No abstract

Poly[(R)-3-hydroxybutyrate] (PHB) 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 mechanical properties of PHB have focused on incorporating comonomers, but at the expense of production costs. Strikingly, it appeared possible to toughen PHB homopolymer using a simple annealing treatment. The present study attributes this remarkable phenomenon to a change in the lamellar morphology, which reduces the amorphous-crystalline 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 favourable fracture behaviour.

Document VersionPublisher's PDF, also known as Version of Record (includes final page, issue and volume numbers)Please check the document version of this publication:• A submitted manuscript is the author's version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. People interested in the research are advised to contact the author for the final version of the publication, or visit the DOI to the publisher's website.• The final author version and the galley proof are versions of the publication after peer review.• The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal ? Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Grisebachstrasse 8, 37077 G6ttingen, Germany (Received 20 September 1993) 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 semicrystalline elastomers. Their applicability is seriously limited by their low melting temperature as well as by their low crystallization rate. Both problems were overcome by crosslinking of unsaturated pendent groups, which were incorporated in the polymer by tailoring the carbon source for biosynthesis. Crosslinking was established by electron-beam irradiation and resulted in a true rubber with constant properties over a large temperature range from -20 to + 170°C. Even after crosslinking, the material was still biodegradable. To our knowledge this is the first microbially produced biodegradable rubber.

Poly[ (R)-3-hydroxyalkanoate]s (PHAs) are bacterial storage polyesters, which are accumulated by a range of micro-organisms as intracellular granules. In contrast to the isolated PHA, the nascent polymer in the granules does not crystallize but remains amorphous at ambient temperature. A lot of studies have been devoted to this phenomenon and all claimed the in vivo presence of a highly effective plasticizer. In contrast, this paper demonstrates that the native granules do not contain a plasticizer and that the amorphous state of in vivo PHA can be explained simply by straightforward crystallization kinetics.

Poly[(R)-3-hydroxybutyrate] (PHB), a bacterial polyester, is subject to a detrimental ageing process, which hampers its application possibilities. This ageing phenomenon is usually studied using moulded specimens, and was found to be related to a loss in segmental mobility. The presence of additives and orientation in moulded PHB samples might influence this ageing process. As a reference for our ageing studies, we therefore conducted a study on the ageing effects in virgin PHB powder. For this purpose a method is required to measure the mobility in a powder without the employment of heat or mechanical strain, since these are known to induce deageing. This paper describes a suitable technique based on the principle that the variation of the radical concentration with temperature after y-irradiation at 77 K provides a measure of the changes in the segmental mobility of the polymer chains.