| Long carbon chain polyamides (such as nylon 11,nylon12,nylon1212) are widely used in the mechanical, electronic appliances, automobile and other important field due to their high strength, good flexibility and high dimensional stability and so on. Their applications on the manufacture of automotive oil, brake pipe, hose medical, hot melt adhesive for high-grade garments, household appliances, etc., have been the hot spot. A series of copolyamide with specific performances ( ranging from high softening point, hardness, difficult to dissolve to lower softening point, soft and easy to dissolve) were prepared by controlling the ratio of copolymer compositions. Nylon 6/66/12 copolyamide is the most worldwidely used hot-melt adhesive due to low water absorption of nylon 12, which make the product has a good washable and dry-cleaning resistant performance. As nylon 11 and nylon 12 are all long carbon chain polyamide, they show a lot of homoplastic properties. In the present study, we synthesized the copolyamide from caprolactam, nylon 66 salt and aminoundecanoic acid. The effects of the content of aminoundecanoic acid on the properties such as melting point, glass transition temperature, cold crystallization, thermal stability and adhesion strength were investigated in detail. To provide a theoretical basis for specific applications and guidance, the main research work related to the content and results are as follows:1. The copolyamide 6/66/11 from caprolactam, nylon 66 salt and aminoundecanoic acid were synthesized by the melt copolycondensation under vacuum. The chemical structure and thermal properties were characterized using Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimeter (DSC). The intrinsic viscosity, water absorption and mechanical properties were also investigated. Polycondensation were suitable for the preparation of nylon copolymer with stable weight and a high peel strength. The copolyamide hot-melt adhesive displayed a maximum T-peel strength (33.2N/25mm) as well as good washable and dry-cleaning resistant performance at a 80 mol % of aminoundecanoic acid .2. The effect of aminoundecanoic acid content on the rheological behavior of the copolyamide was investigated. Non-Newtonian indexes (n) for all specimens in the testing range of shear rate were less than 1, which indicated that the copolyamide was pseudo-plasitc. Non-Newtonian indexes (n)of the copolyamide increased with the temperature increasing. In the case of constant shear stress and shear rate, the apparent viscosity decreased initially and then increased as the increase of the molar fraction of aminoundecanoic acid. The reduced apparent viscous activation energy of copolyamide with the increasing aminoundecanoic acid content indicated that the addition of aminoundecanoic acid reduced the temperature-sensitivity.3. The crystallization and melt behavior were investigated by DSC, WAXD and Polarized Optical Microscopy (POM). In all of the WAXD patterns, there was a strong diffraction peak at 2θ=21.3o, which is characteristics peak of theγnylon crystal. The POM photographs demonstrated that the spherulite size of PA6/66/11 coplymer crystals became smaller but the number increased. The studies on the isothermal crystallization showed that Avrami equation well described the isothermal crystallization of PA6/66/11 copolyamide. The analysis of non-isothermal crystallization showed that Ozawa equation was not suitable to describe the non-isothermal crystallization process of PA6/66/11 copolyamide, while the modified Avrami and Mo equation took great advantages over treating the non-isothermal crystallization kinetics. Additionally, the equilibrium melting temperature and the activation energy of nonisothermal crystallization for the copolyamides were calculated from Hoffman-Weeks equation and Hoffmann-Lauritzen theory.
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