THE VISCOELASTIC BEHAVIOUR OF TEXTILE FABRICS IN RELATION TO THE IRONING PROCESS

Abstract

The project primarily seeks to gain in-depth knowledge about the parameters that define the ironing temperature and the minimum ironing time for various clothing fabrics. This is deemed essential for the development of a better iron. Basically, the study entails research on the viscoelastic relaxation and the dynamic mechanical properties of common clothing fabrics as a function of temperature and moisture content of the fabrics. In the present work, textile fabrics of pure polyester, wool, cotton and acetate are tested. The results are subsequently compared with results from actual ironing tests and analysed in relation with the ironing process. The experimental work for the project is carried out using a dynamic mechanical analyser (DMA) in conjunction with a climatic chamber. The stress relaxation and the dynamic mechanical studies are done on the OMA whilst the climatic chamber provides the desired climatic conditions. Modifications are made to the DMA clamps assembly and a simple interface done with the DMA and the climatic chamber before the set-up is ready for testing. The results show that the ironing process, whereby wrinkles are removed from a fabric, is accelerated by an increase in the supply of heat and steam to the fabric. It is deduced from the stress relaxation study, through determining the relaxation time constants of the fabrics, that the ironing times are shortest in acetate and polyester textile fabrics. The ironing time is comparatively longer in wool and is determined to be longest in cotton. These results agree closely with common belief. The ironing temperature of a textile material is thought to be related to its glass transition temperature, which indicates at what temperature the material may be safely, effectively and efficiently ironed. The glass transition temperature is determined at zero relative humidity for wool (168°C), polyester (121°C) and acetate (105°C). By virtue of the glass temperatures, wool has the greatest ability to retain its heat, followed by polyester and acetate fabrics. Accordingly, this implies that the ironing temperature is highest in wool, second in polyester and lowest in acetate. The transition temperature for cotton is not mentioned here because its value is in doubt. The influence of steam (or moisture content) on the ironing process varies with the fabric type. In general, however, it can be concluded that the act of injecting steam in a textile material during ironing quickens the wrinkle removal rate. This is due to the decrease in the relaxation time as the moisture content increases and the fact that moisture serves to depress the glass transition temperature of the material. The relaxation time constants for the various fabrics obtained through the stress relaxation study are found to be much higher than the actual ironing times. This is perceived to be due to the arbitrary definition of the relaxation time constant and that not enough is understood about the mechanics of the ironing process. It turns out that unless more is understood about the mechanics of textiles during ironing, the relaxation times for the textiles under study in the current work cannot be quantified suitably with reference to the ironing process.