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1.
Enthalpies of vaporization for esters covering a molecular weight range of about 74–939 g/mol · [monocarboxylics; linear esters of sebacic series; branched esters of triglyceride series; and, oligomer esters of poly(hexamethylene sebacate)] and a temperature range of about 273.15–523.15 K have been empirically fitted to within about 5% to an equation of the following form: ΔHv(T,M) = S(T)f(M) + I0(T), where S(T) = C Ln(T) + K0, I0(T) = aT + b0, and f(M) = M/(1 + a0M), M is the molecular weight (molar mass); T is in degrees Kelvin; and, C, K0, a, b0, and a0 are constants. These results were used to determine the heat capacity difference, ΔCp = Cp(l) − Cp(g), and compared to calculated values from functional relationships of Cp(l) and Cp(g), l is liquid g is gas. The heat capacity difference results in conjunction with Cp(l) were used to empirically calculate the heat capacity of the gas, Cp(g), over the molecular weight and temperature ranges investigated and compared to a group contribution method. The functional forms for ΔHv(T,M), ΔCp(T,M), Cp(l), and Cp(g) were also found to be applicable for n-alkanes. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 731–746, 1998  相似文献   

2.
The thermal degradation of poly(3‐hydroxybutyrate) (PHB) and poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) [P(HB‐HV)] was studied using thermogravimetry (TG). In the thermal degradation of PHB, the temperature at the onset of weight loss (To) was derived by To = 0.97B + 259, where B represents the heating rate (°C/min). The temperature at which the weight loss rate was maximum (Tp) was Tp = 1.07B + 273, and the final temperature (Tf) at which degradation was completed was Tf = 1.10B + 280. The percentage of the weight loss at temperature Tp (Cp) was 69 ± 1% whereas the percentage of the weight loss at temperature Tf (Cf) was 96 ± 1%. In the thermal degradation of P(HB‐HV) (7:3), To = 0.98B + 262, Tp = 1.00B + 278, and Tf = 1.12B + 285. The values of Cp and Cf were 62 ± 7 and 93 ± 1%, respectively. The derivative thermogravimetric (DTG) curves of PHB confirmed only one weight loss step change because the polymer mainly consisted of the HB monomer only. The DTG curves of P(HB‐HV), however, suggested multiple weight loss step changes; this was probably due to the different evaporation rates of the two monomers. The incorporation of 10 and 30 mol % of the HV component into the polyester increased the various thermal temperatures (To, Tp, andTf) by 7–12°C (measured at B = 20°C/min). © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2237–2244, 2001  相似文献   

3.
Thermal analyses of poly(3-hydroxybutyrate) (PHB), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(HB–HV)], and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) [P(HB–HHx)] were made with thermogravimetry and differential scanning calorimetry (DSC). In the thermal degradation of PHB, the onset of weight loss occurred at the temperature (°C) given by To = 0.75B + 311, where B represents the heating rate (°C/min). The temperature at which the weight-loss rate was at a maximum was Tp = 0.91B + 320, and the temperature at which degradation was completed was Tf = 1.00B + 325. In the thermal degradation of P(HB–HV) (70:30), To = 0.96B + 308, Tp = 0.99B + 320, and Tf = 1.09B + 325. In the thermal degradation of P(HB–HHx) (85:15), To = 1.11B + 305, Tp = 1.10B + 319, and Tf = 1.16B + 325. The derivative thermogravimetry curves of PHB, P(HB–HV), and P(HB–HHx) confirmed only one weight-loss step change. The incorporation of 30 mol % 3-hydroxyvalerate (HV) and 15 mol % 3-hydroxyhexanoate (HHx) components into the polyester increased the various thermal temperatures To, Tp, and Tf relative to those of PHB by 3–12°C (measured at B = 40°C/min). DSC measurements showed that the incorporation of HV and HHx decreased the melting temperature relative to that of PHB by 70°C. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 90–98, 2001  相似文献   

4.
Poly(D ‐,L ‐lactic acid) (PDLA) and PDLA‐wood pulp fiber injection molded composites were modified with very small amounts (< 1 wt %) of N′‐(o‐phenylene)dimalemide and 2,2′‐dithiobis(benzothiazole) by reactive extrusion and their resulting mechanical and thermal properties characterized. The modification produced an increase in the percent crystallinity (Xc), heat deflection temperature (HDT), impact energy, tensile strength, and modulus in PDLA. A significant reduction in the melting temperature (Tm) and an increase in the thermal resistance (Tmax) were also found. Fourier‐Transform infrared spectroscopy (FTIR) suggests the creation of hydrogen bonds, a thiol ester and/or ester bond during the modification. Reactive extrusion of commercially available poly(lactic acid) (PLA) by means of N′‐(o‐phenylene)dimalemide and 2,2′‐dithiobis(benzothiazole) provides a low cost and simple processing method for the enhancement of the properties of this biopolymer. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012  相似文献   

5.
Thermally stimulated current (TSC) was used to study molecular relaxations in polyethylene terephthalate (PET) bottles. Unstretched PET film, which was used as a model for the bottle preform, exhibited two peaks at 77 and 90°C that correspond to the α and ρ relaxation processes, respectively. The bottles exhibited only the ρ relaxation, which is located within the temperature range for blow molding PET bottles. The α peak is associated with the main glass transition temperature (Tg) and the ρ peak may be associated with a second Tg. The second Tg is attributed to a “constrained state,” which shows dipolar behavior. Heat‐shrinkage behavior was examined at 90°C. The maximum TSC (Im) of the ρ peak decreased with increasing heat set temperature, and with decreasing shrinkage. Bottles blown at 113°C showed a lower Im and shrinkage than those blown at 103°C for equivalent heat set temperatures. The higher blowing temperature allowed a higher stretch speed that produced higher crystallinity bottles with self‐heat generation during rapid deformation. A relationship between the shrinkage mechanism and the dipole relaxation was proposed.  相似文献   

6.
Reaction after mixing of liquid epoxidized natural rubber/poly(L ‐lactide) blend was performed to enhance the compatibility of the blend. The liquid epoxidized natural rubber was prepared by epoxidation of deproteinized natural rubber with peracetic acid in latex stage followed by depolymerization with peroxide and propanal. The resulting liquid deproteinized natural rubber having epoxy group (LEDPNR) was mixed with poly(L ‐lactide) (PLLA) to investigate the compatibility of the blend through differential scanning calorimetry, optical light microscopy, and NMR spectroscopy. After heating the blend at 473 K for 20 min, glass transition temperature (Tg) of LEDPNR in LEDPNR/PLLA blend increased from 251 to 259 K, while Tg and melting temperature (Tm) of PLLA decreased from 337 to 332 K and 450 to 445 K, respectively, suggesting that the compatibility of LEDPNR/ PLLA blend was enhanced by a reaction between the epoxy group of LEDPNR and the ester group of PLLA. The reaction was proved by high‐resolution solid‐state 13C NMR spectroscopy. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008  相似文献   

7.
Hyperbranched poly(silyl ester)s were synthesized via the A2 + B4 route by the polycondensation reaction. The solid poly(silyl ester) was obtained by the reaction of di‐tert‐butyl adipate and 1,3‐tetramethyl‐1,3‐bis‐β(methyl‐dicholorosilyl)ethyl disiloxane. The oligomers with tert‐butyl terminal groups were obtained via the A2 + B2 route by the reaction of 1,5‐dichloro‐1,1,5,5‐tetramethyl‐3,3‐diphenyl‐trisi1oxane with excess amount of di‐tert‐butyl adipate. The viscous fluid and soft solid poly(silyl ester)s were obtained by the reaction of the oligomers as big monomers with 1,3‐tetramethyl‐1,3‐bis‐β(methyl‐dicholorosilyl)ethyl disiloxane. The polymers were characterized by 1H NMR, IR, and UV spectroscopies, differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The 1H NMR and IR analysis proved the existence of the branched structures in the polymers. The glass transition temperatures (Tg's) of the viscous fluid and soft solid polymers were below room temperature. The Tg of the solid poly(silyl ester) was not found below room temperature but a temperature for the transition in the liquid crystalline phase was found at 42°C. Thermal decomposition of the soft solid and solid poly(silyl ester)s started at about 130°C and for the others it started at about 200°C. The obtained hyperbranched polymers did not decompose completely at 700°C. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3430–3436, 2006  相似文献   

8.
This paper presents a method whereby specific heats or heat capacities of natural gases, both sweet and sour, at elevated pressures and temperatures may be made suitable to modern day machine calculation. The method involves developing (1) a correlation for ideal isobaric heat capacity as a function of gas gravity and pseudo reduced temperature over the temperature range of 300 to 1500 K and (2) a mathematical equation for the isobaric heat capacity departure based on accepted thermodynamic principles applied to an equation of state that adequately describes the behavior of gases to which the Standing and Katz Z factor correlation applies. The heat capacity departure equation is applicable over the range of 0.2 ≤ Pr ≤ 15 and 1.05 ≤ Tr ≤ 3. The significance of the method presented here lies in its utility and adaptability to computer applications.  相似文献   

9.
An equation, based on thermodynamic considerations to relate the glass transition temperature, Tg, to compositional variation of a polymer system, is adapted in this article for modeling the Tg vs. fractional conversion (x) relationship of reactive thermosetting systems. Agreement between the adapted equation and experimental Tg vs. x data is found for several thermosetting crosslinking systems (i.e., epoxies and cyanate ester/polycyanurate) as well as for reactive thermosetting linear polymer systems (i.e., polyamic acid and esters to polyimides). The equation models the experimentally obtained Tg vs. x behavior of thermosetting systems which include competing reactions. Agreement for widely varying molecular structures demonstrates the generality of the equation. The entire Tg vs. x relationship can be predicted for a thermosetting material by using the Tg vs. x equation and the values of the initial glass transition temperature, Tg0, the fully reacted system glass transition temperature, Tg∞, and the ratio of the change in specific heat from the liquid or rubbery state to the glassy state (Δcp) at Tg0 and Tg∞, Δcp∞cp0. The values of Tg0, Tg, and Δcp∞cp0 can be measured generally from two differential scanning calorimetric experiments. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 3–14, 1997  相似文献   

10.
The melting temperatures (TM) 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 (TI) 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/TM. ΔH depended on TI, showing that the melting point of gels depended on a thermal hysteresis. The highest polymer concentration CH 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 CH and the reciprocal melting point of the gels with CH, 1/TIM. 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.  相似文献   

11.
A new main‐chain benzoxazine oligomer with o‐norbornene functionality as end groups has been designed and synthesized. As compared to traditional main‐chain type benzoxazine polymers, this benzoxazine oligomer with o‐norbornene terminal functionality can undergo further crosslinking polymerization after general ring‐opening polymerization of oxazine rings. Another main‐chain benzoxazine oligomer has also been designed based on the reaction of bisphenol‐A, 4,4′‐diaminodiphenylmethane, paraformaldehyde, and phenol for comparison. The structure of the synthesized oligomers is confirmed by 1H nuclear magnetic resonance spectroscopy and Fourier transform infrared spectroscopy (FTIR). The molecular weight has been determined by using gel permeation chromatography (GPC). The benzoxazine oligomer containing o‐norbornene functionality can polymerize with multiple polymerization mechanisms rather than the single mechanism common to traditional 1,3‐benzoxazine resins. The polymerization mechanisms are monitored by in situ FTIR and differential scanning calorimetry (DSC). Moreover, the thermoset derived from the benzoxazine oligomer containing o‐norbornene functionality exhibits high thermal stability with the transition temperature of 360 °C and a high Td5 of 404 °C. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45408.  相似文献   

12.
Vicat softening point temperature (T V) and heat deflection temperature (T d) are important parameters for characterization of heat resistant properties of polymeric materials. PP/Al(OH)3/Mg(OH)2 flame retardant composites were prepared using a twin-screw extruder, and the T V and T d of the composites were measured. The results showed that the T V and T d increased nonlinearly with an addition of the weight percentage of the flame retardant additives except for individual data points, while the T V and T d decreased with increasing the filler particle size when the content of flame retardant additives was constant. Under the same conditions, filling small amount of zinc borate into the composites might improve the heat resistant properties of the composite systems. Moreover, the morphology of the impact fracture surface of the specimens was observed by means of scanning electron microscope to understand the dispersion and distribution of the filler particles in the PP matrix.  相似文献   

13.
An equation which relates the volume term (V=M/(ρL-ρg)) of unassociated liquids to pressure P and temperature T has been obtained by the combination of (a) 03V(?I/?V)P→0=Tx-T for the effect of temperature on V at low (atmospheric) pressure and (b) - V(?P/?V)T = Px Vx/6/V6 p→0+9(P-p) for the effect of pressure on volume at constant temperature. In the equations, p is the vapour pressure; pL the density of the liquid and pg the vapour density. Often pg can be neglected compared with pL and p is small compared with the large pressures required to affect the densities of liquids appreciably. There are three constants: Tx, Px, which equals 4.455 × 109 N m2, and Vx which can be calculated by the addition of atomic values for all the atoms in the molecule and subtraction of a value (6.56 × 106 m3 mol1) for each bond. When V approximates to ML, the molar volume, the equation can be integrated to give the work and heat of isothermal compression. The viscosity of a liquid is related to the work of compression and solubilities in a liquid to the work required to bring the solute to the compressibility of the liquid. Many relationships can be derived and can be used to estimate properties of unassociated liquids.  相似文献   

14.
Thermally stimulated current (TSC) and relaxation map analysis (RMA) was used to characterize the low temperature relaxation of epoxy resin modified with siloxane oligomers. In aminopropyl-terminated siloxane oligomer (ATSO) the β-relaxation of epoxy resin and the glass transition temperature of siloxane oligomer were folded regardless of the concentration of diphenyl. The β-relaxation of epoxy resin and the glass transition temperature of oxiranylmethoxy-terminated siloxane oligomer (OTSO) were folded and shifted to higher temperature as the concentration of diphenyl in siloxane oligomer increased. In the systems containing of diphenyl in siloxane oligomer a new relaxation peak due to the space charge was observed in the range of − 80 °C to − 50 °C and − 30 °C to 5 °C. As the concentration of diphenyl increased the compensation temperature (Tc) and the degree-of-disorder (DOD) were increased while the compensation time, τ c was decreased. Received: 26 May 1997/Accepted: 27 June 1997  相似文献   

15.
Sorption and diffusion of benzene in miscible blends of poly(vinyl-acetate), PVAc, and poly(methyl acrylate), PMA, have been studied. The polymer-polymer interaction parameter values calculated from equilibrium vapor sorption data were all negative, indicating favorable interaction between the two polymers. The sorption of benzene vapor into these blends was measured at a temperature above the Tg's of the pure polymers and found to obey Fickian kinetics. The mutual diffusion coefficients were estimated from the initial slopes of the sorption curves. The concentration dependent diffusion coefficients were fitted to the empirical relation D = Do exp(αC) which satisfactorily correlated the data. Values of the constant Do were found to vary continuously with blend composition, while the α values did not. These experimental data were analyzed employing Fujita's free volume theory. It was found that the data was consistent with this theory. If the fo values for the blends are assumed to be the weighted average of the component polymers, then the β parameter values for the blends also obey the additivity rule.  相似文献   

16.
Rates of hydrogen atom attack on o-fluorotoluene (o-FTOL) and m-fluorotoluene (m-FTOL) at temperatures of 988–1144 K and pressures of 2–2.5 bar have been determined in a single-pulse shock tube study. Hydrogen atoms, generated from the decomposition of hexamethylethane, were allowed to react with the substrates and the characteristic products observed. Rate constants for two reaction channels, displacement of fluorine or methyl, were determined relative to displacement of methyl from 1, 3,5-trimethylbenzene (135TMB). Evidence is presented that abstraction of F is unimportant over the studied temperature range. With k(H + 135TMB → m-xylene + CH3) = 6.7 × 1013 exp(–3255/T) cm3 mol−1s−1, the following rate expressions have been derived: k(H + o-FTOL → C6H5CH3 + F) = 8.38 × 1013 exp(–6041/T) cm3 mol−1s−1; (1012–1142 K) k(H + o-FTOL → C6H5F + CH3) = 2.37 × 1013 exp(–2938/T) cm3 mol−1s−1; (988–1142 K) k(H + m-FTOL → C6H5CH3 + F) = 1.33 × 1014 exp(–6810/T) cm3 mol−1s−1; (1046–1144 K) k(H + m-FTOL → C6H5F + CH3) = 2.04 × 1013 exp(–3104/T) cm3 mol−1s−1; (1008–1144 K) Uncertainties in the relative rate constants are estimated to be factors of about 1.1, while the above absolute values have estimated expanded uncertainties of about a factor of 1.4 in rate, 10 kJ mol−1 in the activation energy, and a factor of 3 in the A-factor. The present data are compared with relevant literature data. From our data and the thermochemistry, a model of the elementary steps comprising displacement of F is developed. On the basis of the model fit to our data, rate constants for the addition of atomic fluorine to toluene at 1100 K are derived. Rate expressions for fluorination reactions of toluene are also determined. The significance of the present results is discussed in the context of the formation of fluorinated byproducts in high-temperature systems.  相似文献   

17.
It is shown that the presence of a “slotted draft tube” results in reduced air requirements for spouting and improved drying performance. Experimental data are presented on batch as well as continuous spouted bed drying of wheat, paddy, maize and peas. The variables studied are feed moisture content (Qo), inlet air temperature (To), bed mass hold-up (Mp), inlet superficial air velocity (uo) and bed diameter (Dc) in batch drying, and the above variables and solids feed rate (Fs) in continuous drying. The data on average overall drying rate, ?m, in kg moisture evaporated per unit time per kg bed solids, is found to be correlatable as ?m, = k (50Qo + 0.118To ? 12.5) 10?5, and the single parameter k is presented for wheat, paddy, maize and peas for both batch and continuous modes of spouted bed drying. The correlation obtained should be useful in dryer design for the grains studied as well as for other similar materials.  相似文献   

18.
Numerical results are presented for effects of latent heat transport associated with film vaporization on laminar mixed convection heat and mass transfer in a vertical channel with a half channel width b = 0.01 m. The influences of the inlet liquid mass flowrate and wall temperature on the film vaporization and the associated heat and mass transfer characteristics are examined for air-water and air-ethanol systems with gas Reynolds number Reg = 2000. Predicted results obtained by including transport in the liquid film are contrasted with those where liquid film transport is neglected, showing that the assumption of an extremely thin film made in Lin et al. (1988) and Yan and Lin (1989) is only valid for systems having small liquid mass flow rates. Additionally, it is found that the interfacial heat flux is predominantly determined by latent heat transfer connected with film evaporation.  相似文献   

19.
Reaction‐induced vitrification takes place in the network‐forming epoxy–amine system diglycidyl ether of bisphenol A (DGEBA) + methylenedianiline (MDA) when the glass‐transition temperature (Tg) rises above the cure temperature (Tcure). This chemorheological transition results in diffusion‐controlled reaction and can be followed simultaneously with the reaction rate in modulated‐temperature DSC (MTDSC). To predict the effect of Tcure and the NH/epoxy molar mixing ratio (r) on the reaction rate in chemically controlled conditions, a mechanistic approach was used based on the nonreversing heat flow and heat capacity MTDSC signals, in which the reaction steps of primary (E1OH = 44 kJ mol?1) and secondary amine (E2OH = 48 kJ mol?1) with the epoxy–hydroxyl complex predominating. The diffusion factor DF as defined by the Rabinowitch approach expresses whether the chemical reaction rate or the diffusion rate determines the overall reaction rate. A model based on the free volume theory together with an Arrhenius temperature dependency was used to calculate the diffusion rate constant in DF as a function of conversion (x) and Tcure. The relation between x, r, and Tg, needed in this model, can be predicted with the Couchman equation. An experimental approximation for DF is the mobility factor DF* obtained from the heat capacity signal at a modulation frequency of 1/60 Hz, normalized for the effect of the reaction heat capacity in the liquid state and the change in Cp in the glassy region with x and Tcure. In this way, an optimized set of diffusion parameters was obtained that, together with the optimized kinetic parameters set, can predict the reaction rate for different cure schedules and for stoichiometric and off‐stoichiometric mixtures. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2814–2833, 2004  相似文献   

20.
Epoxy‐terminated siloxane‐contained resin (BCDS/OBBA‐ETS) with high tensile strength and lap shear strength as well as good thermal stability was synthesized and characterized by 1H‐NMR and Fourier transform infrared spectroscopy. Carboxy‐capped disiloxane‐4,4′‐oxybis (benzoic acid) ester oligomer (BCDS/OBBA) was firstly prepared from the reaction between 1,3‐bis(chloromethyl)‐1,1,3,3‐tetramethyl‐disiloxane and 4,4′‐oxybis(benzoic acid) (OBBA) in N,N‐dimethylformamide in the presence of triethylamine. Then, the BCDS/OBBA oligomer was reacted with epichlorohydrin to obtain the title BCDS/OBBA‐ETS resin. Cured with liquid polyamide L‐651, or diethylenetriamine, the mechanical and thermal properties as well as the lap shear strength of the BCDS/OBBA‐ETS resin were evaluated. The results indicated that the BCDS/OBBA‐ETS resin exhibited good thermal stability below 200°C, and the glass transition temperature (Tg) was about 64°C after cured with L‐651. The tensile strength of same cured BCDS/OBBA‐ETS resin was 27.46 MPa with a stain at break of 42.11%, and the lap shear strength for bonding stainless steel was 18.59 MPa. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012  相似文献   

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