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Nylon/cotton blend fabrics have long been used in military protective clothing. Because fire risk has drastically increased in recent warfare, developing flame retarded military nylon/cotton fabrics becomes extremely important for protecting military personnel. It was previously discovered that a hydroxy-functional organophosphorus oligomer (HFPO) was bound to a nylon fabric in the presence of dimethyloldihydroxylethyleneurea (DMDHEU) as a bonding agent. In this research, the bonding mechanism of HFPO/DMDHEU on the nylon/cotton blend fabrics was investigated. HFPO was bound to the nylon/cotton blend fabrics by (1) forming HFPO/DMDHEU crosslinked polymeric networks on both nylon and cotton and (2) forming a DMDHEU bridge between cellulose and HFPO on cotton. The relative quantity of the HFPO/DMDHEU crosslinked networks and that of the DMDHEU-bridging formed on the treated blend fabrics was controlled by the HFPO-to-DMDHEU ratio. The HFPO/DMDHEU system was an effective and durable flame retarding treatment system for nylon/cotton military blend fabrics. The treated fabrics passed the fabric vertical burning test after 50 home laundering cycles. The fire performance and hydrolysis-resistance of different nylon/cotton blend fabrics treated with HFPO/DMDHEU was fully evaluated, and the performance data were analyzed in relation with the bonding mechanism. [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]

Abstract: Evaluating and analyzing the performance of flame retardant (FR) textiles are a critical part of research and development of new FR textiles products by the industry. The testing methods currently used in the industry have significant limitations. Most analytical and testing techniques are not able to measure heat release rate (HRR), the single most important parameter in evaluating the fire hazard of materials. It is difficult to measure HRR of textile fabrics using cone calorimetry because textile fabrics are dimensionally thin samples. The recently developed micro-scale combustion calorimetry (MCC) is able to measure the following flammability parameters for textile using milligram sample sizes: heat release capacity, HRR, temperature at peak heat release rate (PHRR), total heat release and char yield. In this research, we applied MCC to evaluate the flammability of different textile fabrics including cotton, rayon, cellulose acetate, silk, nylon, polyester, polypropylene, acrylic fibers, Nomex and Kevlar. We also studied the cotton fabrics treated with different flame retardants. We found that MCC is able to differentiate small differences in flammability of textile materials treated with flame retardants. We were also be able to calculate the limiting oxygen index (LOI) using the thermal combustion properties of various textile samples measured by the MCC. The calculated LOI data have yielded good agreement with experimental LOI results. Thus, we conclude that MCC is an effective new analytical technique for measuring textile flammability and has great potentials in the research and development of new flame retardants for textiles. [Copyright &y& Elsevier]

Abstract: In this research, we studied the mechanism of bonding a hydroxy-functional organophosphorus oligomer (HFPO) to nylon 6.6 fabric using the formaldehyde derivatives of urea and melamine, including dimethyloldihydroxyethyleneurea (DMDHEU) and trimethylolmelamine (TMM), as the bonding agents. The nylon fabric treated with HFPO/DMDHEU or HFPO/TMM retained significant amount of phosphorus after multiple launderings. The laundering durability of the HFPO applied to nylon was probably attributed to the formation of a crosslinked polymeric network on the nylon fiber. The nylon fabric treated with HFPO/DMDHEU showed higher percent phosphorus retention than that treated with HFPO/TMM. The percent phosphorus retention of the treated nylon increased as the DMDHEU or TMM concentration was increased, and the nylon fabric''s stiffness follows the same trend. The micro-scale combustion calorimetry and thermal analysis data indicate that the HFPO bound to nylon reduced peak heat release rate and heat release capacity of the nylon fabric, decreased decomposition temperature and promoted the char formation of the treated fabric. The nylon/cotton blend military fabric treated with HFPO/DMDHEO or HFPO/TMM demonstrated flame retardant performance after 10 laundering cycles. [Copyright &y& Elsevier]

Abstract: Flame retardancy is a desirable property for silk textiles, and it becomes necessity when silk textiles are for interior decorative use in building with public access. However, the flame retardant finishing technology available for silk has significant limitations. In this research, we studied the use of the combination of a hydroxyl-functional organophosphorus oligomer (HFPO) and 1,2,3,4-butanetetracarboxylic acid (BTCA) as a formaldehyde-free flame retardant finishing system for silk. When BTCA is applied to silk, most of BTCA reacts with the hydroxyl group on silk by single ester linkage. In the presence of HFPO, BTCA is able to bond HFPO onto silk by either a BTCA “bridge” between silk and HFPO or a BTCA–HFPO–BTCA cross-linkage between two silk protein molecules. We evaluated the flammability and physical properties of the silk fabric treated with HFPO and BTCA. The treated silk fabric demonstrated a high level of flame retardancy with modest loss in fabric tensile strength. The treated silk passed the vertical flammability test after 15 hand wash (HW) cycles. Increasing the HFPO concentration from 20% to 30% does not show significant improvement in the flame retardant performance of the treated silk. The thermal analysis data demonstrated that HFPO reduces silk''s initial thermal decomposition temperature and promotes char formation. [Copyright &y& Elsevier]

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]

Abstract: Cotton/nylon blends have been commonly used as the material for protective clothing, but those blend fabrics are not flame retardant finished because of the unavailability of effective flame retardant finishing systems. Previously, we investigated the use of a hydroxyl-functional flame retardant organophosphorus oligomer (FR) in combination with the mixture of dimethyloldihydroxyethyleneurea (DMDHEU) and trimethylolmelamine (TMM) as the binders for flame retardant finishing of cotton. In this study, we investigated the application of FR to the 50/50 cotton/nylon fabric. When the FR/DMDHEU/TMM system is applied to the fabrics of nylon-6,6 and nylon-6, approximately 40% of the FR applied is permanently bound to the nylon fabrics. FR is bound to the nylon fabrics mainly through the formation of a FR/TMM crosslinked polymeric network, thus becoming durable to multiple launderings. The cotton/nylon blend treated with FR shows high levels of flame retardant performance and excellent laundering durability. The treated fabric passes the vertical flammability test even after 50 home laundering cycles. The fabric stiffness as a result of the finishing process is still an obstacle to be overcome for practical use of this finishing system. [Copyright &y& Elsevier]

In our previous research, we developed flame retarding systems for cotton based on a hydroxy-functional organophosphorus oligomer (FR) and a binder, such as 1,2,3,4-butanetetracarboxylic acid (BTCA), dimethyloldihydroxyethyleneurea (DMDHEU) and melamine–formaldehyde (M–F), which are able to form covalent binding between FR and cotton. In this research, we used a factorial experimental design method to study the performance of the flame retarding system based on FR and the mixture of DMDHEU and M–F. We found that an increase in the DMDHEU/(DMDHEU + M–F) ratio in the mixture increases the amount of FR bound to cotton, increases the laundering durability of FR on cotton, and reduces the fabric tensile strength retention. DMDHEU and M–F also function as nitrogen providers and enhance the flame retarding performance of the treated fabric due to phosphorus–nitrogen synergism. M–F is a more efficient nitrogen provider than DMDHEU. The effect of reduced phosphorus–nitrogen synergism as a result of increasing the relative amount of DMDHEU in the mixture (DMDHEU + M–F) outweighs that of the improved bonding of FR to cotton. An increase in FR concentration in a formula increases the amount of FR bound to cotton, whereas it reduces the percent retention of FR on the fabric and also reduces the fabric strength loss. Desirable performance of treated cotton fabrics can be achieved by adjusting the concentrations of FR and the ratio of the two binders in a formula. [Copyright &y& Elsevier]

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]