Chemical upcycling of end-of-life poly(lactide) plastics to lactide,lactate ester and new poly(lactide)has been achieved by using magnesium bis[bis(trimethylsilyl)amide][Mg(HMDS)_(2)]as promoter.Mg(HMDS)2 showed high ...Chemical upcycling of end-of-life poly(lactide) plastics to lactide,lactate ester and new poly(lactide)has been achieved by using magnesium bis[bis(trimethylsilyl)amide][Mg(HMDS)_(2)]as promoter.Mg(HMDS)2 showed high efficiency in L-lactide polymerization and poly(lactide) depolymerization.Mg(HMDS)_(2)/Ph_(2) CHOH catalytic system displayed high ring-opening selectivity and the characteristic of immortal polymerization.Taking advantage of transesterification,depolymerizations of end-oflife poly(lactide) plastics to lactate ester (polymer to value-added chemicals) and lactide (polymer to monomer) were achieved with high yields.Besides,a new“depolymerization-repolymerization”strategy was proposed to directly transform poly(lactide) into new poly(lactide).This work provides a theoretical basis for the design of polymerization and depolymerization catalysts and promotes the development of degradable polymers.展开更多
The effects of the plasticizer poly(ethylene glycol)(PEG)on crystallization properties of equimolar poly(L-lactide)(PLLA)/poly(D-lactide)(PDLA)blends were investigated.Forma-tion of the stereocomplex-type poly(lactide...The effects of the plasticizer poly(ethylene glycol)(PEG)on crystallization properties of equimolar poly(L-lactide)(PLLA)/poly(D-lactide)(PDLA)blends were investigated.Forma-tion of the stereocomplex-type poly(lactide acid)(sc-PLA)crystallites was confirmed by Wide-angle X-ray diffraction(WAXD)and differential scanning calorimetry(DSC)analyses.Sc-PLA crystallites without any homochiral poly(lactide acid)(hc-PLA)formed,as the result of the incorporation of the plasticizer PEG(more than or equal to 10%(wt))at a processing temperature(240℃).More-over,when the Mw of PEG reached 1000 g·mol^(-1),the crystal-lizability of stereocomplex crystallites was the best.Isothermal crystallization kinetics further revealed that PEG could accelerate the crystallization rate of sc-PLA,with the optimum crystallization kinetic parameters being obtained at 10%(wt)PEG.Several crys-tallization kinetics equations were applied to describe the effect of PEG on the crystallization behavior of sc-PLA.The influence of PEG on the spherocrystal morphologies of sc-PLA was also inves-tigated using polarized optical microscopy.展开更多
The crystalline structure and morphology of the PLA crystallized isothermally from the glassy state on highly oriented PE substrates at 130℃ were investigated by means of optical microscopy, AFM and X-ray diffraction...The crystalline structure and morphology of the PLA crystallized isothermally from the glassy state on highly oriented PE substrates at 130℃ were investigated by means of optical microscopy, AFM and X-ray diffraction. The results indicate that the PE substrate influences the crystallization behavior of PLA remarkably, which leads to the growth of PLA crystals on PE substrate always in edge-on form rather than the twisted lamellar crystals from edge-on to flat-on when crystallizing the PLA on glass surface under the same condition. The edge-on PLA lamellae on the PE substrate are preferentially arranged with their long axes in the chain direction of the PE substrate crystals. It is further demonstrated that except for the different crystal orientation, the PE does not influence the crystalline modification and crystallinity of the PLA.展开更多
Poly(lactide acid)(PLA)foams have shown considerable promise as eco-friendly alternatives to nondegradable plastic foams,such as polystyrene(PS)foams.Nevertheless,PLA foam typically suffers from low heat-resistance an...Poly(lactide acid)(PLA)foams have shown considerable promise as eco-friendly alternatives to nondegradable plastic foams,such as polystyrene(PS)foams.Nevertheless,PLA foam typically suffers from low heat-resistance and poor cellular structure stemming from its inherent slow crystallization rate and low melt strength.In this study,a high-performance PLA foam with well-defined cell morphology,exceptional strength and enhanced heat-resistance was successfully fabricated via a core-back microcellular injection molding(MIM)process.Differential scanning calorimetry(DSC)results revealed that the added hydrazine-based nucleating agent(HNA)significantly increased the crystallization temperature and accelerated the crystallization process of PLA.Remarkably,the addition of a 1.5 wt%of HNA led to a significant reduction in PLA’s cell size,from 43.5µm to 2.87µm,and a remarkable increase in cell density,from 1.08×10^(7)cells/cm^(3)to 2.15×10^(10)cells/cm^(3).This enhancement resulted in a final crystallinity of approximately 55.7%for the PLA blend foam,a marked improvement compared to the pure PLA foam.Furthermore,at 1.5 wt%HNA concentration,the tensile strength and tensile toughness of PLA blend foams demonstrated remarkable improvements of 136%and 463%,respectively.Additionally,the Vicat softening temperature of PLA blend foam increased significantly to 134.8°C,whereas the pure PLA foam exhibited only about 59.7℃.These findings underscore the potential for the preparation of lightweight injection-molded PLA foam with enhanced toughness and heat-resistance,which offers a viable approach for the production of high-performance PLA foams suitable for large-scale applications.展开更多
To develop a new generation of absorbable fracture fixation devices with enhanced biocompatibility, the biodegradation mechanism and its influence on the cellular response at the tissue/implant interface of hydroxyapa...To develop a new generation of absorbable fracture fixation devices with enhanced biocompatibility, the biodegradation mechanism and its influence on the cellular response at the tissue/implant interface of hydroxyapatite/ poly DL lactide (HA/PDLLA) composites were investigated in vitro and in vivo.HA/PDLLA rods were immersed in phosphate buffered saline,or implanted in muscle and bony tissue for 52 weeks.Scanning electron microscopic and histological studies were done.The degradation rate was the slowest in vitro,slower in muscle tissue and fast in bone.In vitro, the composites degraded heterogeneously and a hollow structure was formed.In bone,the limited clearing capacity leads to the accumulation of oligomeric debris,which contribute totally to the autocatalytic effect.So,the fastest degradation and intense tissue response were seen.In muscle tissue,oligomeric debris migrated into vicinal fibers over a long distance from the original implant cavity and the tissue reactions were,however, quite moderate.For the same size organic/inorganic composite,the environment where it was placed is the major factor in determining its biodegradation process and cellular reaction.In living tissue,factors such as cells,enzymes and mechanical stress have an obvious influence on the biodegradation and biological process at the tissue/implant interface.The biocompatibility of the HA/PDLLA composites is enhanced with the incorporating of the resorbable HA microparticles.展开更多
Graphene nanoplatelets （GNPs） were used as multifunctional nanofiller to enhance thermal and mechanical properties as well as electrical conductivity of two different biodegradable thermoplastics： poly lactide （PL...Graphene nanoplatelets （GNPs） were used as multifunctional nanofiller to enhance thermal and mechanical properties as well as electrical conductivity of two different biodegradable thermoplastics： poly lactide （PLA） and poly （butylene adipate-co-terephthalate） （PBAT）. Morphological investigations showed different levels of GNP dispersion in the two matrices, and consequently physical properties of the two systems exhibited dissimilar behaviours with GNP incorporation. Crystallinity of PLA, determined from differential scanning calorimetry, was observed to increase markedly with addition of GNPs in contrast to the decrease in crystallinity of PBAT. Isothermal and non-isothermal thermogravimetric analyses also revealed a more significant delay in thermal decomposition of PLA upon addition of GNPs compared to that of PBAT. Furthermore, results showed that increasing GNP content of PLA and PBAT nanocomposites influenced their Young＇s modulus and electrical conductivity in different ways. Modulus of PBAT increased continuously with increasing GNP loading while that of PLA reached a maximum at 9wt% GNPs and then decreased. Moreover, despite the higher conductivity of pure PBAT compared to pure PLA, conductivity of PLA/GNP nanocomposites overtook that of PBATIGNP nanocomposites above a certain GNP concentration. This demonstrated the determining effect of nanoplatelets dispersion state on the matrices properties.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
基金support by the National Natural Science Foundation of China (No. 21901249)Taishan Scholars Program of Shandong Province (No. tsqn201812112)the Scientific Research and Innovation Fund Project of Shandong Energy Research Institute (No. SEI I202004)。
文摘Chemical upcycling of end-of-life poly(lactide) plastics to lactide,lactate ester and new poly(lactide)has been achieved by using magnesium bis[bis(trimethylsilyl)amide][Mg(HMDS)_(2)]as promoter.Mg(HMDS)2 showed high efficiency in L-lactide polymerization and poly(lactide) depolymerization.Mg(HMDS)_(2)/Ph_(2) CHOH catalytic system displayed high ring-opening selectivity and the characteristic of immortal polymerization.Taking advantage of transesterification,depolymerizations of end-oflife poly(lactide) plastics to lactate ester (polymer to value-added chemicals) and lactide (polymer to monomer) were achieved with high yields.Besides,a new“depolymerization-repolymerization”strategy was proposed to directly transform poly(lactide) into new poly(lactide).This work provides a theoretical basis for the design of polymerization and depolymerization catalysts and promotes the development of degradable polymers.
基金Supported by the National Natural Science Foundation of China(51403160)the Opening Project of Hubei Key Laboratory Biomass Fibers and Eco-dyeing&Finishing(STRZ2017009)
文摘The effects of the plasticizer poly(ethylene glycol)(PEG)on crystallization properties of equimolar poly(L-lactide)(PLLA)/poly(D-lactide)(PDLA)blends were investigated.Forma-tion of the stereocomplex-type poly(lactide acid)(sc-PLA)crystallites was confirmed by Wide-angle X-ray diffraction(WAXD)and differential scanning calorimetry(DSC)analyses.Sc-PLA crystallites without any homochiral poly(lactide acid)(hc-PLA)formed,as the result of the incorporation of the plasticizer PEG(more than or equal to 10%(wt))at a processing temperature(240℃).More-over,when the Mw of PEG reached 1000 g·mol^(-1),the crystal-lizability of stereocomplex crystallites was the best.Isothermal crystallization kinetics further revealed that PEG could accelerate the crystallization rate of sc-PLA,with the optimum crystallization kinetic parameters being obtained at 10%(wt)PEG.Several crys-tallization kinetics equations were applied to describe the effect of PEG on the crystallization behavior of sc-PLA.The influence of PEG on the spherocrystal morphologies of sc-PLA was also inves-tigated using polarized optical microscopy.
基金supported by the National Natural Science Foundations of China(Nos.50833006,20634050 and 50973008)the 47~(th) postdoctoral granted financial support from China Postdoctoral Science Foundation (No.20100470191)
文摘The crystalline structure and morphology of the PLA crystallized isothermally from the glassy state on highly oriented PE substrates at 130℃ were investigated by means of optical microscopy, AFM and X-ray diffraction. The results indicate that the PE substrate influences the crystallization behavior of PLA remarkably, which leads to the growth of PLA crystals on PE substrate always in edge-on form rather than the twisted lamellar crystals from edge-on to flat-on when crystallizing the PLA on glass surface under the same condition. The edge-on PLA lamellae on the PE substrate are preferentially arranged with their long axes in the chain direction of the PE substrate crystals. It is further demonstrated that except for the different crystal orientation, the PE does not influence the crystalline modification and crystallinity of the PLA.
基金supported by the National Natural Science Foundation of China(No.52003280)the Zhejiang Provincial Natural Science Foundation of China(No.LQ21B040003)+1 种基金the S&T Innovation 2025 Major Special Programme of Ningbo(No.2021Z052)the Chinese Academy of Sciences Pioneer Hundred Talents Program.
文摘Poly(lactide acid)(PLA)foams have shown considerable promise as eco-friendly alternatives to nondegradable plastic foams,such as polystyrene(PS)foams.Nevertheless,PLA foam typically suffers from low heat-resistance and poor cellular structure stemming from its inherent slow crystallization rate and low melt strength.In this study,a high-performance PLA foam with well-defined cell morphology,exceptional strength and enhanced heat-resistance was successfully fabricated via a core-back microcellular injection molding(MIM)process.Differential scanning calorimetry(DSC)results revealed that the added hydrazine-based nucleating agent(HNA)significantly increased the crystallization temperature and accelerated the crystallization process of PLA.Remarkably,the addition of a 1.5 wt%of HNA led to a significant reduction in PLA’s cell size,from 43.5µm to 2.87µm,and a remarkable increase in cell density,from 1.08×10^(7)cells/cm^(3)to 2.15×10^(10)cells/cm^(3).This enhancement resulted in a final crystallinity of approximately 55.7%for the PLA blend foam,a marked improvement compared to the pure PLA foam.Furthermore,at 1.5 wt%HNA concentration,the tensile strength and tensile toughness of PLA blend foams demonstrated remarkable improvements of 136%and 463%,respectively.Additionally,the Vicat softening temperature of PLA blend foam increased significantly to 134.8°C,whereas the pure PLA foam exhibited only about 59.7℃.These findings underscore the potential for the preparation of lightweight injection-molded PLA foam with enhanced toughness and heat-resistance,which offers a viable approach for the production of high-performance PLA foams suitable for large-scale applications.
文摘To develop a new generation of absorbable fracture fixation devices with enhanced biocompatibility, the biodegradation mechanism and its influence on the cellular response at the tissue/implant interface of hydroxyapatite/ poly DL lactide (HA/PDLLA) composites were investigated in vitro and in vivo.HA/PDLLA rods were immersed in phosphate buffered saline,or implanted in muscle and bony tissue for 52 weeks.Scanning electron microscopic and histological studies were done.The degradation rate was the slowest in vitro,slower in muscle tissue and fast in bone.In vitro, the composites degraded heterogeneously and a hollow structure was formed.In bone,the limited clearing capacity leads to the accumulation of oligomeric debris,which contribute totally to the autocatalytic effect.So,the fastest degradation and intense tissue response were seen.In muscle tissue,oligomeric debris migrated into vicinal fibers over a long distance from the original implant cavity and the tissue reactions were,however, quite moderate.For the same size organic/inorganic composite,the environment where it was placed is the major factor in determining its biodegradation process and cellular reaction.In living tissue,factors such as cells,enzymes and mechanical stress have an obvious influence on the biodegradation and biological process at the tissue/implant interface.The biocompatibility of the HA/PDLLA composites is enhanced with the incorporating of the resorbable HA microparticles.
基金the support received from the Australian Government through a Research Training Program(RTP)Scholarshipthe support received from the School of Engineering,RMIT Universitythe support received from the Australian Research Council(ARC)Research Hub for Future Fibres(IH140100018)funded by the Australian Government
文摘Graphene nanoplatelets （GNPs） were used as multifunctional nanofiller to enhance thermal and mechanical properties as well as electrical conductivity of two different biodegradable thermoplastics： poly lactide （PLA） and poly （butylene adipate-co-terephthalate） （PBAT）. Morphological investigations showed different levels of GNP dispersion in the two matrices, and consequently physical properties of the two systems exhibited dissimilar behaviours with GNP incorporation. Crystallinity of PLA, determined from differential scanning calorimetry, was observed to increase markedly with addition of GNPs in contrast to the decrease in crystallinity of PBAT. Isothermal and non-isothermal thermogravimetric analyses also revealed a more significant delay in thermal decomposition of PLA upon addition of GNPs compared to that of PBAT. Furthermore, results showed that increasing GNP content of PLA and PBAT nanocomposites influenced their Young＇s modulus and electrical conductivity in different ways. Modulus of PBAT increased continuously with increasing GNP loading while that of PLA reached a maximum at 9wt% GNPs and then decreased. Moreover, despite the higher conductivity of pure PBAT compared to pure PLA, conductivity of PLA/GNP nanocomposites overtook that of PBATIGNP nanocomposites above a certain GNP concentration. This demonstrated the determining effect of nanoplatelets dispersion state on the matrices properties.
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.
