Biodegradable reactive compatibilizers for efficient in-situ compatibilization of poly (lactic acid)/poly (butylene adipate-terephthalate) blends.

The wide application of fully biodegradable polylactic acid/polybutylene terephthalate (PLA/PBAT) blends in environmentally friendly packaging were limited because of poor compatibility. Normal compatibilizers suffer from poor thermal stability and non-biodegradability. In this work, epoxy copolymer (MDOG) with different molecular structures were made of 2-methylene-1, 3-dioxoheptane, and glycidyl methacrylate as raw materials by free radical copolymerization. MDOG copolymers have good biodegradability and a high thermal decomposition temperature of 361 °C. The chemical reaction of the epoxy groups in MDOG with PLA and PBAT during the melting reaction improved the interfacial bonding by decreasing the particle size of PBAT. Compared to the PLA/PBAT blends, the tensile strength and fracture toughness of PLA/PBAT/MDOG blends were enhanced to 34.6 MPa and 115.8 MJ/m3, which are 25 % and 81 % higher, respectively. As a result, this work offers new methods for developing thermally stable and biodegradable compatibilizers, which will hopefully promote the development of packaging industry.

Highly toughened poly (lactic acid)/poly (butylene adipate-terephthalate) blends in-situ compatibilized by MMA-co-GMA copolymers with different epoxy group content.

Poor compatibility limits the wide application of biodegradable poly (lactic acid)/poly (butylene adipate-terephthalate) (PLA/PBAT) blends in packaging industry. How to prepare compatibilizers with high efficiency and low cost by simple methods is a challenge. In this work, methyl methacrylate-co-glycidyl methacrylate (MG) copolymer with different epoxy group content are synthesized as reactive compatibilizers to resolve this issue. The effects of glycidyl methacrylate and MG contents on phase morphology and physical properties of the PLA/PBAT blends are systematically investigated. During melt blending, MG migrates to the phase interface, and then grafts with PBAT to form PLA-g-MG-g-PBAT terpolymers. When the molar ratio of MMA and GMA in MG is 3:1, the reaction activity of MG with PBAT is the highest and the compatibilization effect is the best. When the M3G1 content is 1 wt%, the tensile strength and the fracture toughness are increased to 37. 1 MPa and 120 MJ/m3, which increase by 34 % and 87 %, respectively. The size of PBAT phase decreases from 3.7 µm to 0.91 µm. Therefore, this work provides a low-cost and simple method to prepare the compatibilizers with high efficiency for the PLA/PBAT blend, and provides a new basis for the design of epoxy compatibilizers.

Enhanced crystallization, heat resistance and transparency of poly(lactic acid) with self-assembling bis-amide nucleator.

The application of poly(lactic acid) (PLA) is limited by its low crystallization rate. Conventional methods to increase crystallization rate usually result in a significant loss of transparency. In this work, a bundled bis-amide organic compound N'-(3-(hydrazinyloxy)benzoyl)-1-naphthohydrazide (HBNA) was used as a nucleator to prepare PLA/HBNA blends with enhanced crystallization, heat resistance and transparency. HBNA dissolves in PLA matrix at high temperature and self-assembles into bundle microcrystals by intermolecular hydrogen bonding at a lower temperature, which induces PLA to form ample spherulites and "shish-kebab-like" structure rapidly. The effects of HBNA assembling behavior and nucleation activity on the PLA properties and the corresponding mechanism are systematically investigated. As a result, the crystallization temperature of PLA increased from 90 °C to 123 °C by adding as low as 0.75 wt% of HBNA, and the half-crystallization time (t1/2) at 135 °C decreased from 31.0 min to 1.5 min. More importantly, the PLA/HBNA maintains good transparency (transmittance > 75 % and haze is ca. 27 %) due to the decreased crystal size, even though the crystallinity of PLA is increased to 40 %, which also led to good heat resistance. The present work is expected to expand the application of PLA in packaging and other fields.

Enhanced flame retardancy and toughness of eco-friendly polyhydroxyalkanoate/bentonite composites based on in situ intercalation of P-N-containing hyperbranched macromolecules.

Polyhydroxyalkanoates (PHA) is a biodegradable polyester, and its application range is limited by the poor flame retardancy and low modulus. Bentonite (BNT) as a green inorganic filler can improve the modulus and flame retardancy of PHA to a certain extent. An in situ polymerization method was designed to intercalate P-N-containing hyperbranched macromolecules (HBM) among BNT layers (HBM-B) and to improve the flame retardancy while improving the dispersion of BNT in the PHA matrix. The layer spacing of BNT was increased from 1.2 nm to 4.5 nm. The effect law of the joint action of in situ intercalation of BNT and the HBM on flame retardancy and mechanical properties of PHA was systematically studied. The HBM-B showed stronger flame retardancy when the mass ratio of HBM to BNT was 75/25. The limiting oxygen index (LOI) of the PHA/HBM-B composite was increased to 27.6 % while maintaining good toughness. Compared to the physical blend of HBM and BNT (HBM/B), the elongation at break of PHA/HBM-B25 composites can be increased by up to 10 times. When the content of HBM-B is up to 15 wt%, the LOI of PHA-Based composites can reach 29.6 % and the UL-94 rating reaches V-0, which meets the standard of flame-retardant material. Therefore, the present work is expected to expand the application of PHA-based composites in the field of flame retardancy.

A Quantitative Study on Branching Density Dependent Behavior of Polylactide Melt Strength.

Polymer melt strength (MS) is strongly correlated with its molecular structure, while their relationship is not very clear yet. In this work, designable long-chain branched polylactide (LCB-PLA) is prepared in situ by using a tailor-made (methyl methacrylate)-co-(glycidyl methacrylate) copolymer (MG) with accurate number of reactive sites. A new concept of branching density (φ) in the LCB-PLA system is defined to quantitively study their relationship. Importantly, a critical point of φc  = 5.5 mol/104  mol C is revealed for the first time, below which the zero-shear viscosity (η0 ) corresponding to MS increases slowly with a slope of Δη0 /Δφ = 1400, while it increases sharply above this critical point due to entanglement of neighboring LCB-PLA chains. Consequently, the MS of PLA increased by >100 times by optimizing the LCB structures while maintaining processibility. Therefore, this work provides a deeper understanding and feasible route in quantitative design of polymers with high(er) melt strength for some specialty applications.

Enhanced crystallization and storage stability of mechanical properties of poly(hydroxyalkanoate)s in the presence of hydrazide compounds with different configurations.

Slow crystallization rates and poor storage stability of mechanical properties limit the widespread use of biosynthesized poly(hydroxyalkanoate)s (PHA). Hydrazide compounds (HCn) with a formula of C6H5CONHNHCO(CH2)nCONHNHCOC6H5 (n = 4 and 8) were used as PHA nucleating agents to improve the crystallization and mechanical properties. The effects of HCn structure and self-assembly on the crystallization kinetics and nucleation efficiency of PHA were systematically investigated. Both HCns can be dissolved in the PHA matrix at high temperatures and then self-assemble into rod-like structures to induce crystallization of PHA. The nucleation efficiency of HC8 is much better than that of HC4 at low subcooling. With only 0.75 wt% HC8, the crystallization half-life time t1/2 of PHA at 100 °C decreased by 91 % and the degree of crystallinity increased to 38.2 % with a large number of tiny nuclei. Moreover, storage stability of mechanical properties of PHA was greatly improved due to the better crystallization ability. Therefore, this work provides a basis for the design of high-efficiency nucleating agents for PHA, which is expected to improve the mechanical properties and expand the application fields of PHA.

Crystallization of microbial polyhydroxyalkanoates: A review.

Polyhydroxyalkanoates (PHAs), produced by the microbial fermentation, is a promising green polymer and has attracted much attention due to its excellent biocompatibility, complete biodegradability, and non-cytotoxicity. The physical properties of PHAs are closely related to their chemical and crystalline structure. Therefore, deep understanding and regulating the structure and crystallization of PHAs are the key factors to improve the performance of PHAs. This review first provides a brief overview of the development history, chemical structure, and basic properties of PHAs. Then, the crystal structure, crystal morphology, kinetics theories and crystallization behavior of nucleation-induced PHAs are systematically summarized to provide a theoretical foundation for improving PHAs crystallization rate and physical properties. In the end, the outlook on the crystallization and application prospects of PHAs is also addressed.

Highly dispersed RuO2-biomass carbon composite made by immobilization of ruthenium and dissolution of coconut meat with octyl ammonium salicylate ionic liquid for high performance flexible supercapacitor.

Poor dispersion of metal oxide-biomass carbon composite limits its further improvement in electrochemical properties. The study reports synthesis of highly dispersed RuO2-biomass carbon nanocomposite (HD-RuO2-BC). Octyl ammonium salicylate ionic liquid was combined with Ru3+ ion to form Ru-based ionic liquid. Followed by addition of coconut meat, microwave treatment to form homogeneous solution, thermal reduction in N2 and oxidation in air in sequence. The resulting HD-RuO2-BC shows three-dimensional architecture and high Ru loading of 9.2%. RuO2 nanoparticles of 6.2 nm were uniformly dispersed in biomass carbon sheets. Excellent dispersion and small size of RuO2 nanoparticles achieve to a significant synergy between RuO2 and biomass carbon. HD-RuO2-BC electrode gives high capacitance of 907.7 F g-1 at 1 A g-1. The value is more than that of BC (150.6 F g-1) and RuO2 electrodes (584.7 F g-1), verifying that introduction of RuO2 achieves to an obviously enhanced capacitance. The symmetrical flexible supercapacitor exhibits excellent supercapacitor performances, including high capacitance (403.8 F g-1 at 1.0 A g-1), rate-capacity (223.1 F g-1 at 50 A g-1), cycling stability (98.2% capacity retention after 10,000 cycles at 50 A g-1) and energy density (378.7 Wh Kg-1at power density of 5199.2 W kg-1).

Design of Intrinsically Flame-Retardant Vanillin-Based Epoxy Resin for Thermal-Conductive Epoxy/Graphene Aerogel Composites.

Vanillin, as a lignin-derived mono-aromatic compound, has attracted increasing attention due to its special role as an intermediate for the synthesis of different biobased polymers. Herein, intrinsically flame-retardant and thermal-conductive vanillin-based epoxy/graphene aerogel (GA) composites were designed. First, a bifunctional phenol intermediate (DN-bp) was synthesized by coupling vanillin with 4, 4'-diaminodiphenylmethane and DOPO, and the epoxy monomer (MEP) was obtained by the epoxidation reaction with DN-bp and epichlorohydrin. Then, various amounts of MEP and diglycidyl ether of bisphenol A (DER) were mixed and cured. Interestingly, the flexural strength and modulus were greatly enhanced from 72.8 MPa and 1.3 GPa to 90.3 MPa and 2.8 GPa, respectively, at 30 wt % MEP, due to the rigidity of MEP and strong intermolecular N-H hydrogen bonding interactions. Meanwhile, the cured epoxy achieved a UL-94 V0 rating with a low P content of 1.06%. The flame-retardant vanillin-based epoxy was then impregnated into the thermal conductive 3D GA networks. The obtained epoxy/graphene composite showed excellent flame retardancy and thermal conductivity [λ = 0.592 W/(m·K)] with only 0.5 wt % graphene in the system. Based on these results, we believe that this work would represent a novel solution for the preparation of high-performance biobased flame-retardant multipurpose epoxies.

Highly-toughened PVA/nanocellulose hydrogels with anti-oxidative and antibacterial properties triggered by lignin-Ag nanoparticles.

In this study, Ag nanoparticles were firstly reduced on the surface of lignin nanoparticles (LNPAg) by direct reaction of silver nitrate without the use of a catalyst. Thermogravimetric analysis, Zeta potential and transmission electron microscopy measurements were performed to give evidence of the effectiveness of the reaction. After that, glutaraldehyde crosslinked PVA hydrogels, were produced by addition of unmodified LNP and Ag loaded LNP (LNPAg) in presence of cellulose nanocrystals (CNC). Thermal, mechanical, rheological, microstructural and biological anti-oxidative and anti-bacterial properties of the resulted hydrogels were investigated. It was proved that all the three nanofillers were homogeneously dispersed in PVA, and the pore diameter of the hydrogels was in the range of 0.5-2.0 µm. Nevertheless, the hydrogels showed high toughness, long-term and repeatable adhesiveness to a variety of substrates. In particular, composite hydrogels containing LNPAg nanoparticles showed excellent radical scavenging and antibacterial activities. Consequently, the effects of PVA-2CNC-2LNPAg on wound healing in mice model of full-thickness skin resection were evaluated by hematoxylin and eosin staining, taking as a reference the PVA-2CNC-2LNP system. The results showed that the wound healing time of PVA-2CNC-2LNPAg group was faster than that of neat PVA and PVA-2CNC, highlighting the role of LNPAg in enhancing the contact-active anti-oxidative and antibacterial activities mechanism in composite hydrogels. We expected that PVA hydrogels incorporating LNPAg could be used as green and efficient biomedical wound dressing materials.

Enhanced crystallization and storage stability of mechanical properties of biosynthesized poly (3-hydroxybutyrate-co-3-hydroxyhexanate) induced by self-nucleation.

The poor mechanical properties induced by unsatisfactory crystallization ability limit the widespread use of biosynthesized poly (3-hydroxybutyrate-co-3-hydroxyhexanate) (PHBH). In this work, poly (3-hydroxybutyrate) (PHB) with a high melting point was first used as a homogeneous nucleating agent to increase the crystallization rate of PHBH by a self-nucleation method with a wider processing temperature window and crystallization kinetics and storage stability of mechanical properties of the PHBH/PHB mixtures were systematically investigated. By controlling the processing temperature and PHB content, the crystal nucleus density and crystallization rate of PHBH could be greatly increased while secondary crystallization was inhibited. When the processing temperature is 185 °C and PHB content is 20 wt%, the half crystallization time is shortened by 96% and the crystallinity was increased to 37.2%. Meanwhile, the mechanical performance of PHBH and its storage stability are greatly improved. Therefore, this work provides a simple and efficient way to improve the crystallization and mechanical performance of PHBH, which is expected to be applied to industrial production on a large scale.

Excellent UV Resistance of Polylactide by Interfacial Stereocomplexation with Double-Shell-Structured TiO2 Nanohybrids.

The durable application of polylactide (PLA) under atmospheric conditions is restricted by its poor ultraviolet (UV) stability. To improve the UV stability of polymers, titanium dioxide (TiO2) is often used as a UV light capture agent. However, TiO2 is also a photocatalytic agent, with detrimental effects on the polymer properties. To overcome these two conflicting issues, we used the following approach. TiO2 nanoparticles were first coated with silicon dioxide (SiO2) (with a SiO2 shell content of 5.3 wt %). Subsequently, poly(d-lactide) (PDLA) was grafted onto TiO2@SiO2 nanoparticles, approximately 20 wt %, via a ring-opening polymerization of d-lactide to obtain well-designed double-shell TiO2@SiO2-g-PDLA nanohybrids. These double-shell nanoparticles could be well dispersed in a poly(l-lactide) (PLLA) matrix making use of the stereocomplexation between the two enantiomers. In our concept, the inner SiO2 shell on the TiO2 nanoparticles prevents the direct contact between TiO2 and the PLLA matrix and hence considerably restricts the detrimental photocatalytic effect of TiO2 on PLLA degradation. Additionally, the outer PDLA shell facilitates an improved dispersion of these nanohybrid particles by interfacial stereocomplexation with its enantiomer PLLA. As a consequence, the PLLA/TiO2@SiO2-g-PDLA nanocomposites simultaneously possess excellent UV-shielding property, high(er) tensile strength (>60 MPa), and superior UV resistance, for example, the mechanical properties remain at a level of >90% after 72 h of UV irradiation. In our view, this work provides a novel strategy to make advanced PLA nanocomposites with improved mechanical properties and excellent UV resistance, which enables potential application of PLA in more critical areas such as in durable packaging and fiber/textile applications.

Rheology-determined critical conditions for shear-induced crystallization of biosynthesized polyhydroxyalkanoates.

Shear-induced crystallization plays a crucial role in the manufacturing process of polymers. In this work, crystallization kinetics of biosynthesized polyhydroxyalkanoates (PHA) under different shear conditions were systematically investigated by rheometers. First, rheological properties of PHA melts were performed at different temperature to obtain mastercurves via the time-temperature superposition principle at 170 °C as a reference temperature. Then the stretch relaxation time and corresponding critical shear rate at different temperatures for the flow regime transition were calculated via the discrete Maxwell relaxation time spectrum and Arrhenius equation. Finally, the influence of shear temperature (Ts), shear time (ts) and shear rate (γ̇) on the crystallization process of PHA were discussed. The results showed the crystallization rate of PHA was improved significantly under high shear rate and long shear time. Interestingly, the t1/2 reached the minimum value when the γ̇ or the ts was large enough, which reached around 450 s at isothermal crystallization condition of 100 °C. Moreover, the nucleation density for PHA increased by appx.100 times than that under quiescent conditions. Therefore, this work may provide a useful theoretical guidance on the shear-induced crystallization of PHA.

The crystallization behavior of poly(lactic acid) with different types of nucleating agents.

The effects of six nucleating agents (NAs), i.e., orotic acid (OA), potassium salt of 3,5-bis(methoxycarbonyl)benzenesulfonate (LAK-301), substituted-aryl phosphate salts (TMP-5), talc (TALC), N'1,N'6-dibenzoyladipohydrazide (TMC-306) and N1,N1'-(ethane-1,2-diyl)bis(N2-phenyloxalamide) (OXA), on the crystallization behavior of poly(lactic acid) (PLA) were compared by DSC. Under the same dosing of 0.5wt%, the nucleation effect of the NAs for PLA declines in the order of TMC-306≈OXA>TALC≫TMP-5≈LAK-301≈OA. The nucleation efficiency (NE) of TMC-306 and OXA is around 50%, which is almost 2 times of the NE of TALC. In the best case of the PLA/TMC-0.5% sample, the half-time of crystallization decreases from 30s to 9s with decreasing the crystallization temperature from 120°C to 100°C, which is of great significance to the fast production of highly crystallized PLA materials. As high-efficient NAs, TMC-306 and OXA are able to accelerate the crystallization rate of PLA even upon fast cooling at 50°C/min, while make no difference on PLA crystal form, as identified by WAXD. DMA analysis shows that the storage modulus of PLA is significantly improved by TMC-306 and OXA.

Interfacial modification on polyhydroxyalkanoates/starch blend by grafting ​in-situ.

The interfacial adhesion between polyhydroxyalkanoates (PHAs) and native starch is poor. To improve the interfacial adhesion, PHAs were in-situ grafted onto starch using dicumyl peroxide (DCP) as a free radical initiator. The grafting reaction was carefully characterized and confirmed by gel analysis and Fourier transform infrared spectroscopy (FT-IR). The gel yield of the PHAs/starch/DCP blend increased with the DCP concentration up to 2wt%. Meanwhile, obvious plastic deformation (stretched fibrils) was observed at the interface in the PHAs/starch/DCP blend in comparison with complete interfacial debonding in the PHAs/starch physical blend. The improved interfacial adhesion after grafting was further confirmed by a reduction in adhesion factor (Af) obtained from dynamic mechanical analysis (DMA). The mechanical strength and the crystallization rate of the PHAs were deteriorated after incorporation of starch, and were backed up by the interfacial improvement. A linear relationship between the mechanical properties and the gel yield was discovered. In addition, the PHAs/starch/DCP blend exhibited higher decomposition active energy (Ea) and thus better thermal stability in comparison with the PHAs and the PHAs/starch physical blend. Therefore, this study provides a simple route to utilize low-cost starch as a component in biopolymer blend.

Crystallization behaviours of bacterially synthesized poly(hydroxyalkanoate)s in the presence of oxalamide compounds with different configurations.

Bacterially synthesized poly(hydroxyalkanoate)s (PHAs) suffers from low crystallization rate which is enhanced by using tailor-made oxalamide compounds as nucleators. The influence of nucleator configurations on the crystallization behaviour of the PHAs was investigated using differential scanning calorimetry (DSC), polarized optical microscopy (POM) and X-ray diffraction (XRD). The oxalamide compounds with ringy terminal structures (cyclohexyl and phenyl), notably the phenyl group, show higher nucleation efficiency and a better compatibility in the PHAs matrix, while the linear terminal structure (n-hexane) has poor nucleation effect. The crystallization temperature (Tc) and the crystallinity (Xc) of the PHAs are increased from 58°C to 71°C and from 5% to 48%, respectively, after addition of 0.75wt% of the nucleator (phenyl group) upon cooling from the melt. Meanwhile, the half-life isothermal crystallization time (t0.5) of the PHAs at 110°C is decreased by 70%. The oxalamide compounds increases the nuclei density of the PHAs accompanied with a reduction in spherulitic size. In addition, the crystal form and crystallization mechanism of the PHAs are not altered obviously after addition of the nulceators as confirmed by the POM, XRD and Avrami analysis.

Rapid Stereocomplexation between Enantiomeric Comb-Shaped Cellulose-g-poly(L-lactide) Nanohybrids and Poly(D-lactide) from the Melt.

In this work we report the in situ preparation of fully biobased stereocomplex poly(lactide) (SC-PLA) nanocomposites grafted onto nanocrystalline cellulose (NCC). The stereocomplexation rate by compounding high-molar-mass poly(D-lactide) (PDLA) with comb-like NCC grafted poly(L-lactide) is rather high in comparison with mixtures of PDLA and PLLA. The rapid stereocomplexation was evidenced by a high stereocomplexation temperature (Tc-sc = 145 °C) and a high SC crystallinity (Xc-sc = 38%) upon fast cooling (50 °C/min) from the melt (250 °C for 2 min), which are higher than currently reported values. Moreover, the half-life crystallization time (175-190 °C) of the SC-PLA was shortened by 84-92% in comparison with the PDLA/PLLA blends. The high(er) stereocomplexation rate and the melt stability of the SC in the nanocomposites were ascribed to the nucleation effect of the chemically bonded NCC and the "memory effect" of molecular pairs in the stereocomplex melt because of the confined freedom of the grafted PLLA chains.

[Surgical treatment of calcaneus fracture involving posterior subtalar articular facet].

OBJECTIVE: To investigate the methods of reduction and stable fixation for the treatment of calcaneus fracture involving posterior subtalar articular facet. METHODS: From September 2004 to September 2008, 31 cases(38 feet) of calcaneus fracture involving posterior subtalar articular facet were treated with open reduction and plate fixation through L incision. There were 24 males and 7 females, with an average age of 39.6 years ranging from 20 to 65 years. All patients underwent systematic CT-scan with coronal and horizontal images and sagittal reconstruction. The classification of the fractures by the Sanders scale showed that there were 22 of type II,14 of type III, 2 of type IV. RESULTS: All cases were followed up for from 12 to 36 months with an average of 25 months, and all the fractures healed without skin flap necrosis. According to the Maryland foot scoring, the total score was (96.2 +/- 8.8) on average, the results were excellent in 32 feet, good in 4 feet, fair in 2 feet. CONCLUSION: The replacement of the posterior articular facet by X-ray control of Broden and open reduction and internal fixation with calcaneus plate and Schanz-Screw during the operation can keep stable of articular facet, and promote early rehabilitation of calcaneus fracture affected with subtalar joint.