Effect of Addition of PTFE on the Rheological and Mechanical Properties of CF Reinforced Plant-Derived Semi-Aromatic Polyamide (PA10T) Biomass Composites
Authors: Ono Takayuki , Nishitani Yosuke 
Published: February 2020

For the purpose of this study is to develop the new engineering materials such as structural materials and tribomaterials (for sliding mechanical parts) based on plant-derived materials with sufficient balance among mechanical, processability, tribological properties, eco-friendliness, etc., we investigated the effect of addition of polytetrafluoroethylene (PTFE) on the rheological and mechanical properties of carbon fiber (CF) reinforced plant-derived semi-aromatic polyamide (PA10T) biomass composites. Especially, the relationship between various physical properties such as rheological and mechanical properties of these biomass composites and internal microstructure in the composites when added with PTFE or not were discussed in this study.

PA10T is a kind of polyphthalamide (PPA, semi-aromatic polyamide) biomass polymer made from plant-derived decamethylenediamine and coal-derived terephthalic acid. In this study, PA10T was used as a matrix polymer. CF was used as the reinforcement fiber and its volume fraction was fixed on 20vol.%. PTFE was used as the solid lubricant and its weight fraction was fixed on 20wt.%. Various CF/PA10T/PTFE biomass composites were extruded using a twin screw extruder and injection molded. Rheological properties in the molten state were evaluated by oscillatory flow test using a parallel plate type rheometer. Mechanical properties such as tensile, bending, Izod impact and tribological properties were evaluated. Tribological properties were measured using a ring-on-plate type sliding wear tester at the room temperature under dry condition. The sliding surfaces of the test specimen, wear debris and counterface before/ after observation by a SEM with osmium (Os) sputter coating. To understand the internal microstructure in these biomass composites, the surface of the samples fractured cryogenically in liquid nitrogen was observed using SEM and the fiber length and its distribution were measured for the samples after injection molding.

It was found that rheological properties such as storage modulus and complex viscosity of CF/PA10T biomass composites in molten state changed when added with PTFE. Mechanical properties such as strength and modulus of CF/PA10T/PTFE biomass composites are almost the same as those of CF/PTFE biomass composites, although tribological properties such as frictional coefficient, specific wear rate and limiting pv value improved when filled with PTFE. In particular, the limiting pv value of CF/PA10T/PTFE biomass composites remarkably improved due to the results of the synergistic effect, which is both mechanical and tribological properties are improved when filled with both PTFE and CF. These may be attributed to the change in the internal microstructure of these biomass composites such as fiber length, fiber dispersion and fiber-fiber interactions. Therefore, these results may contribute to the development of new engineering materials based on plant-derived polymer composites with sufficient balance among eco-friendliness, processability, mechanical and tribological properties.