Calorimetry in scanning mode

FIGURE 3.5 Exotherm obtained with calorimetry in scanning mode. (Figure 3 SETARAM, private paper SETARAM from R Le Parlouer and J. M. Vergnaud.)... 

FIGURE 3.6 Calorimetry in scanning mode. Effect of the heating rate on the heat flux-temperature history. (With permission of Elsevier, Figure 9, Thermochim. Acta 1987. 116 111-24. J.Y. Armand and J.M. Vergnaud.)... 

After a few studies, among them these contribution [3,14], almost all researchers were inclined to use the calorimetry in scanning mode. 

The effect of the percent sulfur and other curing additives was precisely shown by using calorimetry run in scanning mode. 

An identical result is obtained with calorimetry driven in scanning mode, the integration of the heat flux being made with respect to temperature. 

Various techniques have been developed in turn the Mooney viscometer, the Wallace-Shawbury curometer, the oscillating disc rheometer (ODR), and the moving disc rheometer (MDR), in addition to the calorimetry techniques. The isothermal calorimetry and its counterpart in scanning mode, the isothermal moving disc rheometer (MDR), and the improvement of this last technique with the rubber process analyzer run in scanning mode, are considered. 

The calorimetry techniques have been used for many purposes in the cure of rubber, including to measure the heat of the overall cure reaction, but also for evaluating the kinetics of the heat evolved from the overall reaction. The only question at first was what way to use the calorimetry In the early eighties, it seemed to a majority of the authors that the isothermal condition would be preferable, but finally the operation in scanning mode was preferred. 

Finally, the history has been similar both with the MDR or the calorimeter. After being utilized under isothermal conditions a few decades ago, the calorimetry technique is now widely used in the scanning mode, and the MDR, quite recently, could be used in scanning mode with the rubber process analyzer. 

The calorimetry, especially used in scanning mode, is the technique appropriated for measuring the aithalpy of the overall leacticm. It may also be used for evaluating the kinetic parameters of this leacliMi, in spite of the low value of the enthalpy. For this last reason, rather large samples should be used so as to get more sensible and precise measurements. 

Vergnaud J.M. 1987. ModeUing in calorimetry working under isothermal conditions or in scanning mode. Thermochim. Acta. 114 15-27. 

Finally, using the above results and theoretical consideration, the kinetics of the cure reaction was established and used for evaluating either the profiles of temperature developed through the material or the corresponding profiles of state of cure [10-12], At that time the kinetics of the cure reaction was determined by calorimetry run under isothermal conditions and finally in scanning mode with a constant temperature program. As the enthalpy of the cure reaction is rather low for rubbers, the problem was tedious, leading to resnlts with sometimes a low level of accuracy. 

In the third chapter, the methods used for evaluating the kinetics of the cure of rubbers are described and studied on the basis of either the heat evolved from the cure reaction (calorimetry) or the change in the mechanical properties during the cure (rheometers). Theoretical studies are made so as to improve either the isothermal MDR, or even the MDR in scanning mode, by considering different temperature-time relationships. 

It conld be of interest to recall the history of this subject, followed by the various techniques considered in our book. It took a long time—up to a decade—for researchers to accept calorimetry in the scanning mode. Calorimetry run under isothermal conditions was considered for several years to be more comfortable, but some showed that in a process where heating plays a primary role, temperature is neither constant nor uniform, without speaking of the heat generated by the reaction. 

To better assess heat losses, twin calorimeters have been developed that permit measurement in a differential mode. A continuous, usually linear, temperature change of calorimeter or surroundings is used in the scanning mode. The calorimetry, described in Sect. 4.3 is scanning, isoperibol twin-calorimetry, usually less precisely called differential scanning calorimetry (DSC). 

Differential scanning calorimetry (DSC) data were recorded on a Du Pont DSC (mod. 2940) in the dynamic mode with a heating rate of 10 C/min or in isothermal mode pre-selecting the final curing temperature. Nitrogen was used as purge gas. 

Much of the intrinsic difficulties with DSC measurements and the tedious data collecting process of traditional adiabatic calorimetry can be avoided by adiabatic scanning calorimetry. In this technique a measured heating power is continuously applied to (or extracted from) the sample and sample holder. It was used in the 1970s for the study of liquid-gas [17] and liquid-liquid critical points [18] and first applied to liquid crystals by us [19] and later also by Anisimov et al. [20]. In the dynamic modes the total heat capacity Cj is now given by ... 

Heat Calvet Calorimetry A Calvet calorimeter is a heat exchanging calorimeter with a cylindrical type detector working in isothermal and scanning modes. 

Dynamic mechanical anlaysis (DMA) measurements were done on a Rheometrics RDS-7700 rheometer in torsional rectangular geometry mode using 60 x 12 x 3 mm samples at 0.05% strain and 1 Hz. Differential scanning calorimetry (DSC), thermomechanical analysis (TMA), and thermogravimetric analysis (TGA) were performed on a Perkin-Elmer 7000 thermal analysis system. 

Differential Scanning Calorimetry (DSC) This is by far the widest utilized technique to obtain the degree and reaction rate of cure as well as the specific heat of thermosetting resins. It is based on the measurement of the differential voltage (converted into heat flow) necessary to obtain the thermal equilibrium between a sample (resin) and an inert reference, both placed into a calorimeter [143,144], As a result, a thermogram, as shown in Figure 2.7, is obtained [145]. In this curve, the area under the whole curve represents the total heat of reaction, AHR, and the shadowed area represents the enthalpy at a specific time. From Equations 2.5 and 2.6, the degree and rate of cure can be calculated. The DSC can operate under isothermal or non-isothermal conditions [146]. In the former mode, two different methods can be used [1] ... 

The complex sorption behavior of the water in amine-epoxy thermosets is discussed and related to depression of the mechanical properties. The hypothesized sorption modes and the corresponding mechanisms of plasticization are discussed on the basis of experimental vapor and liquid sorption tests, differential scanning calorimetry (DSC), thermomechanical analysis (TMA) and dynamic mechanical analysis. In particular, two different types of epoxy materials have been chosen low-performance systems of diglycidyl ether of bisphenol-A (DGEBA) cured with linear amines, and high-performance formulations based on aromatic amine-cured tetraglycidyldiamino diphenylmethane (TGDDM) which are commonly used as matrices for carbon fiber composites. 

Cornwell, P.A., et al. 1996. Modes of action of terpene penetration enhancers in human skin differential scanning calorimetry, small-angle x-ray diffraction and enhancer uptake studies. Int J Pharm 127 9. 

PHOSPHOLIPID SYNTHESIS. Phospholipids were synthesized (H.Schuster, S.S. Hall, and R.Mendelsohn, in preparation) according to the procedures of Tulloch (26), modified with more modern and efficient coupling steps, and scaled up to produce 2-3 grams of specifically deuterated material. Derivatives were fully characterized with NMR, MS, FT-IR, and Differential Scanning Calorimetry (DSC). Purity is estimated from NMR data at > 98X. The extent of deuteration, as estimated from the residual intensity of the CHD rocking modes at... 

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