MaTestLab > Test Standards > ASTM D7191 Standard Test Method for Determination of Moisture in Plastics by Relative Humidity Sensor
ASTM D7191 Standard Test Method for Determination of Moisture in Plastics by Relative Humidity Sensor
ASTM D7191 test method allows for the quantitative detection of water in polymers down to 20 ppm. It employs the use of an airtight, sealed flow system in order to protect the analyzer from contamination by atmospheric water. Considering the temperature of the samples used in this test method can approach or exceed 250°C. Therefore, they require them to be handled with care. Results of the ASTM D7191 test are stated in SI units as they are considered standard units.
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Introduction to ASTM D7191
ASTM D7191 is a widely accepted method as it is intended to be used as a control, acceptance, or assessment test. The level of moisture has a significant impact on the physical properties of various polymers such as surface imperfections or degradation through hydrolysis. Therefore, the ASTM D7191 test method effectively measures the amount of moisture in plastics and has diverse applications in plastic industries.
The ASTM D7191 test method uses capillary columns with thin films, which results in the incomplete separation of C4-C8 compounds in the presence of large amounts of carbon disulfide, and thus yields an unreliable boiling point distribution corresponding to this elution interval. In addition, quenching of the response of the detector employed to hydrocarbons eluting during carbon disulfide elution, results in unreliable quantitative analysis of the boiling distribution in the C4-C8 region.
The ASTM D7191 method is also designed to obtain the boiling point distribution of other incompletely eluting samples such as atmospheric residues and vacuum residues as the sample components are resolved from the solvent. The ASTM D7191 test method is not suitable for the analysis of materials containing a heterogeneous component such as polyesters and polyolefins.
Test Procedure of ASTM D7191
ASTM D7191 involves Relative Humidity Sensor in order to determine moisture content in plastics.
Test Setup and Execution
ASTM D7191 specifies that a sample is loaded into a glass vial and heated to evolve volatiles. Dry carrier gas flows into the vial, allowing high-boiling volatiles to condense on a hydrophobic filter. The filter’s hydrophobic properties measure moisture, which is integrated to measure the total mass of water in the sample. The moisture content is then divided by sample mass.
ASTM D7191 Test Specimens
Specimen Type
ASTM D7191 involves selecting a representative sample; however, the sample must be of a smaller size and accepted in various forms of liquid, powders, pellets, or ground material.
Specimen Details
ASTM D7191 specifies that the specimen is taken in airtight containers made of glass or other qualified or suitable material and then heated to remove moisture and must cool to room temperature before determination.
Results of ASTM D7191
The ASTM D7191 results give significant details regarding the moisture content of the plastic. As moisture content is a critical parameter in plastics processing and manufacturing, excessive moisture can adversely affect the material’s properties and processing characteristics.
Tests Relevant to ASTM D7191The tests relevant to ASTM D7191 include ASTM D6980 (Standard Test Method for Determination of Moisture in Plastics by Loss in Weight) and ASTM D6869(Coulometric and Volumetric Determination of Moisture in Plastics Using the Karl Fischer Reaction)
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