Preparation And Properties Study Of Copolyamide 6/66

The copolyamide 6/66 is widely used in film,fiber and engineering plastics because it has excellent properties such as low melting point,low crystallinity,good transparency,good toughness,wear resistance,etc.,.In addition,by adding functional additives,or rationally adjusting the ratio of comonomer,series of performance vaied copolyamides could be obtained.At present,most of the domestic study focus on the basic research of copolyamide 6/66 and have few researches on the process,while it has been realized industrial production abroad.Therefore,in this study,caprolactam(CPL),nylon 66 salt(AH-salt)and terephthalic acid(PTA)were used as raw materials,by changing the formula and process conditions,a series of copolyamide 6/66 were prepared via atmospheric polymerization and two-step polymerization with the formation of prepolymer in a high pressure stainless steel kettle followed by further polymerization in the molten state.The effects of raw materials formula and proportion,polymerization process and reaction conditions on the yield of comonomer and molecular weight of copolyamide 6/66 were studied systematically.Further investigations on physical properties of the products were also completed in detail.First,copolyamide 6/66 was successfully prepared under atmospheric pressure.The results show that the ring opening agent?-aminocaproic acid obviously promoted the copolymerization.With the increase of AH-salt content,the yield of comonomers increased greatly,making the content of extractables in the copolymer lower to 5.47%.Moreover,the molecular weight regulator(PTA)not only restricted the increase of relative viscosity of copolymer,but also made the monomer conversion rate decrease slightly.Furthermore,the crystal form,melting point and crystallinity of copolyamide 6/66 changed very little as the copolymerization reaction temperature and reaction time varied within a certain range,However,in comparison with PA6,the melting point and crystallinity of copolyamide 6/66 decreased significantly.Based on the investigations,the preparation of copolyamide 6/66 with AH-salt content of 15%was carried out at 250?for 8 h.Secondly,the copolyamide 6/66 was prepared by two-step polymerization with the formation of prepolymer under a high pressure(1.8 MPa)followed by further condensazation in the molten state.The effects of process conditions on the structure and properties of the polymer were investigated in detail:as the prepolymerization time extended from 0 h to 5 h,the content of the extractable kept about 15%,and the relative viscosity were stable at about 1.4,which indicates that the reaction time has little effect on the yield of comonomers and the molecular weight of the prepolymers.The analysis results of FTIR and XRD show that?-form and?-form are coexisted in the copolyamide 6/66prepolymers.The FTIR and ~1H NMR results of the copolyamide 6/66exhibited the prepolymer can be equilibrated at 250°C for 6 h.The GPC measurement revealed that when the AH-salt content is 15%,copolyamide 6/66 prepared in lab has higher molecular weight and narrower distribution compared to BASF sample.Due to the reorganization of the crystal structure,the copolymerized samples show double melt peaks in the DSC heating traces,and the peak intensity is stronger than the prepolymer sample.With the content of AH-salt reached15%,the melting point of sythesized copolyamide 6/66 was close to that of BASF sample,but the crystallinity was higher.When the AH-salt increased to 20%,the melting point and crystallinity of the copolymers dropped significantly.