| Nylon 612 is an excellent crystalline polymer with a wide range of applications,but in some cases it requires high impact strength.In this paper,copolymerization of nylon 612 salt with caprolactam which introduced the structural unit of nylon 6 into the macromolecular chain of nylon612,broke the regular arrangement of the original macromolecular chain and reduced the crystallinity and hydrogen bond density of the polymer system.Thus,a modified nylon 612-6copolymer with good toughness and high light transmittance was synthesized.The results of polymerization kinetics of nylon 612 accords with the second-order reaction kinetics in this process,and the activation energy of polymerization is 49.10 kJ/mol.The preferred polymerization conditions were as follows:polymerization time 57 h,polymerization temperature250260°C.Nylon 612 and its copolymers with caprolactam?CPL?addition amounts of 10 wt%,15 wt%,20 wt%,and 25 wt%,respectively,were successfully prepared.At the same time,the obtained polymer chips were subjected to a series of corresponding characterizations to analyze the reasons for the differences in mechanical properties.Nylon 612-6 copolymer with 15 wt%CPL can obtain better comprehensive mechanical properties compared with nylon 612:the notched impact strength is increased by 113%,the elongation at break is increased by 127%,the tensile strength is decreased by 8%,and the bending strength is decreased by 28%,respectively.The crystallization kinetics,thermal degradation kinetics and rheological properties of nylon612 and nylon 612-6 copolymers were studied.The isothermal crystallization process of nylon 612and nylon 612-6 copolymers was analyzed by Avrami equation which is secondary nucleation.After nucleation,it grows along the crystal nucleus in two dimensions.The Arrhenius equation is used to determine the isothermal crystallization activation energy which is-756.38 kJ/mol and-115.09kJ/mol respectively;The non-isothermal crystallization kinetics of nylon 612 and its copolymers were corrected by Jeziorny's modified Avrami equation,Ozawa equation and Mo Zhishen method.The results show that the crystallization process of nylon 612 is secondary nucleation,and after nucleation,it is a two-dimensional disk shape growth along the crystal nucleus.While the crystallization process of nylon 612-6 copolymer is a homogeneous nucleation.After nucleation,the crystal nucleus grows in a two-dimensional disk shape and three-dimensional spherical shape,and the crystallization rate of nylon 612 is larger than that of nylon 612-6 copolymer;The non-isothermal crystallization activation energy of nylon 612 was calculated by Kissinger equation which was-433.29 kJ/mol,while the nylon 612-6 copolymer was-94.12kJ/mol.The thermal degradation kinetics of nylon 612 and its copolymers also showed that the thermal degradation mechanism was the same.The results show that the thermal degradation process in N2atmosphere is a one-step reaction,and the degradation temperature increases linearly with the increase of heating rate.The decomposition mechanism is R2 by Kissinger equation,Flynn-Wall-Ozawa equation and Coats-Redfern equation.Therefore,the thermal degradation processes of both are cylindrical symmetric shrinkage growth,phase boundary reaction and deceleration degradation curve.The rheological properties of nylon 612-6 copolymer were investigated by capillary rheometer.The results show that the nylon 612-6 copolymer and nylon 612 melts are shear-thinning pseudo-plastic non-Newtonian fluids,and the apparent viscosity?a of both melts gradually decreases with the increase of temperature.The non-Newtonian index is gradually increasing.At the same time,the viscous flow activation energy???of nylon 612-6 copolymer and nylon 612 melts increases first and then decreases with the increase of shear rate,and the shear rate is about 115 S-1.The activation energy reached the maximum,which was 61.49 kJ/mol and 61.27 kJ/mol respectively.Nylon 612 and copolymer chips with stable performance were obtained by amplifying experiments,and the nascent fibers were successfully obtained by melt spinning.The fiber properties of different draw ratios were also investigated.The results show that the fiber breaking strength,boiling water shrinkage and thermal crimping rate,orientation degree and crystallinity increase and the elongation at break decreases with the increase of draw ratio. |
PDF Full Text Request