Abstract
As a novel polymer, polyurethane (PU) has been widely applied in leather, synthetic leather, and textiles due to its excellent overall performance. Nevertheless, conventional PU is flammable and its combustion is accompanied by severe melting and dripping, which then generates hazardous fumes and gases. This defect limits PU applications in various fields, including the leather industry. Hence, the development of environmentally friendly, flame-retardant PU is of great significance both theoretically and practically. Currently, phosphorus-nitrogen (P-N) reactive flame-retardant is a hot topic in the field of flame-retardant PU. Based on this, the preparation and flame-retardant mechanism of flame-retardant PU, as well as the current status of flame-retardant PU in the leather industry were reviewed.
Highlights
Polyurethane (PU) refers to a polymer with repeating carbamate groups (–NHCOO–)in the polymer backbone structure [1]
Polyurethane is widely used in thermal insulation materials and household products [119], so the indoor air pollution caused by flame-retardant polyurethane has been paid attention to, especially as people spend most of their time indoors [120]
With its excellent overall performance, PU has been widely used in leather, synthetic leather, textiles, and other industries, bringing great optimization to human life
Summary
In the polymer backbone structure [1]. PU was first synthesized from hexamethylene diisocyanate and 1, 4-butanediol [2]. Various PU products have been widely applied in leather fabrication, synthetic leather, the light industry, textiles, coatings, building materials, electronics, medicine, automotive, national defense, and aerospace (see Figure 1). The synthesis of PU is based on the chemical reaction of isocyanates, which is obtained by the stepwise addition polymerization of basic raw materials (e.g., polyisocyanate and compounds containing active hydrogen). Industrial PU is produced by the reaction of diisocyanate and polyols (e.g., polyether or polyester polyols, small molecule chain expanders, and/or crosslinkers) (see Figure 2). From the perspective of molecular structure, PU is a typical block polymer in which the macromolecular chains are mainly composed of alternating flexible (soft) and rigid (hard) chain segments. The molecular structure of PU has high tunability through the selection of different types of raw materials, adjusted ratios of monomers, reaction sequence control, and the use of different synthetic process conditions. It can be prepared to generate a variety of structures, morphologies, processing methods, and appearances and media, including PU soft foam, PU rigid foam, PU elastomer, PU fibers, PU coatings, and PU adhesives [7,8,9,10,17]
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