BC-chitosan

Because of the structural similarities of BC and chitosan, the composites of these two biopolymers combine the physicochemical 

Morphology -Well-organized -More compact and -Good dispersion 

The effect of chitosan on the crystallinity of the BC-chitosan composite from biosynthesis was not clearly observed because only a low concentration of chitosan [0-0.75% w/v] was added into the culture. At chitosan concentrations greater than 0.75% w/v, the production of cellulose was significantly affected [19]. 

A reduction crystallinity index [Cl] of the BC-chitosan composite synthesized with the impregnation method was observed when the chitosan content was increased the reduction also corresponded with an increased immersion time [71]. With the incorporation of chitosan in BC fibrils, BC hydrogen bonding was disturbed by the interaction between chitosan and BC [71]. Moreover, it suggested that because of this interaction, BC chains were difficult to move, resulting in the reduction of Cl [72]. 

With the addition of the chitosan solution into the culture medium for BC production, the BC-chitosan composite films were homogeneous with noticeably denser fibrils and smaller pore sizes compared with those of BC film [Fig. 14.6). A smaller pore size was obtained by increasing the MW of chitosan [19,73]. 

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When chitosan is added to the culture medium the BC/chitosan composites formed include the properties of both components, mainly an extraordinary bactericidal and barrier effect against microorganisms. Therefore, this modified BC is well suited for wound dressings [42]. 

Figure 14.6 SEM images of re-swollen films of BC [a], BC-chitosan prepared by adding 0.75% chitosan of MW 30,000 [b] and of MW 80,000 (c) in the culture medium.

Using the biosynthesis approach, a higher tensile strength, and Young s modulus of BC-chitosan composite were obtained by increasing the MW and concentration of chitosan. Because the fibrils became thicker, they could resist a stronger force than pure BC fibrils [19]. 

The WAC of the BC-chitosan composite from biosynthesis was enhanced approximately 120% in comparison with that of the BC film. The improvement of the WAC was affected by increasing the MW and concentration of chitosan in the culture medium [73]. 

During the impregnation technique, chitosan incorporating with BC fibrils could also enhance the WAC of the BC-chitosan composite because of the hydrophilicity of chitosan [71]. However,... 

As mentioned above, due to the small amount of chitosan added in the culture medium, the BC-chitosan composite obtained from the biosynthesis did not show inhibition effect the growth of Escherichia coli [E. coli) and Staphylococcus aureus [S. aureus). For antifungal activity, a slight inhibition was detected on the growth of Aspergillus niger A niger) [19]. 

The improved antibacterial activity of the BC-chitosan composite via the impregnation approach was reported. Firstly, the antimicrobial evaluation was performed by the direct contact of the composite with coli and S. aureus. The growth reductions of 99.9% were observed in both cultures. Secondly, the evaluation was performed by the disc diffusion method. Because of a tight incorporation between chitosan and BC, it resulted in no chitosan diffusion out of the composite. Therefore, no inhibitory clear zone was found [20],... 

Mechanical Properties of BC-Chitosan Films in Comparison to BC Films... 

Lin et al. [110] developed porous BC/chitosan nanocomposite membranes prepared by immersing BC membranes in a chitosan solution followed by freeze-drying. Histological examinations revealed that wormds treated with these BC/chltosan membranes epithelized and regenerated faster than those treated with pure BC membranes and therefore are considered as potential candidates for wound dressing materials. 

In a distinct vein, BC/chitosan membranes have been tested for pervaporative separation of binary aqueous-organic mixtures (ethanol/water) [111]. The substantially high pervaporative separation index (350 kg. x.m. h 0 and low activation energy (10 kj.mol ) are indicative of the high potential of BC/chitosan membranes in the pervaporative separation of ethanol/water azeotrope. Targeting to mimic the intrinsic antimicrobial properties of chitosan on BC nanofibrils, nanostructured BC nanocomposite membranes were obtained by surface functionalization with aminoalkyl groups (Figure 2.14) [114]. These bioactive nanostructured membranes also presented improved mechanical and thermal properties and may be useful for biomedical applications. 

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