impact of lycra filament on extension and characteristics...
TRANSCRIPT
Indian 10urnal of Fibre & Textile Research Vol. 28. December 2003 , pp. 423-430
Impact of lycra filament on extension and rec~)Very characteristics of cotton knitted fabric
A Mukho padhyay"
Department of Textile Technology, National Institute of Technology, lalandhar 144 0 II, India
I C Sharma & A Mohanty
Department of Textile Technology, The Technological Institute of Textil e & Sciences, Bhiwani 127021 , India
Received 24 April 2002; accepted 24 September 2002
The effect of lycra fil ament and full relaxation finisH on the extension at peak load. immediate recovery, delayed recovery, permanent set and resiliency of cotton-Iycra blended knitted fabric has been studied. It is observed that for lycra blended fabric, the immediate recovery, extension and resiliency are higher but delayed recovery and permanent set are lower than those of 100% cotton fabric. Effect of full relaxation treatment is found to be useful in case of all-cotton fabric . On the application of external load, both Iycra and non-Iycra fabrics show higher extension at peak load along course direction than that along the other directions of fabric. However, the biased direction of 100% cotton fabric shows significantly higher immediate recovery and resiliency but lower delayed recovery and permanent set. In general , with repeated load cycles. the extension at peak load increases marginally but immediate recovery and resiliency change considerably during initial number of cycles. Laundering reduces the extension at peak load, immediate recovery and resiliency, whereas del ayed recovery and permanent set become higher.
Keywords: Cotton fabric, Delayed recovery, Extension at peak load, Full relaxation, Immediate recovery, Lycra filament. Permanent set, Resiliency
1 Introduction The yarn is subjected to tensile, bending, torsional
and compressional strains during the process of knitting. Due to the elastic components of strain energy, the loops tend to change shape so as to reach minimum energy level. The shrinkage of knitted fabrics significantly increases with the introduction of home laundering and tumble drying. The deformation caused by the mechanical forces can be reduced by appropriate relaxation. The process occurs when the yarn is bent to stitch loops and the frictional forces at the binding points are brought to a minimum and are in equilibrium. The quality requirement of knitted fabrics becomes highly demanding in terms of appearance and performance. In response to the demand, the fabric producers were inspired to develop a rich source of materials using a variety of yarn with Iycra for stretch and recovery.
The occulTence of elastic recovery is often evident during cyclic loading as well as stretch during body
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movement. It is important to observe the effect of Iycra filament on the shape retention properties of knitted fabrics even after undergoing repeated was h and wear cycles. It may be noted that although the effects of laundering cycles on dimensional and mechanical properties of knitted fabrics have been studied by some research workers 1.3, no studies have been reported on Iycra blended fabrics . Various types of shrink-resist and anti-shrink treatments have been described in literature4
•5
. In mechanical processing, full relaxation treatment is meant for improving the performance of knitted fabrics, but its impact on Iyc ra blended fabrics is not known. In the present work, the extent of influence of full relaxation treatment on the extension and recovery characteristics of knitted fabrics produced by Iycrafilament and cotton ya rn has been examined.
2 Materials and Methods 2.1 Materials
Four different fabric samples were prepared from 19.7 lex (30S) yarns on a circular knitting machine of ninety feeders , 24 gauge and a needle bed of 30 inch diameter in identical condition. Lycra blended fabrics
424 INDIAN J. FIBRE TEXT RES , DECEMBER 2003
were prepared using few feeders wherein Iycra filaments (4% of the total weight of material) form the loop with cotton yarn alternatively with back plating. The samples thus prepared along with their codes are given below:
NLC - Non-Iycra compacted fabrics NLFR - Non-Iycra full-relaxed fabrics LC - Lycra compacted fabrics LFR - Lycra full-relaxed fabrics All the fabrics were processed in the industry using
the sequence of scouring and compaction respectively. Additional full relaxat ion treatment was gi ven to the NLFR and LFR fabrics before compaction in a relaxed dryer, known as horizontal dryer, at 1600 C temperature and 4 mlmin speed with 20% overfeed. All the fabrics were subjected to laundering process in a domestic twin-tub washing machine as per the ASTM standard6 using 0.5 gIL solution of non-ionic detergent Vaptex 1535 (96%). Four specimen were separately given 1,6 and 15 laundering cycles and thus additional 12 specimens were prepared from 4 unlaundered samples. All the laundering cycles were carried out at normal temperature, which was followed by drying in the open space during daylight.
2.2 Methods Fabric dimensional characteristics were measured
and are given in Table 1. Farbic extension and recovery characteristic were measured on Instron tester (Model 4411) in tensile mode using the ASTM standards 7 originally developed for measuring fibre recovery. The maximum load of 250 gf/cm with 12 mm/min cross head speed was used on the fabric samples of 50 mm gauge length and12 cm width.
The maximum extension, immediate recovery, delayed recovery, permanent set and resi liency were
studied by plotting the jaw movement distance on xaxis and the applied load on y-axis (Fig. 1). The fabrics was subjected to 10 loading cyc les and the foll owing characteristics were studied at the interval of 1, 5 and 10 load cycles along wale. course and biased directions :
Extension at peak load (% )=EH/(Gauge length)x I 00 Immediate recovery (%) = GHIEH x 100 Delayed recovery (%) = FGIEH x 100 Permanent set (%) = EF/EH x 100 Resiliency (%) = W21WI x 100
where, WI is the area EIHE above x-axis; W2. the area GIHG above x-axis; and E, F, G, H and I, the points shown in Fig. 1.
For the entire specimen, 15 tests were carried out at standard testing atmosphere.
u ro o -l
r-.----------------__________ ~I
EL-__ ~ ____ ~~ ______ L_ __ ~H
Exten s ion Fig. I-Extension and recovery behaviour of rab ri c
Table 1- Fabric dimensional characteristi cs
Characteristic Non-Iycra compacted Non-Iycra fully Lycra compacted Lycra full y scoured relaxed scoured relaxed
0" I" 6· 15· 0· I" 6· 15· 0' I· 6· 15· 0· I a 6" 1) ,1
Wales/inch 42.0 43.2 43 .5 43.6 40.4 41.4 4 1.6 41.6 42.3 42.6 42.6 42.4 39.0 39.7 40.0 40 .0
Coursesli nch 53.9 54.5 55.2 55.5 608 61.0 6 1.6 6 1. 8 59.3 62.0 62 .9 64.7 71.4 72.92 74.1 74 8
Stitch densit~ , 2264 2354 240 1 2423 2456 2525 2563 257 1 2508 264 1 2679 2743 2746 2873 2964 2992 sti tchesli nch
Stitch length . mm 2.33 2.37 2.38 2.37 2.40 2.39 2.42 2.42 2.73 2.66 2.60 2.59 2.65 2.62 2 .6.J. 2 .58
Fabric weight. g/m2 174.8 180.8 180.9 180.6 198.1 215 .2 226.4 228.2 194. 1 207 .9 209.8 2 11.9 224.0 234 .2 236.5 236.+
Thickness. mm 0.53 0.54 0.54 0.55 060 0.62 0.58 0.55 0.65 0.67 0.67 0.67 0.7 1 0.74 0 .72 0.7.J.
" Laundering c~c1es
MUKHOPADHYAY el at .: EXTENSION & RECOVERY CHARACTERISTICS OF KNITTED FABRIC 425
3 Results and Discussion 3.1 Effect of Direction of Loading on Fabr'ics before and after
Laundering 3.1.1 Extension at Peak Load
It has been observed from Tables 2 - 5 and Fig. 2 that the extension at peak load is higher in course direction whereas it is lowest in wale direction and
intermediate in biased direction (450 angle to wale or course). This is due to the higher loop extension in course direction as the forces are applied directl y in the direction parallel to the axis of line of loop.
The extension of the fabric depends largely on the change in configuration of these initially circular loop
Table 2 - Extension and recovery behaviour of non-Iycra compacted fabrics
Characteristic
Extension at peak load. %
Intermediate recovery, %
Delayed recovery, %
Permanent set, %
Resiliency, %
"Laundering cycles
Characteristic
Extension at peak load, %
Intermediate recovery, %
Delayed recovery, %
Permanent set, %
Resiliency, %
"Laundering cycles
Load
cycles
I
5
10
I
5
10
1
5
10
I
5
10
5
10
Load cycles
I 5 10
I 5 10
I 5 10
I 5 10
I 5 10
Wale direction
0" I"
23.30 22.31
24.41 23.75
24.84 24.07
62.74 60.12
80.28 78.66
80.42 79.13
6" 15"
22.68 22.91
2391 24.11
24.17 24.52
59.62
77.27
78.39
58.16
76.42
76.70
16.01 16.73 16.31
19.72 21.34 22.73
19.58 21.87 21.61
17.13
23 .58
23 .30
21.25
o o
23 .15
o o
24.00 24.71
o 0
o 0
26.02 24.28 23 .97 23.71
39.03 38.07 38.37 37.34
41.26 39.95 39.11 39.03
Course direction
0" I" 6" 15"
51.24 48 .05 45.35 32.8 1
52.62 50.98 47.97 45.33
53.24 51 .68 51 .52 46.01
70.17
86.33
86.20
9.89
13.67
13.80
68.08
84.29
86.73
11.32
15.7 1
13 .27
67.47
83.16
84.24
11.21
16.84
15 .76
66.90
82.69
83.34
11.47
17.31
16.37
19.94 20.69 21.32 21.63
000 0
o o o 26.71 24.59 24.7 1
42.82 42.46 42.03
44.10 44.20 43.58
o 24.12
39.94
42.10
Biased direction
0"
32.8 1
33 .85
34.14
75.33
87.37
87.66
9.92
12.63
12.34
14.75
o o
I"
3 1.27
32.77
33 .1 7
72.19
84.88
87.34
12.79
15 . 12
12.61
15.02
o o
33 .03 28.88
46.18 44.43
48.05 46.41
6" IS"
30.49 30.7 1
32.26 32.38
32.64 3282
69.93
83.59
85 .67
12.95
16.41
14.33
17.12
o o
6909
83.08
8432
13.0 1
16.92
15 .68
1790
o o
27.93 27.53
43.52 42.45
44.23 43.7i
Table 3 - Extension and recovery behaviour of non-Iycra full-relaxed fabrics
Wale direction 0· I" 6" IS"
39.22 37.45 35 .48 32.80 40.62 39.86 37.82 34.88 41.23 40.52 38.42 35.38
69.84 67.04 65.82 64.55 89.92 87.75 85.47 85.37 89.27 88.60 87.43 85.81
11.63 12.08 10.73
18.53 o o
12.50 12.25 11 .40
13 .06 14.53 12.57
20.46 21.12 o 0 o 0
13.39 14.63 14.19
22.06 o o
29.12 27.94 26.61 26.5 1 51.32 49.90 45.35 44.39 52.98 52.80 47.83 45.05
Course direction 0" I" 6" 15"
55 .2 1 53.72 47.09 44.41 57.99 56.76 49.7 46.96 58.42 57.56 50.39 47.50
69.34 64.12 63. 13 62.62 88.71 87.42 86.83 81.55 9004 88.86 87.33 84.84
10.82 11.29 9.96
12.03 12.58 11.l4
19.84 2385 o 0 o 0
13.27 13. 17 12.33
13.54 18.45 15 .16
23.60 23.84 o 0 o 0
28.73 26.70 26.38 25.55 51.76 50.86 48 .54 44.95 56.12 54.39 5 1.62 47.28
Biased direction 0" I " 6" 15"
45 .73 43.69 39.82 37.6 1 47.02 45 .77 41.82 39.59 47 .84 46.42 42.36 40. 11
78 .23 75 .11 72.15 71.83 89.96 88.83 87.95 87.30 90.84 89.66 88.23 87.9 1
7.12 10.04 9. 16
14.65 o o
8.28 11.17 10.34
1661 o o
9.46 12.05 11.77
18.39 o o
9.75 12.70 12.09
18.42 o o
34.23 31 .62 30.59 30.28 53.34 52.45 49.12 48.54 57.03 56.40 51.1 I 50.74
426
Characteristic Load cycles
Extension at peak load, %
Intermediate recovery, %
Delayed recovery, %
Permanent set. %
Resiliency, %
"Laundering cycles
Characteristic
Extension at peak load. %
Intermediate recovery, %
I 5 10
I 5 10
I 5 10
I 5 10
I 5 10
Delayed recovery, %
Permanent set. '7n
Res iliency, %
"Laundering cycles
INDIAN 1. FIBRE TEXT. RES .. DECEMBER 2003
Table 4 - Extension and recovery behaviour of Iycra compacted fabrics
Wale direction 0" I" 6" 15"
68 .95 77.66 78.72 69.97 81.89 83.82 70.74 82.83 84.16
79.26 83.15 83.81
78.69 92.89 94.04
6.61 7.11 5.96
14.70 o o
35.91 53.03 54.69
73 .97 72.72 89.16 87.93 89.56 87.96
72.00 87.45 87.49
8.74 10.84 10.44
17.29 o o
31.45 50.85 53.69
8.93 12.07 12.04
18.35 o o
8.76 12.55 12.5 1
19.24 o o
30.37 30.32 49 .98 49.45 53.14 52.45
0"
115.56 123 .06 124.8 1
77.22 92.90 93 .35
5.72 7.10 6.65
18.06 o o
32.85 49.83 53.04
Course direction I"
111.05 118.52 120.52
72.68 91.99 92.22
6.26 8.01 7.78
21.06 o o
27.85 49.32 5 1.56
6"
101.33 107.86 109.44
71.84 91.20 91.97
6.96 8.80 8.03
21.20 o o
27.67 48 .98 51.34
15"
93.27 100.17 102 .03
71.54 90.88 91.32
7.15 9. 12 8.68
21.30 o o
27.50 48.33 50.38
Table 5 - Extension and recovery behaviour of Iycra full-relaxed fabrics
Load
eycles
I
5
10
Wale direction
0" I" 6" 15"
99.26 115.14 119.26 119.10
104.65 121.14 125.92 127.0
106.09 122.88 127.36 129.36
I 79.96 74.56 74.42 74.29
5 94.31 93.94 92.28 91.09
10 95.67 93.84 92.96 91.84
I
5
10
I
5
10
I
5
10
5.32 6.05 5.42 6.21
5.69 6.06 7.72 8.91
4.33 6.1 6 7.04 8.16
14.71
o o
37.22
56.8 1
60.73
19.39
o o
32.85
56.43
59.75
20. 16
o o
20.50
o o
3 1.44 30.56
55.05 54.56
58.49 57.27
Course direction 0" I" 6" 15"
117 .25 111.1 3 106.92 102.56
120.98 116.68 112.82 109. 16
121.87 11 8.74 114.44 111.22
78.06 75 .02 74.55 73.83
93 .92 92.84 92.80 92.34
95.41 93.75 9332 93.05
5. 19 7.29 6.6 1 6.67
6.08 7.16 7.20 7.66
4.59 625 6.68 6.95
16.74
o o
34.68
57 .88
61.73
17.68
o o
32.89
57.88
60.33
18.84
o o
19.50
o o
31.44 30.43
55.46 5 1.65
58.75 54. 18
0"
79.29 82.00 82.98
80.91 92.49 94.29
5.60 7.51 5.71
13.49 o o
38.22 57.83 59.85
0"
Biased direction I"
78.6 1 8 1. 83 82.79
6"
76.93 7419 8074 78 .-+1 8 1.84 79.43
78 .62 78.17 77.77 91.76 91.66 91.45 92 .92 92.67 92. 58
6.57 8.24 7.08
14.8 1 o o
35.6 1 5345 55 .78
7.67 8.34 7.33
14. 16 o o
33.42 52.71 54.57
Biased direction I" 6"
7.43 8 )')
8.42
14.80 o o
3308 5 1.98 53.62
15
105.06 96.80 94.04 93. 7 1
107. 18 100.30 99.72 97.-+7
107.94 10 1.48 10 1.24 98.83
81.78 80.85 80.3 1 80.2
94.29 93.40 93 . 12 92 .20
94.70 93 .80 94.65 93.00
5.70 601 6.45 7.02
5.7 1 6.60 6.88 7.80
4.95 6.20 5.35 7.00
12.52
o o
41.26
65 .61
68 .33
13. 14
o o
39. 11
63.99
66. 18
13 24 14.70
o 0
o 0
37.35 37 .33
61.20 59 79
62.06 61. 89
segments. These segments remain flat when external tension is applied in course direction . But, owing to the nature of loop interiociGng, the yarn slippage could be expected to occur at an earlier stage for extension in the wale direction than that for extension in wale direction. In order to allow the occurrence of
slippage, the net reaction force must always act in a direction normal to yarn axis , leading a greater extension at peak load in course dircctionx
.
It is further observed from Tables 2-5 that the extension at peak load decreases with the increase in laundering cycles in case of non-I ycra fabric s v"hil e
" ..
MUKHOPADHYAY et at.: EXTENSION & RECOVERY CHARACTERISTICS OF KNITTED FABRIC
120~----------------------------__ ~--~
'* ;100 .. .S! ~80 !. .60 c: o ~ 40 CD lC
-+-NLC __ NLFR
-.-LC
.....-LFR
w 20+-----~----.-----------~----------__4 Wale Biased Course
Direction of loading
Fig. 2-Effect of direction of loading on the extension at peak load of unlaundered knitted fabric
~ ~ CD > 0 Co) Gl ... Gl • '6 Gl
E .E
OOr-----------------------------------~
80
70
60 Wale
-.-LC
.....-LFR
Biased
Direction of loading Course
Fig. 3--Effect of direction of loading on the immediate recovery of unlaundered knitted fabric
the trend is reversed in case of Iycra blended fabrics in wale direction . In case of Iycra blended fabric, there is a prominent increase in courses per unit length due to the laundering (Table 1) which results in greater extension along the wale direction . However, the increase in courses per unit length reduces the load per loop along the course direction, leading to general reduction in extension at peak load due to the laundering.
3.1.2 Recovery Characteristics
It has been observed from Fig. 3 that with the change in direction of loading, the immediate recovery is maximum in biased direction in all the fabrics. However, the difference in values is more prominent in non-Iycra fabrics. This is due to the presence of Iycra in blended fabrics which improves the flexibility and shape retention properties of fabrics, irrespective to the direction of loading9
• Again on the application of load, the fabric behaviour in biased direction neither exhibits greater extension of loop as in course direction nor it shows a greater deformation of knit structure and yam extension as in wale direction, leading to a greater recovery in biased
20 -+-NLC
'* __ NLFR
~ 16 -.-LC GI > .....-LFR 0 2! 12
" ~
J I'G 8 Ii c := • • 4
Wale Biased Course
Direction of loading
Fig. 4--Effect of direction of loading on the delayed recovery of unlaundered knitted fabric
25,-------------------------------------.
~ 20 Gi III
c: 15 CD c III
E CD 10 a..
-+-NLC ___ NLFR
-.-LC
.....-LFR
5+-----------.------------r----------~ Wale . Biased
Direction of loading Course
Fi g. 5--Effect of direction of loading on the permanent set of unl aundered knitted fabric
direction . It is further observed that the immedi ate recovery decreases with the increase in laundering cycles. This may be due to the some amount of damage of fabrics by mechanical action of washing machine and action of detergent during launderingl . Due to laundering, the hairiness of the cotton yarn becomes higher which may cause greater obstruction at crossover points of knitted fabrics during recovery.
Fig. 4 shows that the variation in delayed recovery with the direction of loading is very prominent in case of non-Iycra coUon fabric s. The said va lue is lowest in biased direction. The de layed recovery is increased particularly during first cycle of laundering, and after subsequent laundering the changes become marginal.
It can be seen from Fig. 5 that the permanent set of fabric possesses a lowest value in biased directi on. It also has the tendency to increase with the increase in laundering cycles and in certain fabrics the changes in permanent set become marginal after a parti cu lar number of laundering cycles.
It is observed from Fig. 6 that the resi li ency increases from course to biased direction of loading. In general, the fabric resiliency decreases particularl y during first cycle of laundering.
428 INDIAN 1. FIBRE TEXT. RES. , DECEMB ER 2003
~.-----------------------------------~
45
e:. 40 >I,)
. ~ 35
.~ 30
a:: 25
-+-NLC ___ NLFR
20+-----------,------------r----------~
Wale Biased
Direction of loading Course
Fig. 6 - Effect of direClion of loading on the resiliency of unlaundered kni lled fabric
3.2 Effect of Load Cycles on Fabrics before and after Laundering
3.2.1 Extension at Peak Load Tables 2-5 show that with the increase in load
cycles, the extens ion at peak load increases marginally. This is due to the nature of ex tension and recovery behaviour of fabric which gradually stabili ze with the increase in load cycle.
3.2.2 Recovery Characteristics It is observed fro m Tables 2-5 that the immediate
recovery sharply increases initia lly and thereafter changes become marginal in a ll the fabrics . As the permanent set approaches zero after initia l number of load cycles, the internal reaction forces ac ting on the knitted fabric response immediate ly to the ex ternal force, leading to a greater immediate recovery after the re lease of load.
Tables 2-5 show that in genera l wi th the increase in load cyc les, except in case of non-Iycra compacted fabr ics, the change in fabric delayed recovery along the wale and course directions is significant. During the initial cycles of loading, the change in total e lastic recovery of fabric is therefore domi nated by fabric immediate recovery.
It is again observed from Tables 2-5 that the permanent set approaches zero in fifth cycle of loading in all the fa brics before and after laundering. This is due to the change in loop configuration and loop interlocking points in plain knitted fabrics in case of first load cycle. The loops are unable to retain their shape as there is enough free space in between the loops before the load is applied. Therefore, the permanent set reduces drastically in second load cycle and approaches zero in fifth load cycle. Further, at first load cyc le for a particular ex tension level as the yam extends, the slippage between the fibres occurs up to a certain level and further sli ppage is prohibited with the
increase in load cycle as the extension at peak load levels off, restricting the permanent set to zero.
Fabric tensile res iliency shows an inc reasing trend with the repeated load cycles; the changes however become marginal after the fifth load cyc le .
3.3 Effect of Finishing Treatment on Fabrics before and after Laundering
3.3.1 Extension at Peak Load
It is observed from Tables 2-5 that the extension at peak load in the Iyc ra blended fabrics is approximately three times hi gher than that of non-I yc ra fa brics in wale direction, whereas it is two times higher in course direc tion. Thi s is due to the presence of Iyc ra filaments in the fabric, ass ist ing it to shrin k in wale direction when com.~s off from the knitting machine. Subsequently, the courses per inch of the fabric increase, a llowing more loops to contri bute towards extensi on at peak load, particul arl y in wale direc tion. The Iycra blended fabrics also have higher stitch length (Table 1), the impac t of which is g rea ter in course direc ti on than that in wa le direction. resulting in higher ex tension at peak load in former case. The above-mentioned increase in stitch length also results in higher extension at peak load in a ll the directions of loading.
It is aga in seen that except in course direction , the full-relaxed knitted fabrics possess higher ex tension than that of compacted fabrics . The hi ghe r ex tens ion of fabrics is due to the presence of higher number of courses per inch (Tabl e 1), leading to the possibility of greater extension. Further, the fabric relaxa tion and setting treatment result in the reduction in magnitude of internal forces act ing within the fabric . Consequently, the internal frictional restrai nts with in the fabric are reduced. This effect is found to be very important in relation to the bending behaviour of fabrics, where inter-fibre fricti ona l properties play an importan t ro le . Simil ar effect would be ex pected to occur within a yarn and would lead to a red uction in yarn bend ing rigidity after the decrease in initi a l tensile modulus, leading to higher ex tension at peak load in the fabrics 'o." . The above findings re fl ec t the lac k of course direction sens iti vity due to the difference in relaxation dryer f ini shing technique .
The d ifference between the ex te ns ion a t peak load of full-relaxed and compacted fabr ics is hi gher for lyc ra blended fabrics than that for non-lyc ra fabric s. particularly in wale and biased directions . The above findings are also valid for laundered fabrics at a ll the levels of loading cycle (Tables 2-5).
MUKHOPADHYAY el al.: EXTENSION & RECOVERY CHARACTERISTICS OF KNITTED FABRIC 429
3.3.2 Recovery Characteristics
Tables 2-5 and Fig. 2 show that the immediate recovery value is considerably higher for Iycra blended fabrics in all the directions of loading. This is due to the presence of Iycra filament which possesses higher level of immediate recovery at repeated extension. Lycra helps in redistributing the segments of yarn between the contact points and relocation of these points closely after the unloading. Further, the higher stitch density in Iycra blended fabric results in greater internal forces, leading to the higher immediate recovery of the fabrics.
The immediate recovery of full-relaxed non-Iycra fabric is higher than that of compacted fabrics, particularly in wale and biased directions. However, the immediate recovery of Iycra blended fabric shows insignificant difference between full-relaxed and compacted fabrics in all the directions of loading. The above findings indicate that the Iycra filament nullifies the effect of relaxation dryer in case of immediate recovery. The findings mentioned above are also valid for repeated laundered fabrics at all levels of loading cycles, except for course-wise immediate recovery of non-Iycra fabrics which tends to show the significant difference between compacted and full-relaxed fabrics after repeated laundering (Tables 2-5) .
The difference in delayed recovery of knitted fabric due to the difference in finishing treatments is observed mainly in case of non-Iycra fabrics in wale and biased directions (Fig. 4). It is further seen that at all levels of loading cycles the delayed recovery of non-Iycra fabrics is higher than that of Iycra blended fabrics in all the directions of loading before and after laundering (Tables 2-5). In case of Iycra blended fabrics, the wale-wise delayed recovery shows marginal difference between compacted and fullrelaxed fabrics after laundering.
Fig. 5 shows that the permanent set is higher in case of non-Iycra cotton fabrics than that in case of Iycra blended fabrics . This is due to the presence of Iycra filament in Iycra blended fabrics , which is fully recoverable when unloaded l2
. Again , it can be seen that the difference in permanent set due to the difference in finishing technique is significant only in the wale direction of non-Iycra cotton fabrics .
Fig. 6 shows that the resiliency is considerably higher for Iycra blended fabrics in all the directions of loading. Particularly in non-Iycra fabrics, the fullrelaxed fabrics possess higher resiliency than that of the respective compacted fabrics along the wale direction . The above-mentioned findings on
permanent set and resiliency are also valid for laundered fabrics at all levels of loading. But the difference in resiliency due to the difference in finishing becomes significant after laundering for all the fabrics (Tables 2-5).
4 Conclusions 4.1 Effect of direction of loading is very prominent on both Iycra blended and non-Iycra knitted fabric s. On the application of external load , the biased direction of fabrics shows better shape retenti on characteristics in terms of higher immediate recovery and resiliency and lower delayed recovery and permanent set. Higher extension at peak load is exhibited in course direction of fabric and than that in other directions of loading.
4.2 With the repeated load cycles, the ex tension at peak load increases marginally, the immediate recovery and resiliency change considerabl y. the delayed recovery changes up to a small extent , and the permanent set approaches zero during initial number of cycles .
4.3 Overall performance of Iycra blended fabric s is better than that of non-Iycra cotton fabric s as the immediate recovery, res iliency and extension at peak load are higher, whereas delayed recovery and permanent set are lower for Iycra blended fab rics. irrespective of the direc tion of loading. Variations in the above characteristics are considerably hi gher with the change in direction of loading, particularl y fo r non-Iycra fabric.
4.4 Full relaxation treatment improves the recovery characteristics like immediate recovery and res iliency. pal1icularly for non-Iycra fabrics in the wale direc ti on. The effect of full relaxation finish on the immediate recovery of Iycra blended fabric is nullified by the Iycra filament as the Iycra imparts shape retention characteristics to the fabric . However, the above fini sh improves the extension at peak load for both Iyc ra and non-Iycra fabrics along wale and biased direct ions.
4.5 The changes in ex tension and recovery characteristics are prominent at initial laundering cycles and after that the changes become insignificant. In genera l, the laundering deteri orates the quality of fabrics as the immediate recovery and resiliency of fabric tend to reduce, whereas de layed recovery and permanent set become higher.
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