| As a bio-polymer, polyhydroxyalkanote(PHA) has been developed rapidly in recent years. Because of its biocompatibility, biodegradability and hot workability, PHA can be expected to replace some traditional petroleum-base plastic materials in some application. Poly(3-hydroxybutyrate-co-4-hydroxybutyrate)[P(3,4)HB], a typical kind of PHA, has some drawbacks, such as slow crystallization rate, narrow processing temperature range, low breaking elongation, inflammability and so on. In this thesis, the research progress on PHA-based composites were firstly reviewed, then, silica(SiO2) and polyurethane(PU) were used as additives to prepare two kinds of P(3,4)HB-based composites, respectively. The mechanical properties, crystalline properties and thermal properties of the composites were studied to explore a new method of reinforcing and toughening biodegradable polyesters. The major research contents of this thesis are as follows:Firstly, monodisperse SiO2 nanoparticles were synthesized by modified St?ber method, and the particle size could be controlled in range of 200~400nm. Then silane coupling agent KH-550 was used to modify SiO2 to improve its hydrophobicity and dispersing property. P(3,4)HB/SiO2 nanocomposites with different SiO2 content was prepared by melt blending method and the mechanical properties and crystalline properties were studied. The result indicated that, the tensile strength and modulus of the composites was increased obviously with increasement of SiO2 content, especially for 3wt% SiO2 content. While the elongation at break declined slightly. The analysis of differential scanning calorimetry(DSC) and polarizing optical microscope(POM) showed that SiO2 decreased the cold crystallization temperature(Tcc) and spherulite size of P(3,4)HB, which meant that SiO2 could work as nucleating agent in the composites and promoted crystallization of P(3,4)HB.Secondly, polyester-based polyurethane(PU) with 45wt% hard segment component was synthesized through one-step method, and then P(3,4)HB/PU composites were prepared by solution casting method. The microstructure, mechanical properties, crystallization behavior and thermal properties were studied. The result showed that PU dispersed well in P(3,4)HB matrix in nano-scale. The elongation at break of P(3,4)HB/PU composites were remarkably increased, while the yield strength and elastic modulus were decreased with an increase in PU content. The results of scanning electron microscope(SEM) indicated that the fracture characteristic of P(3,4)HB was obviously transformed from brittleness into ductility with a gradual increase of PU loading. Furthermore, PU improved the thermal stability of the composites and reduced the biodegradation rate of P(3,4)HB/PU composites, but the spherulite size and the Tcc increased, which meant PU retarded the crystallization of P(3,4)HB.Finally, three kinds of polyester-based polyurethane(PU) with different hard segment contents(including 35%PU, 45%PU and 55%PU) were firstly synthesized and then P(3,4)HB/PU composites were prepared by solution casting method, the toughening effects of PU on P(3,4)HB were compared. The results showed that, all three kinds of PU had obvious toughening effects on P(3,4)HB, and the more PU in the composites, the better toughening effects were observed. 55%PU had the best toughening effects on P(3,4)HB, the fracture strength of P(3,4)HB-55%PU were greatly improved and the stress-strain curve were continuously increased. However, 35%PU had the weakest toughening effects on P(3,4)HB. The P(3,4)HB-35%PU lost the most yield strength. All three kinds of PU improved the thermal stability of P(3,4)HB/PU composites, but retarded the crystallization of P(3,4)HB. |
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