Mechanical properties of polypropylene composites

JUAN MORÁN; VERA ALVAREZ; ROBERTO PETRUCCI; JOSÉ KENNY; ANALÍA VÁZQUEZ

JOURNAL OF APPLIED POLYMER SCIENCE

Wiley

Año: 2007 vol. 103 p. 228 - 237

0021-8995

In this work, the influence of multiple extrusion cycles on composite materials based on polypropylene and 20 wt.% of natural fibres was studied. The fibres final dimensions (length and diameter) were measured by means of optical microscopy. Mechanical properties of polypropylene and the composite material were measured after each extrusion cycle. It was observed that the elastic modulus rose due to the addition of natural fibres, showing its reinforcement capabilities. For the case of polypropylene, the elastic modulus increased during the first process cycle, compared to the virgin material, mainly due to intensive chain scission. For the following steps, the modulus kept constant. On the other hand, for the case of the composite material, the experimental elastic modulus measured after a single extrusion step was lower than that predicted by the Halpin – Tsai model; maybe due to a poor mixing and interphase fibre/matrix. The modulus increased for the following two cycles, while a better fibre dispersion was observed and then the modulus decreased slowly. This correlates well with a darkening and poor organoleptic properties observed produced by thermal degradation.