Differences in catalytic liquefaction kinetics of corn stalk fractions

Biomass-based polyol obtained by chemical liquefaction technology is a potential substitute for polyether or polyester polyol in preparation of degradable polymers. To obtain the favorable biomass-based polyol products, one important emphasis is to reveal the liquefaction kinetics. The liquefaction kinetics of different corn stalk (CS) fractions, i.e. whole CS, ear husk and leaf blade, were investigated in this work. The liquefactions were catalyzed with sulfuric acid at 120–180 °C for 15–90 min. The results indicated that the apparent reaction rate constant (k), apparent activation energy (E), ΔG′, and ΔH′ of liquefaction reactions differed remarkably with different CS fractions. The highest k of 1.8 × 10^?4 s^?1 was obtained from ear husk liquefaction at 120 °C, which was twofold and 2.7-fold higher than those of whole CS and leaf blade, respectively. However, k is not correlated with the stalk heterogeneity at temperature over 120 °C. The calculated E _{ear husk}, E _{whole CS} and E _{leaf blade} were 65.88, 81.64 and 85.23 kJ mol^?1, respectively. ΔG′ and ΔH′ values of ear husk liquefaction reactions were lower than those of the other two fractions. This work was the first comparison of kinetics with different biomass fractions, casting light on the effect of heterogeneity on liquefaction, and suggesting that CS fractions should be given themselves optimum applications in future.     

Polyamide derived from 4,4′-thiobis(methylene)dibenzoyl chloride and aliphatic diamine: interfacial synthesis and characterization

A series of processable semi-aromatic polyamides containing thioether and methylene units were synthesized through the reaction of 4,4′-thiobis(methylene)dibenzoyl chloride and aliphatic diamine by the method of interfacial polycondensation. These polyamides had excellent thermal properties with glass transition temperatures (T _g) of 104.3–130.6 °C, melting temperatures (T _m) of 300.3–303.8 °C, and initial degradation temperatures (T _d) of 405.2–410.3 °C. They had wider processing windows than traditional semi-aromatic polyamides (such as PA6T can not be processed by melting) and can be processed by melting method. They had better tensile strengths of 57.6–64.1 MPa, low-temperature mechanical properties, low water absorption of 0.19–0.27 %, low dielectric constants of 3.11–3.95 at 100 kHz, and better melt flowability properties of 232–60.7, 301.9–78.8, and 423.1–83.6 Pa s under a shear rate ranging from 20 to 1,170 s^?1, respectively. In addition, these polyamides showed good corrosion resistance, they did not dissolve in solvents such as NMP, DMSO, hydrochloric acid (6 mol/l), and solution of NaOH (1 mol/l) and so on.     

Studies on the thermal properties of poly(phenylene sulfide amide)

Thermal properties of poly(phenylene sulfide amide) (PPSA) prepared using sodium sulfide, sulfur, and thiourea as sulfur sources which reacted with dichlorobenzamide (DCBA) and alkali in polar organic solvent at the atmospheric pressure, were studied. The glass transition temperature (T_g), melting point temperature (T_m), and melting enthalpy (ΔH_m) of the related polymers were obtained by use of differential scanning calorimetry analysis. The results are: T_g = 103.4–104.5°C, T_m = 291.5–304.7°C, and ΔH_m = 104.4–115.4 J/g. Thermal properties such as thermal decomposition temperature and decomposition kinetics were investigated by thermogravimetric analysis under nitrogen. The initial and maximum rate temperatures of degradation were found to be 401.5–411.7°C and 437–477°C, respectively. The parameters of thermal decomposition kinetics of PPSAs were worked out to be: activation energy of degradation was 135 to 148 kJ/mol and the 60-s half-life temperature was 360 to 371°C. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1227–1230, 1997     

Sonocrystallization of Interesterified Fats with 20 and 30% of Stearic Acid at the sn-2 Position and Their Physical Blends

Physical blends (PB) of high oleic sunflower oil and tristearin with 20 and 30% stearic acid and their interesterified (IE) products where 20 and 30% of the fatty acids are stearic acid at the sn-2 position crystallized without and with application of high intensity ultrasound (HIU). IE samples were crystallized at supercooling temperatures (ΔT) of 12, 9, 6, and 3 °C while PB were crystallized at ΔT = 12 °C. HIU induced crystallization in PB samples, but not in the IE ones. Induction in crystallization with HIU was also observed at ΔT = 6 and 3 °C for IE C18:0 20 and 30% and at ΔT = 9 °C only for the 30% samples. Smaller crystals were obtained in all sonicated samples. Melting profiles showed that HIU induced crystallization of low melting triacylglycerols (TAGs) and promoted co-crystallization of low and high melting TAGs. In general, HIU significantly changed the viscosity, G′, and G″ of the IE 20% samples except at ΔT = 12 °C. While G′ and G″ of IE 30% did not increase significantly, the viscosity increased significantly at ΔT = 9, 6, and 3 °C from 1526 ± 880 to 6818 ± 901 Pa.s at ΔT = 3 °C. The improved physical properties of the sonicated IE can make them good contenders for trans-fatty acids replacers.     

Friedel-Crafts crosslinking methods for polystyrene modification: 2. Tg′Tll and T′ll transitions of grated polystyrene

Polystyrene was grafted with 1,4-dimethyl-2,5-dichloromethyl benzene in dichloroethane solution at 50°C using SnCl₄ as a catalyst. Thermal analysis of grafted polystyrene samples using differential scanning calorimetry revealed two liquid-liquid transitions, T_ll and T′_ll, in addition to the glass transition, T_g′ and the decomposition temperature, T_d. The effect of the number of junctions per polystyrene chain on T_g′T_ll and T′_ll is examined and analysed.     

Self‐nucleation–induced nonisothermal crystallization of nylon 6 from the melt

The effect of thermal treatment over a wide range of temperature (130–280°C) on the crystallization behavior of nylon 6 was studied by using DSC, FTIR, and polarized light microscope equipped with a hot stage. The crystallization and the subsequent melting behavior of the nylon 6 samples treated at different temperatures (T_s) were classified into four types. When T_s was higher than 236°C or lower than 213°C, the crystallization behavior of nylon 6 was insensitive to the variation of T_s. When T_s was in the range of 213–235°C, the crystallization behavior was sensitive to the change of T_s. The polarized light microscopic experiments have demonstrated that a large amount of tiny ordered nylon 6 segments/cluster persisted when nylon 6 film are heated to 231°C. Consequently, the fastest crystallization speed was observed. As T_s was between 214 and 223°C, both the T_m and the ΔH_m were higher than those of the nylon 6 samples treated at other temperature. The polarized light microscopic investigations have also demonstrated that molten nylon 6 crystallizes by using the un‐molten nylon 6 crystals as nucleation center at 220°C. Crystallization at higher temperature produces nylon 6 with thicker crystalline lamella. The above results are helpful for rational design of thermal treatment procedure to obtain nylon 6 with different crystalline features. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42413.     

Temperature memory effect from below glass transition to up to melting range in an ethylene-vinyl acetate copolymer

In this paper, the temperature memory effect (TME) in a commercial ethylene-vinyl acetate copolymer (EVA) is characterized via differential scanning calorimetry (DSC) tests. Three temperatures, which are 35, 60, and 85°C representing temperatures below glass transition (T_g), within T_g and within melting (T_m), respectively, are included for the investigation. It is found that TME in polymers is not as reported to be limited at around either T_g or T_m only, the effective temperature range for TME could be actually much wider that covers from below T_g to up to T_m. In addition, it is concluded that higher heating stop temperature (T_s) erases the memory of previous lower ones in this EVA. Hysteresis (described by ΔT) between the temperature of turning points (T_ts) and their corresponding T_ss is always observable. However, the ΔT decreases at higher T_s.     

High molecular weight poly(p-arylene sulfide ketone): synthesis and membrane-forming properties

High-molecular-weight poly(p-arylene sulfide ketone) (PPSK) was prepared by nucleophilic substitution reaction of 4,4’-diflurobenzophenone (DFBP) and sodium sulfide in the compound solvents of diphenyl sulfone (DPS) and 1,3-dimethyl-2-imidazolidinone (DMI) with catalysts under elevated temperature. The inherent viscosity (η_int) of the PPSK synthesized was 0.703 dl/g. PPSK was characterized by Fourier-transform infrared spectroscopy, elemental analysis, x-ray diffraction, differential scanning calorimetry, and thermogravimetric analysis. It was found that the polymer had excellent thermal properties: glass transition temperature (T_g) was 142.8 °C, melting temperature (T_m) was 362.3 °C. Under nitrogen atmosphere, 5 % (T_5%) and 10 % (T_10%) weight-loss temperatures were about 498.5 °C and 526.2 °C, respectively, while in the air the T_5% and T_10% were about 517 °C and 535.8 °C, respectively. The PPSK was found to be a semi-crystalline polymer, as confirmed by XRD. The polymer was insoluble in any solvent except concentrated sulfuric acid at room temperature. A series of the PPSK separating membranes were prepared by dissolving PPSK to concentrated sulfuric acid. The fluxes and the porosities of the separating membranes were in the range of 230–43 L/(m²?·?h) and 77.7-84.7 %, respectively. At the same time, these separating membranes showed moderate tensile strength of 1.02-1.88 MPa.     

Water effect on the morphology of EVOH copolymers

The effect of water on the morphology of four ethylene vinyl alcohol copolymers (EVOH) with different ethylene contents was studied by differential scanning calorimetry (DSC). EVOH film samples equilibrated in controlled atmospheres at different relative humidities (RH) and 23°C were analyzed. Under dry conditions, the glass transition temperature (T_g) was unaffected by copolymer ethylene content. As RH increases, T_g decreases. It seems that the presence of water within the polymer matrix results in plasticization of the polymer. T_g varies from around 50°C (dry) to below room temperature. EVOH copolymers are glassy polymers when dry and rubbery polymers at high RHs. Fox and Gordon–Taylor's equations well describe T_g depletion at low water uptake, although severe water gain results in a considerable T_g decrease, which is not predicted by these theories. Melting temperature, T_m, and enthalpy, ΔH_m, were also analyzed. When dry, T_m decreases as ethylene content increases. No significant water effect was found on either T_m or ΔH_m. Hence, crystallinity seems to be unaffected by water presence. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1201–1206, 1999     

Two Reaction Pathways in the Selective Catalytic Reduction of NO x by C6H14 Over Ag–Al2O3 with H2 Co-Feeding

The NO _x reduction with n-C₆H₁₄ was studied over a 3% Ag/Al₂O₃ catalyst in the presence of hydrogen. The catalyst performance was evaluated by varying the H₂ concentration from 0 to 1600 ppm and by comparing the results with blank runs in which an empty reactor with no catalyst was used. Two distinct reaction pathways were revealed: one at low-temperature (T_react < 370 °C) and another one at high-temperature (T_react > 370–390 °C). Co-feeding of H₂ promotes the reaction within the 150–360 °C interval. The high-temperature pathway (T_react > 370–390 °C) seems to be almost independent of hydrogen co-feeding. The homogeneous gas-phase NO _x oxidation initiated by NO presumably plays an important role in this high-temperature pathway.     

Effect of thermal hysteresis on melting of syndiotacticity-rich poly(vinyl alcohol) hydrogel

The melting temperatures (T_M) of hydrogels prepared by chilling aqueous solutions of syndiotacticity-rich poly(vinyl alcohol) (s-PVA) at 0°C were measured rising temperature of gels from the initiative temperature (T_I) of 0–70°C (every 10°C). The apparent enthalpies of fusion of a junction ΔH's were estimated from the relation between the logarithm of polymer concentration (log C) and 1/T_M. ΔH depended on T_I, showing that the melting point of gels depended on a thermal hysteresis. The highest polymer concentration C_H in those of the gels which have no melting point above an initiative temperature was determined and ΔH was estimated from the relation between log C_H and the reciprocal melting point of the gels with C_H, 1/T_IM. The ΔH was 15.1 kJ/mol in the range of higher polymer concentrations and 43.9 kJ/mol in the range of lower concentrations.     

Synthesis and characterization of epoxy resin of 9,9′-bis-(3,5-dibromo-4-hydroxyphenyl) anthrone-10 and its jute composite

Epoxy resin of 9,9′-bis-(3,5-dibromo-4-hydroxyphenyl) anthrone-10 (EANBr, EEW 490) was synthesized and was characterized by IR and ¹HNMR . EANBr and EPK3251 cured resin (EANBrC) were characterized by DSC and TGA at 10°Cmin^?1 under nitrogen atmosphere. Broad DSC endothermic transitions of EANBr (265.3 °C) and EANBrC (291.4 °C) are due to some physical change and further confirmed by no weight loss in their TG thermograms. EANBr and EANBrC are thermally stable up to 340 °C and 310 °C, respectively. EANBr has followed single step degradation kinetics, while EANBrC has followed two step degradation kinetics. EANBr followed apparently zero order kinetics, while EANBrC followed apparently second order (1.80) and first order (0.89) degradation kinetics, respectively. Ea and A values of EANBrC (299.7 kJmol^?1 and 6.32?×?10²⁰ s^?1) were found higher than that of EANBr (201 kJmol^?1 and 2.45?×?1013 s^?1) due to more rigid nature of EANBrC. The ΔS^* value of the first step degradation of EANBrC (146.3 JK^?1 mol^?1) was found much more than that of EANBr (4.6 JK^?1 mol^?1). Jute – EANBr composite (J-EANBr) was prepared by compression molding technique at 120 °C for 5 h and under 20 Bar pressure. The observed tensile strength, flexural strength, electric strength and volume resistivity of J-EANBr are 24.7 MPa, 19.0 MPa, 1.8 kVmm^?1 and 3.5?×?10¹² ohm cm, respectively. Water absorption in J-EANBr was carried out at 30 ± 2 °C against distilled water, 10% NaCl, 10% HCl, 10% HNO₃, 10% H₂SO₄, 10% NaOH, and 10% KOH and also in boiling water. The equilibrium time and equilibrium water content for J-EANBr in different environments are 384–432 h; 12.7–15.2%, respectively. The observed equilibrium water content and diffusivity trends of J-EANBr are KOH>H₂SO₄>HCl>NaOH>H₂O>NaCl and H₂O>NaCl>NaOH>H₂SO₄>HCl>KOH, respectively. Good thermo-mechanical, electrical properties and excellent hydrolytic stability of J-EANBr may be useful for high temperature applications in diverse fields.     

Gelation of hyaluronic acid through annealing

The effect of annealing, at a temperature higher than that of the gel‐sol transition, on the junction formation in the gelation process of sodium hyaluronate/water systems was investigated by the falling ball method (FBM) and differential scanning calorimetry (DSC). FBM measurements were carried out for 1, 2 and 3 wt% solutions. Gel formation was not observed for 1 and 2 wt% solutions, but for 3 wt% solution, gel formation was observed for annealing temperature T = 60 °C and annealing time longer than 6 h. The gel‐sol transition temperature measured by FBM was about 15 °C. Gel formation was not observed in measurements at T = 40 °C and 50 °C. However, the enthalpy of melting, ΔH_m per 1 mg of water, (determined by DSC) changed in a complex manner during annealing at 60 °C, ie ΔH_m increased in the initial stage and then decreased in the later stage. This indicates that the amount of non‐freezing water decreased in the initial stage and then increased in the latter stage. The initial stage corresponds to processes of dissociation of the assemblies of hyaluronic acid molecules by desorbing water molecules and subsequent homogenization of the system. However in the later stage, a junction structure which enables the system to form gels was thought to be formed. © 2000 Society of Chemical Industry     

Shape memory thermoplastic elastomer from maleated polyolefin elastomer and nylon 12 blends

Semicrystalline maleated polyolefin elastomer (mPOE) and nylon 12 were melt blended in an internal mixer at 200 °C with proportions of 90/10, 80/20, and 70/30 wt/wt, respectively. Molau test, melt viscosity measurement, differential scanning calorimetry, dynamic mechanical analysis and tensile testing were conducted to characterize the structure and properties of the blends. The results revealed that POE-graft-nylon 12 copolymer was formed during the mixing, and the blends show two melting transitions at 57–60 and 174–178 °C attributed to mPOE and nylon 12, respectively, which are dependent on the blend composition. The blends exhibit typical thermoplastic elastomeric behavior and their tensile modulus, strength and hardness increase with increasing nylon content. It was also observed that the blends form a physically crosslinked structure until the melting transition of nylon 12. The blends exhibit excellent thermally triggered shape memory effect, i.e., almost 100 % shape fixity rate and 100 % shape recovery rate, and the recovery occurs in a few seconds when the temporarily fixed shaped sample is heated just above the T _m of mPOE phase in the blends.     

Potential of the Pb,PbSO4/H2SO4 electrode at temperatures up to 240°C

Standard lead—lead sulphate electrode potential was determined over the temperature range 20–240°C from emf measurements of the Pb, PbSO₄H₂SO₄ (0.05M)K₂SO₄KClHCl(0.1M)/AgCl, Ag and Pb, PbSO₄H₂SO₄(m)K₂SO₄H₂SO₄(0.05M)PbSO₄, Pb cells where m = 0.005, 0.01, 0.1 and 0.5 M. To this effect lead—lead sulphate electrode potential was calculated using the temperature relationship of the standard silver—silver chloride electrode potential and activity coefficients of hydrochloric acid determined by Greeley et al. at temperatures up to 260°C. Diffusion potentials occurring at the phase boundaries in the cells under investigation were calculated using the Henderson's equation. Values of the standard lead—lead sulphate electrode potential were determined by extrapolation of the E°′ function to the zero ionic strength which was calculated using the second sulphuric acid dissociation constant determined by Lietzke et al. at temperatures up to 300°C. The standard electrode potential was described in the temperature range 20–240°C by the following relationship: E°_{Pb, PbSO4/SO^2?4}(V) = 0.040-0.00126T. A change in entropy ΔS° of the electrode reaction Pb + SO^2?₄ = PbSO₄ + 2e^? is constant in this temperature range and is ?243 JK^?1 mol^?1 (?1018 cal K^?1 mol^?1).     

Interaction of self‐nucleation and the addition of a nucleating agent on the crystallization behavior of isotactic polypropylene

The relationship between heterogeneous or homogeneous nucleation and self‐nucleation of polypropylene (PP) and PP nucleated by an organic phosphate salt (PPA) was studied by DSC. For pure PP, it homogeneously nucleated during cooling after melting at the selected temperature (T_s) of 170–200°C for 3 min, but at the T_s of 160–168°C self‐nucleation occurred; PPA only nucleated heterogeneously at the T_s of 168–200°C, and there existed self nucleation at the T_s of 160–168°C. The double melting peaks of PP and PPA at the T_s of 162°C were observed. Once the self‐nucleation occurred, the change of the crystallization temperature and heat of fusion of PP is more significant than that of PPA with the change of the T_s, depending upon the crystallization conditions. Results were explained by homogeneous nucleation, heterogeneous nucleation, self‐nucleation, and annealing crystallization. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 78–84, 2001     

Crystallization Behavior of High-Oleic High-Stearic Sunflower Oil Stearins Under Dynamic and Static Conditions

Soft (SS) and hard (HS) stearins obtained from high-oleic high-stearic sunflower oil were isothermally crystallized under dynamic (with agitation) and static conditions at 16, 17, 18, 19, and 20 °C and 24, 25, 26, 27, and 28 °C, respectively. Both fractions crystallized under the α-form at early stages of crystallization for all temperatures (T _c) tested. Polymorphic behavior strongly changed with T _c and shear conditions for both fractions. SS fractions were characterized by α, β₂ and/or β₁ polymorphs at lower T _c and β₁ crystals at higher T _c when crystallized under dynamic conditions, while this same fat system was characterized by β₂′ crystals at lower T _c and β₂ at higher T _c under static conditions. HS samples were mainly characterized by α and β₂ crystals at lower T _c and α and β₁ crystals at higher T _c when crystallized under dynamic conditions; while the same fat was characterized by β₁′ crystals when crystallized at lower T _c and α when crystallized at higher T _c under static conditions after 90 min at T _c. These different polymorphic behaviors, in combination with the different processing and tempering temperatures are translated in specific textural behavior of the samples.     

Crystaline polymers as heat storage materials in passive thermal protection systems

Previous studies have evaluated low molecular weight crystalline materials as latent heat sinks for passive thermal protection systems. This study evaluated crystalline polymers as heat storage materials. Differential scanning calorimetry and Instron thermomechanical analysis are applied in dynamic studies of cumulative histories of melting and recrystallization. Commercially available crystalline polymers with melting temperatures T_m ≥ 100°C can provide fully reversible heats of fusion ΔH_m ≥ 35 cal/gm under programmed heating-cooling cycles. A linear polyethylene (Marlex 6050) is modified by radiation crosslinking to retain shape stability above T_m with-out loss of heat storage capability. The essentially zero vapor pressure and inherent shape stability of crosslinked crystalline polymers may provide unique advantages as uncontained, non-expendable, heat storage materials.     

Effect of Lactose Monolaurate and High Intensity Ultrasound on Crystallization Behavior of Anhydrous Milk Fat

Crystallization behavior of anhydrous milk fat (AMF) was studied with the addition of 0.025 and 0.05 % lactose monolaurate (LML). The crystallization behavior was studied at low (ΔT = 3 °C) and high supercooling (ΔT = 6 °C). Polarized light microscopy and laser turbidimetry indicated a delay in crystallization on addition of 0.025 % and 0.05 % LML or Tween 20 to AMF. High intensity ultrasound (HIU) was applied to AMF samples with 0.05 % LML and lower supercooling (T _c = 31 °C; ΔT = 3 °C). HIU application in AMF and AMF + 0.05 % LML induced crystallization (p < 0.05) changing the induction time (τ) at 31 °C from 34.20 ± 1.67 min (AMF) and 47.07 ± 1.27 min (AMF + 0.05 % LML) to 23.23 ± 3.26 min (AMF) and 25.00 ± 0.87 min (AMF + 0.05 % LML). Melting enthalpies (ΔH) of AMF were significantly higher (p < 0.05) than the ones observed for AMF + 0.05 % LML when crystallized without HIU, while enthalpy values increased significantly in AMF + 0.05 % LML samples when crystallized with HIU reaching similar values to the ones obtained for AMF without LML. The viscosity of AMF significantly decreased (p < 0.05) on addition of 0.05 % LML and significantly increased on HIU application.     

Stability of electrical properties of vanadium dioxide based ceramics

The influence of thermocycling process at VO₂ phase transition temperature (T_t≈68°C) on the resistivity temperature dependences and dielectric constant (ε) of ceramics on a basis of VO₂ and V₂O₅–P₂O₅ glasses has been studied. The differential thermal analysis and dilatometric measurements for tested ceramics has been made. Vanadium dioxide based ceramics exhibits a variation of electrical properties with thermocycling. The resistivity increases, ε and electrical resistivity jump ρ_s/ρ_m in the vicinity of T_t decrease with a growth of a number of thermocycles. The reason of such behavior is microcracks formation due to a sharp variation of thermal expansion in the vicinity of T_t. After some repetition of thermocycling process the stabilization of ceramics electrical properties has been observed, but the resistivity jump ρ_s/ρ_m has been disappeared practically. Possible reasons of the stabilization have been discussed. The stabilization of electrical resistivity jump ρ_s/ρ_m (ρ_s/ρ_m∼10²–10³) after thermocycling for thin ceramic samples (a thickness ∼0·4 mm or less) has been shown. ©