Novel Crystalline Morphology and Lamellar Assembly of Biodegradable Polymers Induced by Strongly Interacting Amorphous Polymers or Ionic Liquids

Abstract

This study has been focused on the crystalline morphology and lamellar arrangement of biodegradable polymers blended with amorphous polymers or ionic liquid Blends of poly(hydroxybutyrate)/syndiotactic poly(methyl methacrylate) (PHB/sPMMA) and poly(hydroxybutyrate)/isotactic poly(methyl methacrylate) (PHB/iPMMA) exhibited similar phase behavior which is upper-critical-solution-temperature (UCST) at ~225 oC and ~240 oC respectively based on the results of thermal analysis and phase morphology However syndiotacticity in PMMA exerts a prominent effect on altering the PHB spherulites morphology while by contrast isotacticity in PMMA has most no effect at all At high sPMMA contents (e g 30 wt%) in the PHB/sPMMA blend the spherulites are all negative-birefringence and ring-less when crystallized at any crystallization temperature (Tc) between 50-90 oC That is not only the original ring-banded pattern in neat PHB spherulites is completely disrupted but the optical sign is reverted completely from positive- to negative-birefringence in sPMMA/PHB blend but not seen in isotactic PMMA/PHB one A total of nine different types of crystalline morphology were identified in the poly(ethylene succinate)/poly(p-vinyl phenol) (PESu/PVPh) blend with amorphous contents from 10 to 35 wt% and Tc = 40-70 oC in ultra-thin film thickness Multiple types of PESu crystalline morphology at the same Tc are never seen in neat PESu but occur in PESu/PVPh blend with amorphous PVPh higher than 20 wt% Crystallization temperature thickness/space confinement and presence of interacting amorphous PVPh are the main factors for multiple types of spherulites in the blends partly due to strong interactions via hydrogen bonding between PESu and PVPh and likely extra nucleation capacity from the diffusion interfaces Single crystals of PESu were proven by AFM in the PESu/PVPh blend especially when confined in films of around 500 nm melt-crystallized at Tc =70 oC or above The electron diffraction pattern of TEM result further confirmed the formation of PESu single crystals The combination of thin film thickness high crystallization temperature and strong interaction between two polymers were believed as the main factors for melt-crystallized PESu single crystals Novel morphology is found in neat PLLA at specific condition The six-petal spherulite morphology composed of a combination of a central hexagon core hexagon-shape ring bands and fibrous six stalks was discovered in a low molecular weight PLLA (LMw-PLLA) melt-crystallized at a specific Tc =110oC and confined in thin films Discrete lamellae consisting of sequenced wide and small lamellae all in flat-on orientation with periodically up-and-down topology were packed in ring-banded alignment while continuous lamellae in flat-on tilted or edge-on orientation were arranged in fibrous region The geometry of the initial crystal was believed to be the influencing factors in final spherulite patterns Crystalline morphology of poly(L-lactide) (PLLA) is significantly changed by the addition of ionic liquid (IL) to display a diversification of spherulites morphology which never been seen before in neat PLLA A hexagonal crystal with star-shaped core a novel crystal morphology never seen before in LMw-PLLA modified by glycine ester based ionic liquid The plasticizing effect of the ionic liquid leads to faster nucleation and growth rate in the early stage of crystallization In the latter stage of crystal growth the increase in polymer chain mobility enhanced by the ionic liquid addition leads to a morphology transformation from hexagon-shape to star-shape morphology Special dendritic morphology is also observed in PLLA/IL blend with higher IL content The existence of the IL-PLLA interaction impedes the melt crystallization of PLLA indicated by the decrease in spherulitic growth rate with increasing IL content and the glass transition (Tg) of PLLA decreases with the increase in IL content showing the plasticizing effect to PLLA Neat PLLA shows brittleness with extensive crack formation during post-crystallization cooling process; however after the addition of IL the crack formation is reduced or even diminished

Date of Award	2014 Aug 21
Original language	English
Supervisor	Eamor Woo (Supervisor)