Chitosan is a linear heteropolysaccharide composed of 2-amino-2-deoxy-glucose and 2-acetamido-2-deoxy-glucose units1 obtained by chemically deacetylating chitin extracted from shrimp and crab shells. Low-molecular-weight chitosan oligomers have received attention because of their interesting biological properties, including the inhibitory effects on the growth of fungi and bacteria2-6. Several enzymatic and chemical methods for producing chitosan oligomers have been described in literature. The chemical methods include acid hydrolysis with either cold nitrous acid or hot hydrochloric acW, phosphoric acid8 or hydrogen fluoride9. Nordtveit et al10 used hydrogen peroxide, which, in the presence of Fe(III), generates hydroxyl radicals which cleave the molecule by nucleophilic attack.
The chemical treatment is very common and fast, but it has some faults such as high cost, low yield and generation of acidic waste11. The enzymatic digestion is more popular because of its mild reaction conditions and good reproducibility12. Moreover, in enzymatic process, the hydrolysis course and product distribution are subject to more facile control, in spite of the faster rate of chemical reaction6. However, the high cost of specific enzymes, such as chitosanase and chitinase, inhibits their use on an industrial scale. Recently, several hydrolytic enzymes, such as lysozyme13 pectinases 14 , hemicellulase and papain 15 were found to cataylse the cleavage of the glycosidic linkage in chitosan.
Treatment with chitosan and its derivatives does not affect the dye uptake or its fastness in any significant way.
In this work, an attempt has been made to use cellulose enzymes for chitosan hydrolysis. Cellulases are already used commercially for biopolishing in textile processing 12. Experiments have been conducted to study the effect of enzyme concentration on the mol wt and degree of polymerisation (DP) of chitosan. The low molecular weight (LMW) derivatives have been characterised to study if they retain the properties characteristic of chitosan. They were then applied to cotton to study the effect on dye uptake, dye distribution and dye retention.
Materials and Methods
Cotton fabric of 110 gsm, having 98 epi and 84 ppi was used.
Chitosan, as an initial material, was obtained from Aldrich Chemicals. Cellulase enzyme, Ezysoft L Soft was provided by Resil chemicals, Bangalore. The stock solution of chitosan (0.05%) was prepared in 2% acetic acid with pH being adjusted to 5-5.5 with NaOH.
Preparation of sample by enzymatic hydrolysis
To 100 ml solution of chitosan (5%) in 2% acetic acid (maintained at pH 5-5.5), 5 ml enzyme solution was added. This solution was kept in water bath at 50C and 130 rpm for 3 hr after which the contents of the flask were boiled for 10-15 min to deactivate the remaining enzyme present in the flask. The same procedure was done with 7 ml, 9 ml, 11 ml, 13 ml and 15 ml of enzyme solution.
Solubility of samples at various pH
Chitosan is insoluble in water and soluble in aqueous dilute and organic acids. The solubility of chitosan and degraded chitosan was tested in water as well as in solutions of different pH. 2% solution of acetic acid and sodium hydroxide was prepared separately for adjusting the solution pH to 3, 4, 5, 7 and 9 at room temperature.
The degree of deacetylation was determined by FTIR analysis16. FTIR spectra were recorded with KBr pellet on a Perkin Elmer Spectrum 1B spectrophotometer. The viscosity change was investigated using an Ubbelohde Viscometer. The viscosity molecular weight was calculated based on Mark Houwink equation17 ([η] = KM v a). Here, DD is the degree of the deacetylation of chitosan expressed as percentage.