Calorimetry scanning differential

Calorimetry is the measurement of the heat of a process. The first calorimeter was developed by Lavoisier and Laplace in 1782. 

In DSC, differences in heat flow into a reference and sample are measured versus the temperature of the sample. The difference in heat flow is a difference in energy DSC is a calorimetric technique and results in more accurate measurement of changes in enthalpy and heat capacity than 

The heat flow into or out of the sample, in the absence of any transition, is 

AQ/At is the heat flow AQ/AT is the heat capacity AT/At is the heating rate 

When a transition occurs, either the heat capacity changes or some kinetic event changes the heat flow  

Calorimetry is a thermal characterization technique often used to identify and study phase transitions. The technique is particularly valuable in liquid crystal materials as it assists in the accurate measurement of 

FIGURE 2.28 A high-sensitivity differentiai scanning caiorimeter typicaiiy used for iiquid crystai materiais is shown in (a) and a ciose-up picture of the two furnaces in (b). Picture (c) shows an aluminum sample pan used to encapsulate the sample. These sample pans hold a few milligrams of material. 

Different liquid crystal phase transitions will be more or less difficult to detect using DSC. If the transition is first order, meaning that the order parameter is discontinuous across the phase boundary, a significant latent heat will be measurable, and usually a clear peak can be observed. An example of a first-order phase transition in liquid crystals would be the crystalline-to-smectic or -nematic phase. The nematic-to-isotropic phase is also first order. Some liquid crystal phase transitions are much more 

Differential scanning calorimetry (DSC) is a thermal analysis technique where energy changes in a sample are investigated with temperature, as distinct from mass changes 

The source is the furnace temperature (and environment) controller. The required temperature programs, as with the TGA come from here. 

A sample is placed into a tared TGA sample pan attached to a sensitive microbalance assembly. A reference sample (or nothing) is placed into a tared reference pan, which is also attached to the microbalance assembly. Both pans are located in the high temperature furnace, which is often cylindrical in shape. 

The discriminator is the balance within the furnace. The balance allows the measurement of any temperature changes between the sample and reference. For a DSC experiment, the individual heaters under both pans work to keep the temperatures the same (or the differential temperature equal to zero) and the power drawn to maintain this is measured. For a DTA experiment, the difference in temperature between the sample and the reference is recorded as a function of furnace temperature. The environment in the furnace is controlled. 

The temperatures, temperature differences and/or power are recorded as the heating program proceeds. The balance and furnace data are collected during the experiment and sent to the PC for manipulation. 

Differential scanning calorimetry (DSC) is an experimental technique to measure directly the heat energy uptake that takes place in a sample during controlled increase (or decrease) in temperature. At the simplest 

Q What might be the temperature difference between sample and identical buffer reference solutions for a sample comprising 1 mg cm of a protein of RMM 50,000 undergoing a thermal transition with A f=80 kJ mol  

The specific heat capacity of water (assume identical for buffer and protein solution) = 4.2 J K cm  

Assuming that all this heat energy is absorbed by the I cm sample  

In general, differences in heat energy uptake between the sample and reference cells required to maintain equal temperature correspond to differences in apparent heat capacity, and it is these differences in heat capacity that give direct information about the energetics of thermally induced processes in the sample. 

Differential scanning calorimetry has been widely applied in the investigation of numerous phenomena occurring during the thermal heating of organodays and 

The DSC method is commonly applied to investigate the a-transition in polymers and their composites. The a-transition is related to the Brownian motion of the main chains at the transition from the glassy to the rubbery state and the relaxation of dipoles associated with it. 

In a different work, the data obtained by temperature-modulated differential scanning calorimetry (TMDSC) showed the relationship between the interlayer distance (Ad) and the increase of heat capacity (ACp) for PU-clay intercalated nanocomposites [14]. The ACp values of nanocomposites with interlayer distances smaller than the characteristic length of bulk PU (1.45 nm) were reduced. However, for nanocomposites with interlayer spacing larger than 2 nm, cooperatively rearranging of PU was substantially unmodified by the presence of the nanofiller, and ACp values remained the same as that of bulk PU. 

The absence of any other exothermal or endothermal signal confirmed that the nanocomposite was also amorphous. This is in agreement with the results reported by Rattan et al. [17] that the PETg keeps its amorphous state in most practical experimental conditions. The decrease of Tg can be attributed to the plasticization effect of the organic modifier of the OMMT, characterized by a very low Tg. 

Reference. [18] showed the strong infiuence of preparation route on the thermal properties of polystyrene (PS) nanocomposites. An appreciable reduction in Tg was observed only for composites obtained from solution, whereas the composites obtained by melt intercalation showed Tg values approximately equal to that of neat polymer. Some difficulties in detecting changes in Tg for polymer-clay nanocomposites occurring with the conventional DSC [19] method could be overcome using the TMDSC method. 

Differential scanning calorimetry (DSC) measures heat flow to a polymer. This is important because, by monitoring the heat flow as a function of temperature, phase transitions such as crystalline melt temperatures and glass-transition temperatures can be characterized quite effectively. This, in turn, is quite useful to determine how a pol)oner will behave at operational temperatures. 

The technique can also be used in forensic investigations to determine the maximum temperature that a polymer has been subjected to. This can be very useful in establishing whether an equipment/system/part has been subjected to thermal overloads during service. Finally, this method can also be used to determine the thermal stability of polymers by measuring the oxidation induction time/temperature. 

We use differential scanning calorimetry - - vliich we invariably shorten to DSC - to analyze the thermal properties of polymer samples as a function of temperature. We encapsulate a small sample of polymer, typically weighing a few milligrams, in an aluminum pan that we place on top of a small heater within an insulated cell. We place an empty sample pan atop the heater of an identical reference cell. The temperature of the two cells is ramped at a precise rate and the difference in heat required to maintain the two cells at the same temperature is recorded. A computer provides the results as a thermogram, in which heat flow is plotted as a function of temperature, a schematic example of which is shown in Fig. 7.13. 

Measured heat of fusion Theoretical heat of fusion 

The density of a polymer sample depends upon the relative densities and masses of its components according to Eq. 7,4, 

In the case of a semicrystalline polymer, the two components are the crystalline and amorphous regions. If we know the densities of the crystalline and the amorphous regions, can calculate a sample s degree of crystallinity from Eq. 7.5. 

We can measure a polymer s density by one of two methods density gradient column analysis and densimetry. Each of these methods can measure the density of a sample to a precision of four significant figures. 

FIGURE 7.33 Differential scanning calorimetry curve (a, c) and their derivatives (b, d) for soil samples of (a, b) AC horizon of Houston city and (c, d) Houston black clay the reference was an empty pan, the heating rate was 2.0°C/min, and the atmosphere was pure N2. (Reprinted from Tan et al., Methods of Soil Analysis. Part 1. Physical and Mineralogical Methods, American Society of Agronomy-Soil Science Society of America, Madison, Wisconsin, 2010. With permission from the Soil Science Society of America.) 

Prasad and Shanker [95] used a differential scanning calorimeter (DSC) for the quantitative analysis of chemical blowing agents such as azodicarbonamide (azo) in commercial formulations. The DSC results were comparable to those obtained by the commonly used evolved gas analysis (EGA) technique. Advantages of DSC are ease of operation. 

DSC measures the temperature and heat flow associated with the transitions in materials as a function of time and temperature. Such measurements provide quantitative and qualitative information about the physical and chemical changes that involve exothermic and endothermic processes. 

The breadth of the exothermic curve (195 °C to 225 °C) indicates the temperature range over which the decomposition of azo occurs. The shape of the peak indicates the uniformity of the decomposition. In addition, the size of the peak, i.e., the area under the exothermic curve, is a quantitative measure of the amount of blowing agent that has decomposed in the sample. This integrated area under the exothermic peak is referred to as heat of decomposition, AH.  

An exothermic peak at 230 °C followed by an endothermic peak at 250 °C was observed in the DSC heating scan of pure azo (scans are not shown here). The reason for the endothermic peak in pure azo is not known. This endothermic peak at 250 C was not observed in any of the foam concentrates. Because of the overlap of the exothermic peak with the endothermic peak, it is difficult to obtain the heat of decomposition value of the pure azo compound. However, based on the measured heat of decomposition value of samples A-F, the heat of decomposition value of pure azo was estimated to be about 1200 J/g (see Table 1.7). 

Control samples (containing between 10% and 36% of blowing agent and between 90% and 64% of LDPE) were used to construct a calibration plot. These samples are free of any additives that would normally be present in the commercial samples. Some of the normalised DSC curves (total mass of 2.0 mg) as a function of % azo are shown in 

The principles and theory of differential scanning calorimetry (DSC) have been described by various workers [1-4]. 

DSC measures the temperature and the heat flow associated with transitions in materials as a function of the time and temperature (i.e., heat flow-sample temperature plots). Such measurements provide quantitative and qualitative information about physical or chemical changes that involve exothermic or endothermic processes or changes in heat capacity. The technique measures the amount of energy absorbed or released by the sample as it is heated, cooled or held at a constant temperature [5]. 

DSC instruments can be used in the DSC mode, i.e., heat flow-temperature of sample, or the differential thermal analysis (DTA) mode, i.e., sample temperature-temperature of sample. Applications of the technique have been reviewed. 

The somewhat indiscriminate use of the terms DSC and DTA has made it necessary for the lUPAC to offer definitions of these processes in a communication of nomenclature [6, 7]. 

The purpose of differential thermal systems is to record the difference between the enthalpy change that occurs in a sample and that in some inert reference material, when they are both heated. These systems may be classified into three types as follows  

Microcalorimetric studies of nanooxides, carbons, composites, etc. were carried out by means of a DAC 1.1 A (EPSE, Chemogolovka, Russia) differential automatic calorimeter. Before the measurements of the heat of immersion in water (QJ or decane ( 2d). solid samples (50mg) were degassed at 473 K and 0.01 Pa for 2h and then used without contact with air. The amount of a sample used was 50 mg per 3mL of distilled water or decane. The Q values were measured during exposure of the mixture for several hours. The average errors of the Q measurements repeated several times were 5%. The Q values were calculated per surface area unit (i.e., Q measured in J/g was divided by BEm) of samples because the studied oxides differ strongly in the Sbet,n2 values. To estimate the hydrophilicity of nanooxides, the hydrophilicity coefficient K=QJQ was calculated. 

A Perkin-Elmer DSC-2 apparatus was used to determine the polymer glass transition temperatures, Tg at the half-height of a heat capacity step ACp, and the transition breadth AT =T - where 

Tg and T are the temperatures of the transition onset and completion, respectively. The second scans were taken for all compositions to exclude the side endothermic effect of water desorption. The measurements were performed under nitrogen atmosphere at a heating rate of 20°C/min, over the temperature range from -20°C to 197°C, after cooling from 197°C to -20°C with the rate of 320°C/min. Amorphous quartz was used as the reference sample. 

The regeneration can be evaluated by differential scanning calorimetry (DSC), temperature programmed oxidation (TPO), and catalytic tests. 

A first evaluation of the catalytic performance is usually carried out by using DSC. Samples are heated at a rate of lOK/min under synthetic air flow (50mL/min). Enthalpy of reaction (AH) is calculated using the following correlation  

A = quantity of heat (meal) corresponding to the area under DSC curve ((mcal/s) s). By the Kissinger method (Boudart), one can determine the activation energy (E) via DSC curves obtained under three different heating rates (P) at least. Once the rates (P) are known, as well as temperatures corresponding to the maximum on each peak (Tc), it is possible to establish the following linear relationship  

The temperature corresponding to the maximum in the DSC peak is a parameter widely used in the literature for the evaluation of the catalytic performance. This parameter is often known as combustion temperature and represented by Tc. 

Results and Discussion Cooperativity Studies 4.1 Differential Scanning Calorimetry 

This basic instrumentation can be complemented in various ways. For instance, sudden pressure changes may be applied to the system, thus obtaining additional thermodynamic information from the so-called pressure perturbation calorimetry . In this method the heat consumed or released after a pressure jump is measured, and from this volume changes associated with phase transitions may be derived. Another interesting modification is 

The standard DSC experiment with lipid systems requires degassing the samples and instauring an extra pressure of 1-2 atm N2. The cells and the surrounding adiabatic thermal shield are then equilibrated at least 5 °C below the desired start temperature of the experiment. Heating starts at a pre-established rate (e.g. 1 °C/min) in a region where no transition is expected, so that a baseline is obtained. At a temperature above the phase transition the whole system is cooled down, reequilibrated and re-scanned. Three heating scans are routinely recorded sometimes the first scan differs from the other two, owing to insufficient equilibration of the sample, in which case the first scan is discarded. 

From a technological point of view, the dynamic crystallization of composites is of a great interest, because most of processing routes take place under these conditions. Generally, the crystallization and melting behaviour of polymer/CNT nanocomposites is analyzed by differential scanning calorimetry (DSC) analysis the transition temperatures are taken as the peak maximum or minimum in the 

The displayed temperatures are T. initial degradation temperature obtained at 2% weight loss T10 temperature for 10% weight loss Tmr temperature(s) of maximum rate of weight loss, determined from the peaks of the first derivative of TGA curve. 

The displayed data are T crystallization temperature AH apparent crystallization enthalpy Tm melting temperature AHm apparent melting enthalpy X. degree of crystallinity, obtained by DSC (a) and WAXS experiments. D ]0 cystallite size perpendicular to the diffraction plane (110). 

Rate of cure - heat of cure (temperature-heat-flow rate). 

HER Materials HQEE HER-HP TG210 TG225 TG250 TG275 HER-LIQ 

Camacho and Karlsson [8] have examined the thermal stability of recycled HDPE, PP and their blends in their discussion of environmental concerns and producers liability concerning the dispersal, collection and recycling of these polymers. 

All these techniques demonstrate that the blend and its components alone undergo substantial degradation after the first or second extrusion. Accordingly, upgrade of the resin through the addition of a re-stabilising system becomes necessary to avoid their premature failure. 

The thermogravimetric (TG) measurements on the reprocessed blend were shifted towards higher temperatures than the simulated curve indicating that the blends. 

DSC and TG can be used to determine the thermal/oxidative stability of PP, PE and their blends. The oxidation induction time (OIT) and the oxidation temperature (T j ) provide relatively, rapid information about the total amount of effective antioxidants in the reprocessed resin, which is important to establish the need for re-stabilisation or upgrade of the resins. 

Reported T values of polymers cover a wide range, for example, -8°C to -lOO C for polybutadienes and up to lOO C for polystyrene and polymethyl methacrylate. 

Differential scanning calorimetry is probably the most frequently used method for determining 7. In this method, a change in the expansion coefficient and the heat capacity occurs as a sample material is heated or cooled through this transition region. 

Differential scanning calorimetry measures heat capacity directly, rapidly, and accurately, so it is an ideal technique for the determination of the glass transition temperature, 7.  

Determination of the 7 using the idealized output of differential scanning 

Chapter 4 of this book, on single-site catalysts, discusses a wide variety of single-site catalysts that were discovered since about 1980, many 

The thermal results of the synthetic binders show a displacement of the Tg towards higher temperatures, as the resin concentration increases [22]. In contrast, the melting signal, which corresponds to the melting temperature (Tm) of the polymer (60-110 °C), grows as the resin concentration decreases. This change is probably due to the distribution of the polymeric chains in the amorphous oil-resin matrix, which 

Synthetic binders present a unique Tg, which is directly related to the Tg of the oil-resin phase. This, as can be deduced, is evidence that synthetic binders obey the same fitting equation as the oil-resin blends [22], it can therefore be concluded that the displacement of the Tg of the synthetic binders is due to the proportion of the oil-resin phase and not to the polymer concentration. 

DSC measures the amount of energy adsorbed or released by a sample as it is heated, cooled, or held at a constant temperature. DSC is therefore useful in the studying energy 

An alternative technique is pressure differential scarming calorimetry (PDSC). This technique measures heat flow and temperatures of transitions as a function of temperature, time, and pressure (elevated pressure or vacuum). The ability to vary pressure from 1.3 Pa to 6.8 MPa makes PDSC ideal for the determination of the stability of oxidative polymers and for other pressure-sensitive reactions. 

High pressures of oxygen cause polymers to oxidise much faster than they would at atmospheric pressure. The oxidation process is observed as an exothermic peak. Thus, the oxidative stability of a polymer can be measured as the time to the onset of oxidation at a predetermined temperature and pressure. 

DuPont supply a dual sample pressure differential calorimetry cell. 

The advantages of PDSC over DSC and oven ageing for determination of oxidative stability have been identified, as listed next  

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The crystal stmcture of glycerides may be unambiguously determined by x-ray diffraction of powdered samples. However, the dynamic crystallization may also be readily studied by differential scanning calorimetry (dsc). Crystallization, remelting, and recrystallization to a more stable form may be observed when Hquid fat is solidified at a carefully controlled rate ia the iastmment. Enthalpy values and melting poiats for the various crystal forms are shown ia Table 3 (52). 

The product must be formulated and frozen in a manner which ensures that there is no fluid phase remaining. To achieve this, it is necessary to cool the product to a temperature below which no significant Hquid—soHd phase transitions exist. This temperature can be deterrnined by differential scanning calorimetry or by measuring changes in resistivity (94,95). 

Other PDMS—sihca-based hybrids have been reported (16,17) and related to the ceramer hybrids (10—12,17). Using differential scanning calorimetry, dynamic mechanical analysis, and saxs, the microstmcture of these PDMS hybrids was determined to be microphase-separated, in that the polysiUcate domains (of ca 3 nm in diameter) behave as network cross-link junctions dispersed within the PDMS oligomer-rich phase. The distance between these... 

The process known as transimidization has been employed to functionalize polyimide oligomers, which were subsequentiy used to produce polyimide—titania hybrids (59). This technique resulted in the successhil synthesis of transparent hybrids composed of 18, 37, and 54% titania. The effect of metal alkoxide quantity, as well as the oligomer molecular weight and cure temperature, were evaluated using differential scanning calorimetry (dsc), thermogravimetric analysis (tga) and saxs. 

Most hydrocarbon resins are composed of a mixture of monomers and are rather difficult to hiUy characterize on a molecular level. The characteristics of resins are typically defined by physical properties such as softening point, color, molecular weight, melt viscosity, and solubiHty parameter. These properties predict performance characteristics and are essential in designing resins for specific appHcations. Actual characterization techniques used to define the broad molecular properties of hydrocarbon resins are Fourier transform infrared spectroscopy (ftir), nuclear magnetic resonance spectroscopy (nmr), and differential scanning calorimetry (dsc). 

Glass-transition temperatures are commonly determined by differential scanning calorimetry or dynamic mechanical analysis. Many reported values have been measured by dilatometric methods however, methods based on the torsional pendulum, strain gauge, and refractivity also give results which are ia good agreement. Vicat temperature and britde poiat yield only approximate transition temperature values but are useful because of the simplicity of measurement. The reported T values for a large number of polymers may be found ia References 5, 6, 12, and 13. 

The compositional distribution of ethylene copolymers represents relative contributions of macromolecules with different comonomer contents to a given resin. Compositional distributions of PE resins, however, are measured either by temperature-rising elution fractionation (tref) or, semiquantitatively, by differential scanning calorimetry (dsc). Table 2 shows some correlations between the commercially used PE characterization parameters and the stmctural properties of ethylene polymers used in polymer chemistry. 

The cure of novolaks with hexa has been studied with differential scanning calorimetry (dsc) and torsional braid analysis (tba) (46) both a high ortho novolak and a conventional acid-cataly2ed system were included. The dsc showed an exothermic peak indicating a novolak—hexa reaction ca 20°C higher than the gelation peak observed in tba. Activation energies were also calculated. 

Cure kinetics of thermosets are usually deterrnined by dsc (63,64). However, for phenohc resins, the information is limited to the early stages of the cure because of the volatiles associated with the process. For pressurized dsc ceUs, the upper limit on temperature is ca 170°C. Differential scanning calorimetry is also used to measure the kinetics and reaction enthalpies of hquid resins in coatings, adhesives, laminations, and foam. Software packages that interpret dsc scans in terms of the cure kinetics are supphed by instmment manufacturers. 

Thermal analysis iavolves techniques ia which a physical property of a material is measured agaiast temperature at the same time the material is exposed to a coatroUed temperature program. A wide range of thermal analysis techniques have been developed siace the commercial development of automated thermal equipment as Hsted ia Table 1. Of these the best known and most often used for polymers are thermogravimetry (tg), differential thermal analysis (dta), differential scanning calorimetry (dsc), and dynamic mechanical analysis (dma). 

Transitions such as T and are rapidly and conveniently studied using differential scanning calorimetry (dsc). This technique monitors changes in... 

Fig. 5. Differential scanning calorimetry thermogram. Amorphous PPS is heated from room temperature to 325°C at 20°C/min.

Onset value as measured by differential scanning calorimetry. 

The glass-tiansition tempeiatuiesfoi solution-polymeiized SBR as well as ESBR aie loutinely determined by nuclear magnetic resonance (nmr), differential thermal analysis (dta), or differential scanning calorimetry (dsc). 

The thermal glass-transition temperatures of poly(vinyl acetal)s can be determined by dynamic mechanical analysis, differential scanning calorimetry, and nmr techniques (31). The thermal glass-transition temperature of poly(vinyl acetal) resins prepared from aliphatic aldehydes can be estimated from empirical relationships such as equation 1 where OH and OAc are the weight percent of vinyl alcohol and vinyl acetate units and C is the number of carbons in the chain derived from the aldehyde. The symbols with subscripts are the corresponding values for a standard (s) resin with known parameters (32). The formula accurately predicts that resin T increases as vinyl alcohol content increases, and decreases as vinyl acetate content and aldehyde carbon chain length increases. 

By differential scanning calorimetry from 30 to 100°C on dried resia. 

Fig. 10. Differential scanning calorimetry of cellulose triacetate. Second heating at 20°C/min. glass-transition (T temperature = 177 " C crystallization on heating (T)/j) = 217 C melting temperature (Ta) = 289 C. To convert to cal, divide by 4.184.

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