Articulo 3 Ing Mat U3

7/28/2019 Articulo 3 Ing Mat U3

1/10

Review

Green composites: A brief review

F.P. La Mantia a, M. Morreale b ,

a Universit di Palermo, Dipartimento di Ingegneria Chimica dei Processi e dei Materiali, Viale delle Scienze, 90128 Palermo, Italyb Libera Universit Kore Enna, Facolt di Ingegneria e Architettura, Cittadella Universitaria, 94100 Enna, Italy

a r t i c l e i n f o

Article history:

Received 6 June 2010Received in revised form 20 January 2011Accepted 24 January 2011Available online 31 January 2011

Keywords:A. Polymermatrix composites (PMCs)A. WoodB. Mechanical properties

a b s t r a c t

The rising concern towards environmental issues and, on the other hand, the need for more versatile

polymer-based materials has led to increasing interest about polymer composites lled with natural-organic llers, i.e. llers coming from renewable sources and biodegradable. The composites, usuallyreferred to as green, can nd several industrial applications. On the other hand, some problems exist,such as worse processability and reduction of the ductility. The use of adhesion promoters, additives orchemical modication of the ller can help in overcoming many of these limitations. These compositescan be further environment-friendly when the polymer matrix is biodegradable and comes from renew-able sources as well. This short review briey illustrates the main paths and results of research (both aca-demic and industrial) on this topical subject, providing a quick overview (with no pretence of exhaustiveness over such a vast topic), as well as appropriate references for further in-depth studies.

2011 Elsevier Ltd. All rights reserved.

Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2. Polymer matrices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

3. Chemical modification and use of adhesion promoters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5804. Processability and rheology. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5825. Processing and processability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5826. Industrial applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 587. Towards complete environmental sustainability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5838. Environmental impact considerations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5859. Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1. Introduction

Polymer composites have been widely used for several yearsand their market share is continuously growing. It is widely knownthat the use of a polymer and one (or more) solid llers allowsobtaining several advantages and, in particular, a combinationof the main properties of the two (or more) solid phases. Amongthe llers used, it is worthciting [1] calcium carbonate, glass bers,talc, kaolin, mica, wollastonite, silica, graphite, synthetic llers (e.g.PET- or PVA-based bers), high-performance bers (carbon, aram-idic, etc.).

However, this leads also to one of the main limitations of poly-mer composites: the two different components make the reuse and

recycling quite difcult, to such an extent that it is often preferredto perform the direct disposal in a dump, or incineration [2,3] . Thisway is often considered to be unsatisfactory (especially in the rstcase), because of the high costs, the technical difculties and theenvironmental impact. The latter is, indeed, a problem of primaryimportance. Furthermore, it is worsened by the fact that plasticsproduction requires a remarkable consumptionof oil-based resources,which are notoriously non-renewable.

These problems have begun to be particularly evident for about10 years, thus leading the scientic research to look for new alter-natives, able to replace traditional polymer composites with sub-stitutes having lower environmental impact and thus oftenreferred to as ecocomposites or green composites. This taskcan be made easier by the fact that many of the typical applicativeelds of these composites do not require excellent mechanicalproperties (i.e. secondary and tertiary structures, panels, packag-ing, gardening items, cases, etc.) [2,4] .

1359-835X/$ - see front matter 2011 Elsevier Ltd. All rights reserved.doi: 10.1016/j.compositesa.2011.01.017

Corresponding author.E-mail address: [email protected] (M. Morreale).

Composites: Part A 42 (2011) 579588

Contents lists available at ScienceDirect

Composites: Part A

j o u rna l homepa ge : www.e l s ev i e r. com/ loca t e / compos i t e s a
http://dx.doi.org/10.1016/j.compositesa.2011.01.017mailto:[email protected]://dx.doi.org/10.1016/j.compositesa.2011.01.017http://www.sciencedirect.com/science/journal/1359835Xhttp://www.elsevier.com/locate/compositesahttp://www.elsevier.com/locate/compositesahttp://www.sciencedirect.com/science/journal/1359835Xhttp://dx.doi.org/10.1016/j.compositesa.2011.01.017mailto:[email protected]://dx.doi.org/10.1016/j.compositesa.2011.01.017


2/10

In chronological order, the rst attempts in this direction werefocused on the production and characterization of polymer com-posites based on recyclable polymers (e.g. polyolens) lled withnatural-organic llers, i.e. bers and particles extracted fromplants. Several points support this choice; rst of all, the use of natural-organic llers in replacement for traditional mineral-inorganic ones allows a considerable reduction in the use of non-

biodegradable polymers and non-renewable resources. Furthermore,these llers are usually drawn from relatively abundant plants(often from wastes), therefore they are very cheap. They are alsomuch less abrasive than inorganic-mineral counterparts to pro-cessing machinery, less dangerous for the production employeesin case of inhalation, easy to be incinerated, they lead to nal com-posites with lower specic weight (in comparison to mineral-lledcounterparts) and allow obtaining interesting properties in termsof thermal and acoustic insulation [13,510] .

The most widely known and used natural-organic llers arewood our and bers. Wood our can be easily and cheaply ob-tained from sawmill wastes and it is usually used after proper siev-ing. Wood bers are produced by thermo-mechanical processes onwood waste.

Besides wood derivatives, other natural-organic llers have be-gun to nd application as well. Among these, some examples arecellulose, cotton, ax, sisal, kenaf, jute, hemp, starch [1,8,11,12] .Further environment-friendliness can be achieved upon usingpost-consumer recycled plastics in place of virgin polymermatrices.

Wood our and bers are quite interesting because of the lowcost, dimensional stability, elastic modulus, while tensile proper-ties do not improve; the main shortcomings are the poor adhesionbetween the ller particles and the polymer matrix, low impactstrength, thermal decomposition at temperatures over 200 C [2,4] .

Flax, sisal, hemp and kenaf are relatively similar and are basi-cally long bers extracted from the bast of the plants; they canbe used as llers by proper cutting into long or short bers.

Starch is a polysaccharide present in many plants acting as anenergy reservoir. It is made of glucose monomers linked bya -(1-4) bonds [13,14] . In general, the addition of granular starchto a polymer leads to a reduction of the elongation at break (andoften of the tensile stress as well), as high as the starch content in-creases, while the elastic modulus is enhanced. A limitation of thisller type is the tendency to absorb water because of its very highsurface area and its hygroscopic nature.

Other less used natural-organic llers can include rice husk ash,nutshells, oil palm empty fruit bunch bers, corn plants extractedbers, etc. [3,1517] .

2. Polymer matrices

The main polymer matrices used in the eld of green compos-ites (excluding biodegradable ones, which are overviewed in a fol-lowing paragraph) could be summarized as follows.

Polyethylene The scientic literature reports polyethylene basedcomposites, includinga numberof llers, e.g. wood chips and bres[1821] , corn starch [13,22] , sago, tapioca and rice starch [23,24] ,sisal bers [5] , kenaf bers [12] . Furthermore, papers exist regard-ing post-consumer recycled polyethylene, e.g. wood bers andHDPE coming from food containers [25] , wood bers and HDPEcoming from milk bottles [26] , polyethylene coming from green-house lms and wood bers, sago starch, ground olive stones[27] .

Wood bers (as well as the other main natural-organic llers)are usually added to the polymer matrix up to 4070% by weight

[28,29] . In general, an increase of stiffness and exural strength,and a reduction of ductility are observed. This problem can be

mitigated by using polar adhesion promoters such as maleic anhy-dride grafted polyethylene (MAgPE), maleic anhydride graftedpolypropylene (MAgPP), or ethyleneacrylic acid copolymer [13,25,30] .

Polypropylene Literature reports several studies on polypro-pylene in combination with llers derived from wood, ax, sisal,hemp, kenaf, and starch. The spur towards alternate cellulose

sources nds a justication in the fact that these are more easilyrenewable than the wood itself. Adhesion promoters are used aswell. Some examples reported in the literature regard silane-basedcompounds [18] , maleic anhydride grafted polypropylene (MAg-PP), styreneethylenebutadienestyrene rubber grafted withmaleic anhydride (MAgSEBS), ethylenepropylenediene copoly-mer grafted with maleic anhydride (MAgEPDM), which allowedobtaining a signicant improvement of mechanical and morpho-logical properties [31,32] . Interesting results have been also foundregarding the effect of wood bers on crystallization and morphol-ogy of polypropylene-based composites. It has been conrmed thatwood bers do not inuence signicantly the crystal growth kinet-ics, while can enhance nucleation rates. The addition of MAgPP fur-ther increased nucleation phenomena, but it is not clear whetherthe observed improvement of mechanical properties should beattributed mainly to an enhancement of woodpolymer adhesion,to a better wood dispersion, or both. It is also proposed that thepolymer structure, in particular the presence of amorphous re-gions, may have an important role on the worsening of somemechanical properties [33] .

Others Examples of research regarding other kinds of poly-mers in combination with wood (and other natural-organic llers)include sisal bers and polystyrene [8] , wood our [34] or starch[35] and polycaprolactone, phenolic resins and several natural -bers [2] , palm tree our and polyester resins [36] , isora bersand natural rubber [37] .

3. Chemical modication and use of adhesion promoters

As previously mentioned, research is particularly focused on themodication of ller surface in order to improve the interfacialadhesion between ller particles (hydrophilic) and polymer mac-romolecules (generally hydrophobic) and their dispersion in thematrix. This is a very important issue, since the simple additionof natural-organic llers to a polymer matrix may lead to poormechanical properties in comparison to the neat polymer; thiscan be especially true when ller particles with low length-to-diameter ratios are used. An example of the trends of the mainmechanical properties upon simple addition of 30 wt.%, low aspectratio natural-organic llers (OS= olive stones our, SDc = coarsewood our, SDf = ne wood our, SS = sago starch) to a recycledpolyethylene (RPE) is provided in Table 1 .

The overall comment which can be drawn is that the greencomposites can achieve greater stiffness and thermomechanicalresistance but, on the other hand, the ductility and the tensilestrength are signicantly reduced.

It is therefore clear that chemical modication or use of adhe-sion promoters can be interesting paths in order to improve theoverall mechanical properties.

Modication relies on chemical and physical techniques, mainlyfocused on grafting chemical groups capable of improving theinterfacial interactions between ller particles and polymer ma-trix. The main techniques may be summarized as follows [5,3747] :

Alkali treatment (also called mercerization): it is usually per-

formed on short bers, by heating at approx. 80 C in 10% NaOHaqueous solution for about 34 h, washing and drying in

580 F.P. La Mantia, M. Morreale / Composites: Part A 42 (2011) 579588


3/10

ventilated oven. It allows disrupting ber clusters and obtainingsmaller and better quality bers. It should also improve berwetting.

Acetylation: the bers are usually immersed in glacial aceticacid for 1 h, then immersed in a mixture of acetic anhydrideand few drops of concentrated sulphuric acid for a few min,then ltrated, washed and dried in ventilated oven.This is an esterication method which should stabilize the cellwalls, especially in terms of humidity absorption and conse-quent dimensional variation.

Treatment with stearic acid: the acid is added to an ethyl alco-hol solution, up to 10% of the total weight of the bers to betreated the obtained solution is thus added drop wise on thebers, which are then dried in oven. It is an estericationmethod as well.

Benzylation: the bers are immersed in 10% NaOH and thenstirred with benzoyl chloride for 1 h, ltrated, washed anddried, then immersed in ethanol for 1 h, rinsed and dried inoven. This method allows decreasing the hydrophilicity of thebers.

TDI treatment: the bers are immersed in chloroform with fewdrops of a catalyst (based on dibutyltin dilaurate) and stirred for2 h after adding toluene-2,4-diisocyanate. Finally, bers arerinsed in acetone and dried in oven.

Peroxide treatment: the bers are immersed in a solution of dicumyl (or benzoyl) peroxide in acetone for about half anhour, then decanted and dried. Recent studies have high-lighted signicant improvements in the mechanicalproperties.

Anhydride treatment: it is usually carried out by utilizingmaleic anhydride or maleated polypropylene (or polyethylene)in a toluene or xylene solution, where the bers are immersedfor impregnation and reaction with the hydroxyl groups onthe ber surface. Literature reports signicant reduction of water absorption.

Permanganate treatment: the bers are immersed in a solutionof KMnO 4 in acetone (typical concentrations may rangebetween 0.005 and 0.205%) for 1 min, then decanted and dried.Investigations have pointed out a decreased hydrophilic natureof the bers upon performing this treatment.

Silane treatment: the bers are immersed in a 3:2 alcoholwater solution, containing a silane-based adhesion promoterfor 2 h at pH 4, rinsed in water and oven dried. Silanes shouldreact with the hydroxyl groups of the bers and improve theirsurface quality.

Isocyanate treatment: isocyanate group can react with thehydroxyl groups on ber surface, thus improving the interfaceadhesion with the polymer matrix. The treatment is typicallyperformed with isocyanate compounds at intermediate temper-atures (around 50 C) for approximately 1 h.

Plasma treatment: this recent method allows signicantly mod-ifying the ber surface. However, chemical and morphologicalmodication can be very heterogeneous depending on thetreatment conditions, therefore it is not easy to generalize; pro-

cess control is a critical aspect and the nal surface modica-tions strongly depend on it.

More specically, TDI, dicumylperoxide and silane treatmentseem to guarantee the best results with concern to mechanicalproperties, while alkali treatment and acetylation seem to give bet-ter improvements in thermal and dimensional stability.

Chemical modication, therefore, is an interesting way to im-prove the properties of natural organic/polymer composites,though having a primary drawback represented by the costs that,especially in the case of complicated techniques, can rise to sucha level to make this method not suitable for industrial applications.These, in fact, require quicker and cheaper methodologies and itnecessary to assure constant product quality. It is therefore clearthat chemical modication of bers is unlikely to meet all of theserequirements [33] .

Other solutions are therefore preferred in order to producegreen composites with improved matrixber interfacial adhesionand ber dispersion, and to reduce the formation of voids insidethe material (due to the hydrophilic nature of natural-organic ll-ers) [48] . At present, the preferred solution for industrial applica-tions does not rely on chemical modication of bers, but ratheron the addition of small amounts of a third component which,by its intrinsic chemical characteristics, may act as an adhesionpromoter between polymer matrix and cellulosic llers, by form-ing chemical bonds (either covalent, or Van der Waals kind) [32] .Of course, the adhesion promoter molecule should contain ahydrophilic part, able to create the bonds with the polar groupstypically present on cellulosic bers, and a hydrophobic part,which can show higher afnity to the macromolecular chains.

A number of recent papers exist regarding the use of adhesionpromoters/compatibilizers for green plastic composites [32,4968] . The most investigated matrices are polyolens, while theadhesion promoters are mainly based on the same polyolensmodied with maleic anhydride. The results are quite variable,depending on the polymer matrix used, the ller type and quantity,the adhesion promoter used (i.e. the base polymer on which it isprepared, its molecular weight, the modier percentage, etc.) andits amount, the processing techniques, etc. In general, it could beobserved that these adhesion promoters, on average, can signi-cantly improve tensile properties and processability, while waterabsorption is reduced. However, in some cases, impact strengthmay not be enhanced, therefore specic elastomeric impact modi-ers should be used.

An example of the improvements that a maleated adhesion pro-moter can assure to a green composite based on polypropylene and30 wt.% wood our is reported in Table 2 .

Table 1

Main mechanical properties of RPE-based green composites without the use of any adhesion promoter/chemical modication technique (data taken from Ref. [27] ).

Property RPE RPE-OS RPE-SDc RPE-SDf RPE-SS

Elastic modulus (MPa) 129 163 264 282 193Tensile strength (MPa) 12.5 8 10.9 10.4 9.9Elongation at break (%) 100 36 29 17 45Heat deection temperature ( C) 27 35 38 42 37Impact strength (J/m) No break No break 185 99 No break

Table 2

Main mechanical properties of polypropylene/wood our green composite withoutand with the use of a maleated adhesion promoter (reproduced from Ref. [32] withpermission from Brill).

Property PP + 30% WF PP + 30% WF + 3% MAPP

Elastic modulus (MPa) 954 1035Tensile strength (MPa) 19.5 27.2Elongation at break (%) 4.2 4.6Impact s trength (unnotched) (J/m) 83 98

F.P. La Mantia, M. Morreale / Composites: Part A 42 (2011) 579588 581


4/10

4. Processability and rheology

With concern to processability of polymer-natural-organic llercomposites, in comparison to the neat polymer, it can be stated, asa general rule, that an increase in the viscosity is observed (andthus a decrease of the processability), and it is higher upon increas-ing the ller content [27,36,69,70] . However, processability is not

compromised (except, in some case, for very long bers) since tor-que and viscosity increases are not too high and, at high shear rates(typical of the industrial processing techniques) these gaps tend toreduce [27,69,70] .

There are not many papers regarding the rheology of polymersystems lled with natural organic materials. Early studies pointedout an increase of viscosity in polyethylene or polypropylene-based composites lled with wood our [7173] ; it was alsofound that viscosity increases upon increasing the ller content[27,69,74] . Li and Wolcott [70] investigated the behavior of HDPE-wood bers composites, upon changing the ller content (40 and60 wt.%) and the wood type (maple or pine), using a capillary rhe-ometer. They found wall slip phenomena to be present and largelydependent on ller weight percentage and nature; similar consid-erations can be done for the yield stress. Elongational ow analysisshowed that viscosity depends more on the ller content than theller nature; a comparison of the Trouton ratio showed it to bestrongly dependent on ber typology and a strong interaction be-tween the bers was also observed (thus justifying yield stressduring the shear ow).

La Mantia and Morreale [32] investigated also the rheologicalbehavior of PP-wood our composites with and without the addi-tion of a PPgMA based adhesion promoter. The latter acted as amild processing aid, however, upon increasing the ller content,rheology was signicantly modied by the formation of llerpolymer bonds, mediated by the adhesion promoter.

5. Processing and processability

Literature data on green composites show, as discussed before,a clear prevalence of wood, in combination with polyolens: thisinuences, of course, also the information available on processingand processability.

Typical processing techniques include extrusion and subse-quent injection or compression molding [27,30,48,69,7577] .

Filler amount seldom exceeds 5060 wt.%, even though some-times higher percentages, up to 7080%, are reported (especiallyin the US). Of course, being the conditions more extreme, compres-sion molding is preferred to injection molding.

Some typical problems related to the processing of these mate-rials are due to the hydrophilic and hygroscopic nature of the ll-ers, and to their poor thermal resistance (so that processing

temperatures should be kept below approx. 200 C).In particular, the hydrophilic and hygroscopic nature of the ll-

ers is one of the main problems in this eld: in fact, it tends to sig-nicantly inuence ller dispersion in the matrix and theinterfacial adhesion. Thepresence of humidity generally leads, dur-ing the processing, to the formation of water vapor which can, inturn, give rise to several problems, especially in the followingmolding step (in the case of injection molding), if a venting or dry-ing system is not present. In general, the formation of water vapor(but also of gases/vapors of different kind) leads to the formation of voids in the material and thus to poor mechanical properties. Onthe other hand, the presence of volatile substances inside thematerial can negatively inuence the following steps of the prod-ucts life cycle. However, it should be also pointed out that small

amounts of humidity are not detrimental but, on the contrary,may help to soften the cellulosic component, thus acting as a sort

of lubricant [75] . Furthermore, it is a widely accepted techniqueto dry the natural-organic ller prior to processing, by differentways such as hot air jets, rotating driers, ventilated ovens, in orderto reduce the humidity level to approx. 23%.

The early processing techniques basically relied on melt mixingand extrusion of seminished products in the shape of at boards,to be then used especially for car panels [78] . Extruded PP-wood

our sheets soon showed their potential: low humidity absorption,dimensional stability, reduced ame propagation in case of re,good processability especially for compression molding, versatilityand recyclability.

Some years ago, the most used technique was based on thepreparation of the solid blend through a high-speed mixer andthe following feeding of the blend to a counter-rotating twin screwextruder. During the last years, processing techniques have beentailored to operative and market needs, leading to a gradual reduc-tion of the importance of components preliminary mixing, in favorof gravimetric dosage along the extruder, in order to reduce powerconsumption and assure higher uniformity and regularity of dos-age. At the same time, counter-rotating extruders have been grad-ually replaced by co-rotating ones. Newer extrusion systems arealso modular, meaning that they are made up of independent, in-ter-changeable modules.

Literature reports several studies on new technological solu-tions related to WPC processing, e.g. investigations on trial-and-error methodologies for the design of moulds for automotive pan-els production, starting from WPC sheets made of polyolens andwood bers [79] ; simulation of non-newtonian ow of polymer-natural ller systems inside mixers and extruders in order predict-ing nal product quality and heat production through viscousstress [79] ; various attempts of reactive extrusion [80] ; processingwith particular reactive additives or electron beam [81] ; turbinemixing [82] .

Japanese researchers have recently proposed an electromag-netic induction method for jute fabric reinforced thermoplasticmolding [83] . According to the Authors, the system allows aninstantaneous heating of the mold surface, thus shortening theproduction cycle times and leading to a reduction of the produc-tion costs related to composite panels molding. Other Authors havefound a signicant inuence of ber area fraction (besides moldingtemperature and forming pressure) on the mechanical and ther-momechanical properties of green composites [84] .

Scaffaro et al. have studied the inuence of process variablesand processing techniques on the mechanical behavior of greencomposites lled with wood our [85,86] . They found, by meansof statistical analysis, that the most inuencing process variableon the materials rigidity is the ller content, even though preli-minary treatments and mixing speed exert some inuence as well;the impact strength was mainly inuenced by mixing speed andller aspect ratio, while temperature had only a minor effect. With

concern to the role of the processing technique (beyond the basicbatch mixing), they found that injection molding caused a partialdegradation of the macromolecules, leading to a reduction of theviscosity and the stiffness of the material, while twin-screw extru-sion and single-screw extrusion followed by calendering allowedobtaining nal materials with higher moduli. On the other hand,a particularly compact morphology was found in the injectionmolded samples. The comparison between extrusion and mixingis not easy, since similar results were found for the elastic modu-lus, while the tensile strength deeply depended on the ller con-tent ( Table 3 ).

Other Authors [87] found partially comparable trends on PVC-coconut ber composites. However, the above mentioned investi-gations also pointed out that the role of ller type, ller content,

ller aspect ratio and processing temperature is of great impor-tance, so it may be very difcult (and sometimes even inappropri-



5/10

ate) to search and propose general rules which might apply to themechanical behavior.

Takagi and Asano [88] have prepared green composites basedon dispersion-type biodegradable resin and cellulose nanobers,by using a stirring technique at relatively low speed and long timesand upon changing the mold pressure. They found signicant in-creases in exural modulus and strength (up to 100%), uponincreasing the mold pressure, in comparison to the control com-posites (which had not undergone the same stirring process).

6. Industrial applications

With concern to the industrial applications, several paths havebeen undertaken. In short, it can be stated that the most used nat-ural-organic ller is wood (either our or bers), especially as lowcost ller for polyolens [2] . Wood our is usually obtained fromsawmill waste after a simple sieving treatment; wood bers areproduced from sawmill waste by a wet thermomechanical process.Already explored industrial applications include window and doorframes, furniture, railroad sleepers, automotive panels and uphol-stery, gardening items, packaging, shelves and in general thoseapplications which do not require very high mechanical resistancebut, instead, low purchasing and maintenance costs [2,4,8991] .Furthermore, it is possible and convenient to use recycled poly-mers in place of virgin ones, thus assuring improved cost-efciencyand eco-sustainability. Some examples of industrial applicationscan be easily found on the technical literature and on the Internet;these include, for instance, indoor furniture panels, footboards andplatforms, automotive panels and upholstery, noise insulating pan-els, etc., mainly produced by American, German, Japanese, Britishand Italian rms [2,78,92] .

In particular, the role of automotive industry in this eld is of primary importance. The rst carmaker to use polymers lled withnatural bers was Mercedes-Benz in the 90s, by manufacturingdoor panels containing jute bers [92] . This example was soonfollowed by other main carmakers, which have started to utilizepolymer composites with natural-organic llers as materials fordoor panels, roof upholstery, headrests, parcel shelves, etc., thanks

to the advantages they can assure in terms of environmental im-pact, weight, elastic modulus and costs. Depending on the applica-tions, it was sometimes necessary to improve the mechanicalproperties through ber pre-treatment (acetylation, use of MAgPP,etc.), and the treated bers were then used in several ways, in or-der obtaining mats, non-woven structures, etc.

Some authors assert also that, by means of special treatmentson natural bers, these could lead to the production of high-qualitycomposites with mechanical properties comparable to glass berlled composites [92] . A result which would be impossible toobtain otherwise, since the hydrophilic nature of natural-organicllers favors agglomeration, humidity absorption and lack of adhe-sion with the polymer matrix; in fact, many efforts are being doneto overcome the problem of interfacial adhesion. Among these, the

investigations on silane-based adhesion promoters [60,92] or someber treatments with alkaline substances or dilute resins. How-

ever, a proper use of long (i.e. more than approx. 5 cm, at least) -bers can already allow obtaining composites suitable to semi-structural applications.

7. Towards complete environmental sustainability

Some recent developments are pushed by the fact that,unfortunately, even these green composites are not fully eco-compatible, since their recyclability has some limitations (temper-atures cannot exceed 200 C during recycling and all the mainproperties will worsen because of the degradation phenomena)[2,92] and their biodegradability regards only the ller but not,of course, traditional (petroleum-based) polymer matrices.

For this reason, research developments during the last yearshave been focused on the production on 100% eco-sustainableand green composites, by replacing non-biodegradable polymermatrices with biodegradable ones. Several biodegradable, natu-ral-derived polymers exist, such as polysaccharides (starch, chitin,collagen, gelatines, etc.), proteins (casein, albumin, silk, elastin,etc.), polyesters (e.g. poly(hydroxyalcanoate), poly(hydroxybuty-rate), polylactic acid), lignin, lipids, natural rubber, somepolyamides, polyvinyl alcohols, polyvinyl acetates, and polycapro-lactone [2,93105] . In the majority of cases, they degrade throughenzymatic reactions in suitable environments (typically, humid).

As a general rule, biodegradable polymers can be classiedaccording to their origin, i.e. into agropolymers (e.g. starch), micro-bial-derived (e.g. PHA) and chemically synthesized from agro-based monomers (e.g. PLA) or conventional monomers (e.g.synthetic polyesters) [106] .

Several examples are available in literature. For instance, Japa-nese researchers have investigated on composites based on starchand bamboo bers [2] . Others have studied the interesting proper-ties of composites based on Monsanto Biopol (a polyhydroxybutyratehydroxyvalerate copolymer) with ananas and jute bers.In some cases, natural bers were pre-treated by alkali treatmentand chemical groups grafting [9395,107109] .

Work has also been done to use matrices based on soy proteins.For instance, Netravali and coworkers [2,95] used soy proteins in

combination with several natural bers, obtaining interesting com-posites which, in some cases, show global characteristics evensuperior to many wood types. An interesting system for automo-tive applications is a composite where the polymer matrix is basedon soy and corn oil, which are used as raw materials for the pro-duction of the polymer (in a way which is comparable with theoneby which commodity polymers come from oil) with good resis-tance, exibility, lightness and durability properties [92] . Examplesof possible applications are panels, seats, packaging, furnishing,etc.

Some companies have been working on synthetic silk produc-tion by genetic engineering, which may be used for biodegradablematerials as well [2,110] .

A very interesting class of biodegradable polymers which could

be used for eco-composites production is the NovamontsMater-Bi . It is known that Mater-Bi family polymers are usually

Table 3

Tensile properties of wood our lled green composites as a function of the processing technique (data taken from Ref. [85] ).

Mechanical property Processing Neat polymer Composite, 15 wt.% WF

Elastic modulus (MPa) Mixing 410 537Single-screw extrusion 378 535Twin-screw extrusion 373 563Injection molding 200 295

Tensile strength (MPa) Mixing 17 11

Single-screw extrusion 27 17Twin-screw extrusion 28 12Injection molding 15 18



6/10

based on modied starch and synthetic polymers (polyesters inprevalence) [111113] and are compostable [113] . Literature re-ports that Mater-Bi can be conveniently used for the realization of fully biodegradable composites, however mechanical properties,processability and biodegradability strongly depend on the Ma-ter-Bi and the ller used, ller content, processing techniques[113122] . For instance, rigidity of the materials usually increasesupon increasing ller content [85,86,116,118,121] , while ultimatepropertiescan change signicantlydepending on ller content, pro-cessing techniques (mixing, extrusion, injection molding, etc.), pro-cessing parameters (speed, temperature, etc.) [85,119,120,122,123] . Scaffaro et al. [85] found that injection molding can signi-cantly reduce the polymers molecular weight in comparison toextrusion followed by compression molding but, on the other hand,it can improve both surface and internal morphology of the com-posite samples, thus leading to signicant increases of tensilestrength if compared to the neat, unlled samples.

An example of the way how the main mechanical properties canchange upon going from a neat Mater-Bi grade to the correspond-ing, 30 wt.% lled green composites, is provided in Table 4 . Thecomposites were lled with coarse (SDc) and ne (SDf) wood our.The ller was always dried before processing, while the polymerwas dried only in the case of dry-labeled samples.

It can be observed that wood our signicantly enhances thestiffness and the thermomechanical resistance of the materials;

furthermore, tensile strength keeps practically constant, probablythanks to the hydrophilic nature of the chemical groups presentin the Mater-Bi matrix; only the ductility is worsened. However,since polyesters are typically present in the composition of mostMater-Bi grades, a drying pre-treatment is advisable in orderreducing the hydrolytic chain-scission reactions due to the pres-ence of water in the system during processing.

Biodegradability of Mater-Bi based green composites has notbeen much investigated so far. The papers available regard biodeg-radation of composites in soil [112,113,124] and found that thecomposites underwent biodegradation after burial in soil.Rutkowska et al. [125,126] studied biodegradation in different nat-ural environments, nding a complete biodegradation after4 weeks. However, these investigations regarded just neat materi-

als. Scaffaro et al. [114] have studied Mater-Bi/wood our compos-ites biodegradation in active sewage sludge, nding that thecomposites undergo biodegradation with higher weight loss ratesthan the neat Mater-Bi. This effect was attributed primarily tothe morphology achieved and to the capability of wood bers toact as support for the bacterial growth [114] .

Another interesting thermoplastic polymer coming fromrenewable sources is polylactic acid (PLA). In general, PLA showsgood mechanical properties, is biocompatible and is rather easyto produce. Literature reports some studies on PLA and natural-organic llers. Nishino et al. [127] prepared PLA/kenaf bers com-posites with good mechanical properties, thanks to the orientationimparted to the bers. Lee and Wang [128] have studied PLA/bam-boo bers composites and the effect of a lysine-based couplingagent, obtaining an improvement of the mechanical propertiesand an increased thermal stability, even though this may worsen

the biodegradability. Further studies exist on PLA/ax composites[129] and the main problem encountered regards matrixbersadhesion.

Huda et al. [130] investigated the properties of PLA/recycledcellulose composites prepared by extrusion and injection molding,nding that the ller (up to 30 wt.%) signicantly improved therigidity without affecting the crystallinity degree or thermalstability.

Plackett et al. [131] prepared PLA/jute composites, by a lmstacking technique, nding signicant improvements of the tensileproperties, although brittle fracture was observed, affecting alsothe impact strength.

Unfortunately, some limitations have still to be overcome in or-der to support the development and use of fully biodegradablecomposites. First comes the still high price of biodegradable poly-mers in comparison to traditional commodity polymers, which of course discourages their use. Price is slowly decreasing uponincreasing of their utilization, however the latter need to increasemore and more to get to very competitive prices; this is one of the major challenges that biodegradable polymers are facing.

Another problem regards, as predictable, ller dispersion and itsinterface adhesion with the polymer matrix, which are of funda-mental importance for the overall properties of the product.Depending on the biodegradable polymer used, the results maybe more satisfactory than in the case of polyolens, etc. because

of the presence of polar groups along the macromolecules[85,86,111,114] but, sometimes, it is necessary to improve theproperties by treatments such as alkali treatment, acetylation,and silane or maleic anhydride treatments [2,13,18,132,133] . How-ever, from the point of view of industrial applications, chemicalmodication of bers is usually neither convenient nor cheap,therefore being mostly a niche solution.

Finally, it must be pointed out that thermoplastic polymershave been investigated also for use with nano-sized llers inreplacement for traditional micro-sized ones, thus leading to thegreen nanocomposites eld. An extensive review of such sub-eld would be out of the scope of the present paper. However,excellent reviews on it currently exist. Samir et al. [134] reportedon the processing and behavior of nanocomposites obtained by

thermoplastic polymers and polysaccharide microcrystals, ndingthat the use of high aspect ratio cellulose whiskers can lead to sig-nicant improvements of the mechanical properties. Polysaccha-ride nanocrystals may be obtained from several sources such as,for instance, chitin and starch by acid hydrolysis.

Hubbe et al. [135] focused on possible industrial application of cellulose nanocrystals, pointing out that retention of propertiesover time should be guaranteed and the use of water-misciblepolymer matrices such as latex, starch products, polyvinyl alcoholshould be preferred, in order to make cellulose preparation andcompatibilization with the matrix easier. Eichhorn et al. [136] re-ported (similarly as in the previous references cited) the possiblemethods of cellulose nanollers recovery, then focusing on theuse of cellulose nanowhiskers for the manufacturing of shapememory nanocomposites, as well as on the interfacial phenomenaoccurring in polymer/nanocellulose ller composites.

Table 4

Main mechanical properties for a neat Mater-Bi grade (MB) and the corresponding 30 wt.% wood our (SDc = coarse, SDf = ne) lled green composites, without (humid) andwith (dry) drying treatment on the polymer before processing (data taken from Ref. [111] ).

Property MB MB + 30%SDc (humid) MB + 30%SDf (humid) MB + 30%SDc (dry) MB + 30%SDf (dry)

Elastic modulus (MPa) 88 457 483 442 530Tensile strength (MPa) 6 5.5 6.4 7 6.7Elongation at break (%) 73 2.8 2.7 2.3 2.3Heat deection temperature ( C) 39 49 54 48 55

Impact strength (J/m) No break 86 54 63 44



7/10


8/10

Furthermore, the Authors highlighted that phases such as cultiva-tion, harvesting, mercerizing, drying and ber rening were attrib-uted with no impacts, reporting that jute production for severalsmall farmer communities along the Amazon River was consid-ered, with the river providing also the humus and all of the nutri-ents required.

Luz et al. [146] investigated the environmental impact of sugar-

cane bagasse - polypropylene composites for automotive compo-nents applications, in comparison to talc-PP composites, througha complete LCA. Three scenarios were taken into account, namelyScenario 1 (contemplating a reuse for the 50% of materials other-wise incinerated), Scenario 2 (one half of the composite materialis considered to be disposed municipally) and Scenario 3 (analyz-ing the contribution of a hypothetical talc-lled composite havingthe same specic weight as sugarcane bagasse composite). Impactcategories were abiotic depletion, acidication potential, eutrophi-cation potential, global warming potential (100 years basis), ozonelayer depletion potential and photochemical ozone creation poten-tial. The investigation was accurate, since it took into account aux-iliary processes such as diesel, phosphate, nitrogen, potassium,phosphorus and lime production/sources; however, still no landuse impacts were explicitly included. The overall analysis sug-gested that the green composites are better that the talc-lledcomposites in automotive applications, especially when weightreduction is particularly important. It is also suggested that sugar-cane bagasse ber production leads to lower environmental im-pacts compared to talc production, the composites are lighter,sugarcane has a positive contribution in terms of carbon creditsand the reuse of the end-of-life material is the optimum way tominimize the environmental impacts.

The same Authors [147] evaluated the technical performanceand environmental impacts of the same composites in comparisonto neat polypropylene. Different end-of-life options included incin-eration, recycling and landll. The composites showed better envi-ronmental performance during the entire life cycle, especially inthe cultivation phase (with sugarcane consuming carbon duringits growth, thus contributing to decrease global warming effects).Also in this case, recycling with economic reuse of the compositeswas the best alternative to minimize the environmental impacts.

For further in-depth study, an interesting review by Jorge [148]on environmental impact and LCA of lignocellulosic-derived prod-ucts (including lignocellulosic-lled plastic composites) can be ta-ken into account.

9. Conclusions

The use of polymer composites lled with natural-organic ll-ers, in replacement of mineral-inorganic llers, is of great interestin the view of the reduction in the use of petroleum-based, non-

renewable resources, and in general in a more intelligent utiliza-tion of environmental and nancial resources. These greencomposites can nd several industrial applications, although somelimitations occur regarding mainly ductility, processability anddimensional stability. Worldwide research has been spendingmuch effort in order developing suitable solutions through chem-ical modication of the ller, use of adhesion promoters and addi-tives. However, a full biodegradability, and thus a really improvedenvironmental impact, can be obtained only by replacing tradi-tional polymers (coming from non-renewable resources) with bio-degradable ones. In these cases, however, newlimitations arise andcurrent scientic investigation has been focusing on the selectionof the most suitable biodegradable matrix and the optimizationof all of the preparation and processing parameters.

As regards the commercial situation, it can be stated that themarket is still in an opening phase (especially in Europe), therefore

much can still be done in order nding new applications, improv-ing the properties, the appearance and the marketability of thesematerials. All of these issues require, and continue to require, sig-nicant research efforts in order to nd new formulations (virginor recycled polymers, traditional or biodegradable polymers; type,appearance, quality and amount of the llers), characterize them,apply them for the most suitable applications and, in general, to re-

ne processing techniques. As soon as the market for these com-posites increases, reduction of costs and improvement of thequality will be achieved.

References

[1] Gachter R, Muller H. Plastics additives, 3rd ed. Hanser Publishers; 1990.[2] Netravali AN, Chabba S. Composites get greener. Mater Tod 2003;6:226.[3] Rozman HD, Lai CY, Ismail H, Mohd Ishak ZA. The effect of coupling agents on

the mechanical and physical properties of oil palm empty fruit bunch-polypropylene composites. Polym Int 2000;49:12738.

[4] Carroll DR, Stone RB, Siringano AM, Saindon RM, Gose SC, Friedman MA.Structural properties of recycled plastic/sawdust lumber decking planks. ResCons Recycl 2001;31:24151.

[5] Joseph K, Thomas S, Pavithran C. Effect of chemical treatment on the tensileproperties of short sisal bre-reinforced polyethylene composites. Polymer1996;37:513949.

[6] Joseph PV, Joseph K, Thomas S. Effect of processing variables on themechanical properties of sisal-ber-reinforced polypropylene composites.Compos Sci Technol 1999;59:162540.

[7] Canch-Escamilla G, Rodriguez-Laviada J, Cuich-Cupul JI, Mendizabal E, Puig JE, Herrera-Franco PJ. Flexural, impact and compressive properties of a rigid-thermoplastic matrix/cellulose ber reinforced composites. Compos Part A2002;33:53949.

[8] Nair KCM, Kumar RP, Thomas S, Schit SC, Ramamurthy K. Rheologicalbehavior of short sisal ber-reinforced polystyrene composites. Compos PartA 2000;31:123140.

[9] Joshi SV, Drzal LT, Mohanty AK, Arora S. Are natural ber compositesenvironmentally superior to glassber reinforced composites? Compos Part A2004;35:3716.

[10] Selke SE, Wichman I. Wood ber/polyolen composites. Compos Part A2004;35:3216.

[11] RajRB, Kokta BV,Dembele F, Sanschagrain B. Compounding of cellulose berswith polypropylene: effect of ber treatment on dispersion in the polymermatrix. J Appl Polym Sci 1989;38:198796.

[12] Chen HL, Porter RS. Composite of polyethylene and kenaf, a natural celluloseber. J Appl Polym Sci 1994;54:17813.

[13] Willett JL. Mechanical properties of LDPE/granular starch composites. J ApplPolym Sci 1994;54:168595.

[14] Bagheri R. Effect of processing on the melt degradation of starch-lledpolypropylene. Polym Int 1999;48:125763.

[15] Sreekala MS, Kumaran MG, Thomas S. Oil palm bers: morphology, chemicalcomposition, surface modication, and mechanical properties. J Appl PolymSci 1997;66:82135.

[16] Ahmad Fuad MY, Zaini MJ, Jamaludin M, Mohd Ishak ZA, Mohd Omar AK.Determination of ller content in rice husk ash and wood-based compositesby thermogravimetric analysis. J Appl Polym Sci 1994;51:187582.

[17] Ahmad Fuad MY, Yaakob I, Rusli O, Mohd Ishak ZA, Mohd Omar AK.Determination of ller content in thermoplastic composites by FTIR analysis. J Appl Polym Sci 1995;56:155760.

[18] Coutinho FMB, Costa THS, Carvalho DL. Polypropylenewood bercomposites: effect of treatment and mixing conditions on mechanicalproperties. J Appl Polym Sci 1997;65:122735.

[19] Simpson B, Selke S, Composite materials from recycled multilayer poly-

propylene bottles and wood bers. In: Andrews G, Subramamian P, editors.Emerging technologies in plastic recycling. ACS SympSeries; 1992. p. 513.[20] Balasuriya PW, Ye L, Mai YW, Wu J. Mechanical properties of wood ake

polyethylene composites. II. Interface modication. J Appl Polym Sci2002;83:250521.

[21] Raj RB, Kokta VB. Reinforcing high density polyethylene withcellulosic bers.I: the effect of additives on ber dispersion and mechanical properties. J ApplPolym Sci 1991;31:135862.

[22] Wool RP, Raghavan D, Wagner GC, Billieux S. Biodegradation dynamics of polymerstarch composites. J Appl Polym Sci 2000;77:164357.

[23] Sharma N, Chang LP, Chu YL, Ismail H, Ishiaku US, Mohd Ishak ZA. Study onthe effect of pro-oxidant on the thermo-oxidative degradation behaviour of sago starch lled polyethylene. Polym Degrad Stabil 2001;71:38193.

[24] Danjaji ID, Nawang R, Ishiaku US, Ismail H, Ishak ZA Mohd. Sago starch-lledlinear low-density polyethylene (LLDPE) lms: their mechanical propertiesand water absorption. J Appl Polym Sci 2001;79:2937.

[25] Selke SE, Childress J. Wood ber/high density polyethylene composites:ability of additives to enhance mechanical properties. In: Wolcott MP, editor.Wood berpolymer composites: fundamental concepts, processes andmaterial options. Forest Product Society, Madison, Wisconsin; 1993. p.10911.



9/10

[26] Yam KL, Gogoi BK, Lai CC, Christopher C, Selke SE. Composites fromcompounding wood bers with recycled high density polyethylene. PolymEng Sci 1990;30:6939.

[27] La Mantia FP, Tzankova Dintcheva N, Morreale M, Vaca-Garcia C. Greencomposites of organic materials and recycled post-consumer polyethylene.Polym Int 2004;53:188891.

[28] Park RD, Balatinecz JJ. Short term exural creep behavior of woodber/polypropylene composites. Polym Compos 1997;19:37782.

[29] Liao B, Huang YH, Cong GM. Inuence of modied wood bers on themechanical properties of wood ber-reinforced polyethylene. J Appl PolymSci 1997;66:15618.

[30] Myers GE, Chahyadi IS, Gonzales C, Coberly CA. Wood our andpolypropylene or high-density polyethylene composites: inuence of maleated polypropylene concentration and extrusion. In: Wolcott MP,editor. Wood berpolymer composites: fundamental concepts, processesand material options. Forest Product Society, Madison, Wisconsin; 1993, p.4956.

[31] Kolosick PC, Myers GE, Koutsky JA. Bonding mechanisms betweenpolypropylene and wood: coupling agent and crystallinity effects. In:Wolcott MP, editor. Wood berpolymer composites: fundamentalconcepts, processes and material options. Forest Product Society, Madison,Wisconsin; 1993. p. 159.

[32] La Mantia FP, Morreale M. Improving the properties of polypropylenewoodour composites by utilization of maleated adhesion promoters. ComposInterf 2007;14:68598.

[33] Harper D, Wolcott M. Interaction between coupling agent and lubricants inwoodpolypropylene composites. Compos Part A 2004;35:38594.

[34] Nitz H, Semke H, Landers R, Mulhaupt R. Reactive extrusion of polycaprolactone compounds containing wood our and lignin. J ApplPolym Sci 2001;81:197284.

[35] Odusanya OS,MananDMA, IshiakuUS, Azemi BMN. Effect of starch predryingon the mechanical properties of starch/poly( e -caprolactone) composites. JAppl Polym Sci 2003;87:87784.

[36] Khalil HPSA, Rozman HD, Ahmad MN, Ismail H. Acetylated plant-ber-reinforced polyester composites: a study of mechanical, hygrothermal, andaging characteristics. Polym Plast Tech Eng 2000;39:75781.

[37] Lovely M, Joseph KU, Rani J. Isora bres and their composites with naturalrubber. Prog Rubber Plastics Recycl Technol 2004;20:33749.

[38] Belgacem MN, Bataille P, Sapieha S. Effect of corona modication on themechanical properties of polypropylene/cellulose composites. J Appl PolymSci 1994;53:37985.

[39] Gassan J, Gutowski VS. Effects of corona discharge and UV treatment on theproperties of jutebre epoxy composites. Compos Sci Technol2000;60:285763.

[40] Khalil HPSA, Ismail H, Rozman HD, Ahmad MN. The effect of acetylation oninterfacial shear strength between plant bres and various matrices. EurPolym J 2001;37:103745.

[41] Valadez-Gonzalez A, Cervantes-Uc JM, Olayo R, Herrera-Franco PJ. Effect of ber surface treatment on the bermatrix bond strength of natural berreinforced composites. Compos Part B 1999;30:30920.

[42] Dipa R, Sarkar BK, Rana AK, Bose NR. Effect of alkali treated jute bres oncomposite properties. Bull Mater Sci 2001;24:12935.

[43] Samal RK, Mohanty M, Panda BB. Effect of chemical modication on FTIR spectra: physical and chemical behavior of jute. J Polym Mater1995;12:23540.

[44] Raj RG, Kokta BV, Daneault C. Effect of chemical treatment of bers on themechanical properties of polyethylene-wood ber composites. Adhes SciTechnol 1989;3:5564.

[45] Sapieha S, Allard P, Zhang YH. Dicumyl peroxide-modied cellulose/LLDPEcomposites. J Appl Polym Sci 1990;41:203948.

[46] Dominkovics Z, Dnydi L, Puknszky B. Surface modication of wood ourand its effect on the properties of PP/wood composites. Compos Part A2007;38:1893901.

[47] Kalia S, Kaith BS, Kaur I. Pretreatments of natural bers and their applicationas reinforcing material in polymer compositesa review. Polym Eng Sci2009;49:125372.

[48] Bledzki AK, Letman M, Viksne A, Rence L. A comparison of compoundingprocesses and wood type for wood brePP composites. Compos Part A2005;36:78997.

[49] Kuo PY, Wang S-Y, Chen JH, Hsueh HC, Tsai MJ. Effects of materialcompositions on the mechanical properties of woodplastic compositesmanufactured by injection molding. Mater Des 2009;30:348996.

[50] Tasdemir M, Biltekin H, Caneba GT. Preparation and characterization of LDPEand PPwood ber composites. J Appl Polym Sci 2009;112:3095102.

[51] Madhoushi M, Nadalizadeh H, Ansell MP. Withdrawal strength of fasteners inrice straw bre-thermoplastic composites under dry and wet conditions.Polym Test 2009;28:3016.

[52] Nourbakhsh A, Ashori A. Preparation and properties of wood plasticcomposites made of recycled high-density polyethylene. J Compos Mater2009;43:87783.

[53] Zhang 53Y, Toghiani H, Zhang J, Xue Y, Pittman CU. Studies of surface-modied wood our/polypropylene composites. J Mater Sci2009;44:1432151.

[54] Nygard P, TanemBS, Karlsen T, Brachet P, Leinsvang B. Extrusion-basedwood

brePP composites: wood powder and pelletized wood bresacomparative study. Compos Sci Technol 2008;68:341824.

[55] Srebrenkoska V, Gaceva GB, Avella M, Errico ME, Gentile G. Recycling of polypropylene-based eco-composites. Polym Int 2008;57:12527.

[56] Nourbakhsh A, Kokta BV, Ashori A, Jahan-Latibari A. Effect of a novel couplingagent, polybutadiene isocyanate, on mechanical properties of woodberpolypropylene composites. J Reinf Plast Comp 2008;27:167987.

[57] Kaboorani A, Faezipour M, Ebrahimi G. Feasibility of using heat treatedwood in wood/thermoplastic composites. J Reinf Plast Comp 2008;27:168999.

[58] Kim SJ, Moon JB, Kim GH, Ha CS. Mechanical properties of polypropylene/natural ber composites: comparison of wood ber and cotton ber. PolymTest 2008;27:8016.

[59] Mansour SH, Asaad JN, Iskander BA, Tawk SY. Inuence of some additives onthe performance of wood our/polyolen composites. J Appl Polym Sci2008;109:22439.

[60] Prachayawarakorn J, Khunsumled S, Thongpin C, Kositchaiyong A,Sombatsompop N. Effects of silane and MAPE coupling agents on theproperties and interfacial adhesion of wood-lled PVC/LDPE blend. J ApplPolym Sci 2008;108:352330.

[61] Yuan Q, Wu D, Gotama J, Bateman S. Wood ber reinforced polyethylene andpolypropylene composites with high modulus and impact strength. JThermoplast Compos Mater 2008;21:195208.

[62] Cui Y, Lee S, Noruziaan B, Cheung M, Tao J. Fabrication and interfacialmodication of wood/recycled plastic composite materials. Compos Part A2008;39:65561.

[63] Kumari R, Ito H, Takatani M, Uchiyama M, Okamoto T. Fundamental studieson wood/cellulose-plastic composites: effects of composition and cellulosedimension on the properties of cellulose/PP composite. J Wood Sci2007;53:47080.

[64] Danya di L, Renner K, Mo czo J, Puka nszky B. Wood our lled polypropylenecomposites: interfacial adhesion and micromechanical deformations. PolymEng Sci 2007;47:124655.

[65] Nachtigall SMB, Cerveira GS, Rosa SML. New polymeric-couplingagent for polypropylene/wood-our composites. Polym Test 2007;26:61928.

[66] Karimi AN, Tajvidi M, Pourabbasi S. Effect of compatibilizer on the naturaldurability of wood our/high density polyethylene composites againstrainbow fungus (Coriolus versicolor). Polym Compos 2007;28:2737.

[67] Renner K, Mcz J, Puknszky B. Deformation and failure of PP compositesreinforced with lignocellulosic bers: effect of inherent strength of theparticles. Compos Sci Technol 2009;69:16539.

[68] Danya di L, Janecska T, Szabo Z, Nagy G, Moczo J, Puka nszky B. Wood ourlled PP composites: compatibilization and adhesion. Compos Sci Technol2007;67:283846.

[69] La Mantia FP, Morreale M, Mohd Ishak ZA. Processing and mechanicalproperties of organic llerpolypropylene composites. J Appl Polym Sci2005;96:190613.

[70] Li TQ, Wolcott M. Rheology of HDPEwood composites. I. Steady state shear

and extensional ow. Compos Part A 2004;35:30311.[71] Mamunya EP, Mishak VD, Shumskii VF, Lebedev EV. Rheological properties of

polymerwood material based on polyethylene. USSR Vysokomol Soedin SerB 1991;33:83945.

[72] Natov M, Wasilewa S. S. Kowachewa Welewa, Rheologische eigenschaftenvon mit holzmehl geflltem polypropylen. Angew Makromol Chem1995;225:7381.

[73] Maiti SN, Hassan MR. Melt rheological properties of polypropylenewoodour composites. J Appl Polym Sci 1989;37:201932.

[74] Sain M, Khunova V, Hurst J, Balatinecz J. The inuence of llers on compositerheological properties. Plasty Kauc 1998;35:199202.

[75] Rietveld JX, Simon MJ. The inuence of adsorbed moisture on theprocessability and properties of a wood our-lled polypropylene. In:Wolcott MP, editor. Wood ber/polymer composites: fundamentalconcepts, and material options; 1993. p. 3948.

[76] Rana AK, Mandal A, Bandyopadhyay S. Short jute ber reinforcedpolypropylene composites: effect of compatibiliser, impact modier andber loading. Compos Sci Technol 2003;63:8016.

[77] Bledzki AK, Faruk O. Wood bre reinforced polypropylene composites: effectof bre geometry and coupling agent on physico-mechanical properties. ApplCompos Mater 2003;10:36579.

[78] La Mantia FP, Morreale M. Mechanical properties of recycled polyethyleneecocomposites lled with natural organic llers. Polym Eng Sci2006;46:11319.

[79] Igl SA, Osswald TA. A study on the thermoformability of wood ber-lledpolyolen composites. In: Wolcott MP, editor. Wood ber/polymercomposites: fundamental concepts, and material options; 1993. p. 338.

[80] Mohanakrishnan CK, Narayan R, Nizio JD. Reactive extrusion processing of polypropylene-lignocellulosic blend materials. In: Wolcott MP, editor. Woodber/polymer composites: fundamental concepts, and material options;1993. p. 5762.

[81] Czvikovszky T, Lopata V, Boyer G, Kremers W, Saunders C, Singh A. Electron-beam processing of wood ber-reinforced polypropylene. In: Wolcott MP,editor. Wood ber/polymer composites: fundamental concepts, and materialoptions; 1993. p. 6874.

[82] Woodhams RT, Law S, Balatinecz JJ. Intensive mixing of wood bers withthermoplastics for injection-moulded composites. In: Wolcott MP, editor.

Wood ber/polymer composites: fundamental concepts, and materialoptions; 1993. p. 758.



10/10

[83] TanakaK, KatsuraT, KinoshitaY, Katayama T, UnoK. Mechanical properties of jute fabric reinforced thermoplastic moulded by high-speed processing usingelectromagnetic induction. WIT Trans Built Environ 2008;97:2119.

[84] Dauda M, Yoshiba M, Miura K, Takahashi S. Processing and mechanicalproperty evaluation of maize ber reinforced green composites. Adv CompMater 2007;16:33547.

[85] Scaffaro R, Morreale M, Lo Re G, La Mantia FP. Effect of the processingtechniques on the propertiesof ecocomposites basedon vegetable oil-derivedMater-Bi and wood our. J Appl Polym Sci 2009;114:285563.

[86] Morreale M, Scaffaro R, Maio A, La MantiaFP. Mechanical behaviour of Mater-Bi/wood our composites: a statistical approach. Compos Part A2008;39:153746.

[87] Ferreira RL, Furtado CRG, Visconte LY, Leblanc JL. Optimized preparationtechniques for PVC-green coconut ber composites. Int J Polym Mater2006;55:105564.

[88] Takagi H, Asano A. Effects of processing conditions on exural properties of cellulose nanober reinforced green composites. Compos Part A2008;39:6859.

[89] Klason C, Kubat J, Stromwall HE. Efciency of cellulosic llers in commonthermoplastics. Part 1. Filling without processing aids or coupling agents. Int JPolym Mater 1984;10:15987.

[90] Dalvag H, Klason C, Stromwall HE. The efciency of cellulosic llers incommon thermoplastics. Part II. Filling with processing aids and couplingagents. Int J Polym Mater 1985;11:938.

[91] Bataille P, Ricard L, Sapieha S. Effects of cellulose bers in polypropylenecomposites. Polym Compos 1989;10:1038.

[92] Marsh G. Next steps for automotive materials. Mater Tod 2003;6:3643.[93] Luo S, Netravali AN. Mechanical and thermal properties of environment-

friendly green composites made from pineapple leaf bers andpoly(hydroxybutyrate-co-valerate) resin. Polym Compos 1999;20:36778.

[94] Luo S, Netravali AN. Interfacial and mechanical properties of environment-friendly green composites made from pineapple bers andpoly(hydroxybutyrate-co-valerate) resin. J Mater Sci 1999;34:370919.

[95] Lodha P, Netravali AN. Characterization of interfacial and mechanicalproperties of green composites with soy protein isolate and ramie ber. JMater Sci 2002;37:365765.

[96] Van de Velde K, Kiekens P. Biopolymers: overview of several properties andconsequences on their applications. Polym Test 2002;21:43342.

[97] Rodriguez-Gonzalez FJ, Ramsay BA, Favis BD. High performance LDPE/thermoplastic starch blends: a sustainable alternative to pure polyethylene.Polymer 2003;44:151726.

[98] Scott G. Green polymers. Polym Degrad Stabil 2000;68:17.[99] Doi Y. Microbial polyesters. New York: VCH Publishers; 1990.

[100] Saad GR, Seliger H. Biodegradable copolymers based on bacterial poly((R)-3-hydroxybutyrate): thermal and mechanical properties and biodegradationbehaviour. Polym Degrad Stabil 2004;83:10110.

[101] Dufresne A, Vignon MR. Improvement of starch lm performances using

cellulose microbrils. Macromolecules 1998;31:26936.[102] Lenz RW, Marchessault RH. Bacterial polyesters: biosynthesis, biodegradable

plastics and biotechnology. Biomacromolecules 2005;6:18.[103] Godbole S, Gote S, Latkar M, Chakrabarti T. Preparation and characterization

of biodegradable poly-3-hydroxybutyratestarch blend lms. BioresourTechnol 2003;86:337.

[104] Averous L. Biodegradable multiphase systems based on plasticized starch: areview. J Macromol Sci 2004;44:23174.

[105] Yu L, Dean K, Li L. Polymer blends and composites from renewable resources.Prog Polym Sci 2006;31:576602.

[106] Satyanarayana KG, Arizaga GC, Wypych F. Biodegradable composites basedon lignocellulosic bersan overview. Prog Polym Sci 2009;34:9821021.

[107] Khan MA, Idriss Ali KM, Hinrichsen G, Kopp C, Kropke S. Study on physicaland mechanical properties of biopol-jutecomposite. PolymPlast Technol Eng1999;38:99112.

[108] Mohanty AK, Khan MA, Sahoo S, Hinrichsen G. Effect of chemical modicationon the performance of biodegradable jute yarn-Biopol composites. J MaterSci 2000;35:258995.

[109] Mohanty AK, Khan MA, Hinrichsen G. Surface modication of jute and itsinuence on performance of biodegradable jute-fabric/Biopol composites.Compos Sci Technol 2000;60:111524.

[110] Gould P. Exploiting spiders silk. Mater Tod 2002;5:427.[111] Morreale M, Scaffaro R, Maio A, La Mantia FP. Effect of adding wood our to

the physical properties of a biodegradable polymer. Compos Part A2008;39:50313.

[112] Di Franco CR, Cyras VP, Busalmen JP, Ruseckaite RA, Vazquez A. Degradationof polycaprolactone/starch blends and composites with sisal bre. PolymDegrad Stab 2004;86:95103.

[113] Bastioli C. Properties and applications of Mater-Bi starch-based materials.Polym Degrad Stab 1998;59:26372.

[114] Scaffaro R, Morreale M, Lo Re G, La Mantia FP. Degradation of Mater-Bi /wood our biocomposites in active sewage sludge. Polym Degrad Stabil2009;94:12209.

[115] Alvarez VA, Vazquez A. Thermal degradation of cellulose derivatives/starchblends and sisal bre biocomposites. Polym Degrad Stabil 2004;84:1321.

[116] Alvarez VA, Vazquez A, Bernal C. Effect of microstructure on the tensile andfracture properties of sisal ber/starch-based composites. J Compos Mater

2006;40:2135.

[117] Alvarez VA, Fraga AN, Vazquez A. Effects of the moisture and ber contenton the mechanical properties of biodegradable polymersisal ber bio-composites. J Appl Polym Sci 2004;91:400716.

[118] Alvarez VA, Vazquez A, Bernal C. Fracture behavior of sisal ber-reinforcedstarch-based composites. Polym Compos 2005;26:31623.

[119] Alvarez VA, Iannoni A, Kenny JM, Vazquez A. Inuence of twin-screwprocessing conditions on the mechanical properties of biocomposites. JCompos Mater 2005;39:202338.

[120] Alvarez VA, Terenzi A, Kenny JM, Vazquez A. Melt rheological behavior of starch-based matrix composites reinforced with short sisal bers. Polym EngSci 2004;44:190714.

[121] Puglia D, Tomassucci A, Kenny JM. Processing, properties and stability of biodegradable composites based on Mater-Bi and cellulose bres. PolymAdv Technol 2003;14:74956.

[122] Johnson RM, Tucker N, Barnes S. Impact performance of Miscanthus/Novamont Mater-Bi biocomposites. Polym Test 2003;22:20915.

[123] Johnson M, Tucker N, Barnes S, Kirwan K. Improvement of the impactperformance of a starch based biopolymer via the incorporation of Miscanthus giganteus bres. Ind Crop Prod 2005;22:17586.

[124] Alvarez VA, Ruseckaite RA, Vazquez A. Degradation of sisal bre/Mater Bi-Y biocomposites buried in soil. Polym Degrad Stabil 2006;91:315662.

[125] Rutkowska M, Heimowska A, Krasowska K, Janik H. Biodegradation of thermoplastic starchcaprolactone in different natural environments. In:Capparelli Mattoso LH, Leao A, Frollini E, editors. Natural polymers andcomposites. Embrapa Instrumentaao Agropecuaria: Sao Carlos; 2000.

[126] Rutkowska M, Krasowska K, Steinka I, Janik H. Biodeterioration of Mater-Bi Y class in compost with sewage sludge. Polish J Environ Stud 2004;13:859.

[127] Nishino T, Hirao K, Kotera M, Nakamae K, Inagaki H. Kenaf reinforcedbiodegradable composite. Compos Sci Technol 2003;63:12816.

[128] Lee SH, Wang S. Biodegradable polymers/bamboo ber biocomposite withbio-based coupling agent. Compos Part A 2006;37:8091.

[129] Bax B, Mussig J. Impact and tensile properties of PLA/Cordenka and PLA/axcomposites. Compos Sci Technol 2008;68:16017.

[130] Huda MS, Mohanty AK, Drzal LT, Schut E, Misra M. Green composites fromrecycled cellulose and poly(lactic acid): physico-mechanical andmorphological properties evaluation. J Mater Sci 2005;40:42219.

[131] Plackett D, Lgstrup Andersen T, Batsberg Pedersen W, Nielsen L.Biodegradable composites based on L-polylactide and jute bres. ComposSci Technol 2003;63:128796.

[132] Nickel J, Riedel U. Activities in biocomposites. Mater Tod 2003;6:448.[133] Li TQ, Ng CN, Li RHY. Impact behavior of sawdust/recycledPP composites. J

Appl Polym Sci 2001;81:14208.[134] Samir M, Alloin F, Dufresne A. Review of recent research into cellulosic

whiskers, their properties and their application in nanocomposite eld.Biomacromolecules 2005;6:61226.

[135] Hubbe MA, Rojas OJ, Lucia LA, Sain M. Cellulosic nanocomposites: a review.Bioresource 2008;3:92980.

[136] Eichhorn SJ, Dufresne A, Aranguren M, Marcovich NE, Capadona JR, Rowan SJ,et al. Review: current international research into cellulose nanobres andnanocomposites. J Mater Sci 2010;45:133.

[137] Klemchuk PP. Degradable plastics: a critical review. Polym Degrad Stabil1990;27:183202.

[138] Lim ST, Chang EH, Chung HJ. Thermal transition characteristics of heatmoisture treated corn and potato starches. Carbohyd Polym 2001;46:10715.

[139] Tezuka Y, Ishii N, Kasuya K, Mitomo H. Degradation of poly(ethylenesuccinate) by mesophilic bacteria. Polym Degrad Stabil 2004;84:11521.

[140] Schmidt WP, Beyer HM. Life cycle study on a natural ber reinforcedcomponent. SAE Technical Paper 982195, SAE Total Life-CycleConf. Austria: Graz; 1998.

[141] Wotzel K, Wirth R, Flake R. Life cycle studies on hemp bre reinforcedcomponents and ABS for automotive parts. Angew Makromol Chem1999;272:1217.

[142] Corbiere-Nicollier T, Gfeller Laban B, Lundquist L, Leterrier Y, Manson JAE, Jolliet O. Life cycle assessment of biobres replacing glass bres asreinforcement in plastics. Resour Conserv Recycl 2001;33:26787.

[143] Vidal R, Martnez P, Garran D. Life cycle assessment of composite materialsmade of recycled thermoplastics combined with rice husks andcotton linters.Int J Life Cycle Assess 2009;14:7382.

[144] Mil i Canals L, Clift R, Basson L, Hansen Y, Brando M. Expert workshop onland use impacts in life cycle assessment (LCA). Int J Life Cycle Assess2006;11:3638.

[145] Alves C, Ferrao PMC, Silva AJ, Reis LG,Freitas M, Rodrigues LB,et al. Ecodesignof automotive components making use of natural jute ber composites. JClean Prod 2010;18:31327.

[146] Luz SM, Caldeira-Pires A, Ferro PMC. Environmental benets of substitutingtalc by sugarcane bagasse bers as reinforcement in polypropylenecomposites: ecodesign and LCA as strategy for automotive components.Resour Conserv Recycl 2010;54:113544.

[147] Luz SM, Ferro PMC, Alves C, Freitas M, Caldeira-Pires A. Ecodesign applied tocomponents based on sugarcane bers composites. Mater Sci Forum2010;636637:22632.

[148] Caldeira Jorge F. Reducing negative environmental impacts from themanufacturing and utilization of lignocellulosics-derived materials: an

overview on research in 20072009. Molec CrystLiq Cryst 2010;522:32835.


Documents

Articulo 3 Ing Mat U3