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
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.
Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.