Poly(lactic acid) (PLA) is a well known biodegradable thermoplastic with excellent mechanical properties that is a product from renewable resources. However, the brittleness of PLA limits its general applications. Using epoxidized soybean oil (ESO) as a novel plasticizer of poly (lactic acid), the composite blend with the twin-screw plastic extruder at five concentrations, 3, 6, 9, 12, and 15 wt %, respectively. Compared with pure PLA, all sets of blends show certain improvement of toughness to different extents. The concentration with 9 wt % ESO increases the elongation at break about 63%. The melt flow rates of these blends with respect to different ESO ratio have been examined using a melt flow indexer. Rheological behaviors about shear viscosity and melt strength analysis are discussed based on capillary rheology measurements. The tensile strength and melt strength of the blends with 6 wt % ESO simultaneity reach the maximums; whereas the elongation at break of the blends is the second highest level. ESO exhibits positive effect on both the elongation at break and melt strength. The results indicate that the blend obtained better rheological performance and melt strength. The content of 6 wt % ESO in PLA has been considered as a better balance of performance. The results have also demonstrated that there is a certain correlation between the performance in mechanical properties and melt rheological characterization for the PLA/ESO blends.

This study investigated that epoxidized soybean oil (ESO) was blended as plasticizer with poly (lactic acid) (PLA) and its effects on the melt rheological properties, such as melt flow index, apparent shear viscosity, and melt strength of the blends. PLA was blended by the twin-screw plastic extruder at five mass fractions: 3%, 6%, 9%, 12%, and 15% (based on PLA mass). Melt flow index (MFI) was examined with a melt flow indexer. The results indicate that the blends of PLA/ESO had higher MFI than pure PLA, except for MFI at 9% reaching to the lowest point, even lower than that of pure PLA. Melt rheological properties were studied by a capillary rheometer in a temperature range of . The blends e ℃ xhibited shear-thinning behavior and the apparent shear viscosity was well described by the power law in this shear rate region. The melt strength of PLA plasticized with 6% ESO reached the maximums. ESO was more effective in increasing the melt strength at the mass fractions less than 6%, which could toughen the blends to some extent. Therefore, the authors suggested the optimum addition level of 6%-9% ESO will get good melt rheological performance balance.Biodegradable polymers have recently been introduced to various fields as alternatives to traditional materials. Poly (lactic acid) (PLA) is attracting attention as a candidate of non-petroleum-based biodegradable polymeric materials. It has high mechanical properties, thermal plasticity, processing properties, and biocompatibility [1] and has been proposed as a renewable and degradable plastic for uses in service ware, grocery, wastecomposting bags, and mulch films, controlled release matrices for fertilizers, pesticides, and herbicides [2][3][4] . However, it still has some shortcomings restricting its applications, such as the low deformation at break, melt strength, and the quite expensive price [5] .The physical properties of PLA may be modified by blending the polymer with a plasticizer or with a second polymer, and the flexibility of PLA can thereby be improved. The choice of polymers or plasticizers to be used as modifiers for PLA is limited by the requirements of the application. For packaging and hygiene applications, only nontoxic substances approved for food contact and personal care can be considered as plasticizing agents. The plasticizer should not be too volatile because this would cause evaporation to occur at the elevated temperatures used at processing. Furthermore, the plasticizer should not be prone to migration because this would cause contamination of the materials in contact with the plasticized PLA. As plasticizers for PLA, various type of compounds such as citrate ester [6,7] , poly (ethylene glycol) (PEG) [8][9][10][11] , glycerol [12] , partial fatty acid esters, oligomeric lactic acid, and glycerol have been used to improve the flexibility of PLA.

Adhesive bonding construct joining substrates by placing an adhesive between them. This method provides many advantages compared to conventional mechanical fasteners method including lower structural weight, reduced stress concentration, and high performance under fatigue conditions, resulting in an increase of the structural integrity of the system. [1,2] Adhesively