16th International Conference on Composite Structures ICCS 16

A. J. M. Ferreira (Editor) © FEUP, Porto, 2011

THERMOSET MATRICES REINFORCED WITH SUGARCANE

BAGASSE FIBERS

C. G. Silva and E. Frollini Macromolecular Materials and Lignocellulosic Fibers Group, Institute of Chemistry of São Carlos, University of São Paulo, Av. Trabalhador Sancarlense, 400, São Carlos, Brazil, elisabete@iqsc.usp.br

Key words: Sugarcane bagasse, Sodium lignosulphonate, Phenolic-type matrices.

Summary. This study emphasizes the use of reagents obtained from renewable resources and sugarcane bagasse, a residue produced on a large scale by the Brazilian agroindustry. Composites were prepared with resin-based sodium lignosulphonate (product of natural and renewable sources with a high content of phenolic groups), which completely replaced phenol in a phenolic resin. Part of the matrices was also replaced by a high content of fiber, 50 and 70% (wt%). Aiming to improve the adhesion at the interface, lignosulphonate was also deposited on the fiber surface. The composites were characterized by Izod impact strength, SEM and thermal stability (TGA and DSC). In general terms, the results indicate that composites can be prepared from a high content of raw materials obtained from renewable resources, with properties that point to non-structural application.

1 INTRODUCTION Usually fibers such as sisal, sugarcane bagasse, curaua and others are used to reinforce bio-

based composites [1,2]. Sugarcane bagasse is the residue produced in greatest amounts by the Brazilian agroindustry and it was used in the present study, together with sodium lignosulphonate as reagent, to produce composites prepared from a very high content of raw materials obtained from renewable resources.

2 EXPERIMENTAL Sugarcane bagasse fibers (kindly supplied by The Santa Lucia Mill, Araras-São Paulo, Brazil) were treated by sonication in sodium lignosulphonate (NaLS) solution (VIXILEX SD, kindly supplied by LignoTech Brasil, Borregaard) during 1h and dried at 105°C. Phenolic pre-polymers and composites, reinforced with sugarcane bagasse fibers, randomly distributed in the matrix (50 and 70 wt%, near 15mm length), were prepared and characterized, under the conditions established in previous papers [1,2], by Izod impact test, SEM, TGA and DSC.

3 RESULTS AND DISCUSSION Phenolic composites (PC) and sodium lignosulphonate/formaldehyde composites (LTFC)

were prepared with sugarcane bagasse fibers [untreated and treated (7.6wt% of NaLS adsorbed on fiber surface)] as reinforcement. Figure 1a shows that the impact strength of composites increases when the fibers are treated with sodium lignosulphonate (LTFC), mainly

C. G. Silva and E. Frollini

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at 50 wt% of fibers. These results indicate that the presence of moieties typical of lignin on the sugarcane fiber surface, due to the adsorption of NaLS, improves the adhesion at the fiber-matrix interface, as sugarcane has a high content of lignin (22.49%), that is, the affinity fiber-matrix is intensified when the fiber is treated with NaLS.

(a) (b) (c) (d)

Figure1: (a) Izod impact of composites: phenolic/fibers untreated (PC); lignossulphonate/formaldehyde/fibers untreated (LUFC) and treated (LTFC); (b) SEM composite reinforced with fibers treated (50% wt%); (c) dTG fibers untreated (UF) and treated (FT); dTG PC, LUFC, LTFC[synthetic air atmosphere (20 mL min-1), heating rate of 10 °C min-1].

The SEM image of the fractured surface of LTFC (50 wt% of fiber) (1b) confirms the good adhesion at the fiber-matrix interface. The fibers break in the same plane of fracture of the matrix with little propagation of cracks around the fibers. The diffusion of resin in to the fiber channels is an indication of good wetting of the fibers by the resin. The dTG curves (obtained by thermogravimetric analysis) of fibers (untreated, UF, and treated, TF) and lignosulphonate/formaldehyde composites (reinforced with untreated (LUFC) and treated (LTFC) fibers). Figures 1c and 1d show that the treatment of fibers with NaLS shifted the decomposition temperature from 312 to 355 ° C, indicating that the NaLS adsorbed on the surface had protected the hemicelluloses and cellulose (whose thermal decomposition occurred before that of lignin) present in the lignocellulosic fiber. In curves for the composites (Figure 1d), the peaks related to the first step of decomposition occur in a narrower range of temperatures than in those for the fibers (Figure 1c).

4 CONCLUSIONS The results indicate that the treatment of sugarcane bagasse fibers with NaLS strengthened

the interactions at the fiber/matrix interface. Overall, the results available so far indicate that composites can be prepared from a high content of raw materials obtained from renewable resources, with properties that point to non-structural application. Acknowledgments: E.F. and C.G.S are grateful to CNPq, CAPES and FAPESP for financial support.

5 REFERENCES [1] Megiatto, Jr. J. D., Silva, C. G., Ramires, E. C., Elisabete Frollini, “Thermoset matrix reinforced with sisal fibers: Effect of the cure cycle on the properties of the biobased composite”, Polym. Test. 28 793–800 (2009). [2] Paiva, J. M. F, Frollini, E., “Unmodified and Modified Surface Sisal Fibers as Reinforcement of Phenolic and Lignophenolic Matrices Composites: Thermal Analyses of Fibers and Composites”, Macromol. Mater. Eng. 291, 405–417 (2006).