Experimental and multi-scale investigation of the mechanical behavior of mechanically recycled glass fiber reinforced thermoplastic composites

Abstract

Fiber reinforced thermoplastic polymer composites have gained a lot of attention over the past two decades, due to their excellent mechanical performance and their lightweight resulting in lower CO2 emissions for airplanes and vehicles. However, with increased demand for these materials, research regarding environmentally friendly recycling routes has become a central environmental issue. Mechanical recycling by exploiting the melting properties of thermoplastic polymers has proven an excellent way of increasing the value of recycled composites, especially compared to other mainstream techniques. This research aims at investigating the relationship between the microstructure of these materials and their resulting mechanical properties. The studied material is processed by compression molding chopped woven composites chips, made from a polyamide 6 matrix reinforced with glass fibers. A novel microstructural investigation for these types of materials was conducted using multiple destructive and non-destructive techniques, along with tensile and flexural tests on specimens made from different chips sizes. This investigation revealed a hierarchical fiber structure with a mixture of intact woven chips and randomly oriented unidirectional fiber strands. This microstructure causes complex damage propagation mechanisms and variability in mechanical performance. This hinders development and large-scale commercialization of these materials and favors other less eco-friendly recycling strategies. Therefore, developing accurate predictive models for the mechanical response of these materials is important, thus enabling fast design optimization. A multi-scale predictive model is hence proposed based on extensive qualitative and quantitative microstructural investigation and is able to capture the anisotropy of the material. This approach is validated on experimental data from a recycled PA6/Glass fiber composite and can be applied for other recycled materials in the same manner.