No abstract

A series of blends of bacterial poly(R-hydroxybutyrate) (PHB), with different miscible amorphous components, were prepared. The molecular mass of the amorphous components was varied from M n Ϸ 600 to 200,000 g/mol. Several factors were found to influence the stress-strain behavior of PHB blends: the glass-transition temperature, the average molecular mass of amorphous phase, the content of PHB in the blend, the crystallinity, and the drawing temperature. It was found that a high extension ratio at rupture R Ͼ 3 is obtained only if the PHB content is less than 60% (crystallinity X c Ͻ 0.4), although this holds only for blends of bacterial PHB with a high molecular mass (M n Ͼ 30,000) amorphous component. The lowering of glass-transition temperature by the addition of low molecular mass additives (plasticizers) deteriorates the tensile properties. Measurements at elevated temperatures of ductile blends yielded a marked decrease of both stress at rupture R and extension ratio at rupture R .

The influence of nanosized YVO 4 particles as a novel and efficient nucleating agent on the nonisothermal crystallization behaviors of poly(lactic acid) (PLA) was studied. A modified Avrami model was utilized to describe the nonisothermal crystallization kinetics of pure PLA and PLA nanocomposites. The differential isoconversional Friedmann formula was employed to calculate the effective activation energies (E X(t) ) of nonisothermal crystallization from the glass state. The results showed that modified Avrami methods describe the nonisothermal crystallization kinetics of pure PLA and PLA nanocomposites well. The crystallization rate of PLA/1 mass% YVO 4 was faster than that of pure PLA sample by factor 5 × 10 3 at a heating rate of 1 K min −1 . While the values of Lauritzen-Hoffman parameters (K g and U*) of the PLA/YVO 4 nanocomposites were lower than those of pure PLA, indicating the nucleation efficiency of nanosized YVO 4 particles for PLA. Scanning electron microscopy images reflect the uniform dispersion of 1 mass% YVO 4 in PLA matrix. Thermogravimetric analysis results revealed that the thermal degradation parameters are slightly lowered by 7 C on increasing the mass percentage of YVO 4 in the PLA nanocomposites.

Thermal and mechanical properties of binary blends of polypropylene (PP) with a statistical copolymer (85 wt% propylene and 15 wt% ethylene, abbreviated here as VM) have been investigated. Both components were found to be miscible in the melt in the whole range of compositions. No separate domains of VM have been detected by polarizing optical microscopy, and the size of spherulites is going down with increasing VM content. The crystallization temperature of PP as detected by DSC, is going down to 83°C, for PP/VM blends 10:90. This is another evidence for miscibility in the melt. Viscoelastic properties of the melt were measured. Regarding the solid state, the melting enthalpy is exactly proportional to the PP content in the blend. The DSC step height at the glass transition is exactly proportional to the VM content. These results are suggesting a three‐phase model (crystalline, rigid amorphous, and mobile amorphous phase), where the VM component is mainly located in the mobile amorphous regions, while the amorphous part of PP is in the rigid amorphous regions. Stress–strain curves show a systematic increase of elongation at break with increasing VM%, to be extended from 7.8% to more than 550%.

The effects of bacterial poly(hydroxyoctanoate) (PHO) and talc on the nonisothermal cold crystallization behaviours of poly(lactic acid) (PLA) were analysed with differential scanning calorimetry (DSC), and the thermal stability of the samples was observed with thermal gravimetric analysis (TGA). The modified Avrami’s model was used to describe the nonisothermal cold crystallization kinetics of neat PLA and its blends. The activation energies E for nonisothermal cold crystallization were calculated by the isoconversional method of Kissinger-Akahira-Sunose (KAS). The DSC results showed that the PLA/PHO blends were immiscible in the whole studied range, and as the PHO and talc content increased, the crystallization rate of PLA accelerated, and the crystallinity of PLA in the PLA samples increased. The values of the Avrami exponent indicated that the nonisothermal cold crystallization of the neat PLA and its blends exhibited heterogeneous, three-dimensional spherulitic growth. The E values were strongly dependent on PHO and talc. The TGA results showed that the presence of PHO and talc slightly influenced the thermal stability of PLA.