Cold crystallization behavior of glassy poly(lactic acid) prepared by rapid compression

Abstract

The cold crystallization behavior of glassy poly(lactic acid) was studied by comparison among samples obtained through three different treatments, which are naturally cooling (NC), liquid nitrogen quenching (NQ), and rapidly compressing (RC). The crystallization kinetics and structural changes of these glassy samples were analyzed by using in situ Fourier transform infrared (FTIR) and in situ wide angle X-ray diffraction measurements. The results reveal that, the cold crystallization behavior is very similar between NC and NQ samples, but RC sample exhibits higher crystallization rate and lower crystallization temperature than them. FTIR investigation showed that, during the heating process for all the glassy samples, conformational adjustment in the amorphous phase occurs first, and followed by formation of the disordered crystals and then the disordered crystals further perfecting, while for RC sample the onset temperature of each step is much lower. Furthermore, for RC sample, the crystal grain number is larger and its initial a 0 form crystal induced by the heating is higher ordered than that of the others, and this unique crystallization behavior might be caused by the local ordered domains formed during the RC process. POLYM. ENG. SCI., 55:359-366, 2015. FIG. 6. Temperature dependence of the FTIR spectra in the 835-980 cm 21 range and the intensity change of indicated bands with temperature during cold crystallization.

Blends of Poly (L-Lactic Acid) and Glucose Prepared from Mixture Solution

“…PLLA isα-crystalline structure with the strongest peaks at 2θ of 16.52°, as well as other peaks at 14.90°, 19.21° and 22.45° with a crystallinity of 20.8%. The XRD curve of PLLA-Glu blend with PLLA/Glu ratio of 9:1 is similar to that of PLLA [9,12] . This result is probably owing to the strong interaction between PLLA and glucose, which may hinder the crystallization process of glucose and cause imperfect crystal of PLLA, as already demonstrated by DSC.…”

“…The bands at 956 and 922 cm -1 in PLLA spectrum have been separately ascribed to the amorphous and crystalline phase. With increasing Glu, the band at 956cm -1 becomes very weak in blend spectra, while the band at 922cm -1 enhances and shifts to lower wavenumber, which means that the crystallization of PLLA-Glu blends is enhanced [9] . IR results show that several kinds of hydrogen bonds between C=O group of PLLA and OH group in both PLLA and Glu, which indicates that PLLA and Glu are partially compatible.…”

“…TG and DTG results show that the addition of glucose promotes thermal degradation of PLLA due to the trans-esterification reaction between glucose containing hydroxyl groups and PLLA at high temperature, which can reduce PLLA molecular weight and promote the thermal degradation of PLLA. Moreover, the addition of glucose can destroy PLLA crystalline structure to obtain imperfect PLLA crystalline, which also reduces the stability of PLLA Advances in Biological Sciences Research, volume 3 [9] . All these results indicate that partial compatibility between glucose and PLLA performs great effect on the structure and properties of PLLA-Glu blends.…”

Effect of Glucose on the Crystallization and Thermal Properties of Poly(L-Lactic Acid) Prepared Through Mixed Solution Method

“…With increasing Glu, the band at 956cm -1 becomes very weak in blend spectra, while the band at 922cm -1 enhances and shifts to lower wavenumber, which means that the crystallization of PLLA-Glu blends is enhanced [9].…”

“…On the other hand, PLLA and PLLA-Glu blends possess similar Tmax, which denotes that PLLA may play more important role at high decomposition temperature. There are two thermal decomposition peaks in DTG curve of PLLA-Glu blends, which may be caused by the decomposition of glucose at lower temperature [9]. The weight residue of PLLA-Glu blend increases gradually with increasing Glu.…”