Poly(lactic acid)(PLA)is a biodegradable and eco-friendly polymer that is increasingly being incorporated into various applications in contemporary society.However,the limited stability of PLA-based products remains a...Poly(lactic acid)(PLA)is a biodegradable and eco-friendly polymer that is increasingly being incorporated into various applications in contemporary society.However,the limited stability of PLA-based products remains a significant challenge for their broader use in various applications.In this study,poly(L-lactic acid)(PLLA)/poly(D-lactic acid)(PDLA)melt-blown nonwovens were prepared by melt spinning.The structure,thermal properties,thermal stability,biodegradability and crystalline morphology of the melt-blown nonwovens were investigated.DSC and WAXD confirmed the formation of stereocomplex(SC)crystallites in the PLLA matrix.The storage modulus(G′),loss modulus(G″),and complex viscosity(∣η^(*)∣)of the PLLA/PDLA blend increased with an increase in SC crystallite content.The thermal degradation temperatures of PLLA/PDLA melt-blown nonwovens increased with the incorporation of SC crystallites,and the maximum rate of decomposition increased to 385.5℃,thus enhancing the thermal stability.Compared with neat PLLA melt-blown nonwovens,the hydrophobicity of PLLA/PDLA melt-blown nonwovens was improved,and WCA increased to 139.7°.The SC crystallites were more resistant to degradation by proteinase K compared to neat PLLA.However,the degradation rate of PLLA/PDLA melt-blown nonwovens remained at a high level.This work provides an effective strategy to obtain high-performance PLLA melt-blown nonwovens.展开更多
Poly(L-lactic acid)(PLLA)has been widely concerned because of its excellent biodegradability and biocompatibility.However,the poor crystallization ability of PLLA during the molding process not only leads to weak mech...Poly(L-lactic acid)(PLLA)has been widely concerned because of its excellent biodegradability and biocompatibility.However,the poor crystallization ability of PLLA during the molding process not only leads to weak mechanical properties but also reduces the processing efficiency,which limits the application of PLLA greatly.Enhancing crystallization ability of PLLA via introducing inorganic nanoparticles usually sacrifices biodegradability or transparency.Here,the microfine fibers with stereocomplex(SC)crystallites were incorporated into PLLA film to tailor the crystallization ability of PLLA as well as the mechanical properties.The results confirmed that the crystallization ability of PLLA matrix under different circumstances could be greatly enhanced by a few amounts of SC crystalline fibers,and synchronously enhanced tensile strength and ductility were also achieved,especially at relatively high temperature.Due to the relatively homogeneous dispersion of SC crystalline fibers and the similar refractive index between components,the PLLA-based film also exhibited high transparency,up to 85%-90%depending on the content of SC crystalline fibers.This work provides guidance for manufacturing transparent PLLA-based packaging materials with good crystallization capability and mechanical properties.展开更多
A series of host-vip interaction-adjusted polylactide stereocomplex micelles was prepared via the self-assembly of 4-armed poly（ethylene glycol）-block-poly（L-lactide/D-lactide）-cholesterol （4-armed PEG-b-PLLA/P...A series of host-vip interaction-adjusted polylactide stereocomplex micelles was prepared via the self-assembly of 4-armed poly（ethylene glycol）-block-poly（L-lactide/D-lactide）-cholesterol （4-armed PEG-b-PLLA/PDLA-CHOL） and poly（β-cyclodextrin） （PCD） with the molar ratios of CHOL/β-CD at 1：0.5, 1 ：l, and 1：2 in an aqueous environment. The hydrodynamic diameters of the micelles ranged from 84.1 nm to 107 nm depending on the molar ratio of CHOL/β-CD. It was shown that the micelle with the largest proportion of PCD possessed excellent abilities in drug release, cell internalization as well as proliferation inhibitory effect toward human A549 lung cancer cells. The results demonstrated that the stereocomplex and host-vip interactions-mediated PLA micelles exhibited great potential in sustained drug delivery.展开更多
Sustainable blends of poly(propylene carbonate)(PPC)and stereocomplex polylactide(sc-PLA)were prepared by melt blending equimolar poly(L-lactic acid)(PLLA)and poly(D-lactide acid)(PDLA)with PPC to form sc-PLA crystals...Sustainable blends of poly(propylene carbonate)(PPC)and stereocomplex polylactide(sc-PLA)were prepared by melt blending equimolar poly(L-lactic acid)(PLLA)and poly(D-lactide acid)(PDLA)with PPC to form sc-PLA crystals in situ in the melt blending process.Differential seanning calorimetry analysis revealed that only sc-PLA,no homo-crystallization of PLLA or PDLA,formed in the PPC matrix as the sc-PLA con tent was more than 10 wt%.Very in triguingly,scan ning electronic microscopy observati on showed that sc-PLA was evenly dispersed in the PPC phase as spherical particles and the sizes of sc-PLA particles did not obviously increase with in creasing sc-PLA con tent.As a con seque nee,the rheological properties of PPC were greatly improved by incorporation of sc-PLA.When the sc-PLA con tent was 20 wt%,a percolati on n etwork structure was formed,and the blends showed solid-like behavior.The sc-PLA particles could reinforce the PPC matrix,especially at a temperature above the glass transition temperature of PPC.Moreover,the Vicat softening temperature of PPC/sc-PLA blends could be increased compared with that of neat PPC.展开更多
In this study, the poly（L-lactide）/poly（D-lactide） （PLLA/PDLA） blends with different optical purities of PLLA and various molecular weights of PDLA are prepared by solution mixing, and the stereocomplex formatio...In this study, the poly（L-lactide）/poly（D-lactide） （PLLA/PDLA） blends with different optical purities of PLLA and various molecular weights of PDLA are prepared by solution mixing, and the stereocomplex formation and phase separation behaviors of these blends are investigated. Results reveal that optical purity and molecular weight do not vary the crystal structure of PLA stereocomplex （sc） and homochiral crystallites （hc）. As the optical purity increasing in the blends, the melting temperature of sc （Tsc） and the content of sc （AHsc） increased, while the melting temperature of hc （Thin） hardly changes, although the content ofhc （AHhm） decreased gradually. The Tsc and AHsc are also enhanced as the molecular weight of PDLA reduces, and the AHhm reduces rapidly even though the Thin does not vary apparently. With lower optical purities of PLLA and higher molecular weights of PDLA, three types of crystals form in the blends, i.e., PLA sc, PLLA hc and PDLA hc. As molecular weight decreases and optical purity enhances, the crystal phase decreases to two （sc and PDLA hc）, and one （sc） finally. This investigation indicates that the phase separation behavior between PLLA and PDLA in the PLLA/PDLA blends not only depends on molecular weights, but also relies on the optical purities of polymers.展开更多
In the present work, poly（propylene glycol） （PPG） was block copolymerized to form polylactide-poly（propylene glycol）-polylactide （PL-PPG-PL） triblock copolymers for preparing flexible stereocomplex PL （scPL）...In the present work, poly（propylene glycol） （PPG） was block copolymerized to form polylactide-poly（propylene glycol）-polylactide （PL-PPG-PL） triblock copolymers for preparing flexible stereocomplex PL （scPL） blend films. The scPL blend films were prepared by solution blending of poly（L-lactide）-PPG-poly（L-lactide） （PLL-PPG-PLL） and poly（D-lactide）- PPG-poly（D-lactide） （PDL-PPG-PDL） triblock copolymers before film casting. The influences of PL end-block lengths （2 ×10^4 and 4×10^4 g/tool） and blend ratios （75/25, 50/50 and 25/75 W/W） on the stereocomplexation and mechanical properties of the blend films were evaluated. From DSC and WAXD results, the 50/50 blend films had complete stereocomplexation. Phase separation between the scPL and PPG phases was not observed from their SEM images. The tensile stress and elongation at break increased with the sterecomplex crystallinities and PL end-block lengths. The PPG middle-blocks enhanced elongation at break of the scPL films. The results showed that the PL-PPG-PL triblock structures did not affect stereocomplexation of the PLL/PDL block blending. In conclusion, the phase compatibility and flexibility of the scPL films were improved by PPG block copolymerization.展开更多
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 r...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 1×10^(5)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.展开更多
Stereocomplex crystallization in asymmetric diblock copolymers was studied using dynamic Monte Carlo simulations,and the key factor dominating the formation of stereocomplex crystallites(SCs)was uncovered.The asymmetr...Stereocomplex crystallization in asymmetric diblock copolymers was studied using dynamic Monte Carlo simulations,and the key factor dominating the formation of stereocomplex crystallites(SCs)was uncovered.The asymmetric diblock copolymers with higher degree of asymmetry exhibit larger difference between volume fractions of beads of different blocks,and local miscibility between different kinds of beads is lower,leading to lower SC content.To minimize the interference from volume fraction of beads,the SC formation in blends of asymmetric diblock copolymers was also studied.For the cases where the volume fractions of beads of different blocks are the same,similar local miscibility between beads of different blocks and similar SC content was observed.These findings indicate that the volume fraction of beads of different blocks is a key factor controlling the SC formation in the asymmetric diblock copolymers.The SC content can be regulated by adjusting the difference between the contents of beads of different blocks in asymmetric diblock copolymers.展开更多
Classic Avrami model and its modifications have found diverse applications in describing the thermal and phase behaviors of inorganic metals and organic polymers. The direct introduction of classic Avrami equation to ...Classic Avrami model and its modifications have found diverse applications in describing the thermal and phase behaviors of inorganic metals and organic polymers. The direct introduction of classic Avrami equation to offer quantitative analyses of crystallization kinetic parameters for enantiomeric poly（lactic acid） （PLA） blends may, however, lead to contradictory conclusions. As revealed by this study, during the characterization of isothermal melt and cold crystallization for stereocomplex PLA containing equal-weight poly（L-lactic acid） and poly（D-lactic acid）, the kinetic parameters yielded by Avrami equation are not in line with the classic crystallization hypotheses or the direct morphological observations. The underlying mechanisms, to some extent, lie in the generation of stereocomplex crystals （SCs） during the cooling/heating which affects the subsequent crystallization dynamics. The huge gap between the melting enthalpies of 100% crystalline SCs （142 J/g） and homo-crystals （HCs, 93 J/g） is most likely responsible for the confusing kinetic parameters acquired from the deduction of Avrami equation, which is based on the integration of enthalpies as a function of crystallization time. This prompts for great care that the classic Avrami equation is not applicable to accurately describe the crystallization kinetics of stereocomplex PLA, given the generation of SCs prior to crystallization and the coexistence of HCs and SCs during crystallization.展开更多
Blending of poly(levorotatory-lactic acid) (PLLA) and poly(dextrorotatory-lactic acid) (PDLA) produces the stereocomplex crystallites (PLA SC), which present higher melting temperature and mechanical properties than t...Blending of poly(levorotatory-lactic acid) (PLLA) and poly(dextrorotatory-lactic acid) (PDLA) produces the stereocomplex crystallites (PLA SC), which present higher melting temperature and mechanical properties than that of neat PLLA or PDLA. However, in the PLLA/PDLA blends with higher molecular weights, the phase separation occurs and the SC exhibits weak memory after melting, which lead to a small amount of SC together with a large amount of homochiral crystallites (HC) develop during crystallization from the melt. In this study, a small content of graphite oxide was blended with PLLA and PDLA to form ternary blends, and it was exciting to find that the formation of SC was enhanced gradually with the content of graphite oxide. The SC exclusively developed when 2 wt% graphite oxide was incorporated into the PLLA/PDLA, and the crystallinity with ∼50% was received even during fast cooling from the melt (−50 ℃/min). The acceleration formation of SC was speculated due to the interaction between PLA molecular chains and the hydroxyl groups on the surface of graphite oxide and the obstruction of proliferation of graphite oxide.展开更多
基金financially supported by the fund of the Science and Technology Development Plan Project of Jilin Province of China(No.20240304161SF)the Science and Technology Development Plan Project of Jilin Province of China(No.20220203019SF)+1 种基金the Science and Technology Bureau of Changchun City of China(Nos.23SH11,23SH08)the Chinese Science Academy(Changchun Branch)(No.2024SYHZ0038).
文摘Poly(lactic acid)(PLA)is a biodegradable and eco-friendly polymer that is increasingly being incorporated into various applications in contemporary society.However,the limited stability of PLA-based products remains a significant challenge for their broader use in various applications.In this study,poly(L-lactic acid)(PLLA)/poly(D-lactic acid)(PDLA)melt-blown nonwovens were prepared by melt spinning.The structure,thermal properties,thermal stability,biodegradability and crystalline morphology of the melt-blown nonwovens were investigated.DSC and WAXD confirmed the formation of stereocomplex(SC)crystallites in the PLLA matrix.The storage modulus(G′),loss modulus(G″),and complex viscosity(∣η^(*)∣)of the PLLA/PDLA blend increased with an increase in SC crystallite content.The thermal degradation temperatures of PLLA/PDLA melt-blown nonwovens increased with the incorporation of SC crystallites,and the maximum rate of decomposition increased to 385.5℃,thus enhancing the thermal stability.Compared with neat PLLA melt-blown nonwovens,the hydrophobicity of PLLA/PDLA melt-blown nonwovens was improved,and WCA increased to 139.7°.The SC crystallites were more resistant to degradation by proteinase K compared to neat PLLA.However,the degradation rate of PLLA/PDLA melt-blown nonwovens remained at a high level.This work provides an effective strategy to obtain high-performance PLLA melt-blown nonwovens.
基金supported by the Sichuan Science and Technology Program(No.2023ZHCG0050)the China Postdoctoral Science Foundation(No.2023M742883)+2 种基金the Science and Technology Innovation Fund for Basic Scientific Research Operating Expenses of Central Universities(No.2682023CX002)the New Interdisciplinary Cultivation Fund of SWJTU(No.2682022KJ040)SEM characterizations were supported by the Analytical and Testing Center of Southwest Jiaotong University。
文摘Poly(L-lactic acid)(PLLA)has been widely concerned because of its excellent biodegradability and biocompatibility.However,the poor crystallization ability of PLLA during the molding process not only leads to weak mechanical properties but also reduces the processing efficiency,which limits the application of PLLA greatly.Enhancing crystallization ability of PLLA via introducing inorganic nanoparticles usually sacrifices biodegradability or transparency.Here,the microfine fibers with stereocomplex(SC)crystallites were incorporated into PLLA film to tailor the crystallization ability of PLLA as well as the mechanical properties.The results confirmed that the crystallization ability of PLLA matrix under different circumstances could be greatly enhanced by a few amounts of SC crystalline fibers,and synchronously enhanced tensile strength and ductility were also achieved,especially at relatively high temperature.Due to the relatively homogeneous dispersion of SC crystalline fibers and the similar refractive index between components,the PLLA-based film also exhibited high transparency,up to 85%-90%depending on the content of SC crystalline fibers.This work provides guidance for manufacturing transparent PLLA-based packaging materials with good crystallization capability and mechanical properties.
基金financially supported by the National Natural Science Foundation of China(Nos.51673190,51303174,51603204 and 51390484)
文摘A series of host-vip interaction-adjusted polylactide stereocomplex micelles was prepared via the self-assembly of 4-armed poly（ethylene glycol）-block-poly（L-lactide/D-lactide）-cholesterol （4-armed PEG-b-PLLA/PDLA-CHOL） and poly（β-cyclodextrin） （PCD） with the molar ratios of CHOL/β-CD at 1：0.5, 1 ：l, and 1：2 in an aqueous environment. The hydrodynamic diameters of the micelles ranged from 84.1 nm to 107 nm depending on the molar ratio of CHOL/β-CD. It was shown that the micelle with the largest proportion of PCD possessed excellent abilities in drug release, cell internalization as well as proliferation inhibitory effect toward human A549 lung cancer cells. The results demonstrated that the stereocomplex and host-vip interactions-mediated PLA micelles exhibited great potential in sustained drug delivery.
基金the Chinese Academy of scienee and technology service network planning(No.KFJSTS-QYZD-140)a program of Cooperation of Hubei Province and Chinese Academy of Sciences,Innovation team project of Beijing Institute of Science and Technology(No.IG201703N)"13^th five-year"Science and Technology Research Program of the Education Department of Jilin Provinee(No.JJKH20190862KJ).
文摘Sustainable blends of poly(propylene carbonate)(PPC)and stereocomplex polylactide(sc-PLA)were prepared by melt blending equimolar poly(L-lactic acid)(PLLA)and poly(D-lactide acid)(PDLA)with PPC to form sc-PLA crystals in situ in the melt blending process.Differential seanning calorimetry analysis revealed that only sc-PLA,no homo-crystallization of PLLA or PDLA,formed in the PPC matrix as the sc-PLA con tent was more than 10 wt%.Very in triguingly,scan ning electronic microscopy observati on showed that sc-PLA was evenly dispersed in the PPC phase as spherical particles and the sizes of sc-PLA particles did not obviously increase with in creasing sc-PLA con tent.As a con seque nee,the rheological properties of PPC were greatly improved by incorporation of sc-PLA.When the sc-PLA con tent was 20 wt%,a percolati on n etwork structure was formed,and the blends showed solid-like behavior.The sc-PLA particles could reinforce the PPC matrix,especially at a temperature above the glass transition temperature of PPC.Moreover,the Vicat softening temperature of PPC/sc-PLA blends could be increased compared with that of neat PPC.
基金financially supported by the National Natural Science Foundation of China(Nos.5127319851373169+4 种基金510330035130317651321062 and 51403089)863 Program(No.2011AA02A202)from the Ministry of Science and Technology of ChinaInnovative Research Group(No.51321062)
文摘In this study, the poly（L-lactide）/poly（D-lactide） （PLLA/PDLA） blends with different optical purities of PLLA and various molecular weights of PDLA are prepared by solution mixing, and the stereocomplex formation and phase separation behaviors of these blends are investigated. Results reveal that optical purity and molecular weight do not vary the crystal structure of PLA stereocomplex （sc） and homochiral crystallites （hc）. As the optical purity increasing in the blends, the melting temperature of sc （Tsc） and the content of sc （AHsc） increased, while the melting temperature of hc （Thin） hardly changes, although the content ofhc （AHhm） decreased gradually. The Tsc and AHsc are also enhanced as the molecular weight of PDLA reduces, and the AHhm reduces rapidly even though the Thin does not vary apparently. With lower optical purities of PLLA and higher molecular weights of PDLA, three types of crystals form in the blends, i.e., PLA sc, PLLA hc and PDLA hc. As molecular weight decreases and optical purity enhances, the crystal phase decreases to two （sc and PDLA hc）, and one （sc） finally. This investigation indicates that the phase separation behavior between PLLA and PDLA in the PLLA/PDLA blends not only depends on molecular weights, but also relies on the optical purities of polymers.
基金financially supported by the Academic Development Fund of Rajabhat Maha Sarakham University(PhD scholarship for D.Pholharn)the Division of Research Facilitation and Dissemination,Mahasarakham University(2017)
文摘In the present work, poly（propylene glycol） （PPG） was block copolymerized to form polylactide-poly（propylene glycol）-polylactide （PL-PPG-PL） triblock copolymers for preparing flexible stereocomplex PL （scPL） blend films. The scPL blend films were prepared by solution blending of poly（L-lactide）-PPG-poly（L-lactide） （PLL-PPG-PLL） and poly（D-lactide）- PPG-poly（D-lactide） （PDL-PPG-PDL） triblock copolymers before film casting. The influences of PL end-block lengths （2 ×10^4 and 4×10^4 g/tool） and blend ratios （75/25, 50/50 and 25/75 W/W） on the stereocomplexation and mechanical properties of the blend films were evaluated. From DSC and WAXD results, the 50/50 blend films had complete stereocomplexation. Phase separation between the scPL and PPG phases was not observed from their SEM images. The tensile stress and elongation at break increased with the sterecomplex crystallinities and PL end-block lengths. The PPG middle-blocks enhanced elongation at break of the scPL films. The results showed that the PL-PPG-PL triblock structures did not affect stereocomplexation of the PLL/PDL block blending. In conclusion, the phase compatibility and flexibility of the scPL films were improved by PPG block copolymerization.
基金financially supported by the National Natural Science Foundation of China(No.51873129)。
文摘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 1×10^(5)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.
基金supported by the National Natural Science Foundation of China(No.21404050)the Research Foundation of Jiangsu University(No.14JDG059)+2 种基金Hao also thanks the supports from Postdoctoral Science Foundation of China(No.2019M651478)Natural Science Foundation of Jiangsu Province(No.BK20190866)Natural Science Foundation of the Higher Education Institutions of Jiangsu Provinee(No.18KJB150009).
文摘Stereocomplex crystallization in asymmetric diblock copolymers was studied using dynamic Monte Carlo simulations,and the key factor dominating the formation of stereocomplex crystallites(SCs)was uncovered.The asymmetric diblock copolymers with higher degree of asymmetry exhibit larger difference between volume fractions of beads of different blocks,and local miscibility between different kinds of beads is lower,leading to lower SC content.To minimize the interference from volume fraction of beads,the SC formation in blends of asymmetric diblock copolymers was also studied.For the cases where the volume fractions of beads of different blocks are the same,similar local miscibility between beads of different blocks and similar SC content was observed.These findings indicate that the volume fraction of beads of different blocks is a key factor controlling the SC formation in the asymmetric diblock copolymers.The SC content can be regulated by adjusting the difference between the contents of beads of different blocks in asymmetric diblock copolymers.
基金financially supported by the National Natural Science Foundation of China(No.21604016)National Undergraduate Innovation Training Program(No.201610657004)
文摘Classic Avrami model and its modifications have found diverse applications in describing the thermal and phase behaviors of inorganic metals and organic polymers. The direct introduction of classic Avrami equation to offer quantitative analyses of crystallization kinetic parameters for enantiomeric poly（lactic acid） （PLA） blends may, however, lead to contradictory conclusions. As revealed by this study, during the characterization of isothermal melt and cold crystallization for stereocomplex PLA containing equal-weight poly（L-lactic acid） and poly（D-lactic acid）, the kinetic parameters yielded by Avrami equation are not in line with the classic crystallization hypotheses or the direct morphological observations. The underlying mechanisms, to some extent, lie in the generation of stereocomplex crystals （SCs） during the cooling/heating which affects the subsequent crystallization dynamics. The huge gap between the melting enthalpies of 100% crystalline SCs （142 J/g） and homo-crystals （HCs, 93 J/g） is most likely responsible for the confusing kinetic parameters acquired from the deduction of Avrami equation, which is based on the integration of enthalpies as a function of crystallization time. This prompts for great care that the classic Avrami equation is not applicable to accurately describe the crystallization kinetics of stereocomplex PLA, given the generation of SCs prior to crystallization and the coexistence of HCs and SCs during crystallization.
基金financially supported by the National Natural Science Foundation of China (Nos. 51403089 and 21574060)the Major Special Projects of Jiangxi Provincial Department of Science and Technology (No. 20114ABF05100)+5 种基金the Project of Jiangxi Provincial Department of Education (No. GJJ170229)the China Postdoctoral Science Foundation (No. 2019M652282)the Postdoctoral Science Foundation of Jiangxi Province (No. 2018KY37)the Technology Plan Landing Project of Jiangxi Provincial Department of Education (No. GCJ2011-243)the Science Foundation for Excellent Young Scholars of Jiangxi Province (No. 20202ZDB01003)the Science foundation of Jiangxi Province (No. 20202BAB203008)
文摘Blending of poly(levorotatory-lactic acid) (PLLA) and poly(dextrorotatory-lactic acid) (PDLA) produces the stereocomplex crystallites (PLA SC), which present higher melting temperature and mechanical properties than that of neat PLLA or PDLA. However, in the PLLA/PDLA blends with higher molecular weights, the phase separation occurs and the SC exhibits weak memory after melting, which lead to a small amount of SC together with a large amount of homochiral crystallites (HC) develop during crystallization from the melt. In this study, a small content of graphite oxide was blended with PLLA and PDLA to form ternary blends, and it was exciting to find that the formation of SC was enhanced gradually with the content of graphite oxide. The SC exclusively developed when 2 wt% graphite oxide was incorporated into the PLLA/PDLA, and the crystallinity with ∼50% was received even during fast cooling from the melt (−50 ℃/min). The acceleration formation of SC was speculated due to the interaction between PLA molecular chains and the hydroxyl groups on the surface of graphite oxide and the obstruction of proliferation of graphite oxide.
