In this study, the biodegradable plastics of polyolefin/tapioca starch were studied. There is a poor interface adhesion between starch and low-density polyethylene (LDPE) because of the difference from polar character. The monomers including acrylic acid, acrylic amide and (MA) were used to graft onto the surface of PE in this study. The 1,1-diphenyl-2-picrvlhydrazyl (DPPH) method was adopted to estimate the concentration of peroxide and consequently the appropriate plasma treatment condition was determined by its optimal concentration. Then, the appropriate plasma treatment condition and thermal grafting were used to modify the surface of polymer. ATR-FTIR spectra and ESCA analysis were used to evaluate the degree of grafting copolymerization. The maximum of graft degree are 0.55 and 2.41 by ATR-FTIR spectra and ESCA analysis, individually. The graft degree shows they have similar trend by ATR-FTIR and ESCA analysis and the optimal graft time is 4h. The method of surface modification of polymer is suitable for many monomers.
In blending, the different compositions and processing conditions were used. The MA grafted LDPE and the AAc grafted LDPE were used to improve the interface adhesion between starch and LDPE. According to melt flow index, mechanical properties and SEM fracture micrographs analysis, the compatibility between LDPE and starch was investigated. By observing the morphology of A series blends (LDPE/MA-g-PLDPE/TS/GA/MA, in section 3), they could be seen that the size of the PE particles decreased with an increasing amount of MA-g-PLDPE. The well-dispersion that was contributed from MA caused the structure crack rapidly, which enhanced the biodegradation rate. The blends of high content starch present low elongation but excellent biodegradation. The biodegradation measurement method in this study was soil burial. The investigated samples in form of plates (3×3×0.06 cm3) were buried in the test soil from Tatung University campus for one or two weeks. After soil burial, the samples were dried by a vacuum oven for 5h and then weighted. There were two blends series, LDPE/starch and PVA/starch, in this work. After two weeks soil burial, LDPE/starch blends reached the maximum weight loss of about 95 wt%. And after one week soil burial, the maximum weight loss of PVA/starch blends was about 80 wt%.