Manipulation of Nylon-6 Crystal Structures with Its α-Cyclodextrin Inclusion Complex

Abstract

We successfully formed an inclusion complex between nylon-6 and α-cyclodextrin and attempted to use the formation and subsequent disassociation of the nylon-6/α-cyclodextrin inclusion complex to manipulate the polymorphic crystal structures, crystallinity, and orientation of nylon-6. Formation of the inclusion complex was verified by Fourier transform infrared (FTIR) spectroscopy, wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), and CP/MAS 13C NMR. After obtaining the inclusion complex of nylon-6 and α-cyclodextrin, the sample was treated in an acid environment to remove the host α-cyclodextrin and coalesce the nylon-6 guest polymer. Examination of as-received and IC coalesced nylon-6 samples showed that the α-form crystalline phase of nylon-6 is the dominant component in the coalesced sample. X-ray diffraction patterns demonstrate that the γ-form is significantly suppressed in the coalesced sample. Along with the change in crystal form, an increase in crystallinity of ∼80% was revealed by DSC, and elevated melting and crystallization temperatures were also observed for the coalesced nylon-6 sample. FTIR spectroscopy revealed a significant degree of orientaion for the nylon-6 chains coalesced from their α-cyclodextrin inclusion complex crystals. Thermogravimetric analysis indicated that nylon-6 has an ∼30 °C higher thermal degradation temperature after modification by threading into and being extracted from its α-cyclodextrin inclusion complex.