The Research On The High Performance Of Flame-Retarded, Weather-Resistant, Long-Glass Fibre Reinforced Polyoxymethylene Composites

Polyoxymethylene (POM) is wide-ranging application in various industrial fields as one of five engineering plastics. Flame-retarded, weather-resistant, long-glass fibre reinforced POM were studied in this paper against the shortcoming of POM, and acquired a very excellent achievement. Different nitrogen-phosphorus flame retardant systems were investigated base on halogen-free flame-retarded POM. The flamming retarded performance of the composites was determined by limit oxygen index and vertical burning experiment. The result which the best flamming restarded system is ammonium pentaerythritol double phosphate melamine salt, polyphosphate and melamine cyanurate (PDPM/APP/MC). PDPM/APP/MC could make a FV-0classification when the mass fraction is36. The flamme-retarded mechanism was studied by scanning electron microscopy (SEM), and their chemical structures were evaluated by Fourier transform infrared spectroscopy (FTIR). The consequence shows that the it is a typical nitrogen and phosphorus flame-retarded mechanism, which means that a chemical reaction makes phosphorus compouds become polyphosphate in high temperture. Polyphosphate has so absorbent that make colloidal carbon layer arise. Meanwhile, phosphorus compouds decomposite and release gas, make colloidal carbon layer expand and oxygen dilute. The study on the thermal stabilities of these POM compounds revealed that these POM compounds underwent a two-step degradation, where the flame retardants first decomposed to generate the flame retardant effect.The weather-resistant polyoxymethylene (POM) compounds were prepared through the melt-compounding of dimethylsiloxane, UV absorbers, UV stabilizers, UV shielding agents, antioxidants, and formaldehyde absorber. The retention of mechanical properties of these POM compounds was investigated after the light ageing, thermo-oxidative aging, and hydrothermal aging experiments were performed. The thermal stabilities of the weather-resistant POM compounds were evaluated by thermogravimetric analysis before and after the ageing experiments, and the crystalline structures of POM and the additive distribution in matrix were also investigated by polar optical microscopy. The effect of UV light on the impact fracture surface was observed by scanning electron microscopy. The experimental results show that the addition of weather-resistant additives significantly increased the retention of mechanical properties of POM. The aging of POM mainly occurred in the amorphous region, and POM was particularly sensitive to light, heat, and oxygen, but there is a less effect on the hot water. Weather-resistant additives were mainly distributed in the amorphous region, and meanwhile, they performed the weather-resistant effect on POM. These weather-resistant additives were also gradually expended during the aging process with the exposure of UV irradiation.A thermoplastic pultrusion was carried out to prepare the long fibre reinforced thermoplastic composites based on polyacetal (POM) matrix on the custom-designed pultrusion equipment. The study on mechanical performance reveals that the POM-based long fibre reinforced thermoplastic composites achieved much higher tensile, flexural, and impact strength than the short glass fibre reinforced ones at the same fibre loadings. Such a promising reinforcement effect is attributed to the feature that the residual fibre length in the injection-molded long fibre reinforced thermoplastic products is greatly superior to that in short fibre reinforced ones. This takes full advantage of the strength of the reinforcing fibre itself. The scanning electronic microscopy demonstrates that the fiber fracture and fiber pull-out concurred on the tensile and impact fracture surfaces. The crystallization kinetics of the POM-based long fibre reinforced thermoplastic composites were also in-depth studied in terms of the nonisothermal and isothermal crystallization processes. The results indicate that the crystallinity of POM domain was enhanced by the heterogeneous nucleation of glass fibre, but the crystallization rate was postponed due to the interspace restriction toward crystalline growth caused by long glass fibre. These kinetic parameters provide information on the processing conditions of POM-based long fibre reinforced thermoplastic composites for the injection-and compression-molding.