The opportunity for the preparation of high-performance shape memory materials was brought about by the excellent mechanical properties of poly(lactic acid) (PLA). As the effect of crystallization on shape memory was still unclear, this brings constraints to the high-performance design of PLA. The PLA plates with different aggregation structure were prepared by three kinds of molding methods in this paper. The PLA plates were pre-stretched with a series of different strains above glass transition temperature (i.e., 70 °C). The recovery stress and ratio of the material were measured above stretching temperature (i.e., 80 °C). Prolonging of annealing time resulted in more perfect crystal structure and higher crystallinity. The crystal region acted as network nodes in shape memory PLA, and crystal region structure determined the shape memory performance. Based on the experimental results, the structural evolution of network nodes in shape memory PLA was established.

With the further development of secondary exploitation in oil field, it is very important to design high performance rubber used in drilling and mining tools. In this paper, polyamide 6/nitrile rubber (PA6/NBR) blends were prepared by three-step molding process. The reinforcing effect of PA6 in NBR with different acrylonitrile content was explored. The crystal properties, crystal structure, phase separation morphology and mechanical properties of the blends were systematically analyzed. The results showed that the fibrosis degree of PA6 phase was higher and the reinforcement effect was more obvious, when the content of acrylonitrile in NBR matrix was lower. Based on the experimental results, the reinforcement mechanism is fully explained and the morphology evolution model of PA6/NBR was established.

The temperature and strain fields are two key factors in the regulation of fibrous aggregate structure. In this paper, plate specimens of polyamide 6 were prepared by compression molding method. The oriented polyamide 6 plates were systematically analyzed from aspects of mechanical properties, thermal properties, crystal structure and crystal morphology. The maximum tensile strength and elastic modulus of polyamide 6 plate appeared at 120 °C. The stretching process induced the formation of a more thermal stable α -form crystals. With the increase of stretching temperature, α -form crystals transformed into γ -form crystals gradually. The crystal chips transformed into fibrils during the stretching process. The structural evolution model of materials under the temperature and strain fields was established.

During the fiber spinning process, the stretching process is the key to improve the mechanical properties of materials. It is very important to study the effect of hydrogen bond density on the aggregation structure evolution of polyamide for the preparation of high-performance fibers. In this paper, three kinds of polyamides (polyamide 6, polyamide 612 and polyamide 1212) were comparatively studied. In these three polyamides, the hydrogen bond density showed a gradient trend. With the increase of hydrogen bond density, the tensile strength and crystallinity of the materials gradually increased. The phase transition process of the three polyamides had significant difference. This was due to the difference of hydrogen bond density which resulted in different thermally stability of crystal blocks. Finally, the phase evolution schematic of polyamides depending on hydrogen bond density and stretching strains was established.