Research About The Positive And Negative Effects Of Carbon Nanotubes In PA6 And Corresponding Countermeasures

Among the engineering plastics, polyamide 6(PA6) is one of the most commonly used polymers with high strength and impact resistance. However, with the rapid development of related industries, the tensile strength and toughness of PA6 are not high enough to meet practical industrial demands. Therefore, research about further reinforcing PA6 has become a hot topic. Carbon nanotubes(CNTs) are regarded as an ideal composite reinforcer due to their excellent mechanical properties. But in most cases, because of their poor dispersion and interfacial bonding with polymer molecules, the applications in the composites are severely limited. Most importantly, although the addition of CNTs in PA6 could achieve some improvement in strength, it would always cause concomitant deterioration of plasticity or toughness of composites, so the positive and negative effects brought about by CNTs were worth deeply studying.In this thesis, the fundamental cause of the positive and negative effects brought about by CNTs in PA6 was studied and the corresponding countermeasures were proposed. Firstly, taking pure PA6 as the research object, the influence of mold temperature on the mechanical properties of pure PA6 was explored, then on this basis, the effects and intrinsic causes of CNTs on the tensile strength and the elongation at break of PA6 were discussed. Secondly, two solutions of amino-functionalizing CNTs and adding of elastomers in PA6, were tried to alleviate the embrittlement effect of CNTs.The results indicated that:(1)The elongation at break for neat PA6 decreased greatly if the mold temperature was above 100 oC. This should be attributed to the increscent grain size, decreased crystallinity and unfavorable phase transformation.(2)Compared with the neat PA6 and the composites prepared by wet-mixing, the tensile strengths of PA6/CNTs composites were improved by 17.0% and 5.0% for the samples with 0.1 phr of CNTs for dry-mixed samples, respectively. Meanwhile, in both cases, the elongation at break decreased greatly in the range of 29.9%~94.0%.(3)The tensile strength of composites was improved by the addition of CNTs, but the elongation at break was also greatly decreased. This could be ascribed to that although CNTs could make the grain sharply refine, crystallinity of PA6 decreased and unfavorable phase transformation from ? type to ? type crystal form occurred throughly.(4)1,6-diaminohexane-functionalized CNTs(CNTs-NH2) was synthesized by amidation reaction. The tensile strength was 88.9 MPa with 0.1 phr of CNTs-NH2, compared with pure PA6, the increase was slight(~8.7%). But the elongation at break of PA6/CNTs-NH2 composites could still maintain a higher value(~129.3%), as the contrast, the elongation at break of PA6/CNTs composites with the same content of CNTs was only 17.6%.(5)Comparing the toughening effects of SEMS-MAH and VP301 for PA6/CNTs composites, it was found that SEMS-MAH was more favorable. Compared with PA6/CNTs composites, the elongation at break for PA6/CNTs/ SEMS-MAH composites was improved by 198.4% with 1.0 phr of CNTs and more pronounced was that, when the content of CNTs was 0.3 phr, the elongation at break was improved by ~637.1%.