Nattakan Soykeabkaew

Investigation into the structural, morphological, mechanical and thermal behaviour of bacterial cellulose after a two-step purification process.

Bacterial cellulose (BC) is a natural hydrogel, which is produced by Acetobacter xylinum (recently renamed Gluconacetobacter xylinum) in culture and constitutes of a three-dimensional network of ribbon-shaped bundles of cellulose microfibrils. Here, a two-step purification process is presented that significantly improves the structural, mechanical, thermal and morphological behaviour of BC sheet processed from these hydrogels produced in static culture. Alkalisation of BC using a single-step treatment of 2.5 wt.% NaOH solution produced a twofold increase in Youngs modulus of processed BC sheet over untreated BC sheet. Further enhancements are achieved after a second treatment with 2.5 wt.% NaOCl (bleaching). These treatments were carefully designed in order to prevent any polymorphic crystal transformation from cellulose I to cellulose II, which can be detrimental for the mechanical properties. Scanning electron microscopy and thermogravimetric analysis reveals that with increasing chemical treatment, morphological and thermal stability of the processed films are also improved.

Self-reinforced poly(lactic acid) nanocomposites with integrated bacterial cellulose and its surface modification

Abstract Bacterial cellulose (BC) nanofibers, with and without silane surface modification, were incorporated into self-reinforced poly(lactic acid) (SR-PLA) nanocomposites at 1 and 10 wt%. Disintegrated BC was combined with electrospun PLA fiber mats by film stacking and compression molding at 165 °C for 40 sec to obtain SR-PLA/BC hybrid films. The effect of nanocellulose addition and its surface modification on the structure, morphology, and properties of the resulting composites were investigated. It was found that BC was a highly effective reinforcement for SR-PLA nanocomposites, providing a noticeable increase in the film’s strength and modulus. Moreover, surface modification of BC was shown to further enhance the film performances due to an improved PLA/BC interfacial interaction. At an optimum BC content, these hybrid films also exhibited outstanding ductility and toughness. Water vapor barrier properties were also enhanced, especially when modified BC was integrated in the SR-PLA films. Graphical Abstract