Flame retardant, hydrophobic and UV resistant hemp cellulose fabrics constructed by assembly of fluorosilicone waterborne polyurethane and phosphorylated sodium alginate

In this study, a assembly technique based on phosphorylated sodium alginate (PSA) and fluorosilicone waterborne polyurethane (FSiWPU) was developed, and a multifunctional hemp cellulose fabric system which integrates flame retardant, hydrophobic and UV resistant properties was successfully constructed. Stable multilayer structures are formed by utilizing the hydrogen bonding between the phosphate group/carboxylic acid group of PSA and the carbamate group (-NHCOO-) of FSiWPU. The phosphorylation of sodium alginate significantly improves its thermal stability and generates a dense carbon layer with polyurethane decomposition products at high temperatures, resulting in a limiting oxygen index (LOI) of 32.7 % for hemp cellulose fabric, which achieves a UL-94 V-0 rating. Compared with the original fabric, the peak and total heat release rates of phosphorylated sodium alginate/fluorosilicone waterborne polyurethane (PSA/FSiWPU) coated hemp cellulose fabric decreased by 75.2 % and 90.1 %, respectively. Meanwhile, the fluorosilicon component in FSiWPU is enriched on the fabric surface and the water contact angle of the coated fabric reaches 136.05°, which endows the fabric with excellent hydrophobicity and self-cleaning properties. Encouragingly, the functional coating is universal and suitable for a variety of substrates. Moreover, the coated fabric shows excellent UV resistance, with a UV protection factor of 91.26 and a UVA transmission rate of <5 %. Not only that, coated fabrics also have good mechanical properties and washability. Therefore, this work not only opens up new idea for the multifunctional finishing of hemp cellulose fabrics, but also has great potential in practical applications.