Leon Segal

Strength Losses and Structural Changes in Cotton Fabric Crosslinked with Dimethylolethyleneurea 1

Losses in tensile and tearing strengths and other physical properties of cotton fabric given durable-press finishes have been attributed to factors arising mainly from the crosslinking of the cellulose molecule. This conclusion was deduced from the results of textile testing of the treated fabrics. In order to define the sources of these strength losses, a study was made of cotton fabric treated with dimethylolethylene urea and a zinc nitrate catalyst in a commercial manner, but with varying times of cure. Heretofore unobtainable molecular parameters of durahle-press cotton fabric were estab lished from solubilized samples. Correlations made between physical properties of the fabric and the fine-structural features of the fiber, both of which were measured, estahlished the fractions of losses arising from molecular degradation and from crosslink embrittlement as a function of the extent of cure. In the shorter cure times, the predominant strength loss came from crosslink embritttement, but this proportion dropped rapidty and molecular degradation became the major source. Changes in degree of polymerization suggest that the catalyzed crosslinking reaction produces a limited chain extension of the cellulose molecule which becomes evident after removal of the crosslinks.

The Effect of Dyes on the Flammability of Cotton Fabric. 1

A study has been initiated of the effect of dyes on the flammability of cotton fabric. The initial phase reported here concerns the effects of dyes alone on all-cotton fabric, with representative dyes being selected from the reactive, sulfur, vat, ingrain, direct, and acid classes and from the fluorescent brightening agents. The level of Rammability of the dyed fahrics was measured by the oxygen index technique; thermal degradation in a nitrogen atmosphere was followed by thermogravimetric analysis. Many of the dyes increased oxygen index over that of the undyed fabric. Dyes also markedly influenced the path of thermal degradation.

The Effects of a Formaldehyde Pad-Bake-Cure Process on Cellulose Molecular Chain Length and Physical Properties of Cotton Fabrics1

Fabrics treated to several levels of combined formaldehyde by a pad-bake-cure (Form C) process were studied to in vestigate the effects of molecular degradation and crosslink formation on fabric textile properties. Breaking and tearing strengths decreased with increasing severity of treatment. Percentage of strength loss from crosslink embrittlement was initially considerably greater than that from molecular degradation; the former decreased with increasing wrinkle- recovery angle and increasing combined-formaldehyde content while percentage of strength loss from molecular degrada tion increased. A low degree of crosslinking or molecular-chain extension was induced by curing water-wet fabric.

The Horizontal Flame-Propagation Rate of Undyed Cotton Fabrics

Differentiation of the flammabilities of nonflame-retardant, all-cotton fabrics cannot be accomplished by the usual test procedures, as these merely provide the means for determining when a fabric exceeds a certain set standard. The desired differentiation, however, can be obtained by measurement of the flame-propagation rate using the Ahiba Flammability Tester with the sample in the horizontal position. Eight nonflame-retardant, undyed cotton fabrics of different constructions were studied. The weights of the fabrics fell into four groups: 3.1, 3.6–3.8, 4.1–4.4, and 7.5 oz/yd2. Specimens were cut from the warp and filling directions of the fabrics; one set of specimens was oven-dried prior to testing, while another set was conditioned to equilibrium moisture content at 65% relative humidity and 70°F. Burning was different in the warp and filling directions. Differences in flame-propagation rates were found that were not weight dependent. In general, flame-propagation rate was not constant over the length of the specimen; in the warp direction the rates increased with distance from point of ignition, while in the filling direction constant and decreasing rates were also found. Flame-propagation rate was not effected to the extent expected by changing from oven drying to conditioning to equilibrium moisture content; only four of the eight fabrics showed significant changes. Burning in the filling directions of two fabrics was markedly changed; smaller differences were found in the warp direction only of a third fabric and in both the warp and filling directions of a fourth fabric.

Concerning the Restoration by Resin Stripping of the Tensile Properties of Cotton Fabric Finished with Dimethylolethyleneurea

Resin stripping of treated cotton fabric (removal of resin by acid hydrolysis) was investigated by measurements of textile properties, by viscometry, and by gel-permeation chromatography (GPC). Breaking strengths and elongations- at-break, which were reduced by treatment with dimethylolethyleneurea (DMEU), were partially restored by resin stripping. The acid-catalyzed treatment of the fabric with the substituted urea substantially reduced the degree of polymerization (DP) of the cotton cellulose; resin stripping further reduced the DP. The restoration of tensile properties which occurred even though DP had been reduced was due to removal of crosslinks which cause crosslink embrittlement.

The Flammability of Cotton Fabrics Dyed with Indigo Dyes

The fiammability of cotton fabrics dyed with indigo and bromine- and/or chlorine-substiluted indigo dyestuffs was studied by the oxygen index technique and thermogravimetric analysis. The palest shades of dye on the fabric decreased the oxygen index values below that of the untreated control, whereas higher add-on of dye slightly elevated the oxygen index values. Bromine substitution gave the highest oxygen index values, although those for most of the dyeings with halogen-substituted indigoids fell within the range of values for fabrics dyed with pure indigo. However, the presence of bromine in the dyestuff consistently altered the path of thermal degradation of dyed fabrics from that of the untreated control and the indigo-dyed fabric.

A Statistical Study of the Oxygen Index Measurement

hleasurement of the oxygen index (01) of fabrics, the minimum concentration of oxygen in a mixture of oxygen and nitrogen that will just support combustion of the material, is widely used today as an analytical tool in studies of flame retardance of fabrics. The technique was originally developed for use with self-supporting plastic specimens [2-S] and is now an ASTM standard method for plastics El]. Tesoro and bieiser [6] extended use of this test method to textiles. The apparatus commonly employed to date for this measurement incorporates a gas-metering system. There are two systems available; one system uses presSure gages and calibrated orifices to meter the oxygen and nitrogen streams, the second uses calibrated flowmeters to measure the two gas streams. For both instruments the oxygen concentration is obtained indirectly from instrument readings which must be converted to terms relating to concentration. Another type of instrument for measuring 01 incorporates an oxygen analyzer in the system to measure oxygen concentration in the stream of mixed gases. In combination with a digital voltmeter the instrument gives a direct, instantaneous read-out of oxygen concentration. This communication presents some resul ts obtained by means of the oxygen-analyzer apparatus and the flow-rate instrument along with a measure of the precision of the determination. The data in Table I were obtained by one operator using the two different instruments. The mean values of 01 for the untreated sateen are comparable, but standard deviations and coefficients of variation indicate that better precision is realized with the oxygenanalyzer instrument. Low variability could be expected from this fabric because no finishes are present. Eonuniformity in finishing treatments would be exTABLE I. Statistical analysis of data obtained for three cotton fabrics.