Epitaxial crystallization of nylon 6 cast from solution on the surface of poly(p‐phenylene terephthalamide) filament

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Abstract
Poly(p‐phenylene terephthalamide) (PPTA) fiber has the characteristics of high modulus and strength, and has been employed as the reinforcement in composite materials. The interfacial interaction between the PPTA filament and nylon 6 matrix has been investigated to make use of these characteristics of PPTA in fiber‐reinforced composite systems. In the case of composites composed of the PPTA filament and nylon 6, two types of expitaxial crystallization have been observed depending on the concentration of a formic acid solution. From concentrated solution, nylon 6 forms a columnar cystal around the PPTA filament. A two‐dimensional spherulite model, (i.e., a disk shape) is proposed for the aggregated structure of nylon 6 chains on the basis of wide‐angles x‐ray diffraction, small‐angle x‐ray scattering studies, and scanning electron microscopic ebservation. The a*‐axis of the nylon 6 crystal is directed radially in its columnar crystal. In the inner portion, close to the interface, the be‐plane is in contact with the surface of the PPTA filament, also, the directions of the b‐ and c‐axes are paral el and perpendicular to the PPTA filament axis, respectively. On the other hand, their axes rotate about the a*‐axis in the outer portion, far from the interface region. Furthermore, a different type of epitaxy was observed in the case of crystallization from a dilute solution of nylon 6 in formic acid. These two types of crystal growth were investigated from the view of crystallization condition and crystallographic lattice matching at the interface region between the PPTA filament a nylon 6. It is concluded that the hydrogen bonding between PPTA and nylon 6 molecules at the interface plays an important role for epitaxial crystallization, in addition to lattice matching.

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