Yuxian An

Thermal degradation kinetics of uncapped and end-capped poly(propylene carbonate)

In order to improve its thermal stability, poly(propylene carbonate)(PPC) was end-capped by different active agents. Thermogravimetric data show that the degradation temperature of uncapped PPC was lower than that of end-capped PPC. The kinetic parameters of thermal degradation of uncapped and end-capped PPC were calculated according to Changs method. The results show that different mechanisms operate during the whole degradation temperature range for uncapped PPC. In the first stage, chain unzipping dominates the degradation. With increasing temperature, competing multi-step reactions occur. In the last stage, random chain scission plays an important role in degradation. For end-capped PPC, random chain scission dominates the whole degradation process.

Nonisothermal crystallization kinetics of poly(β-hydroxybutyrate)

Kinetics of nonisothermal crystallization of poly(β-hydroxybutyrate) from melt and glassy states were performed by differential scanning calorimetry under various heating and cooling rates. Several different analysis methods were used to describe the process of nonisothermal crystallization. The results showed that both Avrami treatment and a new method developed by combining the Avrami equation and Ozawa equation could describe this system very well. However, Ozawa analysis failed. By using an evaluation method, proposed by Kissinger, activation energies have been evaluated to be 92.6 kJ/mol and 64.6 kJ/mol for crystallization from the glassy and melt state, respectively.

Isothermal crystallization of poly(3-hydroxybutyrate-co-3-hydroxyvalerate)

Isothermal crystallization behavior of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) was investigated by means of differential scanning calorimetry and polarized optical microscopy (POM). The Avrami analysis can be used successfully to describe the isothermal crystallization kinetics of PHBV, which indicates that the Avrami exponent n = 3 is good for all the temperatures investigated. The spherulitic growth rate, G, was determined by POM. The result shows that the G has a maximum value at about 353 K. Using the equilibrium melting temperature (448 K) determined by the Flory equation for melting point depression together with U-* = 1500 cal mol(-1), T-infinity = 30 K and T-g = 278 K, the nucleation parameter K-g was determined, which was found to be 3.14+/-0.07 x 10(5) (K-2), lower than that for pure PHB. The surface-free energy sigma = 2.55 x 10(-2) J m(-2) and sigma(e) = 2.70+/-0.06 x 10-2 J m(-2) were estimated and the work of chain-folding (q = 12.5+/-0.2 kJ mol(-1)) was derived from sigma(e), and found to be lower than that for PHB. This implies that the chains of PHBV are more flexible than that of PHB.

Nonisothermal crystallization and melting behavior of poly(β‐hydroxybutyrate)–Poly(vinyl‐acetate) blends

Nonisothermal crystallization and melting behavior of poly(P-hydroxybutyrate) (PHB)-poly(vinyl acetate) (PVAc) blends from the melt were investigated by differential scanning calorimetry using various cooling rates. The results show that crystallization of PHB from the melt in the PHB-PVAc blends depends greatly upon cooling rates and blend compositions. For a given composition, the crystallization process begins at higher temperatures when slower scanning rates are used. At a given cooling rate, the presence of PVAc reduces the overall PHB crystallization rate. The Avrami analysis modified by Jeziorny and a new method were used to describe the nonisothermal crystallization process of PHB-PVAc blends very well. The double-melting phenomenon is found to be caused by crystallization during heating in DSC

Isothermal crystallization kinetics and melting behavior of poly(β-hydroxybutyrate)/poly(vinyl acetate) blends

The overall isothermal crystallization kinetics and melting behavior of poly(beta-hydroxybutyrate) (PHB)/poly(vinyl acetate) (PVAc) blends were studied by using differential scanning calorimetry(DSC). The Avrami analysis indicates that the addition of PVAc into PHB results in the decrease in the overall crystallization rate of the PHB phase, but does not affect PHBs nucleation mechanism and geometry of crystal growth. The activation energy of the overall process of crystallization increases with the increasing PVAc content in the blends. The phenomenon of multiple melting endotherms is observed, which is caused by melting and recrystallization during the DSC heating run

Crystallization kinetics and morphology of poly(β-hydroxybutyrate) and poly(vinyl acetate) blends

The crystallization behavior and morphology of poly(β-hydroxybutyrate) and poly(vinyl acetate) blends have been studied with DSC, POM, SAXS and WAXD methods. The results indicate that the overall crystallization rate and spherulite growth rate are slower in the blends than that in the pure PHB. The addition of PVAc has no effect on the crystal structure of PHB, but affects its crystalline morphology. During crystallization of PHB, PVAc chains were being rejected into the region between the lamellae of crystalline PHB.

Study of the blends containing core-shell latex polymer

Polycarbonate (PC) and a core-shell latex polymer composed of poly(butyl acrylate) and poly(methyl methacrylate) (PBA-cs-PMMA) as core and shell, respectively, were mixed using a Brabender-like apparatus under different conditions. The mechanical properties, the morphology and the processability of the blends were investigated. Because of the good compatibility of PC and PMMA, even dispersion of PBA-cs-PMMA in PC matrix and good adhesion between the components have been achieved. PBA-cs-PMMA is thus a very good impact modifier for PC. The toughening mechanism is both cavitation and shear yielding, as indicated by SEM observation.