Determination of Melting Parameters of Cyclodextrins Using Fast Scanning Calorimetry

The first evidence of native cyclodextrins fusion was registered using fast scanning calorimetry (FSC) with heating rates up to 40,000 K s⁻¹. The endothermal effects, detected at low heating rates, correspond to the decomposition processes. Upon the increase of the heating rate the onset of these effects shifts to higher temperatures, reaching a limiting value at high heating rates. The limiting temperatures were identified as the melting points of α-, β- and γ-cyclodextrins, as the decomposition processes are suppressed at high heating rates. For γ-cyclodextrin the fusion enthalpy was measured. The activation energies of thermal decomposition of cyclodextrins were determined by dependence of the observed thermal effects on heating rates from 4 K min⁻¹ in conventional differential scanning calorimetry to 40,000 K s⁻¹ in FSC. The lower thermal stability and activation energy of decomposition of β-cyclodextrin than for the other two cyclodextrins were found, which may be explained by preliminary phase transition and chemical reaction without mass loss. The obtained values of fusion parameters of cyclodextrins are needed in theoretical models widely used for prediction of solubility and solution rates and in preparation of cyclodextrin inclusion compounds involving heating.     

人工伴侣促进溶菌酶复性动力学

利用复性和聚集竞争反应动力学模型描述自发复性和人工伴侣系统(十六烷基三甲基溴化铵与b -环糊精)促进溶菌酶复性动力学。在酶浓度为0.5~2.0 mgmL-1、盐酸胍浓度为0.5~2.2molL-1范围内,系统分析了盐酸胍浓度和人工伴侣浓度对复性动力学的影响。与自发复性相似,人工伴侣促进溶菌酶复性亦符合3级聚集反应动力学。人工伴侣系统的主要作用是抑制聚集体的生成速率,从而达到提高复性收率的效果。在盐酸胍浓度小于1.2mol稬-1时,人工伴侣系统和盐酸胍对促进变性溶菌酶复性具有协同作用,两者共同作用对促进蛋白质复性具有显著效果。     

Fast isothermal calorimetry of modified polypropylene clay nanocomposites

Calorimetric experiments at cooling rates comparable to those during injection molding, as an example, are needed to study phase transitions under conditions relevant for processing. Ultra fast scanning calorimetry is a technique which provides a means to analyze the materials of interest under rapid cooling conditions and it is a promising technique by which the crystallization behavior of composite systems based on fast crystallizing polymers like isotactic polypropylene (iPP) can be studied. By combining conventional DSC and ultra fast chip calorimetry isothermal crystallization experiments were performed in the whole temperature range between glass transition and melting temperature of iPP. Because of the very small time constant of the calorimeter, isothermal crystallization processes with peak times down to 100 ms were investigated after cooling the sample from the melt at 2000 K/s. iPP grafted with maleic anhydride (PPgMA) - montmorillonite clay nanocomposites were studied. The influence of various clay loadings on the crystallization behavior of PPgMA at different temperatures was followed by ultra fast isothermal calorimetry. PPgMA clay nanocomposites showed a variation in crystallization peak times with different clay loadings at crystallization temperatures between 70 °C and 100 °C. No influence of clay loading was observed at lower crystallization temperatures. At these temperatures, where the mesophase is formed and homogeneous nucleation is expected, the contribution of the clay as a nucleating agent is negligible. For crystallization at about 80 °C, where the α-phase is formed, the nucleating effect of the clay is observed yielding complex crystallization kinetics. In the temperature range 75-85 °C in some nanocomposites a double peak during isothermal crystallization was observed corresponding to a fast and a slow crystallization processes occurring simultaneously. At higher temperatures, above 120 °C, the clay slightly retards the crystallization process.     

Differential Scanning Calorimetry Cure Studies of Tetra-N-glycidyldiaminodiphenylmethane Epoxy Resins Part 2 - Reaction with 4,4′-Diaminodiphenylsulphone Accelerated by Borontriofluoride-Ethylamine

The curing reaction was monitored by differential scanning calorimetry scans at various heating rates and from isothermal experiments in the range 130–170°C. The catalysed isothermal cure is an initially rapid reaction which approximates to first-order kinetics. Above about 30% conversion there is a transition to a much slower first-order reaction. The differential scanning calorimetry scans show multiple exotherm peaks, indicative of a complex reaction. However, data at a given conversion can be described by a simple general kinetic model. The heat of reaction shows a decreasing trend with increasing catalyst concentration.     

Differential Scanning Calorimetry Cure Studies of Tetra-N-glycidyldiaminodiphenylmethane Epoxy Resins. Part 1 - Reaction with 4,4′-Diaminodiphenylsulphone

Rates and extents of cure are determined using differential scanning calorimetry in the isothermal mode over the temperature range 170–220°C, and from d.s.c. scans at various heating rates. The isothermal data are consistent with an autocatalytic mechanism at conversions up to about 20–30%. Data from d.s.c. scans fit a simple kinetic model which indicates that the apparent activation energy (E) for cure increases with increasing conversion, consistent with an increasing degree of diffusion control. At low levels of conversion the isothermal and dynamic data both provide estimates for E of about 70 kJ mol^?1. The heat of cure is about 105 kJ mol^?1 epoxide, and is constant over a wide range of amine concentration. This indicates that any parallel or competing processes which occur must have the same heat of reaction.     

Nucleation and Self‐Nucleation of Bio‐Based Poly(ethylene 2,5‐furandicarboxylate) Probed by Fast Scanning Calorimetry

The present work focuses on the influence of nucleation processes on the crystallization of bio‐based poly(ethylene 2,5‐furandicarboxylate) (PEF). Nuclei formation has been studied by means of fast scanning calorimetry (FSC) both when cooling from the melt (nonisothermal conditions) and when annealing at either low‐ or high‐temperatures (isothermal conditions). FSC results show that nucleation on cooling can be prevented by using fast rates allowing to keep the polymer in its amorphous state; whereas cooling at moderate rates results in sample nucleation with a subsequent increase of the crystallization rate. Isothermal pretreatment just above the PEF glass transition temperature (T_g) results in nuclei formation whose rate decreases when the nucleation temperature approaches PEF T_g. On the other hand, annealing below the PEF melting point allows determination of the sample self‐nucleation behavior which occurs in a very narrow temperature range, i.e., between 195 and 198 °C.

     

喷气燃料冰点的差示扫描量热法测定

介绍差示扫描量热法(DSC)测定喷气燃料冰点的原理和实验过程。用DSC法测定了不同型号的8种喷气燃料的冰点,测定结果与国标法GB/T 2430-1981测定的一致。     

用差示扫描量热法测量涂膜中的锌粉含量

作为测量锌粉含量最为快捷的一种方法——差示扫描量热法,现已在国际上得到广泛应用,叙述利用其方法测量涂膜中锌粉含量的原理及检测条件,探讨了产生误差的原因。     

用差示扫描量热法研究环氧封端酚酞聚芳醚腈的固化特性

利用差示扫描量热法研究了环氧封端酚酞聚芳醚腈（简称Ｅ－ＰＣＥ）中固化剂类型对Ｅ－ＷＣＥ树脂固化反应温度、反应热的影响,结果表明,固化剂与Ｅ－ＰＣ Ｅ树脂反应的活性为ＭＤＡ＞ＤＤＥ＞ＤＤＳ;Ｅ－ＰＣＥ／ＤＤＳ体系的最低固化反应温度为１６３．２℃,固化反应峰顶温度为２２８,１℃,固化反应表观活化能为８１．２７ｋＪ／ｍｏｌ,固化反应级数为０．９０。     

差示扫描量热法对乙烯-醋酸乙烯酯热性能的研究

乙烯-醋酸乙烯醑（EVA）由于在分子链中引入了醋酸乙烯酯（VA）单体,降低了分子链的规整性．随着VA含量的增加,EVA树脂的结晶度降低。文章通过改变DSC测试条件对EVA树脂的热性能做进一步研究,分别讨论了常规方法与恒温结晶后的方法的玻璃化转变以及结晶的行为。从而估算出EVA的玻璃化转变温度。     

Differential Scanning Calorimetry of Stressed Polymers

Stresses which have been frozen into a polymer by cooling to below its glass transition temperature (Tg) are relieved when the polymer is reheated above its Tg. Polymers which have been elongated will contract above Tg. This sudden contraction just above Tg is detected as a sharp drop in the differential scanning calorimetric curve. This is the reverse of the well known superheating endotherm accompanying the expansion of annealed polymers. The decrease in the differential scanning calorimetric curve immediately after the Tg inflection can be quantitatively related to the residual strain in poly(vinyl chloride) and polycarbonate.     

Kinetic of 8-quinolinyl Methacrylate Polymerization by Differential Scanning Calorimetry

Abstract

The kinetic of 8-quinolinyl methacrylate (8-QMA) polymerization was studied using 2,2′-azobisisobutyronitrile (AIBN) as a free radical initiator by differential scanning calorimetry (DSC) under two different experimental variables viz., heating rate and initiator concentration. Borchardt ‐ Daniel (B [tbnd]) kinetic method was applied to estimate the various kinetic parameters for the free radical polymerization of 8-QMA. The effect of initiator concentration and heating rate on the rate of polymerization was discussed. The importance of isothermal and isoconversion predictive curves in optimizing the polymerization process parameters has also been discussed.     

高密度烃燃料冰点的DSC法测定

介绍了用差示扫描量热法(DSC)测定高密度烃燃料冰点的原理和方法,并对测试中的主要影响因素进行讨论。结果表明,当高密度烃燃料冰点在-80℃以下时,该方法具有较好的重复性和再现性,可作为高密度烃等低冰点燃料的常规检测方法。     

DSC加速老化试验方法在PP寿命估算中的应用

利用差示扫描量热(DSC)加速老化试验方法,以不同温度下测得的氧化诱导时间(OIT)为基础,建立温度–寿命相关的阿伦尼乌斯方程,并以此对不同温度下聚丙烯的寿命进行快速估算。结果表明,其估算结果有效,是筛选抗氧剂配方的一种较好的方法。     

Differential Scanning Calorimetry Cure Studies of Tetra-N-glycidyldiaminodiphenylmethane Epoxy Resins 3 - Reaction with Dicyandiamide

Continuation of work on the curing characteristics of an epoxy resin which is widely used as a composite matrix is reported. Results are given of study of the cure of the resin with dicyandiamide as hardener and diuron as accelerator, using differential scanning calorimetry to monitor the cure. The effect of diuron on the cure of the resin with an aromatic amine curing agent is also described. Distinctive effects of composition are found and values of the apparent activation energy of the curing reaction are derived.     

用DSC法研究环氧树脂/环氧封端酚酞聚芳醚腈的固化特性

利用差示扫描量热法研究了AG - 80环氧树脂和环氧封端酚酞聚芳醚腈 (简称E -PCE)共混物中固化剂含量对树脂基体固化反应温度、反应热的影响。此共混环氧树脂基体的最低固化反应温度为1 61 .3℃ ,固化反应表观活化能为 60 .66kJ/mol,固化反应级数为 0 .875。     

差示扫描量热法测定锌粉和富锌底漆中的锌含量

采用差示扫描量热法（DSC）测定了锌粉与富锌底漆中的金属锌含量。分析了测试过程中可能出现测定误差的原因,提出了提高分析精度的方法。     

海藻糖对变性溶菌酶的促进复性作用及动力学

研究了海藻糖促进变性还原溶菌酶的复性作用,考察了不同盐酸胍浓度下海藻糖浓度对复性收率的影响,并利用表观竞争反应动力学模型分析了海藻糖辅助溶菌酶的复性动力学特性.结果表明,在海藻糖存在下,聚集体生成速率常数k_A明显减小,但复性速率常数k_N变化不大;随海藻糖浓度的增大,k_A先降低后升高,在合适浓度时k_A出现最小值,由于此时k_N/k_A出现最大值,因此复性收率最大.说明海藻糖的主要作用是有效抑制蛋白质分子间聚集,因此在一定范围内提高其浓度可促进蛋白质复性,从而提高复性收率.     

Green Process of Propylene Oxide Reaction for Thermal Hazard Assessment by Differential Scanning Calorimetry and Simulation

In addition to polypropylene, acrylonitrile, and carbonyl alcohol, propylene oxide is the fourth major derivative among propylene derivatives and one of the important basic organic chemicals. A thermal stability test of catalyst, methanol, and hydrogen peroxide (H₂O₂) was conducted via differential scanning calorimetry (DSC). Propylene epoxidation with H₂O₂ over catalyst, methanol, and propylene evenly mixed by specific pressure was carried out, and then the runaway reaction under adiabatic conditions was further simulated by the vent sizing package 2 (VSP2) to measure temperature and pressure data with respect to time of the runaway excursion. Finally, the apparent activation energy of H₂O₂ and propylene oxide reaction was obtained via temperature variation equation to evaluate the degree of potential hazard in industry.