In our attempt to impart certain desired properties to wool fabric, we adopted a degradative method using protease enzyme from either bovine pancreas Type I (Enzyme I) or Streptomyces griseus Type XIV (Enzyme II), additive treatment using poly amino siloxane (PAS), or a combination thereof. Although different classes have been utilize for chemical processing of wool [22–24], yet and up tour knowledge, none of these investigations has been directed towards improvement of the fabric drape for the sake of better aesthetic properties of the final garment.
3.1. Effect of enzyme concentration and bio-treatment time
In our attempt to improve the drapability of wool fabric using degradative (protease from bovine pancreas Type I), additive (polymer deposition using PAS), or even combination thereof; the net weight loss or gain will be of prime importance. In Table 3, the effect of enzyme concentration on the drape coefficient as well as the weight of the bio-treated wool fabric, was elucidated. The data of this table shows that treatment of wool with enzyme I resulted in noticeable improvement in the fabric drapability (as indicated by the decrease in the drape coefficient). As the enzyme concentration increased from 0.5 up to 1.5% (o.w.f.), the drape coefficient decreases. No appreciable change on the fabric drape coefficient was monitored upon increasing the enzyme concentration from 1.5–2%. The limited in the bio-treated fabric drapability could be attributed to the partial removal of the scales of wool surface which constitutes the hardest part of wool [25]; thus the fabric elasticity and drapability would be improved accordingly. On the other hand, a maximum loss in weight of 2.1% was recorded upon bio-treatment of wool with the said enzyme.
Table 3: Effect of enzyme concentration on the bending stiffness and weight of biotreated wool fabric using Enzyme I (Treatment conditions: 1h at pH 7.5 at 37°C; MLR: 1:30)
Enzyme conc. (% o.w.f.)
|
Drape coefficient (%)
|
Weight loss %
|
Untreated
|
43.44
|
0.0
|
0.5% for 1h
|
42.87
|
0.84
|
1.0% for 1h
|
42.29
|
1.17
|
1.5% for 1h
|
42.02
|
1.22
|
2.0% for 1h
|
42.00
|
2.10
|
The effect of bio-treatment duration on the fabric drape coefficient and weight of wool fabric was investigated, and the results were summarized in Table 4. It is obvious from this table that as the treatment duration time increased, the fabric drapability increased. Bio-treatment of wool fabric with 1.5% (o.w.f.) enzyme I for 24 h resulted in improvement of the fabric drape by a factor of ca. 6.5% with a loss in weight within the acceptable limits (4.5%).
Table 4: Effect of bio-treatment time on the bending stiffness and weight of biotreated wool fabric using Enzyme I [Treatment conditions: 1.5% (o.w.f.), pH 7.5 at 37°C; MLR: 1:30]
Treatment duration (h)
|
Drape coefficient (%)
|
Weight loss %
|
Untreated
|
43.44
|
0.0
|
1 h
|
42.02
|
1.22
|
5 h
|
41.74
|
2.17
|
10 h
|
41.37
|
3.05
|
24 h
|
40.62
|
4.50
|
1.5% Enzyme II for 24 h
|
40.02
|
8.5
|
For comparison, wool fabric was treated with 1.5% (o.w.f.) of enzyme II for 24 h. The extent of improvement in the fabric drape coefficient (7.87%) which is higher than the corresponding value in case of enzyme I. The loss in weight in case of enzyme II-treated wool is significantly higher than that in case of wool treated with enzyme I.
It is worthy to mention that loss in weight of the bio-treated wool fabric was compensated by post-treatment with the PAS; thus, there will be no appreciable net weight loss at the final stage of the finished wool fabric.
3.2. Physical properties
The effects of bio-treatment and/or PAS-treatment of wool fabrics on some of its inherent physical characteristics were monitored by testing their yellowness index, wettability, air permeability, water permeability, and electrostatic charge. The results of this investigation, summarized in Table 5, revealed the followings:
-
Bio-treatment of wool with Enzyme I or II resulted in decreasing its degree of yellowness; presumably due to descaling of the fibre surface [26]. On the other hand, the yellowness index of wool was slightly increased under the influence of heat during curing of the PAS-post-treated wool [27].
-
The remarkable improvement in the wettability of the bio-treated wool could be attributed to the removal of the outermost lipid barrier from wool surface as a result of partial descaling of wool [28]. The fabric wettability was even enhanced by post-treatment of wool of the amino-groups containing silicon-based softener.
-
The air permeability (AP) of wool fabric was enhanced to a limited extent upon bio-treatment with the said enzymes, indicating that no alteration in the fabric porosity was taken place upon finishing of wool with enzyme I or II. Treatment of wool with the PAS led to remarkable decrease in its AP, most probably due to a decrease in the fabric porosity by virtue of the encapsulation of wool fibres with a thin layer from the used PAS. Similar trend was observed regarding the water permeability of the treated wool fabrics. These findings assure that the principal parameters which influence the fabric air and water permeability were not drastically affected; such as yarn and fabric type and structure.
-
Whereas the electrical conductivity of the bio-treated fabrics is almost the same as the untreated one, the PAS-treated fabric exhibited higher ability to impede the formation of electrostatic charges, as indicated by the higher AC conductivity value for the latter. This may be attributed to the induction of new hydrophilic groups (the amino groups) into the PAS-treated fabric, a factor which is of great importance in preventing formation of electrostatic charge on fabric surface [29].
Table 5: Effect of bio-treatment of wool fabric with Enzyme I and/or PAS on some of its inherent physical characteristics
Sample code
|
Yellowness index
|
Wettability (min)
|
Air perm. (cm3/s/cm2)
|
Water perm. (cm3/cm2.L)
|
AC conduct. (S/cm)
|
B
|
22.40
|
Up to 30 min
|
74.08
|
1.12
|
3.99 x 10− 5
|
I
|
15.30
|
5.7
|
76.88
|
1.13
|
4.00 x 10− 5
|
II
|
16.44
|
5.1
|
79.37
|
1.03
|
4.00 x 10− 5
|
III
|
24.09
|
12.5
|
60.14
|
9.74
|
4.00 x 10− 5
|
IV
|
23.30
|
1.2
|
70.23
|
9.44
|
9.40 x 10− 5
|
V
|
19.16
|
1.0
|
71.46
|
9.37
|
1.17 x 10− 4
|
3.3. Mechanical properties
The effect of treatment of wool fabric with protease/PAS softener on some of its mechanical properties was monitored. Results of this investigation, tabulated in Table 6, elucidate that bio-treatment of wool fabric with enzyme I or II decreased its tensile strength, while post-treatment with PAS re-increased the tensile strength, compared to the untreated sample. This finding is a direct consequence of the degradative nature of bio-treatment and additive nature of polymer deposition. On the other hand, the elongation at break of either bio-treated or polymer-treated samples was not adversely influenced.
Results in Table 6 reveal also the bending length of wool fabric treated with protease/PAS system is lower than that of the biotreated or PAS-treated fabrics, and each of the latter has lower bending length than the untreated sample. Whereas the removal of the rigid cystine-rich scales of bio-treated wool might be the reason of the decrease in the bending length [30]; the softening action imparted to wool fabric by application of PAS may rationalize the reduced bending length of the PAS-treated fabric [31]. These results are in harmony with the drape coefficient values of the treated sample (c.f. Table 6).
Table 6: Effect of bio-treatment of wool fabric with Enzyme I and/or PAS on some of its mechanical characteristics
Sample code
|
Tensile strength (Kg)
|
Elongation (%)
|
Bending length (Cm)
|
B
|
21.4
|
55.0
|
4.0
|
I
|
17.9
|
50.2
|
3.6
|
II
|
17.4
|
48.9
|
3.8
|
III
|
22.4
|
48.5
|
3.3
|
IV
|
19.8
|
53.6
|
3.0
|
V
|
19.7
|
54.1
|
2.8
|
3.4. Fabric drapability
The drape coefficient of the bio-treated and PAS-treated wool fabric was assessed and the results were abridged in Table 7 The results in this table can be correlated with the bending length of the treated fabric shown in Table 5. The fabric weight is another factor which is crucial in determining the fabric drape. It has been reported that the fabric drape is the extent of distortion in the fabric shape as a result of the change in its weight; or the way in which the fabric falls under the influence of gravitational force, if only a part of it is firmly buttressed [32]. Treatment of wool fabric with PAS increased its weight by a factor of 7%; hence the DC decreased remarkably.
Thorough inspection of Table 7 reveals that the number of pleats in the tested samples increased from 4 to 5 upon bio-treatment with enzyme I or PAS, and to 6 upon treatment of wool with either enzyme I or II followed by post-treatment with PAS. These results indicate that wool fabric treated with protease/PAS system has a more harmonic drape than the untreated or those treated with enzyme or PAS only.
3.5. Fabric aesthetic features
Fabric drape is an important fabric feature which highly influences the garment aesthetic appearance [33]. Based on the results of fabric drape coefficient of the treated fabric; we chose samples IV and V for estimate their aesthetic property on Avatar using CLO3D software. Figure 1 shows the front, back, and side views of dress made from untreated wool fabric as well as those samples treated with enzyme I or enzyme II followed by post-treatment with PAS. It is obvious from this figure that the sample V has the best drapability, compared to the untreated and IV samples. From the aesthetic point of view, sample V affords fabric fall and shape which is distinct to the designer’s inspiration towards distinguished garment.
3.6. Fibre morphology
The alteration in the morphological structure of wool fabric after being bio-treated with protease enzyme I or II, treated with the cationic softener PAS, and combination thereof was investigated and illustrated in Fig. 2.
Table 7: Drape coefficient (DC) of wool fabric treated with protease enzyme followed by poly amino silicone softener
This figure shows that bio-treatment of wool with the protease enzyme I or II caused partial descaling of the fibre surface without severe fibre deterioration. Controlled wool fibre descaling is one of the methods usually adopted for improvement of the resistance of wool to felting shrinkage [34] and pilling [35] with enhanced fibre surface wettability [36] and smoothness [37]. The scanning electron micrographs of untreated or bio-treated wool fabrics after being post-treated with PAS show a thin layer of the used polymer on the fibres surface which would enhance the fabric smoothness and reduce the tendency of the fibres to felt-shrink [38].