A familiar polyalcohol, 1,2-propanediol (12PDO), is among the simple alcoholic solvents with high solubility for lithium tetrafluoroborate (LiBF
4
), as well as a wide temperature range for liquids. ...The viscosity of 12PDO solutions containing LiBF
4
was measured in the temperature range of 280‒340 K using a vibrational viscometer, and it exhibited non-Arrhenius behavior fitted with the Vogel–Fulcher–Tamman (VFT) equation, which is an empirical model for describing liquid dynamics. The viscosity (
η
) increased with the increasing mole fraction of LiBF
4
(
x
), and the variation in
η
was found to be mainly controlled by the pre-exponential factor
η
0
in the VFT expression. The VFT-fitting parameters, the strength parameter (
D
), and ideal glass transition temperature (
T
0
), which indicate the Arrhenius behavior and an ideal glass transition temperature, respectively, correlated with the thermal analysis results that were obtained
via
differential scanning calorimetry. With the increasing
x
, the value of
D
decreased rapidly for
x
< 0.20, whereas it remained approximately unchanged for
x
> 0.20. The concentration dependence of
T
0
also differed at approximately
x
= 0.20. The changes in
D
and
T
0
with
x
indicated that the intrinsic hydrogen-bonding networks between the solvent molecules were rapidly destroyed by the added ions at reduced salt concentrations, while such a structural breaking effect of the added ions weakened owing to ion associations at increased salt concentrations. Thus, it was observed that the solvation structure and dynamics of the solutions strongly depended on the salt concentration.
The effect of ZIF-8 (zeolitic imidazolate framework-8) nanoparticles on the mechanical properties of thermoset epoxy-based nanocomposite is investigated using molecular dynamic (MD) simulation. To ...investigate the effect of the force field type on the results, the mechanical properties and glass transition temperature (Tg) of pure EPON862-TETA polymer were compared at various temperatures using UFF and COMPASS force fields. The results showed that the COMPASS force field provided better simulation results for systems containing polymers. To investigate the effect of ZIF-8 nanoparticle and its size, three simulation boxes were constructed containing cross-linked epoxy resin and ZIF-8 with different sizes while maintaining a weight ratio of 90:10. The mechanical properties and glass transition temperature were calculated for the epoxy/ZIF-8 nanocomposite. The results indicated that adding ZIF-8 nanoparticles improves the Tg, as well as Young's modulus, bulk modulus, and shear modulus at different temperatures compared to the pure epoxy resin.
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•The COMPASS force field predicts epoxy properties better than UFF.•ZIF-8 enhances Young's and shear modulus of epoxy resin, particularly at higher temperatures.•The nanocomposite exhibits improved mechanical properties and Tg compared to pure epoxy.•ZIF-8 (9849.08 Å3) enhances the Young's and shear modulus of cross-linked epoxy at 300 K.•The RDF plots describe epoxy atoms interactions in the nanocomposite.
Vitrimers have been emerged as a new class of polymers with many attractive properties of material processing such as reshaping, recycling and repairing. Herein, a new type of vitrimers (BDSER) based ...on thermosetting dynamic epoxy network with double disulfide bonds was synthesized by the reaction of a difunctional epoxy monomer containing disulfide bonds with 4,4′-disulfanediyldianiline (4-AFD). Our results demonstrated that the relaxation time of BDSER at 200 °C was as short as 9 s without any catalyst. The storage modulus of BDSER was up to about 2.2 GPa and its glass transition temperature was higher than 130 °C. Additionally, the thermodynamic and chemical properties of BDSER were no significant loss after 3 cycles of continuous breaking/compression molding. Furthermore, the resistance of CNT/PPy/Vitrimer composites (CPV), synthesized by doped BDSER with the polypyrrole (PPy) decorated multi-walled carbon nanotubes (WMCNTs), was decreased to 109 Ω even the mass ratio was only 1%wt, which could be used a promising candidate as self-repairing materials in the field of antistatic.
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•A novel epoxy resin monomer containing spirobiindene (TSDEP) was synthesized.•The cured TSDEP/MHHPA resin showed a low dielectric constant (κ ∼ 2.83, 10 GHz).•The cured TSDEP/DDS ...resin exhibited high Tg (∼245 °C) and low coefficient of thermal expansion.
High-temperature thermosetting resin with low dielectric constant (κ), low thermal expansion coefficient (CTE), and high modulus are drawing more and more attention from scientists and engineers in the field of the high-frequency circuit, 5G and 6G communication networks to improve the signal transmission speed. Epoxy resin, as one of the important thermosetting resin members, possesses excellent properties such as heat resistance, cohesiveness, and reactivity. However, Epoxy resin was usually mixed with different inorganic fillers to meet the above requirements, especially to decrease the κ and CTE. In this work, a new class of spirobisindane epoxy resin monomer (TSDEP) was synthesized by a classic two-step method based on 3,3,3′,3′-tetramethyl-1,1′-spirobisindane-6,6′-diol (TSD). Due to the highly distorted rigid structure of TSD, the movement of the TSDEP molecular segment is subject to more restrictions after being cured, and the free volume will increase. After cured by 4,4′-diamino diphenyl sulfone (DDS), the TSDEP/DDS resin exhibited many desirable physical properties, e.g., low dielectric constant (∼3.45, 1 MHz), low dielectric loss (∼0.025, 1 MHz), low coefficient of thermal expansion (CTE, 72 ppm/ °C, 35–150 °C), high glass transition temperature (Tg > 241 °C) and high thermal stability (Td5%∼400 °C). Furthermore, TSDEP/DDS exhibited excellent mechanical rigidity with a storage modulus of ∼ 3.1 GPa. Compared with TSDEP/DDS, 4-methylhexahydrophthalic anhydride (MHHPA) cured TSDEP system showed lower κ (∼3.09) and dielectric loss (0.015) due to weaker polar ester groups instead of more polar hydroxy groups.
The aim of this study was to evaluate the influence of spray-drying on the powder qualities and microstructures of prebiotic xylooligosaccharides (XOS). The relationships between glass transition ...temperature (Tg) and XOS retention, moisture content, drying yield as well as specific surface area under different inlet air temperatures and maltodextrin concentrations were investigated. Antioxidant activity retention, hygroscopicity, color attributes, X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR) of the spray-dried XOS product were also assessed. The results indicated that an increase in inlet air temperature decreased the moisture content, hence the Tg value was increased. Higher maltodextrin concentration increased the Tg value, and was attributed to the molecular weight increase. The wall deposition was a tendency to occur when the temperature beyond the Tg, reduced the drying yield. Higher temperature and wall deposition promoted the decomposition of XOS into monosaccharide. The crust formation rate of droplets and stickiness of microparticles were affected by Tg, and hence, influenced the specific surface area. The antioxidant activity retention of XOS exhibited a concentration-dependent behavior. The hygroscopicity of the microparticles could be reduced by both of the low inlet air temperature and high maltodextrin concentration. According to the results of color attributes, XRD and SEM, the particles were colorless and amorphous, and tended to become more spherical and scattered with the addition of maltodextrin. The FT-IR analysis confirmed that no chemical reaction occurred between XOS and agent, which indicated that maltodextrin is a promising carrier for producing bioactive XOS powder.
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•Water content and molecular weight affect glass transition temperature of the sample.•Increasing temperature enhances drying yield under glass transition temperature.•Drying temperatures and maltodextrin concentrations affect product quality.•Maltodextrin is a promising carrier for producing xylooligosaccharides powder.
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•The introduction of allyl is beneficial in reducing monomer viscosity and curing rate.•After high temperature treatment, Tg drop wasn’t found in the case of allyl-modified epoxy ...resin.•The introduction of allyl ortho to the glycidyl group generates a network that was less cross-linked than para.
Epoxy resins often age during high-temperature use, causing a drop in Tg and a number of safety problems. Currently, no specific reports addressing this Tg drop are available. Here, we proposed that the Tg drop could be prevented by allyl modification, and designed a series of epoxy monomers containing allyl to demonstrate this view. First, the influence of allyl groups on epoxy monomers was evaluated. It was found that allyl groups could reduce the viscosity of the monomers and the curing rate. These monomers were cured by DDM into resin (virgin resin) and treated at 285 °C for 6 h (treated resin) until the double bond was consumed. By comparison, it was found that although the introduction of allyl groups reduces the Tg of the virgin resin, it does not adversely affect the thermal degradation temperature (Td5%). The Td5% and Tg of the allyl-containing treated resin did not drop significantly like those of the treated resin without allyl. Specially, the Td5% and Tg of an allyl-rich resin increased by + 49 and + 289 °C, respectively. According to further study of the network generated by allyl groups, the allyl group in the para position (relative to the glycidyl ether group) would produce greater cross-linking, whereas the intramolecular ring formation in the ortho position results in an imperfect network of the new resin. Finally, through qualitative analysis of the entire resin network, we believe that this is a result of the high-temperature destruction of the epoxy network and the formation of an allylic network.
Four series of CaO-ZnO-B
2
O
3
-SLS (CZBS) glasses have been synthesized by using waste materials which are eggshell (EG) and soda lime silica (SLS) glass. We utilized eggshells to source calcium ...oxide (CaO) in this work, whereas we utilized SLS glass to substitute silica. CZBS1, CZBS2, CZBS3 and CZBS4 are the glass series containing weight percentages of CaO (15%, 20%, 25% and 30%) and SLS (70%, 65%, 60% and 55%), respectively, with the addition of 10% of B
2
O
3
and 5% of ZnO in each sample. A conventional melt and quenching method was applied in this work to fabricate the CaO-ZnO-B
2
O
3
-SLS glass system. The glass transition temperature (
T
g
) was determined using differential scanning calorimetry (DSC), which revealed that the
T
g
increased from 714 to 735 °C, as the CaO content increased. Meanwhile, the glass structural properties were investigated, revealing an amorphous nature with no sharp peak. The experimental elastic moduli obtained by acquiring ultrasonic speeds using the ultrasonic pulse-echo method were compared to the hypothetical elastic moduli obtained by direct estimation of the hypothetical model.
The structural relaxation of chalcogenide glasses is discussed within Tool–Narayanaswamy–Moynihan (TNM) formalism. The TNM parameters for more than 70 different glassy compositions are compared on ...the basis of the relaxation rate defined as Rf(ΔT) = −(dTf/dlogt)i at the inflection point of the isothermal relaxation curve plotted on a logarithmic timescale. The Rf(ΔT) depends on the TNM parameter ß and the parameter σ, combining the nonlinearity parameter x, the effective activation energy h* or the fragility m. It is shown that Rf(10) estimated at 10 K below Tg is useful for the prediction of structural relaxation kinetics in different amorphous materials. The chalcogenide glasses are, for example, compared with oxide glasses and organic polymers. For all these materials, the Rf(10) versus σ plot shows a well‐defined pattern that is thoroughly discussed.
Tellurite and borotellurite glasses containing Bi2O3 and TiO2 were prepared and structure-property correlations were carried out by density measurements, X-ray diffraction, Differential Scanning ...Calorimetry (DSC), Raman, FTIR, UV–visible and 11B MAS-NMR studies. Titanium-tellurite and titanium bismuth tellurite glasses require high melt-cooling rates and were prepared by splat quenching. On adding B2O3, the glass forming ability (GFA) enhances considerably and bulk glasses could be synthesized at lower quenching rates. The density of glasses shows a direct correlation with molecular mass of the constituents. UV–visible studies were used to determine the optical band gap and refractive index. Raman studies found that the co-ordination number of tellurium ions with oxygen (NTeO) remains constant with variation in TiO2 molar content, while the incorporation of B2O3 and Bi2O3 decreases NTeO. DSC studies show that the glass transition temperature (Tg) increases with B2O3 and TiO2 concentrations and that Tg correlates well with bond enthalpy of the metal oxides. 11B MAS-NMR studies found that the co-ordination number of boron with oxygen (NBO) decreases with increase in B2O3 content while increasing TiO2 and Bi2O3 concentration does not significantly modify NBO.
•TiO2 modifies the physical properties of glasses without affecting TeO speciation.•Glass forming ability of tellurite system depends on the modification of TeO speciation.•Addition of B2O3 in TiO2-Bi2O3-TeO2 system enhances the glass forming ability.•Transformation of TeO4→TeO3 and BO4→BO3 with increasing B2O3 concentration•Tg correlates directly with the average single bond enthalpy of the metal oxides.
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•Annealing impacts the glass transition temperature of a frozen sugar solution.•Final volume of dried lyo cakes can be affected during freezing step.•Non-precipitated water in frozen ...solution defines shrinkage of lyo cakes.•Annealing reduces shrinkage and the risk of structural collapse.
Freeze-drying of pharmaceuticals produces lyophilisates with properties that depend on both the formulation and the process. Characterisation of the lyophilisate in terms of appearance is necessary not only to produce a visually appealing product, but also to gain insight into the freeze-drying process. The present study investigates the impact of post-freeze annealing on the volume of lyophilisates. For this purpose, sucrose and trehalose solutions were freeze-dried with different annealing conditions and the resulting lyophilisates were analysed with a 3D structured light scanner. The external structure of the lyophilisates was found to be dependent on the bulk materials as well as the choice of vials, while the volume was influenced by the annealing time and temperature. Additionally, differential scanning calorimetry was used to determine glass transition temperatures of frozen samples. As a novelty, the volumes of the lyophilisates and their corresponding glass transition temperatures were compared. This resulted in a correlation supporting the theory that the shrinkage of lyophilisates depends on the amount of residual water in the freeze-concentrated amorphous phase before drying. Understanding the volume change of lyophilisates, in combination with material properties such as glass transition temperature, forms the basis for relating physicochemical properties to process parameters in lyophilisation.
