Crystallization phenomena in bacterial poly[(R)-3-hydroxybutyrate]. 2. Embrittlement and rejuvenation

Poly[(R)-3-hydroxybutyrate] (I) (Biopol) is a bacterial storage polymer, currently receiving much attention because of its potential as a biodegradable plastic. A major drawback of I is its intrinsic brittleness. Although as-molded I shows ductile behavior, upon storage at ambient temp. is detrimental aging process seriously embrittles the material and restricts its application possibilities. This remarkable embrittlement is delineated in the present study and could be attributed to progressive crystn. By using a simple annealing treatment I can be rejuvenated while subsequent aging is prevented to a large extent. This observation might considerably enlarge the applicability of

Ageing phenomena in bacterial poly[(R)-3-hydroxybutyrate]. 1. A study on the mobility in poly[(R)-3-hydroxybutyrate] powders by monitoring the radical decay with temperature after gamma-radiolysis at 77 K

The use of ESR in combination with g irradn. for examg. the segmental mobility was successful in bacterial poly[(R)-3-hydroxybutyrate] (I) powder. The aging process in the virgin I powder was analogous to that in the molded sampl

Crystallization phenomena in bacterial poly[(R)-3-hydroxybutyrate]: 3. Toughening via texture changes

Poly[(R)-3-hydroxybutyrate] (I) is a bacterial storage polyester that is genuinely biodegradable, but its brittleness hampers its wide applicability as a biodegradable plastic. Most attempts to improve the mech. properties of I have focused on incorporating comonomers, but at the expense of prodn. costs. Strikingly, it appeared possible to toughen I using a simple annealing treatment. The present study attributes this remarkable phenomenon to a change in the lamellar morphol., which reduces the amorphous-cryst. interface area and thus the constraint imposed on the amorphous chains by the crystals. This elevates the relaxation strength of the amorphous regions, giving rise to the favorable fracture behavio

A biodegradable rubber by crosslinking poly(hydroxyalkanoate) from Pseudomonas oleovorans

Poly((R)-3-hydroxyalkanoate)s (PHAs) are bacterial storage polyesters, currently receiving much attention because of their potential application as biodegradable and biocompatible plastics. Among them are the PHAs from Pseudomonas oleovorans, which are semicryst. elastomers. Their applicability is seriously limited by their low melting temp. as well as by their low crystn. rate. Both problems were overcome by crosslinking of unsatd. pendent groups, which were incorporated in the polymer by tailoring the carbon source for biosynthesis. Crosslinking was established by electron-beam irradn. and resulted in a true rubber with const. properties over a large temp. range from -20 to +170 DegC. Even after crosslinking, the material was still biodegradable. To the authors' knowledge this is the first microbially produced biodegradable rubbe