High-tenacity man-made cellulose fibre reinforced thermoplastics – Injection moulding compounds with polypropylene and alternative matrices

High-tenacity man-made cellulose filament yarn (rayon tyre cord yarn) has been used to reinforce polypropylene (PP), polyethylene, high impact polystyrene (HIPS), and poly (lactic acid) (PLA) for injection moulding applications. Highly homogeneous composites are obtained with the pultrusion compounding method developed. For PP the influence of coupling agent, fibre weight fraction, fibre cut length and PP type on basic mechanical properties of the composites have been studied. For a fibre load of 30 wt%, typical values for tensile strength, modulus, Charpy unnotched and notched impact strength are 80 MPa, 3.5 GPa, 85 kJ/m2, and 12 kJ/m2, respectively. A high impact resistance level is maintained also at low temperatures where the matrix material becomes brittle. For the other matrix materials, similar reinforcing effects are observed, except for the impact behaviour of HIPS, where the reinforcing fibres interfere with the impact modification of the matrix polymer. In contrast, the impact characteristics of PLA are drastically improved increasing the unnotched and notched Charpy strengths by 380% and 200%, respectively. With the property level obtained, cellulose man-made fibre reinforced composites prove to be an alternative to short glass fibre reinforced plastics.