Stanley R. Hobart

An Investigation of the Reversibility of N-Methylolacrylamide Cross Links on Cotton1

N-Methylolacrylamide (NMA) was reacted reversibly in successive, acid-catalyzed and base-catalyzed steps to cross-link cotton cellulose. The occurrence of cross-linking was confirmed by development of cuene insolubility and wrinkle recovery. The ease of crease introduction or removal was used to indicate the extent of breaking and reforming the cross links on treatment of the ether linkages with the respective catalysts. It was found that good, durable creases could be introduced into flat NMA-cross-linked fabrics with either acidic or basic catalysis, the latter being slightly more effective. Removal of creases was only partially successful, regardless of the catalyst used, indicating that the sites of the ether linkages at the crease location were inaccessible to the catalyst. Breaking strengths and formaldehyde and nitrogen analyses were determined during these treatments.

Differential thermal analysis of polyester/cotton blends treated with Thpc—urea—poly(vinyl bromide)

Abstract Differential thermal analyses (DTA) were made on a series of polyester/cotton blend fabrics before and after treatment with Thpc—urea—poly(vinyl bromide). This flame retardant did not affect the polyester melting endotherm, which was proportional to the polyester content and appeared at approximately 250°C. In nitrogen atmosphere, DTA of the treated blends showed exothermic peaks at 285°C for the cotton decomposition. and at 415°C for the polyester decomposition. In air, DTA of the treated blends showed exothermic peaks at 333°C for cellulose decomposition, at 431°C for polyester decomposition and at 490°C for char decomposition. The Thpc-urea component of the flame retardant is effective on the cotton cellulose portion of the blend; the poly(vinyl bromide) appears to decompose and act in the vapor state on the polyester.

Reaction of Aryl Isocyanates With Cotton Cellulose Part IV: Reaction Via Phenyl N-Arylcarbamates

Eleven N-arylcarbamylated celluloses were prepared by a pad-cure treatment of cotton with phenyl N-arylcarbamates as isocyanate generators. Add-ons up to 8.5% were obtained by impregnating the fabric with a dimethylformamide (DMF) solution of the phenyl carbamate and curing at 180-200°C for 4-5 min. The extent and efficiencies of these cotton cellulose reactions were observed by means of add-ons, nitrogen contents, and change in pickup of acid dyes. The activating aryl substituents were dialkylamino, methoxyl, methylthio, and methyl electron-donating (+E) groups. N-pyridylcarbamates were also used. The modified cotton fabrics exhibited improved rot resistance and those containing amine groups had ion-exchange properties.

Thermal Stability of the THPOH-NH3 Flame Retardant on Cotton

The thermal degradation of the ammonia-cured, neutralized, tetrakis(hydroxymethyl)phosphonium chloride finish (called THPOH-NH3) on cotton was investigated. Thermogravimetric analysis (TGA) in nitrogen showed a two- stage weight loss on heating, a small loss at about 240°C, and a large loss at about 300°C that was associated with cellulose pyrolysis. Electron spectroscopy for chemical analysis indicated that the small weight loss resulted from loss of a trivalent phosphorus-containing moiety. Oxidation by air or hydrogen peroxide eliminated the TGA weight loss in nitrogen at 240°C, apparently by conversion of the trivalent phosphorus structure to a stable pentavalent phosphorus- containing material. Differential scanning calorimetry examination of the THPOH-NH,-treated materials confirmed the TGA findings.

Reaction of Aryl Isocyanates with Cotton Cellulose: Part V: Reaction via Diphenyl N,N′–Arylenedicarbamates

Nine cellulose N,N′-arylenedicarbamates have been formed by thermal reaction of the respective diphenyl arylenedicarbamates with cotton. Cotton print cloth was padded with a dimethylformamide (DMF) or dimethylsulfoxide (DMSO) solution of the diphenyl arylenedicarbamate and the reaction effected by in situ generation of the arylene diisocyanate in the curing step. Add-ons ranging from 3.8 to 12.0% were obtained; under comparable reaction conditions, more rapid reaction occurred with DMSO solvent rather than DMF. High degrees of cross-linking were indicated by high conditioned and high wet wrinkle recoveries. Decreases in breaking strengths, tearing strengths, and flex abrasion resistance were approximately of the same extent as normally encountered in other cross-linking treatments. Resistance to microbiological degradation for more than 89 days was shown by soil burial tests on the treated samples. Ease and extent of introduction and removal of creases by ironing were used to measure breaking and re-forming of carbamate cross links (reversibility). Ring methoxyl group activation of the N-phenyl carbamates appeared to be slightly more effective in achieving reversibility.

The Wrinkle Recovery Properties of Acethydrazide Disulfide-Crossr-Linked Dialdehyde and Dialcohol Cottons

Disulfide-containing cross-links have been introduced into cotton fabric via the dialdehyde derivative. Periodate-oxidized (dialdehyde) cotton. was reacted in an aqueous system under mild conditions with acethydrazide disulfide, H2NNHCOCH2S- SCH2CONHNH2, giving a product of high wrinkle recovery (wet and dry). Sodium borobydride reduced excess dialdehyde groups and ruptured the disulfide cross-links. , Low wet wrinkle recoveries of the reduced samples are cited as evidence for cross link rupture. However, low dry wrinkle recoveries could not be demonstrated for the reduced fabrics due to the facile air-oxidation of the mercapto groups to reform the disulfide cross-links. Although air oxidation appears to occur readily, the moderately high wrinkle recoveries obtained indicate that the number of cross-links reformed falls short of the number originally present. The sulfur contents before and after reduction of the acethydrazide disulfide-treated samples were used to approximate the relative amounts which were reacted monofunctionally (thus parrially lost on reduction) and difunctionally (forming cross links). Syntheses of accthydrazide disulfide are described.

Reaction of Aryl Isocyanates with Cotton Cellulose Part VI : Thermal Dissociation of Cellulose N-Pyridylcarbamates

The thermal dissociations of cellulose N-(2-, 3-, and 4-pyridyl)-carbamates to their respective isocyanates and cellulose were investigated using dynamic and isothermal thermogravimetric analyses. With the aid of a digital computer, kinetic parameters were determined for the dissociation reactions measured by both techniques. First-order kinetics were ob served in every case. Activation energies ranged from 28 to 45 kcal/mole. Entropy of activation values were positive for the 4-isomer and negative for the 2- and 3-isomers. The intermediate postulated for the more thermally labile 4-isomer results from intermolecular catalysis, while those for the 2- and 3-isomers resulted from intramolecular catalvsis.

Thermal Investigation of Diethylaminoethyl-Substituted Cotton Celluloses

The thermal behavior of diethylaminoethyl-substituted cotton celluloses was examined by thermogravimetric analysis, differential thermal analysis, and differential scanning calorimetry. Samples at levels up to 10% substituent content (prepared via an anhydrous sodium cellulosate method) were compared with other samples prepared by the conventional aqueous sodium hydroxide method. All thermal analyses were carried out in purified dry nitrogen or high vacuum at heating rates of 5-40°C/min. Considerable variation was observed when the samples in the base form were compared with those placed in the salt (hydrochloride) form. The effect of basic diethylaminoethyl groups on the cellulosic thermal degradation was shown in altered thermal patterns and ΔH of pyrolysis. In the hydrochloride form, lower Δ H of pyrolysis and decreased decomposition temperature were observed. These observations together with other minor thermal effects which were found to be associated with the decomposition, are compared with recent studies on the effect of inorganic bases on the pyrolysis of cotton cellulose.

Interaction of Flame-Retardant and Untreated Cotton Fabrics during Burning1

Transfer of flame retardancy from fabric treated with THPOH-NH3 to untreated cotton fabric during burning was observed on fabric samples sewed together with glass thread. The transfer effect was evidenced by the development of substantial char and the presence of phosphorus and nitrogen in the char of the untreated fabric. Oxygen-index determinations on multilayered combinations of flame-retarded (FR) and untreated fabrics also supported this observation. The extent of FR transfer varied with the geometrical configuration of the layers and the FR add-on. Tests showed that smoke from combustion of THPOH-NH3-treated fabric, passed through untreated cotton fabric, was the means of transfer of phosphorus, nitrogen, and flame retardancy. The FR transfer effect was also demonstrated for several other phosphorus-containing flame-retardancy treatments.

Flame-Retardancy Transfer from FR Cotton Fabric to Cotton/Polyester Blends

Flame-retardancy transfer from cotton fabrics flame-retarded (FR) with phosphorus-containing compounds to adjacent, untreated cotton/polyester blend fabrics was observed during burning. Reduced flammability was found for blends containing 35% or less polyester; this was indicated by the fact that the char weight for burning FR cotton and untreated blend was higher than that for separate burning; however, when the level of polyester was above 35%, there was essentially no evidence of reduced flammability. Transfer of phosphorus from FR to blend fabric was detected by analysis of chars from blends of high cotton content. Preferential pickup of flame retardant by the cotton portion of the blend is indicated.