Production of PP composites reinforced with flax and hemp woven mesh fabrics via compression molding

Hemp and flax fibers are among the most interesting vegetable fibers that can be used to reinforce polymeric matrices. In line with the global environmental requests, the use of these fibers especially coupled with thermoforming polymers are increasing more and more in order to expand their applications and replace synthetic fibers and thermosetting plastics. However, one of the major limitations of vegetable fibers is their poor adhesion with polymeric matrices that is often overcome by fibers chemical treatments or by using coupling agents within the matrix. Aiming to produce polypropylene (PP) bio composite laminates reinforced by hemp and flax fibers without additional process steps, this paper deals on the study of their production via the compression molding technique by using woven fabrics characterized by a large mesh size able to ensure a mechanical anchoring between fibers and matrix. Two different forming strategies that differ in the time required for reaching the maximum values of compression pressure and in the dwelling time at this value were used in order to investigate how the yarn impregnation was affected by them. To expand the applications of composites under investigation, tensile, bending, Izod, heat deflection temperature (HDT) and bearing tests were carried out. The results highlighted how the use of a waiting time before the reaching of the maximum moulding pressure allowed a better matrix flow within the vegetable yarn leading to higher mechanical performances.