Vicat softening 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.)... 

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. 

The Vicat softening temperature is the temperature at which a standard deflection occurs for defined test samples subjected to a given linear temperature increase and a compression loading from a defined indenter of a specified weight. The load used is often ION (Vicat A) or SON (Vicat B) and must be indicated with the results. In either case the polymer cannot be used under this compression load at this temperature. 

ISO 2507-2 1995 Thermoplastics pipes and fittings - Vicat softening temperature - Part 2 Test conditions for unplasticized poly(vinyl chloride) (PVC-U) or chlorinated poly(vinyl chloride) (PVC-C) pipes and fittings and for high impact resistance poly(vinyl chloride) (PVC-HI) pipes... 

ISO 727-1 2002 Fittings made from unplasticized poly(vinyl chloride) (PVC-U), chlorinated poly(vinyl chloride) (PVC-C) or acrylonitrile/butadiene/styrene (ABS) with plain sockets for pipes under pressure - Part 1 Metric series ISO 727-2 2002 Fittings made from unplasticized poly(vinyl chloride) (PVC-U), chlorinated poly(vinyl chloride) (PVC-C) or acrylonitrile/butadiene/styrene (ABS) with plain sockets for pipes under pressure - Part 2 Inch-based series ISO 2507-3 1995 Thermoplastics pipes and fittings - Vicat softening temperature - Part 3 Test conditions for acrylonitrile/butadiene/styrene (ABS) and acrylonitrile/styrene/acrylic ester (ASA) pipes and fittings... 

The following polymer characteristics were obtained on the variously irradiated test specimens melt index (ASTM 1238-62T), Vicat softening temperature (modified ASTM 1525-58T) heat distortion (ASTM D 1220-63T) physical strength yield strength ultimate tensile strength percent elongation at break (ASTM D 412-64T) chemical resistance to boiling toluene. 

ASTM D1525, Test Methodfor Vicat Softening Temperature of Plastics, Vol. 8.01, ASTM, Philadelphia, Pa., 1991. 

At elevated temperatures al polymers soften, dependent on their glass-rubber transition points, Tg, and/of their melting points, Tm. These temperatures limit the practical use of plastics. To characterize the softening behaviour, in practice various types of standard tests are being carried out, resulting in values for the softening temperature , defined in different ways. The values mostly used are the ISO Heat Deflection Temperature (HDT) and the Vicat Softening Temperature (VST or... 

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. 

Another standard heat distortion test is the Vicat test where a flat-ended needle (diameter 1 mm) penetrates to the depth of 1 mm under a specific load of 50 N (Vicat A) or 10 N (Vicat B). It will be clear that the penetration depth is again determined by the Young modulus, although in a much more complicated way than in the bending test. A rough estimate yields Vicat softening temperatures where E 1000 MPa (Vicat A) or E 200 MPa (Vicat B). 

VanKrevelen-Hoftijzer viscosity-temperature relationship, 539 Van t Hoff equation, 751 Velocities of sound waves, 390 Velocity gradient, 526 Vertical Burning Test, 854 Vicat softening temperature, 849 Vickers hardness test, 837 Viscoelasticity, 405... 

ASTM D 1525-87 Standard Test Method for Vicat Softening Temperature of Plastics, 3 pp (DOD Adopted) (FSC 9330) (MR) (Comm D-20)... 

Covers the determination of the temperature at which a specified needle penetration occurs when specimens are subjected to specified test conditions. The method is useful for many thermoplastic materials. The specimen and needle are heated at either of two permissable rates. The temperature at which the needle has penetrated to a depth of 1 mm is the Vicat softening temperature. 

The VICAT softening temperature is defined as the temperature at which a circular probe of 1.0 mm2 cross section, under a load of 1000 g, penetrates 1.0 mm into a sample 12.7 mm thick (33). Using the same samples as were used for the DTUL tests, the correlation between TM A and VICAT softening temperatures are given in Table 11.5 (32). 

ASTM D1525 provides a third type of the softening temperature test. A hat-ended needle of 1 mm circular cross-section is pressed into a thick sheet of the polymer with a load of 1.0 kg. The polymer is heated at a rate of either 50 or 120 K/h. The Vicat softening temperature is the temperature at which the needle has penetrated the polymer to a depth of 1 mm. For such a depth of penetration, the material must be very soft, hence the Vicat softening temperature is higher than other HDT data. 

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.)... 

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. 

The Vicat softening temperature (VST) is the temperature (in °C), at which an indentation tip has penetrated 1 mm deep into the test specimen surface. The indentation tip has a circular cross-section area of 1 mm. The testing method is standardized in ISO 306. It defines four different methods by varying heating rate (50 K h and 120 K h ) and load (A 10 N and B 50 N). The most common method is the B50-method (50 N and 50 K h ). The specimens have to be plane and parallel with a thickness between 3 mm and 6.5 mm and a minimum diameter resp. edge length of 10 mm (Fig. 3.5). 

Fig. 3.5 Test setup for measuring Vicat softening temperature (a) and heat distortion temperature (b) 13Gre.

ASTM D1525-06 Standard Test Method for Vicat Softening Temperature of Plasties... 

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