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1、Mechanical Properties of Polyurethane Coated Knitted Fabrics,Introduction Samples and working method Results and discussion Conclusions,Part1 introduction,Polyurethane-coated knitted fabrics are of interest because they exhibit several positive properties, and yet they are little studied, especially
2、 those used in the garment industry. The advantages of polyurethane coatings in comparison to other polymers are greater resistance to abrasion and splitting, increased strength and durability.,Polyurethanes are formed by the polyaddition reaction of a polyisocyanate with a polyalcohol (polyol) in t
3、he presence of a catalyst and other additives. Polyisocyanate is a molecule with two or more isocyanate functional groups,R-(N=C=O)n 2 and a polyol is a molecule with two or more hydroxyl functional groups, R-(OH)n 2. The reaction product is a polymer containing the urethane linkage, -RNHCOOR- 3.,Th
4、ere is a chance to develop coated knitted fabrics as protective clothing, work clothing, sportswear and casual wear more comfortable than clothes made out of coated woven fabric because movements are less restricted if clothing is made of elastic knitted material.,Coated knitted fabrics are generall
5、y more stretchable and elastic than woven fabrics.,Part2 Samples and working method,Samples Seven knitted fabrics with different structures (designations KF1 - KF7) were chosen to cover a wide interval of values of the characteristics of elongation and breaking forces tested (Tables 1 & 2).,They wer
6、e coated under the same conditions, on the same coating line, with three different polyurethane coatings (designated PU1 - PU3).,The polyurethane coatings have nearly equal average thicknesses and weights, but different mechanical properties (Table 3).,As described above, the total number of coated
7、knitted fabrics was 21 (7 knitted fabrics 3 polyurethane coatings).,Working method This time we observed mechanical properties before and after coating, and formed conclusions on the prediction of their behaviour. The behaviour of knitted and coated knitted fabrics in the linear application of force
8、 was compared with that of the same specimens in the case of spherical force application. The samples were statistically analysed (descriptive statistics, hypothesis testing- t-test, regression analysis).,Part3 Results and discussion,Elongation of coated knitted fabrics in relation to the knitted fa
9、bric,Elongation in the wale direction,The knitted fabrics elongated from 46.41% to 309.93%, which is a consequence of their different structures. The coated knitted fabrics elongated in the wale direction from 44.41% to 382.44%.,The coated knitted fabric has a considerably higher average elongation
10、in the wale direction in relation to the knitted fabric - on average about 16%, apart from the least stretchable knitted fabric (KF3),which was not affected by the coating.Namely the KF3 sample was knitted in a power-net structure (Table 1), where elongation in the wale direction depends directly on
11、 elongation properties of the vertically laid yarn (and not formed into loops).,The t-test shows that there is no statistically considerable difference between the mean values of elongation of the groups of samples tested (p = 0.92) or they can be observed as the same type of polyester coating for e
12、longation in the wale direction.,Regression analysis indicates the relationship between the elongation of the knitted fabric and that of the polyurethane-coated knitted fabric.,cw = 1.2312kw - 8.4717,The coefficient of determination R2 = 0.9915 It is possible to use the regression model obtained for
13、 easy prediction of the behaviour of the coated knitted fabric and the choice of an appropriate knitted fabric substrate.,Elongation in the course direction,The knitted fabrics elongated from 34.96% to 157.93%, which is a consequence of the different structures of knitted fabrics and yarns used. The
14、 coated knitted fabrics elongated in the course direction from 96.15% to 358.75%. The coated knitted fabric has a considerably higher average elongation in the course direction in relation to the knitted fabric - on average about 102%.,The t-test shows that there is no statistically considerable dif
15、ference between the mean values of elongation of the knitted fabrics coated with three different types of PU coating (p = 0.72) for the elongation in the course direction.,Regression analysis showed that the relationship between the elongation of the knitted fabric and the coated knitted fabric in t
16、he course direction have only a medium correlation (r=0.79).The relationship between variables is not linear. Exponential regression model cc = 103.53 e0.0064kc with a coefficient of determination R2 = 0.6262, is the best explanation of elongation variance in the course direction of the samples of coated knitted fabrics (ecc) studied with regard to the elongation of the samples of the same knitted fabrics (ekc) examined.,It is interesting to investigate which elements togethe
