SynopsisThe poly(viny1 alcohol)-iodine blue color reaction in dilute aqueous solution haa been investigated, and extinctions a t the absorption maximum have been measured aa a function of the concentrations of polymer, iodine, iodide ions, and boric acid. Depending upon the reaction conditions, the main absorption maximum can be made to appear at any wavelength between 580 and 700 mp, with the longest wavelengths and highest extinctions per vinyl alcohol group showing up at high boric acid concentrations. Poly-(vinyl alcohol) samples from various sources displayed, under identical reaction conditions, great differences in staining intensities. This can be ascribed to differences in the regularity of the polymer chain structures. To account for the behavior of poly(viny1 alcohol) towards iodine under a wide variety of reaction conditions, aa well aa for a number of irrevemible or only slowly reversible phenomena, a model for the mechanism of the PVA-iodine complex formation is proposed involving a dual process of helix formation and intramolecular helix association. There is evidence to indicate that at full iodine saturation of the polymer, 12 vinyl alcohol residues supported by one boric acid molecule form a single turn of a helix which enwraps one iodine atom, out of a 101ig polyiodide chain nested in the interior of a poly(viny1 alcohol) helix.
The swelling behavior of crosslinked gels of polymethacrylic acid, partially or wholly neutralized by mixtures of sodium and barium hydroxide, is described. At high degrees of neutralization and high barium content there is a contractile region of rapid transition from a swollen to an unswollen state. A new type of contractile polyacid fiber made of Krilium and polyvinyl alcohol was developed. The force–elongation curves are given for these fibers at different degrees of neutralization with sodium and barium hydroxide in solutions containing sodium and barium chloride of various ionic strength. The dimensional changes caused by ion exchange can be utilized in a mechanochemical engine. An irreversible work cycle for such an engine is described in which the energy of mixing of mono‐ and divalent ions on polyelectrolyte fibers is partially converted into mechanical work.
The considerations that influence the selection of polymers and spmning conditions for the purpose of preparing a high-strength, low-elongation type of polyvinyl alcohol fiber for use as a reinforcing component in rigid, cold-hardening resins are discussed. A number of polyvinyl alcohol products from commercial sources were spun, and their fibers evaluated. The two products that gave the best over-all results yielded fibers with a tensde strength of 9-10 g/den and a breaking elongation of 4.5-5%. Elongations at break as small as 3.5% were obtamed with two low-molecular-weight samples. ' To attain optimum values of strength and stiffness with any polyvinyl alcohol, a careful build-up of the fiber fine structure is necessary. This was brought about in wet spinning by slowing down fiber coagulation, as well as other processing steps.
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