Polylactide/Biopolyethylene bioblends
In this work, Polylactide/Biopolyethylene blends were developed. Although some studies have been carried out on polylactide/polyethylene blends, none of them has used polyethylene synthesized with raw material obtained from natural sources. Due to the incompatibility between polylactide and polyethylene, E-GMA and EMA-GMA compatibilizers were used. These compatibilizers present glycidyl methacrylate groups in their structure, which may react with the functional end-groups of polylactide. To evaluate the properties, the blends were characterized by mechanical tests, scanning electron microscopy (SEM) and melt flow index (MFI). The results indicated that the compatibilizers played an important role in the blends, interacting with the blends components, modifying the morphology and improving the mechanical properties.
Contribution of Catalytic Transesterification Reactions to the Compatibilization of Poly(lactic acid)/Polycarbonate Blends: Thermal, Morphological and Viscoelastic Characterization
Samarium acetylacetonate (Sm-Acac) was added to catalyze interchange reactions between poly(lactic acid) (PLA) and polycarbonate (PC) in order to promote compatibilization and enhance the performances of the PLA/PC blend. The effects of the composition and catalyzed transesterification reactions were investigated using differential scanning calorimetry (DSC), thermogravimetry (TG), dynamic mechanical thermal analysis (DMTA) and scanning electron microscopy (SEM). DMTA and DSC analysis revealed the immiscibility of the uncatalyzed PLA/PC blends for the studied compositions because the glass transition temperatures of PC and PLA were unchanged after blending. In the PLA glassy region, PLA/PC blends exhibited lower storage moduli which increased upon heating due to the cold crystallization process. During melt mixing with Sm-Acac catalyst, PLA/PC blends were submitted to two competing processes. In one hand, Sm-Acac acted as a plasticizer and contributed in decreasing significantly the glass transition, crystallization and melting temperatures of PLA phase. In the other hand, Sm-Acac proved its efficiency in catalyzing the transesterification reactions that were evidenced by the decrease of the PLA aptitude to crystallization due to the hindering effect of the PC units inserted into the PLA chains. PLA/PC blends melt mixed with 0.25% of Sm-Acac showed a significant strengthening effect, corresponding to an increase in the storage modulus in the temperature range comprised between 70 and 90 °C. This indicated the formation of a copolymer at the interface and the promotion of adhesion as it is confirmed from the decrease in the height of the PLA Tan δ peak. At 0.5% of Sm-Acac, (90/10) PLA/PC blend revealed a new peak assigned to the glass transition of the PLA-PC copolymer, whereas the (50/50) PLA/PC blend was converted into a new random copolymer. TG analysis proved the presence of a copolymer structure presenting an intermediate thermal stability in both the catalyzed and uncatalyzed blends.
Thermal degradation of polymers: Part XXVIII — Vacuum pyrolysis of poly(m-acetamidostyrene): Products volatile at ambient temperature
Abstract The products obtained on degradation of poly(m-acetamidostyrene) (Pm-AAS) in vacuo are described. The effects of molecular weight and pyrolysis temperature are discussed and compared with those observed for polystyrene (PS) under identical conditions. The liquid products of pyrolysis were separated and identified by gas-liquid chromatography and mass spectrometry. Monomer was not present in the liquid fraction from Pm-AAS and product analysis revealed significant differences in the degradation behaviour relative to PS. This behaviour was ascribed to differences in volatility of the parent monomers, their relative susceptibility to thermal polymerisation and the ability of the side grouping to undergo cleavage in the substituted polymer. Mechanisms involving side group cleavage are proposed and discussed to account for the products obtained. Quantitative studies are also described and compared with results from PS.