Development of a novel organoclay for poly(lactic acid) nanocomposites

This thesis describes a programme of work whose aim was to develop and characterise a novel organoclay derived from montmorillonite clay and the amphoteric surfactant cocamidopropylbetaine (CAB), a plant oil derivative, and to test its compatibility with poly(lactic acid) (PLA). Clay minerals such as montmorillonite increase the mechanical and physical properties of polymers when well dispersed within the polymer matrix, a condition that is more easily achieved when the clay layers are coated with a surfactant such as a quaternary alkyl ammonium compound (QAC). In the first part of the thesis the structure, purity and thermal behaviour of the CAB were characterised and the solubility parameter of the molecule was calculated and compared with that of a surfactant used in a commercial organoclay. The effects of concentration and pH on the uptake of the surfactant by montmorillonite were characterised by analytical and spectroscopic methods including X-ray diffraction analysis. The effect of surfactant loading on the thermal stability of the organoclay was studied using thermogravimetric analysis (TGA). The possibility of a reaction between CAB and PLA was also investigated by thermal and spectral methods. In the second part of the thesis, composites of the novel organoclay and PLA were manufactured by solution casting from chloroform, and melt compounding using a torque rheometer. It was found that intercalated/exfoliated nanocomposites could be made by either method. The biodegradability of the nanocomposites in composting conditions was also investigated. The study showed that CAB can be used to manufacture organoclays that confer useful improvements in the properties of PLA in terms of thermal stability and mechanical strength and on this basis merits further study. It also showed that organoclays based on CAB are a useful addition to the range of tallow-derived organoclays currently available.