Knitted fabrics from bamboo yarns tend to pill less and have better drapability besides exhibiting superior dyeing absorption and aesthetic level, affirms Alaa Arafa Badr.
The growing consumer requests for textile products that give protection are comfort and environmental products. Therefore, there are many new developments in the textile production for the use of renewable and biodegradable resources. One of the newest developments in new fibre investigations is the use of bamboo fibre in different textile products that has been applied in hygienic products, geo-textiles, filters, decorating items and furniture[2 - 6].
Bamboo fibre is a kind of regenerated cellulose fibre and is extracted from the bamboo stem and leaves by wet spinning, including a process of hydrolysis alkalisation and multi-phase bleaching[2, 7, 9]. It is one of the fastest growing plants and exists in great quantity in several countries like China. Bamboo does not require replanting after harvesting and yields 50 times as much fibre per acre as cotton[1, 7, 10, 11].
Since the cross-section of the bamboo fibre is filled with unparalleled micro-structure, different micro-gaps and micro-holes, bamboo fibre clothing has high air permeability and can absorb and evaporate human sweat quickly. Additionally, it has an anti-bacterial character, eco-friendly and is being used in apparels including intimate apparels and socks[2-5].
Xul analysed the properties of bamboo viscose, tencel and conventional viscose fibres to give an explanation the similarity and diversity in their molecular and fine structures. The density of cotton and bamboo fibre is identical (1.5 g/cm3). The bamboo fibres are having longer length than cotton fibres. In addition, the bamboo fibres have lower bending and torsional rigidity[5, 13]. Bamboo-based fabrics have low amount of pilling accumulation, creasing and bursting strength[5, 7, 14]. Nevertheless, Wang investigated the poor anti-pilling performance of bamboo knitted fabrics.
Although some sporadic efforts have been made to study and evaluate the properties of bamboo fibre, there is a shortage of detailed research on the gamut of bamboo fabric properties. Therefore, the object of this work is to investigate the effect of bamboo fibre properties on some physical properties of knitted fabrics. The results are compared to that of similar fabrics produced from 100% viscose, cotton and mercerised cotton yarns.
Mercerisation makes cotton easier to dye, produce luster and fuller shades and enhances cotton with high strength and dimensional stability[16-18]. Also, enzymatic scoured and bleached knitted fabrics have enhanced stitch density, thickness and improved abrasion resistance and pill reduction. Stitch length and knit structure affect the dimensional properties of the knitted fabrics where the stitch length is the dominating variable in influencing the dimensional behavior. There is a direct and indirect relationship between the fabric tightness and lengthwise and widthwise shrinkage respectively[20-21].
Material and fabric manufacture
30/1, 100% bamboo, cotton Giza 88, Mercerised cotton (same cotton) and viscose yarns were used to produce single jersey and single pique knitted fabrics on the same knitting machine. The properties of the Egyptian cotton are given in Table 1. The fibre length of the Bamboo and viscose are 38 and 36.5 mm and their fineness are 1.4 and 1.52 dtex respectively. Moreover, Table 2 shows the properties of the yarns applied in this research work.
The knitting machine specification was Mayer & Cie, 28 gauge, 15 inch diameter, 45 feeders and with total number of needles 1320. The loop length was changed to produce three levels of fabric tightness.
All fabric samples were dyed in industry with a sky-blue colour shade, and then finished through the same standard finishing line used for the knitting goods. Table 3 shows the properties of the knitted fabric samples used, in which the following symbols are used: B = Bamboo, V = viscose, C = cotton, MC = mercerised cotton, SJ = single jersey and SP = single pique.
The influence of the experimental factors: yarn material, fabric structure and fabric loop length on the fabric bursting strength, abrasion resistance, pilling, drapability, colour difference and shrinkage was evaluated for significance using R statistical programme through applying the ANOVA analysis.
After leaving the finished samples 72 hours in standard conditions, the fabric properties were measured. The fabric bursting strength, pilling and abrasion resistance were evaluated in accordance with the standards ASTM D6797, D3512 and D4158 respectively. Furthermore, fabric shrinkage "after five washing times" was measured according to AATCC 135-2003.
Drape coefficient was measured according to BSI 5058 by putting the sample on a circular disc and measure the radius of drapability at both sides of the disc. The equation used to calculate the drape coefficient is: Drape coefficient = (r2 – 56.25)/100, in which r is the average radius of drapability. The colour difference was evaluated on the data colour instrument. Where, the reference sample which has been taken as a zero level to assess the colour difference is the 100% cotton, single jersey sample having loop length 2.9 mm.
Results and discussion
The influence of the yarn material, fabric structure and fabric loop length on some fabric properties was assessed for significance using ANOVA analysis as shown in Table 4. All the physical properties: bursting strength, abrasion resistance, drapability, fabric shrinkage are significantly affected at 5% significance level by fibre type, fabric structure and loop length except pilling grade and colour difference which are significantly affected only by fibre type and fabric loop length.
It can be observed from the Figure 1 that fabrics made of 100% bamboo yarns seems to have less bursting strength than cotton and mercerised cotton fabrics. This may be attributed to the fact that the bursting strength of the fabrics varies depending on the strength of the yarns. Also, the smoothness of the Bamboo yarns makes a low friction at the contact points between the loops and as a result the fabric will be easy to be penetrated. Mercerised cotton fabric has a lower bursting strength than the pure cotton fabric, as a result for the drop in its yarn diameter and hairiness level after singeing and mercerising operations despite of its higher yarn strength. Moreover, SJ endured a higher bursting strength than the SP. The SP structure contains tuck loops which are more prone to penetrated easily through its small and week formed holes inside the fabric.
Fabrics produced from 100% cotton and mercerised cotton has higher abrasion resistance than bamboo fabrics as shown in the Figure 2. This case could be due to the higher tenacity of the yarns used to produce these fabrics. Besides, the bamboo fabrics have the least hairy level. Moreover, the bamboo yarns have lower bending rigidity, so their fabrics can be compressed easily and will have a lower thickness and mass per square metre than others produced from cotton fibres. Additionally, the mercerised cotton fabric has a higher abrasion resistance than untreated cotton fabric, due to the improvement in its yarn tensile characteristics after mercerising.
Because of its higher thickness, the SP samples exhibits more abrasion resistance than SJ fabrics. The condensed loops formed at the tuck area could help in increase fabric thickness and strengthen the ability of its abrasion resistance.
According to the statistical analysis and Figure 3 there is a significant relationship between the fibre type and the fabric drape coefficient. The bamboo fabric has the least drape coefficient against the other samples. The Bamboo fibres have a longer length and lower bending and torsional rigidity than cotton fibres. So, they are consistently and compactly packed better inside the yarn structure. However, the least hairiness level, higher elongation and smoothness degree of the bamboo yarns than the viscose, cotton and mercerised cotton yarns have enhanced the drape property of its knitted fabric. So, there is a high flexibility level for Bamboo fabric during end use.
Fabric structure is a very important parameter from the point of view of fabric drapability. The sample contains tuck loops tend to be stiff during the drape test and this is the case for the SP fabric.
The loop length has a great effect on the fabric drape coefficient as noticed in Figure 4. As the loop length increases the fabric drape coefficient decreases. The decreasing of courses and wales density with the increase of loop length might be the cause for this decline.
From Figure 5, the knitted fabric produced from bamboo yarn has a better pilling grade than others knitted from the other fibre types. The lower hairiness level of the bamboo yarn is the possible reason of this result. Therefore, there is a lower friction degree during the end use of bamboo fabrics with any other surface and consequently these fabrics tend to form fewer pills. Additionally, the bamboo yarn has lower breaking strength and lower twist level, which makes the pills pull out of fabric surface easily.
For mercerised cotton, the pilling grade is better than 100% untreated cotton due to the singeing operation which decreases the hairiness percentage and reduces the opportunity of the outside fibres to accumulate over the fabric surface to form pills.
The colour difference of the bamboo sample is higher than samples produced from other fibres as noticed in Figure 6. The cross-section of the bamboo fibre is filled with different micro-gaps, so the bamboo fibre clothing can absorb colouring agent by far. When compared to cotton fabrics, bamboo fabrics require a lower amount of dye for the same dying level. In addition, the mercerised cotton sample has a higher colour difference than 100% untreated cotton, due to the absorption capability of the mercerised sample which increased after mercerising. As the loop length decreases the colour difference increases. The tightest fabrics for all fibres types posses the highest quantity of material and high fabric thickness, which leads to an increase in absorbed dyestuff.
The high elongation value and moisture absorption capacity of bamboo fibre can result in high lengthwise shrinkage during wet processing as obvious in Figure 7. This high elongation makes the yarn to be more prone for any lengthwise stress during dyeing stage. The mercerised cotton fabric has the least lengthwise shrinkage due to its bulkiness and higher courses density. The mercerisation process improves dimensional stability of knitted fabric. SP fabric has higher courses density than SJ sample which related to its contained tuck loops. Consequently, tuck loops lead to an increase in fabric width and a decrease in fabric length.
Also, the bamboo fabric tends to have less widthwise shrinkage as in figure 8. This might be clarified by the effect of the thermosetting which applied for the samples during finishing inside the compressive shrinkage calendar.
All the physical properties: bursting strength, abrasion resistance, drapability, fabric shrinkage are significantly affected by fibre type, fabric structure and loop length except pilling grade and colour difference which are significantly affected only by fibre type and loop length. The fabrics knitted from 100% bamboo seem to have the least values of bursting strength and abrasion resistance than fabrics produced from cotton and mercerised cotton. This might be due to the least tenacity and smoothness of the bamboo yarns.
SJ endured a higher bursting strength than the SP. Tuck loops are more prone to penetrated easily through its small formed holes inside pique fabric. Pique exhibits more abrasion resistance due to the effect of the condensed loops formed at the tuck area.
The bamboo fabric has more drapability than other fibre samples. The bamboo fibres are packed better inside the yarn structure. Bamboo knitted fabrics has a better pilling grade and higher colour difference, where pills pull out of fabric surface easily. For the mercerised cotton, the pilling grade and colour difference are better and higher respectively than the untreated cotton. The high elongation value and moisture absorption capacity of bamboo fibre results in high lengthwise and less widthwise shrinkage after wet processing.
The author is grateful to the co-operation of El Nasr Clothing and Textile Company (KABO) for their support to use their production and testing facilities. He would also like to express his thanks to Mr Osman AY, the Country Manager of CSA textile for his helpful contribution in providing the bamboo yarn which helped them to introduce a new and unusual material.
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Alaa Arafa Badr
Department of Textile Engineering
Faculty of Engineering
Alexandria University, Egypt.