Fabrication, structures and properties of nano/microencapsulated phase change materials, thermo-regulated fibres and fabrics

Abstract

This project aims to fabricate and characterize the structures and properties of thermo-regulated fibres and fabrics that can intelligently regulate temperature by absorbing and evolving latent heat, to enhance the development of temperature regulating fabrics and improve the thermo-physiological comfort of textile materials. In this study, nano/microencapsulated n-alkanes (Nano/MicroPCMs) were synthesized by in-situ polymerization of urea-melamine-formaldehyde. Parameters affecting the structures, thermal stabilities and properties of Nano/MicroPCMs, such as oil phase composition and content of cyclohexane, shell composition, stirring rates, content of emulsion and heat-treatment on the properties of MicroPCMs were studied. To analyze the effects of increased content of Nano/MicroPCMs, polypropylene (PP) composite fibres containing 4-24wt% MicroPCMs and polyacrylonitrile-vinylidene chloride (PAN/VDC) fibres containing 5-40wt% Nano/MicroPCMs were melt and wet-spun respectively. The composition and properties of thermo-regulated non-woven fabrics made of the fibres, PET and PP fibres and Nano/MicroPCMs coated knitted fabric were also studied. Results indicated that the average diameters of the microcapsules with enthalpies of melting and enthalpies of crystallization of approximately 160 J/g varied from 9.2 um to 0.8 um with the increase of stirring rates. The core material diffused out of the shell in the heating process. The thermal stability was enhanced by adding 5-28wt% expansion space inside the microcapsules and using copolymer shell. The maximum thermal stable temperatures of the microcapsules were 230 C and 268 C in air and nitrogen atmosphere, respectively. The multiple peaks in the DSC cooling curves, which were mainly affected by the average diameters of the microcapsules, were associated with the liquid-rotator, rotator-crystal and liquid-crystal transitions. Adding 10.0wt% 1-octadecanol in the core decreased the degree of supercooling of microencapsulated n-octadecane from 26.0 C to 10 C. The heat absorbing and evolving temperatures of the melt-spun fibres in which the microcapsules were evenly impregnated in core polymer matrix were approximately 32 C and 15 C respectively. The enthalpy of melting and enthalpy of crystallization of the fibres containing 24% MicroPCMs was 11 J/g respectively. The heat absorbing and evolving temperatures of the wet-spun fibres were approximately 30 C and 22 C, respectively. The enthalpy of melting of the PAN/VDC fibre containing 30wt% MicroPCMs was 27 J/g. The spinnability of the fibre was affected by content of MicroPCMs, diameters, ratio of aggregate microcapsules and spinning parameters etc. The wet-spun fibre had a higher efficiency of enthalpy of melting than that of the melt-spun one. The fabrics absorbed and released heat at 25-34 C and 10-25 C respectively. The maximum inner temperature difference between the wool felt and the non-woven fabric was 8 C and -6.5 C in the heating and cooling process, respectively. The inner temperature difference lasted 16-50min, which depended on the contents of PCM, fabric composition and the measuring condition. The knitted fabrics absorbed and released heat at 32 C and 17 C respectively with an amount of 8-20 J/g. The integral heat flux of MicroPCMs coated fabric is significantly higher than that of the control. The research results build up knowledge basis for the development of Nano /MicroPCMs, thermo-regulated fibres and fabrics. The thermo-regulated fabric has a significant temperature regulating function, which can be used as professional clothing materials, decorative fabrics and medical textiles.