Wanda Meissner

Structure and properties of degradable polyolefin-starch blends

The structure, mechanical properties and susceptibility to degradation of blends of low density polyethylene (PE) or isotactic polypropylene (PP) and glycerol plasticized starch (GS) was investigated. Monoethers of glycerol and fatty alcohols (GA) and in some cases epoxidized rubbers (ER) were used as compatibilizers for the investigated systems. It was found that mechanical properties and ageing susceptibility of blends depend strongly on their composition, i.e. the content of plasticized starch in the blend and the content of glycerol in the starch. In some cases an increased susceptibility to biodegradation during soil or fungus ageing not only of the starch phase but also of the polymer phase was observed. The susceptibility of these systems to accelerated artificial weathering was also investigated.

Thermal dehydrochlorination of poly(vinyl chloride)-epoxidized butadiene/styrene triblock copolymer blends

The effect of the type of epoxidized butadiene/styrene block copolymer [ESBS; linear (B/S) or radial (E(B/S)n), containing 0–27% of epoxy groups] on the thermal dehydrochlorination of poly (vinyl chloride) (PVC)-ESBS blends (ESBS content 10%) was investigated in the temperature range 170–180 °C, under a non-oxygen atmosphere. Thermal stability of the PVC-ESBS blends was estimated on the basis of induction time, t0, and maximum rate of hydrochloride emission, Vmax from the system. It was found that, for a similar degree of epoxidation of the SBS copolymer, the induction time i.e. the time after which emission of HCl begins, is longer in the series PVC < PVC-SBS < PVC-EB/S < PVC-E(B/S)n, and the same is true for thermal stability. However, the maximum rate of emission of HCl is lowest in the case of PVC-EB/S blends, in the range of molar ratios from 0.5 to 2.0 × 1O−2. On the basis of the dependence Vmax = f(EBVC), it was found that there is a certain content of epoxidized butadiene (EB) units in a mixture which causes the optimum stability of poly (vinyl chloride) during heating. During thermal destruction of the PVC-ESBS blends, the HC1 evolved undergoes addition both to epoxy fragments and to double bonds. The degree of conversion of EB units in time t0 is 20% at 170 °C and 30% at 180 °C. The glass transition temperature, Tg, of PVC in the PVC-ESBS blends shifts towards higher temperatures by about 6–8 °C, proving the existence of crosslinking processes during moulding of the blends. The epoxidized butadiene/styrene radial block copolymer, E(B/S)n, is a better thermal stabilizer of PVC than the linear EB/S copolymer.