Preparation,Morphology And Properties Of PA11/EVOH Composites With High-barrier Property

Polyamide 11(PA11) was mostly used as automobile pipe-laying and municipal gas pipeas well as offshore oilfield application. With the more strict controls on the environmentalrequirements, the barrier properties of neat PA11 can not meet with the industry standards. Inorder to improve its barrier properties, PA11/EVOH composites were pr epared by meltingcompounding, and their mechanical properties, barrier properties, gel content, morphologystructure, rheological behavior and crystallization properties were investigated by scanningelectron microscopy (SEM), capillary rheometer, X -ray diffraction (WAXD), differentialscanning calorimeter (DSC) , polarizing microscopy (POM) and capillary rheometer ,respectively.The experimental results of mechanical properties and barrier properties showed that theoil-absorption reached the minimum value (0.244%, xylene), impact strength and tensilestrength was increased up to 5.31KJ/m2 and 53.54MPa in the case ofPA11/EVOH/DCP=80/20/1.5. In comparison with that of the neat PA11, the barrier property ,impact strength and tensile strength of the PA11/EVOH/DCP composi tes were increased by500%, 18% and 17.6%, respectively . SEM micrographs showed that the EVOH was dispersedwithin PA 11 matrix in the form of discontinuous mutual crossover laminar structure, whichwere contributed to the improvement of the barrier property.It was found that the gel content of PA11/EVOH composites initially increased and thenreduced with the increasing loading of the DCP, and reached its maximum at the level of1.5% DCP content. furthermore, the variation of gel content of EVOH/DCP system togetherwith FT-IR results indicated that the co-crosslinking between EVOH and PA 11 predominatedover the self-crosslinking of EVOH.The effect of DCP content on the rheological behavior of PA11/EVOH blends wasinvestigated. The results showed that all PA11/EVOH blends with or without DCP were pseudo-plasitc and exhibited shear-thinning. The non-Newtonian indexes (n) decreased withthe addition of DCP, which indicated that the sensitivity of composite to shear rate decreased.In the case of constant shear stress and shear rate, the apparent viscosity decreased initiallyand then after increased with the increasing DCP content , and displayed a maximum value atthe level of 1.5% DCP content. The reduced apparent viscous activation energy of compositeswith the increasing DCP content indicated that the addition of DCP decreased thetemperature-sensitivity.The crystallization kinetics of PA11/EVOH/DCP composites was investigated by DSC.The studies on the isothermal crystallization showed that Avrami equation well describedthe isothermal crystallization of PA11 and its composites, the co-crosslinked domains formedafter the addition of EVOH and DCP might act as the heterogeneous nucleating agent andthus increased the crystallization rate of PA11; The mechanism of crystallization nucleationand growth of PA11/EVOH composites was also changed by the addition of DCP. Theequilibrium melting point of PA11/EVOH composites obtained by the Hoffman -Weekstheory was lower than that of neat PA11, which indicated that the addition of EVOH and DCPdecreased the perfect of crystallization.The analysis of non-isothermal crystallization showed that Ozawa equation was notsuitable to describe the non-isothermal crystallization process of PA11 and its composites,while the modified Avrami and Mo equation took great advantages over treating thenon-isothermal crystallization kinetics. The addition of EVOH and DCP impeded the growthof crystals, reduced the crystal growth, and changed the crys tallization nucleation and thegrowth of crystals.