Vicat softening point temperature

The alkyl group also produces subde changes in the processing of the PVC, the use level and cost of the stabilizer, and in some cases even the final properties of the article, especially the heat distortion temperature or Vicat softening point. Overall, methyl derivatives are most widely used. Butyls are second and octyls a distant third. 

Two particular test methods have become very widely used. They are the Vicat softening point test (VSP test) and the heat deflection temperature under load test (HDT test) (which is also widely known by the earlier name of heat distortion temperature test). In the Vicat test a sample of the plastics material is heated at a specified rate of temperature increase and the temperature is noted at which a needle of specified dimensions indents into the material a specified distance under a specified load. In the most common method (method A) a load of ION is used, the needle indentor has a cross-sectional area of 1 mm, the specified penetration distance is 1 mm and the rate of temperature rise is 50°C per hour. For details see the relevant standards (ISO 306 BS 2782 method 120 ASTM D1525 and DIN 53460). (ISO 306 describes two methods, method A with a load of ION and method B with a load of SON, each with two possible rates of temperature rise, 50°C/h and 120°C/h. This results in ISO values quoted as A50, A120, B50 or B120. Many of the results quoted in this book predate the ISO standard and unless otherwise stated may be assumed to correspond to A50.)... 

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. 

Vicat softening point (°C) 80 70 flexible at room temperature... 

A glass transition temperature of 215°C, a deflection temperature of 200°C and a Vicat softening point of 219°C. 

To enhance the resistance to heat softening his-phenol A is substituted by a stiffer molecule. Conventional bis-phenol A polycarbonates have lower heat distortion temperatures (deflection temperatures under load) than some of the somewhat newer aromatic thermoplastics described in the next chapter, such as the polysulphones. In 1979 a polycarbonate in which the bis-phenol A was replaced by tetramethylbis-phenol A was test marketed. This material had a Vicat softening point of 196 C, excellent resistance to hydrolysis, excellent resistance to tracking and a low density of about l.lg/cm-. Such improvements were obtained at the expense of impact strength and resistance to stress cracking. 

The TMC polycarbonate homopolymer has a glass transition temperature of 238°C, nearly 100°C above that of the bis-phenol A polycarbonate. Therefore, copolymers will have intermediate glass transitions depending on the relative proportions of TMC and bis-phenol A. Commercial grades (marketed by Bayer as Apec HT) have Vicat softening points from 158 to... 

Polycarbonates based on tetramethylbisphenol A are thermally stable and have a high Vicat softening point of 196°C. On the other hand they have lower impact and notched impact resistance than the normal polymer. Blends with styrene-based polymers were introduced in 1980, and compared with PC/ABS blends, are claimed to have improved hydrolytic resistance, lower density and higher heat deflection temperatures. Suggested applications are as dishes for microwave ovens and car headlamp reflectors. 

The Vicat softening point was determined according to ASTM D 1525 58 T, with a 5-kg load on a circular specimen with a diameter of 3 cm. The specimens were obtained by sintering the samples of CPVC (without stabilizers) in a molding press, at temperatures near T0 and at pressures varying according to the chlorine content of the CPVC. 

The presence of the elastomer phase determines a slight decrease of the Vicat softening point with respect to PVC also the heat distortion temperature shows the same trend, although the values are less differentiated. 

With the Vicat test a steel needle, at the end flattened to an area of 1 mm2 is pressed into a block of the material with a standard force (1 kgf for Vicat-A, 5 kgf for Vicat-B). The temperature is increased at a standard rate of 50 °C / hour until the needle has penetrated 1 mm into the sample then the Vicat softening point has been reached. As well as we have seen with the Shore hardness ( 7.5.1), this process of penetration is, in fact, also governed by the E-modulus of the material, though in a much more complicated way. Globally, also to the Vicat test a characteristic E-modulus can be ascribed, which is lower than with the ISO bending test, namely about 200 MPa for Vicat-B and 40 MPa for Vicat-A. 

As another example we consider two (amorphous) polymers with strongly different Tg, namely high for A and low for B. If we choose rpu = 0.4, then for each of the three types of dispersion the -modulus can be calculated as a function of temperature from the E(T) curves of the components. The result is shown in Figure 9.13, in which also the values of the ISO and Vicat softening points have been schematically indicated. It again appears that the type of dispersion has a strong effect on the properties (see also Qu. 4.24,9.13,9.15 and 9.23). 

A major disadvantage of PVC is its relatively low service temperature (60-70 °C) and the addition of high levels of some polymers can improve the heat distortion temperature and Vicat softening point. An example of such a polymer is alphamethyl styrene-acrylonitrile (AMSAN) copolymer. AMSAN-ABS polymer can be used as a combined heat and impact modifier. 

The most commonly used are the measurement of the Vicat softening point (ASTM D1525, DIN 53460, ISO 306) and the deflection temperature under load (DTUL, ASTM D648). Both measurements monitor the modulus change with temperature, and determine an endpoint when a macroscopic change can... 

ASTM D648 ISO R75 measured as °C. A specimen bar is placed in a heated chamber, clamped in supports and loaded to 1856 KN/m2 while temperature is raised 2°C every minute until the specimen bar has deflected by 0.25 cm. The apparatus used can be shared with the Vicat softening point. 

The Vical softening point shown here is the temperature al which a specified penetrating body has penetrated 1 mm deep vertically into the test piece under a specified force. The Vicat softening point was determined in accordance with DIN 53 460. (Melhod B 50 force — 49.01 N, temperature increase 50 K per hour.)... 

Two particular test methods have become very widely used. These are the Vicat softening point test and the test widely known as the heat distortion temperature test (also called the deflection temperature under load test). In the Vicat softening point test a sample of polymer is heated at a specified rate temperature increase and the temperature is noted at which a needle of specified dimensions indents into the polymer a specified distance under a specified load. 

Vicat Softening Temperature See Vicat Softening Point. 

---