Introduction

In recent years, the use of low-environmental impact biotechnology has increased in the textile sector, giving rise to new types of treatment. The use of enzymes to improve white colour, shrinking behaviour, dyeing affinity, and hand & pilling behaviour in the woollen sector is particularly interesting [2, 6, 1].

To reach this last objective, two knitted fabrics (single jersey) were produced with the same construction characteristics: mass per unit area, cover factor, and yarn count used. To evaluate the effect of enzyme treatment on the yarn structure with the different fibre diameters in relation to the pilling behaviour, the only variable was the mean diameter of the wools used to produce the yarns,

19.2 µm and 25.6 µm. Both fabrics were given the IWS Super Wash treatment.

These fabrics were treated at different enzyme concentrations, and then subjected to a pilling test using the pilling box method (Woolmark TM 12); furthermore the fibre damage caused by the enzyme treatments were highlighted by the perforation strength test using the sphere method (Standard UNI 5421), and by observations made using a Scanning Electron Microscope (Cambridge model 435 PV).

Experimental

Knitted fabric

The knitted fabrics used has the following characteristics: Yarn count: Tex 42 *2 Twist folded yarn: 199 turns/m S Twist single yarn: 466 turns/m Z Rows/cm: 8 Stitches/cm: 6.5 Cover factor: 14.2 Mass per unit area: 292 g/m²

The fabric samples will be referred to as sample 19.2 µm and sample 25.6 µm in the following work.

Enzyme treatment

The two fabrics were treated with proteolytic enzyme, active at pH 6 and a temperature of 65°C at the following concentrations: 0.5, 1, 2.5 and 5 g/l.

The treatments were performed in an Ahiba PC 100 dyeing machine, which permits temperature control and constant movement of liquor.

Four samples with a diameter of 20×20 cm were treated using a liquor ratio of 1:50, immersing them in the different enzyme concentrations, at 65°C in a buffer solution (at pH 6) of 0.1M citric acid and Na2HPO4, containing 0.1 g/l non-ionic surfactant Tween 60, in the Ahiba device, in agitation for 55 min.

The entire solution was then raised to a temperature of 80°C for 30 min. to deactivate the enzyme. At the end, the samples were removed from the bath, washed with distilled water, and spun and dried in a fan oven at 45°C for about 1 hour. To provide more homogenous comparisons, the control sample (0 g/l) underwent the same treatment.

Results

Pilling strength

One important quality aspect of knitted fabrics is their pilling strength. To check whether enzyme treatments modify the pilling behaviour of knitted fabric samples, tests were preformed on the samples using the ’pilling box’ method (Woolmark Standard TM 152).

The results, expressed as a number from 5 to 1, are defined as follows: 5 – no change; 4 – slight change; 3 – moderate change; 2 – significant change; 1 – severe change.

Figure 1. Resistance to pilling versus enzymatic concentration

From Figure ,1 we can note that both samples improve their pilling strength with an increase in enzyme concentration; in particular, sample 25,6 µm showed a more marked improvement in pilling behaviour, since the fibres have a greater diameter [7].

To complete what has been said above, below is a series of photographs (Figure 2, 3, 4, 5, 6) showing the pilling strength of sample 19.2 µm as a function of the different enzyme concentrations.

Figure 2. 0 g/l -19.2 Figure 3. 0.5 g/l -19.2 µm

µm 

Figure 4. 1g/l -19.2 Figure 5. 2.5 g/l -19.2 µm

µm 

Figure 6. 5 g/l -19.2 µm Fibre damage: perforation strength and SEM observations The fibre damage caused by the enzyme treatments is highlighted both by the perforation strength test (Standard UNI 5421-sphere method) and by observations made using a scanning electron microscope.

Figure 7 shows the percentage reduction in perforation strength plotted against the enzyme concentration.

The 25.6 µm sample shows a greater loss in percent of perforation strength in comparison with the

19.2 µm sample. This is probably demonstrated by a smaller quantity of fibres in section in the 25.6 µm sample in comparison with the 19.2 µm sample, as well as an easier penetration of enzyme on the yarn structure.

Figure 7. Loss in percent of perforation strength versus enzymatic concentration

The breakage of the fibres is the consequence of the loss of the structure and of the leakage of cortical cell material. The proteases preferentially attack the CMC, and can penetrate it by channelling beneath the cuticular scales. After diffusion into the interior of the fibre, the protease is able to hydrolyse the proteins of the cell membrane complex, completely damaging the fibre unless properly controlled [4, 3, 5].

Figure 8. 25.6 µm sample with 2.5 g/l of enzyme (SEM 243X)

The type of damage to the 25.6 µm sample caused by the enzyme action at 2.5 g/l and 5 g/l is shown respectively in Figure 8 and Figure 9, in which we can see that at a concentration of 2.5 g/l the fibrillar damage is quite contained, while it is decidedly greater at 5 g/l.

Figure 9. 25.6 µm sample with 5 g/l of enzyme (SEM 243X)

This is also demonstrated by the analysis shown in Figure 10, which shows the percentage loss of weight plotted against the enzyme concentration.

Concluding remarks

It is evident that both samples improve their performances with regard to pilling strength. It should be noted that at an enzyme concentration of 2.5 g/l, which corresponds to an acceptable level of fibre damage, the 19.2µm sample improves its pilling strength going from grade 2 of the sample treated without enzymes to grade 3; while for the 25.6 µm sample, an acceptable level of fibre damage corresponds to 1g/l of enzyme concentration; this sample improves its pilling strength going from grade 2-3 of the sample treated without enzymes to grade 3-4.

The probable explanation for the reduction in pilling following the enzyme treatment can be explained by the mechanism of pill formation as described by Cooke when he speaks of ‘anchor’ fibres which bind the pills to the fabric surface. The action of the enzymes weakens the structure of the fibres and leads to their fracture, with consequent detachment of the pills from the surface of the fabric.

References

1. Bishop D. P., Dhen J., Heine E., Hollfelder B., ‘The use of proteolytic enzymes to reduce wool-fibre stiffness and prickle’, JTI, 89, 546-553, 1998.
2. Clark D., ‘Enzyme treatment for removing pills from garment dyed goods’, International Dyer, 178, 20-21, 1993.
3. Galante Y. M., Foglietti D., Tonin C., Innocenti R., Ferrero F., Monteverdi R., Enzyme Applications in Fiber Processing, American Chemical Society, 24, 294-305, 1998.
4. MacLaren J. A., Milligan B., Wool Science, Structure and Composition, Science Press, 1981.
5. Mossotti R., Innocenti R., Galante Y. M., ‘Studies and properties of wool treated with proteases’, Quimica Têxtile-Calquim, 71, 6-16, 2003.
6. Nolte H., Bishop D. P., Hocker H., ‘Effects of proteolytic and lipolytic enzymes on untreaded and shrink-resist-tested wool’, JTI, 87 part I, 212-226, 1996.
7. Ukponmwan J.O., Mukhopadhyay A., Chatterjee K. N., Pilling, Textile progress, 28, 1998.

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