The nature of the interaction of trimethylolmelamine resin with cotton substrates, arising from the dry curing (ca. 140° C for 4 min) of the resin on cotton, has been investigated. A new chemical analytical method is described for the elucidation of the chemical structure of the resin-treated cottons. It is expected that this method will constitute the basis of a general method for the chemical structural analysis of resintreated celluloses. Data are presented which show cheruical evidence for covalent bonding of the resin to cellulose and that some of the cellulose hydroxyl groups at each position, i.e., C6, C2, and C3, are involved in resin substitution (C6 > C2 > C3).The presence of interchain cross links is indicated. The results also indicate lower DS than anticipated from the resin content of the treated cottons analyzed.
Results of measurements of the shear modulus and density of a sample of nylon-6 in the temperature range -50° to 250° C are discussed. The modulus-temperature curve obtained indicated several distinct types of viscoelastic behavior. As in the case of poly ethylenes and polypropylenes studied earlier, annealing increased the modulus and density. Vacuum drying the nylon-6 samples was found to increase the shear modulus.
Burning experiments in enclosed spaces have shown that oxygen depletion leading to flame extinction occurs even in a relatively large volume of air, because convection is only partially effective in supplying air to a burning flame and removing products of combustion and pyrolysis. Quantitative evaluation of extinguishability through oxygen depletion determined under realistic burning conditions would, therefore, be a valuable indication of the hazard potential of a material. Accordingly, a method has been developed for establishing a characteristiol minimum-burning condition in terms of oxygen concentration which results in a more stringent criterion for the innate flammability of a material than the conventional oxygen index (O.I.) value. The TRI Flammability Analyzer is used to measure steady-state flame propagation rates at several oxygen concentrations high enough to support steady burning. Extrapolating the resultant linear burning rate oxygen concentration relation to zero burning rate-yields an intrinsie (O.I.) 0 . With the analyzer. it is possible to determine intrinsic indices for the more common and vigorous upward directions of burning, and the upward indices obtained for a group of natural and synthetic fabrics, woven and knitted, are appred iably lower than the indices for the downward direc ion. Indeed, all fabrics studied. except Nomex®. are found to be inherently capable of upward burning in air.
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