Study On Preparation Technology Of Aromatic Copolvamide PA(66-co-6T)

Although aliphatic polyamides such as polyhexamethylene adipamide(PA66)have excellent comprehensive performances,their thermal resistance cannot meet the demand for the development of the automobile,electronic and electrical industry.So it has drawn tremendous reserch interests for aromatic-contained polyamides with a higher thermal resistance.An aromatic-contained copolyamide of PA66 and polyhexamethylene terephthalamide(PA6T),denoted as PA(66-co-6T),can combine the good processing performance of PA66 and the high thermal resistance of PA6T.Moreover,raw materials for preparing PA(66-co-6T)are easy to get So PA(66-co-6T)exhibits a good industrialization prospect.However,it is currently lack of in-depth and systematical understanding for the industrial production of PA(66-co-6T)owing to the weak industrial base of the aromatic-contained polyamide in China.Therefore,this work explored systematically the preparation process of PA(66-co-6T)from prepolymerization to melting polycondensation and solid state polycondensation using terephthalic acid,adipic acid,hexamethylenediamine as raw materials.The detailed results are as follows:1.The formation process of polyamide salts from diacid and diamine was studied by pH online monitoring.Results show that,at 55?,adipic acid and terephthalic acid,slightly soluble in water,can quickly react with hexamethylenediamine to form the correponding PA66 salt and PA6T salt.The reaction solutions become clear and transparent from suspended because the salts are soluble in water.Additionally,the reaction rate of adipic acid and hexamethylenediamine is faster than that of terephthalic acid and hexamethylenediamine.2.The prepolymer of aromatic-contained polyamide was prepared via a facile one-step polycondensation approach using adipic acid,terephthalic acid and hexamethylenediamine as raw materials and water as the solvent.The prepolymerization process could be divided into four stages:the formation of polyamide salt,temperature rising,polycondensation with constant temperature,and venting.In the first stage,adipic acid,terephthalic acid can react completely with hexamethylenediamine to form their corresponding salts in 40 min at 50?.Further prolonging the reaction time of this stage hardly affect on the intrinsic viscosity of the prepolymer.In the stage of temperature rising,the salts do not react until the temperature reaches 200?,irrespective of the heating rate.So it can reduce the time of this stage by enhancing the rate of temperature rising.After temperature is above 200?,the polymerization degree of the prepolymer increases with increaseing temperature and/or increasing time.In the venting stage,the polycondensation reaction continues to proceed.After 40%of total amount of water is removed,the polycondensation rate obviously accelerates and the molecular weight of the prepolyamide increases dramatically.Moreover,a longer venting time or a lower venting rate is beneficial for the polycondensation of polyamide salts.In addition,the molecular weight of the as-synthesized prepolyamide decreases with increasing feed ratio between terephthalic acid and adipic acid.3.Through comparing the melt polycondesation of as-synthesized prepolyamide in the autoclave and the extruder,it can be known that a longer reaction time is benefical for enhancing the degree of polymerization due to the more amounts removal of small molecules.Moreover,the rate of melt polycondesation in the extruder is faster than that in the autoclave.However,it should be noted that,irrespective of melt polycondesation in the autoclave or in the extruder,a too long reaction time can cause the degradation of PA(66-co-6T),which results in that it is difficult to obtained aromatic-contained copolyamide with a high molecular weight by melt polycondesation of prepolyamide.4.The aromatic-contained copolyamide with a high molecular weight was prepared successfully by the solid state polycondensation of PA(66-co-6T)prepolymer.The intrinsic viscosity of PA(66-co-6T)-20 can reach 1.37 dL/g after solid state polycondensation for 10 h at 230?.The reaction rate is fast in the initial stage of solid state polycondensation,and then slows down after 4 h.The intrinsic viscosity of obtained product increases with the reduction of the aromatic unit content and the particle size of prepolyamide.Moreover,the molecular weight of product first increase with the acceleration of flow rate of nitrogen,and then leveled off after the flow rate reached the threshold value of 60 mL/min.5.The introduction of aromatic unit can increase the crystalliztion temperature and usage temperature of aliphatic polyamide.And the introduction of 20%to 80%aromatic unit can increase the melting temperature of obtained PA(66-co-6T)from 267 to 335?.