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In this research, we studied cross-linking of cottonfabrics usingthe combination of itaconic acid (ITA) and sodium hypophosphite (NaH2PO2). ITA, a bifunctional carboxylic acid, wasable to esterify cotton cellulose to form a single ester linkage,but it was not able to form cross-linking between two cellulose molecules.In the presence of NaH2PO2, the amount of esterformed on cotton fabric was increased substantially and the esterificationtemperature of ITA was reduced. Therefore, NaH2PO2functioned as a catalyst for esterification of cotton by ITA. Moreover,we found that wrinkle resistance of the cotton fabric was significantlyimproved when cotton fabrics were treated with the combination ofITA and NaH2PO2.We also found that phosphoruswas bound to the treated cotton fabric and that the increase in thewrinkle recovery angle of the treated fabric was correlated to theincrease in the amount of phosphorus bound to cotton. All the dataindicated that H–P–H of sodium hypophosphite probablyreacts with the >CC< of two ITA molecules, which arealsoesterified with cellulose, thus forming a cross-linkage between thetwo cellulose molecules. The cotton fabrics treated with the ITA/NaH2PO2system demonstrated a high level of durablepress performance with significantly lower tensile strength loss thanthose treated with the formaldehyde-based dimethyloldihydroxyethyleneurea. [ABSTRACT FROM AUTHOR]

Abstract: Polycarboxylic acids have been used as nonformaldehyde crosslinking agents for cotton with sodium hypophosphite (NaH2PO2) as the catalyst to replace the formaldehyde-based dimethyloldihydroxyethleneurea (DMDHEU). Maleic acid (MA), an α, β-unsaturated bifunctional carboxylic acid, can esterify cotton but is not able to form crosslinking between two cellulose molecules by itself. In this research, we discovered that the wrinkle resistance of the cotton fabric treated with MA and NaH2PO2 was significantly increased and phosphorus was bound to cotton when the treated fabric was exposed to temperatures higher than that required for esterification of cotton by MA. Elevation of the fabric wrinkle resistance and increase in quantity of the phosphorus bound to cotton had similar dependency on curing temperature, on MA concentration, and on NaH2PO2 concentration. All the data support the hypothesis that H–P–(residual of NaH2PO2) added to >Cf the MA already bound to cotton by esterification, thus forming a new crosslink between two cotton cellulose molecules. The cotton fabrics treated by MA/NaH2PO2 showed fabric wrinkle resistance similar to that treated with DMDHEU, but the breaking strength and tearing strength of the MA-treated cotton fabrics were significantly improved. [Copyright &y& Elsevier]

Multifunctional carboxylic acids have been used as durable press finishing agents for cotton with sodium hypophosphite (NaH2PO2) 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 NaH2PO2is cured at ≥150 °C. The data suggested that H−P−H of hypophosphite likely reacts with >CC< 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 NaH2PO2treatment 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. NaH2PO2catalyzes 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 ≥140 °C. When the curing temperature reaches ≥150 °C, the reaction between NaH2PO2and 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 NaH2PO2at low concentrations is able to achieve class 1 flammability specified by 16 CFR 1610 at low concentrations. [ABSTRACT FROM AUTHOR]

Abstract: N-Methylol dimethylphosphonopropionamide (MDPA) is one of the most commonly used durable flame retardant agents for cotton. In our previous research, we developed a new flame retardant finishing system based on a hydroxy-functional organophosphorus oligomer (HFPO) and bonding agents, such as dimethyloldihydroxyethyleneurea (DMDHEU) and trimethylolmelamine (TMM). In this research, we compared the flame resistant performance as well as physical properties of the cotton fabric treated with these two flame retardant finishing systems. The cotton fabric treated with MDPA/TMM has a higher initial limiting oxygen index (LOI) than that of the fabric treated with HFPO/TMM due to higher nitrogen content in the system. The LOI of the cotton fabric treated with the HFPO and MDPA systems becomes identical when the treated fabric contains equal amount of phosphorus and nitrogen. The MDPA/TMM shows higher laundering durability on cotton than HFPO/TMM system. The fabric treated with HFPO/TMM and MDPA/TMM has low wrinkle resistance and low strength loss whereas the fabric stiffness significantly increases when the TMM concentration is increased. [Copyright &y& Elsevier]

Abstract: N-Methylol dimethylphosphonopropionamide (MDPA), known as “Pyrovatex CP” and “Pyrovatex CP New” commercially, has been one of the most commonly used durable flame retardant agents for cotton for many years. In our previous research, we developed a flame retardant finishing system for cotton based on a hydroxy-functional organophosphorus oligomer (HFPO) in combination with a bonding agent such as trimethylolmelamine (TMM) and dimethyloldihydroxyethyleneurea (DMDHEU). In this research, we investigated the bonding of these two flame retardant finishing agents to cotton. We found that the majority of MDPA is bound to cotton by its N-methylol group and that the use of TMM as a co-reactant modestly increases the fixation of MDPA onto cotton. For HFPO, however, the use of a bonding agent is necessary to form a covalent linkage between HFPO and cotton. Both the fixation of HFPO on cotton and its laundering durability are influenced by the effectiveness and concentration of the bonding agent. The commercial product of HFPO contains approximately 33% more phosphorus than that of MDPA and the percent fixation of HFPO on cotton is also moderately higher than that of MDPA. The bonding between MDPA and cotton is significantly more resistant to hydrolysis during multiple launderings than that between HFPO and cotton. The selection of catalyst also plays a significant role in influencing the bonding of the flame retardant agents to cotton. [Copyright &y& Elsevier]

In previous research, it was found that the anhydride intermediates of a homopolymer and a terpolymer of maleic acid (PMA and TPMA, respectively) esterified citric acid (CA) in-situ on the cotton fabric under curing conditions. CA was thus transformed from a trifunctional crosslinking agent into one with a higher functionality and created a synergistic effect for crosslinking cotton cellulose. In this research, the performance of TPMA/CA as a nonformaldehyde durable press finish system applied to cotton fabrics by a pre-cure technique was evaluated. The cotton fabrics treated with TPMA/CA showed durable press performance and mechanical properties better than that treated with a low formaldehyde DMDHEU. The TPMA/CA-treated cotton fabric also demonstrated satisfactory home laundering durability. [ABSTRACT FROM AUTHOR]

The increasing demand for easy care cotton apparel in the marketplace has made it urgent to develop competitively priced formaldehyde-free durable press finishes to replace the traditional N-methylol reagents. A cost-effective nonformaldehyde durable press finishing system was developed based on citric acid and a terpolymer of maleic acid. This system was applied to garment finishing on both laboratory and industrial production scales and compared with the traditional DMDHEU systems as well as one commercial nonformaldehyde system. The durable press rating, crease retention rating, wrinkle recovery angle, mechanical strength, and abrasion resistance of the garments finished with the new system are comparable to those treated with the conventional DMDHEU systems. The garments finished with the new system maintained satisfactory fabric smoothness and crease retention after 30 home laundering washing/ drying cycles. [ABSTRACT FROM AUTHOR]

It is essential to understand the molecular level response of crosslinked cellulose chain segments upon deformation, in order to develop new agents which convey high durable-press (DP) rating to cellulose fibers with minimal strength loss. In this work models of amorphous cellulose crosslinked with both rigid and flexible crosslinks were constructed computationally for this purpose. Rigid crosslinks bound cellulose molecular segments together and blocked the chain slippage, providing cellulose models with a higher initial modulus and better elastic response. However, the loss of the chain slippage led to stress being distributed unevenly among cellulose chains. Chains in some regions were subjected higher stress and these regions were opened up much more than the rest of the cellulose, which presumably caused models to fail. When conformationally flexible crosslinks were used, breaking strain of cellulose was not significantly reduced but deformation recovery was not improved either, in comparison with the models of untreated cellulose. Conformational transitions were observed in the flexible crosslinks during extension. These results help to explain how and why rigid crosslinks work to provide wrinkle resistant properties and why they also lower tensile strength, and that just using a conformationally flexible crosslinking will not provide any recovery. [Copyright &y& Elsevier]

Molecular modeling was utilized to provide insight into the yielding behavior and poor recovery from applied strain for cellulose. Amorphous cellulose models were successfully built and examined with the use of force field pcff_300_1.01. High-temperature molecular dynamics, followed by minimization, was used to generate relaxed structures for amorphous cellulose. Properties related to inter-molecular interactions were calculated for these models and found to be comparable with literature values. The observed yielding for these models, which occurred at approximately 7–8% strain, was found to be due to the disruption of hydrogen bonds between cellulose chain segments. New hydrogen bonds were formed in extension but only 1/3 of these were broken during recovery. These newly formed hydrogen bonds were found to hold the cellulose chain segments in the new positions thus resulting in poor deformation recovery. [Copyright &y& Elsevier]