The Properties And Modification Of Poly(3-hydroxylbutyrate-co-4-hydroxylbutyrate) With Different Counit Content

Since Poly(3-hydroxyalkanate)s [(PHA)s] were discovered, they have attracted wide attention due to their biodegradability and biocompatibility. They are extensively used as a degradable thermoplastic material for agricultural, marine, and medical applications. They can be accumulated under unbalanced growth conditions by lots of bacterial as carbon and energy storage materials. The most familiar types of PHAs are the homopolymers and copolymers of Poly(3-hydroxybutyrate) (PHB) . PHB has an unusually high degree of crystallinity due to the stereoregularity of the perfectly isotactic chains. This high crystallinity lead to a rather brittle and hard material that is not very useful for many applications, and its very high melting point (>170℃) make it difficult to use melt processing equipment. The incorporation of a comonomer unit, 4-hydroxybutyrate, can decrease the excessively high T_m and control efficiently the degree of crystallinity for 4HB unit cannot crystallize in the sequence of 3HB units and act as defects in the P(3HB) crystal lattic.In this investigation, poly(3HB-co-4HB) copolymers were supplied by Tianjin Green Bioscience Company. At first, The basic properties of poly(3-hydroxybutyrate-co-4-hydroxybutyrate)s[poly(3HB-co-4HB)s] with the 4HB contents from about 9 to 34 mol % were investigated. Their crystallinity, crystalline structures, thermal and mechanical properties were characterized by DSC, XRD, TG, DMA and tensile test. It was found that the melt temperatures (T_m), glass transition temperatures (T_g), thermal stability , storage modulus (E') and mechanical properties of all the [poly(3HB-co-4HB)s] copolymers investigated have something to do with the amount of the 4HB, Furthermore, the parking time also affect the copolymers' mechanical properties.Second, using solution cast film method, three modified blends of poly(3HB-co-4HB)s were prepared, they were TA/ poly(3HB-co-4HB), SO/ poly(3HB-co-4HB) and TEC/ poly(3HB-co-4HB) blends separately. Via comparing their thermal and mechanical properties, we found that TEC was the best in improving poly(3HB-co-4HB)' capabilities.Up to now, nearly all the solid experiments about P(3HB-co-4HB) including XRD, biodegration and tensile test are based on the CH₂Cl₂ casting films. It's well known that the remnant of solvent will spoil the properties of material. Compared to solution casting, compression molding can avoid the remnant of solvent and is close to the real practice process. However, there is few research about poly(3HB-co-4HB) melt molding sheets. In the third chapter, we investigate the TEC/P(3HB-co-4HB) melt molding sheets with 4HB content from 9 to 34 mol % by DSC, XRD, and tensile test.