2.8 WATER ABSORPTION (ASTM D 570):
The tendency of plastics to absorb moisture simply cannot be overlooked since even the slight amount of water can significantly alter some key mechanical, electrical, or optical property. Water absorption characteristic of plastics depend largely upon the basic type and the final composition of the material. For example, materials containing only hydrogen and carbon, such as polyethylene and polystyrene, are extremely water resistant, where as plastics having oxygen or oxy-hydrogen groups are very susceptible to water absorption. Cellulose acetate and nylons are good example of the preceding type. Materials containing chlorine, bromine, or fluorine are water repellent. Fluorocarbon, such as PTFE, is one such type of water repellent material. Water absorption characteristics of plastic material are altered by the addition of additives such as fillers, glass fibers, and plasticizers. These additives show a greater affinity to water, especially when they are exposed to the outer surface of the molded article. Some plastics absorb very little water at room temperature, but at higher temperatures that tend to take in a considerable amount of water and loose properties rapidly. Washing machine agitator, plastic dinnerware, irrigation valves, and sprinklers are examples of application requiring low water absorption.
2.8.1 PROCEDURE:
The test to determine water absorption of plastics is relatively simple. Only two equipments are required, an analytical balance and an oven capable of maintaining a uniform temperature. The test specimen may be molded disc or a piece cut from a sheet, rod, or tube. Dimensions vary according to the type of specimen. A special conditioning procedure must be followed before actual testing. The specimens are dried in an oven at a specified temperature for a predetermined time, cooled in a desiccator, and immediately weighed. The percent increase in weight during immersion is calculated as follows:
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5 comments:
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In an experiment I am getting weight percentage of water absorbed in acrylic coating more than 100 %. is that sensible? the coating was supported by a solid substrate. not a stand free polymer film
regards,
Uma
What are the standard temperatures and time for drying? Does it vary with polymer type or is the same for all types?
Also, is there a site that lists the entire ASTM procedure for determining water absorption of polymers? (for free)
Dear Uma,
Basically Acrylic polymers are considered as super absorbers of water. That's why they are largely used in diapers. So in your case also its absorbing more than 100% water. Its a good sign only. Please go ahead with your work and wish you all the best.
Dear Randy,
The standard temperature and time for drying cannot be simply decided randomly. It should be based on your particular system chosen for study. Obviously it will vary with every polymer because of the fact every polymer is unique based on the kind of side chains attached to them. In fact even a same polymer system will have a different time length based on their difference in molecular weight etc.,
anyone know about the case for calcium carbonate filled PMMA nanocomposite？
My result for water absorption is not increasing, but flutuating... Is it something wrong for the result?
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