R. Turner

The Transfer of Flame-Retardant Effects

Burning-rate measurements on double layers of the same fabric having one layer treated with flame retardant reveal that effects of the retardant can be transferred to the untreated layer. A system consisting of a layer of cotton sheeting treated with a phosphate flame retardant placed underneath a layer of untreated material burns at about the same rate as two identically treated layers with the same net average add-on. When this average is low, the combination bums more rapidly than two untreated layers, in accordance with evidence that inorganic phosphate retardants can increase the flame-propagation rate of cotton at low add-on levels. For the double layers of synthetic fabrics studied thus far, it was found that treating only one of the layers results in almost as good and sometimes better reduction of burning rate as treating both layers to the same net add-on. Such transfer effects need to be recognized and understood by those using flame retardants in practical heterogeneous textile systems.

The Concept and Measurement of Extinguishability as a Flammability Criterion

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 apprediably lower than the indices for the downward direcion. Indeed, all fabrics studied. except Nomex®. are found to be inherently capable of upward burning in air.

Design and use of a cyclic tensile abrader for filaments and yarns ― A study of polyester monofilament wear

An apparatus has been developed that imposes an adjustable constant axial tensile load on filaments, yarns, or fabric strips during cyclic rubbing over pins in various configurations and under controlled temperatures and specific chemical environments. The action is intended to simulate the combinations of tensile, bending, and abrasive stresses experienced by fibrous materials during processing and end use. The number of cycles to rupture (or specimen lifetime) is automatically recorded, and there is provision for monitoring the elongation of the specimen under stress. The use of the cyclic tensile abrader is demonstrated by means of a study of the influence of tensile loading, temperature, and rubbing configuration on the wear of a polyester monofilament sample in air. The reproducibility of both lifetimes and elongations is good, and the results are in accord with expectations for the behavior of this material under the stresses and conditions imposed. It appears that the basic design of the cyclic tensile abrader makes it suitable as a research tool as well as an accelerated wear testing device.

Temperature Dependence of Modulus, Density, and Crystallinity of Linear Polyethylenes

Experiments undertaken to determine the dependence of the shear modulus upon the density and degree of crystallinity of three samples of linear polyethylene over a range of temperatures are described. In most instances, the data show good agreement between crystallinity values calculated from density and from x-ray diffraction measurements. Annealing the polyethylene samples was found to increase both the shear modulus and density. Shear modulus and density appeared to be inversely related to molecular weight for the three polyethylene samples investigated.

Fabric Ignition by Flame Impingement

An apparatus has been constructed and data evaluation techniques developed for quantifying the ease of ignition of fabrics exposed to a small flame. The method takes careful account of fabric moisture content, which can have a substantial influence on this form of ignitability. A proposed specific ignition resistance coefficient, obtained from yes-no trials at preset exposure times, is inde pendent of fabric weight and ambient humidity, so that ignitability can be compared on a common basis.

Chemical Structure of Resin-Treated Cellulose1 Part I: Trimethylolmelamine-Treated Cotton

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 in vestigated. 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 resin- treated 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.

Temperature Dependence of Shear Modulus and Density of Nylon-6

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.

Chemical Structure of Resin-Treated Cellulose: Part II: Trimethylolmelamine Bonding with Cotton

The chemical covalent bonding of trimethylolmelamine (TMM) with cotton cellu lose produced under wet and dry curing conditions has been further investigated. The extent of chemical reaction with cellulose and the location of substituents on the anhydroglucose units were determined by an analytical scheme embodying chemical modification, complete hydrolysis, and gas chromatography of the analysis products. High temperature (160°C) curing gave rise to much greater extents of reaction with cellulose than curing under wet conditions. In the case of TMM, reaction at the primary. hydroxyl (C6) predominated at DS 0.16, whereas the major reaction of a methylated TMM having DS 0.30 occurred at C2.

Temperature Dependence of Shear Modulus, Density, and Crystallinity of Isotactic Poly Polypropylene

Experiments were undertaken to determine the dependence of the shear modulus upon the density and degree of crystallinity of two samples of isotactic polypropylene over a range of temperatures. Annealing the polypropylene samples was found to increase both the shear modulus and the density. Both quantities appeared to be inversely related to the molecular weight of the two polypropylene samples investigated. These phenomena are similar to those observed for polyethylene in our earlier studies. On the other hand, the variation of crystallinity with temperature, as measured by changes in density and by x-ray diffraction, was not the same in polypropylene as in linear polyethylene.

EFFECTS OF ANNEALING UPON SHEAR MODULUS AND DENSITY OF LINEAR POLYETHYLENE

().(1~7 for regenerated cellulose filer,. Keecly. Fowers, and Stein have calculated two values of theoretical birefringence for polypropylene based on lOO~1c crystallinity. The values are O.Ufi7 and 0.0l.;. dep<&dquo;IHlin1{ upon the choice of hond polarizahility values. In this case. the coiled structure of the polymer chain complicates the picture. AdditiofBal experintental data are shown in Figure 2. These data are taken f rom Fujino 151 and are based