Ultra High Modulus Fibers from Solution and Melt Spinning
Titel:
Ultra High Modulus Fibers from Solution and Melt Spinning
Auteur:
Ciferri, A.
Verschenen in:
International journal of polymeric materials
Paginering:
Jaargang 6 (1978) nr. 3-4 pagina's 137-158
Jaar:
1978-07-01
Inhoud:
In recent years several methods for developing high strength-high modulus polymers have been reported. Restricting our consideration to the case of fibers, a general requirement for superior tensile properties appears to be a high degree of extended chains and of molecular orientation along the fiber axis. Various methods which have been used for developing ultra high modulus properties are summarized in Table I . The approach for maximizing chain extension and orientation differs depending whether the polymer molecule exhibits a flexible or a rigid conformation. In the case of flexible molecules, one seeks to reduce preformed chain folds, or avoid their formation, while simultaneously increasing the orientation. For samples crystallized under isotropic conditions this may be done by specialized cold drawing or extrusion processes, as reported by Capaccio and Ward, by Porter and co-workers, by Clark, and by others. The highest modulus thus obtained (E11) is already within a factor three from the theoretical modulus (ET). Alternatively, chain extension and orientation may be induced in a strain polymer solution, with the aid of a parallel velocity gradient, followed by crystallization of the oriented material. The approach has been discussed by Keller and co-workers in the case of polyethylene solutions flowing from opposed jets. Recently, Penning and coworkers have been able to grow continuous fibrilar polyethylene from seeded crystallization in a Couette apparatus. They reported the highest modulus so far attained for a polyethylene specimen. The case of melt spinning of flexible polymers is also based on the maximization of chain extension and orientation in a strained melt, followed by crystallization of the oriented material.
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