Julien Bras

Non leaching biomimetic antimicrobial surfaces via surface functionalisation of cellulose nanofibers with aminosilane

Uncontrolled growth of bacteria is always a major concern for various industries such as food, cosmetic and pharmaceutical industries. Taking this issue into account, a non-leaching antimicrobial surface was developed using cellulose nanofibers with a post grafting green method to mimic the antibacterial activity of chitosan. A series of experiments was designed for silylation of nanofibers with 3-aminopropyl trimethoxysilane, varying the initial concentration of silane and the solvent employed during the grafting. The results, validated by Fourier transform infrared spectroscopy, thermogravimetric analysis and elemental analysis, provided evidence of successful functionalization. Moreover, SEM–EDX indicated that a heterogeneous grafting occurred at the surface and cross section of the film. Strong antimicrobial activity against gram positive (Bacillus subtilis and Staphylococcus aureus) and gram negative (Escherichia coli) was recorded. In aqueous solution, the optimum results were obtained using grafting silane concentration of 50xa0g/L. The grafted CNF showed no change in the morphology or thermal stability, meanwhile a significant reduction in bacterial concentration of 1.3 logs for B. subtilis, 1.8 log for S. aureus and 3.8 logs for E. coli was observed. Regarding the solvent used during the grafting, acetone showed the reversibility of bonds between silanol groups and cellulose nanofibers or high self-condensation reaction which was depicted by the Si NMR and formation of zones of inhibition. Furthermore, water employed as grafting solvent depicted better grafting efficiency than acetone, 10.2 versus 6.4xa0% respectively, at the similar concentration with apparent lower grafting time.

Engineered pigments based on iridescent cellulose nanocrystal films.

A simple method to produce biobased iridescent pigments from cellulose nanocrystal (CNC) films is reported. The process consists of forming nanostructured films from a CNC liquid-crystalline suspension and an appropriate dry grinding. The features of the iridescent pigments are described; they have a flake-like morphology with a thickness of 25 μm. However, because of the presence of sulfate groups, thermal degradation and high redispersion in water occur, which affect the iridescent property of these biobased pigments. To overcome such limitations, two post-treatments are proposed. The sulfate ester groups are removed from the iridescent pigments with vacuum overdrying. The mass loss of iridescent pigment in water is reduced with an increase of the ionic strength in the aqueous medium by NaCl addition. These post-treatments have proven to be efficient and engineered pigments based on CNC films can be used to add anticounterfeiting features to packaging manufactured by classical paper techniques or extrusion.