Effect of Polylactide Stereocomplex on the Crystallization Behavior of Poly(l-lactic acid)

Abstract

Effects of the addition of PDLA on the crystallization behavior of PLLA was investigated by means of differential scanning calorimetry, wide-angle X-ray diffraction, melt rheology, and polarized optical microscopy. Nonisothermal and isothermal crystallization behavior of PLLA including low (l-PDLA) and high molecular weight PDLA (h-PDLA) were studied. PLLA/PDLA asymmetric blends form stereocomplex (SC) crystal and stay unmelted at 200 °C in the PLLA melt. Nonisothermal crystallization measurement from 200 °C showed monotonous rise in the crystallization temperature for PLLA/h-PDLA blend, while peculiar concentration dependence was observed for PLLA/l-PDLA blends. The acceleration effect was more pronounced in PLLA/h-PDLA, although the crystallinity of SC was lower than PLLA/l-PDLA blends, which implies the importance of higher order structure of SC for the crystallization of PLLA. From isothermal crystallization kinetics measurements, the acceleration effect in PLLA/h-and l-PDLA blends was found to enhance the nucleation of crystallization but slightly interrupts the crystallization growth. The above results were reasonably explained by the model where SC crystallites are not isolated in PLLA melt but connected like a physical gel.

Differences Between Stereocomplex Spherulites Obtained in Equimolar and Non‐Equimolar Poly(L‐lactide)/Poly(D‐lactide) Blends

“…It is believed that the as-formed stereocomplex crystals can act as nucleation agents for the polyenantiomer in excess, as already reported in the literature. [8,20,21] Enthalpies of fusion of the homopolymer and stereocomplex crystals calculated from the T c ¼ 160 8C curve of Figure 5 are 30.8 and 14.8 J Á g À1 , respectively. Whereas the enthalpy of fusion of the stereocomplex crystallized at the same T c from an equimolar blend is 46.7 J Á g À1 .…”

Computational investigation of spectroscopic parameters in putative secondary structure elements for polylactic acid and comparison with experiment

“…The crystal structures were also analyzed by computational chemistry. The poly(lactic acid) polymorphs were studied by rotational isomeric state models [20,21], molecular dynamics [9,10], Monte Carlo models [21,22], molecular mechanics [9] and quantum chemical [23][24][25] simulations. It was found that neither a pre 10 3 nor 3 1 helix could fit the experimental data perfectly, suggesting a certain degree of disorder in the structure.…”

Comparison of thermal, mechanical and thermomechanical properties of poly(lactic acid) injection-molded into epoxy-based Rapid Prototyped (PolyJet) and conventional steel mold

“…One example is the joint usage of the rather cheap additives Talc and Poly(Ethylene Glycol) (PEG), which allows fast crystallization [27,28]. Another possibility to highly increase crystallinity of PLA and thus its HDT is the 50-50m% blending of optically pure PLLA and PDLA produced entirely by using L-Lactide and D-Lactide respectively to develop stereocomplex crystalline structure [29,30]. Although this crystalline structure improves PLA with a HDT value of even 150°C, the cost of producing PDLA is the bottleneck of this technology, since during fermentation almost entirely L-Lactic acid is generated making the price of D-Lactic Acid and PDLA high.…”