| In this research, biodegradable polyurethane with poly propylene carbonate (PPC) as the soft-segment elastomer is synthesized. The first part of the thesis elaborates the preparation of thermoplastic polyurethane (TPU) elastomer through the comparison of one-step method and two-step method’s influence on the mechanical property. In the study of TPU, mechanical and degradation properties are researched via the variation of chain extender, isocyanate, molecular weight of PPC and hard-segment content respectively. The second part of this thesis means to verify cross-bonding’s influence on the properties, mainly via the three aspects of isocyanate index R, the type and the content of cross-bonding agent. The last part is on the relationship between PU’s heat-resistant property and its structure. The research of thermal properties is carried out through variable isocyanate, chain extender, hard-segment content, and cross-bonding.The synthesis of TPU shows that two-step method is superior to the one-step one, reflected in mechanical property and the distribution of molecular weight, which two-step method leads to a narrower distribution. TPU synthesized with the four different chain extenders bears different mechanical properties, the strength may characterized with the following sequence, EG>CHDM>DEG>BDO. Keeping R as a constant, tensile strength and hard-segment content increases while breaking elongation decreases when more NCO-base is introduced into the system. TPU synthesized with PPC whose soft-segment weight is2,000shows up some plastic rigidity, bearing higher hardness and tensile strength but lower elongation and permanent deformation rate than PPC of2,500and3,500. The study on the isocyanate indicates that aromatic diisocyanate-synthesized TPU is stronger than the aliphatic diisocyanate ones. Besides, symmetrical and high rigidity aromatic diisocyanate endows PU elastomer with higher hardness and tensile strength. The research on the degradation of TPU elastomer shows that PPC-based TPU bears better hydrolysis resistance and degradation. The samples’water absorption and weight-loss rate are far from high, which water absorption’s peak remains around (12+1.5)%and weight-loss rate lower than5%, and tensile strength remains the same simultaneously. However, the properties tested via soil buried method are different, for tensile strength decreases obviously and weight-loss rate is higher.The study on cross-bonding’s influence on the mechanical and degradation properties of PPC-based PU elastomer shows that when the component is fixed, the variation of R, namely [NCO]/[OH], has a remarkable effect on PU properties. Tensile strength and hardness increases and breaking elongation decreases while R is increasing. The research on chain-extending cross-bonding agent TMP’s content shows that tensile strength increases along with the content. But there exists an extremum, beyond which the strength will decline. The results indicate that moderate cross-bonding is beneficial to the enhancement of tensile strength and hardness and an improper cross-bonding will lead to side-effect. The research on cross-bonding’s influence on degradation shows that the degradation rate can be controlled by degree and method of cross-bonding, the higher degree, slower it degrades.The study on the thermal properties of PPC-based TPU shows that chain extenders, diisocyanate as well as hard-segment content all have remarkable influence on thermal stability. More symmetrical, higher ordered and hard-segment rigidity will lead to higher thermal stability. If adopting CHDM as chain extender and MDI as diisocyanate, the optimum thermal stability can be obtained. Increase hard-segment content to a moderate degree, microphase-separation is enhanced, hence thermal stability is enhanced simultaneously. But nevertheless, overtoped hard-segment content will result in the decline in microphase-separation degree and thermal stability for more hard segments dissolve in soft segments. |
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