Flash DSC Characterization Of Crystallization Kinetics In Copolyamides

Polyamides(PA)contain repeating amide groups(-CONH-)forming sheet-like hydrogen-bonding interactions.Owing to excellent chemical resistance and mechanical properties,polyamides have been widely used as high-performance engineering plastics in electrical appliance and automobile part.But its strong water absorption and poor low-temperature toughness have limited its application to a certain extent.The appearance of copolyamides can make up for this deficiency.However,the systematic research about the isothermal crystallization kinetics of copolyamides is scarce.In this report,we employed commercial chip-calorimeter Flash DSC1 apparatus to characterize the crystallization kinetics of amide-6-based random copolymers(C66 and C12)and polyoxamide(PAM-174).The reason that make the difference have been analyzed theoretically.In Chapter 1,we first introduced the structure of polyamides.Polyamides(PA)contain repeating amide groups(-CONH-)forming sheet-like hydrogen-bonding interactions as well as methylene sequences forming planar zigzag conformation.Different stacking modes make them crystallize with different crystal structure in various conditions.The crystallization and melting behavior of polyamides and copolyamides are described with examples.Then we introduced the nucleation kinetics and crystal growth kinetics of polymer crystallization in detail.The theoretical basis for analysis of the isothermal crystallization behavior of polymers is provided.In the end of the chapter,we described the development history and usage method of Flash DSC1,as well as how to characterize the isothermal crystallization kinetics of polymer.In Chapter 2,we took the advantage of the Flash DSC1 to characterize the crystallization kinetics of amide-6-based random copolymers which separately marked by C66 for randomly copolymerized between amide 6 and amide 66 with the mole composition 82/18,and by C12 copolymerized between amide 6 and amide 12 with the mole composition 80/20.We got the isothermal crystallization kinetic curves of two copolymers after determining the isothermal crystallization conditions.The results showed that the curves exhibit double parabolic curves representing the supposed heterogeneous and homogeneous crystal nucleation dominating separately in the high and low temperature regions.The results in comparison to the corresponding homopolymers crystallization kinetics revealed the chemical confinement effects of hydrogen-bonding mismatching in copolymer crystallization kinetics,and in addition,comonomers keep the crystallization habits of their homopolymers due to their inclusion in the crystalline lattice of polyamide 6.In Chapter 3,we employed Flash DSC1 to investigate the isothermal crystallization kinetics of copolyoxamide PAM-174.When the samples were scanned with different cooling rates after erasing the thermal history,we found that the crystallization during cooling process showed rate dependence that vary in singledouble-single mode.The multiple melting peaks in heating curves prove that the unstable crystal of PAM-174 would reorganize during heating process.The result of isothermal crystallization kinetic of PAM-174 was also obtained.We further compared these data to PA6 and draw the conclusion that PAM-174 crystallizes faster that PA6 at the same temperature.In Chapter 4,we made a summary and outlook.