Cost-Effective Microfibrillar Reinforced Composites for Lightweight Applications

Abstract

Microfibrillar reinforced composites (MFC) are self-reinforced polymer-polymer composites, consisting of a cold drawn (fibrillized) phase in an isotropic matrix. They are manufactured via melt blending of two immiscible polymers with different melting temperatures, followed by a subsequent cold drawing and thermal annealing step. The present study examines the manufacturing of composite material out of melt-spun microfibrillar reinforced filaments. Polypropylene (PP) and Polyethylene terephthalate (PET) were chosen as the low-melting matrix and the high-melting reinforcement phase, respectively.The filaments were woven to flat textile structures and processed to composites via hot pressing. They represent a bidirectional reinforced composite, comparable to other fiber reinforced polymers. To ensure optimized processing the influence of relevant parameters has been investigated with respect to mechanical properties of the MFC‑filaments and the derived composites. In addition, the morphology was visualized by SEM imaging after all manufacturing steps. An important observation was that the reinforcing fibrils are still intact after thermal processing, leading to a significant increase in mechanical properties of the resulting composites. Quasistatic tensile tests show more than 100 % higher modulus and more than 50 % higher strength of the only 20 wt-% reinforced PET‑PP composites compared to neat PP. The influence of the amount of PET reinforcement, the variation in processing conditions and composite layup were investigated. Additionally, an outlook on the melt-spinning of blends with Polyamide (PA) is given. In future work it is meant to show that a broad spectrum of tailored properties can easily be achieved by such polymer blends and composites outperforming existing homopolymers as well as thermoplastic composites like short glass‑fiber‑reinforced Polypropylene.The material cost reduction thanks to adding cheaper mass‑production polymers and the transfer onto conventional manufacturing lines is meant to ensure the feasibility of industrial production. The low density and excellent recycling options of these composites underline their potential for automotive and aircraft applications.