Melting temperature measurement

Investigating coextrusion of com meal and WPI, Onwulata et al. (2003b) found that the melt temperature of the extmdate was more of an indicator of physical properties than specific mechanical energy. Quality attributes such as breaking strength, color, and expansion index were related to melt temperature measured at the die. 

Melt temperature measurements indicated that the thermodynamic stability of the probe molecules can be adjusted using the oligomer matrix to achieve lower Tm values by as much as 5 °C, with retention of selectivity for discrimination of single base pair mismatches [14]. The enhanced temperature sensitivity may ultimately provide for the development of analytical devices of extremely high selectivity. Devices containing immobilized... 

The melt temperatures measured at the output decreases with increasing throughput rate, while the screw speed remains constant, which reflects the lower average shear stress on the melt. The melt temperature will also be lowered by approx. 5°C by the addition of a... 

On the other hand, the temperature of melting and crystallinity measurement can describe only those stereosequences that crystallize. In propylene oxide polymers which we have studied, for example, isotactic sequences are the only ones that crystallize. Therefore, in these polymers we can determine only the stereosequence length of isotactic units and the average length of the uncrystallizable units. The syndiotactic and atactic sequences in the uncrystallizable blocks are not distinguishable from the crystallinity and melting temperature measurements. 

Amorphous materials usually exhibit an apparent second-order thermal transition, the glass transition, at about two-thirds of the crystalline melting temperature (measured in Kelvin)... 

EXAMPLE 11.5 Assume that you estimate the total systematic error in the melting temperature measurement of Example 11.3 as 0.20 °C at the 95% confidence level. Find the total expected error. 

Methods for determining the presence, kind, and amount of configurational base units can be classified as relative or absolute. Absolute methods do not require calibration with polymers of known tacticity. Relative methods, on the other hand, require comparison with standard substances. X-ray crystallography, nuclear magnetic resonance, infrared spectroscopy, and optical activity measurements are all absolute methods. Relative methods include crystallinity, solubility, glass transition temperature, and melting temperature measurements as well as chemical reactions (Table 3-2). 

TPP triphenyl phosphite, T melting temperature measured on die reheating scan (10 °C/min), Hf heat of fusion, TS tensile strength, and EB elongation at break. 

Numerous detailed studies have been devoted to the measurement of temperature profiles in polymer melts flowing through channels. One of the most comprehensive studies on the theoretical and experimental aspects of temperature measurement of polymer melts was carried out by van Leeuwen [15-18]. Other studies on melt temperature measurement are listed in the following references [19-23]. When a polymer melt flows through a channel, a certain temperature profile will establish itself in the polymer melt. The temperature profile in a steady-state process after some time will become constant with respect to time this is the so-called fully developed temperature profile. 

The UTT measurement can be used in total extrusion line control. The use of UTT measurement reportedly has resulted in considerable technical improvements in product performance in several extrusion operations [68]. It should be noted, however, that the pressure compensation is rather involved and that the accuracy of the resulting temperature is only as good as the pressure measurement. In this respect, the melt temperature measurement by IR radiation is less complicated (see Section 4.3.1). 

The elements of an infrared melt temperature sensor are a sapphire window, an optical fiber, and a radiation sensor with associated signal-conditioning electronics as shown in Fig. 4.17. IR melt temperature probes are commercially available [85, 86] and fit in standard pressure transducer mounting holes. Because the sapphire window is flush with the barrel or die, the sensor does not protrude into the polymer melt. As a result, the sensor is less susceptible to damage, there is no chance of dead spots behind the sensor, and the melt velocities are not altered around the sensor. When melt velocities are changed, the melt temperatures will change as well. Therefore, the melt temperatures measured with an IR sensor are less affected by the actual measurement than with an immersion sensor. 

Ultrasonic measurements have also proven useful in the characterization of polymer melts (see Section 4.3.3.1). The ultrasonic transit time ( Laufzeit ) is dependent on the elastic properties of the material, pressure, temperature, chemical composition, and structure. It has been found [37] that the ultrasonic transit time is a sensitive measure of the condition of the polymer melt, in particular melt homogeneity. In a process control system, the ultrasonic transit time can provide a more useful feedback control signal than a single melt temperature measurement. 

In reality, the temperature distribution is dynamic in other words, melt temperature changes with time. These changes can be significant, but short-term (0-10 seconds) temperature changes cannot be measured with a conventional melt temperature sensor because the thermal mass of the probe is too large. Infrared melt temperature measurement allows detection of rapid (millisecond range) melt temperature fluctuation [114-118]. 

E.C. Brown, P. Olley, and P.D. Coates, In-line Melt Temperature Measurement during Real Time Ultrasound Monitoring of Single Screw Extrusion, Piast. Rubber Comp., 29, 3-13 (2000)... 

Extrusion grade SVA is Suprel 9806. It should be extruded at 180-185°C melt temperature, measured with a hand-held p5rrometer. Screws should be 1.5-2.0 compression ratio with no mixing section. Tooling should be stainless steel or plated with chrome or nickel. Resin drying is not required. Overheating the melt will cause thermal degradation. 

Thermal Expansion of Polymeric Materials In addition to the glass transition and melting temperature measurements, the other major application of TMA is determination of the thermal expansion of polymeric materials. The coefficient of linear thermal expansion (CLTE or a) is the slope of the relative change in the length (AL/Lo) with respect to the temperature range of interest, as defined by Eq. (4.2) (see Fig. 4.2b). CLTE measurements are important for many reasons. For example, mismatch in CLTE values may cause dimensional change or delamination in composites and adhesives due to the thermal stresses. 

Although the copolymers shown in Figure 11.1 were crystallized very slowly to allow most favorable conditions for equilibrium crystallization at each temperature, and the reported melting temperatures, measured by dilatometry, were determined by locating the temperatures where the melting curves merged with the liquidus line [11], these conditions were still far removed from the thermodynamic equilibrium upon which the Flory model was built. Furthermore, the formation of thick crystallites that correspond to the equilibrium melting temperature in Flory s model is an extremely rare occurrence. Even if they were present, their minute quantity would make detection difficult. Thus, the... 

Note Injeet into the air in order to check the melt temperature. Measure temperature with a needle thermometer. 

DSC data T bulk melting temperature measured by DSC Reproduced with permission from N. Uryu and K. Alyiiruk, Journal of Polymer ... 

A data acquisition system was used to collect real time temperature, pressure, and position data for each cycle. A type J intrusive temperature probe having a diameter of 3.2mm was inserted into the machines nozzle to obtain melt temperature measurements. The radius of the nozzle bore was 6.4 mm and the probe protruded in by 3.2mm. Additionally, three type J thermocouples were used to monitor the steel temperature of the nozzle assembly. Figure 1 shows the nozzle assembly and the locations of the thermocouples. The data acquisition system was calibrated by submerging all of the thermocouples in boiling water and then adjusting the signal gains until each read 100 +/- 0.3°C. The recorded temperature data was filtered prior to data analysis. 

Finally, it was found that the temperature of the nozzle in which the sensor was mounted significantly affected the magnitude of the melt temperature measurements. While an intrusive temperature probe provides significant advantages over manually measuring melt temperature, the measurements were largely affected by the temperature of the nozzle steel. It is likely that this behavior damped out some of the effects of injection velocity and screw recovery conditions that would have otherwise been evident. 

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