| With the traditional energy becoming more tense, it is very important to improve the energy efficiency and develop the new energy in the21st century. Phase change materials (PCMs) are the materials that can absorb, store and release large amount of thermal energy during the phase change process. And PCMs has been used to manufacture thermoregulated fibers and textiles to improve the thermal self-regulation of the wearer. Encapsulation is an effective means of energy storage. In this study, microencapsulated paraffin wax with urea-formaldehyde (UF) resins and polyurea shells were synthesized through in situ polymerization and interfacial polycondensation, respectively. The aim of this work was to guide the synthesis process from the emulsification mechanism and encysted mechanism in order to fabricate MicroPCMs with small particle size and uniform distribution, a large thermal storage capacity and heat resistance. Moreover, MicroPCMs and PP were blended using micro-twin-screw. The spinnability of this system was studied by capillary rheometer. At last, the melt-blown spinning process and produced80g/m2melt-blown warm cotton were investigated. The content and achievements of this thesis include the following five points.(1) MicroPCMs containing low melting point paraffin as phase change core were synthesized by two-step in situ polymerization which the urea and formaldehyde as a reactive monomer. The aggregation principle and encysted mechanism of UF resin were explored. We focused on the effects of the molar ratios of core and shell materials, the molar ratios of monomer, the prepolymerization temperature, the dropping speed of prepolymer, the acidification time and the curing temperatures on the heat storage capacity, the particle size and distribution, the morphology and heat resistance of MicroPCMs. It was found that increasing the proportion of dimethylol urea was helpful to improve the encysted rate and the heat storage capacity. The acidification stage mainly affected the enrichment capacity of UF resin to lowing melting point paraffin. It was also found that the curing stage mainly affected the crosslinking degree of UF resin and the encysted rate of MicroPCMs, respectively. The results showed that the formaldehyde and urea in the ratio of1.8:1, the prepolymerization temperature at60℃, the core and shell material in the ratio of1.5:1～1.8:1, the dropping time of prepolymer for30min, the acidification time for60min, the curing temperature at60℃were the chosen conditions for the synthesis of MicroPCMs. Under the conditions, the appearance of MicroPCMs was nearly spherical with the latent heat of76J/g, the phase transition temperature of27.4℃, the volume average particle diameter of4.5μm and with220℃heat resistance.(2) The action mechanism of non-ionic emulsifiers and anionic emulsifiers in the synthesis process of UF/low melting point paraffin MicroPCMs was researched. And along with the contents of emulsifier styrene-maleic anhydride copolymer (SMA) potassium salts or sim alkylphenol polyoxyethylene ether (OP-10), the effects of emulsifying,shearing velocity on the emulsification, microencapsulation heat storage capacity, particle size, morphology were analyzed and discussed. Uniform and stable O/W emulsion and higher encysted rate of UF/low melting point paraffin MicroPCMs were obtained using SMA/OP-10combined emulsifier, this was attributed to high steric hindrance of OP-10and great enrichment of SMA to the resin in the initial process. The results showed that the optimum conditions were pH9of emulsion system, SMA and OP-10in the mass ratio of4:1and SMA/OP-10content of9wt.%low melting point paraffin.(3) Cyclohexane as the oil phase solvent,2,4-diisocyanatotoluene (TDI) as the oil phase monomer, ethylene diamine (EDA) as the water phase monomer, MicroPCMs with low melting point paraffin as core materials were fabricated via interfacial polymerization. The generation rate of shell materials depended on the diffusion rate of EDA to microenvironment (oil phase droplet). The influences of the type of emulsifier, the amount of OP-10, emulsion shear rate, the ratio of core and shell materials, the molar ratio of EDA and TDI on the emulsion droplets and MicroPCMs performance were investigated, and the influences of the ratio of oil and water, the dropping rate of EDA, the polymerization temperature were also discussed. The results illustrated that the optimum conditions were OP-10accounted for1.8wt.%of the emulsion, emulsion shear rate was7000r/min, the ratio of core and shell was3:1-3.5:1, the ratio of TDI and EDA was1:3, the ratio of water and oil was1:8, the dropping rate was2mL/min. Under the optimized conditions, the appearance of MicroPCMs was nearly spherical and the properties of MicroPCMs were the latent heat of85J/g, the phase transition temperature of28.7℃, the volume average particle diameter of7.5μm and with210℃heat resistance.(4) MicroPCMs/PP blends were prepared with high melt index PP as the substrate, UF/low melting point paraffin as the functional additives using a miniature conical twin-screw extruder. The effects of the content of MicroPCMs, melt temperature, shear rate on the rheological properties, the apparent viscosity, non-Newtonian index, structural viscosity index and flow activation energy of MicroPCMs/PP melts were studied by using high melt index melt flow rate meter and capillary rheometer. The80g/m2melt blown warm cotton was produced with the content of12wt.%MicroPCMs. Moreover, the thermal and mechanical properties were analyzed and discussed. The MicroPCMs/PP blends showed non-Newtonian pseudoplastic fluid behavior. When the MicroPCMs content was12wt.%, the melt had a good spinnability. The latent heat of obtained melt-blown warm cotton was8.52J/g, and the phase transition temperature was28.2℃. The mechanical properties of melt blown warm cotton compared with pure PP had not changed.The melt-blown expanding test results obtained show that the research achievement has industrial application prospect. |
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