Growth-Packed PPT-A Fiber for the Replacement of Native Asbestos

Abstract

AbstractA now type of crystal that can be defined as a “gel crystal” was first made with oligomeric poly-p-phenyleneterephthalainide (PPT-A), associating a large amount of dimethylacetamide (DMAc) liquid molecules, in which catalytic amount of heterocyclic tertiary amine, coupled with alkali metal cations or phosphoric triamidos are incorporated. Under mechanical orientation of the growing PPT-A, before gelation of the reaction “mixture, a hark agar-like gel crystal is formed. It shows a strong optical birefrin,- gence with four clear extinction positions under crossed polarizers when the gel was sectioned either along the direction of PPT-A orientation or perpendicular to it. When the gel formed without orientation it exhibitil speckled birefringence due to a large number of tiny spherulitic crystallites. The degree of crystalline order was similar to that of lyotropic, nematic liquid crystals when evaluated from X-ray diffractograins. The same type of gel crystals with extinction positions were observed in animal and vegetable tissues. It is assumed that the gel crystal has a threedimensionally ordered molecular network structure in which oligo-PPT-A's are arranged end-to-end in parallel lines. The lines are connected laterally, to form sheets, by DMAc bridges that are linear associations of DMAc molecules, which are connected to the oligo-PPT–A at the CONH groups. PPT-A molecular growth and self-ordering occurs within this gel crystal. A similar process gives rise to wool, cotton and ol.her fibrous biological materials.The high molecular weight PPT-A fiber thus grown in the gel crystal is constructed with numerous unit fibrils which connect themselves in a three-dimensional network, that resembles native flax or ranie fibers. The molecular growth of PPT-A in the gel crystal reaches ultra high molecular weight that can rarely be attained in ordinary solvent polyinerization. The gel state of PPT-A fibrils are initially formed spontaneously by selfsubdivision of the gel crystal after the molecular growth of PPT-A. Solid fibrils and fibers are finally fortoed by removing DMAc. The PPT-A gel fibrils thus formed resemble closely “the nascent fibril” of cellulose, and the microstructure and morphology of PPT-A fibrils are consequently very similar to those of native cellulose. The thickness of PPT-A fibrils can readily be controlled by the temperature in the gel crystal before fibril formation. The direction of the fibrils depends on the initial orientation of oligo-PPT-A's immediately before the formation of the gel crystal.This growth-packed PPT-A fibril, that can be produced by a one step chemical reaction, is considered as a good candidate for the replacemerit of native asbestos, because of the lower production cost, microfibrillation property, and inherently high heat-resistance.