Impact of material,structure and relaxation process parameters of elasticized single-knitted fabrics on loop length

Abstract

The development of knitted fabrics with incorporated elastane has increased in recent decades. Knitting with these elasticized yarns usually results in a very compact structure. Loop length is considered to be the primary parameter for knitted structures. Consequently, knowledge of all factors influencing loop length is vital for planning yarn consumption, comfort fit, quality, performance and aesthetic properties of knitted fabrics made from elasticized yarns. The objective of this research was to study the impact of material, knitted structure and relaxation process parameters on loop length. In addition, the objective was to examine the differences in loop length of single weft knitted fabrics, produced from different types of elasticized and non-elasticized yarns. For both groups of knitted fabrics, elasticized and non-elasticized, knitted fabric density and relaxation process influence the loop length most of all. Loop length decreases during the process of consolidation, but this decrease is not substantial. Addition of elastane does not significantly influence the loop length.

Keywords

analysis of variance knitted loop loop length single jersey weft knitting

Dimensional sensitivity, complex geometry and compound behavior are general characteristics of knitted structures. Variations in geometrical parameters significantly influence dimensional, performance, comfort and aesthetic properties of knitted fabrics.

As demand for comfortable and adaptable clothing has burgeoned in recent decades, the use of incorporated elastane in knitted fabrics has increased. Fabrics incorporating elastane exhibit increased extensibility, elasticity, a high degree of recovery, good dimensional stability and require only simple care.¹ Apart from bare threads incorporated into various structures through interlacing, elastane fibers may be used in core-spun yarns where a non-elastic fiber sheath is spun around an inner core of elastane, or other elastomeric yarn. Core-spun elastane yarns supplement the recovery properties of knitted structures, improving dimensional stability.²

The relaxation after knitting usually involves shrinking of the finished knitted fabric.³ Behavior of a knitted fabric during relaxation from a yarn's internal stresses, imposed during knitting, depends on many factors. The extent of shrinking depends on three major factors:

yarn parameters – material composition; linear density; twist; evenness; tenacity; extensibility; friction; moisture content; yarn package type; compactness of yarn package etc.;

machine parameters – gauge; cam shape and settings; yarn input tension; fabric take-down tension; yarn feeding system, etc.;

knitted fabric parameters – knitted structure type; wale and course density; loop shape coefficient; loop length; stitch density, etc.⁴

In order to be able to control fabrics' dimensions during knitting and after-treatment processes, extensive studies on the relaxation characteristics of knitted structures were undertaken. In professional and scientific literature, numerous procedures and methods of knitted fabric relaxation have been presented. Initially, these focused mainly on cotton knitted fabrics, followed by fabrics from regenerated cellulose and man-made fibers and, most recently, elasticized single-weft knitted structures have also been studied. Both elasticized structures plated with bare elastane threads and those knitted from core-spun yarns were investigated.^4–20 The significance of static dry and wet relaxation, in addition to dynamic wet relaxation (i.e. consolidation) was acknowledged as early as 1956, by Munden (Munden and Fletcher²¹; Munden²²). Munden stated that the starting point for the study of the yarn/knitted fabric parameters' interdependence is the elimination of the yarn and knitted fabric history, that is, the annulment of the previous strains and the restoration of the reference, or relaxed state, of the fabric.²¹ Extensive research related to the setting of the reference state was later performed within the frame of the Starfish project.^23,24

Owing to the three-dimensional curved shape of the basic unit – the loop – knitted structures are generally more porous and extensible than other textile structures. The appearance and performance properties of various knitted structures may differ, due mainly to differences in material composition and structural parameters. Knitting yarns with incorporated elastane usually results in a compact to very compact, that is, supercompact, structure. Structural compactness, described with loop modules and loop constants, directly influences the performance and mechanical and comfort properties of knitted fabrics.²⁵ Because of the compact nature of relaxed fabrics, the properties of knitted fabrics made from highly elastic yarns with an elastane core differ significantly from those of knitted fabrics, made under similar process conditions, but using yarns without an elastane core.²⁶ As loop length is considered to be the primary knitted structure parameter,²⁷ knowledge about the factors influencing the loop length is vital for predicting yarn consumption, comfort fit and appearance, plus quality and performance properties of knitted fabrics based on elasticized yarns.

The principal objective of the research was to study the impact of material, knitted structure and relaxation process parameters on the loop length. Another focus of the investigation was to examine the differences in loop length of single-weft knitted fabrics, produced from different types of elasticized and non-elasticized yarns, under the same regime of knitting machine settings.

Experimental details

Sample preparation

For the preparation of knitted test samples, ring-spun yarns were employed. These were made to order from two types of staple fibers – viscose (CV) and polyacrylonitrile (PAN). These CV and PAN fibers were selected because of their different origins – natural and synthetic polymers – consequently displaying dissimilar hydrophilic properties and shrinking behavior during wet processes. Previous research into the dimensional stability of knitted structures with an identical material composition^5,6,9,10 formed the basis for test material parameters selection. From each raw material, elastomeric core-spun yarns were made to order, by three different spinning/twisting processes, that is, mouliné twisted yarn (composed of elastomeric core-spun yarn and yarn without elastane, both ring-spun); core-twisted yarn (elastane filament yarn, core-twisted with two ring-spun yarns) and core-spun yarn (yarn with an elastane core and staple fiber sheath covering). For comparison, ring-spun yarns without elastane, from 100% CV and 100% PAN fibers, possessing an equal linear density to elastane core-spun yarns, were produced. The linear density of all yarns was 100 tex; yarn twist was 221Z, for single yarns without elastane and 281Z for single elastomeric core-spun yarns and 500S for twisted elastomeric yarns, that is, mouliné-twisted and core-twisted yarns.

The knitted samples were produced on the electronic flat weft knitting machine UNIVERSAL MC 720, gauge E8. From each yarn, samples were knitted in two discrete densities, termed tight and loose, accomplished by selecting two cam settings on the machine. All samples were knitted with an equal yarn input tension, equal knitted fabric take-off, employing the same needle bed width (324 working needles) throughout and in identical environmental conditions.

The relaxation process employed was based on the Starfish procedure^23,24 and the findings of Fletcher and Roberts^5,6 and Hurley.⁹ Firstly, all samples were statically dry relaxed and then placed unloaded to the standard environment for 72 hours. After dry relaxation, one half portion of each sample was additionally dynamically wet relaxed (consolidated). The dynamic wet fabric relaxation process involved laundering at a 30°C – delicate laundry program; short spinning: 40-minute drying – delicate laundry program, four cycles of alternating short rinsing and 40-minute tumble drying. Throughout the dynamic wet relaxation process, no chemicals were added. Then, the wet relaxed samples were placed flat in the standard environment for at least 24 hours after the last drying cycle was completed.

Combining the two fiber types; four yarn structures; two density levels and two relaxation procedures – altogether 32 different knitted samples were prepared (Figure 1).

Figure 1.

Sample preparation diagram.

Loop length was measured by unraveling threads from the knitted samples and straightening the curls on the dynamometer. The speed of the dynamometer’s movable clamp was set to 3 mm/s²⁶ and the test thread was considered straight when a load increase was detected. Ten measurements of loop length were made for each knitted sample.

Research methods

For statistical analyses of the measurement data, multifactorial analysis of variance (ANOVA) was selected. This method enables the estimation of the effects of individual independent variables – factors – to the response variable and also their interactions. ANOVA determines the statistical significance of individual factors at a given confidence level and also defines their magnitude.^28,29 In the investigations into structural parameters of knitted fabrics with incorporated elastane, the independent variables – factors – were as follows (Table 1): fiber type (F); yarn structure (Y); relaxation process (R); and knitted fabric density (D). Each factor may have two or more values, or levels, as stated herein. The dependent variable – response – was the loop length ℓ. According to Munden,²⁷ it is the most important parameter, dependent on the other parameters listed above.

Table 1.

Experimental design diagram and sample labeling

Influencing parameter	Factor		Level
Material	Fiber (F)	Fiber type	Polyacrylonitrile (PAN)
	Fiber (F)	Fiber type	Viscose (CV)
	Yarn (Y)	Yarn structure	Twisted	Mouliné (MOU)
			Twisted	Core-twist (C-TW)
			Single spun	Core-spun (C-SP)
			Single spun	Conventional (CONV)
Structure	Density (D)	Knitted fabric density level	Density 1 (D1)
Structure	Density (D)	Knitted fabric density level	Density 2 (D2)
Process	Relaxation (R)	Relaxation process type	Dry relaxation (DR)
Process	Relaxation (R)	Relaxation process type	Dynamic wet relaxation – consolidation (CR)

The experimental results were statistically processed by ANOVA, first as a whole on the basis of the 4 × 2³ factorial design and then separately on the basis of four and three factorial designs, as shown below. The impacts of the relaxation process and structural parameters of knitted fabrics and also of their interactions on the basic parameter of the knitted fabric – loop length – were evaluated. In Tables 2 –13, SS denotes Sum of Squares, Df denotes Degrees of Freedom and MS indicates Mean Square.

Table 2.

Impact of material, relaxation process and structural parameters of knitted fabrics on loop length: four-factorial design for all samples (main effects and interactions)

All samples	SS	Df	MS	F-ratio	P-value
Main effects
F: fiber	0.81709	1	0.81709	9.66	0.0021
Y: yarn	2.46796	3	0.822654	9.73	0.0000
R: relaxation	4.2897	1	4.2897	50.71	0.0000
D: density	651.996	1	651.996	7707.70	0.0000
Interactions
FY: fiber yarn	0.590203	3	0.196734	2.33	0.0750
FR: fiber relaxation	0.0969528	1	0.969528	1.15	0.2853
FD: fiber density	0.0585903	1	0.0585903	0.69	0.4060
YR: yarn relaxation	0.260378	3	0.0867928	1.03	0.3814
YD: yarn density	0.381506	3	0.127169	1.50	0.2138
RD: relaxation density	0.126008	1	0.126008	1.49	0.2233
FYR: fiber-yarn relaxation	0.0909459	3	0.0303153	0.36	0.7831
FYD: fiber-yarn density	0.6511173	3	0.217058	2.57	0.0548
FRD: fiber-relaxation density	0.000165312	1	0.000165312	0.00	0.9648
YRD: yarn-relaxation density	0.439596	3	0.146532	1.73	0.1605
FYRD: fiber-yarn relaxation density	0.550353	3	0.183451	2.17	0.0919
Residual	24.362	288	0.0845902
Total (corrected)	678.179	319

Table 3.

Impact of material, relaxation process and structural parameters of knitted fabrics on loop length: four-factorial design for elasticized samples (main effects and interactions)

All samples	SS	Df	MS	F-ratio	P-value
Main effects
F: fiber	0.905282	1	0.905282	9.23	0.0027
Y: yarn	1.02103	2	0.510515	5.21	0.0062
R: relaxation	3.8052	1	3.8052	38.81	0.0000
D: density	498.99	1	498.99	5088.90	0.0000
Interactions
FY: fiber yarn	0.476451	2	0.238225	2.43	0.0905
FR: fiber relaxation	0.0426667	1	0.0426667	0.44	0.5102
FD: fiber density	0.04056	1	0.04056	0.41	0.5208
YR: yarn relaxation	0.161761	2	0.0808804	0.82	0.4397
YD: yarn density	0.179376	2	0.0896879	0.91	0.4022
RD: relaxation density	0.130667	1	0.130667	1.33	0.2496
FYR: fiber-yarn relaxation	0.0750208	2	0.0375104	0.38	0.6826
FYD: fiber-yarn density	0.650902	2	0.325451	3.32	0.0380
FRD: fiber-relaxation density	0.0120417	1	0.0120417	0.12	0.7264
YRD: yarn-relaxation density	0.427906	2	0.213953	2.18	0.1153
FYRD: fiber-yarn relaxation density	0.511466	2	0.255733	2.61	0.0760
Residual	21.1798	216	0.0980545
Total (corrected)	528.61	239

Table 4.

Impact of relaxation and material parameters of knitted fabrics on loop length: three-factorial design for density 1 – tight knitted samples (main effects and interactions)

Tight knitted samples	SS	Df	MS	F-ratio	P-value
Main effects
F: fiber	0.656641	1	0.656641	8.56	0.0040
Y: yarn	1.10112	3	0.367041	4.78	0.0033
R: relaxation	1.47264	1	1.47264	19.19	0.0000
Interactions
FY: fiber yarn	0.626012	3	0.208671	2.72	0.0468
FR: fiber relaxation	0.0445556	1	0.0445556	0.58	0.4474
YR: yarn relaxation	0.138502	3	0.0461673	0.60	0.6150
FYR: fiber-yarn relaxation	0.403777	3	0.134592	1.75	0.1588
Residual	11.0522	144	0.0767517
Total (corrected)	15.4955	159

Table 5.

Impact of relaxation and material parameters of knitted fabrics on loop length: three-factorial design for density 2 – loose knitted samples (main effects and interactions)

Loose knitted samples	SS	Df	MS	F-ratio	P-value
Main effects
F: fiber	0.21904	1	0.21904	2.37	1.1259
Y: yarn	1.74835	3	0.582782	6.31	0.0005
R: relaxation	2.94306	1	2.94306	31.84	0.0000
Interactions
FY: fiber yarn	0.615365	3	0.205122	2.22	0.0855
FR: fiber relaxation	0.0525625	1	0.0525625	0.57	0.4520
YR: yarn relaxation	0.561473	3	0.187158	2.02	0.1131
FYR: fiber-yarn relaxation	0.237523	3	0.0791742	0.86	0.4653
Residual	13.3097	144	0.0924288
Total (corrected)	19.6871	159

Table 6.

Impact of material and structural parameters of knitted fabrics on loop length: three-factorial design for dry relaxed samples (main effects and interactions)

Dry relaxed samples	SS	Df	MS	F-ratio	P-value
Main effects
F: fiber	0.175562	1	0.175562	2.07	0.1528
Y: yarn	1.38801	3	0.462669	5.44	0.0014
D: density	335.125	1	335.125	3942.74	0.0000
Interactions
FY: fiber yarn	0.333608	3	0.111203	1.31	0.2741
FD: fiber density	0.03249	1	0.03249	0.38	0.5374
YD: yarn density	0.72338	3	0.241127	2.84	0.0403
FYD: fiber-yarn density	0.56502	3	0.18834	2.22	0.0888
Residual	12.2397	144	0.0849981
Total (corrected)	350.583	159

Table 7.

Impact of material and structural parameters of knitted fabrics on loop length: three-factorial design for dynamically wet relaxed samples (main effects and interactions)

Dynamically wet relaxed samples	SS	Df	MS	F-ratio	P-value
Main effects
F: fiber	0.738481	1	0.738481	8.77	0.0036
Y: yarn	1.34033	3	0.446777	5.31	0.0017
D: density	316.997	1	316.997	3765.60	0.0000
Interactions
FY: fiber yarn	0.347542	3	0.115847	1.38	0.2525
FD: fiber density	0.0262656	1	0.0262656	0.31	0.5773
YD: yarn density	0.0977219	3	0.032574	0.39	0.7626
FYD: fiber-yarn density	0.636507	3	0.212169	2.52	0.0603
Residual	12.1223	144	0.0841824
Total (corrected)	332.306	159

Table 8.

Impact of relaxation process and structural parameters of knitted fabrics on loop length: four-factorial design for the group of single-spun yarns (main effects and interactions)

Single-spun yarns	SS	Df	MS	F-ratio	P-value
Main effects
F: fiber	0.654081	1	0.654081	7.44	0.0072
Y: yarn	0.187006	1	0.187006	2.13	0.1470
R: relaxation	2.21606	1	2.21606	25.19	0.0000
D: density	321.064	1	321.064	3650.05	0.0000
Interactions
FY: fiber yarn	0.339481	1	0.339481	3.86	0.0514
FR: fiber relaxation	0.160656	1	0.160656	1.83	0.1787
FD: fiber density	0.231801	1	0.231801	2.64	0.1067
YR: yarn relaxation	0.167056	1	0.167056	1.90	0.1703
YD: yarn density	0.170956	1	0.170956	1.94	0.1654
RD: relaxation density	0.267806	1	0.267806	0.30	0.5820
FYR: fiber-yarn relaxation	0.000680625	1	0.000680625	0.01	0.9300
FYD: fiber-yarn density	0.841806	1	0.841806	0.96	0.3296
FRD: fiber-relaxation density	0.159391	1	0.159391	1.81	0.1804
YRD: yarn-relaxation density	0.00203063	1	0.00203063	0.02	0.8794
FYRD: fiber-yarn relaxation density	0.0278256	1	0.0278256	0.32	0.5747
Residual	12.6664	144	0.0879615
Total (corrected)	338.158	159

Table 9.

Impact of relaxation process and structural parameters of knitted fabrics on loop length: three-factorial design for the group of single-spun yarns with elastane (main effects and interactions)

Single core-spun yarns with elastane	SS	Df	MS	F-ratio	P-value
Main effects
F: fiber	0.968	1	0.968	7.35	0.0084
R: relaxation	1.8	1	1.8	13.66	0.0004
D: density	168.026	1	168.026	1275.58	0.0000
Interactions
FR: fiber relaxation	0.091125	1	0.091125	0.69	0.4083
FD: fiber density	0.29768	1	0.29768	2.26	0.1371
RD: relaxation density	0.02178	1	0.02178	0.17	0.6855
FRD: fiber-relaxation density	0.160205	1	0.160205	1.22	0.2738
Residual	9.48424	72	0.131726
Total (corrected)	180.849	79

Table 10.

Impact of relaxation process and structural parameters of knitted fabrics on loop length: three-factorial design for the group of single-spun yarns without elastane (main effects and interactions)

Conventional yarns without elastane	SS	Df	MS	F-ratio	P-value
Main effects
F: fiber	0.0255612	1	0.0255612	0.58	0.4494
R: relaxation	0.583111	1	0.583111	13.19	0.0005
D: density	153.209	1	153.209	3466.47	0.0000
Interactions
FR: fiber relaxation	0.0702112	1	0.0702112	1.59	0.2116
FD: fiber density	0.0183012	1	0.0183012	0.41	0.5220
RD: relaxation density	0.00703125	1	0.00703125	0.16	0.6912
FRD: fiber-relaxation density	0.0270112	1	0.0270112	0.61	0.4369
Residual	3.18221	72	0.0441974
Total (corrected)	157.122	79

Table 11.

Impact of yarn structure, relaxation process and structural parameters of knitted fabrics on loop length: three-factorial design for the group of viscose single-spun yarns (main effects and interactions)

Viscose single-spun yarns	SS	Df	MS	F-ratio	P-value
Main effects
Y: yarn	0.0112812	1	0.0112812	0.20	0.6537
R: relaxation	1.78503	1	1.78503	32.10	0.0000
D: density	169.275	1	169.275	3044.46	0.0000
Interactions
YR: yarn relaxation	0.0945312	1	0.0945312	1.70	0.1964
YD: yarn density	0.247531	1	0.247531	4.45	0.0383
RD: relaxation density	0.0277512	1	0.0277512	0.50	0.4822
YRD: yarn-relaxation density	0.00741125	1	0.00741125	0.13	0.7161
Residual	4.00327	72	0.055601
Total (corrected)	175.452	79

Table 12.

Impact of yarn structure, relaxation process and structural parameters of knitted fabrics on loop length: three-factorial design for the group of polyacrylonitrile single-spun yarns (main effects and interactions)

Polyacrylonitrile single-spun yarns	SS	Df	MS	F-ratio	P-value
Main effects
Y: yarn	0.515205	1	0.515205	4.28	0.0421
R: relaxation	0.59168	1	0.59168	4.92	0.0297
D: density	152.021	1	152.021	1263.45	0.0000
Interactions
YR: yarn relaxation	0.073205	1	0.073205	0.61	0.4379
YD: yarn density	0.007605	1	0.007605	0.06	0.8022
RD: relaxation density	0.15842	1	0.15842	1.32	0.2550
YRD: yarn-relaxation density	0.022445	1	0.022445	0.19	0.6671
Residual	8.66318	72	0.120322
Total (Corrected)	162.053	79

Table 13.

Loop length

Loop length
Samples		D1			D2
Samples		x (mm)	s (mm)	CV (%)	x (mm)	s (mm)	CV (%)
CV MOU	DR	8.68	0.16	1.89	11.99	0.61	5.06
CV MOU	CR	8.67	0.29	3.37	11.39	0.35	3.07
PAN MOU	DR	8.86	0.25	2.80	11.75	0.22	1.89
PAN MOU	CR	8.62	0.28	3.26	11.49	0.27	2.33
CV C-TW	DR	8.93	0.24	2.64	11.57	0.24	2.08
CV C-TW	CR	8.71	0.24	2.73	11.46	0.15	1.31
PAN C-TW	DR	8.97	0.33	3.64	11.85	0.24	2.00
PAN C-TW	CR	8.72	0.24	2.76	11.70	0.14	1.18
CV C-SP	DR	8.67	0.20	2.32	11.64	0.20	1.73
CV C-SP	CR	8.25	0.36	4.31	11.33	0.22	1.92
PAN C-SP	DR	8.86	0.44	5.02	11.76	0.41	3.45
PAN C-SP	CR	8.75	0.41	4.74	11.40	0.51	4.51
CV CONV	DR	8.72	0.18	2.06	11.50	0.21	1.80
CV CONV	CR	8.47	0.21	2.53	11.29	0.26	2.31
PAN CONV	DR	8.69	0.16	1.89	11.48	0.19	1.65
PAN CONV	CR	8.64	0.25	2.92	11.32	0.19	1.69

D1: tight structure, D2: loose structure, CV: viscose, MOU: mouliné, PAN: polyacrylonitrile, C-TW: core-twisted, C-SP: core-spun, CONV: conventional fabrics, DR: dry relaxation, CR: relaxation consolidation.

Results and discussion

Initially, all samples were treated as a whole (4 × 2³= 32 experiments) in order to evaluate the overall impacts of material, structure and relaxation influencing parameters on loop length, and also to define the magnitude of these individual factors. The multifactorial ANOVA (Table 2) shows that these four factors have statistically significant effects on loop length at the 99.0% confidence level, as the P-values of all main effects are less than 0.01. The investigated system is dominated by knitted fabric density (D) as being by far the most important factor. The knitted fabric density is dependent on the machine cam setting, which has a direct impact on the course density of the knitted structure and consequently influences the loop length. The relaxation process also has a major impact on loop length, as it influences shrinking after the knitting process. This correlates directly with previous studies, investigating the effects of fabric density and relaxation on loop length and knitted fabric geometry.^{3–6,9–12,14,16–19} From Table 2, it can also be seen that no two-factorial or higher-order – three- and four-factorial – interactions were found to be statistically significant at the 95.0% confidence level.

Next, the knitted fabrics made from yarns without elastane – samples denoted as CONV – were excluded from the ANOVA processing as they differ from the samples made from elasticized yarns, not only in yarn structure but also in fiber content. Knitted fabrics made from mouliné (MOU), core-twisted (C-TW) and core-spun (C-SP) yarns were therefore analyzed. The ANOVA results (Table 3) are very similar to those obtained by processing all 32 samples (Table 2).

On the basis of the ANOVA results showing the major significance of the knitted structure density (Tables 2 and 3), the samples were divided into two groups, with 16 experiments each. These were separated according to the knitted structure density level: density 1 – tight structure and density 2 – loose structure. They were processed by three-factorial (2 × 4 × 2 = 16 experiments) ANOVA (Tables 4 and 5).

The results of these statistical analyses of both density level groups show that the relaxation process (R) has a major impact on loop length produced at a defined density level. This is in agreement with the findings from previous studies by various authors, investigating the relaxation of single-weft knitted fabrics.^{3–6,9–12,14,16–19} Yarn structure impact (Y) is also statistically significant, for both density levels, at the 99.0% confidence level (Tables 4 and 5). The structure of the investigated yarns differs in fiber arrangement, twist, extension properties, etc., all of which influence loop formation during the knitting process. For tight knitted structures, the combined impact of fiber type and yarn structure (FY) is important as well (95.0% confidence level, P-value less than 0.05). The interaction plot fiber-yarn is presented in Figure 2. For all tight knitted structures, PAN samples exhibit longer loops than CV samples, which contributes to the different extension and relaxation behavior of yarns made from the two fiber generics during the knitting process. Samples made from single core-spun yarns display the greatest difference in loop length for CV and PAN knitted structures. This may be explained by the different mechanical properties of the two fiber types, forming a sheath around the elastane core within a single core-spun yarn. Studies on loose knitted structures showed no two-factorial or three-factorial interactions that were statistically significant.

Figure 2.

Impact of relaxation and material parameters of knitted fabrics on loop length: three-factorial design for density 1 – tight knitted samples (interaction plot).

As relaxation proved to have major impact on loop length (Tables 2 –5), the original 32 samples were again divided into two groups, with 16 experiments each. These were separated according to the relaxation process employed: dry relaxed and dynamically wet relaxed samples. They were processed by three-factorial (2 × 4 × 2 = 16 experiments) ANOVA (Tables 6 and 7).

The statistical analysis proved the significance of the knitted structure density (D) for both dry relaxed and dynamically wet relaxed knitted fabrics. The yarn structure (Y) impact is also statistically significant, for both dry relaxed and dynamically wet relaxed structures, at the 99.0% confidence level (Tables 6 and 7). The position and capture of the staple fibers within the yarn and their mechanical and hydrophilic properties influence the yarn’s characteristics. Moreover, the interactive influence of yarn structure and knitted structure density (YD) has some significance for the dry relaxed fabric samples (95.0% confidence level, P-value less than 0.05).

Next, the impact of elastane addition to the knitted loop length was assessed. The group of single-spun yarns (core-spun yarns, incorporating elastane and conventional yarns without elastane) was investigated as a whole (Table 8), by four-factorial ANOVA (2⁴= 16 experiments). Then, it was split into two groups, with respect to the yarn structure and elastane content presented in Figure 1 and Table 1. One group included core-spun yarns with an incorporated elastane core (Table 9), while the other included conventional yarns, without elastane (Table 10). Each individual group was processed by three-factorial (2³= 8 experiments) ANOVA.

From Table 8, it can be seen that for single-spun yarns, in addition to density level (D) and relaxation (R), the fiber type (F) influences the loop length at the 99.0% confidence level (P-value less than 0.01). The effect of yarn structure was not found to be statistically significant when focusing on the group of single-spun yarns.

The magnitude of effects for the individual groups, containing elasticized or non-elasticized yarns, respectively, may be deduced from Tables 9 and 10. For both groups, relaxation process (R) and knitted fabric density (D) influence loop length at the 99.9% confidence level (P-value less than 0.001), as proven previously by numerous researchers.^{3–6,9–12,14,16–19} Tables 9 and 10 show that density has a much greater impact on loop length than relaxation. Furthermore, it may be concluded, on the basis of the ANOVA analysis, that the fiber type (F) influences the loop length only in the case of elasticized yarns (99.0% confidence level, P-value less than 0.01), while in the case of conventional yarns, its influence is not statistically significant.

Finally, the group of single-spun yarns was split into two groups with respect to the fiber type. One group included CV samples, while the other included PAN samples. Each individual group was processed by three-factorial (2³= 8 experiments) ANOVA (Tables 11 and 12).

For both groups, knitted fabric density (D) has a statistically significant impact on loop length at the 99.9% confidence level (P-value less than 0.001). The relaxation process influences the loop length as well. Yarn structure has a significant impact on the loop length for the PAN samples, while for the CV samples, the interaction yarn structure–density is statistically significant. PAN samples exhibit longer loops than comparable CV samples in most cases, which contributes to the different loop configuration and relaxation of yarns made from the two fiber types.

Loop length of the investigated knitted structures was also examined, in order to evaluate the impact of elastane addition on loop length and, consequently, yarn consumption. Table 13 shows that loop length decreases during the process of dynamic wet relaxation, but this decrease is not substantial (0.1–4.8%), as shown by ANOVA statistics. According to the findings of other researchers,¹⁵ the loop configuration and geometry changes during relaxation. Loop geometry changes affect the loop width (wale density) and height (course density) and also fabric thickness, but not the loop length significantly. Moreover, Table 13 shows that there are only minor differences in loop length among the structures knitted from elasticized and non-elasticized yarns. Again, elastane addition does not significantly influence the loop length of the fabrics knitted at the same machine cam setting and relaxed by the same process. However, their loop configuration changes. Consequently, loop width (wale density), loop height (course density) and fabric thickness will also change, as seen from Table 14. This is associated with a variation of other parameters describing the compactness of the knitted structure, as was established in previous investigations.³⁰

Table 14.

Structural characteristics of the samples

Sample		Knitted fabric characteristics
		Wale density w (dm⁻¹)		Course density c (dm⁻¹)		Stitch density S (dm⁻²)		Fabric thickness t (mm)
		D1	D2	D1	D2	D1	D2	D1	D2
CV MOU	DR	50	48	81	79	4086	3803	1.62	1.95
CV MOU	CR	65	52	119	89	7680	4650	1.87	2.03
PAN MOU	DR	48	44	78	58	3709	2557	1.53	1.78
PAN MOU	CR	58	52	103	93	5959	4849	2.18	2.54
CV C-TW	DR	49	43	83	66	4091	2867	1.50	1.75
CV C-TW	CR	61	53	114	98	6930	5243	1.97	2.34
PAN C-TW	DR	47	46	75	58	3537	2663	1.55	1.88
PAN C-TW	CR	59	54	104	89	6127	4800	1.96	2.17
CV C-SP	DR	52	47	97	83	5056	3877	1.76	2.27
CV C-SP	CR	67	57	137	111	9131	6387	2.06	2.34
PAN C-SP	DR	47	41	82	66	3847	2714	1.72	2.06
PAN C-SP	CR	58	50	114	94	6646	4717	2.39	2.71
CV CONV	DR	45	34	59	40	2654	1372	1.03	0.90
CV CONV	CR	38	30	69	46	2576	1408	1.26	1.08
PAN CONV	DR	46	38	62	35	2844	1339	1.17	1.16
PAN CONV	CR	47	38	64	44	2995	1709	1.37	1.32

D1: tight structure, D2: loose structure, CV: viscose, MOU: mouliné, PAN: polyacrylonitrile, C-TW: core-twisted, C-SP: core-spun, CONV: conventional fabrics.

Conclusions

Fiber type, yarn structure, knitted fabric density level and the relaxation process all have a statistically significant effect on loop length. For both groups of knitted fabrics – elasticized and non-elasticized – knitted fabric density and the relaxation process influence the loop length the most. This is in correlation with previous studies investigating the effects of fabric density and relaxation on loop length and knitted fabric geometry. Knitted fabric density is dependent on the machine cam setting, affecting directly the course density of the knitted structure and influencing the loop length. Knitted fabric density has a greater impact than relaxation, which affects shrinking characteristics, after the knitting process.

The fiber type influences the loop length only in the case of elasticized knitted fabrics, whilst in the case of conventional yarns, its influence is not statistically significant.

The loop length decreases during the process of fabric wet relaxation, but this decrease is not substantial. Only minor differences are exhibited in loop length, in structures knitted from elasticized and non-elasticized yarns. Once more, elastane addition does not significantly influence the loop length of fabrics knitted using the same machine cam setting and relaxed by the same process.

The results of this research will contribute to production strategy; control of dimensional parameters of knitted structures; repeatability of the processes and products; and production efficiency in the manufacture of knitted fabrics incorporating elastane.

Footnotes

Funding

This research received no specific grant from any funding agency in the public, commercial or not-for-profit sectors.

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