Influence of multiple recycling on the mechanical, rheological and thermal properties of styrene maleic anhydride

This work contributes to the understanding of material changes during the repeated recycling of glass fibre-reinforced styrene maleic anhydride (SMA). The present study investigates the influence of repeated recycling on its mechanical, rheological and thermal properties. The injection-moulded SMA was shredded, regranulated and subsequently injection-moulded. This was repeated five times in order to compare the material behaviour after multiple recycling runs with respect to the virgin material. In order to distinguish between the influence of polymer degradation and that of reinforcing fibre deterioration, pure SMA was also investigated. Tensile properties, melt volume rate (MVR) and fibre length were evaluated after each recycling run. Gel permeation chromatography (GPC) and infrared spectroscopy (IR) provided insight into the structural changes. The IR spectra and GPC analyses show that the chemical structure of the material is largely retained. The rheological tests show a decrease in the MVR values after each recycling path, indicating an increase in polymer viscosity. It was observed, that the tensile strength of the pure SMA under investigation increased after each recycling path, which could be attributed to the increase in the average molecular weight, as evidenced by the GPC analysis. Despite this increase in strength, the tensile tests of the fibre reinforced polymer showed a significant decrease in strength with each recycling run, while the elongation at break remained relatively constant. The impact strength decreases by 45% compared to the initially processed material. The deterioration in mechanical properties was mainly attributed to the shortened glass fibres. This is supported by the fibre length measurements, which show an average length reduction from 284 µm for the virgin material to 104 µm after five recycling runs. The research results show that SMA with and without glass fibre reinforcement can be mechanically recycled with little loss in mechanical performance.