Gelation of Poly(L-lactic acid) Induced by Complex Crystallization with Solvents

Gels of poly(L-lactic acid) (PLLA) in several solvents, including N,N-dimethylformamide (DMF) were formed by cooling solutions of PLLA. Polarizing optical micrographs showed the formation of spherulites of PLLA in the gels below 70 degrees C. The storage modulus of the gel decreased abruptly below 70 degrees C, which suggest that the crystalline structure of PLLA prevented the flow of DMF and induced the gelation. The X-ray diffraction (XRD) patterns of the gels were similar to those of the epsilon-crystals of PLLA which were induced by the formation of complex crystallization with DMF. The mechanism of the formation of the gel is discussed based on the experimental data.