Thermal-regulation of nonwoven fabrics by microcapsules of n-eicosane coated with a polysiloxane elastomer

Synthesis of microcapsules composed of a paraffin core coated with polysiloxane, which were developed in one of our laboratories, was adapted for preparation of the microcapsules for thermoregulation of textiles. n-Eicosane with melting temperature 37 °C was used as a phase change material (PCM). Shells of the microcapsules were made of a polysiloxane elastomer. The microcapsules were fabricated in an aqueous emulsion, which was prepared by mechanical co-emulsification of the paraffin with a reactive polysiloxane. The process yielded microcapsules consisting of n-eicosane coated with polysiloxane, which later was cross-linked in the emulsion. Chemical structure of the microcapsules was characterized by FT-IR, 29Si MAS NMR and EDX methods. SEM and TEM techniques were used for studies of microcapsule diameters, diameter distributions and thickness of the polysiloxane shells. Core-shell structure of the microcapsules and complete coating of the paraffin with polysiloxane were confirmed. Phase change enthalpy of the microcapsules was 146 J/g. Encapsulation coefficient (Xen) and energy storage coefficient (Xes) were close, which indicated that the absorbed and released heat was due to the melting and crystallization of n–eicosane, respectively. The PCM microcapsules were incorporated into the needled fabrics using a padding method. SEM, FT-IR and EDX determined their presence and location in the fabrics. It was found that content of the PCM microcapsules in the dry mass of the nonwovens was 37 wt percent. The high value of the coefficient energy storage capability (Ces) for the microcapsules alone, for the microcapsules with binder and for the modified nonwoven were close to 99% and indicated a tight encapsulation of the paraffin by polysiloxane shells. This ensured heat absorption and release during in many cycles. Indeed, the DSC results (over 100 cycles of phase changes) confirm high thermal stability of the microcapsules also in the modified nonwoven. The heat effect corresponding to the phase change was equal 34 J per gram of the modified textile.