CHEMICAL PROPERTIES

IDENTIFICATION CODE OF PLASTICS Corporate Training & Planning 2

Corporate Training & Planning CHEMICAL PROPERTIES Chemical resistance is define in terms of stability of properties in contact with chemicals like water, oxidizing agents, oils, lubricants, industrial solvents and food stuffs. The Interaction of chemicals with plastics can take place in different ways, affecting adversely their useful properties at varying rates and to varying degrees. The mechanisms involved can be chemical reaction, solvation, absorption, plasticization and stress cracking. The strength of the chemical bonds, the degree of crystallinity, branching, and polarity are the deciding factors for the chemical resistance of polymers. Rise in temperature increases the rate of chemical interaction. Corporate Training & Planning

Corporate Training & Planning IMMERSION TEST Acetone immersion test : Significance : This test method is applicable only for distinguishing between inadequately fused and adequately fused PVC. Test Method : ASTMD 2152: Adequacy of fusion of extruded poly (vinyl chloride) PVC pipe and moulded fittings by acetone immersion. Test Specimen : Specimen shall be a size that is convenient to immersion in the test container but not less than 13 mm in height. Corporate Training & Planning

Corporate Training & Planning IMMERSION TEST Conditioning Specimen shall be kept in an oven for 24 h at 50 ± 30C, cooled in desiccators and immediately weigh to the nearest 0.001 g. Equipment Weighing balance: up to 0.001 g precision Micrometer flat ended: up to 0.025 mm precision Reagents Acetone: maximum density of 0.7857 g /ml at 25 0 C. Corporate Training & Planning

Corporate Training & Planning IMMERSION TEST Procedure Place sufficient dried acetone in to the container to ensure complete immersion of the specimen Place the test specimen in the acetone, seal the container and do not agitate. Allow specimen to stand immersed for 20 min. After 20 min remove the specimen from the container ad subject for sign of attack. Attack is described as lifting, raising or removing of any material outside surface inside surface or mid wall of the specimen. Swelling surface of test specimen shall not be considering attack. Corporate Training & Planning

Corporate Training & Planning IMMERSION TEST Result Results can be expressed in terms of lifting, raising or removing of any material outside surface inside surface or mid wall of the specimen. Factors influencing Thickness of the specimen Test condition: Temperature, Time (with in saturation) Concentration of chemical. Corporate Training & Planning

Corporate Training & Planning IMMERSION TEST Acetic Acid immersion test Significance: This test is applicable for distinguishing between specimens that are highly stressed and specimen that are not provided that other conditions are the same. Test Method ASTMD 1939: Determining residual stresses in extruded or moulded Acrylonitrile- Butadiene- Styrene (ABS) parts by immersion in Glacial Acetic Acid. Test Specimen Specimen shall be complete moulding or a cut piece of the extrusion or moulding of sufficient size to not influencing the stress being observed. . Corporate Training & Planning

Corporate Training & Planning IMMERSION TEST Conditioning Specimen shall be kept in an oven for 24 h at 50 ± 30 C, cooled in desiccators and immediately weigh to the nearest 0.001 g. Equipment Weighing balance: up to 0.001 g precision Micrometer flat ended: up to 0.025 mm precision Reagents Glacial Acetic Acid: 99.7% assay. Corporate Training & Planning

Corporate Training & Planning IMMERSION TEST PROCEDURE Place the acetic acid in container to ensure complete immersion of the specimen. Place test specimen in to the acitic acid for 30 s. At the end of time, remove and rince the specimen at once in running water, wipe dry. Then carefully observe the cracking. If no crack the keep another specimen and observe cracking at interval of 90 s, 2 min with same way. Corporate Training & Planning

Corporate Training & Planning IMMERSION TEST Result Results can be expressed in terms of no cracking, slight cracking, moderate cracking , extensive cracking. Factors influencing Thickness of the specimen Test condition: Temperature, Time (with in saturation) Concentration of chemical. Corporate Training & Planning

SOLVENT STRESS CRACKING RESISTANCE The solvent stress cracking resistance of plastics is a prime consideration in se­lecting the proper material. Most polymers will under­go stress cracking when exposed to certain chemical environments under high stress for a given period of time. Such cracking will occur even though some chemicals have no effect on unstressed parts and, therefore, simple immersion of test specimens is an inadequate measure of chemical resistance of polymers. Corporate Training & Planning

SOLVENT STRESS CRACKING RESISTANCE Figure Jig for solvent stress cracking test Corporate Training & Planning

SOLVENT STRESS CRACKING RESISTANCE This method employs a specimen of size 4 X 1 X 0.03 in. strapped to an elliptical jig. The entire assembly, as shown in Figure, is immersed in a reagent. Because of the elliptical design of the jig, the stress at the high end of the jig is extremely low. Conversely, the stress at the low end of the jig is extreme­ly high. The level of stress in the specimen at different points on the jig can be calculated. After 1 min, the specimen is observed for crazing. The point at which the crazing stops is considered the critical stress point. The critical stress value at this point is determined from a previously calculated value. If no crazing is observed after 1 min, the test is continued for several hours. The test may also be carried out at elevated temperatures to accelerate the stress-cracking process. The biggest advantage of this method is that one can look at the stress-cracking process over the entire range of stress values using only one specimen. Corporate Training & Planning

SOLVENT STRESS CRACKING RESISTANCE Case study: Solvent stress crack resistance of HIPS is studied in n- butane and air, and stress relaxation with time to rupture is presented herewith Corporate Training & Planning

Corporate Training & Planning REFERENCES Vishu shah, “Hand Book of Plastics Testing Technology” second edition, John Willy & Sons, 1998. Related Indian & International Standard. Handbook of plastics test methods, R.P.Brown, George Goodwin Publication Testing and Evaluation of Plastics, A. B. Mathur, I. S. Bhardwaj, Allied Publication, New Delhi. Allen. W.S and Baker, P.N, “Hand Book of Plastics Technology” Vol.2, CBS Publishers, New Delhi, 2004 Corporate Training & Planning

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