Novel Waterborne P–N Polyurethane and Its Application in Leather Finishing for Flame-Retardant and Antimicrobial Properties

Abstract A novel aliphatic and aromatic waterborne polyurethane (WPU) compounds were synthesized by incorporating phosphorus and nitrogen into the WPU as flame-retardant and antimicrobial agents in leather finishing. A spirocyclic pentaerythritol bisphosphorate disphosphoryl dihydrazone (SPDPDH) as a novel compound and as a source of phosphorus–nitrogen was prepared by reacting hydrazine hydrate with spirocyclic pentaerythritol bisphosphorate disphosphoryl chloride (SPDPCl). The structure of SPDPDH was characterized using FTIR, 1 H NMR, and 13 C NMR spectroscopy. The process of creating water-based polyurethane (WPU) involves a poly-addition polymerization reaction. This reaction relies on a few different variables, such as the polyethylene glycol (PEG, 300), isophorone diisocyanate (IPDI) used for aliphatic PU, or toluene diisocyanate (TDI) used for aromatic PU, in conjunction with 1,4-butanediol (BDO) with dimethylolpropionic acid (DMPA) and along with SPDPDH. Subsequently, an aqueous polyurethane coating containing SPDPDH compound was applied to the leather and compared to the uncoated. The physical properties, water absorption %, and water vapour permeability % were investigated. The surface structure morphology and element composition of leather before and after treatment were examined using scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS). The mechanical properties, tensile strength, and elongation % of coated leather were considered. The limited oxygen index (LOI) can achieve 30.8%, and the vertical burning test UL-94 was adopted to estimate the flame-retardant property. The antibacterial activities of the samples were evaluated using Gram-negative bacteria (Pseudomonas aeruginosa (ATCC 27853)), Gram-positive bacteria (Micrococcus luteus (ATCC 10240) and Staphylococcus aureus (ATCC 6538)), and pathogenic fungi such as Candida albicans ATCC 10231 test methods, proving a high synergistic antimicrobial efficiency of the modified leather. Results indicated an improvement in leather characteristics; this may be due to satisfactory dispersion and strong interfacial interaction of waterborne phosphorus–nitrogen polyurethane with the leather matrix. These treatments improved thermal stability, physical morphology, surface mechanical properties, and flame retardancy with obvious results. Graphical Abstract