A study on ultraviolet protection factor of cotton and coolmax based on plain knitted structure

Abstract

In order to prevent human from the acute and chronic effects bring out by ultraviolet radiation (UV radiation), plain knitted clothing becomes a feasible alternative to prevent direct contact with UV radiation. One of the main features of knitted fabric is its certain elasticity that different from woven structure, given they are produced from same type of fibre and yarn. Such extension may favour wearer from ease of body movement. Fifteen types of plain knitted samples were produced from normal cotton, Supima cotton (both conventional and torque-free ring spun yarn of 20Ne and Coolmax yarn of 150dtex. These samples were divided into three groups, single cotton yarn (Group I), two cotton yarns combination (Group II) and Coolmax and cotton yarns combination (Group III). Ultraviolet protection factor (UPF) of samples in each group were measured in the following conditions, (a) dry and relax, (b) dry and stretch, (c) wet and relax and (d) wet and stretch. Furthermore, there were three different level of stretching, i.e. 10%, 20% and 30% stretching in both machine and cross-machine directions. Samples were wetted separately with five types of solutions including (a) chlorinated pool water, (b) sea water, (c) acidic perspiration, (d) alkaline perspiration and (e) deionized (D.I.) water respectively. The UPF values at dry and relax state of Group III was the highest while Group II and Group III came second and third. When it was in dry and stretch state, UPF of all Groups dropped and the decrease in rating is most severe in 30% stretching then 20% and 10%. While samples subjected to wetting and measured in relax condition, UPF was further reduced. UPF measured at wet and stretch state were the lowest among four testing conditions. Statistical regression models were used to predict UPF at the four different conditions by using Tightness Factor, Pore size ratio, Stitch density and Fibre combination. The coefficients of determination (R²) of all the models were all over 0.81. It could be concluded that these models are a successful tool for predicting UPF of cotton and Coolmax/cotton blends at different possible real-life wearing conditions.