Void Content of Reinforced Plastics ASTM D2734

Void Content of Reinforced Plastics ASTM D2734

Test method A of ASTM D2734 is used for Void content testing of reinforced plastics or composites. High void content in polymers and plastics significantly reduces the strength of composite materials. Monitoring the void content of every lot ensures consistency in the manufacturing process.


    ASTM D2734 (Test method A) test is used for the determination of the void content of reinforced plastics or composites. The test method is appropriate to composites for which the effects of ignition on the materials are recognized. Most plastics, glasses, and reinforcements fall into this class. This test method is not applicable to composites for which the effects of ignition on the plastics, reinforcement, and any fillers are unidentified. This class may comprise silicone resins, which do not burn off entirely, reinforcements consisting of organic materials, metals, or inorganic materials which may gain or lose weight, and fillers containing oxides and carbonates that may gain or lose weight.

    Test Procedure:

    For the ASTM D792 Method A test, the measured density of the material is calculated by the dry/wet weight method. To calculate the void content of a material, theoretical densities of both the resin and the reinforcing material are required. Generally, the individual densities of the resin and reinforcing material are received from the supplier. Then, the actual density of the material is calculated. After that, the weighed sample is kept in a pre-weighed crucible and burnt at a higher temperature of 600°C in a muffle furnace in the air. It is burnt until only the particles of reinforcing material remain. The crucible is then cooled and weighed. From the available data, the resin content is determined as a weight percent. Finally, the void content is calculated by comparing the actual density to the theoretical density.

    Specimen size:

    The size is usually 1 inch by 1 inch thickness.


    T = Theoretical Density
    Td = Theoretical composite density
    R = Resin weight %
    r = Reinforcement weight %
    T = 100 / (R / D + r / d)
    V = Void content (volume %)
    Md = measured composite density
    D = Density of resin
    d = Density of reinforcement
    V = ( Td – Md ) / T


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