Effect of hot calendering on physical properties and water vapor transfer resistance of bacterial cellulose films

This work investigates the effect of hot calendering on bacterial cellulose (BC) films properties, aiming the achievement of good transparency and barrier property. A comparison was made using vegetal cellulose (VC) films on a similar basis weight of around 40 g.m-2. The optical-structural, mechanical and barrier property of BC films were studied and compared with those of highly beaten VC films. The Youngs moduli and tensile index of the BC films are much higher than those obtained for VC (14.5 16.2 GPa vs 10.8 8.7 GPa and 146.7 64.8 N.m.g-1 vs 82.8 40.5 N.m.g-1), respectively. Calendering increased significantly the transparency of BC films from 53.0 % to 73.0 %. The effect of BC ozonation was also studied. Oxidation with ozone somewhat enhanced the brightness and transparency of the BC films, but at the expenses of slightly lower mechanical properties. BC films exhibited a low water vapor transfer rate, when compared to VC films and this property decreased by around 70 % following calendering, for all films tested. These results show that calendering could be used as a process to obtain films suitable for food packaging applications, where transparency, good mechanical performance and barrier properties are important. The BC films obtained herein are valuable products that could be a good alternative to the highly used plastics in this industry.The authors thank FCT (Fundação para a Ciência e Tecnologia) and FEDER (Fundo Europeu de Desenvolvimento Regional) for the financial support of the project FCT PTDC/AGR-FOR/3090/2012— FCOMP-01-0124-FEDER-027948 and the awarding of a research grant for Vera Costa

Pretreatment-dependent surface chemistry of wood nanocellulose for pH-sensitive hydrogels

Nanocellulose from wood is a promising material with potential in various technological areas. Within biomedical applications, nanocellulose has been proposed as a suitable nano-material for wound dressings. This is based on the capability of the material to self-assemble into 3D micro-porous structures, which among others have an excellent capacity of maintaining a moist environment. In addition, the surface chemistry of nanocellulose is suitable for various applications. First, OH-groups are abundant in nanocellulose materials, making the material strongly hydrophilic. Second, the surface chemistry can be modified, introducing aldehyde and carboxyl groups, which have major potential for surface functionalization. In this study, we demonstrate the production of nanocellulose with tailor-made surface chemistry, by pre-treating the raw cellulose fibres with carboxymethylation and periodate oxidation. The pre-treatments yielded a highly nanofibrillated material, with significant amounts of aldehyde and carboxyl groups. Importantly, the poly-anionic surface of the oxidized nanocellulose opens up for novel applications, i.e. micro-porous materials with pH-responsive characteristics. This is due to the swelling capacity of the 3D micro-porous structures, which have ionisable functional groups. In this study, we demonstrated that nanocellulose gels have a significantly higher swelling degree in neutral and alkaline conditions, compared to an acid environment (pH 3). Such a capability can potentially be applied in chronic wounds for controlled and intelligent release of antibacterial components into biofilms

Hydrothermal decomposition of various crystalline celluloses as treated by semi-flow hot-compressed water

Various types of crystalline celluloses I, II, IIII, IIIII, IVI and IVII that have been adjusted for their degree of polymerization were treated by semi-flow hot-compressed water (HCW) at 230–270 °C/10 MPa/15 min to study their hydrothermal decomposition. The treatments resulted in either partial or complete decomposition of the celluloses and the decomposed products were primarily recovered as hydrolyzed, dehydrated and fragmented ones as well as organic acids in the water-soluble (WS) portions. Their results of hydrothermal decomposition and its kinetics revealed that the celluloses decomposition is dependent on the types of crystalline celluloses as well as temperature of the HCW treatment. The outcome from the WS portions at 270 °C/10 MPa/15 min showed that the degree of difficulty for decomposition is lower in group II (cell II, cell IIIII, cell IVII) than group I (cell I, cell IIII, cell IVI), indicating that group II is less resistant to decomposition by HCW treatment. Therefore, the decomposition behaviors of the cellulose are due to the inherent differences in the crystalline structures

Decomposition behaviors of various crystalline celluloses as treated by semi-flow hot-compressed water

Various types of crystalline cellulose consisting of group I (cell I, IIII, IVI) and group II (cell II, IIIII, IVII) prepared from cotton linter were adjusted for their degree of polymerization (DP) as starting materials. These celluloses were then treated by semi-flow hot-compressed water (HCW) at 230–270 °C/10 MPa/2–15 min to study their decomposition behaviors. The treatments performed resulted in residues of celluloses and water-soluble (WS) portions. Consequently, the crystallinity of the residues was found to remain the same, but the DP was reduced as the temperature increased. Additionally, X-ray diffractometry and Fourier transform-infrared analyses demonstrated that crystallographic changes occurred for residues of cell IIII, IVI and IIIII. Despite these changes, the overall results of the residues showed that group I has higher resistance to decomposing than group II. As for the WS portions, the yields of the hydrolyzed and degraded products were higher in group II than group I, indicating that group II is less resistant to decomposition by HCW treatment. Results for both the residues and WS portions are in agreement with each other, showing that the degree of difficulty of decomposition was higher in group I than group II. Therefore, the decomposition behaviors of the celluloses are due to differences in the crystalline forms