首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 883 毫秒
1.
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   

2.
《先进技术聚合物》2018,29(7):2121-2133
Polylactide (PLA)/poly(butylene succinate) (PBS) blend films modified with a compatibilizer and a plasticizer were hot‐melted through a twin screw extruder and prepared by hydraulic press. Toluene diisocyanate (TDI) and polylactide‐grafted‐maleic anhydride (PLA‐g‐MA) were used as compatibilizers, while triethyl citrate and tricresyl phosphate acted as plasticizers. The effects of the type and content of compatibilizer and plasticizer on the mechanical characteristics, thermal properties, crystallization behavior, and phase morphology of the PLA/PBS blend films were investigated. Reactive compatibilization at increasing levels of TDI improved the compatibility of the PLA and PBS, affecting the toughness of the films. As evidenced by scanning electron microscope, the addition of TDI enhanced the interfacial adhesion of the blends, leading to the appearance of many elongated fibrils at the fracture surface. Furthermore, PLA/PBS blending with both TDI and PLA‐g‐MA led to an acceleration of the cold crystallization rate and an increment of the degree of crystallinity ( ). Toluene diisocyanate could be a more effective compatibilizer than PLA‐g‐MA for PLA/PBS blend films. The synergistic combination of compatibilizer and plasticizer brought a significant improvement in elongation at break and tensile‐impact toughness of the PLA/PBS blends, compared with neat PLA. Their failure mode changed from brittle to ductile due to the improved compatibility and molecular segment mobility of the PLA and PBS phases. Differential scanning calorimeter results revealed that the plasticizers triethyl citrate and tricresyl phosphate changed the thermal behavior of Tcc and Tm, affecting α′ and α crystal formations. However, these plasticizers only slightly improved the thermal stability of the films.  相似文献   

3.
Preparing a polylactide (PLA)/plasticizer system has been regarded as an effective solution to improve the ductility of brittle PLA. In this reach, a novel type of alkyl phosphine oxides consisting of three aliphatic ester substituents was prepared from PH3 tail gas, and its potential to be employed as a PLA plasticizer was studied. Differential scanning calorimeter tests confirmed that the newly-prepared plasticizer decreased the Tg of PLA (28 wt% plasticizer) from 52°C (neat PLA) to 11°C, and increased the elongation at break from 11% (neat PLA) to 271% (plasticized PLA). X-ray diffraction results showed that the crystallization degree of PLA (28 wt% plasticizer) increased from 0.12% of neat PLA to 14.04%, while Young's modulus of PLA remained as high as 121.3 MPa, which was much higher than that of the PLA/citrate ester systems with same plasticizer content. These novel phosphorus-containing plasticizers exhibited excellent thermal stability and a weight-loss of the system no more than 2.5% at 180°C; therefore, no unpleasant volatiles were released during processing. In contrast, the weight loss of the PLA/citrate system was as high as 10.8% at 180°C, forming heavy fog with an unpleasant smell during thermal mixing. Scanning electron microscopy was employed to observe the microstructure of the PLA/plasticizer systems, which indicated that the carboxylic butyl ester-containing phosphine oxides was compatible with PLA matrix.  相似文献   

4.
The Knudsen mass-loss effusion technique was used to measure the vapour pressures at different temperatures of the following six compounds: 2-methyl-3-nitrobenzoic acid, between T =  357.16 K and T =  371.16 K; 2-methyl-6-nitrobenzoic acid, between T =  355.16 K and T =  369.16 K; 3-methyl-2-nitrobenzoic acid, between T =  371.16 K and T =  385.14 K; 3-methyl-4-nitrobenzoic acid, between T =  363.21 K and T =  379.16 K; 4-methyl-3-nitrobenzoic acid, between T =  363.10 K and T =  377.18 K; 5-methyl-2-nitrobenzoic acid, between T =  355.18 K and T =  371.08 K. From the temperature dependence of the vapour pressure, the standard molar enthalpies of sublimation were derived by the Clausius–Clapeyron equation and the molar entropies of sublimation at equilibrium pressures were calculated. Using estimated values for the heat capacity differences between the gas and the crystal phases of the studied compounds the standard, po =  105Pa, molar enthalpies ΔcrgHmo, entropies ΔcrgSmoand Gibbs energies ΔcrgGmoof sublimation at T =  298.15 K, were derived:  相似文献   

5.
The formulation of appropriate dental adhesives is critical to achieve efficient polymerisation and reduced fluid permeability. The aim of this study was to evaluate the degree of conversion, the crosslink density and the fluid permeability of experimental 2-Hydroxyethyl methacrylate (HEMA)-containing or HEMA-free resin adhesives formulated with the use of a hydrophilic ternary photoinitiator system (DPIHP: diphenyliodonium hexafluorophosphate). The final FTIR/Raman degree of conversion (DC), DSC glass transition temperature (Tg) and the resin permeability (rP) were then characterised. The inclusion of the hydrophilic ionic salt DPIHP increased the affinity between amphiphilic monomers and binary photoinitiator system enhancing the DC, Tg and the resistance to fluid permeability (p < 0.05). A significant correlation was observed between rP and FTIR/Raman-DC or Tg (p < 0.05). In conclusion, new generation resin adhesives containing hydrophilic monomers and solvents should be formulated on a ternary photoinitiator system including hydrophilic ionic accelerator in order to achieve enhanced physical–chemical characteristics especially when light-cured in a relatively short period time (10–20 s).  相似文献   

6.
Se96Sn4 chalcogenide glass was prepared by melt quenching technique and exposed, at room temperature, to different doses of 4, 8, 12, 24 and 33 kGy of high-energy 60Co gamma irradiation. Differential scanning calorimeter (DSC) was used under non-isothermal condition to determine the glass transition temperature Tg, onset Tc and peak Tp temperatures of crystallization, of un-irradiated and γ-irradiated samples, at four different heating rates. The variation of Tg with heating rates was utilized to calculate the glass transition activation energy Et for un-irradiated and γ-irradiated glass, using the methods suggested by Kissinger and Moynihan. Based on the obtained values of the characteristic temperatures Tg, Tc and Tp, thermal stability was monitored through the calculation of the S parameter and the crystallization rate factor 〈Kp〉 for irradiated and un-irradiated glass. Results reveal that, as γ-dose increases Tg increases up to 12 kGy then decreases at higher doses but remains more than that of un-irradiated glass. Meanwhile, both Et and 〈Kp〉 attain their minimum values at the same dose of 12 kGy and the glass is thermally stable at this particular dose.  相似文献   

7.
In contrast to well established experimental results of vibronic coupling effects in octahedral dn complexes with Eg ground states (Cu2+, Ag2+; Cr2+, Mn3+ etc.), not much useful material is available for the Jahn–Teller (JT) effect in orbital triplet ground states. The present study is concerned with this deficiency, providing data for octahedral halide model complexes with 3dn cations – in particular for TiIII, VIII and high-spin CoIII, NiIII with T2g and T1g ground states, which involve, to first-order, solely splitting of the π-antibonding t2g MOs. Besides experimental results – structural and spectroscopic, mainly from d–d spectra – data from computations are needed for a quantitative treatment of the Tg ? (?g + τ2g) vibronic interaction as well as in the Eg ? ?g coupling case (MnIII, low-spin NiIII); DFT was the method of choice, if only critically selected outcomes are utilised. The theoretical bases of the treatment are the dn ligand field matrices in Oh, extended by the inclusion of lower-symmetry distortion parameters, and the conventional theory of vibronic coupling. Caution is needed when classifying the effects of interelectronic repulsion; DFT does not reproduce the magnitudes of the Racah parameters B, C, as deduced from the d–d spectra, properly – the presumed reasons are analysed. DFT even allows one to deduce reliable vibronic coupling constants via the analysis of orbitally degenerate excited states (CrIII, 4A2g ground state). The group-theoretical analysis of the interaction with the JT-active ?g and τ2g modes yields D4h, D3d and D2h as the possible distortion symmetries in the case of a Tg ground state. The DFT-calculations give clear evidence, that the D4h stationary points represent the absolute minima in the Tg ? (?g + τ2g) potential surface – in agreement with experiment, where available. For the first time, vibronic coupling constants, characterising JT splitting of ground and excited Tg states, can be presented for trivalent 3dn cations in octahedral halide ligand fields. They turn out to be smaller by a factor of almost 3 in comparison to those, which determine the coupling in σ-antibonding eg MOs.The tetragonal splitting of Tg states is typically only small, around 0.1 eV, and suggests that strain influences from a specific ligand arrangement and/or the presence of different ligands may modify the potential surface considerably. We have studied such effects via compounds AIMIIIF4, where an elastic strain induced by the host structure, and a binding strain, due to the simultaneous existence of (largely) terminal and of bridging ligands, are active. A novel strain model, in its interplay with JT coupling, is proposed and applied – using energies from the d–d spectra, structural results and data from DFT.Chloride complexes are only known for TiIII to FeIII; the rather small electronegativity already of CoIII suggests a reducing ligand-to-metal (3dn) electron transfer for n  6. Similarly, the low-lying ligand-to-metal charge transfer bands in the d–d spectra of the CuIIIF63? complex and the reduced Tg ? ?g coupling strength suggest a pronounced covalency of the CuIII–F, and, even more distinctly, of the CuIII–O bond, which is of interest for superconductivity. The NiIIIF63? polyhedron possesses a low-spin configuration in the elpasolite structure. The spectroscopic evidence and the DFT data indicate, that the minimum positions of the alternative a2A1g(a2Eg) and a4A2g (a4T1g) potential curves are only ≤0.02 eV apart, giving rise to interesting high-spin/low-spin phenomena. It is the strong Eg ? ?g as compared to the T1g ? ?g coupling, which finally stabilises a spin-doublet ground state in D4h.We think, that the selected class of solids is unique particularly for the study of Jahn–Teller coupling in T ground states, with model character for other systems. In our overview a procedure is sketched, which uses reliable computational results (here from DFT) for supplementing incomplete experimental data, and presents – on a semiquantitative scale – convincing statements, consistent with chemical intuition. It is also a pleading for ligand field theory, which rationalises d-d spectra in terms of chemical bonding; though the latter spectra provide frequently only rather coarse information, their assistance in the energy analysis is crucial.  相似文献   

8.
The influence of accelerated thermal treatment of thermosetting epoxy laminate on its glass transition temperature was studied. Lamplex® FR-4 glass fibre-reinforced epoxy laminate (used for printed circuit board manufacturing) was used in these experiments. The composite was exposed to thermal treatments at temperatures ranging from 170 °C to 200 °C for times ranging from 10 to 480 h. The glass transition temperature (Tg) was analysed via dynamic mechanical analysis (DMA). It has been proven that the glass transition temperature rapidly decreases in reaction to thermal stress. The obtained Tg data were used for Arrhenius plots for different critical temperatures (Tg-crit. = 105–120 °C). From their slopes (?Ea/R), the activation energy of the thermal degradation process was calculated as 75.5 kJ/mol. In addition to this main relaxation mechanism, DMA also recorded one smaller relaxation process in the most aged samples. Microscopic analysis of the sample structure showed the presence of pronounced small regions of degradation both on the surface and in the inner structure, which are probably the causes of microscopic delamination and the smaller relaxation process.  相似文献   

9.
The stacks of multi-layer Ti3C2Tx and other types of MXene materials limit their electrochemical performance. Herein, we report a facile exfoliation technique to improve the exfoliation efficiency through Li-intercalation into Ti3C2Tx interlayers in isopropyl alcohol (IPA) with LiOH as intercalant. This de-intercalation method presented here not only effectively delaminates the stacked Ti3C2Tx multi-layers into separate few-layer MXene sheets, but also achieves high-rate supercapacitive performance of Ti3C2Tx electrode. The as-produced delaminated Ti3C2Tx shows highly improved electrochemical capacitive properties from 47 to 115 F g 1 at 200 mV s 1. Even at extremely high scan rate of 1000 mV s 1, a specific capacitance of 82 F g 1 is still obtained. The high-rate capability can be attributed to improved ions accessibility into the few-layer structures. This study offers a new and simple exfoliation pathway for MXenes materials to exploit their full potential in energy storage applications.  相似文献   

10.
Cellulose acetate (CA) with a degree of substitution (DS) of 2.5 has been plasticized using eco-friendly plasticizers such as triacetin, tripropionin, triethyl citrate, tributyl citrate, tributyl 2-acetyl citrate and poly(ethylene glycol) of low molecular weight. Thermo-mechanical properties and hydrophilicity of the modified CA have been measured and correlated with the content and nature of the plasticizer used and compared with unplasticized CA. The increase in toughening and the change in the hydrophilicity by the plasticization were evaluated in terms of aging and weathering stability under accelerated conditions. Samples were exposed to UV-degradation with water spray periods. The treated samples were removed periodically and characterized by several analytical techniques. The results are discussed with particular emphasis toward the effects of plasticization on enhancement of the degradation rate of CA. The plasticization of CA triggered an increase of the weight loss between 50 and 90%, where low molecular weight plasticizers were shown to be more effective. A right balance between hydrophilicity and plasticization efficiency (reduction of Tg) is needed to increase the degradation rate of CA.  相似文献   

11.
The Knudsen mass-loss effusion technique was used to measure the vapour pressures at different temperatures of the following compounds: 3-phenylpropionic acid, between T =  305.17 K and T =  315.17 K; 3-(2-methoxyphenyl)propionic acid, between T =  331.16 K and T =  347.16 K; 3-(4-methoxyphenyl)propionic acid, between T =  341.19 K and T =  357.15 K; 3-(3,4-dimethoxyphenyl)propionic acid, between T =  352.18 K and T =  366.16 K. From the temperature dependence of the vapour pressure, the standard molar enthalpies of sublimation ΔcrgHmowere derived by the Clausius–Clapeyron equation and the molar entropies of sublimation at equilibrium pressures were calculated. On the basis of estimated values for the heat capacity differences between the gas and the crystal phases of the studied compounds the standard, p   =  105Pa, molar enthalpies, entropies and Gibbs energies of sublimation at T =  298.15 K, were derived:  相似文献   

12.
Electron beam (e-beam) curing is a technology that offers advantages over the thermal curing process, that usually requires high temperature and are time-consuming. E-beam curing is faster and occurs at low temperatures that help reduce residual mechanical stresses in a thermoset composite. The aim of the present study is to analyze the effects of cationic initiator (diaryliodonium hexafluoroantimonate) ranged from 1 to 3 wt% in DGEBA (diglycidyl ether of bisphenol A) epoxy resin when cured by a 1.5 MeV electron beam. The specimens were cured to a total dose of 200.4 kGy for 40 min. Analyses by dynamic mechanical thermal analysis (DMTA) and differential scanning calorimetry (DSC) show that the e-beam irradiated samples with 2 wt% cationic initiator were 96% cured obtained a glass transition temperature (tan δ) of 167 °C. The same epoxy resin, thermally cured for 16 h with an anhydride hardener, reached a Tg (tan δ) of 136 °C. So, the irradiated sample had its Tg increased approximately 20% and the curing process was much less time consuming.  相似文献   

13.
The relative permittivity, loss and dielectric strength have been measured for a polycarbonate-based material, tetraaryl bisphenol A polycarbonate, that has been fluorine substituted (DiF p-TABPA-PC). The new material has a glass transition temperature, Tg = 489 K, that is higher than that for either conventional bisphenol A polycarbonate (BPA-PC) for which Tg = 421 K or for a copolymer of tetraaryl bisphenol A (TABPA) and bisphenol A (BPA) (TABPA-BPA-PC) for which Tg = 464 K. In addition, the dielectric strength of DiF p-TABPA-PC is almost identical to that for purified BPA-PC and slightly larger than the value for TABPA-BPA-PC. The relative permittivity and loss measurements were carried out from 10 to 105 Hz over a wide temperature range and at pressures up to 0.25 GPa. Variable temperature results for the α relaxation and both temperature and pressure results for the γ relaxation regions are reported. The α relaxation exhibits standard behavior. The γ relaxation exhibits unusual characteristics such as a strong increase in peak height as temperature increases and a strong decrease in peak height with increasing pressure. The data for the γ relaxation have been analyzed using several formulations. Expressions for the peak height and peak position based on a two state (inequivalent well) model and the resulting parameters are discussed in terms of the insight they provide into the molecular mechanisms responsible for the sub-Tg relaxation. Ab initio SCF results for a related model compound are presented. Finally, the real part of the relative permittivity for the new polymer is about 10% higher than for BPA-PC.  相似文献   

14.
In this report, we describe the synthesis and characterization of photosensitive poly(l-lactide) with a pendent cinnamate group. α,ω-Dihydoxy terminated poly(l-lactide) (PLLA-diol) [molecular weights (MW); 2000, 4000 and 9000 g/mol ] was chain-extended with a diacyl chloride of 5-cinnamoyloxyisophthalic acid (ICA) to obtain high-molecular-weight photocrosslinkable poly(l-lactide)s (ICA/PLLA). The resulting polyesters were characterized by proton nuclear magnetic resonance spectroscopy, gel permeation chromatography, ultraviolet–visible spectroscopy, differential scanning calorimetry, thermomechanical analysis and thermogravimetry. The glass transition temperature (Tg), the melting temperature (Tm) and the degree of relative crystallinity (Xc) of ICA/PLLAs increased with the increasing MW of the PLLA-diols. The photosensitive ICA/PLLAs were irradiated with a 400 W high-pressure mercury lamp (λ > 280 nm) for various times to produce the PLLA gel films without a photoinitiator. The crosslinking rate monitored by a UV–vis spectrum decreased with the increasing MW of the PLLA-diols. The crosslinking of the ICA/PLLA ?4000 film enhanced the Tg slightly and the tensile strength and Young’s modulus significantly, while reduced the Tm and Xc. The enzymatic degradation was measured by the weight loss of the films in a phosphate buffer solution with proteinaze-k. The crosslinking of the films decreased markedly the degradation rate.  相似文献   

15.
Glasses with composition 50Bi2O3–(50 ? x) B2O3xGeO2 (x = 0, 5, 10, 15 mol%) were prepared by conventional melting method. The thermal properties were investigated by differential thermal analysis (DTA) and the structures of the glasses were probed by Infrared, Raman and X-ray photoelectron spectroscopy (XPS). The results show that density, refractive index and optical basicity increase with the increase of GeO2. The glass transition temperature (Tg), onset crystallization temperature (Tx) and ΔT (Tx ? Tg) increase as well. The cut-off edges in ultraviolet and infrared shift to longer wavelength by the addition of GeO2. Infrared, Raman and XPS results indicate that the glass network consists of [Bi–O6] octahedron, [BO3] triangle, [BO4] tetrahedron and [GeO4] tetrahedron and borate oxide mainly exists in [BO3] units. XPS result indicates Ge4+ ions form steady [GeO4] tetrahedra units in the glass network and the number of non-bridging oxygens decreases with the addition of GeO2.  相似文献   

16.
A heat-flow Calvet microcalorimeter was adapted for the measurement of sublimation enthalpies by the vacuum-drop method, with samples of masses in the range 1 mg to 5 mg. The electrically calibrated apparatus was tested by determining the enthalpies of sublimation of benzoic acid and ferrocene, at T =  298.15 K. The obtained results, ΔcrgHmo(C7H6O2)  =  (88.3  ±  0.5)kJ · mol  1and ΔcrgHmo(C10H10Fe) =  (73.3  ±  0.1)kJ · mol  1, are in excellent agreement with the corresponding values recommended in the literature. Subsequent application of the apparatus to the determination of the enthalpy of sublimation of η5-bis-pentamethylcyclopentadyenyl iron, at T =  298.15 K, led to ΔcrgHmo(C20H30Fe)  =  (96.8  ±  0.6)kJ · mol  1.  相似文献   

17.
A mild pre-irradiation method was used to graft glycidyl methacrylate (GMA) onto polyethylene (PE) non-woven fabric (NF). The polymer was irradiated by electron beam in air atmosphere at room temperature. The degree of grafting (Dg) was determined as a function of reaction time, absorbed dose, monomer concentration and temperature. After 30 kGy irradiation, with 5% GMA, surfactant Tween 20 (Tw-20) of 0.5% at 55 °C for 15 min, the trunk polymer was made grafted with a Dg of 150%. Selected PE-g-PGMA of different Dg was modified with aminated compounds such as ethylenediamine (EDA), diethylenetriamine (DETA), triethylenetetramine (TETA) and tetraethylenepentamine (TEPA). The obtained amine-type adsorbents were prepared to remove copper and uranium ions from solution. It was shown that at least 90% of copper and 60% of uranium with the initial concentration from 3 to 1000 ppb can be removed from water.  相似文献   

18.
The diffusion of ferrocene methanol in super-cooled aqueous solutions containing sucrose has been studied, using disk and cylindrical microelectrodes, over a wide viscosity range. The solution viscosity and the reduced temperature T/Tg (Tg being the glass transition temperature) were varied by changing the sucrose concentration and the temperature of the system. The voltammetric limiting current obtained with a disk microelectrode and the i(t) response on a cylindrical microelectrode after a potential step were used to determine diffusion coefficients from 7 × 10−6 cm2 s−1 down to 2 × 10−11 cm2 s−1. The electrochemical procedure described in this work allows a simple and accurate measurement of the dynamics of electroactive solutes in glass-forming liquids.  相似文献   

19.
Here, we have measured the glass transition temperature (Tg) of the ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate–H2O mixed solutions as a function of H2O concentration (x mol% H2O). The glass-forming composition region was also determined. Contrary to the results of the quaternary ammonium type of ionic liquid, N,N-diethyl-N-methyl-N-(2-methoxyethyl) ammonium tetrafluoroborate–H2O mixed solutions, we did not observed the multiple glass transition behaviour. We also measured the glassy Raman spectra of the solutions at T = 77 K. We find that the “nearly free” hydrogen bonded Raman band of water molecules in the aqueous [bmim][BF4] solution exists up to around x = 60 mol% H2O, even at T = 77 K.  相似文献   

20.
An adiabatic calorimetric and direct microscopic observation of crystallization at low temperatures was performed for salol and benzophenone. Both of the materials in the supercooled-liquid phase exhibited a low-temperature crystallization proceeding in the glass-transition temperature ( Tg) region. The crystallization was observed to proceed as the advance of the crystal front into the liquid phase, and stopped suddenly atT =  227 K and T   215 K for salol and benzophenone, respectively. This anomalous temperature dependence of the crystal-growth rate is a characteristic feature of the homogeneous-nucleation-based (HNB) crystallization, which has been reported for o -terphenyl and triphenylethylene, and the presently observed low-temperature crystallization in salol and benzophenone was concluded to be the HNB crystallization, in which the crystal growth is brought about by the coalescence of crystal nuclei to the crystalline phase on the liquid-crystal interface. The substances exhibiting the HNB crystallization were revealed to have almost the same characteristics with respect to configurational entropy, and undergo the HNB crystallization in the same range of temperature normalized by Tg. These results indicate that the HNB crystallization is potentially a universal phenomenon in fragile liquids, and imply that the process is closely related to the liquid structure changing with temperature.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号