Charles H. Meiser

Some Effects of Chemical Composition on the Flammability Behavior of Textiles

The oxygen index method is shown to be a valuable tool for the investigation of the flammability of textile samples as a function of their chemical composition. Measurements of limiting oxygen index (LOI) are reported for polyester/cotton blends of varying composition, and for 50/50 polyester/cotton blends in which one component fiber has been selectively treated with flame-retardant additives. LOI values are also reported for cotton fabric treated with nitrogen-containing resins at various levels of nitrogen content, in conjunction with a flame-retardant additive.

The Flammability of Polyester-Cotton Mixtures

Polyester-cotton blended fabrics have the reputation of being “difficult to flame retard.” Treatments developed for flame retarding 100% polyester or 100% cotton fabrics do not seem to have the same effect when the two fibers are combined. Quantitative data are presented which pinpoint how the flammability behavior of polyester-cotton blends differs from that of the components. Physical and chemical aspects of pre-ignition and post-ignition phenomena are discussed for mixtures in which one or both of the polymers has been flame retarded, as well as for untreated combinations.

Heat Emission from Burning Fabrics; Potential Harm Ranking

A technique for continuous monitoring of the heat released when a freely-suspended fabrie burns under natural con vection is described. The primary responses obtained from this measurement include (1) the maximum rate of heat emission, (2) the time to reach the maximum rate, and (3) the postmaximum time required for the heat-emission rate to subside to one-half its maximum value. Two different ways of combining these three responses are presented, leading to two single-valued expressions which describe relative potential harm, the functions [H]1 and [H]2. These functions haue been evaluated using data obtained for two large collections of fabries, one comprising a wide variety of fiber and fabrie types, and the other, cotton fabrie samples treated with flame retardants. Both the [H]1 and [H]2 functions show a strong direct correlation with Mushroom Apparel Flammability Test heat-transfer values obtained for the same mate rials. For the flame-retardant cotton fabries the two potential harm functions show a systematic response to flame- retardant add-on level.

The Effects of Moisture on the Flammability Characteristics of Textile Materials

The TRI Flammability Analyzer has been used to determine the effects of moisture on the flammability characteristics of textile materials. Both moisture in the fabric and in the test environment have been considered for a number of un treated and flame-retardant-treated fabrics. The results are reported and interpreted in terms of several measurable quantities: mass transformation rate (MTR), oxygen sensitivity (ΔMTR/Δ% O2), and extrapolated oxygen index (O. I.)0. Variations in fabric moisture content appear to have a greater effect on the behavior of relatively hydrophobic fibers (such as polyester), as compared to cotton or nylon.

The Use of Textile Yarns in Separation Processes

A new method has been developed for preparing chromatography columns quickly, uniformly, and with high reproduci bility, using textile yarns as the solid adsorbent. Gas-chromatography experiments using columns packed in this way have revealed that rayon yarns have a high affinity for water vapor but allow other species, even those quite similar to water in size and chemistry, to pass through essentially unretarded. The degree of water retardation by rayon yam- filled columns has been found to depend on a number of controllable factors: charge volume and frequency of injection, column pressure and temperature, and yarn packing density. To demonstrate the usefulness of the rayon-water specificity for removing water from mixtures, two novel devices have been built that are capable of producing dry ethanol from aqueous mixtures on a laboratory scale at modest energy cost. One of these designs, taking advantage of the high tensile strength of yarn, makes use of a moving yarn loop to achieve almost continuous separation and a high yield of ethanol. Even if such processes do not turn out to be economically practicable for large-scale ethanol production, the concept of gas or liquid chromatography using bundles of yarns with suitable chemical properties should find application in many practical separation problems.

Influence of Preadsorbed Water on Chromatographic Detention of Organic Volatiles by Cellulosic Substrates

A modified gas chromatographic system was used to measure the effects of pread sorbed water on the adsorption and desorption of various organic volatiles by cellulosic substrates. To minimize diffusion effects, short columns and fast carrier gas flow rates were used. The data yielded sticking coefficients, residence times, equilibrium constants (adsorption isotherms), and surface concentrations for a group of adsorbates including a homologous series of alcohols. In general, sticking coefficients increased, and residence time, equilibrium constants, and surface concentrations decreased as the concentration of water vapor increased. Sticking coefficients correlated with the total solubility pa rameters of the adsorbates.

The Quantification of Fabric Extinguishability

A method has been developed for quantifying the extinguishability of burning fabrics which sepa rates extinguishability due to thermal loss from that due to blocking the transport of vaporized fuel and/or oxygen to the combustion zone. The maximum rate of heat emission during upward burning is measured using convective calorimetry for freely-hanging samples having asbestos paper stapled to one side in several arrangements. The mass of the heat sink is varied by using different numbers of asbestos layers; the vapor transport barrier is varied by drilling different numbers of holes in the asbestos. It is found that vapor blockage generally affects extinguishment to a much greater extent than heat loss. In addition, the effectiveness of the barrier is different for different fabrics, so that extinguishability ranking in terms of heat-emission rate depends on whether or not the fabrics are burned in contact with an inert substrate.

The Use of Moving Yarn Belts for Continuous Dehumidification

A novel low-energy alternative to conventional dehumidification systems has been devised. A moving loop of cellulosic yarns adsorbs water vapor from an air space, transports it outside where it is desorbed by solar or other heating, and returns to the interior to repeat the process, so that moisture is removed and disposed of continuously. The method is based on the potential of cellulosic yarns for rapid interaction with water vapor, the strong inverse dependence of water uptake on temperature and the tensile strength and flexibility of yarns. A laboratory-scale unit, found capable of reducing humidity to a satisfactory level in a reasonable time, has supplied data for potential scaling-up using practical equipment dimensions, air flow rate, yarn velocity, etc. Experience with the demonstration unit indicates that the yarn is far from saturated under the dynamic conditions of operation, and that the transient water is taken up on the most accessible yarn surfaces and does not diHuse to any great extent into the interior.

The Auto-Ignition of Multicomponent Fiber Systems

Using a simple experimental procedure for determining the time until ignition after a material is plunged into a heated air environment, it is possible to obtain kinetic data for this auto-ignition process. Results on homogeneous polymeric materials show that, while the rate controlling factors in every case are physical rather than chemical, ignition times at any single temperature depend on the basic thermal degradation process of each polymer. The study also includes work on multicomponent systems, including a mixed fiber blend as well as polymers treated with non-polymeric additives. For each combination studied it is possible to detect whether the presence of a second component has had only a physical influence on ignition, or whether thermal degradation has been affected by chemical interaction. Such data can serve to distinguish modifiers of flammability that act on the ignition process from those that are literally flame retardants or accelerators.