Quiescent and strain‐induced crystallization of poly(p‐phenylene terephthalamide) from sulfuric acid solution

Abstract

Quiescent and strain‐induced crystallization of poly(p‐phenylene terephthalamide) (PPTA) from sulfuric acid solution has been studied. Negative spherulites (SA‐PPTA spherulites) are formed from hot concentrated solutions by cooling. The spherulite consists of radiating fibrous lamellae several hundred angstroms wide. The electron diffraction pattern indicates that PPTA molecules are oriented perpendicular to the long axes of the fibrous lamellae and that the [010] or [110] direction of the modification I crystal and [010] direction of the modification II crystal are parallel to the long axes of the fibrous lamellae. The width of the lamellae is much smaller than the chain length of the starting PPTA. It appears that hydrolysis of PPTA during melting crystallization determines the chain length, i.e., the width of the fibrous lamella. Stacked, lamellar structures like “row structures” are formed under shear. The longer axes of the fibrous lamellae are oriented perpendicular to the shear direction. It is confirmed by electron diffraction studies that the PPTA molecules are oriented parallel to the shear direction. Well‐developed fibrils with the PPTA molecules oriented to the fibril axis, are formed by adding the SA‐PPTA spherulites to water with vigorous stirring.

Preparation of solution-grown lozenge-shaped poly(p-phenylene terephthalamide) single crystals and their structural stabilization by heat treatment

“…Liu et al [15] prepared a PPTA single crystal using the confined thin film melt polymerization method, resulting in the formation of lath-shaped modification I crystals with the long axis of the laths corresponding to the b-axis, which is the hydrogen-bonded direction. Takahashi et al [16] prepared negative PPTA spherulites using strain-induced crystallization from a sulfuric acid solution, and the prepared crystals consisted of "fibrous" lamellae of several tens of nanometers. The molecular chain axes were perpendicular to the long axis of each lamella, and the long axis of the "fibrous" lamellae corresponded to the b-axis.…”

Crystalline morphology of a thermotropic aromatic polyester crystallized from nematic melt

“…The crystalline morphology of a main chain lyotropic liquid crystalline polymer prepared from nematic solution has been studied in many cases like poly(1,4-phenyleneterephthalamide) [1][2][3] , polybenzamide 4) etc. Large spherulites could be grown from nematic solution and the crystalline morphology does in principle not differ from that of polymers with flexible chains.…”