Interlocked chitosan/poly(dl-lactide) blends

A novel processing method was developed to prepare chitosan/poly(dl-lactide) blends. These blends were further examined for their structures. SEM micrographs exhibited that under optimized processing conditions and with appropriate composition proportions, the resulting blends could possess interlocked internal microstructures. The results obtained from TGA and DMA measurements complementarily confirmed that two components could be well blended into a solid construct at a partially miscible level. The main mechanical properties of the blends were also investigated in both dry and hydrated states.     

Utilization of polymer degradation to modify electrical properties of poly(l-lactide)/poly(methyl methacrylate)/carbon filler composites

This research attempts to utilize polymer degradability in modifying electrical properties of poly(l-lactide) (PLLA)/poly(methyl methacrylate) (PMMA)/carbon fillers composites. Three kinds of carbon particles, i.e. carbon black, vapor-grown carbon fiber, and carbon nanotube, were compounded with PLLA/PMMA blend, followed by hydrolytic degradation of the composites, resulted in degradation of PLLA molecular chain from the surface of samples, with PMMA and carbon particles remained undegraded. By controlling degradation rate, it was possible to prepare samples with low surface resistivity, yet at the same time exhibited high value of volume resistivity. It was also found that final electrical properties of degraded composites depend on the size and the shape of the fillers.     

PPDO/PDLLA共混物的结晶行为

通过溶液共混的方法得到了一系列PPDO/PDLLA生物可降解复合物。利用差示扫描量热法(DSC),配带热台的偏光显微镜(POM)和X射线衍射法(XRD)研究了聚对二氧环己酮(PPDO)与外消旋聚乳酸(PDLLA)共混物的结晶行为。结果表明,PPDO/PDLLA复合物的DSC曲线具有两个明显不同的Tg,分别与其均聚物的Tg相对应,说明二者是不相容的,同时PDLLA的加入并未明显影响PPDO的晶体结构,同时PDLLA的存在提高了PPDO的结晶度,并显著加速了PPDO的结晶过程。     

Degradation and miscibility of poly(DL-lactic acid)/poly(glycolic acid) composite films: Effect of poly(DL-lactic-co-glycolic acid)

The in vitro degradation behaviour of poly(glycolic acid) (PGA) and its composite films containing poly(DL-lactic acid) (PDLLA) and poly(DL-lactic-co-glycolic acid) (PDLGA) were investigated via mass loss, scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). All the films were prepared by solution casting, using 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) as the solvent. Since the degradation rate of PDLLA is lower than that of PGA, those of the PDLLA/PGA composite films decreased. As a compatibilizer, PDLGA improved the compatibility and hydrolytic stability of PDLLA/PGA composite films. Changes in the composite films indicate that this kind of PGA-based composite biomaterial may be applicable to device design for clinical application in the future.     

Influence of fiber surface-treatment on interfacial property of poly(l-lactic acid)/ramie fabric biocomposites under UV-irradiation hydrothermal aging

The present study is devoted to the effect of fiber surface-treatment on the interfacial property of biocomposites based on poly(l-lactic acid) (PLLA) and ramie fabric. Ramie fiber is used as reinforced material because it's lowest water absorption among sisal, jute, kenaf and ramie fiber. Fiber surface-treatment can increase the water absorption of natural fibers. SEM images show that PLLA biocomposites with treated ramie fabric exhibit better interfacial adhesion character. DMA results show that the storage modulus of PLLA biocomposites with treated ramie increase compared to neat PLLA and PLLA biocomposites with untreated ramie. Unexpectedly, fiber surface-treatment can cause an accelerated decline in mechanical properties of PLLA biocomposites after UV-irradiation hydrothermal aging. Finally, GPC results show that there is no obvious decline in the molecular weight of PLLA. The main reason for this decline is the interfacial destructive effect induced by the water absorption of ramie fiber.     

Thermal stability and melt rheology of poly(<Emphasis Type="Italic">p</Emphasis>-dioxanone)

Melt viscosities of poly(p-dioxanone) (PPDO) samples having different molecular weights were studied using a controlled-strain rotational rheometer under a nitrogen atmosphere. First, PPDO’s thermal stability was evaluated by recording changes in its viscosity with time. The result, that samples’ viscosities decreased with time when heated, demonstrated that PPDO is thermally unstable: its degradation activation energy, obtained by using a modified MacCallum equation, was a relatively low 71.8 kJ/mol K. Next, viscoelastic information was acquired through dynamic frequency measurements, which showed a shear thinning behavior among high molecular weight PPDOs, but a Newtonian flow behavior in a low molecular weight polymer (M _w = 18 kDa). Dynamic viscosity values were transferred to steady shear viscosities according to the Cox–Merz rule, and zero shear viscosities were derived according to the Cross model with a shear thinning index of 0.80. Then flow activation energy (48 kJ/mol K) was extrapolated for PPDO melts using an Arrhenius type equation. This activation energy is independent of polymer molecular weight. A linear relationship between zero shear viscosity and molecular weight was obtained using a double-logarithmic plot with a slope of 4.0, which is near the usually observed value of 3.4 for entangled linear polymers. Finally, the rheological behaviors of PPDO polymer blends having bimodal molecular weight distributions were investigated, with the results indicating that the relationship between zero shear viscosity and low molecular weight composition fraction can be described with a Christov model.     

Thermal stability and thermal degradation kinetics of poly(ethylene 2,6-naphthalate)/poly(trimethylene terephthalate) blends

The kinetics of thermal degradation of poly(ethylene 2,6-naphthalate)/poly(trimethylene terephthalate) (PEN/PTT) blends with different weight ratio were investigated by thermogravimetry analysis from ambient temperature to 800 °C in flowing nitrogen. The kinetic parameters, including the activation energy E _a, the reaction order n, and the pre-exponential factor ln(Z), of the degradation of the PEN/PTT blends were evaluated by three single heating rate methods and advanced isoconversional method developed by Vyazovkin. The three single heating rate methods used in this work include Friedman, Freeman–Carroll, and Chang method. The effects of the heating rate, the calculation methods, and the content of the PEN component on the thermal stability and degradation kinetic parameters of the PEN/PTT blends were systematically discussed. The PEN/PTT blends which degraded in two distinct stages were stable under nitrogen, also, the maximum rate of weight loss increased linearly with increasing of heating rate and decreased with increasing of PEN content. The obtained kinetics data suggested that the introduction of PEN component increased the activation energy, enhanced the stability of the blend system, and affected the process of degradation of PEN/PTT blend.     

Preparation,crystallization and hydrolytic degradation of biodegradable poly(l-lactide)/polyhedral oligomeric silsesquioxanes nanocomposite

Biodegradable poly(l-lactide) (PLLA)/polyhedral oligomeric silsesquioxanes (POSS) nanocomposite was prepared via solution casting method for the first time in this work. Scanning electron microscopy observation indicates that POSS were homogeneously dispersed in the PLLA matrix. Effect of POSS on the crystal structure, crystallization kinetics, dynamical properties, and hydrolytic degradation of PLLA in the nanocomposite was investigated in detail. It is found that the presence of POSS has enhanced significantly the crystallization rate, improved mechanical properties and accelerated the hydrolytic degradation of PLLA in the nanocomposite with respect to neat PLLA.     

In vitro bioactivity of chitosan/poly (d,l-lactide-co-glycolide) composites

Porous composites scaffolds of chitosan/poly(d,l-lactide-co-glycolide) were fabricated for tissue engineering applications by thermally induced phase separation and lyophilization techniques. The in vitro bioactivity evaluation of the scaffolds was carried out by analyzing the apatite layers produced on them using SBF as incubation medium. The apatite formation was analyzed using FTIR spectroscopy and Field emission scanning electron microscopy coupled to energy-dispersive electron X-ray spectroscopy. The cumulative results obtained from the IR spectra and SEM-EDS suggest that the developed composites might have potential applications in tissue engineering.     

Fabrication and characterization of poly-d-l-lactide/nano-hydroxyapatite composite scaffolds with poly (ethylene glycol) coating and dexamethasone releasing

The control of pore size and structure, drug release capacity, and biodegradation of scaffolds is of importance for bone tissue engineering. In this study, a technique combining polymer coagulation, cold compression molding, salt particulate leaching and drug coating method was developed to fabricate poly (ethylene glycol)/dexamethasone coated porous poly-d-l-lactide/nano-hydroxyapatite (PDLLA/nano-HAp) scaffolds. These scaffolds possess homogenous pore networks with high porosity (66-82%) and controllable pore size (200-300 μm). The compressive moduli and strength of the scaffolds after incorporation of nano-HAp were improved by 50% and 20%, respectively. The surface hydrophilicity of the scaffold was significantly improved by poly (ethylene glycol)/dexamethasone coating and nano-HAp addition, leading to a higher initial drug loading amount. The results showed that the drug release behavior of the scaffolds after 35-day immersion in water could be adjusted by varying the porosity level and by incorporation of 20 wt.% of nano-HAp.     

Surface wetting phenomena of plasma polymer-coated sheets of poly(l-lactic acid)/poly(butylene succinate)

Water-repellent surfaces were fabricated on blend sheets of poly(l-lactic acid)/poly(butylene succinate) with various blending ratios by the successive processing; (1) plasma etching, followed by (2) the hydrophobic plasma polymer coating. Rough morphology was formed effectively on the mosaic structured surface of blend sheets via the oxidative etching, and advanced water repellency was achieved after the thin membrane coating was synthesized with a hydrophobic plasma polymer coating by use of hexamethyldisiloxane or hexamethyldisilazane. High water repellency is expressed through the columnar hair-like structured model, where the air-water surface interaction in the voids is taken into account.     

Synthesis and characterization of a novel multiblock copolyester containing poly(ethylene succinate) and poly(butylene succinate)

Multiblock copolyester (PBS-b-PES) containing poly(butylene succinate) (PBS) and poly(ethylene succinate) (PES) was successfully synthesized by chain-extension of dihydroxyl terminated PBS (HO-PBS-OH) and PES (HO-PES-OH) using 1,6-hexmethylene diisocyanate (HDI) as a chain extender. The chemical structures, molecular weights, crystallization behaviors, thermal and mechanical properties of the copolyesters were characterized by proton nuclear magnetic resonance spectroscopy (¹H NMR), gel permeation chromatography (GPC), differential scanning calorimetry (DSC), thermogravimetry analysis (TGA), wide-angle X-ray diffraction (WAXD), tensile testing and hydrolytic degradation. High-molecular-weight copolyesters with M_w more than 2.0 × 10⁵ g mol⁻¹ were easily obtained through chain-extension. The copolyesters showed a single glass transition temperature (T_g) which increased with PES content. The melting point temperature (T_m) and relative degree of crystallinity (X_c) of the copolyesters decreased first and then increased with PES content. The copolyesters manifested excellent mechanical properties, for example, PBS₅-b-PES₅ had fracture stress of 61.8 MPa and fracture strain of 1173%. The chain-extension reaction provided a very effective way to produce high molecular weight multiblock copolyesters.     

Effect of multi-walled carbon nanotubes on the crystallization and hydrolytic degradation of biodegradable poly(l-lactide)

Biodegradable poly(l-lactide) (PLLA)/carboxyl-functionalized multi-walled carbon nanotubes (f-MWNTs) nanocomposites were prepared via solution blending. Scanning electron microscopy observations reveal a fine dispersion of f-MWNTs in the PLLA matrix. The presence of f-MWNTs enhances the crystallization of PLLA in the nanocomposites compared with that of neat PLLA; moreover, the overall crystallization rate of PLLA increases with increasing the f-MWNTs content in the PLLA matrix. The incorporation of f-MWNTs improves the storage modulus of the PLLA/f-MWNTs nanocomposites, with this effect being more pronounced at lower f-MWNTs content. The exciting aspect of this research is the enhanced hydrolytic degradation of PLLA after nanocomposites preparation with f-MWNTs, which may be of great interest for its wide practical application.     

羟基磷灰石/聚乳酸/聚氨酯生物材料的降解性能

以聚乳酸(PDLLA)和聚氨酯(PU)为基体,将纳米羟基磷灰石(n-HA)与其复合,制备了多孔n-HA/PDLLA/PU生物材料,通过模拟体液(SBF)浸泡试验评估材料的生物降解性和矿化活性,测定了降解过程中材料的吸水率和pH变化,以及浸泡前后的质量损失。通过红外光谱分析生物材料浸泡前后结构组成变化,采用热重分析(TG)材料降解前后的热稳定性,并用扫描电镜观察材料降解前后表面形貌特征。结果表明,n-HA/PDLLA/PU生物材料在模拟体液中随浸泡时间的延长由外到内不断降解,可以通过控制PDLLA的含量调节材料的降解速率;随着PDLLA和PU的水解以及n-HA形成新的结晶,生物材料降解后热稳定性降低。     

In vitro degradation and drug release from polymer blends based on poly(<Emphasis Type="SmallCaps">dl</Emphasis>-lactide), poly(<Emphasis Type="SmallCaps">l</Emphasis>-lactide-glycolide) and poly(ε-caprolactone)

Bioresorbable materials are extensively used for a wide range of biomedical applications. Accurately modifying and evaluating the degradation rate of these materials is critical to their performance and the controlled release of bioactive agents. The aim of this work was to modify the physical properties, degradation rate and drug delivery characteristics of thin films for medical applications by blending poly(dl-lactic acid) (PDLLA), poly(l-lactide-co-glycolide) (PLGA) and poly(ε-caprolactone) (PCL). The thin films were prepared using solvent casting and compression moulding and the in vitro degradation study was performed by immersing the films in a phosphate-buffered saline at elevated temperature for a period of 4 weeks. The degradation rate of the materials was analysed by differential scanning calorimetry, tensile testing and weight loss studies. The thermal analysis of the blends indicated that the presence of PLGA or PDLLA in the film resulted in increased degradation of the amorphous regions of PCL. It was observed that the samples consisting of PDLLA with PCL demonstrated the greatest weight loss. The decrease in mechanical properties observed for both sets of polymer blends proved to be similar. The solvent cast technique was selected as the most appropriate for the formation of the polymer/drug matrices, due to the potentially adverse thermal processing effects associated with compression moulding. It was found that modulation of drug release was achievable by altering the ratio of PCL to PDLLA or PLGA in the thin film blends.     

Crystallization kinetics of poly(hydroxybutyrate- co -hydroxyvalerate) and poly(dicyclohexylitaconate) PHBV/PDCHI blends: thermal properties and hydrolytic degradation

The influence of poly(dicyclohexylitaconate) (PDCHI) content, on the crystallization kinetics, thermal properties, and hydrolytic degradation of poly(hydroxybutyrate-co-hydroxyvalerate), PHBV, was studied. Irrespective of the blend composition, the calorimetric and FTIR spectroscopy analyses indicate that the blend components are immiscible. The kinetics of non-isothermal crystallization and melting behavior of PHBV were studied by differential scanning calorimetry (DSC) and examined using non-isothermal Avrami and Mo’s analyses. Based on Mo’s model, the PDCHI content has significant effect on the crystallization kinetics of PHBV matrix. Despite the immiscibility of these polymers, the amorphous polyvinyl ester could extensively control the rate of hydrolytic degradation.     

The influence of polymer blend composition on the degradation of polymer/hydroxyapatite biomaterials

The in vitro degradation of biodegradable polymer/ceramic composites was assessed in two different environments under both static and pseudodynamic conditions. The blends, consisting of polycaprolactone, poly(lactic-co-glycolic acid), and hydroxyapatite, have potential use in bone tissue engineering applications, thus it is essential to establish a standardized method of characterizing the degradation of new biomaterials. In this study, the variation in polymer blend ratio was examined to observe a change in degradation rate. The porous blends were degraded in water and serum-containing media. A previous study examined in vitro degradation in serum-free buffer. Molecular weight loss, gravimetric weight loss, pH changes and morphological changes were evaluated. The changes in porosity were observed with scanning electron microscopy and quantitatively assessed using image analysis. There was a significant difference in molecular weight loss and gravimetric weight loss between the blends after 10 weeks in vitro. Blends containing the greatest amount of poly(lactic-co-glycolic acid) degraded most rapidly. © 2001 Kluwer Academic Publishers     

Concentration dependence of solution crystallization for poly(l-lactide) in p-xylene

The macromolecular chain conformation in solution changes with the solvent and temperature, which will affect the formation of crystalline structure in the subsequent crystallization process. The crystallization behavior of poly(l-lactide) samples prepared from solutions with various concentrations was studied by differential scanning calorimetric and X-ray diffraction. It is found that the sample recovered from a dilute solution exhibits higher crystallinity, higher non-isothermal crystallization temperature and faster crystallization rate. The condensation process of polymer chain in dilute solutions has an influence on the crystallization of polymer in the solid state. This results in the acceleration of the melt crystallization rate and the rise of non-isothermal crystallization temperature of PLLA recovered from the dilute solution.     

NMR analysis of poly(ethylene naphthalate) + poly(butylene terephthalate) blends

Melt blends of poly (butylene terephthalate) (PBT) and poly (ethylene naphthalate) (PEN) with 30, 40, 50, 60 and 70 wt% PEN were prepared using a single screw extruder and injection moulding machine. ¹³C and ¹H nuclear magnetic resonance (NMR) spectra were obtained with a Bruker DRX-400 instrument, on solutions prepared by dissolving samples of the homopolymers and each blend in deuterated trifluoroacetic acid + chloroform mixtures (1:1 by volume). The absence of new signals in ¹H and ¹³C spectra, that would be expected to result from transesterification reactions in the PBT + PEN blend system, provides convincing evidence that such reactions do not occur in these blends under the melt processing conditions that were used. In the light of published work on solid-state NMR studies of these and related blend systems, and our observations of partial miscibility with a very small domain size, together with substantial enhancement of the mechanical properties of PBT by blending with PEN, we conclude that the improvement in mechanical properties arises from molecular scale mixing of the homopolymers and strong but non-covalent bonding interactions over the very large interfacial area between the PBT-rich and PEN-rich phases.     

Liquid sensing properties of melt processed polypropylene/poly(ε-caprolactone) blends containing multiwalled carbon nanotubes

The sensing properties of polypropylene (PP)/poly(ε-caprolactone) (PCL) blends containing multiwalled carbon nanotubes (MWNT) were studied in terms of their electrical resistance change in presence of liquids (solvents). The preparation of co-continuous blends based on the double percolation concept was done by melt mixing of electrically conductive PCL composites containing 3 wt.% MWNT and neat PP in ratios of 30:70, 40:60, and 50:50. The electrical resistance change of the PCL-MWNT composites and blends was monitored in a solvent immersion/drying cycle. Various solvents, such as n-hexane, ethanol, methanol, water, toluene, chloroform, and tetrahydrofuran were successfully detected, yielding different responses and reversibility of the resistance changes.PP and PCL were tested separately for solvent sorption using ethanol and n-hexane, both showing a low sorption of n-hexane. Ethanol sorption was large for PCL and almost absent for PP. The 50/50 blend composites with 3 wt.% MWNT in the PCL phase presented larger resistance changes for n-hexane, showing larger sensing ability for this solvent compared to PCL composites with 1 and 3 wt.% loadings. The opposite response was observed for immersion in ethanol where the PCL-MWNT composites showed larger changes than the blends. As the ratio of the conductive PCL phase over PP in the blend composition (i.e. the overall MWNT content) decreased, larger resistance changes were observed. The liquid sensing properties of compression-moulded discs and melt-drawn filaments were compared indicating higher responses for the discs.