Flexural, impact and compressive properties of a rigid-thermoplastic matrix/cellulose fiber reinforced composites

The mechanical behavior of rigid-thermoplastic matrix-cellulose fiber reinforced composites is investigated. These materials exhibit a brittle behavior, that is, they possess a high modulus and therefore, a very limited amount of deformation to fracture. Such behavior makes the characterization of interfacial properties difficult to evaluate. In this paper, the flexural, impact and compressive behavior of cellulose fibers reinforced polymeric matrices, such as poly(methyl methacrylate) (PMMA) and poly(styrene-co-acrylonitrile) (SAN) are investigated and special attention is given to the effect of fiber surface treatment on the effective properties. The flexural strength of the composites remains constant when the fiber is grafted with PMMA and a brittle interface is formed around the cellulose fibers, regardless of fiber content. This behavior is not observed in composites reinforced with untreated cellulose fibers or poly(butyl acrylate)-grafted fibers, which show a low flexural strength at higher fiber contents. In the case of impact loading, the presence of an elastomeric type material, in this case, poly(butyl acrylate)-grafted cellulose fibers seems to provide an alternative mechanism for energy dissipation in the composite, thus, showing a better impact behavior than the composites with the other fiber surface treatments. The impact behavior seems to be improved by the mechanical properties of the cellulose fibers. Specifically, the low elastic modulus of the cellulose fiber resulting from the attack of the grafting process, contributes to decrease the rigidity of the composite. Using the fact that glassy materials such as PMMA and SAN are able to yield when they are loaded under compression, even at room temperature, compression experiments were performed using two different sample geometries. The first was the typical rectangular sample and the other was the hourglass shaped specimen. Due to the compressive state of stress induced at the middle portion of the last specimen, a better indication of fiber matrix adhesion could be evaluated as compared to the other sample geometry that induced mixed stress component signs in the test area. The fiber-matrix interfacial properties are assessed from scanning electron microscope photographs. (C) 2002 Elsevier Science Ltd. All rights reserved.