Physical properties of lyocell-reinforced polypropylene composites from intermingled fibre with varying fibre volume fractions

Polypropylene (PP)-cellulose fibre blends exhibit substantial potential for the production of high-performance textile fibre–reinforced composites. The production of reinforced parts from PP-cellulose composites through thermal shaping of intermingled fibre blends is a strategy to form parts which exhibit superior mechanical properties. In this study, the use of intermingled fibre slivers with different ratios of lyocell fibres (CLY) and PP fibres as raw materials for thermally formed composites was investigated. Such a concept will maximize the interface between the reinforcement fibres and polymer matrix. The cellulose fibres remain oriented along the direction in which the drawing process was performed, which forms the basis for tailored fibre placement in technical production. Because of good surface contact between the cellulose fibre surface and PP matrix, no special coupling agents were required to improve the interfacial adhesion between the two different polymers. The share of CLY and PP fibres in the composite varied from 50% w/w CLY content, up to 70% w/w CLY. Besides analysis of the mechanical properties, such as tensile strength and E-modulus, attention was directed towards moisture sorption of the composites. The rate of sorption and amount of water bound in the composite were found to be dependent on the cellulose fibre content. Composites with a higher CLY content exhibited a more rapid and higher moisture uptake. In water saturated state, the ultimate tensile strength of composites reduced from 160 MPa to 90 MPa, which is an indicator for a reduced adhesion between the CLY surface and PP matrix. The results indicate the potential of the intermingled fibre concept blend for the efficient manufacturing of composite parts.