Vicat softening point test

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.)... 

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. 

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. 

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. 

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. 

ASTM D1525-91, "Test for Vicat Softening Point of Plastics f Philadelphia (1992). 

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.)... 

See also ball-and-ring test, melting point, and vicat softening point. 

Vicat softening point n. The temperature at which a flat-nosed needle of 1-mm circular cross section penetrates a thermoplastic specimen to a depth of 1 mm under a specified load using a uniform rate of temperature rise (www.astm.org). This test is used... 

Vicat softening point One standard test for measuring temperature at which a thermoplastic will soften, involving the penetration of a flat-ended needle into the plastic under controlled conditions. 

Vicat softening points are usually higher than heat-distortion temperatures and are used primarily on thermoplastics. Vicat readings are not affected by sample size and molded-in stresses as some other melting or softening point test processes are. 

D1238, flow rate (melt index) by extrusion plastometer D569, flow properties D1525, Vicat softening point D746, brittleness temperature Analytical tests... 

Heat deflection temperature and the Vicat softening point provide a simple measure of melting transitions. Both tests involve placing a specimen under a stress state in an oil bath that can be heated at a programmed rate. The temperature at which the material undergoes a specified amount of deformation is recorded. 

These tests relate to the temperature-dependence of the properties of a polymeric material. Common tests include softening behaviour (particularly of thermoplastics) and low-temperature flexibility, for example Vicat softening point, heat-deflection temperature and Gehmann, Clash and Berg apparatus testing. 

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