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J. Mater. Res. Tecnol. 2012; 1(2):117-126

2012 Brazilian Metallurgical, Materials and Mining Association. Published by Elsevier Editora Ltda. All rights reserved.

Journal of Materials Research and Technology

www . jm r t . com .b r

Environmental, economic, and technical reasons justify research efforts aiming to provide natural materials with possibility ofreplacing synthetic fiber composites. Commonly known lignocellulosic fibers, such as jute, sisal, flax, hemp, coir, cotton, wood, and

bamboo have not only been investigated as reinforcement of polymeric matrices but already applied in automobile components. Less

common fibers, such as curaua, henequen, fique, buriti, olive husk, and kapok are recently being studied as potential reinforcement

owing to their reasonable mechanical properties. The relatively low thermal stability of these fibers could be a limitation to their

composites. The works that have been dedicated to analyze the thermogravimetric stability of polymer composites reinforced with

less common lignocellulosic fibers were overviewed.

*Corresponding author.

E-mail address:[email protected] (S. N. Monteiro)

REVIEW ARTICLE

Thermogravimetric Stability ofPolymer Composites Reinforced with Less CommonLignocellulosic Fibers an Overview

Sergio Neves Monteiro1,*, Vernica Calado2,

Rubn J. S. Rodriguez

3

, Frederico M. Margem

3

1Instituto Militar de Engenharia (IME), Materials Science Department, Rio de Janeiro, Brazil.2Escola de Qumica, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil.3Universidade Estadual do Norte Fluminense, Campos dos Goytacazes, Brazil.

Manuscript received April 14, 2012; in revised form June 19, 2012

Sergio Neves Monteiro(June 24, 1943) graduated as a Metallurgical Engineer (1966) at the UniversidadeFederal do Rio de Janeiro (UFRJ). Received his MSc (1967) and PhD (1972) from the University of Florida,followed by a course (1975) in Energy at the Escola Superior de Guerra (Brazilian War College) andPost-doctorate (1976) at the University of Stuttgart. Joined the Metallurgy Department (1968) and was

appointed (1977) Full Professor of the Post-Graduation Program in Engineering (COPPE) of the UFRJ. Hewas elected Head of the Department (1978), Coordinator of COPPE (1982) and Under-Rector for Research(1983). Invited as Under-Secretary of Science for the State of Rio de Janeiro (1985) and Under-Secretaryof College Education for the Federal Government (1989). Retired in 1993 and joined the Universidade Es-tadual do Norte Fluminense (UENF). Published over 900 articles in journals and conference proceedings.Has been honored with several awards including the ASM Fellowship. Is presently top researcher (1A) ofthe Conselho Nacional de Desenvolvimento Cientfico e Tecnolgico (Brazilian Council for Scientific and

Technological Development CNPq), vice-president of the Fundao de Amparo Pesquisa do Estado do Rio de Janeiro (SuperiorCouncil of the State of Rio de Janeiro Research Foundation FAPERJ), consultant for the main Brazilian R&D agencies and memberof the Editorial board of three international journals.


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Monteiro et al.118


1. Introduction

The first engineered composites materials were probablyreinforced with natural fibers and produced in theprimor-diumof mankind. Evidence of adobe construction blocks ofsun-dried clayey mud incorporated with straw was found inthe ancient Egyptian civilization. According to our currentinterpretation, these first composites would be consideredenvironmentally friendly owing to their all natural compo-nents. Even today, the rudimentary technique used by ourancestors to fabricate such composites persists in many lowincome regions of the world. As mentioned by Bledzki andGassan[1], in a seminal review on natural fiber composites,only at the end of the 19th century the industrial manu-

facture of naturalfibers with small content of polymericbinder was reported for airplane seats and fuel tanks. Large

amounts of sheets, tubes, and pipes for electronic pur-pose were continuously fabricated as earlier as 1908, usingnatural fibers, paper, or cotton incorporated into phenolicmatrix[1,2]. With the rising performance of petroleum-basedpolymers and synthetic fibers as well as the facility to com-bine them into more uniform and stronger composites, theindustrial production of traditional natural fiber compositesdeclined.

In another classic review on biofibres and biocomposites,Mohanty et al.[2]indicated that the synthetic fiber compos-ites reached commodity status in the 40s with glass fiberreinforcing (fiberglass) unsaturated polyesters. These syn-

thetic fiber composites experienced an exponential growthafter the World War II to become the most successful classof engineering materials[35]with application in practicallyall fields of human interest, from appliances and sports tosurgical prosthesis and aerospace components. At the endof the last century, increasing environmental concerningover generalized pollution caused by non-degradable ma-terials, especially long lasting plastics, and climate changesresulting from CO

2emission, promoted a growing tendency

towards the substitution of synthetic fibers composites.Natural materials, particularly cellulose-rich fibers, alsoknown as lignocellulosic fibers, were renewed as reinforce-ment of polymer composites. A considerable number of re-

searches have, in the past few decades, been dedicatedto lignocellulosic fibers as engineering materials and theirreinforced polymer composites for applications in substi-tution of synthetic fiber composites. Several reviews andgeneral articles covered this trend[1,2,615]. In these publica-tions, advantages are emphasized and drawbacks discussedaiming at reduce the limitation, which exists in practicaluse. Despite the drawbacks, a growing industrial applica-tion of lignocellulosic fiber composites is nowadays occur-ring in sectors such as building construction, packaging,sport devices, electrical parts, and vehicle components[14].Automotive industries, initially the Europeans followed byAmericans and Japanese, are adopting this type of compos-ites in several interior and exterior parts[1620].

It was emphasized[21,22]that, as compared to fiberglass,

the lignocellulosic fiber composites are lighter, cheaper,and less abrasive in contact with processing equipments.Furthermore, fiberglass represents a problem to the envi-ronment with restriction to final destination by incinerationin thermo-electric plants. Glass fiber particulates also rep-resent potential health hazardous both in the initial com-posite processing and latter at the end-of-life degradation.By contrast, the thermal stability of a lignocellulosic fibercomposite is inferior to similar matrix composite reinforcedwith glass fiber. This could be a critical restriction for condi-tions associated with relatively high temperatures attainedduring the curing of the composite or its in-service use.In fact, temperature usually causes an initial degradation

of thefiber organic structure and thus limits the polymercomposite application.

2. Thermal Decomposition of LignocellulosicMaterial

Several review articles[2326]have, since more than five de-cades ago, been dedicated to the thermal decompositionof lignocellulosic materials. Beall and Eickner[23]reviewedworks on thermal analysis results of wood and its cellulose,hemicelluloses, and lignin constituents. Kilzer[24]reviewedworks on the thermal decomposition of cellulose. Nguyenet al.[25,26]conducted subsequent reviews on the applicationof differential thermal analysis (DTA), differential scanning

calorimetry (DSC), and thermogravimetry (TG) to the studyof lignocellulosic materials as well as modified forms of li-gnocelluloses. These review articles[2326]indicated the fol-lowing results:

2.1 Cellulose

Cellulose decomposition takes place by major reaction in-volving depolymerization, thermoxidation, dehydration,and formation of glycosans, depending on the presence ofoxygen or an inert atmosphere. In a non-oxidative atmo-sphere, dehydration occurs in a range of 210C260C anddepolymerization with volatilization of levoglucosans, at

about 310C. Under oxygen, thermoxidative reactions oc-cur in the temperature range of 160C250C. The degra-dation of cellulose by pyrolysis has been assumed to followa first-order kinetic. In the specific case of wood, cellu-lose decomposition in air begins at 320C with a maximumweight loss at 350C. In helium it also begins at 320C, butthe maximum rate is shifted to 375C. Cotton cellulose dis-plays two endothermic DTA peaks at 100C and 367C.

2.2 Hemicellulose

Hemicellulose constituents decompose at temperatures aslow as 159C175C, as in the case of acetyl galactogluco-mannan. DTA of xylan in oxygen exhibits a first exothermic

KEY WORDS:Natural fibers; Polymer-matrix composites (PMCs); Thermogravimetric analysis.

2012 Brazilian Metallurgical, Materials and Mining Association. Published by Elsevier Editora Ltda. All rights reserved.


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Thermogravimetry of Composites with Less Common Natural Fibers 119


peak at 215C. Both arabinogalactan and deacetylated ga-lactoglucomannan begin degradation at 195C, reaching amaximum at 280C.

2.3 Lignin

Obtained by hydrolysis of wood, it was found to decomposein three stages. At temperatures below 220C250C, con-

densation and splitting of the side chains takes place. Be-tween 300C400C, active pyrolysis leads to the formationof free radicals. Above 400C, decomposition is associatedwith a series of degradation and condensation reactionswith accumulation of aromatic products.

2.4 Wood

In its natural and unmodified form, showed, under helium,a first endothermic peak at 107C, corresponding to wa-ter loss. Weak endothermic peaks were found at 207C and330C, corresponding to dehydration and depolymerizationof various constituents, probably including hemicellulose.

A very strong endothermic peak at 367C was attributed tocellulose decomposition. An exothermic peak rises above400C, presumably related to recombination of celluloseand lignin fragments. Under oxygen, it was reported an en-dothermic peak at 87C, owing to evaporation of water, andtwo exothermic peaks at 343C and 470C, probably due tocellulose and lignin.

3. Thermal Analysis of CommonLignocellulosic Fiber Composites

A short review on the thermal stability of polymer com-posites reinforced with few common lignocellulosic fiberswas, for the first time, presented as one of the sections of

the Nabi Saheb and Jog[6]review on natural fiber polymercomposites. They indicated that the thermal degradationof natural fibers is a crucial aspect in the development oftheir composites and thus has a bearing on the curing tem-perature in the case of thermosets and extrusion tempera-ture in thermoplastic matrix composites. Nabi Sahed andJog[6]also stated that thermal stability improvement havebeen attempted by coating and/or grafting the fibers withmonomers, quoting the works of Mohanty et al.[27]and Sa-baa[28]. The effect of the composite fabrication ambient wasdiscussed by the authors[6]as a possibility of lignocellulosicfiber degradation, quoting the work of Sridhar et al.[29], andindicating that the actual practice is carried out under air

and that thermal degradation can lead to inferior mechani-cal properties. As a final remark, Nabi Saheb and Jog[6]con-cluded that the thermal degradation of the lignocellulosicfiber inside the polymeric composite matrix also results inproduction of volatiles at processing temperatures above200C. This could result in porous composites with lowerdensities and inferior mechanical properties.

Since this first short review[6], numerous works haveinvestigated the thermal stability of polymer compositesreinforced with common lignocellulosic fibers. The readermay find specific data and conclusions on the following ar-ticles listed by employed reinforced fiber:a) Jute Fiber Composites, in phenol formaldehyde[30], poly-ester[31], vinyl ester[32], polyester with acrylic acid[33], high

density polyethylene[34], polypropylene[35], and polylacticacid[36]matrices;b) Hemp Fiber Composites, in polyester[37], cashew nut shellresin[38], epoxy[39], polypropylene[40,41], and starch-base ther-moplastic[42]matrices;c) Sisal Fiber Composites, in polypropylene[43,44], blend ofpolypropylene with high density polyethylene[43], polysty-rene[45], polypropylene and maleic acid anhydride grafted

styrene-ethylene-co-butylene-styrene copolymer[46,47], epoxy[48],phenolic and lignophenolic[49], and soy protein blended withgelatin[50]matrices;d) Flax Fiber Composites, in polypropylene[51], epoxy[39], andpolylactic acid[52]matrices;e) Coir Fiber Composites, in copolymer of starch with ethyl-ene vinyl alcohol[53], and polyester[54]matrices;f) Cotton Fiber Composites, in phenolic thermoset[55]matrix;g) Kenaf Fiber Composites, in epoxy[39] chitosan[56,57], andstarch-based thermoplastic[40]matrices;h) Wood Fiber Composites, in polypropylene[5860], low andhigh density polyethylene[59,61], and polyhydroxy(butyrate-

co-valerate)[60]

matrices;i) Pineapple Fiber Composites, in polyethylene[62],polyhydroxy(butyrate-co-valerate)[63], and polycarbonate[64]matrices;j) Bamboo Fiber Composites, in polylactic acid[65], polybu-tylene succinate[65], epoxy[66], and polyhydroxy(butyrate-co-valerate)[67]matrices;k) Ramie Fiber Composites, in polylactic acid[36]matrix;l) Banana Fiber Composites, in polyvinyl chloride[68]matrix;m) Bagasse Fiber Composites, in polyurethane (PU)[69], andrecycled high density polyethylene[61]matrices.

As a general comment, one may conclude from all theseworks on the thermal stability of polymer matrix compositesreinforced with commonly known and used lignocellulosic

fibers that their processing and applications are restrictedto a safe temperature of 250C, or to a maximum of 367C,in case of more stable specific polypropylene and maleicanhydride grafted styrene-ethylene-co-butylene-styrenecopolymer matrix reinforced with sisal fiber[46]. The readershould also bear in mind that all these composites, owing tothe contribution of the lignocellulosic fiber, display a DTGwater loss peak which is found at temperatures as low as37C[32]and inferred at about 140C144C[48,53].

4. Thermogravimetric Stability of LessCommon Lignocellulosic Fiber Composites

In principle, a complete assessment of the thermal be-havior of a material would require not only temperaturedifference, DTA, thermogravimetric, TG/DTG, differentialcalorimetric, DSC, and dynamic-mechanical (DMA) thermoanalyses, but also the evaluation of properties such as ther-mal conductivity, specific heat, and thermal diffusivity. Thescope of this overview is limited to thermal stability re-sults associated with weight loss variation with tempera-ture obtained by thermogravimetric analysis. These results,displayed as TG thermograms as well as its derivative DTG,will be covered for relevant works on polymer compositesreinforced with less known fibers published in internation-ally recognized sources. Numerous less common lignocel-lulosic fibers such as curaua, henequen, fique, buriti, olive


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Monteiro et al.120


husk, kapok, abaca, isora, piassava, artichoke, milkweed,sabei, okra, caroa, sansevieria, palmyrah, maize, phrag-mite, esparto, malva, paina, sponge gourd, communis, pitafloja, roselle, canary, rye, mesta, barley, raphia, oat, andrape are commercially available and currently being inves-tigated for their potential as engineering materials[14,15,70].Only a few of these less common fibers, however, have beenstudied for thermogravimetric stability in association with

polymer composites. These few fibers curaua, henequen,fique, buriti, olive husk, and kapok serve as sub-titles inreviewing the following related thermogravimetric stabilityworks on their polymer composites.

4.1 Curaua Fiber Composites

Moth and Arajo[71] showed TG/DTG and DTA curves forPU matrix composites reinforced with up to 20 wt.% ofcuraua fibers. For the neat PU, the DTG curve displays asmall initial peak at 260C that was assigned to the de-composition of additives in the PU. A broad shoulder peakaround 360C followed by a major peak at 422C were

attributed to decomposition of the rigid and soft urethanebonding, respectively. The DTA curve shows three endo-thermic events at 250C, 330C, and 420C that corrobo-rate those found in the DTG peaks. The investigated com-posites[71]also display faint DTG peaks around 60C, dueto the release of water. Two other decomposition peakswith temperatures (wt.% of curaua fibers) can be seen at358C and 418C (5 wt.%); 356C and 420C (10 wt.%);and 356C and 418C (20 wt.%). Endothermic DTA peaksare also seen at the same temperatures and conditions.These results indicate that the thermal stability of thecomposites is practically the same of the PU. Moreover,the amount of curaua fiber in the composite causes noapparent change in the thermal stability.

Arajo et al.[72]presented results from TG/DTG curvesof isolated curaua fiber as well as high density polyethyl-ene (HDPE) and HDPE matrix composites reinforced with20 wt.% of either unmodified (natural) or poly(ethylene-co-vinyl-acetate) (EVA) and maleic anhydride graftedpolyethylene (PE-g-MA) compatibilized curaua fibers.The DTG curve of the neat HDPE shows a peak at 478C.The DTG curves of the composites display two distinctpeaks. The first, coinciding for all composites at 349C,occurred closer to the main decomposition peak of thecuraua fiber, 363C. Additionally, the authors calculated aweighted mean expected DTG curve if there was no inter-action among the degradative process for the composites,

quoting the work of Waldman and de Paoli[73]

. The secondpeak was found at about 468C471C for the composites.A comparison of TG curves with the calculated curve al-lowed the authors[72]to indicate that the composite com-patibilized with PE-g-MA is less stable, while those withEVA as well as with no compatibilization are more stable.

Ferreira et al.[74]showed TG/DTG curve, obtained at aheating rate of 10C/min in nitrogen, for polyester com-posites reinforced with up to 30 vol.% of untreated curauafibers. A small initial peak observed for all compositesaround 70C was attributed to moisture release. The neatpolyester begins to decompose around 250C and displaysa major DTG peak at about 410C related to the degra-dation of its molecular chains. The composites display a

shoulder peak around 370C, which is more pronouncedfor higher volume fractions of curaua fiber, as well as amajor peak almost coincident with that of the neat poly-ester. Fig. 1 illustrates the TG/DTG curves of neat poly-ester and composites reinforced with up to 30 vol.% ofcontinuous and aligned curaua fibers, adapted from theFerreira et al.[74] work. In this figure, an enlarged insertreveals shoulder peaks associated with curaua fiber ther-

mal degradation in the composite. By considering theseoverviewed works, and based on the results for the iso-lated curaua fibers[71,72,7577]with shoulder at 268C290Cand major peak at 310C365C, one should conclude thatPU[71], HDPE[72], and polyester matrices[74]composites arethermally more stable than the pure curaua fiber.

4.2 Henequen Fiber Composites

Sgriccia and Hawley[39]presented thermogravimetric re-sults on epoxy matrix composites reinforced with 15 wt.%of hemp (section 3, item b), flax (section 3, item d), kenaf(section 3, item g), and henequen fibers. These compos-

ites were both oven and microwave cured. For compari-son, similar glass fiber composites were also investigat-ed. Although no TG curves were shown, the authors[39]

Fig. 1 TG/DTG curves of polyester composites reinforced with different

volume fraction of curaua fibers. (a) Plain curves; (b) enlarged DTG curves.

Adapted from Ferreira et al.[74].

(a)

(b)


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presented the degradation temperature associated with5 wt.% to 75 wt.% of weight loss. Tables 1 and 2 repro-duces these results and the reader can observe that theisolated henequen fiber shows degradation temperature(weight loss) of 61C (5 wt.%) up to 392C (75 wt.%). Onthe other hand, the microwave cured composites show asignificant increase: 355C (5 wt.%) up to 483C (75 wt.%).These values are closer (Tables 1 and 2) to those corre-

sponding to the neat epoxy microwaved of 403C (5 wt.%)and 484C (75 wt.%). Fig. 2, adapted from Sgriccia andHawley[39] with necessary corrections, illustrated ESEMimages of microwave cured composites. The authors[39]indicated that the natural fiber composites investigated,including the henequen/epoxy, both oven and microwavecured, composites would not be suitable for applicationsat temperatures as high as those of similar glass fibercomposites.

4.3 Fique Fiber Composites

Gan and Mondragon[78]performed thermogravimetric anal-ysis on both polypropylene (PP) and polyoxymethylene (POM)matrices composites reinforced with 20 wt.% fique fibers,untreated as well as modified with maleic anhydride (MA),propionic acid (PA), glycidyl-methacrylate (G) and formalde-hyde (F) or compatibilized with a copolymer of polypropylene

(Fluka) and maleic anhydride (MAPP). The discussed compos-ite results were limited to some of the fiber treatments. Forinstance, a major decomposition peak was reported for theneat PP at 473C, while the untreated as well as PA andMAP treated fiber composites display three peaks. Fig. 3,adapted from the work of Gan and Mondragon[78], showsTG/DTG curves for neat PP and PP composites reinforced with20 wt.% of fique fibers as well as neat POM and POM compos-ites reinforced with 20 wt.% of fique fibers. The authors[78]indicated that the first (310C) and second (387C) peaks forthe untreated fiber composites, as well as the correspondingfirst (344C) and second (393C) peaks for the MAPP treatedfiber composites, are related to those of the isolated fiquefiber, 301C and 356C, respectively, quoting their previouswork[79]. The third peak at 451C for untreated and at 476C

for MAPP treated fiber composites correspond to the decom-position of the PP matrix. As a general comment, Gaan andMondragon[78]stated that the lower thermal stability of POMwith respect to PP does not allow for separating the con-tributions for thermal degradation of fique fibers and POMmatrix in related composites. Higher temperatures than thatfor the neat POM are necessary for complete degradation ofits composites, possibly due to fiber degradation delayingand matrix crystallinity variations.

4.4 Buriti Fiber Composites

Santos et al.[80]conducted thermogravimetric experimentson cardanol-formaldehyde (CFR-thermoset resin) matrixcomposite incorporated with 5 wt.%, 10 wt.%, and 15 wt.%of buriti fibers obtained from leaf straw. Buriti fibers wereboth untreated and subjected to NaOH alkali (merceriza-tion) or silanization treatments. TG curves show that the

Table 1 Degradation temperatures for glass and henequen fibersassociated with different levels of TG weight loss

Weight loss (%)T(C) 5wt.%

T(C) 25wt.%

T(C) 50wt.%

T(C) 75wt.%

Henequen 61.1 301.4 337.4 391.6

Glass 586.4

Adapted from Sgriccia and Hawley[39].

Table 2 Degradation temperatures for glass and henequen fiberreinforced epoxy matrix composites associated with differentlevels of TG weight loss

Weight loss (%)

T(C) 5

wt.%

T(C) 25

wt.%

T(C) 50

wt.%

T(C) 75

wt.%

Glass oven 400.3 N/A 401.8 538.6

Glass microwave 400.4 N/A 401.7 481.7

Henequen oven 305.8 374.6 391.0 455.9

Henequenmicrowave

355.0 389.1 392.0 483.0

Neat epoxy oven 396.6 N/A 397.9 489.8

Neat epoxymicrowave

403.3 N/A N/A 484.3


Fig. 2 ESEM micrographs of microwave cured epoxy composites reinforced

with: (a) henequen and (b) glass fibers.


Fig. 3 TG/DTG curves: (a) neat PP; (b) PP composites with 20wt.% of fique

fibers; (c) neat POM; (d) POM composites with 20 wt.% of fique fibers.

Adapted from Gan and Mondragon[78].

(a) (c)

(b) (d)


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Monteiro et al.122


CFR has, apparently, an onset temperature for thermaldegradation, around 320C, which is higher than those forthe 10 wt.% buriti fiber composites, around 240C. In fact,the authors[80] indicated that both composites present anintermediate thermal stability in relation to the isolatedburiti fiber and the matrix. Furthermore, the mercerizedfiber composite curve shows an inflection at about 305Cbecause of the thermal fiber degradation and another at

400C owing to the thermal degradation of the thermo-set resin. Fig. 4, reproduced from the work of Santos etal.[80], shows SEM micrographs of untreated, mercerizedand silanized buriti fibers as well as 10 wt.% buriti fiberreinforced CFR matrix composites. As indicated by the au-thors[80], the mercerized fiber (Fig. 4a) displays a roughaspect, probably due to the removal of low molar masscompounds, which leaves cavities at the surface. The si-lanized fiber (Fig. 4c) presents a more regular surface.This suggests that the silanization produces a film coatingon the entire fiber surface. The composite (Fig. 4d) dis-plays a lamellar-like morphology with evidence of excel-lent adhesion between the matrix and mercerized fiber.

This good coverage of thefiber by the resin may contrib-ute to improve its thermal stability.

4.5 Olive Husk Fiber Composites

Amar et al.[81] performed thermogravimetric analysis at aheating rate of 10C/min in nitrogen on polypropylene (PP)matrix composites added with 10 wt.% and 20 wt.% of olivehusk flour (OHF), the solid portion remaining after pressingolives, which contains significant amounts of lignocellulosicfiber. The OHF were both untreated and subjected to vinyl-triacetoxysilane (VTAS) chemical treatment or grafted with

maleic-anhydride-polypropylene (PPMA). The pure untreatedOHF begins to degrade at 210C, while the VTAS treated OHFat 201C. This reduction was attributed by the authors[81]tothe elimination of hydrogen bonds that requires significantenergy. DTG peaks were also related to the OHF degradation.The first, around 100C, was assigned to water evaporation;the second, at 260C, for untreated and 250C for treatedOHF were ascribed to both hemicellulose and glycidic bonds

of cellulose decomposition. The third peak, at 325C, wasattributed to cellulose decomposition, while the fourthpeak, at 350C, to the lignin decomposition. The authors[81]indicated that these results are in agreement with those ofMder et al.[35]and Pracella et al.[40].

As for the neat matrix, a single DTG peak was observedat 397C in association with 97% of weight loss. The au-thors[81] also concluded that the grafting reaction of MAonto the PP, for the OHF treatment, generates a 16C re-duction in thermal stability. TG/DTG curves for the com-posites showed an intermediate behavior between the pureOHF and the neat PP. In fact, according to Amar et al.[81],the thermal degradation of the olive husk fiber composites

occurred in a three step degradation process. However,the 20 wt.% OHF composites apparently display four DTGpeaks. A small first peak at about 100C, not mentioned byauthors[81], is probably due to water release from the OHF.A second, in the temperature range of 232C308C, anda third at 308C350C, shoulder peaks were attributed tothe decomposition of hemicellulose and cellulose, respec-tively. The main DTG peaks around 400C, related by theauthors to the third decomposition stage between 350C454C, were assigned to the PP matrix and OHF lignin jointdegradation. It was also indicated by the authors that thecomposite modified by PPMA revealed a better thermalstability than those with untreated or VTAS treated OHF.

4.6 Kapok/ Cotton Fibers Hybrid Composites

Mwaikambo et al.[82] employed hybrid kapok/cotton fi-bers wove as a fabric, which was both untreated andchemically treated by either one hour soaking in aceticanhydride at 70C (acetylation) or dipped in 2% NaOHsolution for 48 hours (alkali/mercerization), reinforcingboth conventional isotactic polypropylene (iPP) and an-hydride grafted polypropylene resins (MAiPP) matricescomposites. In addition, the authors[82] also investigatedthe effect of accelerated weathering of the composites byimmersion in boiling water for two hours before conduct-ing thermogravimetric analysis at a heating rate of 10C/

min in nitrogen. Table 3, reproduced from their work[82]

,summarizes the main parameters obtained from TG curvesfor all distinct composites.

Although not mentioned in the abstract, the authors [82]indicated in the experimental procedure that the plainweave kapok/cotton fabric was used together with non-woven glass mat. Along the article, no comment or discus-sion was given regarding the role of the glass mat on thethermogravimetric analysis. As shown in Table 3, all com-posites display a dehydration temperature in the range of59C78C, which is probably related to the water releasefrom the kapok and cotton fibers, as usually reported inother lignocellulosic fiber composites[3032,50,53,54,56,71,74]. Asmajor thermal stability results, Mwaikambo et al.[82], em-

Fig. 4 SEM micrographs: (a) untreated; (b) mercerized; and (c) silanized

buriti fibers as well as (d) composite with 10 wt.% mercerized fibers,

indicated by white arrows. Inserts with high magnification details.

Reproduced from Santos et al.[80].


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phasized that the weathered kapok/cotton-iPP compositeshows the highest degradation temperature followed bykapok/cotton-MAiPP composite. As for the fabric treat-ment, the acetylated kapok/cotton fabric-iPP compositesdisplay a higher onset temperature of degradation thanboth the weathered composite and mercerized kapok/cotton fabric-iPP composites, but lower than MAiPP com-posites. The authors[82]stated that the maleic anhydrideis likely to be the possible source for the improved ther-mal properties of PP as also evidenced by the rise in the

degradation temperature of the composites. By contrast,mercerization of fibers, which is known to result in re-duced crystalline cellulose, has been found to decreasethe thermal stability of the kapok/cotton fabric-iPP com-posites. As a general conclusion, it has also been found,with exception of mercerization kapok/cotton fabric-iPP(Table 3), that all composites exhibit two degradationtemperatures. Mwaikambo et al.[82] suggested that thefirst degradation temperature is a result of depolymer-ization of the cellulose materials. The second degrada-tion temperature was caused by the polymeric matricesbreakdown into monomers and/or decomposition of thelevoglucosan.

5. Concluding Remarks

A few points are worth being discussed concerning the re-sults presented in this overview. First, the reader shouldnoticed the relatively small number of papers[39,71,72,74,78,8082]covering the thermogravimetric stability of polymer com-posites reinforced with less common lignocellulosic fibers.Indeed, it was rather surprising that only such limitedworks have so far been dedicated to these composites inspite of the potential presented by less common lignocel-lulosic fibers. For instance, Fiore et al.[83] reported ten-sile strength above 300 MPa and elastic modulus above1.5 GPa for artichoke fibers, while De Rosa et al.[84]found

tensile strength above 800 MPa and elastic modulus above4 GPa for okra fibers. These less common lignocellulosicfibers certainly possess an engineering potential, of bothstrength and stiffness, for polymer composite reinforce-ment. In addition to future specific works on the mechani-cal properties of these less common natural fiber com-posites, the thermal stability of such composites will alsoneed to be investigated for practical use.

A second point of the present overview is the alerton the growing demand for studies covering the several

less common lignocellulosic fibers with potential applica-tion as engineering materials. Consequently, the generalproperties and, in particular, the TG/DTG analysis of nov-el composites based on these fibers have to be assessed.Despite the limited and fragmented information existingin the literature, this overview conveys relevant conclu-sion regarding the thermogravimetric stability of polymercomposites reinforced with less common lignocellulosicfibers. Apparently, an initial weight loss associated with awater release DTG peak below 200C is a common featureof these composites[39,71,74,81,82], although not emphasizedin some works[73,78,80]. This initial peak is most probablya result of the evaporation of water from the fiber sur-

face, since the polymeric matrix contribution, if existing,should be relatively small. For practical use, however, thetemperature related to the onset of thermal degradationcan be considered the composite thermal stability limit.In the overviewed works, this limit was found to be inthe range of 240C[80]355C[39], and attributed to the li-gnocellulosic fiber decomposition. According to Santos etal.[80], these onset degradation temperatures are interme-diate between the isolated fiber and the polymer matrix.Other higher temperature DTG peaks, 422C[71]463C[81],are related to the polymer matrix macromolecular deg-radation or depolymerization but not as important as theonset degradation temperature to define the compositethermogravimetric stability.

Table 3 Thermogravimetric results of polypropylene reinforced with kapok/cotton for different alkali- or acetylated-treated fabricsconventional or maleic anhydride grafted matrices and unweathered and weathered composites.

PropertiesAlkali-treated kapok/cotton-iPP composite

Acetylated kapok/cotton-iPP composite

Unweathered kapok/cotton-iPP composite

Dehydration temperature (oC) 74.1 59.3 76.3

Onset temperature (oC) 332.3 339.5 316.4

Degratation temperature 1 (o

C) 372.8 372.63 370.4Degratation temperature 2 (oC) 431.7 428.2

Decomposition temperature (oC) 656.7 655.3 656.4

PropertiesUnweathered kapok/cotton-MAiPP composite

Weathered kapok/cotton-iPP composite

Weathered kapok/cotton-MAiPP composite

Dehydration temperature (oC) 77.5 71.8 71.8

Onset temperature (oC) 339.5 318.5 339.2

Degratation temperature 1 (oC) 381.9 380.6 384.2

Degratation temperature 2 (oC) 459.1 423.7 462.5

Degratation temperature 2 (oC) 657.9 658.7 655

Reproduced from Amar B et al.[81]

.


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Monteiro et al.124


Acknowledgements

The authors thank the support to this investigation by theBrazilian agencies: CNPq, CAPES and FAPERJ.

References

Bledzki AK, Gassan J. Composites reinforced with cellulose-1.

based fibers. Prog Polym Sci 1999; 4:22174.

Mohanty AK, Misra M, Hinrichsen G. Biofiber, biodegradable2.

polymers and biocomposites: an overview. Macromol Mat Eng

2000; 276/277:124.

Agarwal BD, Broutman LJ. Analysis and Performance of Fiber3.

Composites. 2.ed. New York: Wiley, 1990.

Ashbee KH. Fundamental Principles of Fiber Reinforced Com-4.

posites. 2.ed. Lancaster, PA: Technomic, 1993.

Chawla KK. Composite Materials Science and Engineering.5.

2. ed. New York: Springer-Verlag, 1998.

Nabi Sahed D, Jog JP. Natural fiber polymer composites: a re-6.

view. Adv Polym Technol 1999; 18(4):35163.

Eichhorn SJ, Baillie CA, Zafeiropoulos N, Mwaikambo LY, An-7.

sell MP, Dufresne A et al. Review Current international re-

search into cellulosic fibres and composites. J Mat Sci 2001;

36:210731.

Mohanty AK, Misra M, Drzal LT. Sustainable bio-composites from8.

renewable resources: opportunities and challenges in the green

materials world. J Polym Environ 2002; 10:1926.

Netravali AN, Chabba S. Composites get greener. Mater Today9.

2003; 6:229.

Mohanty AK, Mishra M, Drzal LT. Natural Fibers, Biopolymers10.

and Biocomposites. Boca Raton: CRC press, 2005.

Satyanarayana KG, Guimares JL, Wypych F. Studies on lignocel-11.

lulosic fibers of Brazil. Part I: Source, production, morphology,

properties and applications. Compos Part A 2007; 38:1694709.

Crocker J. Natural materials innovative natural composites.12.

Mater Technol 2008; 23:1748.Monteiro SN, Lopes FPD, Ferreira AS, Nascimento DCO. Natural13.

fiber polymer matrix composites: cheaper, tougher and envi-

ronmentally friendly. JOM 2009; 61:1722.

Kalia S, Kaith BS, Kaurs I (eds.). Cellulose Fibers: Bio- and14.

Nano- Polymer Composites. New York: Springer, 2011.

Monteiro SN, Lopes FPD, Barbosa AP, Bevitori AB, Silva ILA,15.

Costa LL. Natural lignocellulosic fibers as engineering materi-

als. Metal Mater Trans A 2011; 42:296374.

Larbig H, Scherzer H, Dahlke B, Poltrock R. Natural fiber re-16.

inforced foams based on renewable resources for automotive

interior applications. J Cell Plast 1998; 34:36179.

Marsh G. Next step for automotive materials. Mater Today17.

2003; 6:3643.

Holbery J, Houston D. Natural-fiber-reinforced polymer com-18.posites in automotive applications. JOM 2006; 58:806.

Zah R, Hischier R, Leo AL, Brown I. Curaua fibers in automo-19.

bile industry A sustainability assessment. J Clean Prod 2007;

15:103240.

Alves C, Ferro PMC, Silva AJ, Reis LG, Freitas M, Rodrigues LB.20.

Ecodesign of automotive components making use of natural

jute fiber composites. J Clean Prod 2010; 18(4):313-27.

Wambua P, Ivens I, Verpoest I. Natural fibers: can they replace21.

glass and fibre reinforced plastics? Compos Sci Technol 2003;

63:125964.

Joshi SV, Drzal LT, Mohanty AK, Arora S. Are natural fiber com-22.

posites environmentally superior to glass fiber reinforced

composites? Compos Part A 2004; 35:3716.

Beall FC, Eickner HW. Thermal degradation of wood compo-23.

nents: a review of literature. USDA Forest Service Research

Paper 1970; FPL 130.

Kilzer FJ. Cellulose and Cellulose Derivatives. New York: Wiley-24.

Interscience, 1971, p. 101722.

Nguyen T, Zavarin E, Barral EM. Thermal analysis of lignocel-25.

lulosic materials. Part I - Unmodified materials. J Macromol

Sci Rev Macromol Chem 1981; C 20:165.

Nguyen T, Zavarin E, Barral EM. Thermal analysis of lignocel-26.lulosic materials. Part II - Modified materials. J Macromol Sci

Rev Macromol Chem 1981; C 21:160.

Mohanty AK, Patnaik S, Singh BC, Misra M. Graft copolymeriza-27.

tion of acrylonitrile onto acetylated jute fibers. J Appl Polym

Sci 1989; 37(5):117181.

Sabaa MW. Thermal degradation behavior of sisal fibers graft-28.

ed with various vinyl monomers. Polym Degrad Stab 1991;

32(2):20917.

Sridhar MK, Basavarajjappa G, Kasturi SS, Balsubramanian N.29.

Thermal stability of jute fibers. Indian J Tex Res 1982; 7:8791.

Das S, Saha AK, Chourdhury PH, Basak RK, Mitra BC, Todd T30.

et al. Effect of steam pre-treatment of jute fiber on dimensional

stability of jute composite. J Appl Polym Sci 2000; 76:165261.

Dash BN, Rana AK, Mishra HK, Nayak SK, Tripathy SS. Novel low-31.

cost jute-polyester composites. III. Weathering and thermal

behavior. J Appl Polym Sci 2000; 78:16719.

Ray D, Sarkar BK, Basak RK, Rana AK. Thermal behavior of vinyl32.

ester resin matrix composites reinforced with alkali-treated

jute fibers. Appl Polym Sci 2004; 94:1239.

Manfredi LB, Rodriguez ES, Wladyka-Przybylak M, Vazquez A.33.

Thermal degradation and fire resistance of unsaturated poly-

ester, modified acrylic resins and their composites with natural

fibres. Polym Degrad Stab 2006; 91:25561.

Mohanty S, Verma SK, Nayak SK. Dyamic mechanical and ther-34.

mal properties of MAPE treated jute/HDPE composites. Compos

Sci Technol 2006; 66:53847.

Doan T-T-L, Brodowsky H, Mder E. Jutefibre/polypropylene35. composites. II. Thermal, hydrothermal and dynamic mechani-

cal behavior. Compos Sci Technol 2007; 67:270714.

Yu T, Li Y, Ren J. Preparation and properties of short natural36.

fiber reinforced poly(lactic acid) composites. Trans Nonferrous

Met Soc China 2009; 19:s6515.

Aziz SH, Ansell MP. The effect of alkalinization and fibre align-37.

ment on the mechanical and thermal properties of kenaf and

hemp bast fibre composites: Part 1 Polyester resin matrix.

Compos Sci Technol 2004; 64:121930.

Aziz SH, Ansell MP. The effect of alkalinization and fibre align-38.

ment on the mechanical and thermal properties of kenaf and

hemp best fibre composites: Part 2 Cashew nut shell liquid

matrix. Compos Sci Technol 2004; 64:12318.

Sgriccia N, Hawley MC. Thermal, morphological, and electrical39.characterization of microwave processed natural fiber compos-

ites. Compos Sci Technol 2007; 67:198691.

Pracella M, Chionna D, Anguillesi I, Kulinski Z, Piorkowska E.40.

Functionalization, compatibilization and properties of polypro-

pylene composites with hemp fibre. Compos Sci Technol 2006;

66:221830.

Beckermann GW, Pickering KL. Engineering and evaluation of41.

hemp fibre reinforced polypropylene composites:fibre treatment

and matrix modification. Composites Part A 2008; 39:97988.

Moriana R, Vilaplana F, Karlsson S, Ribes-Greus A. Improved42.

thermo-mechanical properties by the addition of natural fibres

in starch-based sustainable biocomposites. Composites Part A

2011; 42:3040.


9/10



Albano C, Gonzalez J, Ichazo M, Kaiser D. Thermal stability of43.

blends of polyolefins and sisal fiber. Polym Degrad Stab 1999;

66:17990.

Joseph PV, Joseph K, Thomas S, Pillai CKS, Prasad VS, Groen-44.

inckx G et al. The thermal and crystallization studies of short

sisal fibre reinforced polypropylene composites. Composites

Part A 2003; 34:25366.

Nair KCM, Thomas S, Groeninckx G. Thermal and dynamic me-45.

chanical analysis of polystyrene composites reinforced withshort sisal fibres. Compos Sci Technol 2001; 61:251929.

Xie XL, Fung KL, Li RKY, Tjong SC, May Y-W. Structural and46.

mechanical behavior of polypropylene maleated styrene-

(ethylene-co-butylene-styrene/sisal fiber composites prepared

by injection molding. J Polym Sci Part B: Polym Phys 2002;

40:121422.

Xie XL, Li RKY, Tjong SC, May Y-W. Structural properties and me-47.

chanical behavior of injection molded composites of polypropyl-

ene and sisal fiber. Polym Compos 2002; 23(3):31928.

Gan P, Garbizu S, Llano-Ponte R, Mondragon I. Surface modi-48.

fication of sisal fibers: effects on the mechanical and thermal

properties of their epoxy composites. Polym Compos 2005;

26:1214.

Paiva JMF, Frollini E, Macromol J. Unmodified and modified sur-49.

face sisal fibers as reinforcement of phenolic and lignophenolic

matrices composites: Thermal analyses of fibers and composites.

Mater Eng 2006; 291:40517.

Kim JT, Netravali AN. Mechanical and thermal properties of sisal50.

fiber-reinforced green composites with soy protein/gelatin res-

ins. Biobased Mater Bioenergy 2010; 4(4):33845.

Arbelaiz A, Fernandez B, Ramos JA, Mondragon I. Thermal and51.

crystallization studies of short flax fibre reinforced polypropyl-

ene matrix composites: effect of treatments. Thermochim Acta

2006; 440(2):11121.

Aydin M, Tozlu H, Kemaloglu S, Aytac A, Ozkoc G. Effects of Alkali52.

Treatment on the Properties of Short Flax FiberPoly(Lactic Acid)

Eco-Composites. J Polym Environm 2011; 19(1):117.Rosa MF, Chiou B-S, Medeiros ES, Woods DF, William TG, Mat-53.

toso LHCet al. Effect of fiber treatments on tensile and thermal

properties of starch/ethylene vinyl alcohol copolymers/coir bio-

composites. Bioresource Technol 2009; 100(21):5196202.

Santaf Jr. HPG, Rodriguez RJS, Monteiro SN, Castillo TE. Char-54.

acterization of thermogravimetric behavior of polyester compos-

ites reinforced with coir fiber. In: Characterization of Minerals,

Metals and Materials Symposium TMS 2011 Annual Conference,

San Diego, CA, USA, March 2011, p. 16.

Silva CG, Benaducci DB, Frollini E. Lyocell and cotton fibers as55.

reinforcements for a thermoset polymer. BioResources 2012;

7(1):7898.

Julkapli NM, Akil HM. Thermal Properties of Kenaf-Filled Chito-56.

san Biocomposites. Polym-Plast Technol Eng 2010; 49(2):14753.Akil HM, Omar MF, Mazuki AAM, Safiee S, Ishak ZAM, Bakar AA.57.

Kenaf fiber reinforced composites: A review. Mater Design 2011;

32(8-9):410721.

Coutinho FMB, Costa THS, Carvalho DL, Gorelova MM, de San-58.

ta Maria LC. Thermal behaviour of modified wood fibers. Polym

Test 1998; 17(5):299310.

Doh GH, Lee S-Y, Kang I-A, Kong Y-T. Thermal behavior of liq-59.

uefied wood polymer composites (LWPC). Compos Struct 2005;

68(1):1038.

Bhardwaj R, Mohanty AK, Drzal LT, Pourboghrat F, Misra M. Re-60.

newable resource-based green composites from recycled cel-

lulose fiber and poly(3-hydroxybutyrate-co-3-hydroxyvalerate)

bioplastic. Biomacromolecules 2006; 7(6):204451.

Lei Y, Wu Q, Yao F, Xu Y. Preparation and properties of recy-61.

cled HDPE/natural fiber composites. Composites Part A 2007;

38(7):166474.

George J, Bhagawan SS, Thomas S. Thermogravimetric and62.

dynamic mechanical thermal analysis of pineapple fibre re-

inforced polyethylene composites. J Thermal Anal Cal 1996;

47(4):112140.

Luo S, Netravali AN. Mechanical and thermal properties of envi-63.

ronment-friendly green composites made from pineapple leaffibers and poly (hydroxybutyrate-co-valerate) resin. Polym Com-

pos 1999; 20(3):36778.

Threepopnatkul P, Kaerkitcha N, Athipongarporn N. Effect of sur-64.

face treatment on performance of pineapple leaf fiberpolycar-

bonate composites. Composites Part B 2009; 40(7):62832.

Lee S-H, Wang S. Biodegradable polymers/bamboo fiber biocom-65.

posite with bio-based coupling agent. Composites Part A 2006;

37(1):8091.

Shih Y-F. Mechanical and thermal properties of waste water66.

bamboo husk fiber reinforced epoxy composites. Mater Sci

Eng A 2007; 4456:28995.

Singh S, Mohanty AK, Sugie T, Takai Y, Hamada H. Renewable67.

resource based biocomposites from natural fiber and polyhy-

droxybutyrate-co-valerate (PHBV) bioplastic. Composites PartA 2008; 39(5):87586.

Zainudin ES, Sapuan SM, Abdan K, Mohamad MTM. Thermal68.

degradation of banana pseudo-stem filled unplasticized poly-

vinyl chloride (UPVC) composites. Materials and Design 2009;

30(3):55762.

Moth CG, de Arajo CR, de Oliveira MA, Yoshida MI. Thermal69.

decomposition kinetics of polyurethane-composites with ba-

gasse of sugar cane. J Therm Anal Cal 2002; 67(2):30512.

Jawaid M, Abdul Khalil HPS. Cellulosic/synthetic fibre rein-70.

forced polymer hybrid composites: A review. Carbohydrate

Polym 2011; 86(1):118.

Moth CG, de Araujo CR. Thermal and mechanical character-71.

ization of polyuretane composites with curaua fibers (in Portu-

guese). Polmeros: Cincia e Tecnologia 2004; 14(4):27488.Arajo JR, Waldman WR, de Paoli M-A. Thermal properties of72.

high density polyethylene composites with natural fibres: Cou-

pling agent effect. Polym Degrad Stab 2008; 93(10):17705.

Waldman WR, de Paoli M-A. Thermo-mechanical degradation73.

of polypropylene, low-density polyethylene and their 1:1

blend. Polym Degrad Stab 1998; 60(23):3018.

Ferreira AS, Rodriguez RJS, Lopes FPD, Monteiro SN. Thermal74.

analysis of curaua fiber reinforced polyester matrix compos-

ites. In: Characterization of Minerals, Metals and Materials

Symposium TMS Conference (TMS 2010), Seattle, WA, USA,

March 2010, p. 17.

Santos PA, Spinac MAS, Fermoselli KKG, de Paoli M-A. Poly-75.

amide-6/vegetal fiber composite prepared by extrusion and

injection molding. Composites Part A 2007; 38(12):240411.Tomczak F, Satyanarayana KG, Sydenstricker THD. Studies76.

on lignocellulosic fibers of Brazil: Part III Morphology and

properties of Brazilian curaua fibers. Composites Part A 2007;

38(10):222736.

Spinac MAS, Lambert CS, Fermoselli KKG, de Paoli M-A. Char-77.

acterization of lignocellulosic curaua fibres. Carbohydrate

Polym 2009; 77(1):4753.

Gan P, Mondragon I. Thermal and degradation behavior of78.

fique fiber reinforced thermoplastic matrix composites. J

Therm Anal Cal 2003; 73(3):78395.

Gan P, Mondragon I. Surface modification of fique fibers.79.

Effect on their physico-mechanical properties. Polym Compos

2002; 23(3):38394.


10/10

Monteiro et al.126


Santos RS, Souza AA, de Paoli M-A, Souza CML. Cardanolform-80.

aldehyde thermoset composites reinforced with buriti fibers:

Preparation and characterization. Composites Part A 2010;

41(9):11239.

Amar B, Salem K, Hocine D, Chadia I, Juan MJ. Study and81.

characterization of composite materials based on polypro-

pylene load with olive husk flour. J Appl Polym Sci 2011; 122:

138294.

Mwaikambo LY, Martuscelli E, Avella M. Kapok/cotton fabric82.polypropylene composites. Polym Test 2000; 19(8):90518.Fiore V, Valenza A, di Bella G. Artichoke (Cynara carduncu-83.lus L.) fibres as potential reinforcement of composite struc-tures. Compos Sci Technol 2011; 71(8):113844.De Rosa IM, Kenny JM, Puglia D, Santulli C, Sarasimi F. Mor-84.phological, thermal and mechanical characterization of okra(Abelmoschus esculentus) fibres as potential reinforcement inpolymer composites. Compos Sci Technol 2010; 70(1):11622.

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