Melting standards

These adhesives differ from normal hot-melt adhesives, such as the standard ethylene vinyl acetate hot melts. Standard hot-melt adhesives like EVA have no curing mechanism. They are heated above the crystalline melting point and applied as a low-viscosity liquid in the same manner as is the curing hot melt. The bond is closed in the same manner and strength is developed upon crystallization. 

The incident began during a normal mn when the operator noted an electrical short not long after the start of the melt. Standard shutdown procedures were initiated, and the titanium electrode was retracted at a rate of about 30 cm/min using a chain hoist. During shutdown, what proved later to be a water leak into the cmcible occurred with a concomitant pressure rise. Three mpture discs failed at about 4 bar. Some 2 min... 

Determination of Hot Melt — Visually. Weigh accurately a 1 g sample of HBX into a tared sintered glass filtering crucible, medium porosity, 30-ml capacity. Using approx 5ml of ethylene chloride, divided into 5 equal portions, 1 min contact time each, extract sample on a Fisher filtrator with water vacuum. Collect filtrate in a 50-ml volumetric flask and dilute to the mark with ethylene chloride. Compare the color of the filtrate visually with previously prepd standards to det the weight of hot melt present. The prepn of the hot melt standard solns are described in 4.4.3.5.14... 

Determine the spectral absorbance of the hot melt standard solns at 430mu as described in 4.4.3.4.14... 

After a series of melting standards (see Table 3.1) have established a correlation between indicated temperature and correct temperature, this table may be entered into the program. The routine determines between which two calibration points a particular temperature in the experimental data set fall, and then it shifts the temperature to a corrected temperature in accordance with a calibration line between the points. For experimental data whose temperature values fall before the lowest calibration temperature or above the highest calibration temperature, extrapolation of the line defined by the two nearest calibration points is used. 

Table 1 Example of calibration of Perkin-Elmer DSC-7 instruments with melting standards at lOKmin under nitrogen...

Table 4 Example of calibration of the temperature of TGA 850 with melting standards...

Calibration and Standards. Thermal analysis methods are not absolute and calibration is needed to record the correct abscissa value of temperature T (in Kelvin) and time t (in seconds or minutes). On the ordinate, calibration is necessary for the amplitude of deflection, AT, expressed as the difference in temperature (in Kelvin) for DTA or as heat flux, dQldT (in joules per second or watts) for DSC. Each instrument manufacturer provides methods and standard materials for these calibrations. In addition, ICTAC, in collaboration with the National Institute of Standards and Technology (NIST), has developed a series of materials as calibration standards for DSC/DTA. These reference materials can be used to calibrate both the temperature scale (K, abscissa) and heat flow (J/g, ordinate) on the basis of the integrated area under the curve. Figure 4 shows the heat flow-temperature relationship for various solid-solid and solid-liquid melting standards. Table 3 lists the solidi-to-solid2 transitions, melting points, and Curie temperatures of various pure metals, and also their transition enthalpies (J/g) (11). 

Fig. 4. Typical enthalpy calibration curve for DSC. Salt (Solidi-solid2 standard) Metal (melting standard) (14).

Fig. 3. Differential thermal analysis of linear low density polyethylene on cooling (continuous lines), followed by heating (broken lines), showing a high content of reversing crystallization and melting. Standard DSC thin lines TMDSC thick lines. The overall supercooling contrasts the partially reversible crystallization and melting after an overall metastable, semicrystalline structure has been set up on the initial cooling. The modulation amplitude on TMDSC is given by the letter A, and the modulation period by p.

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