Differential scanning calorimetry sample

Differential Scanning Calorimetry Sample and inert reference materials are heated in such a way that the temperatures are always equal. Onset-of-reaction temperatures reported by the DSC are higher than the true onset temperatures, so the test is mainly a screening test. 

A DuPont Model 990 thermal analyzer equipped with a Model 910 DSC cell base was used for differential scanning calorimetry. Samples were analyzed as 15 (w/w) solutions of freeze-dried RDP which had been dialyzed to remove excess buffer salts. A heating rate of 5°C/min was used runs were performed in a nitrogen atmosphere (5 psi). A known weight of water was used in the reference pan to balance the heat capacity of the sample pan. 

Differential scanning calorimetry Samples of gels (8 to 11 mg) were placed in hermetically sealed stainless steal pans and analyzed with a DSC QlOO (TA Instruments, New Castle, DE, USA). An empty pan was used as reference. Samples were heated at 10°C/min from -40 to 120°C. At least triplicate samples were analyzed for each gel. The endothermic melting peak around 0°C was taken as an evidence of ice melting. Endothermic peaks in the 50 to 70°C range were taken as evidence of starch retrogradation (stored samples). 

We can investigate a polymer s molecular and supermolecular organization in various ways, which provide information on either a direct or indirect basis. For instance, microscopy of various types provides us with images of small regions of polymers, allowing us to directly visualize certain types of structure. Other methods, such as X-ray diffraction and differential scanning calorimetry, sample larger volumes of material and provide information representative of the material as a whole. 

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 procedures of measuring changes in some physical or mechanical property as a sample is heated, or alternatively as it is held at constant temperature, constitute the family of thermoanalytical methods of characterisation. A partial list of these procedures is differential thermal analysis, differential scanning calorimetry, dilatometry, thermogravimetry. A detailed overview of these and several related techniques is by Gallagher (1992). 

Differential scanning calorimetry (DSC) is fast, sensitive, simple, and only needs a small amount of a sample, therefore it is widely used to analyze the system. For example, a polyester-based TPU, 892024TPU, made in our lab, was blended with a commercial PVC resin in different ratios. The glass transition temperature (Tg) values of these systems were determined by DSC and the results are shown in Table 1. 

The SCB distribution (SCBD) has been extensively studied by fractionation based on compositional difference as well as molecular size. The analysis by cross fractionation, which involves stepwise separation of the molecules on the basis of composition and molecular size, has provided information of inter- and intramolecular SCBD in much detail. The temperature-rising elution fractionation (TREE) method, which separates polymer molecules according to their composition, has been used for HP LDPE it has been found that SCB composition is more or less uniform [24,25]. It can be observed from the appearance of only one melt endotherm peak in the analysis by differential scanning calorimetry (DSC) (Fig. 1) [26]. Wild et al. [27] reported that HP LDPE prepared by tubular reactor exhibits broader SCBD than that prepared by an autoclave reactor. The SCBD can also be varied by changing the polymerization conditions. From the cross fractionation of commercial HP LDPE samples, it has been found that low-MW species generally have more SCBs [13,24]. 

The modified NBR samples were characterized by differential scanning calorimetry [11,78-80,98]. The glass-transition temperature (T ) decreased with the level of hydrogenation. In the case of HFNBR, Tg increased with an increase in the addition of aldehyde groups to the polymer chain. Thermogravimetric analysis of the modified polymers have also been carried out [15]. 

The techniques referred to above (Sects. 1—3) may be operated for a sample heated in a constant temperature environment or under conditions of programmed temperature change. Very similar equipment can often be used differences normally reside in the temperature control of the reactant cell. Non-isothermal measurements of mass loss are termed thermogravimetry (TG), absorption or evolution of heat is differential scanning calorimetry (DSC), and measurement of the temperature difference between the sample and an inert reference substance is termed differential thermal analysis (DTA). These techniques can be used singly [33,76,174] or in combination and may include provision for EGA. Applications of non-isothermal measurements have ranged from the rapid qualitative estimation of reaction temperature to the quantitative determination of kinetic parameters [175—177]. The evaluation of kinetic parameters from non-isothermal data is dealt with in detail in Chap. 3.6. 

In differential scanning calorimetry (DSC), higher precision can be obtained and heat capacities can be measured. The apparatus is similar to that for a DTA analysis, with the primary difference being that the sample and reference are in separate heat sinks that are heated by individual heaters (see the following illustration). The temperatures of the two samples are kept the same by differential heating. Even slight... 

Differential Scanning Calorimetry (Fig. 9) can be used to evaluate the purity of tetrabromodipentaerythritol, a tetrabrominated derivative of dipentaerythritol. Even so, the validity of the results depends on the purity of the sample. The results shown here should be considered extremely borderline. The brorainated derivatives of the pentaerythritols cannot be analyzed with this technique because of the inherent limitations of DSC. 

FIGURE 31.2 Plots of crystalline melting point, heat of fusion and percent crystallinity of ethylene-vinyl acetate (EVA) samples versus (a) radiation dose (b) trimethylolpropane trimethacrylate (TMPTMA) level from differential scanning calorimetry (DSC) studies. (From Datta, S.K., Bhowmick, A.K., Chaki, T.K., Majali, A.B., and Deshpande, R.S., Polymer, 37, 45, 1996. With permission.)... 

DSC (differential scanning calorimetry) was performed using a Netzsch Phoenix El apparatus. Typically, samples of about 20 mg were applied in aluminium cold-sealed crucibles with heating/cooling rates of 5 °C/min. 

Differential Scanning Calorimetry. A sample and an inert reference sample are heated separately so that they are thermally balanced, and the difference in energy input to the samples to keep them at the same temperature is recorded. Similarly to DTA analysis, DSC experiments can also be carried out isothermally. Data on heat generation rates within a short period of time are obtained. Experimental curves from DSC runs are similar in shape to DTA curves. The results are more accurate than those from DTA as far as the TMRbaiherm is concerned. 

We use differential scanning calorimetry - which 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. 

Another important technique is the thermal analysis technique of differential scanning calorimetry (DSC). Current high-speed DSC equipment (sometimes also referred to as hyper-DSC) allows for rapid heating (up to 500°C/min) and cooling of (small) samples and therefore an increased rate of analysis per sample... 

Figure 2. Comparison of the Differential Scanning Calorimetry (DSC) thermograms of the homopolymer HB and various block copolymers to that of the LDPE. Weight of each polymer sample is indicated in the parentheses. The instrument range is 2 mcal/s for all the runs.

Measurements of differential scanning calorimetry (DSC) were obtained on a TA Instruments 2910 thermal analysis system (Fig. 2). Samples of approximately 1-2 mg were accurately weighed into an aluminum DSC pan, and covered with an aluminum lid that was crimped in place. The samples were then heated over the range of 20-140 °C, at a heating rate of 10 °C/min. Valproic acid was found to boil at 227 °C. 

Cross-linking constrains the conformational flexibility of biopolymers and, as a rule, stabilizes their secondary, tertiary, and quaternary structures against the denaturing effects of high temperatures.29 We used differential scanning calorimetry (DSC) to compare the heat-induced conformational transitions of selected RNase A samples that were characterized in Figure 15.2. A brief introduction to DSC is provided in Section 15.15.1 for those readers unfamiliar with this biophysical method. Trace 1 in Figure 15.3a is the heat absorption... 

From the discussion presented of reactions in solids, it should be apparent that it is not practical in most cases to determine the concentration of some species during a kinetic study. In fact, it may be necessary to perform the analysis in a continuous way as the sample reacts with no separation necessary or even possible. Experimental methods that allow measurement of the progress of the reaction, especially as the temperature is increased, are particularly valuable. Two such techniques are thermo-gravimetric analysis (TGA) and differential scanning calorimetry (DSC). These techniques have become widely used to characterize solids, determine thermal stability, study phase changes, and so forth. Because they are so versatile in studies on solids, these techniques will be described briefly. 

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