Preparation And Properties Of Polyamide-6 Composites With High Tensile Strength And Good Toughness

Polyamide 6(PA6)is an engineering plastic with excellent abrasion resistance,high tensile strength and good processing abilities,which is widely used in many applications such as mechanical parts,electronic component and automotive industry.However,its notch-sensitivity makes it brittle after notching.Furthermore,its heat deflection temperature(HDT)is low and its moisture resistance is poor.Blending with an elastomer or maleic anhydride grafted elastomer is a common way to improve the impact strength of PA6.However,owing to the soft characteristic of the elastomer,the toughened PA6 with elastomer always brings the apparent decline of tensile strength and HDT.To improve the HDT and the moisture resistance,PA6 was usually blended with poly(phenylene oxide)(PPO).As PA6 and PPO are thermodynamically immiscible in the whole composition range,compatibilizer such as styrene-maleic anhydride copolymer(SMA)was also needed.Adding organo-montmorillonite(OMMT)was also a common method to modify the polymer blends,which could also improve the HDT.This dissertation focused on the preparation of PA6 composites with high tensile strength,good impact strength.The structure-property relationships were also investigated.The main work and results are as follows.OMMT and SMA were introduced into the PA6/PPO blends and showed synergistic effect in compatibilizing PA6/PPO blends.Both OMMT and SMA could reduce the particle size of the dispersed PPO domains.OMMT tactoids formed in PA6/PPO/OMMT ternary blend would become smaller or disappear with the addition of SMA.Besides,the viscosity of SMA compatibilized PA6/PPO blend decreased significantly with the addition of OMMT.The water absorption and tensile properties of the PA6/PPO/SMA/OMMT nanocomposites were also investegated.OMMT was introduced into styrene-ethylene-butadiene-styrene block copolymer grafted with maleic anhydride(SEBS-g-MA)toughened PA6/PPO blends by melt extrusion.The effects of OMMT on morphology,rheology and mechanical behaviors of toughened PPO/PA6 nanocomposites were studied.The addition of OMMT could decrease the size of dispersed PPO domains in PA6 matrix and melt viscosity of the toughened PPO/PA6 nanocomposites.Besides,exfoliated OMMT also brought significant improvement of tensile properties,HDT and impact strength,simultaneously.Consequently,PA6/SEBS-g-MA/PPO nanocomposites with high tensile strength,excellent impact performance,improved HDT and good processibility were obtained.The role of PPO and PS in toughened PA6/SEBS-g-MA/(PPO/PS)blends was studied.The effects of weight ratio and content of PPO/PS on the morphology and mechanical behaviors of PA6/SEBS-g-MA/(PPO/PS)blends were studied by scanning electron microscope(SEM)and mechanical tests.Driving by the interfacial tension and the spreading coefficient,the "core-shell" particles formed by PPO/PS(core)and SEBS-g-MA(shell)played the key role in toughening the PA6 blends.As PS improved the distribution of the "core-shell" particles due to its low viscosity,and PPO guaranteed the entanglement density of the PPO/PS phase,the 3/1 weight ratio of PPO/PS supplied the blends optimal mechanical properties.Within certain range,the increased content of PPO/PS could supply more efficient toughening particles and bring better mechanical properties.Thus,by adjusting the weight ratio and content of PPO and PS,the PA6/SEBS-g-MA/(PPO/PS)blends with excellent impact strength,high tensile strength and good heat deflection temperature were obtained.The role of PP and SEBS-g-MA in toughening PA6/SEBS-g-MA/PP blends was studied.PP and SEBS-g-MA could in situ form "core-shell" particles in the PA6 matrix simply by melt extrusion.The effect of PP and SEBS-g-MA on morphology,rheological properties,tensile properties and notched Izod impact strength were studied.The loading of SEBS-g-MA improved the compatibility between PA6 and PP,resulting in fine dispersion of "core-shell" particles and good mechanical properties.The loading of PP inhibited the excess chain-extension reaction between PA6 and SEBS-g-MA,resulting in low viscosity and good mechanical properties.The toughening mechanism was also investigated.There was obvious difference between the semi-tough and tough blends.The shear yielding of the PA6 matrix(tough blends)could only be observed in the blends with suitable "core-shell" particles size(above 0.1 μm).Consequently,by loading only 5-10 parts of SEBS-g-MA,the PA6 blends with high tensile strength and excellent impact strength could be obtained.The(PPO/PS)/SEBS-g-MA/PA6 blends with high tensile strength,good impact strength and excellent HDT was prepared by melt extrusion.PA6 and SEBS-g-MA in site formed "core-shell" particles(PA6 as core and SEBS-g-MA as shell)in PPO/PS-matrix.The difference between the PA6/SEBS-g-MA/PPO blends and the(PPO/PS)/SEBS-g-MA/PA6 blend in morphology and properties was also investigated.