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Poly(3-hydroxybutyrate) (PHB) is a polyester of 3-hydroxybutyric acid (HB) that is ubiquitously present in all organisms. In higher eukaryotes PHB is found in the length of 10 to 100 HB units and can be present in free form as well as in association with proteins and inorganic polyphosphate. It has been proposed that PHB can mediate ion transport across lipid bilayer membranes. We investigated the ability of PHB to interact with living cells and isolated mitochondria and the effects of these interactions on membrane ion transport. We performed experiments using a fluorescein derivative of PHB (fluo-PHB). We found that fluo-PHB preferentially accumulated inside the mitochondria of HeLa cells. Accumulation of fluo-PHB induced mitochondrial membrane depolarization. This membrane depolarization was significantly delayed by the inhibitor of the mitochondrial permeability transition pore - Cyclosporin A. Further experiments using intact cells as well as isolated mitochondria confirmed that the effects of PHB directly linked to its ability to facilitate ion transport, including calcium, across the membranes. We conclude that PHB demonstrates ionophoretic properties in biological membranes and this effect is most profound in mitochondria due to the selective accumulation of the polymer in this organelle.

Polyethylene (PE) powder with different degrees of oxidation was prepared to model end-of life polyethylene that has been oxidized during processing and/or service-life. The nonoxidized and preoxidized PE powders were blended with PCL to evaluate the possibility to recycle PE powder in PCL blends. Good elongation at break was reached for all 25/75 (w/w) PE/PCL films and the elongation at break correlated well with the carbonyl index of the original PE powder, indicating that the oxidation of PE increased the interfacial adhesion with PCL and improved the blend properties. The preoxidized PE powder in combination with surfactant and pro-oxidant greatly accelerated the degradation rate of PCL as measured by molecular weight decrease during low temperature thermo-oxidative aging. This coincided with the fast initial increase in PE carbonyl index. The degradation accelerating effect was larger when preoxidized PE was blended with PCL as compared to when nonoxidized PE was added. However, the degree of preoxidation had minor impact on PCL degradation rate. Without PE powder the degradation rate of PCL was not enhanced by the addition of pro-oxidant and surfactant alone.