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|a The main purpose of this study was to investigate the effects of starch and a new phthalate-free plasticizer, which was modified rock stone (MR) on the mechanical, physical, thermal and biodegrability properties of polylactic acid (PLA). The biocomposites of PLA, MR and starch were prepared by extrusion method and injection molded into standard tensile and flexural shape. The properties of the biocomposites were tested and characterized by using tensile and flexural tests, melt flow index, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and water absorption test. The investigation of biodegradation of the biocomposites was done by soil burial test. Test results showed that MR improved the mechanical properties up to 30 w/w% and the optimum MR content was 16.6 w/w% (PM0). The test results also showed that MR acted as reinforcement filler but not as plasticizer because there was a decrease in flow rate and no change in glass transition temperature. When starch was added to the PLA/MR biocomposites, the mechanical properties of the biocomposites were reduced probably due to the agglomeration of starch particles. Optimum starch content was 15 w/w% (PMS15). After the blending of PLA with MR and starch, the pure PLA, PM0 and PMS15 samples were compared. FTIR and SEM results showed that MR was compatible with PLA and that starch interfered with the compatibility of PLA and MR. DSC results also showed that the addition of MR and starch to PLA did not affect the crystallinity of the biocomposite. Addition of starch improved the amount of water uptake and the percentage weight loss during soil burial test because starch is hydrophilic and can be hydrolyzed by microorganisms.
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