Thermally stable, waterproof, hydrophilic, breathable poly(urethane‐imide) (PUI) films were prepared as a potential replacement for the existing polyurethanes (PU) with a lower degree of thermal stability for waterproof breathable clothing. Hydrophilic PUI films were prepared by reacting 4,4′‐ diphenylmethane diisocyanate (MDI), polyethylene glycol (PEG‐1500), and pyromellitic dianhydride (PMDA), with increasing hard segment (46%–61%) and compared with polyurethane films with similar PEG content. The breathability of PUI film is significantly higher than the PU film (~20%). Interestingly, despite the high degree of water sorption, the PUI films exhibited higher waterproofness (~85%) than the PU, which has been attributed to the presence of imide functionalities. The thermal stability of PUI was higher (Tmax1 ~ 420°C, Tmax2 ~ 600°C and char yield 21%) than the analogous PU (Tmax1 ~ 360°C, Tmax2 ~ 420°C, and char yield 6%). The waterproofness, water contact angle, and glass transition temperature are found to increase with increasing imide content, while the water sorption capacity and breathability decrease. The developed PUI coated fabric withstood hydrostatic pressure of ~3000 mbar, with a WVTR of 1200 g m−2 24 h−1, bestowing it excellent candidature as a waterproof breathable fabric.

One of the primary constituent layers of fire protective clothing is a flame-retardant, waterproof and breathable moisture barrier, which permits the outward transfer of perspiration from the firefighter’s body, while barring the inward entry of water. The introduction of a chemical and biological resistant functionality can greatly enhance the overall applicability of fire protective clothing. In the present work, a chemical & biological resistant waterproof breathable flame retardant moisture barrier fabric was prepared by laminating a biaxially stretched microporous expanded polytetraflouroethylene (ePTFE) membrane with Activated Carbon Fabric using a hot melt reactive breathable polyurethane adhesive. The developed laminate was found to exhibit an excellent balance of waterproofness (23 kPa) and breathability, which was quantified in terms of water vapour transmission rate (WVTR) and water vapour resistance (Ret). High values of WVTR, 1.1025 × 104 ± 9.8×101 g/m2/day complimented with exceptionally low values of Ret, 2.9 m2Pa/W are indicative of its high degree of breathability. Vertical flammability tests clearly revealed the exceptional flame resistance offered by the laminate, where after-flame, after-glow or melt-dripping was not observed and the char length was ∼4.2 cm. Further, the laminate exhibited requisite degree of protection against biological and chemical warfare (CW) agent with no breakthrough of the CW agent being perceived within the time frame of 24 h. The excellent combination of flame retardancy, breathability, waterproofness, chemical and biological protection, bestows the laminate excellent potential for usage as moisture barrier in fire protective clothing applications.

The present work aims at improving the properties of waterproof breathable polyurethane membranes by introducing chemical crosslinks. A series of crosslinked polyurethanes were prepared by chain extension of prepolymer containing varying amounts of a triisocyanate-based crosslinker (0-15% wt/wt). Thin polyurethane films ($40 μm) were prepared by a solution casting technique and the effect of introducing the crosslinker on thermal, mechanical characteristics was established. Crosslinking led to an increase in glass transition temperature. All crosslinked polyurethanes exhibited a sub-ambient T g . Both tensile and tear strengths were found to improve with crosslinking. Crosslinking (15% wt/wt) led to an increase in waterproofness from 112 ± 11 mbar to 574 ± 23 mbar, while the breathability reduced from 1246 ± 52 g/m 2 /day to 678 ± 32 g/m 2 /day. Polyurethane membranes containing 10% crosslinker exhibited an optimal balance of waterproofness and breathability, where the film was found to possess a water vapor transmission rate (WVTR) of 834 ± 37 g/m 2 /day with a hydrostatic pressure of 490 ± 18 mbar. This was subsequently coated on a cotton-polyester fabric to fabricate a breathable textile which was found to exhibit a WVTR of 663 ± 18 g/m 2 /day and a hydrostatic pressure of >3 bar, which was suitable for practical applications.