DSC pans

The heat flow into (endothermic) or out (exothermic) of a sample as a function of temperature and time is measured using the technique of DSC. In particular, it is used to study and determine the temperature of thermal transitions. For polymers, these include Tg, the glass transition temperature, Tc, the (exothermic) temperature of crystallisation for polymers that can crystallise, and Tm, the (endothermic) melting temperature. A DSC measurement requires only a small amount of sample 2-20 mg of a film, powder, fibre or liquid samples can be analysed in a DSC pan. 

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. 

Glass transition temperatures (Tg s) were detemined using a Dupont DSC 910 attached to a 9900 data analysis system. For off-stoichiometric studies, epoxy resin and diamine were cured in situ within a hermetically sealed DSC pan (sample tak from 25 C - 300 C at lO C/min), then cooled rapidly back to 25 C, and finally scanned from 40 C - 220 c to record the Tg. All samples were scanned under nitrogen atmosphere at a rate of 10 C/min. 

A test sample of a resin containing a selected experimental agent was weighed in a DSC pan to 0.0.00001 g. The uncured sample was placed on a sample cell and a precured sample of the same weight was placed in the same type of DSC pan on the reference cell set and maintained at 37°C while being irradiated for 1 hour. From the resulting heat flow (watts/g vs. time curve), the time of maximum reaction rate (peak maximum time), onset of reaction (induction time), and enthalpy of reaction were recorded. These testing results are provided in Table 1. 

A popular reaction model assumes that the reaction may take place by two different mechanisms (a) noncatalytic (b) catalyzed by OH groups (Smith, 1961 Horie et al., 1970). For a batch reactor e.g., a DSC pan, the following mass balances may be stated ... 

To obtain the evolution of the concentration of functional groups and temperature, the constitutive equations for the reaction rates must be introduced into mass balances (in fact, balances of functional groups) and in a thermal energy balance. The form of these balances depends on the characteristics of the reactor in which the thermosetting polymerization is taking place (the reactor may be a DSC pan, a heated mold, a flow reactor, etc.). 

Let us assume a polymerization that may be described by the evolution of the concentration of three functional groups or active species y (i = 1—3). If the reaction takes place in an isothermal DSC pan (a batch reactor with uniform values of composition and temperature), the following mass balances may be stated ... 

Figure 10.5 Principle of photoDSC. (a) The sample (solid or liquid film) is placed in the DSC pan. Light is introduced by two optical fibers. Two sapphire disks filter the wavelength and complete the thermal insulation of the DSC furnace.

Fig. 8. Comparison between experimental and simulated evolutions of the latent heat of a cocoa butter sample in a DSC pan cooled at various cooling rates starting from a completely liquid state at 37°C. See Figure 4 for abbreviation.

Melting of AlMq3 could be observed with DSC, followed immediately by evaporation or decomposition. Figure 3.17 shows DSC traces of sublimed-scraped samples as well as films deposited directly onto the DSC pans. Tm was reproducible in the... 

The Tg of each sample was examined by DSC (Shimadzu DSC-50, Japan). Indium (Wako) and distilled water were used to calibrate the temperature and heat capacity for the DSC measurements. a-Alumina powder (Shimadzu) was used as a reference material. Approximately 10 mg sample was weighed and sealed into an aluminum DSC pan. Each sample was scanned from 0 to 140°C at a heating rate 5°C/min. 

In parallel, a small quantity of lyophilized samples placed into DSC pans was also equilibrated in each chamber at controlled RH to be submitted to DSC analysis. At equilibrium, the pans were sealed and analyzed. Glass-transition temperature was analyzed in a DSC 5200 (Seiko Instruments Inc., Chiba, Japan). Heating rate was 5°C/min and temperature range varied between — 20 and 80°C. The midpoint of the glass transition was considered as the characteristic temperature of the transition. Determinations were carried out in triplicate. 

Low-viscosity liquids can be transferred to the hermetic DSC pan using a Pasteur-pipette or similar apparatus. Dipping one end of an opened paper clip into viscous liquids and then placing it onto the base of the sample pan may transfer higher viscosity samples. Care should be taken not to contaminate the lip of the pan with any liquid as this will result in a poor seal. 

Most general and hermetic DSC pans are punched out of thin aluminum sheet that is contaminated with small amounts of machine oil. If these pans are used... 

FIGURE 2.6 Summary of typical DSC pan configurations used in pharmaceutical DSC... 

Quench-cooling DSC studies can also be conducted to generate physical property information. In this method, the material is heated to a desired temperature, removed from the DSC cell and quench-cooled by placing the DSC pans onto the laboratory bench or a chilled surface, possibly forcing the material to convert to a nonstandard state. Upon cooling, the samples would be reanalyzed to determine if any nonstandard states were generated. 

Polymerization Reaction. The differential scanning calorimetry (DSC) pan, containing 10-15 mg of sample, was sealed under air. It was then... 

Samples should be small, thin and completely encapsulated in the DSC pan. This minimizes temperature gradients and maximizes conductivity during the heating and cooling cycles. Good thermal contact must also be ensured between the pans and the DSC head. 

The depressed glass transition temperatures of the resin at various concentrations of sorbed water were determined using scanning calorimetry. Samples of the resin were first conditioned with an excess of water in large volume stainless steel DSC pans at predetermined temperatures then scanned at 20 deg/min. Heat capacity measurements were also made with a Perkin-Elmer OSC-2 scanning calorimeter. 

Reaction of hydrogen, under pressure in a DSC ceil, was used as a method for the determination of platinum or palladium in various catalysts (85). About 5 mg of catalyst are introduced into a DSC pan and the cell is pressurized to 150 psig with helium. The temperature is then increased to 75°C and the helium gas replaced with hydrogen at 200 psig. From the area of the DTA curve peak (versus time), the amount of platinum or palladium can be calculated. 

Both liquefaction residues were studied by DSC in both inert (dynamic N2) and oxidizing (dynamic air) atmospheres. A computerized DSC system (Perkin-Elmer DSC-2C/TADS) was used in these studies, A flow-thru cover was used with the DSC sample holder asjsembly in all of these studies. Standard gold sample pans were employed for the oxidative profiles obtained in dynamic air atmosphere. For the lower temperature studies conducted in dynamic N2 atmosphere, experiments showed that the results obtained were the same regardless of whether standard aluminum or standard gold DSC pans were employed. All figures given here are hard copy printouts from the Perkin-Elmer Thermal Analysis Data Station. 

---