Vicat temperature

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. 

Whilst the Vicat test usually gives the higher values the differences are quite modest with many polymers (e.g. those of types A, B and C). For example, in the case of the polycarbonate of bis-phenol A (Chapter 20) the heat distortion temperatures are 135-140°C and 140-146°C for the high and low stress levels respectively and the Vicat softening point is about 165°C. In the case of an acetal homopolymer the temperatures are 100, 170 and 185°C respectively. With nylon 66 the two ASTM heat distortion tests give values as different as 75 and 200°C. A low-density polyethylene may have a Vicat temperature of 90°C but a heat distortion temperature below normal ambient temperatures. 

Higher softening point (Vicat temperatures of 110-117°C compared to 89-107°C). 

The most widely used method is that of Vicat in which a blunt steel needle (area of point 1 mm ) is applied vertically to the surface of a test piece (about 1 cm and 3-4 mm thick) under a load of 49 N. The oven temperature is then raised at 50 °C/h and the temperature determined at which the needle has simk 1 mm into the test piece this is taken as the softening point (Vicat temperature). 

Sample Number Me2NH Rate (cc/m g/m) Me2NH Pressure (kPa/ psig) eq. Me2NH/ eq. MMA (Ratio) Vicat Temperature (°C) % Nitrogen (%N) mmol/g total ti-tratable acidity... 

With regard to conventional PVC we observe that the presence of the elastomeric phase causes a decrease in the Vicat temperature and a higher sensitivity of the PVC/EPR materials in the creep tests. 

Figure 16.15 Charpy notched impact strength and Vicat temperature versus PC content in ASA-PC blends...

The Vicat temperature measures the penetration of a needle into a sample under otherwise constant conditions. Thus, the method also measures elasticity and surface hardness. 

The elongation at break, Vicat temperature, and hardness are controlled by both density and MW, while melt viscoelasticity by LCB and MW... 

Figure 5.11 shows the effect of nucleating agent concentration on Vicat temperature. The most extensive changes occur at low concentrations of the nucleating agent. ... 

The adding of charging groups in PU can increase the blends compatibility and enhance the mechanical properties [35]. Blends of copolymers, such as styrene and maleic anhydride [36] or styrene and maleimides [37] with TPU, exhibit improved impact strength at still-high Vicat temperatures. 

Figure 14. Vicat temperature as a function of the Kraton concentration.

The presence of the rubber can give rise to some worsening of the thermal resistance of the blends. To verify this behavior, tests for measuring the Vicat temperature have been carried out. In Figure 14, the Vicat temperature is reported as a function of the content of Kraton. As expected a reduction of the Vicat temperature of the non-compatibilized blend is observed but can be considered still reasonable with 5% of Kraton the Vicat temperature decreases by about 6-7°C for both blends. 

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