Charles Q. Yang

Formation of Cyclic Anhydride Intermediates and Esterification of Cotton Cellulose by Multifunctional Carboxylic Acids: An Infrared Spectroscopy Study

Multifunctional polycarboxylic acids have been used as nonformaldehyde cross linking agents for cotton fabrics to replace the traditional N-methylol reagents. Ester ification of cotton cellulose by seventeen aliphatic and aromatic polycarboxylic acids is studied using Fourier transform infrared spectroscopy. Five-membered cyclic an hydride intermediates formed under the curing conditions are identified on cotton fabrics treated with these acids. Only those polycarboxylic acids that form cyclic an hydride intermediates esterify cotton cellulose. Formation of the cyclic anhydride intermediates and esterification of cotton cellulose take place in the same curing tem perature regions. The infrared spectroscopy data also indicate that the second carboxyl group in a bifunctional carboxylic acid is not able to esterify cotton cellulose effectively. Therefore, we can conclude that a polycarboxylic acid esterifies cotton cellulose through the formation of a cyclic anhydride intermediate. The infrared spectroscopy data also reveal that 1,2,3,4-butanetetracarboxylic acid is the most effective crosslinking agent for cotton cellulose among the acids studied.

Mechanical Strength of Durable Press Finished Cotton Fabrics Part I: Effects of Acid Degradation and Crosslinking of Cellulose by Polycarboxylic Acids

Severe tensile strength loss is the major disadvantage of durable press finished cotton fabrics. Such strength losses have been attributed to two main factors: acid-catalyzed depolymerization and crosslinking of cellulose molecules. In this research, we inves tigate the effects of acid degradation and cellulose crosslinking on the tensile strength of cotton fabric crosslinked by polycarboxylic acids. Multifunctional carboxylic acids such as butanetetracarboxylic acid (BTCA) are used as nonformaldehyde crosslinking agents for cotton fabrics. The strength loss caused by acid degradation is an irreversible process, and the magnitude of the loss is determined by the curing temperature and time, the dissociation constants of the acid, and the concentration and pH of the acid solution applied to the fabric. Crosslinking of cellulose molecules by a polycarboxylic acid causes a reversible fabric strength loss, which increases as the degree of crosslink ing increases. The magnitude of tensile strength loss caused by acid degradation and that by crosslinking for cotton fabrics treated with BTCA is measured. Losses caused by crosslinking can be restored after the ester crosslinking is hydrolyzed under alkaline conditions.

Ester crosslinking of cotton fabric by polymeric carboxylic acids and citric acid

Polycarboxylic acids appear to be the most promising nonformaldehyde durable press finishing agents to replace the traditional N-methylol reagents, 1,2,3,4-Butanetetracarboxylic acid (btca) is the most effective crosslinking agent among the acids investigated, but its exceedingly high cost has prevented its use in the textile industry on a commercial scale. In this research, we evaluate the effectiveness of two polymers of maleic acid, i.e., the homopolymer (pma) and the terpolymer (tpma), along with citric acid (ca) for crosslinking cotton cellulose., pma, tpma, and ca have molecular structures similar to btca, but are more cost effective. We have found that pma and tpma are less effective crosslinking agents for cotton than btca, probably due to the low mobility of the anhydride intermediate formed by pma or tpma to access the cellulosic hydroxyl during the curing process. We have found that the hydroxyl of ca and other α-hydroxylpolycarboxylic acids hinder the esterification of those acids with cellulose. The infrared spectroscopy data indicate that ca esterifies the anhydride intermediates of pma and tpma on cotton fabric under curing conditions. Consequently, ca is transformed from a trifunctional acid to a tetrafunctional one with the formation of an ester linkage with pma or tpma.

Nonformaldehyde Durable Press Finishing of Cotton Fabrics by Combining Citric Acid with Polymers of Maleic Acid

In our previous research, we investigated the use of two polymers of maleic acid, i.e., the homopolymer (PMA) and the terpolymer (TPMA), for crosslinking cotton cellulose. We found that PMA and TPMA were less effective than 1,2,3,4-butanetetracarboxylic acid (BTCA) due to the low mobility of the anhydride intermediates to access the cellulosic hydroxyl during a curing process. We found that the hydroxyl of citric acid (CA) hinders its esterification with cotton cellulose, and so is less effective than 1,2,3-propanetricar boxylic acid as a crosslinking agent for cotton. We also found that CA esterifies the anhydride intermediate of PMA or TPMA on the cotton fabric formed under curing con ditions. In this research, we observed a synergistic effect by combining PMA or TPMA with CA as co-crosslinking agents for cotton fabrics. The combination of TPMA/CA is more effective than the PMA/CA combination for imparting wrinkle resistance to the finished cotton fabrics. Cottons finished with the TPMA/CA combination show superior durable press performance, good laundering durability, and high fabric strength retention. The superior performance and cost effectiveness of this new finishing system makes it feasible as a replacement for formaldehyde-based durable press finishes.

Characterizing Ester Crosslinkages in Cotton Cellulose with FT-IR Photoacoustic Spectroscopy 1:

Polycarboxylic acids are being developed as new nonformaldehyde finishes for cotton fabrics to replace the traditional dimethyloldihydroxylethyleneurea. In this research, Fourier transform infrared photoacoustic spectroscopy (FT-IR/PAS) was used to char acterize the intermolecular ester crosslinkages in cotton cellulose. When esterification occurs between a polycarboxylic acid and cotton cellulose, the carbonyls retained in the cotton exist in three forms: ester, carboxylic acid, and carboxylate anion. The FT- IR data show that the band of the ester carbonyl can be separated from the bands of the other two carbonyls; therefore, the ester crosslinkages of the finished cotton fabrics can be compared on a semiquantitative basis with FT-IR spectroscopy. FT-IR/PAS was used to study the hydrolysis of the ester linkages, the recurability of the finished cotton fabrics, and the distribution of ester crosslinkages between the surfaces of the cotton fabrics and their interiors.

FT-IR Spectroscopy Study of the Ester Crosslinking Mechanism of Cotton Cellulose:

Polycarboxylic acids are being developed as new nonformaldehyde crosslinking agents for cotton fabrics to replace the traditional N-methylol reagents. In this research, the mechanism of esterification between polycarboxylic acids and cotton cellulose was elucidated using FT-IR spectroscopy. All the infrared spectroscopic data support the hypothesis that cyclic anhydrides are formed as intermediates, which in turn esterify with cotton cellulose. The infrared spectroscopic data also demonstrate that cyclic anhydrides are very reactive and are able to esterify with cotton cellulose without a catalyst present and at a temperature much lower than the curing temperatures used for polycarboxylic acids. Therefore, the chief role of catalysts such as sodium hypo phosphite is that they accelerate the formation of a cyclic anhydride from a polycar boxylic acid.

Comparison of DMDHEU and Melamine-Formaldehyde as the Binding Agents for a Hydroxy-Functional Organophosphorus Flame Retarding Agent on Cotton

It is necessary to use a crosslinking agent to bond a flameretarding hydroxy-functional organophosphorus oligomer (FR) to cotton so that the flame resistance of the treated cotton fabric can be durable to multiple homelaundering. Both dimethyloldihydroxyethyleneurea (DMDHEU) and melamine– formaldehyde (M-F) have been used as the binding agents between FR and cotton. The vertical flammability, limiting oxygen index (LOI) and phosphorus content after different numbers of laundering cycles as well as the wrinkle resistance and tensile strength of the cotton fabric treated with FR/DMDHEU and FR/M-F was investigated and compared in this research. We found that DMDHEU is more effective for crosslinking cotton cellulose and for crosslinking between FR and cotton than M-F. We also found that the bonding formed by DMDHEU between cotton and FR is more durable to multiple laundering cycles than that formed by M-F. M-F is a more effective nitrogen provider than DMDHEU to enhance the flame retarding performance of the treated cotton fabric through phosphorus–nitrogen synergism, therefore the presence of M-F in the flame retardant finishing system significantly increases the flame resistance of the treated fabric. DMDHEU, as an effective crosslinking agent for cotton, causes more fabric strength loss than M-F.

Mechanical Strength of Durable Press Finished Cotton Fabric Part II: Comparison of Crosslinking Agents with Different Molecular Structures and Reactivity

In our previous research, we investigated the strength loss of durable press cotton fabric caused by acid-catalyzed depolymenzation. In this paper, we study the relationship between the tensile strength loss of crosslinked cotton fabric and the molecular structures of the crosslinking agents. We use 1,2,3,4-butanetetracarboxylic acid (BTCA) and all-cis-1,2,3,4- petanetetracarboxylic acid (CPTA), linear and cyclic terrafunctional carboxylic acids, respec tively, to treat cotton at different concentrations and different temperatures. We find that BTCA is more effective and imparts higher levels of wrinkle resistance than CPTA, but the relationship between tensile strength loss and wrinkle recovery angle (WRA) for the treated fabric is independent of the differences in their molecular structures and reactivity. We also compare the tensile strength loss of cotton fabric treated with DMDHEU and 1,3-dimethyl-4,5-dihydroxyl ethyleneurea (DHDMI) and observe a similar phenomenon.

Infrared spectroscopy studies of the cyclic anhydride as the intermediate for the ester crosslinking of cotton cellulose by polycarboxylic acids. III. Molecular weight of a crosslinking agent

Polycarboxylic acids have been used as nonformaldehyde crosslinking agents for cotton fabrics to replace the traditional N-methylol reagents. In this research, we compared 1,2,3,4-butanetetracarboxylic acid (BTCA) with poly(maleic acid) (PMA) as crosslinking agents for cotton cellulose. BTCA and PMA have similar molecular structures with carboxyl groups bonded to their molecular backbones, and both form five-membered cyclic anhydride intermediates during a curing process. However, BTCA is a more effective crosslinking agent for cotton cellulose than PMA. This is mainly attributed to the differences in the mobility of the anhydride intermediates to access the cellulosic hydroxyl groups during a curing process. The mobility of the anhydride intermediate of PMA is reduced due to its molecular size and multiple bonding between a PMA molecule and cellulose. Consequently, more anhydride and less ester are detected on the cotton fabric treated with PMA than on the fabric treated with BTCA. The amount of the unreacted anhydride intermediate on the fabric treated with PMA is reduced whereas the amount of ester is increased when another hydroxyl-containing compound of low molecular weight is present. Thus, the infrared spectroscopy data show a clear link between the molecular weight of a polycarboxylic acid and its effectiveness for crosslinking cotton cellulose.

Nonformaldehyde Flame Retardant Finishing of the Nomex/Cotton Blend Fabric Using a Hydroxy-Functional Organophosphorus Oligomer

Multifunctional carboxylic acids, such as 1,2,3,4-butanetetracarboxylic acid (BTCA), have been used as durable press finishing agents to produce wrinkle-resistant cotton. In our previous research, we used BTCA as a nonformaldehyde bonding agent in the flame retardant finishing system based on a hydroxy-functional organophosphorus oligomer (HFPO) for cotton. In this research, we investigate the application of HFPO to the 65%/35% Nomex/cotton blend fabric using BTCA as a bonding agent and triethanolamine (TEA) as a co-reactant. We found that the addition of TEA in the flame retardant finishing system improves the hydrolysis resistance of the HFPO bound to the Nomex/ cotton blend and enhances the flame retardant performance of HFPO by means of phosphorus—nitrogen synergism. Moreover, TEA reduces the deposit of calcium salt on the treated fabric during laundering by esterifying the free carboxylic acid groups on cotton. The Nomex/cotton blend fabric treated with the HFPO/BTCA/TEA system shows high flame retardant performance at relatively low add-on levels. It is a completely nonformaldehyde flame retardant finishing system.