Polymer/montmorillonite nanocomposites : polyamide 6 nanocomposites and polyacrylamide nanocomposite hydrogels

• Main Author: Su, Xing
• Other Authors: Chen, Biqiong
• Published: University of Sheffield 2017
• Subjects: 620.1
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.725020

Polymer/clay nanocomposites have attracted great attention of researchers for two decades because they are light in weight, easy to be fabricated, and have some unique properties such as thermal barrier and corrosion resistant. Montmorillonite (MMT) is frequently chosen as the clay filler for polymer/clay nanocomposites because of its abundance, high functionality and high cation exchange capacity. This project aims to prepare novel polymer/MMT nanocomposites with adjustable microstructure, good mechanical properties and unique stimuli-sensitive properties. As the control over the clay intercalation/exfoliation ratio is difficult for the polymer/clay nanocomposites, the effect on clay exfoliation of polyamide 6/MMT nanocomposites by using a chemical blowing agent (CBA), citric acid, during extrusion was studied. X-ray diffraction confirmed that the decomposition of CBA did improve clay exfoliation. As many surfactants used for treating clay surface are likely to degrade during the melt processing of polymer/MMT nanocomposites, a novel thermally stable surfactant was used. Polyamide 6/MMT nanocomposites were prepared by either twice or triple extrusion. And the effect on the mechanical properties and thermal stability were studied. The incorporation of clays increased Young’s modulus but decreased strain at break. There was no significant improvement on the thermal stability by the incorporation of clays and/or CBA. Polymer nanocomposite hydrogels often showed high hysteresis when subject to cyclic tension, and their mechanical properties were hardly tested at the fully swollen state. Therefore a novel polyacrylamide (PAM)/polysaccharide-treated MMT nanocomposite hydrogel with low cyclic tensile hysteresis was successfully prepared by in situ polymerisation. This was shown to be stretchable, tough and highly compression-resistant at the fully swollen state. An interpenetrating nanocomposite hydrogel using PAM, MMT, alginate and Ca2+ was proposed in the same chapter. At the fully swollen state, apart from the good mechanical properties such as stretchability, toughness and resilience, it displayed significantly pH-dependant shape changes. As for the current alginate/MMT nanocomposites in the literature, only the mechanical properties under the dry state were studied. The mechanical properties of the fully swollen alginate/MMT/Ca2+ nanocomposite were investigated. The nanocomposite films turned out to be stiff, strong and transparent. Also some of the nanocomposite films were ultraviolet light-proof or sensitive to acetone. Based on the above findings, it is concluded that: firstly, there was a large amount of residual citric acid in the extruded materials, which reduced the mechanical properties and thermal stability of polyamide 6/MMT nanocomposites. Secondly, the thermally stable polymeric surfactant has the potential of enhancing the toughness and thermal stability of polyamide 6/MMT nanocomposites. Thirdly, it was likely to achieve low cyclic-tensile hysteresis, high strength, high toughness and stimuli-responsivity by the polymer/clay nanocomposite hydrogels at the fully swollen state. Those nanocomposite hydrogels can be used in a variety of applications including artificial tissues, medicine, agriculture, skin care and other aquatic uses.