Preparation And Properties Of Modified Graphene Oxide/Nylon 6 Composites

As a semi-crystalline thermoplastic engineering plastic,nylon 6 is one of the largest varieties of polyamide materials,which has been widely used in the automotive industry,electronics,electricity,clothing and other fields.However,with the increasing demand of diversified market for products,single nylon 6 resin has been unable to meet the actual demand.Developing high-performance nylon 6 composite materials has attracted more attention.Graphene provides a new train of thought for the development of high performance nylon 6composite materials.But graphene does not contain surface functional groups and its dispersion is very limited in the nylon 6 matrix,which seriously limits the application of graphene in polyamide materials.In this paper,graphene oxide(GO)was prepared from natural flake graphite using the improved Hummers method,and then 4-amino-N-methylbenzamide was used as a modifier to prepare amidated graphene(AGO)at room temperature.GO or AGO was dispersed in caprolactam monomer and water was used as ring opener to synthesize(modified)graphene oxide/nylon 6 nanocomposites by in situ polymerization.The chemical structure,microstructure dispersity,rheological behavior,mechanical properties and crystallization behavior of the composites were studied.The effects of the content of(modified)graphene on the non-isothermal crystallization kinetics of the composites were also investigated.The results show that:(1)The FT-IR,XPS,XRD,Raman,AFM and other test results showed that GO contained a lot of oxygen-containing functional groups.After the introduction of oxygen-containing functional groups,it was a single layer of graphene with increased spacing,destroying the regularity,and the hydrophilicity was enhanced.After the introduction of the amide groups in GO,the layer spacing was further increased,the regularity was further destroyed,the hydrophilicity was weakened and it belonged to monolayer modified graphene.The TGA results showed that the grafting rate of AGO was about 14.6%.(2)The FT-IR and AFM tests respectively proved from the molecular structure and microstructure that GO grafted together through the reaction of the carboxyl group and the terminal amino group of PA6,which played a role as a molecular chain terminator to a certain extent,resulting in the decrease of molecular weight of the GO/PA6 composite.While AGO grafted together with PA6 through the amide exchange reaction of the amide group,which would not affect the molecular weight of the composite material.Compared with PA6,the addition of GO or AGO made the composite materials possess better fluidity.The GO/PA6composites showed a single relaxation process in the molten state,while the AGO/PA6composites showed multiple relaxation processes.The XRD and DSC test results showed that the composites were affected by the grafting reaction of GO and AGO,which changed the crystal growth mode to a certain extent,promoted the formation of multiple crystal forms,and changed its crystallization and melting behavior.The DMA test results showed that GO and AGO were linked with PA6 molecules,which limited the movement of the molecular chains to a certain extent,causing the T_gvalue of the composite material to move to the high temperature direction.The mechanical performance test results showed that the addition of GO could increase the tensile strength and flexural strength of the composite materials,but it would reduce the elongation at break and the impact strength of the composite materials.While AGO could increase the tensile strength,elongation at break and impact strength of composite materials,but the bending strength decreased greatly.The TGA test results showed that both GO and AGO could improve the thermal stability of PA6.(3)The results of non-isothermal crystallization kinetics research showed that the addition of GO and AGO increased the initial crystallization temperature and the crystallization peak temperature of the composites.But it would reduce the crystallization rate and crystallinity of composites.The Ozawa model could fit the non-isothermal crystallization process of composites well.According to Ozawa fitting curve,it was found that the addition of GO and AGO could make composites enter the crystallization process quickly at high temperature and make the crystallization process more stable.The crystal growth dimension of the AGO composite system was higher than that of the GO composite system at the same content.The crystallization activation energies of GO/PA6 and AGO/PA6 composites were higher than that of PA6 by Kissinger equation.