Environmental tests chemical resistance

Rapra have published their own chemical resistance data sheets [9, 10], based on results of tests at Rapra performed by a small team of operators. They are thus comparable one with another and their sources are known. Rapra s Plascams materials selection database provides durability properties on a ranking basis and their Plastics Design Guide includes Plascams and other useful programmes. In 2002 Rapra and Faraday Plastics have launched a new website of environmental stress cracking data (www.esc-plastics.com). 

PDLCOM William Andrew, Inc., Plastics Design Library test data on the chemical compatibility and the environmental stress crack resistance of plastics... 

Chemical resistance test for rubber linings by Atlas blind flange test Determination of effects of liquid chemicals on plastics Determination of environmental stress cracking (ESC) by the bent strip method... 

An example of the dependence of polymer properties on catalyst activation temperature is shown in Table 5. Polymers of various MW were made with a Cr/silica catalyst activated at various temperatures. The polymers were then tested for environmental stress crack resistance (ESCR), a measure of their ability to resist chemical attack when polymer strips are placed under stress (bent). The test is conducted in the presence of hot surfactant, and the time to failure is monitored. Like most other polyethylene physical properties, ESCR is usually improved when the MW is increased. Therefore, comparisons of catalysts are usually made at similar melt indices (a surrogate for MW). A broader MW distribution... 

Because many polymers are resistant to attack by corrosives, tests for chemical resistance of polymers are particularly important. ASTM-D-543-67 (1977) measures weight and dimensional changes of test samples immersed for 7 days in many different test solutions. These tests may be coupled with tensile tests. Other ASTM tests include those under accelerated service conditions [ASTM-D756-76 (1971)], water absorption [ASTM-D570-63 (1972)], and environmental stress cracking of ethylene plastics [(ASTM-D1693-70)]. 

Stress rupture tests on test pieces are very important under conditions where, in addition to the stress, the atmosphere is chosen to accelerate failure. The best known t> pe of test is a test of the so-called environmental. stress cracking of plastics, where the aggressis e atmosphere is a chemical that causes cracking when the material is in a strained state. These tests are usually considered as a form of chemical resistance test and are cosered in Chapter 14. Ozone cracking of rubber, also an environmental resi.stance test, is another example. 

It follows that it is most important that chemical resistance studies of plastics include environmental stress cracking tests, and several have been standardized. These will be detailed in Chapter 16. but they can be classified into constant stress and constant strain methods. Simple bent strip methods are convenient for quality control, but for more... 

Standards related to the chemical analysis of paints or detecdon of lead in paint, along with tests to measure the physical properdes of applied paint films, such as film thickness, physical strength, and resistance to environmental or chemical surroundings. 

Various tests and analytical methods are used for the characterisation and evaluation of the properties of vegetable oil-based polymer composites. Mechanical tests for properties such as tensile, flexural, compressive, impact, hardness and wear are carried out by a universal testing machine (UTM), and by equipment for testing impact, hardness, abrasion loss, and so on. Weather and chemical resistance tests are performed in UV/ozone, an artificial environmental chamber and in different chemical media. Water uptake and biodegradability tests are carried out by standard ASTM methods. Biodegradability and biocompatibility may be studied by the same procedure as described in Chapter 2. However, in practice only a few such studies have been performed for vegetable oil-based composites. 

An important measure of chemical resistance which is often used in household and industrial containers is environmental stress-crack resistance (ESCR). Many variations of the test are known and used, such as ASTM D1693, Conditions A and B. In these tests, the plastic part, a molded bar, a bottle, or a tube, etc, is placed under a standardized stress usually at elevated temperature, and exposed to a surface active agent. For example, one test uses 10% surfactant in aqueous solution at 60° C. The time needed for the sample to break is then recorded. The surfactant is thought to aid in the relaxation and disentanglement of chains. 

Environmental Stress Cracking n The formation of internal or external cracks in a plastic caused by tensile stresses well below its short-time strength, and induced by exposure to heat, solvent vapor, or chemically active solutions. ASTM Test F 1248 describes the measurement of the environmental stress-cracking resistance of polyethylene pipe in the presence of a surface-active agent. Other ASTM tests treating this subject are D 1693, D 2561, D 2951, and, in Section 15.03, F 484, F 791, and F 1164. 

XLPE exhibits high environmental stress-crack resistance, but available data is limited and tests are recommended for severe conditions or chemicals not listed in this chart. 

Environmental stress-crack resistance (tested in accordance with 7.8 ASTM F 876) and chemical resistance in specific media (test method ISO 4433 or BS 1973) are significant in such service. 

The behavior of plastic materials under long-term exposure to elevated temperatures is of prime importance to UL engineers. A procedure to determine the relative thermal indices of polymeric materials is discussed in detail in this standard. The relative thermal index of a material is an indication of a material s ability to retain a particular property when exposed to elevated temperatures for an extended period of time. It is a measure of a material s thermal endurance. Other long-term property evaluation tests include environmental exposure, creep, and chemical resistance. 

The environmental stress crack resistance (ESCR) of glass fiber-reinforced SPS/nylon blends was characterized by exposing the surface of test bars with 0% and 1 % strains applied to drops of solvent and then observing the damage to the surface. In addition, 7-day and 30-day chemical inunersion resistance were evaluated. The results of this testing for glass fiber-reinforced SPS/nylon blends are shown in Table 16.7. 

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