Utilizing unbleached cellulosic fibres in polypropylene matrix composites for injection moulding applications

The aim of this work was to investigate the use of unbleached cellulosic Kraft pulp fibres for reinforcing polypropylene and to compare the performance of these novel composites with the one of state of the art composites like glass and talc reinforced polypropylene. The compounds, consisting of different amounts of fibres, compatibilizer and polypropylene were produced using a 24 mm co-rotating twin screw extruder, and after a subsequent drying step, moulded into universal test specimen for mechanical characterization. Tensile strength and modulus as well as impact properties were determined according to ISO-527 and ISO-179, respectively. Further characterizations with microscopic methods to investigate fibre dispersion and orientation have been carried out. The results from mechanical testing of the cellulose fibre reinforced composites are compared with results obtained from standard polypropylene injection moulding grades, reinforced with glass fibres and mineral particles. Furthermore, small L-shaped components were injection moulded from all the composites and tested in different compression modes, to get data for the composite performance in application. In conclusion, the cellulose fibre reinforced polypropylenes exhibit attractive mechanical property profiles at a level comparable to glass fibre reinforced composites. A further advantage of these materials is the lower composite density compared to glass fibre and mineral reinforced grades.