Novel phosphorus/nitrogen-rich oligomer with numerous reactive groups for durable flame-retardant cotton fabric

A phosphorus/nitrogen-rich oligomer with numerous reactive groups (PEI-P) was synthesized and used as highly efficient durable flame retardant for cotton fabric. The O=P–ONH4 and O=P–OH groups in PEI-P reacted with O–H group in cellulose during finishing process. PEI-P triggered the decomposition of cotton fabric in advance, while markedly increased the char yield at high temperature. Treated fabrics showed superior flame resistance and durability. With the add-on of 19.3%, treated fabric achieved an LOI value of 38.7%. It self-extinguished even after 50 laundering cycles during vertical burning test. The PHRR and THR decreased by 86.10% and 65.11% in contrast to control fabric, respectively. PEI-P exerted gaseous and condensed flame-retardant effects by restraining the release of flammable volatiles, producing nonflammable gases and catalyzing the formation of stable phosphorus/nitrogen-rich char layers. Compared to control fabric, treated fabrics obtained well-maintained crystal structure and physical properties.