Preparation And Properties Of Long Chain Semi-aromatic Heat Resistance Polyamides

Aliphatic polyamides such as poly(?-caprolactam)(Polyamide 6)and poly(hexamethylene adipamide)(Polyamide 66),are a class of engineering thermoplastics used in a wide variety of applications.They can be economically produced by melt processing,but their poor dimensional stability,poor thermal properties and high water absorption limit their applications in several industrial fields,especially in shells of automobile engines,the manufacture of LED reflectors and in the surface mount technology(SMT).In order to improve the thermal properties of polyamides,aromatic rings have been incorporated into the backbone of polymer chains.And lots of available semiaromatic polyamides have been prepared,such as poly(hexamethylene terephthalamide)(Polyamide 6T)copolymers,poly(nonamethylene terephthalamide)(Polyamide 9T),poly(decamethylene terephthalamide)(Polyamide 10T),poly(dodecamethylene terephthalamide)(Polyamide 12T).Polyamide 10 T,a condensation type polymer containing 1,10-decanediamine and terephthalic acid,is a good engineering plastic with excellent thermal durability and low water absorption.However,It has a high melting point,as high as 315 °C,which is close to its decomposition temperature.Hence the melt processing window is narrow,which limits its scope in industrial processing and applications.Amino acid comonomer(e.g.,11-aminoundecanoic acid)can be used as a comonomer to reduce the melting temperature of Polyamide 10 T,while still maintaining the excellent mechanical properties of the modified Polyamide 10 T copolymers.Furthermore,1,10-decanediamine and 11-aminoundecanoic acid are both important starting materials used to synthesize polyamide,which can be obtained from the product of castor oil.Thus,Polyamide 10 T copolymers is identified as a type of green material which is obtained from natural raw materials.In this work,long chain semi-aromatic heat resistant polyamide 10T/11 was prepared by direct melt polycondensation with 1,10-decanediamine,terephthalic acid,11-aminoundecanoic acid,antioxidant and inhibitor.First of all,the influence of salt forming process on polyamide 10 T was studied,and the infrared spectrum analysis was carried out.In addition,the polymerization temperature,polymerization time and polymerization pressure in the pre-polymerization stage,the time of deflation in the post-polymerization stage,the mode of viscosity increase during the viscosity increase stage,mixing speed,deionized water,antioxidant and inhibitor were studied,which effected on polymer properties and overall polymerization process.At last,the optimum polymerization process was determined.After determining the optimum polymerization process,the influence of 11-aminoundecanoic acid with different addition amount on the physical and chemical properties of heat resistant Polyamide 10T/11 was investigated by using 11-aminoundecanoic acid as a variable.The research contents included mechanical properties,density,crystallization property,oil absorption value,water absorption,solvent resistance and chemical resistance.The results showed that the elongation at break and impact strength of Polyamide 10T/11 could be improved by adding 11-aminoundecanoic acid,but had little effect on other properties.The rheological properties of heat resistant Polyamide 10T/11 were studied by capillary rheometer.The results showed that Polyamide 10 T and Polyamide 10T/11 were both pseudoplastic fluids,and the non-newton index increased with the increase of temperature.The apparent viscosity decreased with the increase of shear rate or shear stress.As the shear stress increased,the viscous flow activation energy decreased,and the apparent viscosity was less sensitive to temperature.Compared with Polyamide 10 T,Polyamide 10T/11 can improve the sensitivity of apparent viscosity to shear stress,shear rate and temperature by introducing 11-aminoundecanoic acid,thus improving the processability of Polyamide 10 T.The thermal properties of Polyamide 10 T and Polyamide 10T/11 were studied by thermal deformation temperature test,dynamic mechanical analysis test(DMA),differential scanning calorimetry(DSC)and thermogravimetric analysis(TGA).The results showed that the thermal deformation temperature and the melting temperature of Polyamide 10T/11 decreased gradually with the increase of the amount of 11-aminoundecanoic acid,while the glass transition temperature increased first and then decreased.The thermal degradation process of Polyamide 10 T and Polyamide 10T/11 may be one step degradation process of random broken chain,and the atmosphere had a significant impact on the thermal degradation process of polyamide.The Flynn-Wall-Ozawa equation was more suitable for calculating the thermal degradation activation energy of Polyamide 10T/11 than the Kissinger equation.The average thermal degradation activation energy of Polyamide 10T/11 was 231.14 kJ·mol-1.Meanwhile,the thermal degradation process followed the R1 mechanism in the deceleration curve,viz.,the interphase interface control reaction of one-dimensional motion in the deceleration curve type,which was cylindrical symmetry.The crystallization kinetics of Polyamide 10 T and Polyamide 10T/11 was studied by differential scanning calorimetry.The isothermal crystallization kinetics of Polyamide 10 T and Polyamide 10T/11 was analyzed by Avrami equation,and the avrami index n value ranged from 1.79 to 2.31,which indicated that the crystal growth mode for Polyamide 10 T and Polyamide 10T/11 may be the mixture growth with one-dimensional,needle-like and two-dimensional,lamellar.The related crystallization kinetic parameters were calculated.The isothermal crystallization activation energy of Polyamide 10 T and Polyamide 10T/11 was calculated by Arrhenius equation,and the equilibrium melting point of Polyamide 10 T and Polyamide 10T/11 was obtained by Hoffman-Weeks extrapolation.The crystal growth mode of Polyamide 10 T and Polyamide 10T/11 was studied by using Turnbull-Fisher and Lauritzen-Hoffman equations,respectively.Avrami and Ozawa equations,along with Mo equation were applied to obtain the non-isothermal crystallization kinetics of Polyamide 10 T and Polyamide 10T/11.The non-isothermal crystallization activation energy of the system was calculated by Kissinger,Takhor and Vyazovkin equations,respectively.The results suggested that the crystal growth mode at the primary crystallization stage of the non-isothermal crystallization for Polyamide 10 T and Polyamide 10T/11 may be the mixture growth with one-dimensional,needle-like and two-dimensional,lamellar,and meanwhile there was heterogeneous nucleation phenomenon during the non-isothermal crystallization process.Jeziorny and Mo equations well described the non-isothermal crystallization kinetics of Polyamide 10 T and Polyamide 10T/11,while Ozawa equation failed.As the amount of 11-aminoundecanoic acid increased,the non-isothermal crystallization activation energy of Polyamide 10 T and Polyamide 10T/11 increased first,then decreased,finally increased,which suggested that the crystallization rates decreased first,then increased,finally decreased.