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1.
A miscibility and phase behavior study was conducted on poly(ethylene glycol) (PEG)/poly(l ‐lactide‐ε‐caprolactone) (PLA‐co‐CL) blends. A single glass transition evolution was determined by differential scanning calorimetry initially suggesting a miscible system; however, the unusual Tg bias and subsequent morphological study conducted by polarized light optical microscopy (PLOM) and atomic force microscopy (AFM) evidenced a phase separated system for the whole range of blend compositions. PEG spherulites were found in all blends except for the PEG/PLA‐co‐CL 20/80 composition, with no interference of the comonomer in the melting point of PEG (Tm = 64 °C) and only a small one in crystallinity fraction (Xc = 80% vs. 70%). However, a clear continuous decrease in PEG spherulites growth rate (G) with increasing PLA‐co‐CL content was determined in the blends isothermally crystallized at 37 °C, G being 37 µm/min for the neat PEG and 12 µm/min for the 20 wt % PLA‐co‐CL blend. The kinetics interference in crystal growth rate of PEG suggests a diluting effect of the PLA‐co‐CL in the blends; further, PLOM and AFM provided unequivocal evidence of the interfering effect of PLA‐co‐CL on PEG crystal morphology, demonstrating imperfect crystallization in blends with interfibrillar location of the diluting amorphous component. Significantly, AFM images provided also evidence of amorphous phase separation between PEG and PLA‐co‐CL. A true Tg vs. composition diagram is proposed on the basis of the AFM analysis for phase separated PEG/PLA‐co‐CL blends revealing the existence of a second PLA‐co‐CL rich phase. According to the partial miscibility established by AFM analysis, PEG and PLA‐co‐CL rich phases, depending on blend composition, contain respectively an amount of the minority component leading to a system presenting, for every composition, two Tg's that are different of those of pure components. © 2013 Wiley Periodicals, Inc. J. Polym. Sci. Part B: Polym. Phys. 2014 , 52, 111–121  相似文献   

2.
With the continuous development of the electronics industry, in order to meet the requirements of electronic equipment to reduce the size and increase power consumption, the development of high thermal conductivity materials is crucial. In this study, thermally conductive polylactic acid (PLA) composites were prepared by constructing graphene and alumina (Al2O3) hybrid filler network, and it was further successfully used in additive manufacturing. Due to the synergistic effect of Al2O3 and graphene, the resulting composite achieved the thermal conductivity of 2.4 Wm?1 K?1 with 70 wt% Al2O3 and 1 wt% graphene, which are superior to data reported in the literature in the same filler condition. The Al2O3 and graphene hybrid filler network reduced the agglomeration of graphene and the thermal contact resistance between the fillers, thereby leading a faster cooling rate. Furthermore, the obtained thermally conductive PLA composite has good thermal stability at a normal temperature. The PLA composite powder obtained by the cryogenic pulverization can be used in the laser sintering additive manufacturing process to prepare a heat conductive material with a complicated shape.  相似文献   

3.
B2O3-xLi2O3 (x=0, 0.1, 0.5) glasses have been prepared by the Sol-Gel method. The evolution of the composition and the structure of the materials upon thermal treatments are analyzed. Raman spectroscopy measurements reveal that the structure transforms from crystalline to amorphous. After a thermal treatment at 400°C, the materials exhibit a strong luminescence band which disappears upon further heating. In the case of no dopant (x=0) heating at 1150°C results in a Raman spectrum which is almost identical to the one corresponding to bulk B2O3 glass obtained by melting and quenching.  相似文献   

4.
Positron annihilation lifetime spectroscopy and differential scanning calorimetry (DSC) measurements were performed for blends of polyacrylamide (PAM) and poly(ethylene glycol) (PEG) and blends of poly(dimethylacrylamide) (PDMAM) and PEG. The samples were prepared by codissolution in a concentration range of 0–100 wt % PEG. The thermal behavior, characterized by DSC measurements, showed similar variations of the glass‐transition temperatures (Tg's) with the PEG concentration for the two systems. Pure PAM and PDMAM presented Tg's of 188 and 111 °C, respectively. A relatively small and nearly linearly decreasing Tg was observed for the two systems in the range of 20–80 wt % PEG. PEG crystals were present in all blend compositions, and no melting point depression was observed. The thermal results pointed to the partial miscibility of the blends. The degree of crystallinity of PEG increased with increasing PEG concentration for the PDMAM/PEG systems. The ortho‐positronium lifetime (τ3) increased with increasing PEG concentration for both blends. However, the parameter of the ortho‐positronium formation probability (I3) decreased with the PEG concentration. The product τI3, which was proportional to the total free volume fraction, was approximately constant with the PEG concentration for PDMAM blends and increased with the PEG concentration for PAM systems. This result may be interpreted as a consequence of a more heterogeneous structure in PAM blends. Scanning electron microscopy micrographs of blends with 40 and 80 wt % PEG provided evidence of the regions associated with PEG crystallites. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1493–1500, 2003  相似文献   

5.
In this work, new ways of plasticizing polylactide (PLA) with low molecular poly(ethylene glycol) (PEG) were developed to improve the ductility of PLA while maintaining the plasticizer content at maximum 20 wt.% PLA. To this end, a reactive blending of anhydride-grafted PLA (MAG-PLA) copolymer with PEG, with chains terminated with hydroxyl groups, was performed. During the melt-processing, a fraction of PEG was grafted into the anhydride-functionalized PLA chains. The role of the grafted fraction was to improve the compatibility between PLA and PEG. Reactive extrusion and melt-blending of neat and modified PLA with PEG did not induce any dramatic drop of PLA molecular weight. The in situ reactive grafting of PEG into the modified PLA in PLA/PEG blends showed a clear effect on the thermal properties of PLA. It was demonstrated by DSC that the mobility gained by PLA chains in the plasticized blends yielded crystallization. The grafting of a fraction of PEG into PLA did not affect this process. However, DSC results obtained after the second heating showed an interesting effect on the Tg when 20 wt.% PEG were melt blended with neat PLA or 10 wt.% MAG-PLA. In the latter case, the Tg displayed by the reactive blend was shifted to even lower temperatures at around 14 °C, while the Tg of neat PLA and PLA blended with 20 wt.% PEG was around 60 and 23 °C, respectively. Regarding viscoelastic and viscoplastic properties, the presence of MAG-PLA does not significantly influence the behavior of plasticized PLA. Indeed, with or without MAG-PLA, elastic modulus and yield stress decrease, while ultimate strain increases with the addition of PEG into PLA.  相似文献   

6.
Thermal expansion of four strontium borates has been studied by high-temperature powder X-ray diffraction. Strong anisotropy of thermal expansion is observed for the structures of Sr3B2O6 (0D) and SrB2O4 (1D) based on triangles BO3 only: The high expansion occurs perpendicular to the BO3 plane, i.e. along the direction of the less strong bonds in the crystal structure. The monoclinic Sr2B16O26 (3D) borate expands dramatically due to shear deformations in monoclinic plane: Monoclinic β′ angle changes significantly because it is not fixed by symmetry. In contrast to these borates, SrB4O7 (3D) borate built up from tetrahedra only expands almost isotropically. Average value of volume expansion is 36 × 10?6 K?1 for studied Sr-borates. Tendency of slight decrease in the volume thermal expansion and sharp decrease in the melting points is observed with an increase in B2O3 content as a result of the degree of polymerization increase. As the B2O3 content grows in Sr-borates, the structural complexity increases in the SrO–B2O3 system due to more complex anionic structure. Inverse “melting temperature decrease—structural complexity increase” correlation is revealed.  相似文献   

7.
When PEG (M.W.~5000 Daltons) is conjugated to poly(l ‐alanine), the polymer aqueous solutions (<10.0 wt.%) undergo sol‐to‐gel (thermal gelation), whereas it is conjugated to poly(l ‐lactic acid), the polymer aqueous solutions (>30.0 wt.%) undergo gel‐to‐sol (gel melting) as the temperature increases. In the search for molecular origins of such a quite different phase behavior, poly(ethylene glycol)‐poly(l ‐alanine) (PEG‐PA; EG113‐A12) and poly(ethylene glycol)‐poly(l ‐lactic acid) (PEG‐PLA; EG113‐LA12) are synthesized and their aqueous solution behavior is investigated. PEG‐PAs with an α‐helical core assemble into micelles with a broad size distribution, and the dehydration of PEG drives the aggregation of the micelles, leading to thermal gelation, whereas increased molecular motion of the PLA core overwhelms the partial dehydration of PEG, thus gel melting of the PEG‐PLA aqueous solutions occurs. The core‐rigidity of micelles must be one of the key factors in determining whether a polymer aqueous solution undergoes sol‐to‐gel or gel‐to‐sol transition, as the temperature increases. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, , 52, 2434–2441  相似文献   

8.
Poly(lactic acid) (PLA)/poly(butylene adipate-co-terephthalate) (PBAT) blends were prepared using melt processing. The effects of maleic anhydride grafted PLA (PLA-g-MA) and calcium carbonate (CaCO3) content on mechanical, thermal, and morphological properties of the blends were investigated. PLA-g-MA was synthesized by varying monomer and initiator contents using a reactive melt-grafting process. Tensile properties of PLA/PBAT blend were enhanced with adding 2 phr of PLA-g-MA. SEM micrographs exhibited the improvement of interfacial adhesion between PLA and PBAT in the compatibilized blend. Moreover, thermal stability of the blends improved with presence of PLA-g-MA. With increasing CaCO3 content, Young’s modulus of the composites increased.  相似文献   

9.
Polyethersulfone (PES) and poly(1‐vinylpyrrolidone) (PVP) were used to prepare ultrafiltration membranes with grafted Fe3O4 magnetic nanoparticles (PVP‐g‐Fe3O4@SiO2). The structure of synthesized PVP‐g‐Fe3O4@SiO2 was confirmed by FT‐IR and SEM analysis. Physical properties of blend membranes such as thermal resistance, Tensile strength, water uptake, and hydrophilicity were also investigated. Blended membranes of PES/PVP‐g‐Fe3O4@SiO2 have exhibited higher thermal resistance due to increasing the modified nanoparticle content. The hydrophilicity of the synthesized PES/PVP‐g‐Fe3O4@SiO2 membranes also improved by increasing the PVP‐g‐Fe3O4@SiO2 content. As expected, increasing the hydrophilicity of blended membrane, caused enhancement of fouling resistance in membranes. Results showed that the content of PVP‐g‐Fe3O4@SiO2 has different effects on the properties of synthesized composite membranes. Despite increasing the content of PVP‐g‐Fe3O4@SiO2 has a negative effect on elongation, positive effects on maximum stress was observed. Moreover, the water uptake of synthesized membranes was significantly enhanced in comparison to other similar studies.  相似文献   

10.
Phase equilibria in the SrO-Bi2O3-B2O3 system were studied using powder X-ray diffraction (XRD) and differential thermal analysis (DTA). Quasi-binary sections were determined, and an isothermal section of the system in the subsolidus region at 600°C was constructed using the crossing spections method. A new ternary compound was found: SrBi2B4O10. The existence of SrBi2B2O7 was verified. Bi2O3-SrB2O4 and Bi4B2O9-2SrO: 3B2O3 polytherms were constructed.  相似文献   

11.
The density of melts of the system KF? K2MoO4? B2O3 was measured. The molar volume in the binary system KF? K2MoO4 deviates only little from the ideal course, which indicates the extended thermal dissociation of the congruently melting additive compound K3FMoO4. In the KF? B2O3 binary system the formation of KBF4 and K2B4O7 leads to the volume expansion, like in the K2MoO4? B2O3 system, where the volume expansion may be described by the formation of the heteropolyanions [BMo6O24]9?. The significant deviation from the ideal behaviour in the ternary system KF? K2MoO4? B2O3 refers to the pronounced interaction, most probably due to the substitution of oxygen atoms in the coordination sphere of the heteropolyanion with the fluorine ones.  相似文献   

12.
The effect of polyethyleneglycol (PEG) on gas permeabilities and selectivities was investigated in a series of miscible cellulose acetate (CA) blend membranes. The permeabilities of CO2, H2, O2, CH4, N2 were measured at temperatures from 30 to 80°C and pressures from 20 to 76 cmHg using a manometric permeation apparatus. It was determined that the blend membrane having 10 wt% PEG20000 exhibited higher permeability for CO2 and higher permselectivity for CO2 over N2 and CH4 than those of the membranes which contained 10% PEG of the molecular weight in the range 200–6000. The CA blend containing 60 wt% PEG20000 showed that its permeability coefficients of CO2 and ideal separation factors for CO2 over N2 reached above 2 × 10−8 [cm3 (STP) cm/cm2 s cmHg] and 22, respectively, at 70°C and 20 cmHg. Based on the data of gas permeability coefficients, time lags and characterization of the membranes, it is proposed that the apparent solubility coefficients of all CA and PEG blend membranes for CO2 were lower than those of the CA membrane. However, almost all the blend membranes containing PEG20000 showed higher apparent diffusivity coefficients for CO2, resulting in higher permeability coefficients of CO2 with relation to those of the CA membrane. It is attributed to the high diffusivity selectivities of CA and PEG20000 blend membranes that their ideal separation factors for CO2 over N2 were higher than those of the CA membrane in the range 50–80°C, even though the ideal separation factors of almost all PEG blend membranes for CO2 over CH4 became lower than those of the CA membrane over nearly the full range from 30° to 80°C.  相似文献   

13.
Polylactide (PLA)/starch blend/clay and PLA/clay composites are prepared by melt blending. Structural and thermal characterizations are performed by differential scanning calorimetry, X-ray diffraction analysis, and thermogravimetric analysis. The fire properties are assessed on a dual cone calorimeter. Combustion residue and char formation is characterized by optical microscopy and attenuated total reflection infrared spectroscopy. Although the clay is not fully intercalated/exfoliated, the composites exhibit a higher thermal stability and much reduced peak heat release rate, and the PLA/starch blend composite retains its mechanical properties. For the PLA/starch blend composite, smoke release is also considerably reduced. Catalyzed, oxidative decomposition is shown to occur early in the thermal decomposition of the composites, prior to increased thermal stability. The inclusion of clay promotes char formation and increases the quantity of carbonaceous char in the combustion residue. There is minimal migration of the clay to the surface prior to ignition and char is formed mainly after ignition and during burning. During the later stages of burning some of the char formed is converted to CO2.  相似文献   

14.
The aim of the present work was to evaluate if the presence of a polyethylenglycol (PEG) coating around PLA nanoparticles would affect their interaction with biological surfaces, following oral administration to rats. For this purpose, a model antigen, 125I-radiolabeled tetanus toxoid, was encapsulated in PLA and PLA-PEG nanoparticles by a modified water-in-oil-in-water solvent evaporation technique. Firstly, the stability of the nanoparticles in simulated gastrointestinal fluids was evaluated. Results showed an interaction between the nanoparticles and the enzymes of the digestive fluids, this interaction being considerably reduced by the PEG coating around the particles. On the other hand, the PLA forming the nanoparticles was found to be only slightly degraded (9% converted to lactate for PLA nanoparticles and 3% for PLA-PEG nanoparticles) and that the encapsulated tetanus toxoid remained mostly associated to the nanoparticles upon incubation in the digestive fluids for up to 4 h. Finally, the in vivo experiments showed that, after oral administration to rats, the levels of encapsulated radioactive antigen in the blood stream and lymphatics were higher for PLA-PEG nanoparticles than for PLA nanoparticles. In conclusion, the PLA-PEG nanoparticles have a promising future as protein delivery systems for oral administration.  相似文献   

15.
High crystalline cerium hexaboride (CeB6) nanoparticles (NPs) were synthesized using mixture of mag‐ nesium (Mg), cerium oxide (CeO2) and boron oxide (B2O3) via the mechanochemical process at room tem‐ perature. Based on the results, magnesiothermic reduction of B2O3 occurred after about 2 h of milling in a mechanically induced self‐sustaining reaction (MSR). The significant amount of heat produced by the reduction reaction resulted in CeO2 reduction to elemental Ce which finally reacted with elemental B and formed CeB6 compound. According to XRD analyses, the degree of crystallinity and lattice parameter of the product was calculated about 93 % and 4.1458 Å, respectively. The morphology observations revealed that the synthesized CeB6 had semi‐cubic shape with the range of size 25–60 nm. The synthesis of CeB6 during the thermal treatment was studied by simultaneous thermal analysis (STA) technique. It was found that the reduction of B2O3 took place after melting of Mg meanwhile, no CeB6 phase achieved even up to 1100 °C.  相似文献   

16.
The effect of crystallinity of polylactide (PLA) on the structure and properties of tough PLA blends with PEG-b-PPG-b-PEG block copolymers was studied. PLA was melt blended with a set of the copolymers with varying ratio of the hydrophilic (PEG) and hydrophobic (PPG) blocks. Although the blend phase structure depended on the copolymer molar mass and PEG content, as well as on the copolymer concentration in the blend, crystallinity also played an important role, increasing the copolymer content in the amorphous phase and enhancing phase separation. The influence of crystallinity on the thermal and mechanical properties of the blends depended on the copolymer used and its content. The blends, with PLA crystallinity of 25 ÷ 34 wt%, exhibited relatively high glass transition temperature ranging from 45 to 52 °C, and melting beginning above 120 °C. Although with a few exceptions crystallinity worsened the drawability and toughness, these properties were improved with respect to neat crystalline PLA in the case of partially miscible blends, in which fine liquid inclusions of the modifier were dispersed in PLA rich matrix. About 20-fold increase of the elongation at break and about 4-fold increase of the tensile impact strength were reached at a small content (10 wt%) of the modifier. Moreover, crystallinity decreased oxygen and water vapor transmission rates through neat PLA and the blend, and the barrier property for oxygen of the latter was better than that of neat polymer.  相似文献   

17.
在β-环糊精作保护剂条件下, 制备了高对称的十八面体四氧化三铁(Fe3O4)纳米材料. 通过胶体化学方法, 合成了一系列不同起始计量比的聚乙二醇(PEG)和Fe3O4纳米粒子复合物(CM-1-CM-4). 这些PEG复合材料展示出重要特性: 首先, 它们的表面形貌依赖于Fe3O4的计量; 其次, PEG的熔化过程受Fe3O4的影响, 并且直接与Fe3O4的含量相关; 进一步研究表明, 除CM-4外, Fe3O4的引入导致PEG结晶度下降, 而且Fe3O4纳米粒子量越少, 降低幅度越大; 更为有趣的是, PEG的降解过程受制于Fe3O4纳米粒子的影响, 导致不同降解产物的出现; 而且, 与纯Fe3O4纳米粒子一样, 复合材料中的Fe3O4也显示典型的软铁磁性行为, 但饱和磁化强度相对较小; 此外, X射线光电子能谱(XPS)实验揭示在这些PEG复合材料中, 有从Fe到O的电子转移, Fe电子密度的降低可用来解释复合材料饱和磁化强度的减小; 最后, 这些PEG复合材料呈现出对有机染料的表面增强拉曼效应, 并且这种效应随Fe3O4纳米粒子含量的增加而增加. 这些结果将会对聚合物/无机纳米粒子复合材料的发展起到推进作用.  相似文献   

18.
A combination of solution casting and melt extrusion technique was used to fabricate Boron nitride (BN)-filled Polylactic acid (PLA)/polybutylene adipate terephthalate (PBAT) blend composites. The BN particles were surface treated with a silane coupling agent and functionalization was confirmed via spectroscopic analysis. Field emission scanning electron microscopy confirmed that the BN surface treatment improved the particle adhesion with the polymer matrices and acted as a compatibilizer for the polymers. Moreover, changes in the particle orientation in the blend composite yielded improved thermal conductivity in different directions. The inclusion of the treated BN particles enhanced the in-plane (~1.1 W m−1K−1) and through-plane (~0.8 W m−1K−1) thermal conductivity of the composites as compared to the neat PLA. In addition, the storage modulus of the composite become more than 3 GPa that is twice that of the PLA/PBAT blend with a reasonable tensile property. In general, compared with the PLA/PBAT blend, the blend composites exhibited superior thermal and mechanical properties.  相似文献   

19.
The first silver bismuth borate, AgBi2B5O11 (silver dibismuth pentaborate), has been prepared via glass crystallization in the Ag2O–Bi2O3–B2O3 system and characterized by single‐crystal X‐ray diffraction. Its structure is derived from that of centrosymmetric Bi3B5O12 by ordered substitution of one Bi3+ ion for Ag+, which results in the disappearance of the mirror plane and inversion centre. Second harmonic generation (SHG) measurements confirm the acentric crystal structure. It is formed by [Bi2B5O11] layers stretched along c and comprised of vertex‐sharing B5O10 and BiO3 groups which incorporate the Ag+ cations. The new compound was characterized by thermal analysis, high‐temperature powder X‐ray diffraction, and vibrational and UV–Vis–NIR (near infrared) spectroscopy. Its thermal expansion is strongly anisotropic due to the presence of rigid B5O10 groups aligned in a parallel manner. The minimal value is observed along their axis [parallel to c, αc = 3.1 (1) × 10?6 K?1], while maximal values are observed in the ab plane [αa = 20.4 (2) and αb = 7.8 (2) × 10?6 K?1]. Upon heating, AgBi2B5O11 starts to decay above 684 K due to partial reduction of silver; incongruent melting is observed at 861 K. According to density functional theory (DFT) band‐structure calculations, the new compound is a semiconductor with an indirect energy gap of 3.57 eV, which agrees with the experimental data (absorption onset at 380 nm).  相似文献   

20.
Phase equilibria in the SrO-Bi2O3-B2O3 system have been investigated by X-ray powder diffraction analysis and DTA. Ternary compounds SrBiBO4 and Sr7Bi8B18O46 congruently melting at 820 ± 5°C and 760 ± 5°C have been found. Quasi-binary sections are determined and the isothermal section of the system in the region Bi2O3-Sr2Bi2O6-Sr3B2O6-B2O3 at 600°C has been constructed.  相似文献   

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