Efficient and selective upcycling of waste polylactic acid into acetate using nickel selenide

The conversion of waste polylactic acid(PLA)plastics into high-value-added chemicals through electrochemical methods is a promising and sustainable approach.However,developing efficient and highly selective catalysts for lactic acid oxidation reaction(LAOR)and understanding the reaction process are challenging.Here,we report the electrooxidation of waste PLA to acetate at a high current density of 100 mA cm-2 with high Faraday efficiency(~95%)and excellent stability(>100 h)over a nickel selenide nanosheet catalyst.In addition,a total Faraday efficiency of up to 190%was achieved for carboxylic acids,including acetic acid and formic acid,by coupling with the cathodic CO_(2) reduction reaction.In situ experimental results and theoretical simulations revealed that the catalytic activity center of LAOR was dynamically formed NiOOH species,and the surface-adsorbed SeO_(x) species accelerated the formation of Ni~(3+)species,thus promoting catalytic activity.The mechanism of lactic acid electrooxidation was further elucidated.Lactic acid was dehydrogenated to produce pyruvate first and then formed CH_3CO due to preferential C-C bond cleavage,resulting in the presence of acetate.This work demonstrated a sustainable method for recycling waste PLA and CO_(2) into high-value-added products.

Synergism of Zinc Oxide/Organoclay-Loaded Poly(lactic acid) Hybrid Nanocomposite Plasticized by Triacetin for Sustainable Active Food Packaging

The synergistic effect of organoclay(OC)and zinc oxide(ZnO)nanoparticles on the crucial properties of poly(lactic acid)(PLA)nanocompositefilms was systematically investigated herein.After their incorporation into PLA via the solvent casting technique,the water vapor barrier property of the PLA/OC/ZnOfilm improved by a maximum of 86%compared to the neat PLAfilm without the deterioration of Young’s modulus or the tensile strength.Moreover,thefilm’s self-antibacterial activity against foodborne pathogens,including gram-negative(Escherichia coli,E.coli)and gram-positive(Staphylococcus aureus,S.aureus)bacteria,was enhanced by a max-imum of approximately 98–99%compared to the neat PLAfilm.Furthermore,SEM images revealed the homo-geneous dispersion of both nano-fillers in the PLA matrix.However,the thermal stability of thefilm decreased slightly after the addition of the OC and ZnO.Thefilm exhibited notable light barrier properties in the UV-Vis range.Moreover,the incorporation of a suitable biodegradable plasticizer significantly decreased the Tg and notably enhanced theflexibility of the nanocompositefilm by increasing the elongation at break approxi-mately 1.5-fold compared to that of the neat PLAfilm.This contributes to its feasibility as an active food packa-ging material.

Corrosion resistance of Zn-AI layered double hydroxide/ poly（lactic acid） composite coating on magnesium alloy AZ31

A Zn-AI layered double hydroxide （ZnAI-LDH） coating consisted of uniform hexagonal nano-plates was firstly synthesized by co-precipitation and hydrothermal treatment on the AZ31 alloy, and then a poly（lactic acid） （PLA） coating was sealed on the top layer of the ZnAI-LDH coating using vacuum freeze-drying. The characteristics of the ZnAI-LDH/PLA composite coatings were investigated by means of XRD, SEM, FTIR and EDS. The corrosion resistance of the coatings was assessed by potentiodynamic polarization and electrochemical impedance spectroscopy （EIS）. The results showed that the ZnAI-LDH coating contained a compact inner layer and a porous outer layer, and the PLA coating with a strong adhesion to the porous outer layer can prolong the service life of the ZnAI-LDH coating. The excellent corrosion resistance of this composite coating can be attributable to its barrier function, ion-exchange and self-healing ability.

Mechanical and Morphological Properties of Wood Plastic Biocomposites Prepared from Toughened Poly（lactic acid） and Rubber Wood Sawdust （Hevea brasiliensis）

The present research aims to utilize the acrylic Core-Shell Rubber （CSR） particles to reduce the brittleness in Wood Plastic Composites （WPC） prepared from poly（lactic acid） （PLA） and rubber wood sawdust （Hevea brasiliensis）. Experimental works consisted of two major parts. The first part concentrated on toughening PLA by using CSR particles. Mechanical tests revealed that PLA had become tougher with a more than five times increment in the impact strength when the CSR was added at only 5 wt%. The modified PLA was less stiff with the significant reductions of both elastic and flexural moduli and strengths. The second part focused on producing WPC from the toughened PLA and rubber wood sawdust. The tensile moduli and the strengths of the PLA composites increased with rubber wood content. The composites turned out to be more brittle with reductions of both the impact strength and the tensile elongation at break at all the sawdust contents. Toughening PLA/wood flour with 5 wt% CSR improved both the impact strength and the tensile elongation at break. The toughness enhancement was also depicted by the plastic deformation observed on the surfaces of fractured PLA/CSR/wood sawdust composites.

Effect of DOPO-containing Flame Retardants on Poly（lactic acid）： Non-flammability, Mechanical Properties and Thermal Behaviors

The flame retardancies of three kinds of 9,10-dihydro-9-oxa-10-phosphaphenan-threne 10-oxide（DOPO）- containing flame retardant（A1, A2, A3）/poly（lactic acid）（PLA） composites[PA-n/（Ax-y）, n= 1--12; x= l, 2, 3, denoting three kinds of flame retardants; y= 10%, 20%, 30%, 40%, denoting the mass fraction of Ax] were greatly enhanced by melt blending of flame retardant Ax with PLA, including twin-screw extrusion and injection-molding processes. With only 10%（mass fraction） of Ax added to PLA, good flame retardancy with limiting oxygen index（LOI） values of more than 33% was achieved. As the Ax mass fraction was further increased to 20%, PA-n/（Ax-20%） composites showed much better flame retardancy（LOI~〉35% and UL-94 V-0 rating）. Moreover, the thermal degradation behaviors and mechanical properties of PA-n/（Ax-y） composites were investigated via thermogravimetric analysis（TGA）, differen- tial thermal analysis（DTA）, tensile testing, notched impact-bar testing, and dynamic mechanical analysis（DMA）. TGA results show that PA-n/（Ax-y） composites have slower rate of mass loss and much higher char yield, compared to neat PLA. With the addition of Ax to PLA, the DTA and DMA results indicate slight variations in glass transition tcmpe- ratures（Tg） of PA-n/（Ax-y） composites. Based on TGA results under nonisothermal conditions, the thermal degrada- tion kinetics of PA-n/（Ax-y） composites were studied by KAssinger＇s and Ozawa＇s methods. These thermal degrada- tion dynamic analyses show lower activation energies（EK or Eo） for PA-n/（Ax-y） composites, corresponding to higher mass fractions of Ax（from 10% to 40%）. The PA-n/（Ax-y） composites with good flame retardancy and good mecha- nical properties obtained in this study could be potential candidates for fire- and heat-resistant applications in auto- motive engineering and building fields with more safety and excellent performance.

Blends of Poly(lactic acid) with Thermoplastic Acetylated Starch

Blends of poly（lactic acid）（PLA） and thermoplastic acetylated starch（ATPS） were prepared by means of the melt mixing method. The results show that PLA and ATPS were partially miscible, which was confirmed with the measurement of Tg by dynamic mechanical analysis（DMA） and differrential scanning calorimetry（DSC）. The mechanical and thermal properties of the blends were improved. With increasing the ATPS content, the elongation at break and impact strength were increased. The elongation at break increased from 5% of neat PLA to 25% of the blend PLA/ATPS40. It was found that the cold crystallization behavior of PLA changed evidently by addition of ATPS. The cold crystallization temperature（Tcc） of each of PLA/ATPS blends was found to shift to a lower temperature and the width of exothermic peak became narrow compared with that of neat PLA. The thermogravimetry analysis（TGA） results showed that the peak of derivative weight for ATPS moved to higher temperature with increasing PLA content in PLA/ATPS blends. It can be concluded that PLA could increase the thermal stability of ATPS. The rheological measurement reveals the melt elasticity and viscosity of the blends decreased with the increased concentration of ATPS, which was favorable to the processing properties of PLA.

Comparison of morphological and functional outcomes of mouse sciatic nerve repair with three biodegradable polymer conduits containing poly (lactic acid)

Poly（lactic acid）（PLA）-containing nerve guidance conduits（NGCs） are currently being investigated for nerve repair as an alternative to autograft, which leads to permanent functional impairment in the territory innervated by the removed nerve. Combination of polymers modifies the physical properties of the conduits, altering their nerve-guidance properties. Conduits made from PLA-only or combined with other polymers have been used successfully for nerve repair, but their efficiency has not been compared. We compared the morphological and functional outcomes of peripheral nerve repair by using NGCs made of poly（lactic acid） and combined or not with polycaprolactone（PLA/PCL） or polyvinylpyrrolidone（PLA/PVP）. To assess the functional recovery, we employed a mechanical hyperalgesia analysis, sciatic functional index（SFI）, and electroneuromyography. The mechanical hyperalgesia analysis showed that the PLA group improved more rapidly than the PLA/PVP and PLA/PCL groups; similarly, in the electroneuromyography assay, the PLA group exhibited higher amplitude than the PLA/PCL and PLA/PVP groups. However, the SFI improvement rates did not differ among the groups. Morphologically, the PLA group showed more vascularization, while the nerve fiber regeneration did not differ among the groups. In conclusion, the PLA-only conduits were superior to the other NGCs tested for nerve repair.

Melt Synthesis and Characterization of Poly(L-lactic Acid) Chain Linked by Multifunctional Epoxy Compound

High molecular weight（Mw） poly（L-lactic acid）s（PLLAs） were synthesized using multifunctional epoxy compound（Joncryl-ADR4370） as chain extender. The products were characterized by gel permeation chromatography（GPC） and spectroscopy（1HNMR and FTIR）. The results indicated that the Mw of PLLA increased with the increasing of the ratio of epoxy compound and the extending of reaction time. The highest Mw of PLLA reached 360 000 g/mol when the ratio of epoxy compound was 1.5 wt%. However, the reactants turned to cross-linking when the ratio of epoxy compound was over 1.5 wt%. Differential scanning calorimetry（DSC） measurements demonstrated that the glass transition（Tg） and melting temperatures（Tm） of products increased slightly as the increase of the molecular weight. Analysis of the hydrolytic degradation in vitro showed that the branched PLLA possessed the quicker degradability than that of the linear PLLA.

A novel artificial nerve graft for repairing longdistance sciatic nerve defects:a self-assembling peptide nanofiber scaffold-containing poly (lactic-co-glycolic acid) conduit

In this study, we developed a novel artificial nerve graft termed self-assembling peptide nanofiber scaffold （SAPNS）-containing poly（lactic-co-glycolic acid） （PLGA） conduit （SPC） and used it to bridge a 10-mm-long sciatic nerve defect in the rat. Retrograde tracing, behavioral testing and histomorphometric analyses showed that compared with the empty PLGA conduit implantation group, the SPC implantation group had a larger number of growing and extending axons, a markedly increased diameter of regenerated axons and a greater thickness of the myelin sheath in the conduit. Furthermore, there was an increase in the size of the neuromuscular junction and myofiber diameter in the target muscle. These findings suggest that the novel artificial SPC nerve graft can promote axonal regeneration and remyelination in the transected peripheral nerve and can be used for repairing peripheral nerve injury.

Dorsal root ganglion-derived Schwann cells combined with poly(lactic-co-glycolic acid)/chitosan conduits for the repair of sciatic nerve defects in rats

Schwann cells, nerve regeneration promoters in peripheral nerve tissue engineering, can be used to repair both the peripheral and central nervous systems. However, isolation and puriifcation of Schwann cells are complicated by contamination with ifbroblasts. Current reported measures are mainly limited by either high cost or complicated procedures with low cell yields or purity. In this study, we collected dorsal root ganglia from neonatal rats from which we obtained highly puriifed Schwann cells using serum-free melanocyte culture medium. The purity of Schwann cells （〉95%） using our method was higher than that using standard medium containing fetal bovine serum. The obtained Schwann cells were implanted into poly（lactic-co-glycolic acid）/chi-tosan conduits to repair 10-mm sciatic nerve defects in rats. Results showed that axonal diameter and area were signiifcantly increased and motor functions were obviously improved in the rat sciatic nerve tissue. Experimental ifndings suggest that serum-free melanocyte culture medium is conducive to purify Schwann cells and poly（lactic-co-glycolic acid）/chitosan nerve conduits combined with Schwann cells contribute to restore sciatic nerve defects.

Electrospun and woven silk fibroin/poly(lactic-coglycolic acid) nerve guidance conduits for repairing peripheral nerve injury

We have designed a novel nerve guidance conduit（NGC） made from silk fibroin and poly（lactic-co-glycolic acid） through electrospinning and weaving（ESP-NGCs）. Several physical and biological properties of the ESP-NGCs were assessed in order to evaluate their biocompatibility. The physical properties, including thickness, tensile stiffness, infrared spectroscopy, porosity, and water absorption were determined in vitro. To assess the biological properties, Schwann cells were cultured in ESP-NGC extracts and were assessed by morphological observation, the MTT assay, and immunohistochemistry. In addition, ESP-NGCs were subcutaneously implanted in the backs of rabbits to evaluate their biocompatibility in vivo. The results showed that ESP-NGCs have high porosity, strong hydrophilicity, and strong tensile stiffness. Schwann cells cultured in the ESP-NGC extract fluids showed no significant differences compared to control cells in their morphology or viability. Histological evaluation of the ESP-NGCs implanted in vivo indicated a mild inflammatory reaction and high biocompatibility. Together, these data suggest that these novel ESP-NGCs are biocompatible, and may thus provide a reliable scaffold for peripheral nerve repair in clinical application.

Design,synthesis and characterization of novel biodegradable macrodiols based on poly(DL-lactic acid) and poly(p-dioxanone)

Integrating poly（lactic acid） （PLA）, glycolic acid （GA） and ethylene glycol （EG） will hopefully result in a novel copolymer that combines such advantages as fastened and controllable release rate and improved flexibility together with good biocompatibility. In this study, p-dioxanone （PDO） was employed to copolymerize with DL-lactide （LA） via ring-opening melt polymerization using Sn（Oct）2 as an initiator and ethylene glycol as a co-initiator. The obtained degradable macrodiols （HO-P（LA-co-PDO）-OH） were just such a copolymer consisting of PLA, GA and EG. 1HNMR was employed to characterize the copolymers, and the effect of PDO/LA molar ratios in the feedstock on the molecular weights of HO-P（LA-co-PDO）-OH was investigated by means of endhydroxyl analysis, 1H NMR or GPC-MALLs. The results confirmed the successful synthesis of HO-P（LA-co-PDO）-OH and revealed that one end-hydroxyl of the micarodiols was donated by LA or PDO and the other one by the co-initiator EG. In addition, the molecular weights of HO-P（LA-co-PDO）-OH increased with decreasing PDO/LA ratios.

Poly(lactic-co-glycolic acid) conduit for repair of injured sciatic nerve A mechanical analysis

Tensile stress and tensile strain directly affect the quality of nerve regeneration after bridging nerve defects by poly（lactic-co-glycolic acid） conduit transplantation and autogenous nerve grafting for sciatic nerve injury. This study collected the sciatic nerve from the gluteus maximus muscle from fresh human cadaver, and established 10-mm-long sciatic nerve injury models by removing the ischium, following which poly（lactic-co-glycolic acid） conduits or autogenous nerve grafts were transplanted. Scanning electron microscopy revealed that the axon and myelin sheath were torn, and the vessels of basilar membrane were obstructed in the poly（lactic-co-glycolic acid） conduit-repaired sciatic nerve following tensile testing. There were no significant differences in tensile tests with autogenous nerve graft-repaired sciatic nerve. Following poly（lactic-co-glycolic acid） conduit transplantation for sciatic nerve repair, tensile test results suggest that maximum tensile load, maximum stress, elastic limit load and elastic limit stress increased compared with autogenous nerve grafts, but elastic limit strain and maximum strain decreased. Moreover, the tendencies of stress-strain curves of sciatic nerves were similar after transplantation of poly（lactic-co-glycolic acid） conduits or autogenous nerve grafts. Results showed that after transplantation in vitro for sciatic nerve injury, poly（lactic-co-glycolic acid） conduits exhibited good intensity, elasticity and plasticity, indicating that poly（lactic-co-glycolic acid） conduits are suitable for sciatic nerve injury repair.

A porous poly(lactic-co-glycolic acid) scaffold induces innervation in a rabbit model of disc degeneration following annular injury

BACKGROUND： A degradable poly（lactic-co-glycolic acid） （PLGA） scaffold has been used to construct a degradable porous scaffold. This template can simulate the in vivo microenvironment and promote tissue formation. OBJECTIVE： To observe the histopathological changes during degeneration and regeneration of the intervertebral disc, and to analyze the effects of a PLGA scaffold on nerve fiber ingrowth into the lesion in vivo. DESIGN, TIME AND SETTING： A randomized, controlled animal experiment was performed at the Orthopaedic Laboratory, Clinic Medical Research Institution, Sir Run Run Shaw Hospital, Zhejiang University, from December 2007 to July 2008. MATERIALS： PLGA （China Textile Academy）; growth-associated protein-43 （Life-span, USA）; and protein gene product 9.5 antibody （AbD, United Kingdom） were used in this study. METHODS： Three consecutive segments of the intervertebral disc of thirty-two healthy adult male New Zealand rabbits were exposed, comprising L3-4, L4-5 and L5-6. Experimental intervertebral disc （L4-5 and L5-6） models were established by two different methods. In the test （trephine ＋ scaffold） group, a 5-mm deep hole was drilled into the annulus fibrosus using a 3-mm diameter trephine, and the PLGA scaffold was implanted into the hole. In the acupuncture group, the remaining experimental intervertebral disc annulus fibrosus was damaged using a 16G needle at a depth of 5 mm. The L3-4 disc served as a control. MAIN OUTCOME MEASURES： Intervertebral disc degeneration was assessed using radiography, magnetic resonance imaging, and histological examination at various time points post-surgery. Nerve fiber ingrowth into the degenerated intervertebral disc was observed using immunohistochemical staining for growth-associated protein-43 and protein gene product 9.5. RESULTS： Compared with the normal controls, the heights of the damaged intervertebral discs were decreased, and T2 signal intensity was decreased in the test and acupuncture groups 2 weeks post-surgery. Intervertebral disc degeneration was faster in the test group than in the acupuncture group. PLGA was coated with newly formed tissue, gradually degraded, and absorbed, and could induce tissue ingrowth deep into the annulus fibrosus. Results of immunohistochemical staining showed that nerve fibers were distributed in newly formed tissue in the test group, and in the superficial layer or surrounding scar tissue in the acupuncture group. CONCLUSION： A porous PLGA scaffold provides an important biological channel to induce nerve fiber ingrowth deep into the degenerated intervertebral disc.

Viscoelasticity of repaired sciatic nerve by poly(lactic-co-glycolic acid) tubes

Medical-grade synthetic poly（lactic-co-glycolic acid） polymer can be used as a biomaterial for nerve repair because of its good biocompatibility, biodegradability and adjustable degradation rate. The stress relaxation and creep properties of peripheral nerve can be greatly improved by repair with poly（lactic-co-glycolic acid） tubes. ＂Fen sciatic nerve specimens were harvested from fresh corpses within 24 hours of death, and were prepared into sciatic nerve injury models by creating a 10 mm defect in each specimen. Defects were repaired by anastomosis with nerve autografts and poly（lactic-co-glycolic acid） tubes. Stress relaxation and creep testing showed that at 7 200 seconds the sciatic nerve anastomosed by poly（lactic-co-glycolic acid） tubes exhibited a greater decrease in stress and increase in strain than those anastomosed by nerve autografts. These findings suggest that poly（lactic-co-glycolic acid） exhibits good viscoelasticity to meet the biomechanical require- ments for a biomaterial used to repair sciatic nerve injury.

Preparation and properties of short natural fiber reinforced poly(lactic acid) composites

The natural fiber/poly(lactic acid) (PLA) composites were prepared with ramie and jute short fiber as reinforcement and PLA as matrix. The mechanical and thermal properties of the composites were investigated. The results show that the properties of the composites are better than those of plain PLA. When the content of the fiber is 30%, the composites can get the best mechanical properties. The dynamic mechanical analysis results show that the storage moduli of the PLA/ramie and PLA/jute composites increase with respect to the plain PLA. The Vicat softening temperature of the composites is greatly higher than that of PLA. The results of thermogravimetric analysis show that adding fiber to the PLA matrix can improve the degradation temperature of PLA.

Preparation and phase change performance of Na_2HPO_4·12H_2O@poly(lactic acid) capsules for thermal energy storage

Micro-encapsulated phase-change materials(micro PCMs) with Na_2 HPO_4·12 H_2 O encapsulated in poly(lactic acid)(PLA) shell were prepared by a solvent evaporation–precipitation method that involves the use of a coaxial needle. The effects of PLA concentration, stirring speed, injection rate of core and shell solutions, and polyvinyl alcohol(PVA) concentration on phase change properties were investigated. The thermal properties of microP CMs were characterized by differential scanning calorimetry(DSC). The capsules prepared under the optimal conditions are about 2 mm in diameter and show a latent heat of up to 122.2 J·g^(-1).

Morphological, Mechanical and Thermal Properties of Poly(lactic acid)(PLA)/Cellulose Nanofibrils(CNF) Composites Nanofiber for Tissue Engineering

Composite nanofiber membranes based on biodegradable poly(lactic acid)(PLA) and cellulose nanofibrils(CNF) were produced via electrospinning. The influence of CNF content on the morphology, thermal properties, and mechanical properties of PLA/CNF composite nanofiber membranes were characterized by field scanning electron microscopy(FE-SEM), differential scanning calorimetry(DSC), thermogravimetric analysis(TGA), and dynamic mechanical analysis(DMA), respectively. The results show that the PLA/CNF composite nanofibers with smooth, free-bead surface can be successfully fabricated with various CNF contents. The introduction of CNF is an effective approach to improve the crystalline ability, thermal stability and mechanical properties for PLA/CNF composite fibers. The Young's moduli and tensile strength of the PLA/CNF composite nanofiber reach 106.6 MPa and 2.7 MPa when the CNF content is 3%, respectively, which are one times higher and 1.5 times than those of pure PLA nanofiber. Additionally, the water contact angle of PLA/CNF composite nanofiber membranes decreases with the increase of the CNF loading, resulting in the enhancement of their hydrophilicity.