Abstract
Ph.D. (Chemistry)
This study focuses on the morphology and crystal-growth behaviour of polyactide
(PLA)-based blends and blends modified with organoclay thin films. The study
further examined the effect of blending and the incorporation of organoclays on the
enzymatic degradation behaviour. Thin films of unmodified and nanoclay-modified
PLA/poly(butylene succinate) (PBS) blends were cast on a glass substrate by a
spin coater, while thin films of biodegradable PLA/poly[(butylene succinate)-coadipate]
PBSA blends and blends containing organoclays were cast on a silicon
(100) wafer substrate. The morphology and crystal growth behaviour of the thin
films crystallized at different temperatures were examined with an atomic force
microscopy (AFM) equipped with a hot-stage scanner. In PLA/PBS blend thin
films, AFM images showed that the size of the dispersed PBS phase was
influenced by C30B clay loading on the blends. The dispersed size reduced on the
addition of C30B clay up to 2 wt%, beyond which, dispersed size began to
increase. Transmission electron microscopy studies indicated that this behaviour
was due to the preferential location of silicates in the PBS phase than in the PLA
phase. For thin films annealed at 60 °C, the additi on of organoclays to the blend
quenched the growth of edge-on lamellae. The crystalline morphologies at 120 °C
were dominated by edge-on lamellae grown, around the PBS phase to form
spherulites. Morphologies of thin films crystallized at 120 °C from melt were
dominated by the flat-on lamellae, while those crystallized at 70 °C from melt were
dominated by the edge-on lamellae. In the case of PLA/PBSA blend thin films, the
results indicated that the size and distribution of the dispersed phase were directly
related to the blend composition. The crystal growth behaviours indicated the
presence of homogeneous and heterogeneous nucleations, and the nature of
nucleation was directly related to the blend ratio and the temperature at which
crystallization occurred. Therefore, this study will facilitate the understanding of
crystal growth behaviour in a confined environment and will enable the modulation
of the blend properties.