Experimental study on Temperature regulating bi-component fibres containing paraffin wax in the core

Abstract

Putting on or taking off clothes helps the body to stay within the comfortable temperature range (to avoid shivering or sweating) at different activity levels and ambient conditions. Clothes with built-in thermo-regulating properties would mean maintained comfort without putting on or taking off clothes that frequently. Integration of phase change materials (PCMs) in clothes is one way of achieving thermo-regulating properties. When the body temperature goes up, the PCM melts and absorbs the heat from the body in the form of latent heat (cooling effect). When the temperature drops, the PCM crystallizes and the stored heat is released again (warming effect). Research on thermo regulating fibres of the bi-component type containing PCM in the core has been conducted at Swerea IVF in Mölndal, Sweden, for some time. It has been found that high molecular weight HDPE is a suitable viscosity modifier for hydrocarbon waxes used as PCM. The preparation of core materials has so far been done in a batch wise fashion in the way that molten wax has been soaked into pelletized HDPE at around 180°C during prolonged times followed by melt compounding in a Brabender batch kneader (0.3 kg per batch). Besides being very impractical for larger production volumes the method involves long residence times at high temperatures which may induce thermal degradation reactions. The objective of the present diploma (master’s thesis) work was to develop a continuous mixing method to produce PCM/HDPE blends and to test the resulting material in bicomponent fibers with a Nylon (PA6) sheath and to characterize the resulting fiber properties in terms of strength and latent heat. It was proven possible to compound HDPE with large amounts (70%) of octadecane (PCM) on a Brabender twin screw extruder. HDPE was metered to the extruder hoper by means of a screw feeder and wax was continuously fed to the hoper in the liquid state by means of a heated membrane pump. To facilitate mixing HDPE in form of powder instead of pellets was used. The extruded threads were solidified in a water bath followed by granulation. Bi-component fibers were successfully produced from such materials. Fibers containing 15 to 42% Octadecane were produced showing heat of fusions in the range 26 to 86 J/g and tenacities in the range 33 to 16 cN/tex. The heat of fusion of the fibers compares favorable with existing commercial products showing values in the range 5-15 J/g (acrylic and cellulosic fibres containing microencapsulated hydrocarbon waxes). The peak melting point of octadecane measured by DSC was found to be depressed some 4-5°C in the fibers compared to pure octadecane (28°C). Such a melting point depression is important to consider when choosing type of hydrocarbon wax.