差示扫描量热法对乙交酯开环聚合催化剂的性能评价

采用差示扫描量热法研究了3类催化剂[Bi(OAc)₃、SnCl₂·2H₂O和乙酰丙酮类金属配合物]催化乙交酯(GA)开环聚合的反应动力学。Bi(OAc)₃和SnCl₂·2H₂O在催化GA开环聚合的过程中表现出了较高的活性;Ph₃P的加入使得催化体系的活化能减少25%以上,相关反应速率至少增长30%;向催化剂中加入引发剂甲醇(MeOH)可以使反应的活化能降低30%以上,反应速率增加50%以上。复合催化剂相对于单一催化剂具有更好的催化性能。结果表明,差示扫描量热法是一种高效的筛选聚合用催化剂的方法。     

Isothermal crystallization kinetics of high‐flow nylon 6 by differential scanning calorimetry

The isothermal crystallization kinetics have been investigated with differential scanning calorimetry for high‐flow nylon 6, which was prepared with the mother salt of polyamidoamine dendrimers and p‐phthalic acid, an end‐capping agent, and ε‐caprolactam by in situ polymerization. The Avrami equation has been adopted to study the crystallization kinetics. In comparison with pure nylon 6, the high‐flow nylon 6 has a lower crystallization rate, which varies with the generation and content of polyamidoamine units in the nylon 6 matrix. The traditional analysis indicates that the values of the Avrami parameters calculated from the half‐time of crystallization might be more in agreement with the actual crystallization mechanism than the parameters determined from the Avrami plots. The Avrami exponents of the high‐flow nylon 6 range from 2.1 to 2.4, and this means that the crystallization of the high‐flow nylon 6 is a two‐dimensional growth process. The activation energies of the high‐flow nylon 6, which were determined by the Arrhenius method, range from ?293 to ?382 kJ/mol. The activation energies decrease with the increase in the generation of polyamidoamine units but increase with the increase in the content of polyamidoamine units in the nylon 6 matrix. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Kinetic study of radical polymerization. II. Solid‐state bulk polymerization of sodium methacrylate by differential scanning calorimetry

The solid‐state radical polymerization of sodium methacrylate was investigated. It was initiated by azobisisobutyronitrile, which was used as a radical initiator. Differential scanning calorimetry (DSC) was used to observe the endothermic and exothermic transitions during the polymerization reaction. Structural studies were performed with the DSC thermograms and Fourier transform infrared and ultraviolet–visible spectra, and all of the results confirmed the progress of the reaction. The obtained data revealed that the polymerization reaction proceeded completely with a 100% conversion. ΔH of this reaction was calculated with various amounts of the initiator, and the peak temperatures were determined at different heating rates. The activation energy (19.7 kcal mol^?1) was also obtained by the Kissinger method for this type of solid polymerization reaction. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1648–1654, 2003     

Optimal designs for constant‐heating‐rate differential scanning calorimetry experiments for polymerization kinetics: nth‐order kinetics

Optimal designs have been constructed for differential scanning calorimetry (DSC) experiments conducted under constant‐heating‐rate conditions for materials that are a priori assumed to follow nth‐order kinetics. Two different operating scenarios are considered, including single‐scan and multiscan DSC experiments for eight different kinetic parameter combinations representing a range of typical polymeric curing reactions. The resulting designs are studied to determine which kinetic model parameters are influential in determining the optimal design. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Curing behavior of epoxy resins in two‐stage curing process by non‐isothermal differential scanning calorimetry kinetics method

In this research, a new thermal curing system, with two‐stage curing characteristics, has been designed. And the reaction behaviors of two different curing processes have been systematically studied. The non‐isothermal differential scanning calorimetry (DSC) test is used to discuss the curing reaction of two stages curing, and the data obtained from the curves are used to calculate the kinetic parameters. Kissinger‐Akahira‐Sunose (KAS) method is applied to determine activation energy (E_a) and investigate it as the change of conversion (α). Málek method is used to unravel the curing reaction mechanism. The results indicate that the curing behaviors of two different curing stages can be implemented successfully, and curing behavior is accorded with ?esták‐Berggren mode. The non‐isothermal DSC and Fourier transform infrared spectroscopy test results reveal that two different curing stages can be implemented successfully. Furthermore, the double x fitting method is used to determine the pre‐exponential factor (A), reaction order (m, n), and establish the kinetic equation. The fitting results between experiment curves and simulative curves prove that the kinetic equation can commendably describe the two different curing reaction processes. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40711.     

Effect of anhydride curing agents,imidazoles, and silver particle sizes on the electrical resistivity and thermal conductivity in the silver adhesives of LED devices

This study investigated the preparation of silver adhesives applied to a light‐emitting diode (LED) device as die‐attach materials consisting of silver particles, on epoxy resin, curing agents, and accelerants for complete curing at 150 °C for 30 min. For the epoxy resin, this study used 3,4‐epoxycyclohexyl‐methyl‐3,4‐epoxycyclohexanecarboxylate mixed with different types of anhydride curing agents such as 4‐methylcyclohexane‐1,2‐dicarboxylic anhydride and hexahydrophthalic anhydride as well as imidazole accelerants such as 2‐ethyl‐4‐methyl‐1H‐imidazole‐1‐propanenitrile, 2‐phenylimidazole, 2‐methylimidazole, 2‐phenyl‐2‐imidazoline, and 1,2‐dimethylimidazole. In addition, different size of silver particles and hybrid silver particles were used for the electrical resistivity and thermal conductivity of silver adhesives. Differential scanning calorimetric (DSC) measured conversion of silver adhesives based on different types and contents of the curing agents and accelerants under heating. The silver particles' distribution of silver adhesive also affected electrical resistance, as proved by scanning electronic microscopy (SEM) and four‐point probe. The obtained results showed that the silver adhesive containing an 100 wt % of epoxy resin mixed with 85 wt % of hexahydrophthalic anhydride, 1.0 wt % (weight of epoxy resin) of 2‐ethyl‐4‐methyl‐1H‐imidazole‐1‐propanenitrile, and 80 wt % (weight of epoxy resin) of hybrid silver particles (40 wt % 15 μm and 40 wt % 1.25 μm) was perfect, having the lowest electrical resistivity at 1.11 × 10^?4 Ω·cm and good thermal conductivity at 3.2 W/m·K. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43587.     

A combined differential scanning calorimetry-dynamic mechanical thermal analysis approach for the estimation of constrained phases in thermoplastic polymer nanocomposites

Poly(butylene terephthalate) (PBT) nanocomposites reinforced with different weight fractions of montmorillonite (MMT), and nanoprecipitated calcium carbonate (NPCC) were prepared by a two-step melt compounding method. X-ray diffraction (XRD) and differential scanning calorimetry (DSC) analyses were employed to explore the effect of nanofiller inclusion on the crystalline structure of PBT nanocomposites. The mobile amorphous fraction (MAF) and the rigid amorphous fraction (RAF) were first measured using the specific heat capacity (C_p ) and melting enthalpy data. However, the contributors to total RAF, including interfacial RAF (RAF_int ) and crystalline RAF (RAF_c ), could not be discerned using only DSC. A novel and simple method was hence developed by employing a combined DSC-dynamic mechanical thermal analysis (DMTA) approach (CDDA) to disentangle the RAF components and determine the fractions of constrained volume constituents. To validate the results, the MAF calculated by CDDA were compared to those of DSC. The values obtained using CDDA were relatively higher, owing to the more significant sensitivity of this approach to polymer chain mobility.     

The glass transition temperature of poly(N-vinyl pyrrolidone) by differential scanning calorimetry

Previously a wide range of values have been reported for the glass transition temperature, T_g, of poly(N-vinyl pyrrolidone), PVP, and it was suggested that lower values are due to variable uptakes of water caused by the hygroscopic nature of the polymer. Now it has been found that there are large variations in T_g, even in carefully dried specimens of PVP. Other factors found to influence T_g are residual monomer and the molecular weight of PVP. Polymers prepared by bulk polymerization, either by γ-irradiation or by heating with 2-azobisisobutyronitrile, have much lower values of T_g than dried ones prepared containing 30% water. The difference is mainly due to depression of T_g by residual monomer which, in the absence of water during polymerization, fails to react completely because of conversion to a glassy state. An unexplained observation is that even when all residual monomer has been removed, polymers prepared by bulk polymerization still have a lower T_g than would be expected from their molecular weight.     

Curing behavior of epoxy resin/tung oil anhydride exfoliated nanocomposite by differential scanning calorimetry

The nanocomposite of epoxy resin/tung oil anhydride/organic montmorillonite was prepared by casting and curing. The distance of the clay gallery rose and the exfoliated nanocomposite was formed. The exfoliation behaviors of the nanocomposite had been investigated by X‐ray diffraction (XRD). The curing mechanism and kinetics of epoxy resin with the different amounts of organic montmorillonite were studied using isothermal and dynamic methods by differential scanning calorimetry (DSC). Some parameters, the activation energy and reaction orders, were calculated by the modified Avrami equation in analysis of the isothermal experiment. The total curing mechanism and kinetics of curing reaction were also analyzed by the Flynn–Wall–Ozawa method. It was noted that the instantaneous activity energy during the curing process could be obtained by the Flynn–Wall–Ozawa method and the trend of the results was in agreement with those obtained from the modified Avrami equation. These results show that the activity energy decreases with the addition of organic montmorillonite. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3822–3829, 2004     

Studies on heat capacity of cellulose and lignin by differential scanning calorimetry

Heat capacities (C_p) of wood cellulose, other natural celluloses having various crystallinities and of lignin are given for temperatures ranging from 330K to 450K using differential scanning calorimetry. The calculation of the C_p of completely crystalline cellulose is based on a two-state model of cellulose which assumes linearity between the crystallinity and C_p. The higher C_p found in the amorphous region compared with the crystalline region, is apparantly due to differences in the frequency of molecular vibration in these two areas. The glass transition of lignin was observed as a sudden increase in C_p at 400K. The precise T_g of lignin was dependent on the sample's origin, characterization, thermal history etc. When annealed at around T_g enthalpy relaxation occurs, and this can be detected as an endothermic peak in the C_p curve at the transition temperature. Moreover, the C_p in the glassy state was found to decrease with both annealing time and temperature, suggesting that rearrangement of the local conformation of lignin molecules occurs in the glassy state temperature range.     

Investigation of alkaline hydrolysis of polyethylene terephthalate by differential scanning calorimetry and thermogravimetric analysis

The hydrolytic depolymerization of polyethylene terephthalate (PET) with alkaline hydroxides was investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The reactions of the mixtures were conducted in their solid states under nitrogen atmosphere. The experimental results showed that potassium hydroxide possessed the hydrolytic activity of depolymerizing PET into small molecules such as ethylene glycol; in contrast, sodium hydroxide did not. The production rate of ethylene glycol was enhanced by increasing charge ratio of potassium hydroxide to PET. The presence of water facilitated the alkaline hydrolysis of PET; however, the presence of metal acetates decreased the hydrolysis rate. The activation energy for alkaline hydrolysis of PET determined by the thermograms was in good agreement with the value obtained from the experiments in a batch reactor. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 1939–1945, 1998     

Effect of electronegativity and steric hindrance of the cocatalyst on the activity and selectivity of butadiene polymerization catalyzed by molybdenum

Molybdenum-based random 1,2-polybutadiene (1,2-PB) rubber, with its excellent wet skid resistance, low rolling resistance, and low heat buildup, can be used for green tread rubber, and it has significant benefits for the enhancement of the mechanical strength of 1,2-PB. In this study, we investigated in detail the effects of the electronegativity and steric hindrance of the cocatalyst on the stereoselectivity of the resulting polymers. In the case of cocatalysts with moderate electronegativities, the active centers were more stable; this resulted in a larger molecular weight and a higher conversion, whereas a cocatalyst with excessive electronegativity tended to initiate cationic polymerization. The high sterically hindered substituent restricted the coordination configuration of the monomer; this ultimately resulted in the increase in the 1,2 structure to 90%. Fourier transform infrared analysis showed that the content of trans-1,4 structure increased from 7 to 66%, and its crystallinity reached 59.2%, as calculated with differential scanning calorimetry when triethyl aluminum was used as the cocatalyst. Consequently, trans-1,4-polybutadiene crystals were introduced into the 1,2-PB elastomer in one step; this could be a promising facile route for strengthening 1,2-PB. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 46906.     

Isothermal crystallization kinetics of polypropylene by differential scanning calorimetry. I. Experimental conditions

Reliable isothermal crystallization kinetic studies can be achieved by differential scanning calorimetric techniques only under restricted conditions. In the case of isotactic polypropylene, our results indicate that those conditions are met in the range of 3°C below the isothermal crystallization temperature T_c. Experimentally, it is only in this range when the complete crystallization peak can be registered by the DSC and depicted in a thermogram. Just around this temperature interval, the Avrami exponent n = 3 for bulk crystallization, whereas for any other test the isothermal temperature T_it, nonisothermal conditions prevail and the Avrami exponent deviates from the expected value. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 970–978, 2004     

Curing behavior of a novolac‐type phenolic resin analyzed by differential scanning calorimetry

Curing of a novolac‐type phenolic resin was studied by DSC. The kinetic analysis was performed by means of the dynamic Ozawa method at heating rates of 5, 10, 15, and 20°C/min. This analysis was used to determine the kinetic parameters of the curing process. The activation energy was found to be 144 kJ/mol. It was found that the Ozawa exponent values decreased with increasing reaction temperature from 3.5 to 1, suggesting a change in the reaction mechanism from microgel growth to diffusion‐controlled reaction. The reaction rate constant was found to range from 123.0 to 33.6 (°C/min)ⁿ. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1678–1682, 2003     

Characterization of the thermal properties of PLA fibers by modulated differential scanning calorimetry

Polylactide (PLA) has been melt spun to produce multifilament continuous yarns. The thermal characteristics of PLA filaments have been investigated using modulated differential scanning calorimetry (MDSC). With MDSC, it is possible to separate the different thermal events and to analyze them more precisely. The influence of hot drawing on thermal properties of PLA filaments has been studied. Hot drawing promotes an increase of glass transition temperature (T_g) and a decrease of heat capacity. The cold crystallization spreads on a larger range of temperature and the peak occurs at a lower temperature. The initial degrees of cristallinity of PLA filaments have been calculated thanks to the reversing and non reversing curves of MDSC. Tensile properties of PLA filaments are also investigated.     

差示扫描量热法测定聚丙烯腈纤维玻璃化转变温度

本文采用差示扫描量热法,两段升温模式,以10℃/min加热速度,从30℃加热到150℃,测定了4个聚丙烯腈纤维样品的玻璃化转变温度,探讨了加热方法和样品量试验条件,得到了准确可靠的玻璃化转变温度。     

Isothermal differential scanning calorimetry study of the cure kinetics of a novel aromatic maleimide with an acetylene terminal

An isothermal differential scanning calorimetry (DSC) study on the cure kinetics was performed on N-(3-acetylenephenyl)maleimide (3-APMI) monomer to determine a suitable cure model. The 3-APMI monomer reported in our prior article was a novel aromatic maleimide monomer with an acetylene terminal that would be an ideal candidate for heat-resistant composites. The isothermal DSC study was carried out in the temperature range 150–200°C. Although the cure temperatures were different, the shapes of the conversion curves were similar, and all of the cure reactions could be described by an nth-order kinetic model. In particular, the cure reaction at the initial stage was a first-order kinetic reaction. The cure kinetic parameters of the 3-APMI monomer, including the reaction model, activation energy, and frequency factor, were determined. This information was very useful for defining the process parameters, final properties, and quality control of the cured 3-APMI monomer. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008