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
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
Poly(lactic acid) (PLA)/poly(ethylene oxide) (PEO) blends nucleated by a self-assembly nucleating agent, N,N′,N″-tricyclohexyl-1,3,5-benzenetricarboxylamide (BTCA), were prepared by melt blending. The crystallization behavior and mechanical properties of the materials were investigated by differential scanning calorimetry, polarized optical microscopy, wide-angle X-ray diffraction, dynamic mechanical analyzer and tensile testing. It was found that PEO had a synergistic effect together with BTCA on promoting PLA crystallization, besides its toughening effect on the material. Moreover, BTCA revealed prominent reinforcement effect on both neat PLA and PLA/PEO blends in the glass transition region and above, indicating the improvement on the heat resistance of the materials.
Using pyromelliticdianhydride (PMDA) and polyfunctional epoxy ether (PFE) as branching agent, long chain branching stereocomplex poly(L‐lactide)s and poly(D‐lactide)s was prepared by reactive processing, respectably. Then stereocomplex poly(lactide)s of long chain branching PLLA and PDLA (sc‐PLA/BA) was prepared by solution blending and its fabricated the vascular stents via 3D‐printing.The effects of branching structure on melt crystallization behavior of sc‐PLA/BA investigated by DSC. The influence of the branching agent content on the crystallization ability of samples shows a bell‐shaped relationship, there is a maximum point when the branching agent content is1.5 wt%. When the branching agent content is less than 1.5 wt%, the crystallization ability of the sample increased with the increasing of branching agent content. When the branching agent content exceeded than 1.5 wt%, the crystallization ability of the samples decreased with branching agent content increasing. Such behavior is as the linear PLA branched to dendrite configuration, the enrichment of segments around branching structure within branched chains promoted its nucleation. But the high degree of branching caused inter‐ or intrachians entanglement which obstructed the segments movement and growth into the crystals. The half‐time of crystallization (t1/2) of the samples decreased from 6 minutes for initial sc‐PLA/BA‐0 to 3 minutes of sc‐PLA/BA‐1.5 wt% at 163°C. POM results indicated that nucleation density of sc‐PLA/BA significantly increased with the branching agent increasing. Moreover, mechanical testing demonstrated that forming branching structure could be an effective modification of the mechanical properties for sc‐PLA, its tensile strength and modulus increases from 57.3 MPa and 2.02 GPa to 70.4 MPa and 3.31 GPa, respectively. TGA results analyzed by FWO method and Kissinger method, indicated the apparent activation energy of sc‐PLA/BA samples increases from 96.8 to 113.3 kJ/mol, suggesting the improvement of heat resistance. The CCK‐8 assay, ALP assay and cell Live/Dead assay results indicated that sc‐PLA with branching structure presented very low cell cytotoxicity. Therefore, the long chain branching sc‐PLA matrix with branching agent could effectively improve its crystallization abilities, mechanical properties, heat resistance and biocompatibilities. 相似文献
Crystallization behavior and morphology of PLA blended with 0.05–1.00 wt % loadings of poly(D-lactic acid) (PDLA) forming stereocomplex crystallites as in-situ nucleating agents, were studied using wideangle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), and polarizing-light optical microscopy (POM). Blending PLA with small amount of PDLA does lead to formation of PLA stereocomplex (SC), although the PLA is a random copolymer. The in-situ formed SC crystal acted as nucleation sites in blends and accelerated the crystallization of PLA by decreasing the half-time (t1/2). The nucleation efficiency of PDLA obviously increased and the crystallization induction time decreased while the content of PDLA reached up to 0.20 wt %. While the content of PDLA is 0.2 wt %, the nucleation efficiency of PDLA is up to 43.8%, and the induction time decreased from 430 to 88 s. In addition, compared with pure PLA, t1/2 decreases from 15.1 to 3.5 min at Tc = 127.5°C while the amount PDLA is 1.0 wt %. The equilibrium melting temperature of PLA decreased from 187.2 to 181.2°C with the increase of PDLA content. 相似文献
Poly(lactic acid) (PLA) depolymerases are categorized into protease-type and lipase-type. Protease-types can hydrolyze poly(l-lactic acid) (PLLA) but not poly(d-lactic acid) (PDLA). Lipase-types, including cutinase-like enzyme (CLE) from Cryptococcus sp. strain S-2 preferentially hydrolyze PDLA. Both enzymes degraded not only PLA emulsion but also PLA film, in which amorphous region is preferentially attacked, but crystalline region can be also attacked. Stereocomplex PLA (sc-PLA) formed by 50:50 blending of PLLA and PDLA included no homo crystals, but a tiny homo crystallization peak appeared and crystallinity increased by 5% when attacked by CLE, although no significant change of molecular weight and crystalline size was found. Enantioselective degradation must occur in amorphous region of PLLA/PDLA film and preferentially hydrolyzed PDLA, resulting in a slightly excess amount of PLLA remained, which must be crystallized. 相似文献
Stereocomplex crystallite (SC) between enantiomeric poly(l-lactic acid) (PLLA) and poly(d-lactic acid) (PDLA), with largely improved thermal resistance and mechanical properties compared with PLLA and PDLA, is a good nucleating agent for poly(lactic acid) (PLA). The effects of SC and/or polyethylene glycol (PEG) on the crystallization behaviors of PLA were investigated. The non-isothermal and isothermal crystallization kinetics revealed that SC and PEG can separately promote the crystallization rate of PLA by heterogeneous nucleation and increasing crystal growth rate, respectively. However, their promoting effect is limited when used alone, and the modified PLA cannot crystallize completely under a cooling rate of 20 °C/min. When SC and PEG are both present, the crystallization rate of PLA is greatly accelerated, and even under a cooling rate of 40 °C/min, PLA can crystallize completely and get a high crystallinity owing to the excellent balance between simultaneously improved nucleation and crystal growth rate. 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.
Non-isothermal solution crystallization and dissolution behaviour of both enantiomers (D and L) of poly(lactic acid) (PLA) and their blends were studied by the unique Solution Crystallization Analysis by Laser Light Scattering (Scalls) method. For the first time, we have investigated the crystallization of this biopolymer in solution, as well as the subsequent dissolution or “solution melting”. It was found that addition of the D-enantiomer (PDLA) to the L-enantiomer (PLLA) in solution resulted in the formation of stereocomplex crystals (SC), and the nucleation-effect of the crystals was intensified with increase in PDLA content, leading to an earlier onset of crystallization and increased crystallization peak area. Differential Scanning Calorimetry (DSC) analysis confirmed the formation of SC during solution crystallization. Large re-crystallization events were seen for the pristine polymers, indicative of their low crystallization rates. Overall, results obtained by Scalls provided promising information regarding PLA crystallization kinetics, which significantly influences practical applications of this biopolymer. 相似文献
Due to their high sensitivity to temperature and humidity, the applications of polylactic acid (PLA) products are limited. The stereo-complexation (SC) formed by poly(L-lactic acid) (PLLA) and its enantiomer poly(D-lactic acid) (PDLA) can effectively improve the heat resistance and hydrolysis resistance of PLA products. In this work, the blended melt-spinning process of PLLA/PDLA was carried out using a polyester fiber production line to obtain PLA fiber with a complete SC structure. The effects of high-temperature tension heat-setting on the crystalline structure, thermal properties, mechanical properties, and hydrolysis resistance were discussed. The results indicated that when the tension heat-setting temperature reached 190 °C, the fiber achieved an almost complete SC structure, and its melting point was 222.5 °C. An accelerated hydrolysis experiment in a 95 °C water bath proved that the SC crystallites had better hydrolysis resistance than homocrystallization (HC). The monofilament strength retention rate of SC−190 fiber reached as high as 78.5% after hydrolysis for 24 h, which was significantly improved compared with PLLA/PDLA drawn fiber. 相似文献
Structure and properties are studied for binary blends composed of poly(lactic acid) (PLA) and poly(butylene succinate) (PBS). The rheological measurements in the molten state reveal that the entanglement molecular weight of PLA is lower than that of PBS. Further, the interfacial tension of the immiscible blend system is evaluated employing a rheological emulsion model and found to be 3.5 [mN/m]. Moreover, thermal analysis directly detects that addition of PBS enhances the crystallization of PLA even though PBS is in a molten state. Further, the cold-crystallization for quenched blends occurs at lower temperature than that for a quenched PLA. This would be attributed to the nucleating ability of PBS, leading to generation of PLA crystallites during the quench operation. 相似文献
The well-known bio-based and biocompostable poly(lactic acid), PLA, suffers from brittleness and a low heat distortion temperature. In this paper, we address a possible route to make PLA tough(er) by blending with ethylene-co-vinyl acetate (EVA) with different vinyl acetate contents. The compatibility and phase morphology of the PLA/EVA blends was controlled by the ratio of vinyl acetate and ethylene in the random copolymers. Tough PLA/EVA blends with increased impact toughness, up to a factor of 30, were obtained with a maximum toughness at a vinyl acetate content of approximately 50 wt.%. The local deformation mechanism was well studied by TEM, SAXS and SEM. It revealed that internal rubber cavitation in combination with matrix yielding is the dominant toughening mechanism for the PLA/EVA blends under both impact and tensile testing conditions. 相似文献
In this work, a specific polylactide (PLA) 4032D was melt-mixed with a new toughener: butyl acrylate (BA), ethyl acrylate (EA) and glycidyl methacrylate (GMA) copolymer (BA-EA-GMA). DMA tests showed that PLA/BA-EA-GMA blends were partially miscible. The degree of crystallinity of PLA increased while the cold crystallization temperature shifted to higher temperatures with increasing BA-EA-GMA content. The SEM micrographs showed that PLA/BA-EA-GMA blends had a good dispersion and this phenomenon was in good agreement with their higher impact strength. The result showed that the adding of BA-EA-GMA has enhanced the flexibility of PLA/BA-EA-GMA blends as compared with pure PLA. The impact strength was changed from 3.4 kJ/m2 for pure PLA to 29.6 kJ/m2 for 80/20 PLA/BA-EA-GMA blend. 相似文献