J.L. Williams

Never-Dried Cotton Fibers Part I : Morphology and Transport Properties

New data are presented illustrating the high intrinsic mobility within never-dried cotton fibers. This is shown both from a morphological point of view where a unique form of necking is found on fracture, and from a molecular point of view where the transport properties (sorption and diffusion) are found to be irrecoverable once the first drying has occurred. Contrary to generally accepted ideas, never-dried fibers are found to be highly crystalline and on either drying or stretching interfibrillar hydrogen bonding takes place irreversibly.

Graft copolymers as elastomeric fibers. II. Mechanical properties and morphology of grafted copolymers

Abstract Rayon-g-(ethylacrylate) graft copolymers, prepared via pre-irradiation grafting and also via selected chemically initiated techniques, have been characterized with respect to their mechanical properties. Electron microscopy and X-ray diffraction were used to determine the morphological and structural modifications which must be attained in order to achieve elastomeric behavior in the grafted rayon. The onset of high “rubber-like” elasticity at around 1000 per cent graft is accompanied by a large drop in tenacity. This strength loss may be reduced without any loss in elongation by adding small quantities of bifunctional monomers to the grafting solution. Elastomeric properties were attained even at graft levels below 100 per cent by subjecting the grafted fibers to a treatment capable of decrystallizing the cellulose. In order to achieve elastomeric properties, these studies indicate that grafting must occur evenly throughout the fiber cross-section, expanding the fiber and maintaining its crystalline regions in a disrupted state.

HIGH-YIELD PRE-IRRADIATION GRAFTING TO WOOL LEADING TO HIGHLY ELASTIC FIBERS.

Comparative studies of mutual and pre-irradiation grafting of vinyl monomers to wool [1] have shown that the yields per unit dose are generally lower when the pre-irradiation technique is employed. This is especially true when a common solvent for the swelling agent and monomer is included in the grafting medium. Such pre-irradiation grafting curves generally show a steady decrease in the grafting rate with time until the plateau level of grafting is reached. Considerable detail of this contrast in grafting behavior has been given in recent papers [2, 3, 4] and shows that the maximum level of pre-irradiation grafting is usually well below 100%. However, it has now been found that under special conditions substantially higher grafting yields can be obtained using a pre-irradiation technique of grafting. In fact, grafts of several hundred percent are easily obtained in the case of certain acrylic acid derivatives. A typical grafting-time curve for wool fibers and fabrics using ethyl acrylate is shown in Figure 1. It is apparent that the grafting-time curves are considerably different from those normally encountered in pre-irradiation grafting [1]. Instead of grafting yields leveling off to a plateau value, the yields continue to increase within the time scale of the experiment, reaching eventually levels beyond 5000%. In .this case, the monomer had been dispersed in the swelling agent (water) by using a non-ionic surfactant. Similar grafting behavior was also exhibited in the absence of an emulsifier. ’

Graft copolymers as elastomeric fibers. I. Synthesis of the graft copolymers

Abstract Pre-irradiation grafting, mainly with an ethyl acrylate emulsion system, has been used to produce wool and cellulosic fibers having elastomeric properties. Comparative studies using selected chemically-initiated systems were also carried out. The pre-irradiation grafting-time curves were found to be auto-accelerative and grafting levels in excess of 3000 per cent could be achieved. Circa 1000 per cent graft was required to obtain fibers with high “rubber-like” elasticity. Grafting rates were found to increase substantially with temperature reducing the grafting times necessary to achieve high elasticity to the order of minutes at 35°C compared to 20 hr at ambient temperatures. Reduction of the level of grafting required to obtain elastomeric properties is clearly of interest, and it was found that when rayon fibers containing low levels of graft (below 100 per cent) were subjected to post-treatments with reagents capable of decrystallizing cellulose, the fibers, which heretofore exhibited no significant elastomeric properties, became highly elastic.

Never-Dried Cotton Fibers Part II : Fixation of the Never-Dried State

The intrinsically high internal mobility found in cotton fibers in their botanical growth state can be preserved by preventing the irreversible hydrogen bonding that normally occurs during first drying. Water transport, morphological, and mechanical data are presented to illustrate two examples of the permanent fixation of never-dried cotton, which has been shown in an earlier publication to be highly crystalline. In one, an acidic solution of formaldehyde is suggested to cause intrafibrillar cross-linking; in another mutual irradiation with acrylamide is known to cause grafting to the cellulose molecule. Both treatments effectively block the hydrogen bonding reaction by attachment of foreign groups to the cellulose fibrils.

Never-Dried Cotton Fibers Part VII: Preservation of the Never-Dried State with Ethyl Acrylate and Alkylene Oxides

The preservation of the mechanical and transport properties of never-dried cotton has been accomplished by the treatment of never-dried fibers with ethylene oxide or propylene oxide under mildly alkaline conditions. Fibers subjected to this process display high extensibility, accessibility, and strength comparable or superior to the corresponding properties of never-dried cotton at standard conditions of temperature and humidity. Gamma-initiated radiation grafting of ethylacrylate to never-dried and once-dried cotton indicated that never-dried fibers grafted at higher rates than ordinary cotton.

Never-Dried Cotton Fibers Part V: Density Determination of Never-Dried Cotton

The density (ρc ) of never-dried cotton has been measured in its wet state. It is found to be 1.536 ± 0.006 g cm−3. This quantity is essential when it is necessary to determine add-ons in grafting experiments, and the present method avoids the need of having to know the initial weight of never-dried cotton in such experiments.

Never-Dried Cotton Fibers Part IV: Shrinkage on Mercerization

Longitudinal shrinkage of never-dried cotton fibers is ultimately about twice as high as that in normal once-dried fibers at full mercerization with sodium hydroxide. This is considered to be due to the high accessibility and mobility of the cellulose fibrils in never-dried cotton.

Never-Dried Cotton Fibers: Part VI: Luster

It has been long known that freshly opened bolls of cotton are highly lustrous. This is shown to be due to inherent optical and morphological properties of the individual cotton fibers (“single fiber” luster) and also to the overall packing of the fibers against the inner surface of the boll (“bulk” luster).