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Experiments designed to complement microscopical studies and to attempt a practical evaluation of the effectiveness of various agents which impart resistance to dry soil are reported. Various methods of applying soil to fabric were evaluated, as was the ef fectiveness of a number of soil retardants. Soils included carbon blacks of a range of particle sizes, a natural clay, and a synthetic soil whose formula approximated the com position of natural soil, containing fatty materials. Fabrics were also soiled by foot traffic on the floor. Results were interpreted from reflectance data and from radioactive tracer assays of weight of soil takeup. In attempting to elucidate the mechanism of dry soiling. the effects of textile construction, electrical charge on the fiber, particle size of soil as related to topography of fiber surface, surface hardness, reducing surface rough ness. and lowering surface energy were considered. It was shown that soil takeup is directly related to specific surface. It was found that grey cotton is slightly more re sistant to soil than bleached cotton, and that increased smoothness of fiber. even to com plete obliteration of native rugosities, did not necessarily impart soil resistance to cotton fabrics. The most successful types of antisoiling agents for dry soils appear to be col loidal particulate applications such as silica or alumina, and additive finishes which lower surface energy of the tiber. Only a few of the typical commercially available soil re tardants were used in these studies. The project was a short term one and the experi ments were designed for the study of the mechanism of soiling of cotton textiles which would be subject to in-place cleauing. Many new soil retardants were marketed after the experiments had been initiated.

Electron microscopical studies of changes in cotton fiber microstructure, after ex posure of the fibers to the cellulase in filtrates prepared from cultures of Myrothecium verrucaria, showed evidence of the transverse, jagged cuts into the cellulose structure previously seen by cytical microscopy. The degradation appeared localized in areas along the length of the fiber which were not related to any recognized component of fiber structure. Micrographs of fragmented, degraded fibers showed etching of the macro- fibrils of the sheets of secondary wall and a sharpening of the image of the individual microfibrils. Continued enzyme attack produced smaller fragments and hydrocellulose- like particles. Measurements of changes in tensile strength, swelling in alkali, and in glucose yield were correlated with changes in microstructure. The extent of fiber degradation by cellulolytic culture filtrates was limited and could be continued only if fibers were swollen between filtrate exposures. No evidence of damage to the cellulose structure was seen which could not be explained hy hydrolysis at the β-1,4-glucosidic linkage.

Changes in the internal morphology of chemically modified lint cotton fibers were investigated by measurement of nitrogen adsorption at liquid nitrogen temperature. Surface areas and pore size distributions were calculated from the adsorption isotherms and compared with findings from measurements of changes in crystallinity and of fibrillar aggregation as shown by electron micrographs. Fibers were either preswollen in water or taken from the rinse water and solvent exchanged through methanol and n-pentane to helium before adsorption measurements were made. Unless reacted in the presence of water, the wrinkle resistance treatments studied caused losses in surface area of 55% or greater. Changes in surface area and porosity of cottons reacted with monofunctional reagents designed to give protective and other types of finishes were dependent on the type of reaction used.

Changes in the internal morphology of lint cotton fibers during purification and swelling treatments were investigated by measurement of nitrogen adsorption at liquid nitrogen temperature. Surface areas and pore size distributions were calculated from the adsorption isotherms and compared with findings from measurements of changes in crystallinity and in fibrillar aggregation as shown by electron micrographs. The adsorption measurements were made on fibers which were either preswollen in water or taken from the rinse water after treatment and solvent exchanged through methanol and n-pentane to helium. The large changes found in surface area, pore size distribution, and fibrillar aggregation were accompanied by changes in crystal structure in fibers treated with 5.0M sodium hydroxide. Large changes following treatment with phosphoric acid occurred in pore structure and fibrillar aggregation without concomitant change in crystallinity.

Changes in the structure of cotton fibers after expesure to gamma, high-energy electron, and thermal neutron radiations, in various ambient atmospheres, were evaluated by the techniques of optical and electron microscopy. Radiation exposures evaluated were: gamma rays, 105 to 4 × 108 r.; 2-Mev electrons, 5 × 104 to 108 rep; integrated thermal neutron fluxes, 5 × 1014 to 1017 nvt. Changes in the physical and chemical properties of similarly irradiated fibers have been, or are to be, reported in other pub lications. All irradiated, unmodified cottons could be differentiated from unexposed cottons by optical microscopical observations of samples stained in Nile Blue Sulfate. Gamma ray and electron exposed samples differed from unexposed fibers. in swelling behavior in 0.2 M ( in Cu) cupriethylenediamine hydroxide, but thermal-neutron-irradiated cotton differed from the control only after exposure to an integrated flux of 1017 nvt. Electron micrographs of the fibrillation patterns exhibited by fibers exposed to gamma and electron radiation doses of 5 X 106 to 108 r. or rep on beating in water in a Waring Blender showed the formation of increasingly smaller fragments of samples. Some shortening of fibrils and an increase in number of broken ends of microfibrils were seen in neutron-irradiated cotton exposed to 10" nvt; at lower integrated neutron fluxes, fibrillation was unchanged. No distinct differences were found in microscopical tests between gamma and electron irradiated fibers or between gamma-exposed fibers irradiated in oxygen and nitrogen. At doses of 4 × 10" r. of gamma rays, the trend toward smaller fragments reversed and short chunks of material were observed. Varying amounts of degradation were observed in modified cottons after irradiation. Smaller fragments were observed in cottons modified to change and reduce the total crystalline cellulose; the fibrillation of acrylonitrile-treated cotton appeared unchanged, but irradiation produced a decrease in the size of fragments of dichloropropanol- and dimethylol cyclic ethyleneurea-modified samples.

The location of soiling agents such as colloidal and activated carbon, floor soil. a syn thetic soil, and a clay on gray and modified plain weave cotton fabrics soiled under con trolled conditions was determined by light and electron microscopical examination. Cross and fine geometry of fabric and fiber play a major role in determining the dis tribution of soil in most cases. The mechanical entrapment of soil particles and ag glomerates between fibers near the surface of the fabric is repeated in the accumulation of soil in the natural or induced irregularities of the native and modified fiber surface. The presence of soft films on the fiber surface extends the quantity of soil and its dis tribution. Sorption of the soil particles on apparently smooth areas of the fiber also occurs to a significant extent.

Four modified cottons—mercerized sliver, a partially acetylated fabric, and two cross- linked fabries—were exposed to hydrochloric and sulfuric acids, sodium periodate, nitro gen tetroxide, hydrogen peroxide, ozone, and heat for intervals selected to illustrate early and late stages of fiber degradation. Electron micrographs were made in order to observe changes in tihrillate structure. Parallel changes in moisture regain, crystallinity indices. copper number, carboxyl content, and, in some samples, degree of polymerization were measured. Changes in fibrillate structure and other properties were found to be related to the type of modification and the resistance of substituent groups to the degrad ing agents, the activity of these, agents, and to duration of exposure. In general, where substituents were not removed, degradation decreased with increase in content of sub stituent groups in the chemically modified cottons. Mercerization. without further modi fication, caused an increase in rate of degradation.

The relative swelling of cotton in 67 organic liquids and aqueous solutions of 14 inorganic compounds was evaluated by observing the number of revolutions of a singles yarn of Iquitos variety during untwisting in a 3-min post-immersion interval. Aqueous dilutions of the lower alcohols, two organic acids, acetone, and ethanolamine were also tested. The yarn was used in the unpurified state, after scouring and after scouring and mercerization. The relative swelling of cotton in 17 of the liquids determined by this untwisting technique was in qualitative agreement with values found by microscopi cal measurements of changes in width of fibers taken from the scoured and mercerized yarn. Qualitative agreement with values reported in the literature for measurement of swelling by other techniques was also established. The effects of some experimental variables wrere investigated.

An apparatus is described for measurement of vertical dimension of cotton samples immersed in water, methanol, tiquid ammonia, and NaOH solution. Increase in thickness of cotton showed recovery from compression and swelling. The increases were automatically recorded as a function of time by a chart recorder.