Chemicals, resistance weight change

These test procedures and standards are subject to change, so it is essential to keep up to date if one has to comply with them. It may be possible to obtain the latest issue on a specific test (such as a simple tensile test or a molecular weight test) by contacting the organization that issued it. For example, the ASTM issues new annual standards that include all changes. Their Annual Books of ASTM Standards contain more than seven thousand standards published in sixty-six volumes that include different materials and products. There are four volumes specifically on plastics 08.01-Plastics 1 08.02-Plastics 11 08.03-Plastics III, and 08.04-Plastic Pipe and Building Products. Other volumes include information on plastics and RPs. The complete ASTM index are listed under different categories for the different products, types of tests (by environment, chemical resistance, etc.), statistical analyses of different test data, and so on (56,128,129). 

The classic test for chemical resistance (ASTM D-543) measures the percentage weight change of test samples after immersion in different liquid systems. Tests for chemical resistance have been extended to include changes in mechanical properties after immersion. Since chemical attack involves changes in chemical structure, it can be readily observed by many instrumental methods that measure chemical structure, in particular, surface structure. 

Figure 10.4 The chemical resistance of a diglycidyl ether of bisphenol A (DGEBA) epoxy resin modified with LP-3 (50 parts LP-3 per 100 parts resin). A 5 cm x 3 cm x 2 mm coupon was immersed in the liquid for 28 days at 23°C. Open boxes = percentage volume swell shaded boxes = percentage weight change. Reproduced with permission from Morton International Ltd, Coventry, UK...

Figure 65. Weight change under drying conditions for phenolic foam (5). Table 70 Chemical Resistance (14-days immersion) (5)...

As a rule, the most widespread liquid environments are water solutions of acids, alkalis, and salts. Chemical resistance of RubCon was specified as a change in weight and compressive strength of the samples after their exposure to aggressive liquid environments during a certain period of time. The choice of aggressive environment compositions was based on their prevalence in industrial production. 

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)]. 

This appendix contains extensive chemical resistance data for a number of commercial fluoropolymers. Most of the chemicals are frequently encountered in processing operations. The data for each fluo-ropolymer are organized alphabetically, using the common name of each chemical. The reader should review the next section (Sec. V.2) to understand the basis for the PDL Rating. Exposure conditions for each chemical have been listed because the same chemical could behave in a different way if the conditions of exposure (such as temperature or concentration) are altered. Where data have been available, the effect of exposure on the physical properties such as weight change and tensile properties have been listed. 

The chemical resistance is usually measured by weight, volume, or dimensional change, retention of tensile strength, elongation, or impact strength, or visual comparison with control after specified immersion time and conditions. 

Evaluation of chemical resistance may establish the potential for extraction of plasticizer incorporated in the material as well as an effect of plasticizer on durability of tested material. The standard contains information on testing chemical resistance with 50 test liquids using two methods immersion test and test under mechanical stress. The list of test liquids includes white oil which may be regarded as the only example of plasticizer among test liquids. Samples of known dimensions and weights are immersed in selected liquids for 168 h at room temperature. Containers are stirred every 24 h. Changes in appearance are recorded and samples can be subjected to mechanical property testing. Tensile properties of immersed samples are most frequently compared with control samples but other mechanical tests may also be used. 

The chemical resistance of Lrunax GP-5300 (30 wt% of G/F), a representative of glass fiber reinforced Lrunax grades, is shown in Table 4. Changes of tensile strength, total weight, and dimensions were measured and evaluated after placing test specimens in these chemicals for 7 days at 23°C. The blends showed good resistance with an exception of acetone and tetrahydrofuran. 

Chemical (weight change during 7 days at 23°C) Resistance to acid (20% H2SO4) D543 % 1.15 0.91 ... 

These changes in diffusion coefficient and permeability observed for gases and liquids, are accompanied by substantial changes in chemical resistance. For example, highly drawn LPE shows quite exceptional resistance to attack by concentrated nitric acid, and at A=30 no measurable weight loss occurs even after 10 day etching, compared with a weight loss of about 30% for a sample with X=ll. 

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