Morphology and properties of isotropic and oriented samples of cellulose fibre-polypropylene composites

Thermal, morphological and dynamic mechanical properties of polypropylene (PP)-cellulose fibre (CF) composites were investigated. Two types of CF and a compatibilizer were used. Calorimetric measurements exhibited an increase in the crystallization temperature and crystallinity of the PP component. This is attributed to the nucleating effects of the fibre surfaces, resulting in the formation of transcrystalline regions observed by an optical method. The dynamic mechanical spectra of the composites revealed an increase in the stiffness and a reduction in the damping values with an increasing CF content. The results are consistent with morphological observations, which verify an improved interfacial adhesion between fibre and matrix. The effects of drawing on the structure and physical properties of PP-CF composites were also studied. Increasing draw ratio, the melting peak of PP component was shifted to higher temperatures suggesting a constrained melting, and the uniaxial elastic modulus was considerably enhanced. The biggest influence was observed for the samples of PP-spun cellulose and the lowest for neat PP. In addition to the fibrillar structure of the oriented PP, the highly CF orientation and the efficient compatibilization in composites are responsible for the effects observed in the drawn samples. (C) 1999 Elsevier Science Ltd. All rights reserved.