Preparation Of Nylon 6 With High Viscosity By Chain-extension During Melting Extrusion

Nylon 6 is an engineering plastic with excellent overall performances.Generally,the molecular weights of nylon 6 resin prepared via traditional was high enough to meet the requirement of engineering plastic.On the other hand,nylon 6 is often used for hollow containers due to its excellent barrier property.However, nylon 6 is difficult to blow molding directly as its low melt viscosity in the present work.The intrinsic viscosity, end-group content,melt index,morphology structure,mechanical properties,rheological behavior and crystallization kinetics were investigated by ukraine-viscometer,melt index instrument,capillary rheometer,differential scanning calorimeter (DSC) and polarized optical microscopy (POM).The result of intrinsic viscosity,end-group content, melt index and mechanical properties showed that epoxy resin (EP) predominated over bisoxazoline (BO) as chain extender.End- group concentration was reduced and the intrinsic viscosity of PA6 was improved with the increasing EP content.It gave the highest intrinsic viscosity(1.35dL/g) at 2.5 wt % EP in this case the melt index was 5.66g/10min.Nylon 6 was difficult to be extruded when EP concentration was higher than 2.5wt%. PA6 displayed the highest intrinsic viscosity(1.17dL/g) at the level of 1.5wt% BO.With the further increase of BO, carboxy end-group concentration was decreased while amino end-group concentration kept almost constant.The Izod impact strength was improved as compared with the slight variation of the tensile strength after the chain-extension of PA6.The rheological behaviors of PA6/EP blends were investigated.The results showed that both neat PA6 and its chain-extended blends were pseudo-plasitc and exhibited shear-thinning.The melt viscosity of PA6 was enhanced significantly after the chain-extension. With the increase of EP,melt consistency(K) was increased,but non-Newtonian index (n) was decreased.It was inferred that the melt flow behavior deviated far from the non-Newtonian fluids.The apparent viscous activation energy of blends tended to decrease, indicating that the blends became less temperature-sensitive with the increasing EP concentration.The crystallization kinetics and melting behavior of PA6/EP blends were investigated by DSC.The study on the isothermal crystallization showed that Avrami equation could describe isothermal crystallization of PA6 and its blends very well.The rate of crystallization of PA6 was reduced and the growth of nucleation was hindered by the addition of EP.The equilibrium melting point of PA6/EP blends obtained by the Hoffman-Weeks theory was lower than that of neat PA6, which indicated that the addition of EP decreased the perfection of crystallization.The analysis of non-isothermal crystallization showed that the modified Avrami and mo equation take great advantages over treating the non-isothermal crystallization kinetics. At the same rate of cooling,the crystallization rate constant of chain-extended PA6 was decreased as comparison with neat PA6,and in order to achieve the same degree of crystallinity, the cooling rate of chain-extended PA6 shoud be greater than that of neat PA6, which indicated that the addition of EP reduced the rate of crystal growth and hindered the growth of the nuclei.