Crystallization of nylon 6–clay hybrid by annealing under elevated pressure

Abstract

SYNOPSISNylon 6-clay hybrid ( N C H ) is a molecular composite of nylon 6 and uniformly dispersed silicate layers of montmorillonite. We found that the phase with the high melting temperature (HMT phase) in the NCH annealed under elevated pressure. The melting temperature of the H M T phase was 240°C. Nylon 6 annealed under elevated pressure did not have the H M T phase. Thus, the presence of the H M T phase was characteristic of the NCH. The relative heat of fusion of the H M T phase (heat of fusion of H M T phase/heat of fusion in the pressure annealed NCH ) increased with increase in pressure. High-pressure differential thermal analysis (DTA) measurement revealed that the temperature, a t which the relative heat of fusion showed a maximum value, was below about 20°C of the melting temperature of the original NCH under elevated pressure. It was considered that the nylon 6 crystallite near the melting temperature and the molecular mobility under elevated pressure were necessary to the appearance to the H M T phase. 0 1994 John Wiley & Sons, Inc. I NTRO D UCTlO NNylon 6-clay hybrid ( N C H ) is a molecular composite of nylon 6 in which silicate monolayers of montmorillonite, 1 nm in thickness and 100 nm in width, are uniformly dispersed.'-4 NCH is readily processed in the molten state by injection molding or extrusion molding. It is well known that high pressure above 0.3 GPa strongly enhances the rate at which polyethylene crystallizes in extended forms. Extended-chain crystal (ECC) of polyethylene is grown either by pressure-induced crystallization or by annealing of folded chain crystal near the melting temperature, as was reported by Rees and Bassett.' The melting temperature and the crystallinity of the polyethylene with ECC are higher than those of folded-chain crystals of p~lyethylene.~ In the NCH annealed under elevated pressure, it is expected that the melting temperature and the crystallinity are increased due to the growing of the ECC.In this study, the NCH was crystallized by annealing under elevated pressure above 0.15 GPa. The

Crystallization behavior of nylon 11/montmorillonite nanocomposites under annealing

“…Early investigations of the nylon 6 matrix suggested that the g-crystalline form was enhanced by the addition of the clay. [7][8][9][10] Although the property enhancements of polymer/clay nanocomposites can be explained by the exfoliation and dispersion of montmorillonite (MMT) layers in a matrix, some property changes may be related to the crystalline modification of the polymer matrix. [10][11][12][13] The residual stress formed during the preparation of polymer/clay nanocomposites could affect the microstructure and properties of the composites.…”

High‐Temperature Crystalline Phases in Nylon 6/Clay Nanocomposites

“…[6][7][8][9][10] Vaia et al have suggested that the proximity of the silicate layer surface causes conformational changes which limit the formation of hydrogen-bonded sheets in the nylon 6 matrix. As a consequence, the g phase is favored in the nanocomposites.…”

Investigation on Unusual Crystallization Behavior in Polyamide 6/Montmorillonite Nanocomposites

“…In nanocomposites, the c-crystalline phase was dominant. [15] reported that the presence of MMT induced the c-crystalline form in PA6/MMT injection molded plates. They noted that the degree of crystallinity in the nanocomposite was slightly lower than in PA6, and it was independent of the amount of MMT.…”