Synthesis and application of citric acid dimer as the anti-wrinkle finishing agent for cotton fabric

Citric acid (CA) is often used for the anti-wrinkle finishing of cotton fabrics, but it tends to yellow and undesirable anti-wrinkle effect. To solve the above problems, citric acid dimer (CACA) was synthesized by using the reaction of isocyanate with –OH in CA molecular structure, and it was used as a finishing agent for the anti-wrinkle finishing of cotton fabrics. Thermal analysis experiments demonstrated the stability of the molecular structure of CACA-HMDI and CACA-IPDI obtained from hexamethylene diisocyanate (HMDI) and isophorone diisocyanate (IPDI) respectively in the range of 20–180 °C, which reduced the yellowing of cotton fabrics caused by dehydration of CA molecular structure in high temperature curing. Under the conditions of optimal finishing process, the wrinkle recovery angle of cotton fabrics could be increased to over 270° for CACA-HMDI and 250° for CACA-IPDI, while it could only be increased to a maximum of 240° for CA. The steady-state molecular structure of CACA was analyzed by Gaussian 09W software. The calculation results of Gaussian molecular calculation software showed that compared with CACA-IPDI molecule, CACA-HMDI molecule had certain spatial folding and contained more carboxylic acid groups, which enabled it to be esterified and cross-linked at different sequencing positions of cellulose macromolecular chain, thus obtaining more effective wrinkle resistance.