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Pilling Resistance of Knitted Fabrics

2018-05-18 14:57
Products of knitted fabric are characterized as being elastic, resilient, soft, they have good draping properties,and cling well to body to inhibit movement. However, during exploitation, pills form on the surface of the knitted fabric, remaining on the surface of the product and worsening its exterior. The process of formation of pills consists of three stages [1]: due to mechanical impact to the surface of rasped products, firstly, the tips of several fibres of fibre are pulled out creating a fuzzy surface.
Later, broken fibres grip to felt tips and forms separate,gradually growing pills. Fibres holding these pills are griped strongly, later however, due to the further mechanical impact (attrition, washing and other) they may rub away and fall off.
The resistance of knitted fabrics to pilling depends on the density of fabric, i.e. when the length of knitted fabric loop decreases and the surface density increases, the resistance to pilling grows [2, 3]. When analysing the influence of weave to propensity of pilling and fuzzing of knitted fabrics, it was defined that rib knitted fabrics were resistant to pilling most of all, interlock knitted fabrics are less resistant, and plain weave knitted fabrics are tend to pilling more [2 – 6]. It was defined in previous works that the twist, fuzzing, quantity of fibers, cross-section structure of knitted fabric change resistance to pilling: when the twist of yarn is bigger, the fuzzing of fabric then decreases[7 – 8]. Properly selected formation way of yarn, fabric weave and facing can improve the quality of knitted fabric [9]. Washing intensity the process of pilling [10] which varies depending on chemical softeners used during washing [11], however, their influence to above-mentioned process is not fully investigated.
The aim of the work was to define the influence of fibrous composition and chemical softeners on of fuzzing and pilling of knitted fabrics. 
Knitted fabrics of different fibrous composition made of natural (cotton), artificial (reclaimed bamboo, viscose) and synthetic (polyester, polyamide) fibre were analysed in the present work (Table 1). The structure of the investigated objects was reseached referring the standards as follows: defining of the fiber content – LST EN ISO 1833; measuring of the density – LST EN ISO 14971:2006; defining of the loop length – LST EN 14970:2006; measuring of the surface density – LST EN 12127:1999; measuring of the thickness – LST EN ISO 5084:2000. The change of the thickness ?δ was defined using the thickness gauge SCMIDT DPT 60 DIGITAL, the precise class 0.01 mm: δ1, when p1 = 1 kPa; δ2, when p2 = 5 kPa. The surface density and thickness of plain and plated jersey pattern knitted fabrics chosen for the investigation are similar, respectively from 202 g/m2 to 222 g/m2 and from 0.56 mm to 0.79 mm. Some fabrics have different quantity of elastane (EL), and this enable to determine its impact to pilling of knitted fabrics. To evaluate the influence of washing and chemical softeners to propensity of fuzzing and pilling of knitted fabrics, the washing procedure of a specimens (40 cm × 50 cm) was performed, according to the standard ISO 6330:2000 [12]. After the washing, specimens were rinsed in baths with two different softeners: fatty acid condensate (Tubingal 5051) or silicone micro emulsion (Tubingal SMF). The composition of washing agent and softeners as well as the recipe are submitted in Table 2. The scheme of procedure of knitted fabrics washing and softening using two different softeners is submitted in Figure 1.
The propensity to pill and fuzz of dry (control) and washed as well as softened knitted fabrics was defined following modified Martindale method (standard ISO 12945-2:2000) [13]. Before the investigation all specimens were held in standard conditioned conditions (φ = 65 % ±2 %, T = 20 °C ±2 °C) according to the requirements of standard ISO 139:2005 [14]. 
To define the propensity of fabrics to fuzz and pill, the results of investigation of control (P and TP) and washed(Figure 1) knitted fabrics (Table 1) as well as softened in different softeners (Table 2) were compared.
Knitted fabrics from PES fibres M1 and M2 have the greatest resistance to fuzzing and pilling: their propensity to fuzz and pill to grade 1 was not determined even after 14000 revolutions (Figure 2). Knitted fabric M3 (87 %PES and 13 % EL) is of a very high quality and resistant,after only 14000 revolutions it was evaluated by grade 1,while the maximum recommended number of revolutions in the standard is 7000. Knitted fabrics M1 – M3 resistance to propensity of fuzzing and pilling is determined by the structure of yarn – it is composed influenced by fiber content [3]: M1 – composed from PES fibers (16.7 tex) and elastane (2.2 tex), M2 – composed from PES fibers(16.7 tex, 96 filaments) and elastane (4.4 tex), M3 –composed from PES fibers (11 tex, 164 filaments) and elastane (4.4 tex). The exclusiveness of all three fabrics was also determined by the pattern - plain and plated jersey pattern. The elastane is inserted into the each line of the knitted fabric, for other investigated fabrics, into each second line. Thus, during the pilling investigation of the fabrics M1 – M3, they scrubbed only the polyester layer,that‘s on the top, while the lower level, knitted with the elastane fiber, remained not touched. Therefore elastane fiber, depending on its quantity in the fabric more or less pulls, makes a more thick the polyester top layer [5].
Knitted fabrics M4 and M5 are from polyamide fibres,however their resistance to pilling is different, pilling of knitted fabric M4 (5 % EL) is evaluated by grade 4 after the achievement of 14000 revolutions, while fabric M5(10 % EL) – grade 1 just after 5000 revolutions. Fabric M4 differs from fabric M5 by special method of facing which changes the resistance of the fabric surface to mechanical influence. It is suggested, that resistance to the pilling of the fabrics M4 and M5 differs significantly because of the fiber content and structure differences: M4 is made from polyamide 6,6 (7.8 tex from tow fibers) and elastane(2.2 tex.), and M5 – from polyamide (16.9 tex) and elastane (4.4 tex). The fabric M5 is more thicker with a lower density than fabric M4. When sampling during scrabbling the surface contacts more close to the device top part. The loops of the fabric M5, characterised by less density and bigger loop length, are easier going out with faster fuzzing as well breaking and is less influenced and less resistance to pilling [2, 3]. The fabric M4 is more resistant to pilling than M5, because of its pattern, plain and plated jersey pattern, when elastane is inserted into the each line of knitted fabric, the elastane fiber is not scrabbled directly.
The pattern of the fabric M4 is plain and plated jersey pattern, when elastane is inserted into the each second line of the knitted fabric. Knitted fabric M5 from polyamide fibres is similar to knitted fabrics (M6 and M8) from viscose fibres by its resistance to pilling because permissible pilling grade 3 was achieved from 2000 to 3000 of revolutions, and grade 1 – after 5000 revolutions.Fabric M3 from cotton fibres is of similar resistance to pilling (grade 3 was achieved after 2000 revolutions),however it was evaluated by pilling grade 1 after 6000 revolutions. 
The propensity to fuzz and pill of fabrics M7 (from viscose fibres) and M10 (from reclaimed bamboo fibres) is undesirably large: after just 1000 revolutions, specimens were evaluated by grade 3, and after 3000 revolutions – bygrade 1.
The obtained results showed that the resistance of fabrics which differ by its main fibrous composition (EL5 %) to propensity of pilling is different. Specimens of fabrics from PES and PA fibres were evaluated by grade 4 only after 14000 revolutions, while fabrics from viscose(M6) and cotton (M9) fibres achieved pilling grade 4 after just 1000 revolutions. The worst result was in fabrics of reclaimed bamboo fibres (M10) which achieved pilling grade 3 after just 1000 revolutions.
The influence of fabric softness to their resistance to pilling, it was defined that when a change of fabric thickness increases (Δδ), their resistance to pilling decreases (Fig. 3, a) [3, 4, 7]. The exception is the results of investigation of knitted fabrics M9 and M10 which are determined by fibrous composition of the fabric. The influence of change of thickness to pilling of fabrics strongly correlates (r = 0.984) when comparing the results of knitted fabrics from PES and PA fibres. Strong linear dependence (r = 0.903) between change of thickness and resistance to pilling was obtained comparing the results of fabrics from PES and viscose fibres. 
When the quantity of elastane increases in the composition of knitted fabrics, the change of thickness ?δ increases (Fig. 3, b) [5], and the resistance to pilling decreases (Fig. 2). For example, when the quantity of elastane of knitted fabrics M1, M2, M3 changes respectively 5 %, 10 % and 13 %, it changes the thickness– 0 %, 3.2 % and 3.4 %. First insignificant changes of thesurface of fabric M1 were observed after 6000 rotations(grade 4), M2 fabric just after 1000 rotations was evaluated between grade 5 and 4, and evaluated by grade 4 after 3000 rotations. Figure 2 shows how the resistance to pilling of knitted fabric M3 differs comparing it with M1 and M2. The influence of washing (after 5 cycles) and softening using two different softeners (fatty acid condensate and silicone micro emulsion softener) to propensity of knitted fabrics fuzzing and pilling, it was defined that the procedure of washing and softening increases the propensity of knitted fabrics to pilling(Fig. 4) [10, 11]: the propensity of pilling of M3,M5 – M10 knitted fabrics increases from 33 % to 67 %. Washing and processing using chemical softeners do not have substantial influence to the propensity of pilling of knitted fabrics M1, M2 and M4.
Subjective pilling evaluation method applied in the investigation did not allow to define substantial differences between the results of a specimens influenced by different softeners. The exception is the results of knitted fabrics M3, M8 and M9 which showed that specimens softened by fatty acid condensate are more resistant to pilling than a specimen softened by silicone micro emulsion softener.
After the performance of additional experiment, when the number of rotations is twice less than all knitted fabrics, it was defined that the influence of washing and softening to pilling of knitted fabrics remains tendentious(Figure 5). When applying the number of rotations which was twice less than all investigated fabrics, the lower evaluation of resistance to pilling is up to grade 3 and it confirms that fabrics can be exploitable further.
Knitted fabrics from PES fibres have the greatest resistance to pilling as their resistance is influenced by fibre structure and facing. Investigated knitted fabrics from viscose and reclaimed bamboo fibres have the lowest resistance to pilling. Knitted fabrics from reclaimed bamboo fibre distinguished by quickest pilling process:just after 1000 revolutions it was evaluated by pilling grade 3. When the change ?δ of knitted fabric thickness increases up to 9.7 % the resistance to pilling decreases up to 64 %. It defined a stronger linear dependence between the quantity of elastane in investigated knitted fabrics and thickness change Δδ confirms that the quantity of abovementioned fibre has influence to pilling.
The procedure of washing and softening worsened the resistance to pilling of investigated knitted fabrics from33 % to 67 %. Fabrics M3, M8 and M9 softened using fatty acid concentrate are from 25 % to 50 % resistant to pilling than fabrics softened using silicone micro emulsion softener. In case of other investigated fabrics, substantial differences were not defined. 


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