The majority of cotton denim production today is “surface polished” with enzymes to yield improved softness, reduced pilling propensity and brighter colors. Both nontoxic and environmentally friendly, enzymatic treatment has recently been expanded to cellulosic woven and knitted goods and to cellulosic blends as more specific enzyme preparations became available at affordable costs. Very small quantities are sufficient to achieve the desired effect.
However, many aspects of the hydrolysis reaction are not yet frilly understood on the molecular level, such as the preferred enzyme attacking sites, enzymatic degradation in the presence of dyes or finishing compounds and the role of mechanical action. With this understanding we hope to develop a predictive model.
Enzymatic treatment to enhance wettability and absorbency of textiles:
Textile fibers are treated with enzymes in the absence of surfactants, with the effect of increasing the wettability and absorbency of the fibers. The enzymes are pectinases, cellulases, proteases, lipases or combinations thereof. The wetting properties of cotton fibers are found to be most substantially improved by treatment with a mixture of cellulase and pectinase.
The effects of five hydrolyzing enzymes on improving the hydrophilicity of several polyester fabrics have been studied. Four out of the five lipases studied improve the water wetting and absorbent properties of the regular polyester fabrics more than alkaline hydrolysis under optimal conditions (3N NaOH at 55° C. for 2 hours). Compared to aqueous hydrolysis, the enzyme reactions have shown to be effective under more moderate conditions, including a relatively low concentration (0.01 g/L), a shorter reaction time (10 minutes), at an ambient temperature (25° C.). Contrary to the results with alkaline hydrolysis, the improved water wettability is accompanied by full strength retention. Lipase has also shown to be effective in improving the wetting and absorbent properties of sulfonated polyester and microdenier polyester fabrics.
Enzymatic Hydrolysis of Cellulose:
Enzymatic hydrolysis is a complicated reaction whereby three main components of the cellulase complex work synergistically to break down the substrate. Endo-type cellulases attack the cellulose chain at random in accessible areas while exo-type cellulases cause chain scission from the non-reducing end to form smaller fragments. The smaller fragments are further broken down to yield glucose as the end product (See Figure).
While the enzyme components work as a team, the degradation products have a controlling, inhibiting function. Each factor disturbing the breakdown pattern seriously influences the end result.
Effects of Enzymatic processes on fabric weight:
After the bio-polishing process, 1-5 % loss in fabric weight is an expected result. This amount shows the efficiency of the process. Weight loss of enzymatic-treated fabric samples after pre-treatment was slightly higher than for those which the expense of basic fabric requirements such as strength and weight.
The reasons for the slightly higher weight loss of fabric samples enzymatically treated after pre-treatment than those after dyeing are the high number of process phases, the high amount of mechanical forces and the long process period, which cause the removal of the fuzzes from yarn surface. When the weight loss is compared according to the yarn spinning system, the fabric from carded yarn has the highest value while that from open-end yarn has the lowest. The amount of weight loss that occurs after the double enzymatic treatment is significantly higher. Because of the higher loss of weight, the double enzymatic treatment is not recommended for normal applications.
When the color difference values of dyed fabrics are examined, one readily notices more severe deviations in color shade on the twice enzymatically treated fabrics. This is most probably because of the difference in light reflection together with yarn surface modification. This is consistent with weight and strength loss in twice bio-polished fabrics. However, one should take into account the usage of various reactive dyestuff combinations for different colors in textile applications (which is particularly important for mixed colors such as khaki and grey). This may cause diverse results to be presented.
Effects of Enzymatic processes on strength :
The bio-polishing process partly hydrolyses the cotton, which has a negative effect on fabric strength level. Fabrics from combed yarns gave the best strength values for untreated and enzymatic treated in three different stages, rather than fabrics from carded and open-end yarns.
The fabric samples’ strength loss caused by enzymatic treatment after pre-treatment or dyeing processes is nearly the same in all type of fabrics, approximately around 11%. In fabric samples enzyme-treated twice after pre-treatment together with the dyeing processes, loss in strength is about 25 % in average, and the fabric samples from combed yarn exhibit a noticeably higher loss of strength.
Effects of Enzymatic processes on color change :
The color differences (ΔE) of fabrics after enzymatic processes at different steps and untreated fabrics were measured. As Figure 8 shows, the greatest color difference values were observed in the fabric samples that had been enzyme-treated twice after pre-treatment together with dyeing processes.
Effects of Enzymatic Treatment on Various Spun Yarn Fabrics:
100% open-end, carded and combed ring-spun 20 tex (Ne 30) cotton yarns, produced from the same blend, were used. The physical properties of the yarns are tabulated briefly in Table 1. In this research, single jersey fabrics knitted from the above-mentioned yarns were used.
Table 1. Physical properties of yarns.
|Breaking elongation||% E||5.6||5.6||4.4|
|Variation of strength||% CV||7.5||7.8||8.0|
|Thin places ( -50%)||–||2||17||88|
|Thick places (+50%)||–||19||175||142|