Biodegradability of Poly-3-hydroxybutyrate/Bacterial Cellulose Composites under Aerobic Conditions, Measured via Evolution of Carbon Dioxide and Spectroscopic and Diffraction Methods.

Poly-3-hydroxybutyrate (PHB) and bacterial cellulose (BC) are both natural polymeric materials that have the potential to replace traditional, nonrenewable polymers. In particular, the nanofibrillar form of bacterial cellulose makes it an effective reinforcement for PHB. Neat PHB, bacterial cellulose, and a composite of PHB/BC produced with 10 wt % cellulose were composted under accelerated aerobic test conditions, with biodegradability measured by the carbon dioxide evolution method, in conjunction with spectroscopic and diffraction methods to assess crystallinity changes during the biodegradation process. The PHB/BC composite biodegraded at a greater rate and extent than that of PHB alone, reaching 80% degradation after 30 days, whereas PHB did not reach this level of degradation until close to 50 days of composting. The relative crystallinity of PHB and PHB in the PHB/BC composite was found to increase in the initial weeks of degradation, with degradation occurring primarily in the amorphous region of the material and some recrystallization of the amorphous PHB. Small angle X-ray scattering indicates that the change in PHB crystallinity is accompanied by a change in morphology of semicrystalline lamellae. The increased rate of biodegradability suggests that these materials could be applicable to single-use applications and could rapidly biodegrade in compost on disposal.

In situ modifications to bacterial cellulose with the water insoluble polymer poly-3-hydroxybutyrate.

Bacterial cellulose is a pure, highly crystalline form of cellulose produced from the bacteria Gluconacetobacter xylinus that has become of increasing interest in materials science due to its nanofibrillar structure, ideal for incorporation into other materials as a reinforcing material. The morphology and properties of bacterial cellulose can be altered by including additives not specifically required for growth of the bacteria in liquid media. The bioplastic poly-3-hydroxybutyrate (PHB), along with hydroxypropylmethyl cellulose (HPMC) and Tween 80 were selected and added to the growth media at different concentrations to examine their impact on the resulting cellulose, leading to changes in yield, crystallinity and morphology. The crystallinity index of the nanofibrils was found to vary greatly when using these different methods to calculate it from XRD data, indicating that particular care must be taken when comparing crystallinity results reported in the literature. PHB was able to be incorporated into the bacterial cellulose fibrils during production, increasing the potential for favourable interactions of the bacterial cellulose microfibrils with a neat PHB matrix with the aim of making a fully degradable nanocomposite system.

Altering the growth conditions of Gluconacetobacter xylinus to maximize the yield of bacterial cellulose.

An extensive matrix of different growth conditions including media, incubation time, inoculum volume, surface area and media volume were investigated in order to maximize the yield of bacterial cellulose produced by Gluconacetobacter xylinus, which will be used as reinforcement material to produce fully biodegradable composites. Crystallinity was shown to be controllable depending on the media and conditions employed. Samples with significant difference in crystallinity in a range from 50% to 95% were produced. Through experimental design, the yield of cellulose was maximized; primarily this involved reactor surface area design, optimized media and the use of mannitol being the highest cellulose-producing carbon source. Increasing the volume of the media did achieve a higher cellulose yield, however this increase was not found to be cost or time effective.