Investigation Of The Preparation,morphology And Properties Of PA6/EVOH Barrier Blends With High Toughness

Polyamide 6 (PA6) has wide engineering applications due to their easy processing, lowfriction, wear resistance, and high thermal-resistance. However, its notch-sensitivity andcritical brittleness at low temperature are generally inadequate for various end-use. Poly(ethylene-1-octene) (POE), as a thermoplastic elastomer, can commendably promote thetoughness of PA6. Unfortunately, the incorporation of nonpolar polyolefin decreases not onlythe tensile strength but the barrier to hydrocarbons. Ethylene-vinyl alcohol (EVOH)copolymers are semicrystalline materials showing excellent gas and aroma barrier propertiesin their dry state. Therefore,the addition of EVOH to PA6 can potentially enhance the barrierproperties of the latter polymer. However, the mechanical properties of the blends will bedeclined at high EVOH loading due to the limited compatibility between PA6 and EVOH.Therefore, two following methods were adopted to improve the compatibility among thecomponents. The first one is in-situ grafting technology, and the second one is the usage ofPOE-g-MAH as both compatibilized and toughner. The mechanical, barrier, rheologicalproperties, crystallization kinetics and morphology were investigated in terms oftensile/impact testing, oil absorption, dynamic mechanical analysis (DMA), rotationalrheometer/ capillary rheometer, differential scanning calorimeter (DSC), FTIR and scanningelectron microscopy.The main research work and results were listed as following:1. The PA6/POE/EVOH ternary blends were prepared in the presence of both maleicanhydride and peroxide via melt blending, and their mechanical and barrier properties,morphology, rheolgoy and non-isothermal crystallization kinetics were investigated. Theresults of the mechanical and barrier properties showed that the tensile strength and barrierproperties were significantly improved while the impact strength was increased initially andthen decreased with increasing the EVOH content, and the elongation at break was reduced. The analysis of rheological behavior revelaed that PA6/POE/EVOH blends were pseudoplastic fluid and exhibit shear thinning behavior, the apparent viscosity and viscous activationenergy of PA6/POE/EVOH blends increased with the incorporation of EVOH, whichindicates that the blends are temperature-sensitive. The nonisothermal crystallization behaviorwas investigated via DSC, it was found that both modified Avrami equation and Mo methodwell described the nonisothermal crystallization kinetics of PA6/POE/EVOH blends, Thecyrstallization process of PA6/POE/EVOH blends contained the primary and secondary stages.The crystallization of PA6 was impeded with the increasing EVOH content.2. PA6/POE-g-MAH/EVOH ternary blends were also prepared via melt-blending. Themorphology, mechanical and barrier property and rheological behavior of the blends wereinvestigated in detail. The SEM images demonstrated that the compatibility of EVOH orPOE-g-MAH with PA6 was improved significantly after the incorporation of POE-g-MAHand EVOH, respectively; the toughness of the ternary blends was thus improved significantly.Additionally, The tensile strength, storage modulus and barrier properties of thePA6/POE-g-MAH/EVOH ternary blends were increased evidently, which was contributed tothe formed network structure through the reaction among PA6, POE-g-MAH and EVOH. Theanalysis of the rheological behavior showed that PA6/POE-g-MAH /EVOH blends werepseudo plastic fluid, and all specimens exhibited shear thinning behavior. The storagemodulus, loss modulus and the complex viscosity of PA6/POE-g-MAH /EVOH blends wereincreased after the incorporation of EVOH. Phase separation did not occur in the blends asdemonstrated by the analysis of the Han method.