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1.

In order to develop a new functional product from lignin, sodium lignosulfonate (LS)-based polyurethane (LSPU) hydrogels were prepared from LS and hexamethylene diisocyanate (HDI) derivatives in water. Isocyanate/hydroxyl group ratio (NCO/OH ratio) was varied from 0.05 to 0.8 mol mol−1, and water content (Wc = mass of water/mass of dry sample) of the obtained LSPU hydrogels was varied from 0 to 3.0 g g−1. Phase transition behavior of hydrogels with various Wc’s was investigated by differential scanning calorimetry (DSC) and thermogravimetry (TG). In DSC heating curve of LSPU hydrogels, glass transition, cold crystallization, melting and liquid crystallization were observed. Cold crystallization, two melting peaks and variation of melting enthalpy indicate that three kinds of water, i.e., non-freezing water, freezing bound water and free water, exist in LSPU hydrogel. Glass transition temperature (Tg) decreased from 230 to 190 K in a Wc range where non-freezing water was formed in the hydrogel. Tg increased when freezing bound water was formed in the system. Tg leveled off in a Wc range where normal ice was formed. The effect of NCO/OH ratio on molecular motion of LSPU hydrogel is examined based on Tg and heat capacity difference at TgCp). Water vaporization curve measured by TG also indicates the presence of bound water which evaporates at a temperature higher than ca. 410 K. By atomic force microscopic observation, the size of molecular bundle of LSPU hydrogel is calculated and compared with that of LS-water system. By cross-linking, the height of molecular bundle decreased from ca. 3–1 nm and lignin molecules extend in a flat structure.

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2.
Lignin-and molasses-based polyurethane (PU) foams with various lignin/molasses mixing ratios were prepared. The hydroxyl group in molasses and lignin is used as the reaction site and PU foams with various isocyanate (NCO)/the hydroxyl group (OH) ratios were obtained. Thermal properties of PU foams were investigated by differential scanning calorimetry (DSC), thermogravimetry (TG) and thermal conductivity measurement. Glass transition temperature (T g) was observed depending on NCO/OH ratio in a temperature range from ca. 80 to 120°C and thermal decomposition temperature (T d) from ca. 280 to 295°C. Mixing ratio of molasses and lignin polyol scarcely affected the T g and T d. Thermal conductivity of PU foams was in a range from 0.030 to 0.040 Wm−1 K−1 depending on mixing ratio of lignin and molasses.  相似文献   

3.
Phase transition of locust bean gum-, tara gum- and guar gum-water systems   总被引:1,自引:0,他引:1  
Phase transition behaviour of neutral galactomannans, i.e., locust bean gum (LBG), tara gum (Tara-G) and guar gum (GG)-water systems is investigated. In this study, water content {Wc=(gram of water)/(gram of dry sample)} of these systems was varied from 0.2 to 3.6 g g-1. In the DSC heating curves, glass transition (Tg), cold crystallization (Tcc) and melting (Tm) were observed in all three samples. In addition, liquid crystal transition (T*) was observed in GG-water systems at a temperature higher than Tm. Using Tg, Tcc, Tm and T*, phase diagrams of each system were established. From the melting enthalpy of ice in the systems, three types of water, non-freezing water (Wnf), freezing bound water (Wfb) and free water were calculated. The maximum amount of Wnf was observed at Wc=0.7 g g-1, where Tg showed the lowest temperature. The amount of Wnf in LBG and GG is higher than that of Tara-G, whereas the highest amount of Wfb is found in GG. T* was only observed in GG-water systems. It is concluded that frequency of the side chains in the repeating unit of the main chains of these three galactomannan affects the frozen structure of the glassy state in the presence of water. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

4.
Thermal properties of polyurethane (PU) films prepared from solvolysis lignin (SL), polyethylene glycol (PEG) and diphenylmethane diisocyanate (MDI) were examined by differential scanning calorimetry and thermogravimetry. In the SL—PEG—MDI system, the SL content, the molecular weight (Mn) of PEG and the NCO/OH ratio were changed in order to control the thermal properties. Glass transition temperatures (Tg's) of the prepared PU's were dependent on the SL content, the Mn of PEG and the NCO/OH ratio. However, the Tg of PU was significantly influenced by the SL content: the increment of Tg was ca. 150 K when the SL content in PEG increased from 0 to ca. 50%. The decomposition of the PU's was markedly dependent on the content of SL. Other factors, such as the NCO/OH ratio and the Mn of PEG, are less dominant compared with the SL content. This fact suggests that the dissociation between the isocyanate groups and the phenolic OH groups in SL may be the major factor in the whole process of the thermal decomposition of the PU containing SL  相似文献   

5.
The glass transition temperature Tg of nylon 6 decreases monotonically toward a finite value Tgl upon increase of the moisture content. The mechanism of this decrease entails the reversible replacement of intercaternary hydrogen bonds in the accessible regions of the polyamide. The limiting glass transition temperature Tgl is approached when the moisture content approaches Wl, which corresponds to the amount of water required for complete interaction with all accessible amide groups. Denoting with Tg0 the glass transition temperature of the dry polymer, the effect of water on Tg is represented by the equation, Tg = (ΔTg)0 exp{?[ln(ΔTg)0]W/τWl} + Tgl, where (ΔTg)0 = Tg0 ?Tgl, and τ = W(Tgl+1)/Wl. This equation appears to be generally applicable to hydrophilic polymers, since correspondingly calculated data are also in very good agreement with experimental data for polymers such as nylon 66, poly(vinyl alcohol), and polyN-vinylpyrrolidone. The effect of water of Young's modulus E of nylon 6 is represented by an analogous relationship, and the quantity In[(E?El)/(Tg?Tgl)] is a linear function of the moisture content.  相似文献   

6.
Thermal properties of glasses from the system Bi x (As2S3)100−x were studied by differential scanning calorimetry of a representative series of samples with x = 0.5, 2, 4, 6, 8, and 10 at.% Bi by determining the characteristic temperatures (T g, T onset, T c, T m) and enthalpies (H c, H m) of the processes taking place in the samples during their thermal treatment. Analysis of DSC recordings for the samples at the same heating rate allowed characterization of the phase transition temperature T g as a function of the content of doping atoms in accordance with the criteria of chemical bonds formation in amorphous materials. Samples with 4 and 6 at.% Bi were thermally treated at different heating rates with the aim of determining, among the others, the parameters of their thermal stability. The assessment was done based on three different criteria. A higher tendency toward crystallization was observed with the glasses having a higher Bi content. Also, a trend of T g shifting toward higher values, observed with increase in the heating rate, is in concordance with the Lasocka equation.  相似文献   

7.
A number of samples of sodium phosphate glasses doped with Cd/Co or Ag chlorides were prepared and characterized by X-ray diffraction, IR spectral, ion transport and DSC studies. It was found from DSC studies that the glass transition temperature (T g) and crystallization temperature (T c) values increased with the increasing concentrations of the dopants Cd/ or Co chlorides. However, the T g and T c values were found to decrease when the AgCl was taken as the dopant and the following sequence is observed: T g(CoCl2)>T g(CdCl2)> T g(AgCl) T c(CoCl2)>T c(CdCl2)>T c(AgCl) These results have been discussed and explained on the basis of changes in the structure of sodium phosphate glassy matrix by the addition of different cations as dopants.The authors are thankful to Prof. M. L. Srivastava, Head, Department of Chemistry, D. D. U. Gorakhpur University, Gorakhpur, and Prof. Suresh Chandra, Department of Physics, B. H. U. Varanasi for providing necessary laboratory facilities and help in carrying out the present work. The financial support from the Department of Science and Technology and University Grants Commission, New Delhi is also gratefully acknowledged.  相似文献   

8.
This study was focused on evaluating the suitability of a wide range of lignins, a natural polymer isolated from different plant sources and chemical extractions, in replacing 20 wt.% of petroleum-based polyol in the formulation of PU flexible foams. The main goal was to investigate the effect of unmodified lignin incorporation on the foam’s structural, mechanical, and thermal properties. The hydroxyl contents of the commercial lignins were measured using phosphorus nuclear magnetic resonance (31P NMR) spectroscopy, molar mass distributions with gel permeation chromatography (GPC), and thermal properties with differential scanning calorimetry (DSC) techniques. The results showed that incorporating 20 wt.% lignin increased tensile, compression, tear propagation strengths, thermal stability, and the support factor of the developed PU flexible foams. Additionally, statistical analysis of the results showed that foam properties such as density and compression force deflection were positively correlated with lignin’s total hydroxyl content. Studying correlations between lignin properties and the performance of the developed lignin-based PU foams showed that lignins with low hydroxyl content, high flexibility (low Tg), and high solubility in the co-polyol are better candidates for partially substituting petroleum-based polyols in the formulation of flexible PU foams intended for the automotive applications.  相似文献   

9.
Semi-rigid polyurethane (PU) foams were prepared using lignin-molasses- poly(ethylene glycol) polyols. Two kinds of lignin, kraft lignin (KL) and sodium lignosulfonate (LS), were used. Both lignin and molasses polyols were mixed with various ratios and were reacted with poly(phenylene methylene) polyisocyanate (MDI) in the presence of silicone surfactant and di-n-butyltin dilaurate. A small amount of water was used as a foaming agent. The apparent density of PU foams increased with increasing lignin content. The compression strength and elastic modulus linearly increase with increasing apparent density, suggesting that mechanical properties are controllable by changing reaction conditions. The PU foams were amorphous and glass transition was detected by differential scanning calorimetry. The glass transition temperature (Tg ) maintained an almost constant value, regardless of the mixing ratio. This indicates that both the phenolic group of lignin and the glucopyranose ring of molasses act as rigid components in PU crosslinking network structures, and both groups contribute to the main chain motion to the same extent. By thermogravimetry (TG), it was confirmed that PU foams are thermally stable up to around 300 °C. By differential scanning calorimetry, Tg was observed at temperatures from 80 to 120 °C.  相似文献   

10.
A number of samples of sodium and silver phosphate glasses doped with various compositions of some transition metals viz. iron, manganese and zinc chlorides alongwith undoped samples of sodium and silver phosphate glasses were synthesized and characterized by X-ray diffraction, IR spectral, electrical conductivity and differential scanning calorimetry (DSC). The glass transition temperature (T g) and crystallization temperature (T c) values obtained from DSC curves were found to increase with increasing concentration of the dopant Fe/Mn/Zn chlorides in both sodium and silver phosphate glasses and the following sequence is observed: T g(–FeCl3)>T g(–MnCl2)>T g(–ZnCl2) T c(–FeCl3)>T c(–MnCl2)>T c(–ZnCl2) The increase in T g and T c values indicate enhanced chemical durability of the doped glasses. The electrical conductivity values and the results of FTIR spectral studies have been correlated with the structural changes in the glass matrix by the addition of different transition metal cations as dopants.  相似文献   

11.
Summary The sorption property of water vapor by poly(vinyl acetate) (PVAc) of relatively low glass transition temperature (T g) was studied at temperatures nearT g.Tcg of humidity-controlled samples of various moisture contents was measured and its variation with the moisture content was determined.T g of the dry sample was estimated by dilatometry and DSC methods, and to confirm the value, the temperature dependence of mutual diffusion coefficient of the system of water vapor + PVAc was determined. A difference between the sorption mechanisms of water vapor by PVAc at 20 and 30 °C was observed: two sorption mechanisms are involved at 30 °C, while three mechanisms at 20 °C are involved which include the above two and another intermediate one. In earlier stage of sorption, at both 20 and 30 °C, water molecules sorbed by PVAc showed a tendency towards aggregation, while a mixing effect was found at higher stage of the sorption.
Zusammenfassung In der Arbeit werden Wasserdampfsorptionseigenschaften von Polyvinylacetat mit relativ niedriger Glastemperatur (T g) in der Nähe vonT g untersucht. Es wurden Plastizitätseinflüsse und Veränderungen vonT g mit dem Wassergehalt studiert. Es wurde gefunden, daß bei 30 °C ein 2-Stufen-Sorptionsmechanismus, bei 20 °C ein 3-Stufen-Mechanismus existiert.


With 7 figures  相似文献   

12.
Solid-state coextrusion has been used to prepare uniaxially drawn films from isotropic poly(ethylene 2,6-naphthalate) (PEN) of a minimum degree of crystallinity (ca. 5%) both below and above its glass transition temperature Tg. The onset of cold crystallization (Tc) of the drawn films has been studied as a function of the extrusion temperature (ET) and the draw ratio (EDR). It has been shown that Tc decreases markedly on draw, as much as 95°C, and, at constant draw ratio Tc goes through a minimum in the Tg region. For undrawn PEN, annealing below 153°C has no significant effect on Tc. To evaluate the crystallization rate constant (k) and the activation energy (Ea) of the drawn specimens, a nonisothermal DSC procedure has been used. With increasing EDR, k increases markedly and Ea goes down over threefold compared with the undrawn polymer. At high ET, strain-induced crystallization has also been shown to play an important role in lowering Ea for cold crystallization. Thermal shrinkage above Tm indicates a high elastic recovery, underlining the efficiency of deformation, ca. 93%, achieved by solid-state coextrusion.  相似文献   

13.
The optimal mixing coefficient C of the exchange energy Ex and the electron-electron interaction part of the exchange-correlation energy W1xc in the formula for the total exchange-correlation energy Exc was expressed through the ratio of the kinetic Tc and potential Wc contributions to the correlation energy Ec. This expression can be derived from a Heavyside step function model of the dependence of Wλxc on the coupling parameter of the electron interaction λ. Values of Tc and Wc obtained from ab initio wave functions were used to estimate C for a number of atoms and molecules. A strong dependence of Tc, Wc, and C on the bond distance was demonstrated for the case of the H2 molecule. Tc and C approach zero in the bond-dissociation limit; so for an electron-pair bond, the admixing of exact exchange to obtain an accurate Exc is strongly dependent on the bond length and has to disappear for weak interaction/large bond distances. The potential of the exchange-correlation hole constructed for H2 from an ab initio second-order density matrix was compared with its generalized gradient approximation (GGA). © 1996 John Wiley & Sons, Inc.  相似文献   

14.
It is shown that the 13C NMR spectral collapse temperatures Tc reported by Axelson and Mandelkern tend to give a constant ratio of Tc/Tg averaging 1.21 ± 0.05 and independent of Tg or of polymer structure. It is further shown that Tc is not a high-frequency value for Tg because this would require Tc/Tg to decline with increasing Tg. Tc/Tg agrees in numerical value with Tu/Tg, where Tll is the liquid-liquid transition lying above Tg. Direct comparison of Tc and Tu for four polymers PIB, PnBA, atactic PP, and isotactic PMMA shows very close agreement. The various results suggest, but do not prove, that Tc from 13C NMR spectroscopy may be a new, direct measure for Tll. A measured Tc of 233K for linear PE is compatible with a Tg near 195 K (233/195 = 1.19), whereas a Tg of 148 K gives the ratio 233/148 = 1.57, which is outside any value shown in tabulated form.  相似文献   

15.
The course of a randomization process in the melt of poly(ethylene terephthalate) and other polyesters during melt-blending was observed by determining changes in Tg, Tc and Tm measured by DSC. the melting point of isothermic annealed copolyesters is the most advantageous criterion for determining the degree of randomization process. On the other hand, Tg and Tc are influenced by further processes taking place during the melt-blending of two kinds of homopolyesters, e.g. the changes of molecular mass and molecular mass distribution etc.  相似文献   

16.
An exotherm, observed in differential scanning calorimetry (DSC) scans of amorphous food materials above their glass transition temperature,T g, may occur due to sugar crystallization, nonenzymatic browning, or both. In the present study, this exothermal phenomenon in initially anhydrous skim milk and lactose-hydrolyzed skim milk was considered to occur due to browning during isothermal holding at various temperatures above the initialT g. The nonenzymatic, Maillard browning reaction produces water that in amorphous foods, may plasticize the material and reduceT g. The assumption was that quantification of formation of water from theT g depression, which should not be observed as a result of crystallization under anhydrous conditions, can be used to determine kinetics of the nonenzymatic browning reaction. The formation of water was found to be substantial, and the amount formed could be quantified from theT g measured after isothermal treatment at various temperatures using DSC. The rate of water formation followed zero-order kinetics, and its temperature dependence well aboveT g was Arrhenius-type. Although water plasticization of the material occurred during the reaction, and there was a dynamic change in the temperature differenceTT g, the browning reaction was probably diffusioncontrolled in anhydrous skim milk in the vicinity of theT g of lactose. This could be observed from a significant increase in activation energy. The kinetics and temperature dependence of the Maillard reaction in skim milk and lactose-hydrolyzed skim milk were of similar type well above the initialT g. The difference in temperature dependence in theT g region of lactose, but above that of lactose-hydrolyzed skim milk, became significant, as the rate in skim milk, but not in lactose-hydrolyzed skim milk, became diffusion-controlled. The results showed that rates of diffusion-controlled reactions may follow the Williams-Landel-Ferry (WLF) equation, as kinetic restrictions become apparent within amorphous materials in reactions exhibiting high rates at the same temperature under non-diffusion-controlled conditions.  相似文献   

17.
The glass-transition temperatures of a series of copolymers of ethyl acrylate and acrylic acid neutralized with various cations were investigated. It was found that a plot of Tg as a function of ion content, for every type of ion investigated here, gives an unusual sigmoidal curve, which can be correlated with the onset of the failure of time–temperature superposition in viscoelastic studies, as will be shown in a future publication. Also, all of the Tg versus concentration curves for the various counterions can be superposed if the plots are made against cq/a, where c is the metal acrylate content, q the cation charge, and a the distance between centers of charge. Furthermore, in one region of water content, a linear relation is obtained between the glass transition and the water content (in weight-%) independent of the ion concentration over wide ranges of ion content. Finally, above an ion concentration of 12 mole-%, the rate of change in Tg per water molecule per ion pair at constant ion content, (?Tg/?n)c is linear but with different slopes above and below two water molecules per ion pair.  相似文献   

18.
Environmentally compatible polymers such as poly(ε-caprolactone) (PCL) and polyurethane (PU) derivatives from PCL's were synthesized from saccharides, polysaccharides and lignins such as glucose, fructose, sucrose, cellulose, cellulose acetate, alcoholysis lignin, kraft lignin and sodium lignosulfonate. Flexible and rigid PU sheets and foams were also prepared by the reaction of OH groups of saccharides and lignins with isocyanates such as toluene diisocyanate (TDI) and diphenylmethane diisocyanate (MDI). Glass transition temperatures (Tg's), cold-crystallization temperatures (Tcc's) and melting temperatures (Tm's) of saccharide- and lignin-based PCL's and PU's were determined by differential scanning calorimetry (DSC), and phase diagrams were obtained. Methods of controlling mechanical properties such as stress and elasticity of PU's through changing thermal properties such as glass transition temperature were established. Thermogravimetry (TG) and TG-Fourier transform infrared spectrometry (FTIR) were also carried out in order to analyze the degradation temperature and evolved gases from the above obtained polymers. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

19.
Well-defined A-block-B type cellulose derivatives consisting of cellulose triacetate (CTA) and oligoamide-15 were synthesized. Chemical structures of the diblock copolymers were characterized by MALDI-TOF MS, 1H-NMR, and GPC. Influence of length of CTA and oligoamide-15 segments on their thermal properties was investigated by means of differential scanning calorimetry (DSC). All diblock copolymers displayed T g, T c, and T m transition temperatures. Their T g and T m values increased with the increase of molecular weight of CTA segment. The crystallinity of diblock copolymers increased after isothermal crystallization at 200 °C. Its X-ray analysis revealed that the diblock copolymer had CTA II crystal structure. Thermal analysis supported microphase separation between CTA and oligoamide-15 segments at room temperature, because T g and T m values of polyamide-15 are −7 °C and 170–180 °C, respectively.  相似文献   

20.
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