Published: April 05, 2011 r2011 American Chemical Society 5889 dx.doi.org/10.1021/ie1022892 | Ind. Eng. Chem. Res. 2011, 50, 5889–5897 ARTICLE pubs.acs.org/IECR Cross-Linking Cotton Cellulose by the Combination of Maleic Acid and Sodium Hypophosphite. 2. Fabric Fire Performance Charles Q. Yang,* ,† Qingliang He, † and Bojana Voncina ‡ † Department of Textiles, Merchandising and Interiors, The University of Georgia, Athens, Georgia 30602, United States ‡ Faculty of Mechanical Engineering, Department of Textiles, University of Maribor, Maribor, Slovenia ABSTRACT: Multifunctional carboxylic acids have been used as durable press finishing agents for cotton with sodium hypophosphite (NaH 2 PO 2 ) as the most effective catalyst. In our previous research, we found that cellulose cross-linking takes place when cotton fabric treated with a combination of maleic acid and NaH 2 PO 2 is cured at g150 °C. The data suggested that HÀPÀH of hypophosphite likely reacts with >CdC< of the maleic acid already esterified with cotton cellulose, thus making it possible to form cross-linking on cotton. In this research, we studied the effect of the maleic acid (MA) and NaH 2 PO 2 treatment on the fire performance of cotton using microscale combustion calorimetry. We found that esterification of cotton by MA reduces the flammability of the cotton cellulose. NaH 2 PO 2 catalyzes the esterification of MA on cotton, thus further reducing the cotton fabric’s flammability by increasing esterification on cotton. The quantity of ester formed on cotton reaches the optimum range when the curing temperature is increased to g140 °C. When the curing temperature reaches g150 °C, the reaction between NaH 2 PO 2 and MA takes place on cotton. The bonding of hypophosphite to cotton further enhances the flame retardancy of the MA-treated cotton fabric as indicated by further decrease in heat release rate and further increase in char formation. The cotton fleece treated with the combination of maleic acid and NaH 2 PO 2 at low concentrations is able to achieve class 1 flammability specified by 16 CFR 1610 at low concentrations. ’ INTRODUCTION Polycarboxylic acids, with 1,2,3,4-butanetetracarboxylic acid (BTCA) in particular, are among the most effective cross-linking agents for cotton. 1À3 Polycarboxylic acids have been used as non- formaldehyde durable press agents with sodium hypophosphite (NaH 2 PO 2 ) as the catalyst since the late 1980s. 1,2 Extensive efforts have been made to develop those formaldehyde-free cross-linking agents to replace the traditional dimethyloldihy- droxyethyleneurea (DMDHEU). 3 In our previous research, we found that a polycarboxylic acid first forms a five-membered cyclic anhydride as a reactive intermediate for esterification of cotton cellulose. 4À6 We also found that maleic acid (MA), an R,β-unsaturated bifunctional acid, has two reactions on cotton under elevated temperatures. Beside esterification forming single ester linkage with cellulose (Scheme 1), >CdC< of MA likely reacted with HÀPÀH of H 2 PO 2 À , thus bonding phosphorus to cotton. The reaction makes it possible to form cross-linking between two cellulose molecules as shown in Scheme 2. 7,8 Phosphorus is an element which functions as an effective condensed phase flame retardant. 9 The most important and most commonly used nondurable, semidurable, and durable flame retardants for cotton are phosphorus-based organic or inorganic compounds. 10,11 The bonding of phosphorus to cotton by the esterification of MA on cotton and the reaction between sodium hypophosphite and MA make it possible to use such a treatment to reduce the flammability of cotton. Polycarboxylic acids were first applied to reduce the flamm- ability of cotton/polyester blend carpet. 12,13 In our previous research, we found that esterification of cotton by polycarboxylic acids, including BTCA, succinic acid, and MA, were effective in reducing the flammability of cotton fleece. 14À16 Microscale combustion calorimetry (MCC) is an analytical technique for measuring heat release properties of polymeric materials. It was capable of differentiating the small differences in the flammability of polymers and textiles on a quantitative basis. 17 In this research, we evaluated the effectiveness of the combination of MA and NaH 2 PO 2 as flame retardants for cotton fleece using MCC as a quantitative method for evaluating the heat release and other flammability parameters. ’ EXPERIMENTAL SECTION Materials. MA and NaH 2 PO 2 were reagent grade chemicals supplied by Aldrich (Milwaukee, WI, USA). The cotton woven fabric used was a desized, scoured, and bleached plain weave fabric (Testfabrics style 400) weighing 108 g/m 2 provided by Testfab- rics, West Pittiston, PA, USA, and the cotton fleece with a density of 370 g/m 2 was supplied by Esquel Group (Gaoming, China). Cotton Fabric Treatment. The cotton fabric was first im- pregnated in a solution containing MA. The fabric was then passed through a laboratory padder with two dips and two nips, and the wet pickup was approximately 100% for the woven fabric and 105% for the fleece. The impregnated woven fabric was dried at 85 °C for 3 min and cured at a specified temperature for 2 min in a laboratory curing oven manufactured by Werner Mathis, Oberhasli, Switzerland. The impregnated cotton fleece was dried Received: November 12, 2010 Accepted: March 13, 2011 Revised: February 11, 2011