Thermal behavior, miscibility, and crystalline morphology in blends of low-molecular-weight poly(l-lactic acid) (LMw-PLLA) or high-molecular-weight PLLA (HMw-PLLA) with various polyesters such as poly(butylene adipate) (PBA), poly(ethylene adipate) (PEA), poly(trimethylene adipate)
(PTA), or poly(ethylene succinate) (PESu), respectively, were explored using differential scanning calorimeter (DSC), and
polarized-light optical microscopy (POM). Phase behavior in blends of PLLA with other polyesters has been intriguing and not
straight forward. Using a low- and high molecular weight PLLA, this study aimed at mainly using thermal analyses for probing
the phase behavior, phase diagrams, and temperature dependence of blends systems composed of PLLA of two different molecular
weights (low and high) with a series of aliphatic polyesters of different structures varying in the (CH2/CO) ratio in main chains. The blends of LMw-PLLA/PEA and LMw-PLLA/PTA show miscibility in melt and amorphous glassy states. Meanwhile, the LMw-PLLA/PESu blend is immiscible with an asymmetry-shaped upper critical solution temperature (UCST) at 220–240 °C depending
on the blend composition. In contrast to miscibility in LMw-PLLA/PTA and LMw-PLLA/PEA blends, HMw-PLLA with polyesters are mostly immiscible; and HMw-PLLA/PTA blend is the only one showing an asymmetry-shaped UCST phase diagram with clarity points at 195–235 °C (depending
on composition). Reversibility of UCST behavior, with no chemical transreactions, in these blends was proven by solvent recasting,
gel permeation chromatography, and Fourier transform infrared spectroscopy (FT-IR). Crystalline morphology behavior of the
LMw-PLLA/PEA and LMw-PLLA/PTA blends furnishes addition evidence for miscibility in the amorphous phase between LMw-PLLA and PTA or PEA. 相似文献
Stereoblock poly(lactic acid) (sb-PLA), consisting of poly(L-lactic acid) (PLLA) and poly(D-lactic acid) (PDLA) in a blocky sequence, can successfully be synthesized by solid-state polycondensation of a stereocomplexed mixture of PLLA and PDLA. First, the melt polyconden-sation of L- and D-lactic acids is conducted to obtain PLLA and PDLA with medium molecular weights. Then, both polymers are melt-blended to easily form the stereocomplex. The resulting stereocomplexed mixture (melt-blend) is subjected to solid-state polycondensation for chain extension. The molecular weight (Mw) of the resultant sb-PLA is strongly affected by the lactide/oligomer content in the melt-blend, which is determined by the melt-blending conditions, because it is directly correlated with the polymer crystallinity of the polycondensation products. 相似文献
Isotactic and optically active poly(D ‐lactic acid) (PDLA) and phenyl‐substituted poly(lactic acid)s (Ph‐PLAs), i.e., poly(D ‐phenyllactic acid) (Ph‐PDLA) and poly(L ‐phenyllactic acid) (Ph‐PLLA), were synthesized and stereospecific interactions between the synthesized polymers were investigated by their thermal properties and crystallization behavior using differential scanning calorimetry (DSC). The DSC measurements indicated that PDLA is miscible with Ph‐PLAs and that the attractive interaction between PDLA and L ‐configured Ph‐PLA is higher than that between PDLA and D ‐configured Ph‐PDLA. In other words, the latter result means that poly(lactic acid) (PLA) has a higher stereoselective attractive interaction with Ph‐PLA with the reverse configuration than with Ph‐PLA of the same configuration. These results strongly suggest that PLA‐based materials with a wide variety of physical properties and biodegradability can be fabricated by blending them with substituted PLAs with the reverse and same configurations.
Stereocomplex-type polylactide (SC-PLA) consisting of alternatively arranged poly(L-lactide) (PLLA) and poly(D-lactide) (PDLA) chains has gained a good reputation as a sustainable engineering plastic with outstanding heat resistance and durability,however its practical applications have been considerably hindered by the weak SC crystallizability.Current methods used to enhance the SC crystallizability are generally achieved at the expense of the precious bio-renewability and/or bio-degradability of PLAs.Herein,we demonstrate a feasible method to address these challenges by incorporating small amounts of poly(D,L-lactide) (PDLLA) into linear high-molecular-weight PLLA/PDLA blends.The results show that the incorporation of the atactic PDLLA leads to a significant enhancement in the SC crystallizability because its good miscibility with the isotactic PLAs makes it possible to greatly improve the chain mixing between PLLA and PDLA as an effective compatibilizer.Meanwhile,the melt stability (i.e.,the stability of PLLA/PDLA chain assemblies upon melting) could also be improved substantially.Very intriguingly,SC crystallites are predominantly formed with increasing content and molecular weight of PDLLA.More notably,exclusive SC crystallization can be obtained in the racemic blends with 20 wt% PDLLA having weight-average molecular weight of above 1 ×10s g/mol,where the chain mixing level and intermolecular interactions between the PLA enantiomers could be strikingly enhanced.Overall,our work could not only open a promising horizon for the development of all SC-PLA-based engineering plastic with exceptional SC crystallizability but also give a fundamental insight into the crucial role of PDLLA in improving the SC crystallizability of PLLA/PDLA blends. 相似文献
The superb heat resistance poly(lactic acid) (PLA) were prepared by blending PLA and poly(d ‐lactic acid) (PDLA) with various molecular weight (Mn). Formation of the stereocomplex in the blends was confirmed by differential scanning calorimetry and wide‐angle X‐ray diffraction. The results of the heat resistance implied it is possible that elevating the Vicat penetration temperature of PLA up to 150°C by blending with PDLA. The cold crystallization of homochiral crystallites is proven to be the critical factor affecting the heat resistance of PLA. While the PLA or PLA/PDLA blends were heated to cold crystallization temperature of samples, both the crystal content and the rigid amorphous region content are increased due to the cold crystallization and tethering effect, and the stiffness and heat resistance of the sample are improved. The cold crystallization homochiral crystallites kinetics of PLA and PLA/PDLA blends was also studied. The results showed the activation energy (?E) of cold crystallization increased from 120.30 kJ/mol to 144.66 kJ/mol with the increasing of PDLA content from 2% to 10%. 相似文献
The blends of poly(1,3‐trimethylene carbonate‐b‐(l ‐lactide‐ran‐glycolide)) (PTLG) with poly(d ‐lactide) (PDLA) were prepared via solution‐casting method using CH2Cl2 as solvent. The poly(l ‐lactide) (PLLA) segments of PTLG with PDLA chain constructed as stereocomplex structures and growth stereocomplex crystals of PLA (sc‐PLA). The effects of sc‐PLA crystals on thermal behavior, mechanical properties, thermal decomposition of the PTLG/PDLA blends were investigated, respectively. The differential scanning calorimetry (DSC) and wide‐angle X‐ray diffraction (WAXD) results showed that the total crystallinity of the PTLG/PDLA blends was increased with the PDLA content increasing. Heterogeneous nucleation of sc‐PLA crystals induced crystallization of the PLLA segments in PTLG. The crystallization temperature of samples shifted to 107.5°C for the PTLG/PDLA‐20 blends compared with that of the PTLG matrix, and decreased the half‐time of crystallization. The mechanical measurement results indicated that the tensile strength of the PTLG/PDLA blends was improved from 21.1 MPa of the PTLG matrix to 39.5 MPa of PTLG/PDLA‐20 blends. The results of kinetics of thermal decomposition of the PTLG/PDLA blends by TGA showed that the apparent activation energy of the PTLG/PDLA blends was increased from 59.1 to 72.1 kJ/mol with the increasing of the PDLA content from 3 wt% to 20 wt%, which indicated the enhancement of thermal stability of the PTLG/PDLA blends by addition of PDLA. Furthermore, the biocompatibility of the PTLG/PDLA blends cultured with human adipose‐derived stem cells was evaluated by CCK‐8 and live/dead staining. The experiment results proved the PTLG/PDLA blends were a kind of biomaterial with excellent physical performances with very low cytotoxicity. 相似文献