Mechanical properties of polypropylene composites based on natural fibres subjected to multiple extrusion cycles

MORÁN JUAN; ALVAREZ VERA; VAZQUEZ ANALÍA

JOURNAL OF APPLIED POLYMER SCIENCE

Wiley InterScience

Año: 2007 vol. 103 p. 228 - 237

0021-8995

The influence of multiple extrusion cycles on the behaviour of natural fibres reinforced polypropylene was studied. Composites were fabricated with 20 wt.% of flax fibres. Final fibres dimensions (length and diameter) were measured by means of optical microscopy. Mechanical properties of matrix and composites were measured after each extrusion cycle. It was observed that the elastic modulus increased by fibres incorporation. The elastic modulus of the matrix was higher after the first process cycle than that of the virgin material, mainly due to chain scission. In the next cycles, the modulus kept constant. On the other hand the elastic modulus of the composite after a single extrusion step was lower than that predicted by the Halpin – Tsai model probably due to a poor mixing and to low adhesion at the fibre/matrix interphase. In the following two steps, modulus increased because the better fibre dispersion was observed. For the final two extrusion cycles, the slow decrease in this property was correlated with the darkening and poor organoleptic properties observed as a result of thermal degradation.