Durable press finishing agents used to produce wrinkle-resistant cotton garments are cross-linking agents for cotton cellulose. Polycarboxylic acids have been the promising durable press finishing agents to replace the formaldehyde-based reagents when sodium hypophosphite (NaH2PO2) was used as the catalyst. In our previous research, we found that a polycarboxylic acid esterifies cotton cellulose by first forming a five-membered cyclic anhydride as a reactive intermediate. Maleic acid (MA) is a bifunctional carboxylic acid, therefore is not able to form the second cyclic anhydride intermediate once it forms the first ester linkage with cotton. However, we discovered that MA imparted wrinkle resistance to cotton fabrics when NaH(2)PO2 was present, thus indicating that MA was able to cross-link cotton. Sodium hypophosphite functions as the catalyst for the esterification of cellulose by MA, and the esterification takes place at relatively low temperatures (>= 130 degrees C). Esterification of MA forms single esterlinkage with cellulose and does not cross-link cotton cellulose. As the temperature increases >= 160 degrees C, NaH2PO2 starts to be bound to cotton. The data suggested that H-P-H of hypophosphite likely reacts with the >C=C< bonds of the two MA molecules already esterified with cellulose, thus forming a cross-linkage between two cellulose molecules. Even though this proposed cross-linking mechanism of MA on cotton is supported indirectly by the data presented here, direct experimental evidence are still needed to prove such a mechanism.