Physical structure of polyolefin-starch blends after ageing

Low density polyethylene- or polypropylene-starch blends containing 40-50 w t% of glycerol plasticized starch were subjected to four months long soil t est, and then they were etched with 10% aqueous natrium hydroxide solution during 5 days at room temperature. On every stage of degradation the superm olecular structure of blends was investigated by means of SAXS and WAXS met hods. It was found that during biodegradation in soil ca. 75% of the initia l starch phase content was removed from blends. Further decrease of the sta rch phase content up to 80-85% was observed after chemical degradation in N aOH solution. The WAXS measurements have shown that biodegradation in soil does not affect significantly the crystalline phase content in polyethylene (45%) or polypropylene (55%). However, the additional chemical treatment o f polyolefin-starch blends with NaOH solution leads to some increase of the crystallinity index both for polyethylene (48%) and polypropylene (65%). T he SAXS measurements indicated the heterogenity changes in blends after the degradation processes on larger spatial length than the long period in sem icrystalline polyethylene or polypropylene. These changes can affect the me chanical behaviour of blends, e.g. an increase of elongation at break, obse rved after the degradation tests. (C) 1999 Elsevier Science Ltd. All rights reserved.