Study On Aging Resistance Of PA66-Based Composites To Thermal Oxidation And Hot Oil

With the continuous progress of society,the exploration and research of polymer science has become more and more in-depth.PA66 is one of the most abundant and widely used varieties of nylon series products,which has good process-ability,thermal properties,mechanical properties,insulation properties and corrosion resistance.Now it has been widely used in aerospace,electronics and electrical appliances,precision instruments,automobiles,chemical industry,construction and other industries.However,PA66 often faced with the problem of aging in practical applications,which leads to the decline of its performance in different degrees and making it difficult to meet the actual requirements.Therefore,the research and development of PA66 composites with excellent anti-aging performance has become an urgent problem to be solved for the material industry.In this paper,N,N’-bis(β-naphthyl)p-phenylenediamine(DNP)and bis(2,4-dicumylphenyl)pentaerythritol di(phosphite)ester(9228)were selected as anti-aging components to prepare PA66-based composites by ball milling blending-melt blending-injection molding,and the PA66-based composites were prepared by electric heating air drying box.The properties of PA66 composites before and after aging were investigated by tensile,impact,SEM,FT-IR,XRD,DSC and TG,and the anti-aging mechanisms of antioxidant DNP and antioxidant DNP/9228 were discussed.The main research contents and conclusions are summarized as follows:(1)DNP/PA66 composites were prepared by melt blending-injection molding technology with PA66 as matrix material.The samples were accelerated by thermal oxidation and thermal oil aging,and the effects of thermal oxidation and thermal oil aging on the structure and properties of DNP/PA66 composites were systematically studied.With the addition of DNP,the thermal oxygen resistance and thermal oil resistance of PA66-based composites were improved;compared with pure PA66,the change degree of characteristic peaks of DNP/PA66 composites before and after aging was reduced;the test results of mechanical properties show that the thermal stability of PA66 matrix material is obviously improved after the addition of antioxidant DNP,and the best effect is obtained when the addition amount of DNP is added at 0.1wt.%;compared with pure PA66 samples,the fracture morphology of DNP/PA66 composites after aging is rougher,the number of low-melting-point small molecular debris is less,and the surface morphology of the samples is smoother.In the crystallization performance test,the characteristic temperature of the sample decreased after aging,and the corresponding characteristic temperature of DNP/PA66 material decreased slightly after aging,and the shoulder peak with poor stability was preserved.In the thermal stability test,the characteristic temperature of the sample decreased after aging,and the corresponding characteristic temperature of DNP/PA66 composite decreased slightly after aging.(2)Based on the study of the thermal oxygen and thermal oil stability of DNP/PA66 composites,the antioxidant 9228 and antioxidant DNP were selected to modify PA66 matrix,and the effects of thermal oxygen and thermal oil aging on the structure and properties of 9228/DNP/PA66 composites were investigated.As an anti-aging component,9228 compounded with DNP was added to PA66 matrix,which further improved the thermal oxygen and thermal oil resistance of PA66-based composites.Compared with pure PA66 and DNP/PA66 composites,the changes of corresponding structural functional groups and crystal region characteristic peaks decreased after aging of 9228/DNP/PA66 composites.The degradation of tensile and impact properties of 9228/DNP/PA66 composite modified by compound was alleviated after aging with thermal oxygen and thermal oil,and the best effect was obtained when the addition amount of 9228 was added at 0.5wt.%.Compared with pure PA66 and DNP/PA66 composites,9228/DNP/PA66 composites had better protection effect on impact fracture morphology and sample surface morphology after aging.In the crystallization performance test,the characteristic temperature of the sample decreased after aging,and the corresponding characteristic temperature change range of the compound modified 9228/DNP/PA66 composite was relatively small after aging,and the shoulder peak with poor stability became a single peak independently.In the thermal stability test,the characteristic temperature of the sample decreased after aging,and the thermal stability of the 9228/DNP/PA66 composite material was improved after compound modification.(3)After aging of PA66 matrix material,the unsaturated bonds and active functional groups in the molecular chain are oxidized into free radicals,and the free radicals further react,which leads to the fracture and cross-linking of the matrix molecular chain,which makes the properties of the material worse.In9228/DNP/PA66 composite material,antioxidant DNP can capture free radicals and slow down the oxidation speed of the molecular chain,antioxidant 9228 can decompose the hydroperoxide generated by the oxidation of the matrix,block the chain reaction,and antioxidant 9228 and DNP work synergistic ally and can promote each other’s antioxidant reaction to significantly improve the ability of PA66 matrix composites to resist aging.When the content of 9228 and DNP are 0.5wt.% and0.1wt.%,respectively,the combined effect of PA66 matrix composites to improve the resistance to thermal oxygen and thermal oil aging is the best.