Prediction of the Miscibility of PBAT/PLA Blends

Abstract

Designing polymer structures and polymer blends opens opportunities to improve the performance of plastics. Blending poly(butylene adipate-co-terephthalate) (PBAT) and polylactide (PLA) is a cost-effective approach to achieve a new sustainable material with complementary properties. This study aimed to predict the theoretical miscibility of PBAT/PLA blends at the molecular level. First, the basic properties and the structure of PBAT and PLA are introduced, respectively. Second, using the group contribution methods of van Krevelen and Hoy, the Hansen and Hildebrand solubility parameters of PBAT and PLA were calculated, and the effect of the molar ratio of the monomers in PBAT on the miscibility with PLA was predicted. Third, the dependence of the molecular weight on the blend miscibility was simulated using the solubility parameters and Flory–Huggins theory. Next, the glass transition temperature of miscible PBAT/PLA blends, estimated using the Fox equation, is shown graphically. According to the prediction and simulation, the blends with a number-average molecular weight of 30 kg/mol for each component were thermodynamically miscible at 296 K and 463 K with the possibility of spinodal decomposition at 296 K and 30% volume fraction of PBAT. This study contributes to the strategic synthesis of PBAT and the development of miscible PBAT/PLA blends.

Experimental Determination of Molecular Weight-Dependent Miscibility of PBAT/PLA Blends

“…The largest holes and most obvious unevenness on the surface were found in the blend B0L0-55, indicating that with the same M n values, the blend with the PBAT/PLA weight ratio of 50/50 was more difficult to mix than the blend with the composition of 80/20 or 20/80. This phenomenon is in agreement with the previous experimental study [13] and the prediction [24].…”

“…Moreover, with the same M n values, the phase separation was more noticeable at the weight ratio of 50/50 than at 80/20 and 20/80. These two tendencies determined experimentally are consistent with the tendencies predicted and simulated for PBAT/PLA blends [24].…”

“…Subsequently, the resulting PBAT molecules can further react with water molecules to generate smaller molecules. These products of hydrolysis may contain different ratios of monomers than the original polymer [24].…”

“…The T g values of PBAT/PLA blends with different molecular weights and compositions are summarized in Table 3. These blends contained three different M n combinations, and each had three different weight ratios (80/20, 50/50, and 20/80), since both the molecular weights and the composition had influences on the blend miscibility according to the prediction [24].…”

“…Dil et al [23] melt blended PLA with high and low molecular weight PBAT and found the increase of molecular weight of PBAT reduces the miscibility in the PLA-rich phase dramatically. In addition to these experimental studies, Su [24] recently predicted the miscibility of PBAT/PLA blends concerning the molecular weights, composition, and temperature; blends tend to be more miscible (1) when the number-average molecular weights decrease; (2) when the PBAT weight fraction is <20 wt% or >80 wt%; and (3) when the blends are processed at a high temperature.…”