The symmetrical A/B/A structure of multilayer blown films was fabricated in this study. The immiscible low-density polyethylene/polylactic acid (LDPE/PLA) blend was set as a core (B) layer and LDPE was used as skin (A) layers. The compositions of PLA in the core layer were varied from 20 to 50 wt%. The thickness of each layer was 10 μm (total film thickness of~30 μm). In a blown film co-extrusion process, the morphology of the fiber/ribbon-like structures of LDPE/PLA blend was developed.Such structures had interesting effects on gas permeability and aroma barrier properties of the films. For instance, multilayer LDPE films containing 40 and 50 wt% PLA (P40 and P50) showed the reduction of oxygen permeability (PO 2 ) approximately 20% and 43%, respectively, compared with the neat LDPE film. A long tortuous path for gas and aroma transportation through film thickness was created from the developed ribbon-like structures of the PLA minor phase. For durian packaging application, fresh-cut durian of 300 g was packed in the developed multilayer films, LDPE, and HDPE (Control), stored at 4°C for 7 days. Results demonstrated that the steadystate condition of 10% to 13% O 2 and 8% to 10% CO 2 was achieved in all packages except in the HDPE. Moreover, the P40 and P50 films exhibited an outstanding aroma barrier property for three major durian volatiles: diethyl sulfide, ethyl propanoate, and 2-ethyl-1-hexanol. Overall results clearly indicated that the multilayer LDPE films containing PLA exhibited a significantly improved aroma barrier performance with optimum gas permeability desirable for modified atmosphere packaging to retain quality of fresh-cut durian throughout the storage period. KEYWORDS aroma barrier packaging, low-density polyethylene, modified atmosphere packaging, multilayer film, polylactic acid
This study investigated the effect of polylactic acid (PLA) on the mechanical properties and biodegradability of a ternary blend comprising of thermoplastic starch (TPS), Polybutylene adipate terephthalate (PBAT) and PLA. The binary blend (TPS/PBAT) and ternary blend (TPS/PBAT/PLA) with various contents of PLA were prepared through a twin-screw compounding using an intensive mixing screw design. In order to observe the microstructure in blends, the SEM observation revealed the two types of morphology in the blends including (1) some TPS domain that still remained immiscible in all blends and (2) the partially compatible of binary and ternary blends. For the mechanical properties of the blends, the addition of the PLA component led to an improvement of the tensile strength and modulus. For the simple soil burial test, it found that binary film was fully disintegrated within one month, whereas the ternary blend films were also broken down but still remained in small pieces of fragile films. Finally, it can be suggested that the presence of TPS brought to the biodegradation of blends in soil burial test, while incorporating with PLA led to retardation in degradation rate.
This study investigated the influence of dynamic vulcanization of sterecomplex PLA/PDLA (ST) containing various types of rubbers by using dicumyl peroxide (DCP) as a vulcanizing agent. In this work, natural rubber (NR), isoprene rubber (IR), silicone rubber (SI), acrylic rubber (AR), thermoplastic copolyester (TPE) and thermoplastic polyurethane (TPU) were selected. Here, 5 wt% of PDLA, 15 wt% of rubber and 2 wt% DCP as an initiator were melt-blended with PLA in an internal mixer at 180 0C and 50 rpm. It was found that the addition of DCP in (NR and IR) led to a significantly increase in the impact strength and % elongation at break. On the other hand, for the rubbers that do not have double bonds in the main chain (SI, AR, TPE and TPU), the addition of DCP led to a decrease in impact strength and % elongation at break compare to the case without DCP due to the lack of double bonds to react with DCP. For the effect of DCP on the rubber dispersion, it was found that the addition of DCP on the NR and IR could improve the interface compatibility of the rubber and PLA leading to smaller average rubber domain sizes than without DCP. For other types of rubbers, the average rubber domain sizes were bigger with poorer interface compatibility than without DCP. For the effect of DCP on the crystallinity, it was found that the addition of DCP could increase the crystal density and could consequently reduce the crystal sizes of the ST/rubber blends.
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