Polymer Testing 20 (2001) 869–872www.elsevier.com/locate/polytest

Material Behaviour

Impact behavior of sugarcane bagasse waste–EVAcomposites

G.C. Staela, M.I.B. Tavaresa, J.R.M. d’Almeidab,*

a Instituto de Macromole´culas, Universidade Federal do Rio de Janeiro, PO Box 68525, 21945-970, Rio de Janeiro, RJ, Brazilb Materials Science and Metallurgy Department, Pontifı´cia Universidade Cato´lica do Rio de Janeiro, Rua Marqueˆs de Sa˜o

Vicente, 225-22453-900, Rio de Janeiro, RJ, Brazil

Received 8 November 2000; accepted 5 February 2001

Abstract

The impact performance of chopped bagasse–EVA matrix composites is evaluated and compared with the behaviorof bagasse filled PP and PE matrix composites and wood-based materials. The volume fraction and size of the choppedbagasse used as filler was varied. The experimental results show that the incorporation of bagasse strongly reduces thedeformation capacity of EVA polymer. The reduction of the deformation capacity of the composites was also inferredby solid-state NMR relaxation analysis. The impact strength was independent of the bagasse size, but varied with thevolume fraction. As a function of the volume fraction it was shown that the mechanical performance of bagasse–EVAcomposites could be tailored to reproduce the behavior of wood-based particle boards. 2001 Elsevier Science Ltd.All rights reserved.

Keywords:EVA matrix composites; Chopped sugar cane bagasse; Impact behavior; NMR analysis

1. Introduction

Nowadays, composite materials are largely used inmany industrial applications that range from offshorestructures used by the petroleum industry to commonhousehold goods [1,2]. The great majority of these com-posites are resin matrix-based materials. In fact, the largenumber of polymers that have a good performance asmatrix materials provides a vast range of properties and,therefore, the versatility of resin matrix compositematerials [3].

Poly(ethylene-co-vinyl acetate), EVA, polymer couldbe a feasible possibility as resin matrix, although its lowmechanical properties could restrict the use of EVA-based composites [4–6]. Nevertheless, due to the highflexibility presented by EVA polymer, EVA-based com-

* Corresponding author.E-mail address: dalmeida@dcmm.puc-rio.br (J.R.M.

d’Almeida).

0142-9418/01/$ - see front matter 2001 Elsevier Science Ltd. All rights reserved.PII: S0142 -9418(01 )00014-9

posites could present some advantages under impact con-ditions, where toughness plays an important role.

In this work, the impact performance of choppedbagasse–EVA matrix composites were evaluated. TheIzod impact strength of the composites was measured asa function of the volume fraction and size of the bagasseand the values obtained were compared to those ofbagasse filled-polyethylene, PE, and polypropylene, PP,matrix composites and common wood-based materials.Solid-state NMR analysis was performed to provideinformation on the matrix–bagasse interaction.

2. Experimental methods and materials

The bagasse used as filler was directly obtained fromsugar cane mills, after being processed to extract sugarand liquor. This “as received” material was dried at 80°Cfor 48 h and then was chopped and sieved. Bagassepieces with lengths,l�3 mm, 3� l �5 mm and 20� l�30 mm were separated and used in this work. Herein-

870 G.C. Stael et al. / Polymer Testing 20 (2001) 869–872

after these chopped materials will be referred to as thesmall length (SL), medium length (ML) and long length(LL) bagasse pieces. The chopped bagasse was driedagain at 80°C for 48 h before being incorporated into theEVA matrix.

The composites were fabricated by mixing the properquantities of EVA and chopped bagasse in a HaakeRheocord 9000 plastograph using the rollermix rotor at60 rpm for 20 min. The processing temperature used was200°C. The mixed material was then pressed at 3.5 MPafor 15 min at 200°C to obtain plates of the composites.These processing parameters were shown to give the bestfabrication performance for these EVA–bagasse mix-tures [6]. Composites with volume fraction, Vf, ofbagasse of 0.13, 0.30, 0.48 and 0.59, respectively, corre-sponding to a matrix to bagasse ratio of 80/20, 60/40,40/60 and 30/70 in weight, were fabricated.

The specimens for the impact tests were machinedfrom the fabricated plates and were 62 mm long,12.7 mm wide and 4 mm thick. The notch to depth ratiowas 0.20 and the radius of the notch tip was 0.25 mm.The included angle of the notch tip was 45°, as specifiedby the ASTM standard D-256. The tests were conductedat room temperature, 23±3°C, in a non-instrumentedequipment with a maximum pendulum capacity of 2.7 J.At least 10 specimens were tested per composite.

Using the same fabrication procedure bagasse–PP andbagasse–PE composites were also fabricated. Thesecomposites have a volume fraction of 0.48 and thechopped bagasse used was the SL material. Test speci-mens from these materials and from three commercialwood-based materials, were also machined and testedusing the same experimental parameters as for thebagasse–EVA composites. Only the thickness of thewood-based materials were different, because thesematerials were tested with their commercial thickness,without any machining. The three wood-based materialstested were a 4.4 mm thick low density particle board(LDPB); a high density particle board (HDPB), 3 mmthick, composed of pressed cellulosic material; and a softplywood, SP, 3.7 mm thick plate.

The fracture surface of the tested specimens were ana-lyzed by scanning electron microscopy (SEM), on gold–palladium coated specimens. The SEM observation wasperformed with secondary electrons imaging and acceler-ation of the electron beam between 15 to 20 kV.

The solid state NMR spectra were obtained on aVARIAN INOVA 300 spectrometer operating at 299.9and 75.4 MHz for 1H and 13C, respectively. All experi-ments were performed at probe ambient temperatureusing gated high power decoupling. A zirconium oxiderotor with a diameter of 7 mm was used to acquire theNMR spectra at rates of 6 kHz. 13C spectra are refer-enced to the chemical shift of the carbon atoms of themethyl group of hexamethyl benzene (17.3 ppm). The13C measurements were carried out in the cross-polariz-

Table 1Impact strength (in kJ/m2), of the chopped bagasse–EVA com-posite as a function of the volume fraction and bagasse length

Volume Bagasse length

fraction SL ML LL

0.13 – 20.0±2.2 20.1±0.60.30 8.4±1.1 7.8±0.8 8.8±0.60.48 3.7±0.5 3.9±0.4 4.2±0.40.59 2.7±0.5 2.9±0.4 3.6±0.3

ation mode with magic-angle spinning (CPMAS) with2 s of delay. A variable contact-time experiment was alsorecorded and the range of contact-time established rangefrom 200 to 8000 µs. The T1

Hr values were determinedfrom the intensity decay of carbon-13 peaks withincreasing contact-time [7–9].

3. Experimental results and discussion

The experimental results obtained are shown in Tables1 and 2 for the chopped bagasse–EVA composites andfor the materials used for comparison, respectively. FromTable 1, one can see that the impact behavior of EVA-based composites is almost independent of the bagasselength. Only for the higher volume fraction, viz. 0.59, isthere a slight tendency for the energy absorbed toincrease with increase of the bagasse length. This sametrend was also observed for the tensile behavior of thesecomposites [10] and, in practice, it implies that forchopped bagasse with sizes smaller than 30 mm there isno need for sieving the bagasse pieces. On the otherhand, the variation of volume fraction causes a strongeffect on the impact strength of the composites. As onecan see from the data in Table 1, the incorporation ofchopped bagasse produces a strong decrease in theimpact strength. The brittle behavior associated with thecomposites with higher volume fractions could be attri-buted to the inhibition of the deformation capacity ofEVA matrix due to the presence of the much more stiff

Table 2Impact strength of the chopped bagasse–PP and PE compositesand commercial wood based materials

Material Impact strength (kJ/m2)

48% ML/PP 17.1±2.148% ML/PE 19.7±1.8LDPB 3.9±1.1HDPB 7.4±0.7SP 28.2±2.3

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Fig. 1. Common aspects observed at the bagasse–EVA inter-face, showing stretched polymer attached to a bagasse piece.ML bagasse–EVA composite with Vf=0.13.

bagasse material. In fact, the Young modulus of bagasseis on the order of 1800 MPa [11] against the low valueof only 28 MPa for the bare and flexible EVA polymer[10]. Besides that, the topographic aspects observed atthe fracture surfaces show that there was a good interac-tion between EVA matrix and chopped bagasse. Hence,not only the difference between the stiffness of the resinmatrix and bagasse contributed to decrease the defor-mation capacity of the composites, but the matrix defor-mation was also constrained by the chopped bagassematerial.

Fig. 1 shows the common aspects observed at thebagasse–EVA interface. One can see fibrils stretchedfrom the matrix and adhered to the bagasse material.This is a clear evidence that a good bagasse–EVA inter-action occurred. Fig. 2 shows another evidence that a

Fig. 2. Cohesive fracture of bagasse. ML bagasse–EVA com-posite with Vf=0.30.

good EVA–bagasse interface was developed. One cansee a bagasse piece that was split in two parts, i.e. thecrack run inside the bagasse and not at the interface.Cohesive fractures of this nature are usually found insystems showing good adhesion [12,13]. The goodadherence developed between bagasse and EVA is alsoshown in Fig. 3, where one can see a piece of bagassethat was torn apart from the bulk bagasse pieces but isstill adhered to the EVA resin matrix.

The results of the solid-state NMR relaxation timemeasurements that were also carried out in these com-posites corroborated the fractographic analysis. From thevalues obtained for the proton spin–lattice relaxationtime in the rotating frame, T1

Hr, that was measuredthrough the variable contact-time experiment, it wascharacterized that EVA–bagasse composites have a bet-ter physical interaction between bagasse and the poly-meric matrix at molecular level, due to the decrease inthe T1

Hr values in relation to those shown by the barebagasse. This interaction can come from the polar groupsrandomly distributed in the EVA macromolecular chains.This good interaction between bagasse–EVA could beinterpreted as a sign that bagasse is really acting as areinforcement.

From the above results, one can highlight the variationof the impact strength as a function of volume fractionsas the one with the greatest practical interest. In fact,although showing a lower performance than the PP andPE composites, as shown in Tables 1 and 2, EVA com-posites could be tailored to have the same performanceof wood-based particle board materials. From the experi-mental results obtained, one can see that for compositeswith a volume fraction of 0.30, which corresponds to40% in weight of bagasse, the impact strength is compa-rable to that of HDPB. With the higher volume fractions,what means more material usually disregarded as waste

Fig. 3. Broken bagasse with attached polymer. SL bagasse–EVA composite with Vf=0.48.

872 G.C. Stael et al. / Polymer Testing 20 (2001) 869–872

being used on an useful way, the impact strength of thechopped bagasse–EVA composites are comparable to thevalue shown by LDPB, largely used in low cost furni-ture. The soft plywood has a much higher impactstrength than EVA composites and, therefore, cannot beconsidered as substitutable by these low strength com-posites.

4. Conclusions

From the experimental results obtained one can con-clude that:

1. The incorporation of chopped bagasse reduces thedeformation capacity of EVA polymer;

2. A good bagasse/EVA interface was developed, asrevealed by the topographic features observed at thefracture surface;

3. The impact strength varies with the volume fractionof bagasse, which enables tailoring the mechanicalperformance of these composites to reproduce themechanical behavior of wood-based particle boards.

This last conclusion points to a feasible applicationfor these bagasse–EVA composites. The environmentalproblems posed today by bagasse wastes could be par-tially reduced if new low cost applications could beenvisaged for these wastes to replace wood products.

Acknowledgements

The authors would like to acknowledge the NationalCouncil for Scientific and Technological Development(CNPq).

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