Physical structure of polyolefin--starch blends after ageing

摘要

Low density polyethylene- or polypropylene-starch blends containing 40-50 wt of glycerol plasticized starch were subjected to four months long soil test, and then they were etched with 10 aqueous natrium hydroxide solution during 5 days at room tem- perature. On every stage of degradation the supermolecular structure of blends was investigated by means of SAXS and WAXS methods. It was found that during biodegradation in soil ca. 75 of the initial starch phase content was removed from blends. Further decrease of the starch phase content up to 80-85 was observed after chemical degradation in NaOH solution. The WAXS measurements have shown that biodegradation in soil does not affect significantly the crystalline phase content in poly- ethylene (45) or polypropylene (55). However, the additional chemical treatment of polyolefin-starch blends with NaOH solution leads to some increase of the crystallinity index both for polyethylene (48) and polypropylene (65). The SAXS mea- surements indicated the heterogenity changes in blends after the degradation processes on larger spatial length than the long period in semicrystalline polyethylene or polypropylene. These changes can affect the mechanical behaviour of blends, e.g. an increase of elongation at break, observed after the degradation tests.