Flow Temperature of Poly(Lactic Acid) Gel in Solvents with Different Solubility

Abstract

Poly(L-lactid acid) (PLLA) forms complex crystals (ε-crystal) with some solvents including N,N-dimethylformamide (DMF), and can be easily gelled in such solvents. The solvent of these gels can be exchanged to some other solvents which do not form ε-crystal with PLLA. The flow temperatures of PLLA gels after exchanging DMF to various solvents were investigated to clarify the relation between the exchangeability and the solubility of solvents to PLLA. After changing the ε-crystals to α-crystals (crystal form of PLLA in films without special treatments) by immersing the gels into 1-propanol, the flow temperatures of PLLA gels could be expected by Hansen solubility parameters. The results suggest that the exchangeability of the solvent of the PLLA gel is determined both by the solubility to PLLA and the ability of the new solvent to induce the change from ε-crystals to α-crystals.

Elevation of Flow Temperature and Structural Change of Poly(Lactic Acid) Gel Induced by Formation of Stereocomplex Crystals

“…PLLA was dissolved in DMF at an elevated temperature, and the solution was successfully formed gels by cooling. [24][25][26][27][28][29][30] The X-ray diffraction pattern of this gel was very similar to the one which had been reported for the PLLA films forming 𝜖-crystals by Marubayashi et al [15] although the peak intensity was weak because the weight fraction of PLLA in the gel was less than 5 wt%. [24] Because the number of solvents inducing PLLA to form 𝜖-crystals is limited, the solvent of the gel was exchange to other solvents by immersing the gel into other solvents which do not form 𝜖-crystals with PLLA, such as water.…”

“…PLLA was dissolved in DMF at an elevated temperature, and the solution was successfully formed gels by cooling. [ 24–30 ] The X‐ray diffraction pattern of this gel was very similar to the one which had been reported for the PLLA films forming ε‐crystals by Marubayashi et al. [ 15 ] although the peak intensity was weak because the weight fraction of PLLA in the gel was less than 5 wt%.…”

“…The flow temperatures of the gels, of which solvent was exchanged to 25 solvents, were measured to elucidate the relation between the flow temperature and solvent of the gels. [ 28 ] The gels were first immersed in 1‐propanol to change ε‐crystals to α‐crystals, then immersed in another solvent. The flow temperatures of the gels correlated to the solvent quality to PLLA, which was estimated with Hansen solubility parameters.…”

Polylactide cocrystals and gels

“…In another work, Matsuda et al described three procedures to elevate the flow temperature of PLLA gel. [ 89–92 ] In the first process, they took PLLA of higher molecular weight and prepared its gel in DMF. The obtained gel was immersed in a DMF solution of PLLA with lower molecular weight and cooled to a temperature of −18°C.…”

“…From the experiments, it was reported that the flow temperature of the PLLA gel after immersing to 1‐propanol, increased with an increase in the distance of HSPs between PLLA and solvents except for the solvents with low boiling temperature. [ 91 ]…”