical properties (Dalmay et al.,2010).
To value the Tunisian natural fibers (alfa, rush, date palmtree stipes, date palm and dwarf palm leaflet) by using them as
reinforcing agents in polymers or materials for boards, we studiedand characterized these local raw material.
In Tunisia, we use actually plant fibers to make decoration falseceiling. Commercial fibers (like jute or sisal) are imported. So, we
ave studied the possibility of replacing commercial plant fibers byocal one.
Alfa (Stipa tenacissima) is a tussock grass distributed in semi-aridnd arid regions of Tunisia (Kasserine, Sidi Bouzid, Kairouan, Gafsa,abes) and occupies 743 thousand hectares (Khiari et al., 2010).he alfa production is estimated by 42 thousand tons in 2009, andre mostly used in the production of paper (Paiva et al., 2007) andandcrafts.
Date palm (Phoenix datylifera) is cultivated in oasis. Tunisia hasore than 4 millions date palms which occupy nearly 41 thou-
and hectares. After the date fruit harvesting, important quantitiesf date palm rachis and leaflets wastes accumulated every year inunisian agricultural lands. Leaflets are generally woven to makeultiple utensils and basketwork, such as dishes, jars, baskets and
ats.Dwarf palm (Chamerops humilis) is a plant that grows on rocky
lains and mountains of Europe and Maghreb (Algeria, Moroccond Tunisia). The dwarf palm leaflets are traditionally used to makerooms and basketworks.
Rush (Juncus maritimus var. typicus) is a plant which grows inet places (as lake, river, pond, etc.). We count approximately 200
pecies (Lisse and Louis, 1954; Ozenda, 1954). In Tunisia, rush isound in different regions (Kasserine, Sidi Bouzid, Gafsa, Gabes, Capon, etc.). It is commonly used in handcrafts but bio-compositesroduction could be new ways of valorizing these abundant renew-ble resources.
. Materials and methods
Raw materials used in this study are consigned in Table 1. Dur-ng the study, they were stabilized in a controlled atmosphereRH = 64 ± 2%) and temperature (T = 20 ◦C ± 2).
The plaster used in this study is intended for decoration (manu-acture of false ceilings) and is provided by “la société industriellee plâtre du Sud”, Oued el Ghar, Tunisia.
Commercial plant fiber used to prepare plaster based compos-tes was purchased from a Tunisian supplier on January 2012.
.1. Determination of moisture content:
The moisture content was evaluated by an infrared desiccantalance (Denver Instrument IR60) using 1 ± 0.001 g of vegetables;
t was shown at time intervals until reaching a constant value. Veg-tables particles were obtained using a grinder (RETSCH ZM200)ith a 40 mesh sieve.
.2. Density measurement of different plants
The density was determined on three randomly selected sam-les for each plant type.
A small fragment was cut from each sample. Masses wereeighted and diameters, lengths and thicknesses were measured
y optical microscopy in reflection mode and at (1×) magnifica-ion. The date palm tree stipe’s fragment length was measured
able 1aw materials description.
Reference Material Harvesting region
AfKaONA Alfa leaves KasserinAfAmHS Alfa leaves AmrounJcMoNc Rush stems with flowers MokeninJcAmHs Rush stems with flowers AmrounFoGaONA Palm leaflets GabesFoPnAmHs Dwarf palm leaflets AmrounBpGa Date palm stip Gabes
Products 49 (2013) 357– 365
using a ruler. The volume of the different plants was calculatedby treating alfa leaves and rush stems fragments as a cylinder andby treating palm leaflets and date palm tree stipe fragments as aparallelepipedic shape.
The experiment was carried out in triplicate. The results wereexpressed as means ± SD and evaluated by analysis of varianceaccording to Cochran test with a probability P ≤ 0.05.
2.3. Determination of the fiber saturation point (FSP)
The upper hygroscopic limit or FSP is obtained for a relativehumidity of 100% that is reached with deionized water (Gonzalez,1997). The dried samples (105 ◦C, 24 h) were sterilized by UVfor 20 min and placed in a closed system containing deionizedwater. The water absorption was determined by gravimetry intriplicate. The weight of samples was measured at time inter-vals until reaching a constant value. The FSP is calculated usingEq. (1):
FSP (%) =[
w2 − w1
w1
]× 100 (1)
W1 is the initial weight of dried sample and W2 is the final weightof sample.
The experiment was carried out in triplicate. The results wereexpressed as means ± SD and evaluated by analysis of varianceaccording to Cochran test with a probability P ≤ 0.05.
2.4. Water impregnation kinetic of fibers
The samples were cut from different plants, dried at 105 ◦Cfor 24 h and immersed in deionized water. The impregnation wasdetermined by gravimetry. The samples were retired from water,wiped to eliminate the access of water on the surface and weighted.These operations were repeated at time intervals until reaching aconstant weight. The impregnation is expressed as a percentageand calculated in Eq. (2):
Imp (%) =[
wt − w0
w0
]× 100 (2)
wt is the weight of the sample at time t and w0 is the weight of thedried sample at time 0.
2.5. Determination of the ash content
The ash content was determined using 1 ± 0.0001 g of particlesdried at 105 ◦C for 48 h. The samples put in porcelain crucibleswere placed in an oven and calcinated at 550 ◦C for 4 h. The contentpercentage of ash was calculated using Eq. (3):
Ash (% on dry basis) =[
w2 − w0
w1 − w0
]× 100 (3)
w0 is the weight of the empty porcelain crucible, w1 is the weightof crucible-dried sample system and w2 is the weight of crucible-calcined sample system.
The experiment was carried out in triplicate. The results wereexpressed as means ± SD and evaluated by analysis of varianceaccording to Cochran test with a probability P ≤ 0.05.
The organic matter content and organic carbon content arededucted and given by Eqs. (4) and (5) respectively:
OM (%) = 100 − ash (%), (4)
OC (%) = 0.48 × OM (5)
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.6. Chemical analysis of plants
The plant samples were reduced in particles using a grinderquipped with a 40 mesh sieve. Dryness was made separately using
desiccant balance to determine the dry weight for each sample.
.6.1. Extractives estimation10 g of sample was extracted by three successive Soxhlet reflux
f acetone–ethanol (2:1), ethanol and water for 4 h for eachxtraction. The solvent was evaporated to dryness and extractsere weighted. The extractives concentration was estimated using
q. (6):
xtractives (% on dry basis) =(
extractsdry material weight
)× 100
(6)
.6.2. Klason lignin estimationKlason lignin content was evaluated on the basis of polysaccha-
ide hydrolysis by concentrated sulfuric acid (72%). 15 ml of 72%ulfuric acid was added to 1 ± 0.001 g of dewaxed and defatted sam-le. The mixture was kept at room temperature for 4 h. Then, theample was transferred in an Erlenmeyer of 1 l and diluted with60 ml of distilled water to reach an acid concentration of 3%. Theystem was then kept under reflux for 4 h. The remaining solidas filtered (sintered glass funnel, number 4, previously weighted),ashed, dried (105 ◦C, 24 h) and weighted. The Klason lignin con-
entration was estimated using Eq. (7):
lason lignin (% on dry basis) =(
residuedry material weight
)× 100
(7)
.6.3. Holocellulose estimationThe holocellulose content was determined by degrading the
ignin polymer.80 ml of sodium acetate and 2 ml of sodium chlorite solution
27%) were added to 2 g of dewaxed and defatted sample. The mix-ure was covered and kept at 76 ◦C with occasional manual stirring.he addition of sodium chlorite solution was conducted 5 times forne hour. Then, after this time, the system was cooled and the holo-ellulose was filtered (sintered glass funnel, number 2, previouslyeighted) and washed exhaustively with cold water and then with
5 ml of acetone and dried at room temperature.For the determination of �-cellulose content, 25 ml of sodium
ydroxide solution (17.5%) was added to holocellulose sample. Theixture was kept at room temperature for 50 min. After that, itas filtered (sintered glass funnel, number 2, previously weighted),ashed exhaustively with 500 ml of distilled water and 15 ml of
cetic acid (10%) and dried at 105 ◦C for 24 h. The �-cellulose residueas estimated using Eq. (8):
-Cellulose (% on dry basis) =(
residuedry weight holocellulose
)× 100
(8)
The hemicelluloses content was obtained by subtracting the �-ellulose rate from the holocellulose content.
.7. Thermogravimetry analysis
Thermal decomposition was performed using a TA InstrumentTGA Q50 instrument). Temperature program was from 25 to 600 ◦Ct a heating rate of 10 ◦C/min. The measurements were conductednder air (60 ml/min).
Products 49 (2013) 357– 365 359
2.8. Preparation of the fiber-plaster based composites:
Only alfa fiber (AfKaONA, AfAmHs), rush (JcAmHs) and datepalm leaflets (FoGaONA) were used in this part of the study.
2.8.1. Fiber alkali treatment:Before treatment, plant fibers were cut to approximately
10 ± 2 cm long spieces. Then, they were soaked in 2.5% NaOH boiledsolution during 90 min (S/L = 1/20). Treated plant fibers were sepa-rated by decanting and were well washed with water. Fiber bundleswere then subjected to a mechanical action. It comes to hammerthem with a piece of wood in order to separate the individual fibers.Hammered fibers were then soaked in a 1% acetic acid solution for10 min, then washed again with water and dried at 40 ◦C for 24 h.
2.8.2. Elaboration of the fiber-plaster based composites:Specimens were made in ‘sandwich’ structure and were of
dimensions 4 cm×4 cm×16 cm. The water over plaster mass ratio(W/P) was equal to 0.7. Hammered fibers were incorporated intothe inorganic matrix for volume fractions equal to 3%, 5%, 7%, 10%and 15%. Specimens were triplicated for each studied volume frac-tion. After the curing time, the specimens were removed from themold and placed in an oven at 50◦ C for 72 hours to dry. Failure testsby three-point bending are performed according to the standardNT 47.23 (1988) and using a bending apparatus like “Automaticflexural tensile tester L15”.
3. Results and discussion
3.1. Moisture content
The moisture contents obtained for alfa (AfKaONA), alfa(AfAmHs), rush (JcMoNc), rush (JcAmHs), date palm leaflets(FoGaONA), dwarf palm leaflets (FoPnAmHs) and date palm treestipe (BpGa) and shown in Table 2. Results are between 6.22% and10.22%. Many factors may influence these values, like the atmo-spheric conditions, type of fibers, age of plants, soil condition inwhich the plant was grown and the method and duration of preser-vation. These results are lowers than previous observations doneby Spinacé et al. (2009) with percentage of moisture in the fiberunder normal atmospheric conditions between 9.16 and 12.09%.
3.2. Density measurement
The density, consigned in Table 2, is calculated for samplespresenting an average moisture content equal to 8.1 ± 1.26% andequal to 890 kg/m3,454 kg/m3, 450 kg/m3, 385 kg/m3, 710 kg/m3,447 kg/m3and 220 kg/m3 for AfKaONA, AfAmHs, JcMoNc, JcAmHs,FoGaONA, FoPnAmHs and BpGa respectively. These values areslightly lower than the values found with other natural fiberslike coconut (1150 kg/m3), sisal (1500 kg/m3) and banana fibers(1350 kg/m3). In general, vegetal fibers present densities lower thanglass fibers (2500 kg/m3) (Bledzki and Gassan, 1999; Spinacé et al.,2009).
The AfKaONA density is equal to the value reported in the lit-erature (890 kg/m3) (Bessadok et al., 2007). However, the AfAmHsrepresents a lower density (454 kg/m3). Various parameters couldexplain this difference such as the plant variety, the soil quality, theweathering conditions and the plant maturity (Baley, 2002).
The two samples of rush represent closed densities with a meanof 417.5 kg/m3. This lower density is due to the rush morphology.
Indeed, the rush marrow has a spongy character. This parenchymais an aerenchyma composed of cells keeping between them anopened and continuous gaseous space, which is at the origin of thelightness and the amortization of the rush (Raven et al., 1999).
360 S. Hamza et al. / Industrial Crops and Products 49 (2013) 357– 365
Table 2Moisture content (H%), dry matter (DM%) content and density of the fibers samples.
difference can be attributed to the chemical composition and thenature of soil in which plants are grown (Khiari et al., 2010). TheAfkaONA presents the lowest ash content 3.64% (±0.65). This valueis comparable to that found in the literature (2%) (Paiva et al.,
a Values are means ± SD. Means are significantly different at P ≤0.05, as assessed
The palm wood is the least dense, because the fibers are com-ined into stipe.
About leaflets, it seems that those of date palm are denser thanhose of dwarf palm. This could be explained by their specific mor-hology.
.3. Impregnation of water
The humidity is one of the important factors that can influ-nce generally the physical characteristics of wood and plant fibers.ndeed, moisture content changes have an influence on density,imensions, strength and resistance to fungal attacks. The fiberaturation point (FSP) is the moisture content for which cellularembranes are saturated with water (bound water), whereas cell
avities are empty (no free water) (Madison, 1944). It constituteslso the limit of the wood swelling and is estimated by around8%. Beyond this point, moisture exists as free water in the cellsoid spaces and the fungus appear. When the water content isnder the FSP, there is a balance between the wood water con-ent and the relative humidity (Gonzalez, 1997). The FSP of theifferent plants are summarized in Table 3. The values are 35.61%,6.72%, 118.62%, 75.20%, 80.52%, 55.39 and 126.45% for AfKaONA,fAmHs, JcMoNc, JcAmHs, FoGaONA, FoPnAmHs and BpGa respec-
ively. These values are higher than the value found generally withood. On the one hand, this result is linked with the chemical com-osition of raw materials. In fact, the absorbed water moleculesill interact with hydroxyl groups of polymers (lignin, hemicellu-
oses, cellulose) constituting fibers. So, more the hydroxyl groupsre abundant more water molecules are absorbed by association.he cellulose cristallinity degree would also explain this result.ore the structure is amorphous more the water molecules are
ccessible to hydroxyl sites. Lignin and hemicelluloses are gener-lly considered as amorphous (Mominul Haque et al., 2009; Spinacét al., 2009). On the other hand, the FSP gives information about thebility of fiber to absorb moisture from the environment; for alfaollected from the semi arid zone of Kasserin, it captures less waterapor than that of the Cap Bon plain. For rush of Moknin collectedrom swamp, it presents a weakened wall that makes it more able tobsorb moisture, while the cap Bon plain rush is more stable. Aboutate palm leaflets, they have more surface area; therefore, moisturebsorption is more evident than that of dwarf palm leaflets. Con-erning palm wood, it is represented by compacted stipes under thesmotic effect after a treatment with brine solution. So it would beore absorbent to moisture by hygroscopic effect.
.4. Water impregnation kinetic
The curve giving the impregnation rate versus time (Fig. 1)hows that at the beginning, the water intake is faster for date palm
tree stipe than for the other studied plants. This result could beexplained by the soft and the porous structure of date palm treestipe (Cecil, 1993; Kriker et al., 2005). The impregnation kinetic isconsidered rapid for all studied plant fibers and the saturation isachieved after 24 h of immersion. The impregnation rate classesfibers into three categories. The first, corresponding to the highestvalue, is related to the date palm tree stipe which shows a dis-tinguished behavior for most parameters; the second set includesthe two samples of rush with date palm leaflets and having inter-mediate values ranging between 144% and 168%. The third oneassembles the two samples of alfa and dwarf palm leaflets withan impregnation rate included between 63% and 96%. This couldbe due to the wax layers that waterproof plants surface partially.The three classes of impregnation rate correspond respectively tothe results of the literature (Table 4), i.e. hibiscus cannebinus forthe first category, sisal for the second and coir and piassava for thethird one.
3.5. Determination of the ash content
The ash contents are shown in Table 5. Minerals are of 3.64%,8.15%, 7.30%, 5.29%, 6.48%, 4.75% and 4.60% for AfKaONA, AfAmHs,JcMoNc, JcAmHs, FoGaONA, FoPnAmHs and BpGa respectively. This
Fig. 1. Impregnation kinetic for alfa leaves, rush stems, palm leaflets and date palmstipe.
S. Hamza et al. / Industrial Crops and Products 49 (2013) 357– 365 361
Table 4Example of water absorption rates of different plant fibers.
Water absorption (%) Reference Water absorption (%) Reference
Sisal fiber 190–250 Toledo et al. (2005) Piassava 34–108 Savastano et al. (1999)110 Savastano et al. (1999) Date palm surface fibers 97–203 Kriker et al. (2005)200 Ramakrishma and
Sundararajan (2005)Bamboo 145 Savastano et al. (1999)
a Values are means ± SD. Means are not significantly different at P ≤ 0.05, as asses
007). The FoGaONA has an ash content of 6.48% (±0.19) whichs similar to that 6.5% determined by Bendahou and al (2007). Palm
ood is very rich in minerals compared to coniferous and decidu-us wood. They present generally contents lower than 1% (Rowellt al., 2000), while palm wood presents 4.6% content. The palmree anatomy could explain this difference in content. In fact, thealm is a monocotyledonous plant whose stem is composed of aoft central cylinder and a hard extern bark. The massive heart inoft marrow is formed of a set of conducted units and scatteredisorderly in a lignified parenchyma (Cecil, 1993). The soft struc-ure would facilitate absorption and transport of minerals from theoil.
The organic matter rate is deduced from ash content and it coulde converted into organic carbon as a result of multiplication by theoefficient 0.48. Obtained rates are of around 45% of organic carbon.
.6. Determination of extractives content
The extractives contents obtained with different solvents areisted in Table 6. They show that raw materials are characterized
y relatively high amounts of extractives. They present 12.78%,7.99%, 17.42%, 17.45%, 21.82%, 28.48% and 11.50% for AfKaONA,fAmHs, JcMoNc, JcAmHs, FoGaONA, FoPnAmHs and BpGa respec-
ively. These values are higher than those found generally with
able 6xtractives, Klason lignin, hemicellulose and cellulose contents of alfa leaves, rush stems,
(%) Alfa Rush
AfKaONA AfAmHs JcMoNc
Aceton/ethanol extractives 4.89 7.15 4.21
Ethanol extractives 2.00 2.54 5.48
Hot water extractives 5.89 8.30 7.73
Total extractives 12.78 17.99 17.42
Lignin 19.54 18.54 18.54
�-Cellulose 44.86 47.37 40.99
Hemicellulose 28.90 35.13 27.84
Holocellulose 73.76 82.50 68.84
%): percentages are given on raw material dry basis.
95.40 ± 0.11 45.79 ± 0.05
y Cochran test.
coniferous and deciduous wood (<10) (Longui et al., 2012) andcomparable to levels reported for other fibers source like barely:20.7% and wheat straw: 17.6% (Khiari et al., 2010). The dwarfpalm leaflets present the highest extractives content (28.48%). TheFoGaONA presents a similar content to that found by Khristova et al.(21.2%) in their study conducted on the date palm rachis and leaflets(Khristova et al., 2005). The date palm wood corresponds to thelowest extractives content.
It is important to evaluate the plant fibers extractives content.Although this constituent presents a minor fraction of the fiberchemical composition, it can affect physical and chemical prop-erties of composites based on lignocellulosic fibers. Boustingorryand al. (2005) have shown the influence of polar extracts on theplaster hydration kinetic as well as the gypsium setting time.Where Shebani and al (2008) illustrated in their study the improve-ment of the wood thermal stability after removing extractives; itshould be preferable to use extracted wood as reinforcement inwood-polymer-composites (WPC) which require preparation tem-perature acceding 200 ◦C; the same study showed the improvementof the thermal stability by removing the polar extractives (Shebani
et al., 2008).
Alfa leaves and dwarf palm leaflets are characterized by thehighest extractives rates corresponding especially to those of ace-ton/ethanol extracts.
.7. Determination of Klason lignin and holocellulose content
The Klason lignin and holocellulose contents are illustratedn Table 6. The date palm stipe presents the highest ligninontent (27.86%). This value is close to that reported for conif-
rous wood (26–34%) (Reddy and Yang, 2005). The valuesvaluated for other materials are about 20%, which character-zes deciduous wood and other annual plants such as kenaf
Fig. 2. The TG and DTG of studied plant fibers (
Products 49 (2013) 357– 365
(15–21%), bagasse (19–24%) and jute (21–26%) (Rowell et al.,2000). The �-cellulose and hemicellulose contents are compara-ble to values characterizing wood and annual plants (Rowell et al.,2000).
Table 6 shows the alfa and the date palm leaflets chemical
composition evaluated in this study. If we compare with resultsreported in other studies, differences could be attributed to the cli-matic conditions, the soil chemical composition, the plant variety
a, b and c) heated at 10 ◦C/min under air.
S. Hamza et al. / Industrial Crops and Products 49 (2013) 357– 365 363
Table 7Limits of the second phase in the thermal decomposition of plant fibers.
nd age (Bledzki and Gassan, 1999; Guimarãesa et al., 2009; Paivat al., 2007).
The results reported in the literature indicate that alfa containsbout 23% of lignin, 44.4% of �-cellulose and an average of 26%or hemicellulose, which means that we have 70.9% of holocel-ulose. Similar rates are found with alfa of Kasserin. Alfa samplesrom Amroun is richer in holocellulose with lower lignin content.he same findings are valid for rush samples of Moknin. Literatureesults show a rich lignin content for a Brazilian date palm leafletsample (27%) with a rate of about 60% for holocellulose. Date palmeaflets of Gabes are richer in holocellulose and lower in lignin thanrazilian one with differences of 7%. However, all studied fibersre composed of lignin and holocellulose with proportions close toommon values (Bahloul et al., 2009; Guimarãesa et al., 2009).
.8. Thermogravimetry analysis
The thermogravimetry analysis curves are all characterized byhe same evolution of the mass loss versus temperature. We thenistinguish three major phases:
1) Between 25 and 200 ◦C: it corresponds to a mass loss ofabsorbed moisture of approximately 5%, 6%, 8%, 7%, 8%, 5%,and 8% for AfKaONA, AfAmHs, JcMoNc, JcAmHs, FoGaONA,FoPnAmHs and BpGa respectively (Fig. 2). The endothermicevaporation of residual water was occurred between 25 and100 ◦C (Albano et al., 1999; Arbelaiz et al., 2006). Between 100and 200 ◦C the evolution of the mass loss is practically absent,which means that the fibers constituents are thermally stablein this temperature range.
2) The second phase is characterized by a significant mass loss. Itslimits are slightly different between samples (Table 7).
The DTG curves showed the presence of peaks and shoul-ders that characterize the dry plant material decomposition.According to Ouajai and Shanks (2005), the decompositionof hemicelluloses and pectins take place between 250 and320 ◦C, while the decomposition of cellulose occurs between390 and 400 ◦C. Tanobe et al. (2005) indicates that hemicel-luloses degrades about 200 and 260 ◦C, followed by cellulosebetween 240 and 350 ◦C, while Lignin degrades about 280and 500 ◦C. Comparing the decomposition temperatures of thedifferent plant materials is not evident because thermal degra-dation depends on the nature of the analyzed samples).
3) The third phase is characterized by the decrease in the rate ofmass loss and corresponds to the thermal degradation of therest of organic matter resulting from the decomposition dur-ing the second phase and residues of high molecular weight(Sreekala et al., 1997). It should be noted that some complex ofstructural hemicelluloses could undergo decomposition in thistemperature range (Mellon and Sharma, 2002).
.9. Flexural strength of fiber-plaster based composites
The alkaline treatment is a good technique to remove impuritiesnd to modify the fiber surface to get a better adhesion between
Fig. 3. Flexural strength as a function of hammered fibers fraction.
the fiber and the matrix (Cao et al., 2006). It is also consideredas the most economical treatment, the most viable and withoutenvironmental impact (Ray and Sarkar, 2001).
Flexural strength shows a modest improvement of the rein-forced specimens resistance compared to the ‘blank’ (Fig. 3). Inaddition of the lightness they brought to the plaster material, fibersgenerate behavior changes even if they are added in small quanti-ties. In fact, the break becomes more controlled and the compositebecomes ductile since the microcracks propagation is delayed bythe presence of fibers that serve to bridge cracks and to supporta part of the applied load (Dalmay et al., 2010). Commercial plantfiber (Fil) has a maximum bending strength equal to 4.8 MPa for avolume fraction of 5%. Whereas hammered lab made filasses have amaximum resistance between 4.8 and 5.6 MPa. The correspondingflexural strength is 4.8, 5.0, 5.2 and 5.6 MPa for FoGaONA, AfKaONA,JcAmHs and AfAmHs respectively. These values correspond to astrengthening rate of 5% for JcAmHs and AfAmHs and of 7% forAfKaONA and FoGaONA.
We observed a drop in resistance for high reinforcing fibersamounts. This could be explained by the creation of porosity inthe material due to an intra-and extra fiber emptiness (Bentchikouet al., 2007), that reduces the composite compactness and cohesion.
A lower stiffness was noted in the case of composite reinforcedby 3% of JcAmHs compared to the ‘blank’. According to Dalmayet al. (2010), fibers incorporation could create defects within thematerial.
Flexural strength decrease observed for JcAmHs (7%) andAfAmHs (7%) could be due to a poor distribution of fibers (Djoudiet al., 2009) or to the mechanical effects of hammering.
The flexural strength is also controlled by the quality, the length(Morlier and Khenfer, 1991) and the orientation of fibers (Djoudiet al., 2009). According to Morlier and Khenfer (1991), growth infiber length significantly increases the flexural strength and affectsthe failure mode. Indeed, the break is ductile and stable for longlengths of fiber, while it is unstable and weak with sudden drop inforce after its maximum for small fiber lengths. The same authorsshowed that the failure mechanism is in relation with the fiberlength. In fact, for short lengths, the failure occurs by loosening,while for longer lengths, rupture takes place by fracture of the fiber.
A study conducted by Herrera-Franco and Valadez-Gonzalez(2005) on henequen fibers reinforced polyethylene composites,demonstrated that the micromechanical events that occur for along fibers reinforced composite are different from those observedfor a short reinforced composite. In short fibers there are varia-
tions in stress distribution along the fibers-matrix interface, andend effects can be neglected in the case of long fibers, but theycan be very important with short fibers reinforced composites.
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A
A
B
B
B
64 S. Hamza et al. / Industrial Cro
his hypothesis suggested by Herrara-franco and Valadez-Gonzalez2005) could explain the negligible change in resistances obtainedith FoGaONA for different volume fractions. In fact, FoGaONAbers have almost kept their original length after alkali treatment.
. Conclusion
This experimental study has led to the determination of param-ters helping to select the most adequate Tunisian plant fibers toound new way for its valorization and to reinforce composites oro improve their value. For example, fibers with a high impregna-ion degree may lead to difficulties when implementing materialsased on hydraulic lime due to the mobilization of an importantart of mixing water by fibers.
In Tunisia, the natural fibers composites could partially sub-titute for timber-wood and wooden board in buildings area. Toeach these applications, our study has established preliminaryata-sheets for three fibers and stipe i.e. alfa (leaves), rush (steams)nd palm (leaflets and stipe). Hygroscopic properties (Moistureontent, FSP, impregnation kinetic) were determinated. Strong dif-erences have been observed (from 35.6% mean for alfa of Kasserino 1265% for date palm tree stipe. The impregnation kinetic is quickor all plant fibers. Alfa of Kasserin presents the highest density890 kg/m3) while date palm tree stipe presents the lowest one220 kg/m3).
The analysis of ash content shows rates between 3.6% and 8.2%.ignin, holocellulose and extractive contents are comparable toevels reported in literature on other fibers sources.
Thermogravimetry analysis has shown the stability of fiberselow 200 ◦C. All these results permit to give better understand-
ng of potentiality use of Tunisian fibers in future fiber compositeroduction. Further, research will have to be develop on extrac-ives, and relationship between fibers and resins during compositerocessing.
As an application for these plant fibers, we investigated theossibility of integrating them as reinforcement in plaster matrix.unisian fibers were found to enhance the flexural strength of fiber-laster composites in comparison with commercial plant fiber.arious flexural strength results observed show that fiber-plasteromposites strength depends on the chemical, mechanical andorphological properties of plant fibers.
cknowledgements
We gratefully acknowledge French and Tunisian governmentsor financial support from the “PHC Utique-CMCU 2010”, and thecentre technique des matériaux de construction, de la céramiquet du verre, CTMCCV” for allowing us to achieve the mechanicalests within their “béton et liants” department. This work was alsounded by ANR-10-EQPX-16 XYLOFOREST.
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