1、Mechanical Properties of Polyurethane Coated Knitted FabricsIntroductionSamples and working methodResults and discussionConclusions.Part1 introduction Polyurethane-coated knitted fabrics are of interest because they exhibit several positive properties, and yet they are little studied, especially tho

2、se 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 the p

3、resence 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.There i

4、s 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 generally more

5、 stretchable and elastic than woven fabrics.Part2 Samples and working methodSamples 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 were coated

6、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 knitted fab

7、rics was 21 (7 knitted fabrics 3 polyurethane coatings).Working methodThis 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 was compared

8、with that of thesame 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 fabricElongation in

9、 the wale direction.The knitted fabrics elongated from 46.41% to309.93%, 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 in the wale directio

10、n 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 elongation properti

11、es of the vertically laid yarn (and not formed into loops).The t-test shows that there is no statistically considerabledifference 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 forelongation in the wale d

12、irection.Regression analysis indicates the relationship between the elongation of the knitted fabric and that of the polyurethane-coated knitted fabric.cw = 1.2312kw - 8.4717The coefficient of determination R2 = 0.9915It is possible to use the regression model obtained for easy prediction of the beh

13、aviour of the coated knitted fabric and the choice of an appropriate knitted fabric substrate.Elongation in the course directionThe knitted fabrics elongated from 34.96% to 157.93%, which is a consequence of the different structures of knitted fabrics and yarnsused. The coated knitted fabrics elonga

14、ted 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 difference between the mean values

15、 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 fabricin the course direction have only a m

16、edium correlation (r=0.79).The relationship between variables is not linear. Exponential regression modelcc = 103.53 e0.0064kcwith 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

17、 with regard to the elongation of the samples of the same knitted fabrics (ekc) examined.It is interesting to investigate which elements together with the elongation of the knitted fabric affect the elongation of thecoated knitted fabric in the course direction.The samples of coated fabric KF3, KF4

18、and KF5 show a greater difference in the elongation of the coated fabric and uncoated fabric (Figure 4, Table 5) and more significantly deviate from the adapted theoretical curve of the exponential model.They were produced from a low thickness knitted fabric (Table 1).The ratio between knitted fabri

19、c thickness and coating thickness in comparison with other knitted fabrics is lower (Table 5)There is relatively more coating, making a greater contribution to elongation in such coated fabrics.The relationship between the ratio of thicknesses (Tr) and that of elongation(er) clearly shows (r = 0.89)

20、r = 5.9156 Tr-0.8882the elongation decreases if there is relatively less coating on the coated fabric.By using multiple linear regression, a much better relationship between the elongation of the coated fabric in the course direction and both variables (elongation of the knitted fabric and ratio ofk

21、nitted fabric thickness and coating)cc =149.3042 + 2.032309 kc - 44.866TrThe coefficient of multiple correlation (R = 0.91) indicates a strong relationship between the elongation of the coated knitted fabricin the course direction and the two variables observed.In addition to the elongation of the k

22、nitted fabric, the ratio of the knitted fabric thickness and coating should be considered.Technologically these findings show how extremely sensitive it is to predict the behaviour of coated knitted fabrics with a very thin substrate (thickness 0.4 mm).Comparison of the elongation of the knitted fab

23、ric and coated knitted fabric during spherical elongationThe knitted fabrics elongated from 26 to 68 mm until ball bursting. The coated knitted fabrics elongated from 25 to 66 mm.The t-test shows again that there is no statistically significant difference between the arithmetic means of the three ty

24、pes (PU1 - PU3) of samples tested (p = 0.8372), and they can be observed as one group of samples.The lower elongation of the coated knitted fabric during spherical elongation, on average 8%.It is possible to conclude that coating fixes the yarn and the knitted fabric structure, i.e. the polyurethane

25、 adhesive glues the yarn which forms loops, hence it cannot move freely and deformthe fabric structure nor adapt to spherical elongation, causing an early burst of the coated knitted fabric.The same coated knitted fabric, which will show better characteristics than the knitted fabric itself during e

26、longation inthe course or wale direction, exposed to spherical elongation will show poorer characteristics.The model of linear regression cb = 0.7468 kb + 6.1557with coefficient of determination R2 = 0.9292.Breaking force of the coated and uncoated knitted fabricsBreaking force in the wale direction

27、Breaking forces from 104.6 N to 907.5 N were measured in the knitted fabric of different structures. Breakingforces from .7 N to 1053 N were measured in the coated knitted fabrics. The coating caused slightly higher breakingforces on average 24%.The t-test shows again that there is no statistically

28、significant difference betweenbetween the breaking forces of the three polyurethane-coated groups of samples tested (p = 0.93).Linear regression model Fcw = 1.098 Fkw +48.736, with the coefficient of determinationR2 = 0.9802.Breaking force in the course direction of the knitted fabricBreaking forces

29、 from 66.27 N to 501.8 N were measured in the knitted fabric. The bursting of the coated knitted fabrics in the course direction occurred at breakingforces from 108.1 N to 672.2 N. The coating caused an increase in breaking forces in the course direction of the knitted fabric - on average about 27%.

30、The t-test shows again that there is no statistically significant difference between the breaking forces of the three polyurethane-coated groups of samples tested (p = 0.88).Regression modelFcc = 99.511,0039Fkc,with the coefficient of determination R2 = 0.9367.Breaking force of the spherical burst o

31、f the knitted fabric and coated knitted fabricBreaking forces from 73 N to 1058 N were measured in the knitted fabrics and from 91 N to 1228 N in the coated knitted fabricsCoating caused an increase in the resistance to spherical bursting- on average about 13%.the t-test shows again that there is no

32、 statistically significant difference between the breaking forces of the threepolyurethane-coated groups of samples tested (p = 0.989).Linear regression modelFcb = 1,1214 Fkb + 4,0992explains the relationship between the occurrences observed (Figure 13). The coefficient of determination R2 = 0.9956.

33、Part4 ConclusionsAlthough coating significantly changes the mechanical properties of knitted fabrics, the properties of coated knitted fabrics are primarily determined by the properties of the knitted substrate.Elongation in the course direction of the knitted fabric significantly increases after co

34、ating - on average by about 102%, while the increase in elongation by coating in the wale direction is lower, amounting to about 16%.Elongation in the wale direction of coated knitted fabrics can be predicted with great certainty knowing that of the knitted fabric. A linear regression model explains 99.15% of the relationship between the elongation of the knitted fabricand coated knitted fabric.Elongation in the course direction of coated knitted fabrics can be predictedwith great certainty knowing that of the