Viscoelastic Polyurethane Foams for Use in Seals of Respiratory Protective Devices

A key factor in effective protection against airborne hazards, i.e., biological and nonbiological aerosols, vapors, and gases, is a good face fit of respiratory protective devices (RPDs). Equally important is the comfort of use, which may encourage or discourage users from donning RPDs. The objective of the work was to develop viscoelastic polyurethane foams for use in RPD seals. The obtained foams were characterized using scanning electron microscopy, infrared spectroscopy, thermogravimetry, and differential scanning calorimetry. Measurements also involved gel fraction, apparent density, air permeability, elastic recovery time, compression set, rebound resilience, and sweat uptake. The results were discussed in the context of modifications to the foam formulation: the isocyanate index (I_NCO) in the range of 0.6-0.9 and the blowing agent content in the range of 1.2-3.0 php. FTIR analysis revealed a higher level of urea groups with increasing water content in the formulation. Higher I_NCO and water content levels also led to lower onset temperatures of thermal degradation and higher glass-transition temperatures of the soft phase. A decrease in apparent density and an increase in mean pore sizes of the foams with increasing I_NCO and water content levels was observed. Functional parameters (air permeability, elastic recovery time, compression set, rebound resilience, and sweat uptake) were also found to be satisfactory at lower I_NCO and water content levels.