UNIVERSITY OF MAURITIUS RESEARCH JOURNAL – Volume 17 – 2011 University of Mauritius, Réduit, Mauritius Research Week 2009/2010
Increasing the Functionality of Knitted Fabrics through Integration of Conductive Threads using a V-bed Hand Knitting Machine Bahadur G K * Faculty of Engineering, University of Mauritius Reduit Email:
[email protected] Bradshaw M Department of Fashion and Textiles, De Montfort University, Leicester United Kingdom Email:
[email protected] Chummun J Faculty of Engineering, University of Mauritius Reduit Email:
[email protected] Rosunee S Faculty of Engineering, University of Mauritius Reduit Email:
[email protected] Paper Accepted on 23 February 2011 Abstract In line with the growing demands for electronic integrated commercial garments worldwide, this paper demonstrates how conductive thread can be knitted together with conventional yarn using V-bed hand knitting machine. 36.5 tex white cotton yarn and 98.0 tex dull-silver coloured conductive thread were used for that purpose. The conductive thread consisted of 4-ply of steel and nylon thread with an electrical resistance of 4Ω per 100 mm. The dimensional stability and the electrical resistance of the knitted samples were measured and compared with those of 100% cotton samples. Drape and pilling tests were also carried out. The results show that knitting with conductive thread is easily achievable and could be considered by 256
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designers thereby opening the doors for low-cost creative and exciting garments. Such garments would also meet the conventional requirements such as comfort and look and also in terms of value added, the garment could be made interactive and functional.
Keywords: Conductive threads, dimensional stability, drape, pilling tests, interactivity and functional *For correspondences and reprints
1. INTRODUCTION
The fashion industry faces constant challenges to offer functional, smart and innovative products at increasingly competitive prices due to global competition. The market for smart textiles is growing and research is now focusing on making garments increasingly intelligent [1]. For instance, brands such as Burton, Zegna, O’Neill and Adidas have incorporated the Apple iPod into jackets operated by textile-based controls (Softswitch). Zegna alone had sales of 713 million Euros in 2005 [2]. In addition, new types of conducting fibres are being developed that will enable the integration of electronics into textiles. However, the cost for manufacturing of smart textiles and garments is high. Therefore, it is felt that there is an opportunity to manufacture ‘value-added’ conductive textiles garments at relatively low cost. Such garments would also meet the conventional requirements such as comfort and look. Conductive yarns are used together with conventional yarns during manufacture of the fabrics/panels. Electronic devices may be connected to the latter.
The different techniques in knitting technology offer a very wide range of possibilities [3] as far as the yarn path is concerned. For instance, a yarn can be knitted conventionally as a continuous weft, to emulate a weft in a woven fabric; else the yarn may be knitted across a panel in a single line using the intarsia or jacquard technique. Table 1 summarises the different techniques that can be used 257
Increasing the Functionality of Knitted Fabrics through Integration of Conductive Threads using a V-bed Hand Knitting Machine
to integrate a conductive yarn into a fabric as well as the advantages of each technique.
Most of the techniques may be used to introduce a conductive yarn into the body of the fabric and enable a direct current (DC) to flow from one point of a garment to another. The source of power could be a light alkaline battery or button cell battery.
In addition, the batteries may also be easily dissimulated within the
garment structure making it unnoticeable. Table 1 Knitting techniques Knitting technique Plating
Advantages Two yarns knitted simultaneously tend to appear on different sides of the fabric.
Intarsia
Yarn is knitted on a specific area on the panel and/or along a line across the fabric.
Jacquard
Yarn can ‘appear’ or kept hidden on any part of the panel;
Yarns can float on any side of the fabric;
Fully-fashioning
Panels may be shaped to reduce/cutting cutting waste.
Loop transfer
Open structures can be made within the fabric.
The connection would require the conductive yarns of opposite charges (positive and negative poles) not to touch each other. One or a combination of the different options may be used for that means:
One of the two conductive yarns is coated;
The two conductive yarns are knitted alternately making sure that they do not touch each other;
The conductive yarns from the battery to the ‘power point’ are knitted in opposing directions. 258
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It would require the creativity of a knitter to make use of the enormous possibilities available to achieve this target. The work is expected to help knitters and designers to tap a very conventional but readily available technology to bring a new dimension in garment manufacture while keeping the manufacturing cost minimal.
This project is aimed at manufacturing basic knitted fabrics that would be able to conduct electricity by integrating conductive yarns into fabrics knitted with commonly available yarns such as cotton, wool or blends of the latter. Furthermore, the samples would be knitted on a V-bed hand knitting industrial machine.
The main objective of this research is to knit with 100% Cotton yarns together with conductive threads and measure the dimensional stability and the resistance of the samples and compare them to samples knitted in only 100% cotton yarns. The results will help to determine whether the conductive threads can be used in knitwear garment to conduct DC from one point to another to perform a particular function such as powering an integrated MP3 player.
2. EXPERIMENTAL
Materials For the purpose of this work, 36.5 tex white cotton yarn and 98.0 tex dull-silver coloured conductive thread were used in all experiments. Conductive threads (Plate 1) were purchased from Lame Lifesaver, Canada. The threads were supplied in 200-yard spools and used as received. They are made from 4-ply of steel and nylon thread with an electrical resistance of 4Ω per 100 mm. They are available in different colours and tones. Initial trials have shown that the conductive yarn can easily be knitted together with the cotton yarn chosen. Furthermore, it has been noted that its applications have been restricted to woven fabrics only.
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Plate 1: Conductive Threads 200-yard Spools
Machine Stoll recommends knitting cotton yarn in the range of 143 – 222 tex on a gauge 7 (needles per inch). All samples were therefore knitted on an Industrial V-Beds Knitting ‘Flying Tiger’ Machine of gauge 7 n.p.i., 50 needles were selected on each bed and the samples were knitted in 50 courses (100 rows). Two sets of samples were knitted in a 1x1 all needles rib structure: the first set was knitted with 100% cotton yarns.
The second set of samples was knitted by feeding the
conductive yarn together with the 100% cotton yarns.
3. TESTING
Resistance of the conductive thread along different length
The standard test BS 6500:2000 was taken into consideration to measure the resistance of the conductive thread along different length. The procedure under BS6500 state that the cord should be left in a room with a constant temperature for sufficient time to ensure that the cord temperature is equal to the ambient temperature. Measurement should be taken on a length not less than 1 meter in length.
The thread was cut in several lengths and the resistance was measured and recorded. These readings were then compared to an electrical wire of the same lengths with a diameter of 0.75 mm.
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Conditioning
All samples were conditioned at a relative humidity of 65 ± 5% at a temperature of 20 ± 20 C for 4 hours before any measurements were taken.
Washing and Finishing
Washing tests and conductive tests were carried out on all samples. The same standard of washing and measuring was maintained in order to get consistent and accurate results. For the washing test the BS 4923: 1980 standard was followed and as for determining the dimensional change, BS 5807: 1987/ ISO 5077-1984 standard was applied.
Preparation of samples prior to washing
Washing tests were carried out on all the samples so as to measure and compare the dimensional stability of the knitted samples.
The edges of all samples were over-locked, steamed-pressed and were conditioned. After which, the full width, height and weight of all samples from both sets were measured and recorded.
A template of 15 cm by 15 cm (width x height) was used to mark the centre and the four corners of the samples as shown in Figure 1. In addition, the resistance value of each sample from the second set was also measured and recorded. Given that no standard was available, the following procedure was adopted for the measurement: A digital multi-meter (FLUKE 115) was used to measure the resistance value of the samples as shown in Plate 2.
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Plate 2: Using the alligator clips to measure the resistance value of the knitted sample Measurement for the resistance value was taken from point 1 to point 2, point 1 to point 3 and from point 1 to point 4 as shown in Figure 1.
Figure 1: Drawing shows the four points where the readings for the resistance value were taken.
Washing and tumble-drying the knitted samples The samples were machine washed at normal temperature (400 C). 4 g of Sodium Perborate Tetrahydrate and 16 g of ECE test detergent were added to each washing. The first set of samples was washed separately from the second set of samples. Both sets were washed with polyester bags totalling to a total weight of 2 kg. After washing, which lasted for 40 min. the two sets of knitted samples were tumble-dried separately in a dryer for another 45 min. and were left to rest flat at room temperature for at least 2 hours. The size of all samples was measured and recorded under the conditioned environment. The resistance value of the second set of samples was also measured and recorded. 262
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Draping and Pilling Tests Draping and pilling tests were carried out to measure the drape coefficient and the fuzziness of the knitted samples from both sets respectively. For the pilling test, the number of cycles was 10800 equivalents for 3 hours. Standard ISO 12945/2 was used to carry out the tests.
4. RESULTS AND ANALYSIS Resistance value of the conductive thread along different lengths
The thread provides little risk of snapping or cutting and fraying. However, during the knitting operation, the yarn tension increases as it comes into contact with the knitting elements [4&5]. Thus, the thread is likely to be subjected to some degree of abrasion that may affect its conductivity. The type of conductive thread used in the experiments is shown in Plate 3; it is made up of 6 fine wires, twisted together. The resistance value of the conductive thread increased with the length whereas that of the electrical wire did not change (Table 2). This increase may be attributed to the varying amount of contact between fibres as explained by Au [6].
Plate 3: Structure of Conductive Thread
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Table 2 Resistance of conductive thread and electrical wire Length
Resistance of conductive thread
Resistance of Electrical
(cm)
()
Wire ()
10
9.2
0.3
20
15.7
0.3
30
25.5
0.3
100
85.7
0.3
150
89.1
0.3
200
106.7
0.3
Dimensions of the knitted samples before washing
All samples were manufactured on the same type of machine, using the same number of needles and the same number of courses was knitted, Plate 4 and 5. As expected, the size and the mass of the sample which contains conductive yarn increase. The presence of the conductive yarn makes the resulting yarn thicker. As a result, the loop assumes more space thus increasing its width and length by 12 – 15 %. The mass of each sample also increases. The results are summarised in Table 3.
Plate 4: Sample knitted in 100%
Plate 5: Samples knitted with 100%
Cotton
cotton yarns mixed with conductive thread
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Table 3 Dimensions and mass of samples before washing
Average Dimensions (cm) (width x length)
Mass (g)
100% cotton yarn
16.0 x 19.0
20.0
With conductive yarn
18.0 x 22.0
38.6
Knitted Samples
Results obtained after washing the samples
Tables 4 and 5 show the results obtained from the measurements taken for the sizes and the resistance values of the knitted samples respectively.
Table 4: Results obtained for the size after carrying the washing tests. 1st wash
2nd wash
3rd wash
100% Cotton (cm)
100% cotton mixed with Conductive Thread (cm)
100% Cotton (cm)
100% cotton mixed with Conductive Thread (cm)
100% Cotton (cm)
100% cotton mixed with Conductive Thread (cm)
Sample 1
15.5 x 12.4
15.5 x 12.7
15.5 x 12.5
15.75 x 12.5
16.0 x 12.0
16.0 x 12.5
Sample 2
15.5 x 12.3
15.5 x 12.7
15.5 x 12.5
15.75 x 12.5
15.8 x 12.0
15.5 x 12.5
Sample 3
15.5 x 12.5
15.5 x 12.7
15.5 x 12.5
15.75 x 12.5
15.8 x 12.0
16.0 x 12.5
Note: The size of the template used was 15 cm x 15 cm (Section 2) Table 5: Resistance values between different positions
Sample 1
1st wash 2nd wash 3rd wash Resistance values () between points 1 to 1 to 1 to 1 to 1 to 1 to 1 to 1 to 1 to 1 to 1 to 1 to 2 3 4 2 3 4 2 3 4 2 3 4 2.3 4.2 4.3 3.0 5.9 5.5 2.7 6.4 6.0 2.9 6.2 5.2
Sample 2
2.0
3.6
3.0
3.2
7.0
6.8
3.0
7.5
7.2
2.9
5.8
5.5
Sample 3
2.0
3.9
3.4
2.8
7.2
6.2
2.5
6.8
6.8
2.6
7.2
6.4
Before Wash
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Point 1, in Figure 1, was nearer to point 2 and therefore the resistance value was low compared to point 1 to 3 and point 1 to 4. The distance between points 1 to 4 was less than the distance from points 1 to 3, thus determining a lower resistance value.
Tables 4 and 5 show the results obtained after the washing tests. The width of all the fabrics increased by an average of 6-7 %, while the length decreased by about 17%. This reduction in length is expected in flat bed knitting fabrics as mentioned by Doyle and Munden [7 & 8]. The total weights used as take down in knitting the samples were 900g. The take-down weight stretches the fabric lengthwise during manufacture and the fabrics always contain residual distortion even after the weights are removed [9]. To relax completely, the yarns need to overcome the yarn-to-yarn friction within the knitted structure [10]. This can happen during washing and tumble-drying where the forces of the process help the yarn to move to overcome the friction [11].
The overall resistance increases, showing that the washing process or the detergent used during washing may have damaged the conductivity of the conductive yarn.
Draping and Pilling Tests
The average drape-coefficient of the cotton-only knitted sample was 73.0% whereas that of the sample with conductive threads was 66.5%. As expected, the increase in mass of the sample due to the addition of conductive yarn decreases the drape-coefficient of the sample. However, the change does not seem to be too significant. Table 6 shows the results obtained from the pilling test.
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Table 6: Pilling properties of samples
Direction
Along wales Across wales Appearance
100% cotton sample
Cotton yarn mixed with Conductive threads sample
Before
After
Before
After
5
4
5
4
5
4
5
4
Slight
Increased
Slight
Slight
fuzziness
Fuzziness
fuzziness
fuzziness
5. SAFETY
Safety remains a very important part that needs to be looked into. Garments are expected to shield the body from external hazards including electrical.
6. DISCUSSION
The aim of this work was to investigate the possibility of knitting cotton yarn together with a conductive yarn in order to develop low-cost garments into which electronic gadgets could be fitted. The results show that knitting with a conductive yarn is possible without any considerable effort. The obvious increase in mass has contributed in the decrease in drape-coefficient of the conductive fabric. This is the only major change that has been found. On the other hand, the presence of the conductive yarn does not seem to have significantly affected the shrinkage and pilling properties of the fabrics. The decrease in conductivity of the fabric after washing has been noted. This can be remedied by using a suitable washing detergent or use a different conductive yarn which is water / detergent resistant.
For further tests, it is recommended to use lighter and more flexible conductive yarn that would be water / detergent resistant. 267
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7. CONCLUSION
The most easily available conductive yarn was used for this project. The results also give a clearer indication of the type of conductive yarn. It is suggested to use a lighter, more flexible yarn that is water/detergent resistant.
There is a new opportunity that can be tapped in the knitwear industry: that of manufacturing low-cost garments onto which electronic gadgets may be fitted. A new dimension is now open to designers and manufacturers. Garments knitted with the conductive yarns would therefore meet the conventional requirements such as comfort and look with additional properties such as interactive and functional as well.
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