Crystallization Behaviors of Poly(3-hydroxybutyrate) and Poly(l-lactic acid) in Their Immiscible and Miscible Blends

Abstract

By adjusting the molecular weight of the poly(l-lactic acid) (PLLA) component in poly(3-hydroxybutyrate) (PHB)/PLLA blends, we investigated the crystallization behaviors of the two components in their immiscible and miscible 50:50 blends by real time infrared (IR) spectroscopy. In the immiscible PHB/PLLA blend, the stepwise crystallization of PHB and PLLA was realized at different crystallization temperatures. PLLA crystallizes first at a higher temperature (120 degrees C). Its crystallization mechanism from the immiscible PHB/PLLA melt is not affected by the presence of the PHB component, while its crystallization rate is substantially depressed. Subsequently, in the presence of crystallized PLLA, the isothermal melt-crystallization of PHB takes place at a lower temperature (90 degrees C). It is interesting to find that there are two growth stages for PHB. At the early stage of the growth period, the Avrami exponent is 5.0, which is unusually high, while in the late stage, it is 2.5, which is very close to the reported value (n approximately 2.5) for the neat PHB system. In contrast to the stepwise crystallization of PHB and PLLA in the immiscible blends, the almost simultaneous crystallization of PHB and PLLA in the miscible 50:50 blend was observed at the same crystallization temperature (110 degrees C). Detailed dynamic analysis by IR spectroscopy has disclosed that, even in such apparently simultaneous crystallization, the crystallization of PLLA actually occurs faster than that of PHB. It has been found that, both in the immiscible and miscible blends, the crystallization dynamics of PHB are heavily affected by the presence of crystallized PLLA.

Combined compatibilization and plasticization effect of low molecular weight poly(lactic acid) in poly(lactic acid)/poly(3-hydroxybutyrate-co-3-hydroxyvalerate) blends

“…Zhang et al [21] found that melt blended samples exhibited greater compatibility than those prepared by solvent casting at room temperature, possibly due to a transesterification reaction between PHB and PLA occurring at high temperature. This transesterification, or more generally the presence of specific interactions between the two polymers, has been evidenced by many other authors [14,15,[22][23][24], especially for blends containing a low amount of PHB(V). For such PLA/PHBV blends (typically weight fractions of 90%/10%), Gerard and Budtova [22] observed a peculiar morphology, with very small PHBV nodules (about 400 nm) well dispersed in PLA matrix, with increased adhesion at the interface, presumably explaining the increase of ductility (elongation at break of 200% when tested immediately after sample preparation) measured for this composition by the authors.…”

Blending of Polyhydroxybutyrate-co-valerate with Polylactic Acid for Packaging Applications – Reflections on Miscibility and Effects on the Mechanical and Barrier Properties

“…Due to the general shape of the free mixing enthalpy curve, derived by Flory and Huggins, which predict less miscibility at equal parts and better miscibility with a major phase (Equation 1, Figure 1), three weight ratios of PLA to PHBV were used: 80:20, 50:50 and 20:80 weight percent. As densities are equal 43 , weight fractions are volume fractions.…”

Characterization of the Thermal Behavior of Poly(hydroxybutylate) by Principal Component Analysis-based Two-Dimensional Correlation Spectroscopy

“…[6][7][8][9][10] It is well known that FTIR spectroscopy is a powerful technique for investigating polymers. [6][7][8]10,[11][12][13][14] However, the overlap of spectral features sometimes limits the utility of the technique. To overcome any shortcoming of conventional spectral analysis, two-dimensional (2D) correlation spectroscopy has been applied to FTIR spectra.…”

“…To overcome any shortcoming of conventional spectral analysis, two-dimensional (2D) correlation spectroscopy has been applied to FTIR spectra. [11][12][13][14][15] Generalized 2D correlation spectroscopy is a well-established analytical technique that provides considerable utility and benefit in various spectroscopic studies of polymers. [16][17][18] Some of the notable features of generalized 2D correlation spectra are: the simplification of complex spectra consisting of many overlapped peaks; an enhancement of the spectral resolution by spreading peaks along the second dimension; the establishment of unambiguous assignments through the correlation of bands that are selectively coupled by various interaction mechanisms; and the determination of the sequence of the spectral peak emergence.…”

“…To overcome any shortcoming of conventional spectral analysis, two-dimensional (2D) correlation spectroscopy has been applied to FTIR spectra. [11][12][13][14][15] Generalized 2D correlation spectroscopy is a well-established analytical technique that provides considerable utility and benefit in various spectroscopic studies of polymers.…”