This paper presents results of spectral and microscohical studies designed to relate observed differences in fabric properties to changes detected in fine structures of cottons chemically moditied with d , l -isomers of butadienediepoxide (BDO) under conditions of base catalysis. Cottons pretreated with aqueous NaOH (2% to 23%) can be etherified with BDO in CCl 4 while the fibers are in a wet and swollen condition at room temperature. w ith the resultant production of fabries possessing both high dry-and high wetcrease resistance. All concentrations of base pretreatments caused increased wet crease recoveries at low ad-ons of BDO. High dry crease recoveries were obtained at low add-ons only on fabries pretreated with dilute NaOH. For 10% to 15% NaOH pretreatments. higher add-ons of BDO were needed to impart high dry as well as high wet recovery. X-ray diffraction tracings indicate structural differences related to caustic pretreatments, and infrared spectral changes, coupled with x-ray data, suggest changes in cellulosic reaction sites with changes in reaction conditions. Microscopical examinations indicate formation of BDO cross links after all pretreatment conditions, but reflect differences in swelling behavior as a result of base pretreatment.
SynopsisElectron microscopical observations of radiation-induced rayon-styrene graft copolymers were published by Kaeppner and Huang in 1965. The present paper reports electron microscopical investigations on the relationship of the structure of vinyl-cotton graft polymers to the original morphology of the cotton fiber and into the distnbntion of the grafted vinyl polymer in the cotton fiber structure. The grafted vinyl monomers investigated in this study were acrylonitrile, styrene, methyl methacrylate, and vinyl acetate. Two radiation-induced procedures were used: simultaneous irradiation grafting and post-irradiation grafting. Ceric ion grafting of acrylonitrile to cotton was included for purposes of comparison. Distribution of the vinyl polymer within the cotton fiber is illustrated by a series of electron micrographs, selected as typical of the particular grafted species under considerat.ion. Results indicate that the ditrasion rate of monomer into the cellulose fiber plays an important role in the final distribut.ion of polyacrylonitrile grafts within the fiber. Uniform distribution of polyacrylonitrile in the fiber was achieved by simultaneous irradiation grafting of acrylonitrile on a highly substituted cyanoethylat,ed cotton. In samples of low degree of cyanoethylation the distribution of graft polymer was non-uniform. I n grafting initiated by ceric ion the acrylonitrile graft polymer was evenly distributed. Polystyrene-cotton copolymers from grafts, made by simultaneous iiradiation of cotton in methanol solutions of the st,yrene monomer, were uniform throughout the fiber but showed opening of structure associated with the amount of graft formed. Grafting of methyl methacrylate occurred only in the peripheral regions of t.he fiber; by contrast, grafting of vinyl acet,ate was uniform throughout the fiber wall. Important factors governing the successful irradiation grafting in cott,on fibers are choice of solvent., ratio of monomer to cellulose, nature of prior chemical modifirat,ion of t,he celldose, and t,ot,al irradiat>ion dosage.
The effects on cotton of esterification to low degrees of substitution have been investigated by light and electron microscopy. Observations were made on partially esterified celluloses which included esters of acetic, palmitic, stearic, 12-hydroxystearic, linoleic, and ricinoleic acids and of the aromatic benzoic, cinnamic, naphthoic, and pkenylundecanoic acids.The uniformity of the esterification of cellulose was followed by dyeing and swelling techniques. Refractive index measurements were used to follow changes in optical anisotropy which accompanied the chemical modification. The average refractive indices of cellulose esters containing aromatic groups were greater than those of the esters with aliphatic substituents, the greatest difference being between indices measured perpendicular to the fiber axis.The normal fibrillate texture of the scoured surface appeared to become smooth upon esterification.Fragmentation of the esters in water in a laboratory blendor produced long strands of fibrillate material intermingled with clumps of spongy or amorphous material. On de-esterification of the fragments with an alcoholic base, the structure of the material reverted to that of unesterified cotton—fibrils became distinct and, in some cases, saponification proceeded to a stage where hydrocellulose-like particles were formed. , Many of the esterified fibers of low degrees of substitution swelled in the conventional methacrylate embedding technique. The swelling caused the cell wall to separate into layers, and the internal structure could then be studied by examination of thin sections of these fibers with the electron microscope. By use of an alternative embedding medium, aqueous polyvinyl alcohol, in the preparation of thin sections, compact unlayered structures of the esterified cottons were obtained. This permitted observations of the undisturbed structure of the modified cottons. Both types of observations were used in the microscopical evaluation of cotton fibers esterified to low degree of substitution to demonstrate structural changes brought about by the esterification reaction.
SynopsisWhen effect of the substrate is nullified, resiliency can be defined as a function of strain, time, and humidity. Determination of improvement in the immediate, or rapid, tensile recovery readily delineates differences due to chemical modifications. Delayed recovery is usually less improved than immediate. Crosslinking cotton with dimethylolethyleneurea (DMEU) increases tensile strain recovery as the number of crosslinks increase, reduces dependency of recovery upon external strain, and produces maximum recovery at about 65% R.H. Noncrosslinking treatments produce limited increases in tensile strain recovery. Measurements on yarns crosslinked with DMEU and then hydrolyzed indicate that incalculably few residual links may contribute to tensile recovery. A'-Methylol-S'-methylethyleneurea treated cotton displays physical blocking and water swelling which aid recovery. Oleoyl chloride esterified cellulose has tensile recovery probably due to molecular entanglement?. Its delayed or viscoelastic recovery is the most improved with immediate recovery being the least improved. The higher the moisture regain, the greater tensile modulus reduction under wet conditions. Crosslinking with DMEU under dry conditions lessens this reduction in modulus. Improvements in the tensile recovery of strain and energv, for all samples and with varied conditions of humidity and strain, correspond linearly with unit slope.
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