The effect of heat treatment on water sorption in polylactide and polylactide composites via changes in glass‐transition temperature and crystallization kinetics

Water sorption into polylactide (PLA) and polylactide‐montmorillonite (PLLA‐MONT) composites containing 5 wt % of montmorillonite (MONT) under different heat treatment conditions was studied using the quartz crystal microbalance/heat conduction calorimetry (QCM/HCC) technique. Results showed that water sorption in neat polymer films and composite films increased with heat treatment temperature up to 120 °C. Differential scanning calorimetry was used to measure the glass‐transition temperature and isothermal crystallization kinetics of all samples. The mobility of the amorphous domain in all samples increased with heat treatment temperature, indicated by the decrease in glass‐transition temperature. PLA composites crystallized at a much faster rate than neat PLA did because MONT acted as a nucleating agent. Under the same heat treatment condition, water sorption in PLLA‐MONT composites was always higher than that in neat PLA due to the presence of the hydrophilic hydroxyl groups on the surface of MONT particles. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Polycondensation of diglycerol with H3PO4. Reversibly degradable gels giving multireactive,highly branched macromolecules

Polycondensation of H₃PO₄ with diglycerol (DGL) involves biobased, commercial products and leads, via hydrolyzable gels, to highly branched reactive macromolecules. These reactive macromolecules have been applied as multiacidic catalysts with hydroxyl groups in polymerization of l ‐lactide, consuming entirely the starting highly branched macromolecules. Polycondensation was performed in bulk, at 110–120 °C with efficient elimination of water under vacuum. The process with DGL differs substantially from the previously studied polycondensation with ethylene glycol and glycerol. Formation of pyrophosphoric acid (PY) constitutes the rate determining step: the rate of PY formation is the same in the absence and presence of DGL. Kinetic studies explained why the rate of monoesters (M) accumulation may be the same as the rate of accumulation of di‐ (D), and triesters (T). This is because the rate of M formation is relatively low when compared with rates of further reactions of M, leading to D and T. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3303–3317     

New insights into polylactide biodegradation from molecular ecological techniques

Molecular ecological techniques for direct identification of microbes involved in PLA degradation under aerobic composting conditions are described. Gene sequences from genera Paecilomyces, Thermomonospora, and Thermopolyspora were most abundant in the compost samples. Members of these phylogenetic lineages are therefore likely to play an important role in PLA degradation. The use of molecular ecological techniques to design cultivation strategies may also provide a new tool for identification and investigation of biodegradation mechanisms and for future development of efficient biological treatment or recycling processes for PLA and other biodegradable polymers.     

Thoroughly Hydrophilized Electrospun Poly(L-Lactide)/ Poly(ε-Caprolactone) Sponges for Tissue Engineering Application

Biodegradable electrospun sponges are of interest for various applications including tissue engineering, drug release, dental therapy, plant protection, and plant fertilization. Biodegradable electrospun poly(l -lactide)/poly(ε-caprolactone) (PLLA/PCL) blend fiber-based sponge with hierarchical pore structure is inherently hydrophobic, which is disadvantageous for application in tissue engineering, fertilization, and drug delivery. Contact angles and model studies for staining with a hydrophilic dye for untreated, plasma-treated, and surfactant-treated PLLA/PCL sponges are reported. Thorough hydrophilization of PLLA/PCL sponges is found only with surfactant-treated sponges. The MTT assay on the leachates from the sponges does not indicate any cell incompatibility. Furthermore, the cell proliferation and penetration of the hydrophilized sponges are verified by in vitro cell culture studies using MG63 and human fibroblast cells.     

Investigation of the synthesis of poly-D,L-lactide-co-poly(ethylene glycol) flexible thermoplastic

A series of biodegradable poly(D,L-lactide)-poly(ethylene glycol) multiblock poly(ether-ester-urethane)s with various lactide-to-poly(ethylene glycol) (LA/PEG) mole ratios has been successfully synthesized by ring-opening polymerization (ROP) followed by chain extension reaction through formation of urethane linkage. Resulting FT-IR spectra indicate complete polymerization of lactide monomers, while NMR analysis quantitatively marks the chain length of polymer blocks. The molecular weight and dispersion index of copolymers were investigated by GPC analysis. DSC thermogram and XRD diffractogram of the prepared copolymers were studied as well for revealing the thermal and crystallinity behavior of the copolymer as LA/PEG mole ratios varied.     

Flame retardant properties and mechanism of an efficient intumescent flame retardant PLA composites

The charring agent (CNCA‐DA) containing triazine and benzene rings was combined with ammonium polyphosphate (APP) to form intumescent flame retardant (IFR), and it was occupied to modify polylactide (PLA). The flame retardant properties and mechanism of flame retardant PLA composites were investigated by the limited oxygen index (LOI), vertical burning test (UL‐94), thermogravimetric analysis, microscale combustion calorimetry, scanning electron microscopy, laser Raman spectroscopy analysis and X‐ray photoelectron spectroscopy. The analysis from LOI and UL‐94 presented that the IFR was very effective in flame retardancy of PLA. When the weight ratio of APP to CNCA‐DA was 3:1, and the IFR loading was 30%, the IFR showed the best effect, and the LOI value reached 45.6%. It was found that when 20 wt% IFR was loaded, the flame retardancy of PLA/IFR still passed UL‐94 V‐0 rating, and its LOI value reached 32.8%. The microscale combustion calorimetry results showed that PLA/IFR had lower heat release rate, total heat release, and heat release capacity than other composites, and there was an obvious synergistic effect between APP and CNCA‐DA for PLA. IFR containing APP/CNCA‐DA had good thermal stability and char‐forming ability with the char residue 29.3% at 800°C under N₂ atmosphere. Scanning electron microscopy observation further indicated that IFR could promote forming continuous and compact intumescent char layer. The laser Raman spectroscopy analysis and X‐ray photoelectron spectroscopy analysis results indicated that an appropriate graphitization degree of the residue char was formed, and more O and N were remained to form more cross‐linking structure. Copyright © 2016 John Wiley & Sons, Ltd.     

硫磺素型聚乳酸/苯磺酸室温磷光体系的构建

在硫磺素上分别引入给电子基氧、 硫和甲氧基, 合成出2-[4-(苯并噻唑-2-基)苯氧基]乙-1-醇(BT-OH)、 2-{[4-(苯并噻唑-2-基)苯基]硫代}乙-1-醇(BT-SH)和2-[4-(苯并噻唑-2-基)-2-甲氧基苯氧基]乙-1-醇(BT-M-OH) 3种硫磺素衍生物. 利用硫磺素衍生物作为引发剂引发D,L-丙交酯聚合, 得到3种硫磺素型聚乳酸, 再加入苯磺酸, 构建出可在室温下产生磷光的硫磺素型聚乳酸/苯磺酸体系, 实现了从荧光到磷光的可调分子发射, 其中磷光寿命最长达108.19 ms. 研究发现, 引入苯磺酸会使硫磺素型聚乳酸产生分子内电荷转移态, 质子化效应导致绿色和橘色的磷光发射.     

Synthesis and characterization of novel carboxymethyl chitosan grafted polylactide hydrogels for controlled drug delivery

Novel carboxymethyl chitosan‐polylactide (CMCS‐g‐PLA) hydrogels were prepared by using 1‐(3‐dimethylaminopropyl)‐3‐ethylcarbodiimide hydrochloride/N‐hydroxysuccinimide (EDC/NHS) as crosslinking agent and catalyst at room temperature. Solid‐state ¹³C‐NMR, SEM, and FT‐IR measurements showed that PLA blocks are successfully grafted onto the CMCS main chains. DSC measurements confirmed the effective crosslinking of carboxymethyl chitosan. With increasing the amount of EDC/NHS, the crosslink destiny of CMCS‐g‐PLA copolymers is improved. The swelling ratio of CMCS‐g‐PLA hydrogels is pH dependent, showing a minimum in the pH range of 3 to 5. Rheological studies confirmed the formation of hydrogels. The higher the crosslinking density, the higher the storage modulus of hydrogels. CMCS‐g‐PLA hydrogels only slightly degrade in PBS for 10 days. In the presence of lysozyme, however, hydrogels with low crosslink density are totally degraded in 10 days. Drug release studies show that after 96 h, 95% of thymopentin is released under in vitro conditions. Copyright © 2015 John Wiley & Sons, Ltd.     

Covalent VEGF protein immobilization on resorbable polymeric surfaces

Vascular endothelial growth factor type protein (VEGF), a potent angiogenic effector molecule, was successfully covalently immobilized onto the surfaces of the resorbable polymers poly(L‐lactic acid) (PLLA) and poly(ε‐caprolactone) (PCL) through a three‐step strategy. The surfaces were first covalently grafted with poly(acrylic acid) using non‐destructive and solvent free vapor‐phase grafting. A diamine spacer was coupled to the carboxylic acid pendant groups on the graft chains using EDC/NHS chemistry and VEGF was finally covalently attached to the amine linkers. The chemistry and topography of the modified substrates were quantitatively and qualitatively verified with XPS, ATR‐FTIR, UV–VIS, SEM, and ELISA. Copyright © 2010 John Wiley & Sons, Ltd.     

Emission Color Tuning with Polymer Molecular Weight for Dyes of 4‐Dicyanomethylene‐2‐methyl‐6‐{4‐[(2‐hydroxyethyl)(methyl)amino]styryl}‐4H‐pyran

A series of novel polylactide (PLA) polymers were synthesized initiated by 4‐dicyanomethylene‐2‐methyl‐6‐{4‐[(2‐hydroxyethyl)(methyl)amino]styryl}‐4H‐pyran (DCM) with Sn(Oct)₂ as catalyst. The color and emission of the polymer can be tuned just with polymer molecular weight.