Study Based On The Structure And Service Performances Of Long Glass Fibre Reinforced Polyamide 6 Composites

In recent years, it has been well established that the properties of engineer plastics are affected in different environment factors. However, there is lack of information on long glass fibre reinforced PA6 (PA6/LGF) composites for serving against several environment factors. In this work, the ageing performances of PA6/LGF serving in ultraviolet irradiation and hygrothermal environment are analyzed. To modify the ultraviolet and hygrothermal resisitance of the composites, Zinc Oxide (ZnO) and Sepiolite (Sep) are added as filler, respectively. Then the thermal degradation kinetics analysis is applied to evaluate the effect of ageing process and the fillers. Meanwhile, the flame retardancy properties of PA6/LGF are modified by filling Diethyl aluminium phosphate (OP).After ultraviolet ageing, PA6/LGF composites show an increase in the tensile strength and a decrease in the impact strength, which means an embrittlement occuring. While the samples filled with ZnO have a higher retention rate both in the tensile and impact strengths after ageing. The crystallinity of composites decreases because of the photo-crosslinking caused by ultraviolet which also causes the embrittlement. Then the thermal degradation kinetics of the composites is analyzed by Kissinger, Friedman and Flynn-Wall-Ozaza method. The calculated values of apparent activation energy (E) indicate that ultraviolet ageing makes E of PA6/LGF higher while the E of samples filled with ZnO remain unchanged.After long time hygrothermal ageing, PA6/LGF composites show a decrease in the tensile strength and an increase in the impact strength, which is caused by the water plasticizing in hygrothermal environment. For those samples filled with 6-8%wt sepiolite, a much higher retention rate of the tensile and impact strengths is observed. The PA6/LGF/Sep composites show a lower crystallinity because of the steric effect of sepiolite, which can be intensified by the expanding after absorbing water. On the other hand, the SEM photos of impact fracture show that interface debonding of PA6/LGF is even more serious than those filled with sepiolite. It is also the reason why the lower retention rate of mechanical properties is obtained for the former. Then the results from the thermal degradation kinetics analyzed by the above 3 methods indicate that the PA6/LGF composites have a much lower E after hygrothermal ageing, while the PA6/LGF composites filled with sepiolite have a slight increase in the value of E.In the modification of flame retardancy of PA6/LGF composites, the UL-94 level can reach V-1 rating when filled with 6%wt OP, and it can just reach V-0 rating when filled with 8%wt OP. The limited oxygen index (LOI) testing shows that the values of the PA6/LGF/OP composites increase with increasing the content of OP. The morphology analysis shows that compact carbon layers formed by OP in burning process of PA6 can wrap the glass fibres to restrain the wick effect. Then the degradation kinetic analysis by the three methods indicates that the value of E has a decrease when the content of OP is low. But for those samples with UL-94 V-0 ratin (the content of OP＞8%), the value of E is much higher, which means a better flame retardancy is obtained.