Miscibility and Crystallization of Poly(L-lactide)/Poly(ethylene glycol) and Poly(L-lactide)/Poly(ε-caprolactone) Blends

Abstract

ABSTRACT:The miscibility and crystallization behavior of two binary blends, poly(L-lactide) (PLLA)/poly(ethylene glycol) (PEG) and PLLA/poly(e-caprolactone) (PCL), with PLLA as the main component (PLLA composition was not lower than 50wt%) have been investigated by differential scanning calorimetry (DSC) and optical microscopy. PEG and PCL with moderate molecular weight (MW"" 10000) were used as the blending components for PLLA. PLLA and PEG were miscible in the melt over the composition range investigated. The variation of the bulk crystallization rate of PLLA with PEG composition displayed a maximum at IO wt% PEG. On the other hand, a monotonic increase in spherulite growth rate with increasing PEG composition was observed. Since the bulk crystallization rate is determined by both the nucleation density and the growth rate, the depression of nucleation density coupled with the increase of growth rate with increasing PEG composition may give rise to the observed maximum in the composition variation of the bulk crystallization rate. The crystallizability of PLLA and PEG in the blends was also evaluated. The crystallizability of PEG was reduced by blending with PLLA, while that of PLLA was essentially unaffected by blending with PEG. For the PLLA/PCL system, a phase-separated morphology was identified in the melt. However, the crystallization rate of PLLA could be enhanced upon blending with PCL. Since no preferential nucleation at the domain interface was observed, the promotion of PLLA crystallization rate was attributed to its partial miscibility with PCL.KEY WORDS Poly(L-lactide) / Poly(ethylene glycol) / Poly(e-caprolactone) / Blends / Miscibility / Crystallization Behavior / Biodegradable polymers have attracted increasing attention due to their potential applications as biomedical and environment-friendly materials. In addition to mechanical and thermal properties, the rate and extent of degradation are the essential considerations for biodegradable polymers. The degradation behavior of biodegradable polymers has been frequently controlled by modifying the chemical or stereochemical compositions of the polymers. 1 -5 Copolymerization, for example, is a popular method for such a modification, 1 • 2 • 5 Besides the chemical nature, the morphology of a biodegradable polymer may also be an influential factor on its degradation behavior. For example, when a semicrystalline biodegradable polymer is subjected to a degradation medium such as water and enzyme, the molecules of the medium would enter into the amorphous regions more easily than into the crystalline regions. The degradation rate will then depend on the degree of crystallinity and the chain packing in the amorphous regions, which are determined by the thermal history and the molecular weight. Therefore, morphological controls through thermal history and molecular weight variations, physical aging, and chain orientation may also be useful for controlling the degradation behavior of a biodegradable polymer. crystallizability and the morphology of biodegr...

Melt Structure and its Transformation by Sequential Crystallization of the Two Blocks within Poly(L‐lactide)‐block‐Poly(ε‐caprolactone) Double Crystalline Diblock Copolymers

“…A natural choice is poly(e-caprolactone) (PCL) since it is also biodegradable and has a T g of À65 8C. Since PLLA with a high molecular weight is reported to be immiscible with PCL, [17][18][19] the morphology of PLLA/PCL blends would be coarse and with low adhesion strength, thus desirable mechanical properties are not anticipated. On the other hand, PLLA-b-PCL block copolymers cannot macroscopically phase segregate and exhibit various microdomain structures at the nanoscale depending upon the block length ratio between the blocks.…”

The effects of plasticizers on the dynamic mechanical and thermal properties of poly(lactic acid)

“…Examples of polymers that have been blended with PLA are thermoplastic starch, 4 poly(ethylene oxide), 5 poly(ethylene glycol), 6 poly(⑀-caprolactone), [7][8][9] and poly(hydroxybutyrate). 10,11 As plasticizers for PLA, oligomeric lactic acid, glycerol, 4 and low molecular weight esters such as citrates 12 were investigated.…”

Amine-linked thioxanthones as water-compatible photoinitiators

“…The investigation of watercompatible photoinitiators has been reviewed. 4 Water-soluble photoinitiators derived from thioxanthone are particularly applicable for the UV curing of white pigmented water-borne coatings and inks because of their extended absorption up to 400 nm. Green et al synthesized a series of quaternary ammonium salt and sulfonate derivatives of thioxanthone as water-compatible photoinitiators and studied their photoinitiating performance as well as photochemical properties.…”