Fabrication of Polymer Structure among Fibrous Structure of Poly(lactic acid) Gel and Improvement of Physical Properties

Abstract

Polymer structure of a block copolymer of poly(l‐lactic acid) (PLLA) and polystyrene (PS) is formed among a fibrous structure of PLLA inducing the gelation of PLLA in N,N‐dimethylformamide (DMF). The results of static and dynamic light scattering show the formation and growth of aggregates of the block copolymer (PLLA‐b‐PS) to form aggregates in DMF. The gels formed by the fibrous structure of PLLA in DMF are immersed in DMF solutions of PLLA‐b‐PS to allow the PLLA‐b‐PS chains to penetrate among the fibrous structure. The morphology of PLLA‐b‐PS in the gel is observed by field emission scanning electron microscopy. Viscoelastic measurements of the gel before and after the immersion indicate that the structure of the PLLA‐b‐PS elevates the flow temperature.

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.…”

“…This study was elaborated by immersion of gels in DMF solutions of block copolymers of PLLA and PS with different lengths of PLLA blocks and polymer concentrations. [ 90 ] The block copolymers with shorter PLLA blocks were observed to elevate the flow temperature with lower concentrations. [ 89 ]…”

“…FE‐SEM images of the immersed and mixed gels and the gel without PLLA‐ b ‐PS. The white circles in magnified images (×10,000) indicate the formation of the spherical structure by the block copolymer. Source : Reproduced with permission from Wiley, 2017 [ 90 ] …”

“…In another work, Matsuda et al described three procedures to elevate the flow temperature of PLLA gel. [89][90][91][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 À18 C. PLLA chains with lower molecular weight were entered into the network structure formed by PLLA of higher molecular weight, which resulted in the formation of an additional network and subsequently increased the gel's flow temperature.…”

“…[91] As another attempt to elevate the flow temperature of the PLLA gel formed by the fibrous ε crystals, the gel was immersed in the DMF solution of PLLA-b-PS to allow the block copolymer chains to penetrate into the network of PLLA. [89,90] The FE-SEM analysis revealed that the spheres of PLLA-b-PS caught inside the nanofibrous structure of PLLA gel, reinforcing the nanofibrous structure and ultimately resulting in an increment of flow temperature (Figure 11). They proposed the promotion of the transformation of the ε-crystals to α-crystals by the addition of block copolymer of PLLA-b-PS.…”