Even as new yarn is developed, one that merits looking at is cotton-rich poly (lactic acid) fibre. The fibres are blended together in certain proportions so that the final product has all the positive attributes, say R. Guruprasad, G. Krishna Prasad, G.T.V. Prabu and T. Senthilkumar.

There is no perfect fibre that can impart all desirable properties required. So, cotton is generally blended with other fibres like polyester, viscose or acrylic to produce blended yarn and fabric meeting different requirements.

In recent years, there is focus on the environmental friendliness of fibres. So, it is important for a fibre to be biodegradable. Poly (lactic acid) fibre is one of the recent biodegradable fibres. Poly (lactic acid) or PLA is the first commodity polymer produced from annually renewable resources like corn, wheat starch and beet. Until now, use of PLA was limited to biomedical applications like sutures.

PLA fibres can be melt spun or wet spun, which is an advantage. Extruded fibres can then be cut into staple fibres to blend with other staple fibres. PLA fibres are generally circular in cross-section and have a smooth surface. The density of the fibre is 1.25 g/cm3 and moisture regain is 0.4-0.6per cent. The load-elongation behaviour is similar to that of wool with which the fibre blends well. The stress-strain curves of cotton, PLA and other common fibres are shown in Figure 1. PLA fibres are said to feel soft, drape better and manage moisture well. They have good wicking, facilitate faster moisture spreading and drying. Hence, blending PLA with cotton will be useful in improving drape and moisture management behaviour of cotton. Here, blending of cotton with PLA staple fibres has been studied and yarn properties were evaluated.

Figure 1. Tenacity-extension curves of common fibres (Figure reproduced from Ref. [2])

Spinning of blended yarns

The cotton material in the study was of MCU-5 variety with a length of 30 mm and fineness of 3.3 mic. The bulk tenacity of the fibre was 25 g/tex. The length of PLA fibres was 38 mm, and its fineness was 1.4 D. The PLA fibres were mixed with cotton fibres in three different proportions, namely, 20 per cent, 35 per cent and 50 per cent. The blending was done in the blow room stage. Blended fibres were then taken through the process of carding, drawing, roving and finally spun into yarn using a compact ring spinning system to a nominal count of 14.76 tex (40 s Ne) with four different twist levels i.e 3.3, 3.6, 3.9 and 4.2. To enable comparison between the yarns, 100 per cent cotton and 100 per cent PLA yarns were also spun to the same count.