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This is the first study investigating how polycarbodiimide (PCDI) delays thermal degradation of poly(lactic acid)/natural rubber blends (PLA/NR) during the preparation of PLA/NR masterbatches (MB) and PLA/MB compounds for the film blowing process. The PCDI concentration used in this work was from 0 to 1 wt%. The torque plastograms, FTIR, and 1H-NMR spectra indicated the successful chain extending reaction between the PCDI carbodiimide group and the PLA carboxyl group, and there was no reaction with NR domains. The reaction increased the PLA/MB compounds' viscosity and improved processability and mechanical properties of PLA/MB blown films. The optimal PCDI content for the highest melt strength, film blowing stability, and mechanical properties was at 0.25 wt% PCDI. Undesirable gel spots were observed in the PLA/MB blown film at PCDI concentrations higher than 0.5 wt%. [ABSTRACT FROM AUTHOR]

This research investigated the degradation of polylactic acid (PLA) and polylactic acid/natural rubber (PLA/NR) films submerged in water by focusing on the effect of film constituents, which were natural rubber and an organic peroxide, as well as an exposure to outdoor sunlight. The degradation of film samples was characterized by the changes in molecular structure, toughness, morphology, thermal properties and weight loss of the films and pH of water. It was found that hydrolysis was the primary degradation mechanism of the films submerged in purified water in the indoor condition, while photo-degradation was more prominent in the outdoor condition. Moreover, the presence of NR in PLA led to faster degradation of the films in aqueous environment both indoor and outdoor, while the addition of 0.02 wt% organic peroxide did not delay the degradation of PLA/NR films. These results indicate the potential of NR as it not only improved the toughness of PLA films during their useful life but also accelerated the films' degradation in aqueous environment after use. [ABSTRACT FROM AUTHOR]

This study investigated the effects of natural rubber (NR) and an organic peroxide on the rheological properties, mechanical properties, morphology, and bubble stability during film blowing of poly(lactic acid) (PLA). The NR and peroxide contents were varied from 0 wt% to 25 wt% and 0 wt% to 0.5 wt%, respectively. The results confirmed that the presence of well-dispersed NR could significantly improve the toughness, elongation at break, and processability of PLA films, where the optimal amount of NR was 15 wt%. For the reactive blending with peroxide, a suitable peroxide content for good film toughness and clarity was 0.03 wt%, while the higher content of 0.1 wt% could provide slightly higher processability. These contents are considered much lower than that in the PLA system (without NR), which required up to 0.5 wt% peroxide. The rheological studies indicated that the melt strength, the storage modulus (G′) and complex viscosity (η′) at low frequency could be correlated with good film blowing processability of the PLA/NR films at low gel contents. These parameters failed to correlate in the films having high gel contents as the deformation rate experienced by each test was different leading to the different levels of response to the type and amount of gels. [ABSTRACT FROM AUTHOR]

The effects of dynamic vulcanization systems including sulfur, peroxide, and sulfur/peroxide mixed vulcanization were investigated for dynamically-vulcanized blends of polylactic acid (PLA) and natural rubber (NR) at the PLA/NR ratio of 85/15. For the sulfur system, the CV sub-system (CV1), which used much lower accelerator (TBBS) content than the EV sub-system, rendered higher impact strength and higher %crystallinity. When compared to the peroxide system using DCP as a curative, the impact strength of CV1 sample was almost 4 times lower than the peroxide-cured sample even though their rubber domain sizes and size distributions were comparable. Interestingly, the highest impact strength which was almost 6 times that of the unmodified PLA/NR was achieved when using the mixed sulfur/peroxide system at the CV1/peroxide ratio of 30:70 (S30/DCP70). The lower impact strength of the sulfur-cured system (CV1) compared to those of the peroxide and the mixed-vulcanization systems was potentially due to its significantly higher % crystallinity. [ABSTRACT FROM AUTHOR]