The Effect of Fibre Composition and Washing Conditions upon Hand Properties of Knitted Materials

The behaviour of knitted plated jersey materials made from natural and man-made fibres was tested after certain washing conditions. Surface density and thickness of investigated materials differed insignificantly, from 206 g/m up to 222 g/m and from 0.56mm up to 0.79mm, respectively. Special device for textile materials hand evaluation based on the principle of pulling of a discshaped specimen through a rounded hole was used.The aim of this study was to investigate the effect ofmaterials’ fibre composition and washing conditions upon the changes of hand properties of knitted materials. Analysis of obtained results showed that, during washing, textile materials shrink and become more dense and rough, and their rigidity increases as well. Thus, the most significant effect of 5-cycle washing was obtained for knitted material with bamboo fibres.


Introduction
The objective evaluation of textile hand is based on physical parameters, that is, numeric values, which are estimated with the help of specialised devices.Objective evaluation of textile hand is performed on the basis of the dependency (deflection height-force), which is obtained when tested sample is pulled through the hole [1][2][3].The advantage of such method is the possibility to define one complex criterion for textile hand characterization which is obtained on the basis of pulling curves' characteristic zones.In previous studies, it was established that KTU-Griff-Tester deviceis suitable for investigating the changes of fibrous materials behaviour and hand variations [4,5].

Materials and Methods
Knitted fabrics with the different fibre compositions and the same type of weave were chosen as the objects of the investigation.Table 1 shows the characteristics of investigated knitted fabrics.
For the investigation, knitted materials after five cycles of the washing process were used.One cycle of the washing process was at water temperature of 40 ∘ C, washing duration of 31 minutes, and centrifugation duration of 10 minutes (number of rotations: 600), following the standard ISO 6330:2002.After washing a knitted materials were dried in a horizontal position (duration >10 hours).In this study, the washing agent BEICLEAN RG-N which is a detergent and emulsifier was applied.For better performance, it was used together with washing intensifier BEIMPLEX NWS, which acts upon alkaline ions and heavy metals by preventing the formation of deposits, that is, allowing the avoidance of the formation of plaque on washed materials and sediments in washing machines.In other words, BEIMPLEX NWS strengthens the feature of BEICLEAN RG-N to disperse the contaminants.In this research, the water of average hardness (pH 7-14) was used, and washing conditions were selected corresponding to laundry state which is slight soiling.Table 2 shows the chemical composition of the used washing agent.
Tests were performed using KTU-Griff-Tester device, which was fixed in standard tensile testing machine [6][7][8].Disc-shaped samples with the radius  = 56.5 mm   were pulled by spherical punch  = 5 mm with the needle through the central hole of the device.Extraction speed was 100 mm/min.The distance between the limiting plates ℎ = 5.6 ⋅  mm and radius  = 10 mm of the hole was chosen according to the tested fabric thickness 0.5 <  < 1.0.The distance between the plates was calculated for each tested material and was kept constant for nonwashed samples and after washing.
During testing pulling curves - (deflection height force) were registered on the basis of which such parameters were defined: maximum extraction force  max , maximum deflection height  max and the tangent of nominal slope angle of the - curve .The pulling work , Ncm, and complex hand rate   also were calculated.The changes of thickness Δ were defined using thickness gauge SCMIDT DPT 60 DIGITAL; under two different loads (ratio 1 : 5) [6,8,9].Knitted samples were tested and evaluated under controlled environmental conditions ( = 65 ± 2%,  = 20 ± 2 ∘ C).For each sample, six specimens were tested, and the error level was within the limits of 5%.KTU-Griff-Tester device, typical extraction curve -, and optimisation diagram on the basis of the complex hand rate are shown in Figure 1.

Results and Conclusions
Seeking to define the effect of fibre composition upon the rate of hand evaluation of knitted materials of different fibre content and having a certain percent of elastane were investigated.The characteristics of knitted materials pulling through a hole process are shown in Table 3.
Typical pulling curves of knitted materials with different fibre content and the diagrams of complex hand rates  NW calculation for nonwashed specimens are shown in Figures 2(a  The values of hand rates of constituent parts for materials M3 and M2 are also close:  max varied from 1.37 N to 2.00 N (the difference is 46%) N;  varied from 0.68 to 0.86 (the difference is 26%);  max varied from 54.0 mm to 56.2 mm (the difference is 4%).The material with cotton fibres M1 ( NW = 11.50)differs mostly by poor hand results.Its complex hand rate  NW is more than 4 times higher compared to those of the other investigated materials.Pulling force  max , the rigidity described by , and pulling work  of M1 material are also up to 5 times higher compared to corresponding values of M3 material.The value  max which describes the deformability of tested samples is higher by 14%.According to the character of pulling curves and taking into account the determined values of hand rates, it can be stated that knitted materials from viscose and bamboo fibres are soft, thin, smooth, and easily slipping.
Analysis of obtained results has shown that the washing process of knitted materials reduces their hand rates; that is, the ratio  of hand rates  W / NW for all investigated fabrics after 5 washing cycles became worse from 1.3 times for material from cotton fiber with 5% elastane up to 5.4 times for material from bamboo fiber with 5% elastane (Table 3).The same results were also obtained in earlier research works, which showed that hand rates after washing became worse by 2.5 ÷ 4.1 times [5].This phenomenon is illustrated by typical pulling through hole curves - which are shown in Figure 2(a) and the optimisation diagrams of hand rates  NW and  W calculation for samples after washing which are shown in Figures 2(b) and 2(c).
During washing, textile materials shrink and become more dense and rough, and their rigidity increases as well.Thus, constituent values of hand rate,  max , , and , increase.Pulling force  max increased from 1.28 for material from cotton fiber with 5% EL up to 6.36 for material from bamboo fiber with 5% EL times,  up to 2.74 for material from bamboo fiber with 5% EL, and pulling work  from 1.3 for material from cotton fiber with 5% EL up to 5.43 for material from bamboo fiber with 5% EL times.The values of pulling height  max vary in the limits of 0.25% ÷ 3.75%, except for M2 knitted material, for which  max increases up to 26%.Thus, the most significant effect of 5-cycle washing was obtained for knitted material M2 from bamboo fiber with 5% EL.Comparative analysis performed with viscose knitted materials M3, M4, and M5 has revealed that, with the increase of elastane in their content from 5% to 12%, pulling force  max and slope angle  increase by 20%, but pulling work  and pulling height  max decrease by 18% and 11%, respectively.Typical pulling curves of viscose knitted materials with different fibre content and the diagrams of complex hand rates  NW calculation for nonwashed samples are shown in Figures 3(a) and 3(b).The curves of viscose materials M3, M4, and M5 pulling through a hole show that the behaviour of these materials is similar; that is, the increase of elastane in their content perfected their hand property insignificantly- NW decreased only by 17%.
Typical pulling curves of viscose knitted materials with different elastane content and the diagrams of complex hand rate  W calculation for samples after washing are shown in Figures 3(a) and 3(c).The results of the investigation of the washing effect upon hand rates  W confirmed previous conclusions for the materials with different elastane content; the decrease of hand rate  W varies form 32% (for 8% EL) to 51% (for 12% EL) when compared to knitted material from viscose with 5% EL.The most significant effect of 5cycle washing process was defined for knitted material from viscose, having 5% of elastane in its content.Hand ratio  becomes worse by 3 times in this case.The lowest effect of 5-cycle washing is defined for material from viscose with 12% elastane.Its hand rate  W became worse by 51%.
) and 2(b).Obtained results revealed that viscose knitted material M3 has the best hand rate:  NW = 2.30.Hand rates of material M2 from bamboo fibres are worse by 27%.

Figure 3 :
Figure3: Typical pulling curves of viscose knitted materials with different elastane content (a); the diagrams of complex hand rates  NW calculation for nonwashed specimens (b); the calculation of complex hand rates  W after sample washing (c).

Table 2 :
Chemical composition of washing agent.

Table 3 :
The characteristics of knitted materials pulling through a hole.: nonwashed specimen, W: specimen after washing; the hand ratio  was determined as ratio  NW / W , where  W is the area of washing treatment and  NW is the area of nonwashed specimen. NW