ASTM D787 Standard Specification for Ethyl Cellulose Molding and Extrusion Compounds

Get Certified ASTM D787 Testing for Reliable Ethyl Cellulose Compound Data

A property value for a plastic compound means little unless the specimen preparation and test conditions are known. A report that follows ASTM D787, with dried pellets, molded specimens of the required thickness, standard conditioning, and documented test methods, gives results that suppliers and buyers can compare. The report states the type and grade, the molding conditions, and the result for every Table 1 property, so buyers can check conformance of a lot. Laboratories use the data for incoming material checks, lot release, and supplier comparison.

The scope of ASTM D787 includes:

• Material type: Plasticized ethyl cellulose thermoplastic molding and extrusion compounds
• Types and grades: Two types and eleven grades, with Type I for general purpose and Type II for improved impact resistance, especially at low temperatures
• Form: Pellets, unless otherwise specified
• Properties: Specific gravity, Rockwell hardness, tensile strength, Izod impact strength, deflection temperature, water absorption, and weight loss on heating
• Specimen basis: Injection molded specimens 3.2 mm (1/8 in.) thick
• Sampling: Statistically adequate, with a lot defined as a unit of manufacture prepared for shipment
• Routine testing: Limited to the properties in Table 1
• Units: SI units are standard, and the English values are for information only
• ISO equivalent: None known

What are the Uses of ASTM D787 Testing?

ASTM D787 helps compound suppliers, molders, extruders, and buyers specify and accept ethyl cellulose compounds. Buyers call out a material by the specification number, the type, and the grade, for example, D787 Type I, Grade 1. This standard:

• Classifies ethyl cellulose molding and extrusion compounds into two types and eleven grades.
• Sets minimum and maximum property limits for each grade in Table 1.
• Defines the material requirements for pellets, uniformity, contamination, and color.
• Specifies how technicians dry, mold, and condition the test specimens.
• Names the test methods that determine each property.
• Supports acceptance of a batch or lot against the grade the purchase order names.
• Gives buyers a common call-out for ordering a compound by type and grade.

What Materials Can Be Tested Under ASTM D787?

ASTM D787 applies to plasticized ethyl cellulose thermoplastic compounds in pellet form that suit injection molding and extrusion. The compounds may contain colorants in the nominal amounts that producers ordinarily use, and only materials that meet the specified properties fall under the standard. The color and transparency or opacity of molded items must match samples that the manufacturer submits within commercial match tolerances. Special materials compounded for special applications fall outside the specification.

Why is ASTM D787 Important?

Ethyl cellulose compounds vary widely in strength, hardness, and impact resistance, so purchases need a clear grade. ASTM D787 sets those properties for eleven grades, from Grade 1 with a minimum tensile strength of 44.8 MPa to Grade 11 with a minimum Izod impact strength of 320.3 J/m at 23 °C. The specification also sets limits on water absorption and weight loss on heating, which describe how the compound handles moisture and heat. Common test methods and specimen preparation let different laboratories report comparable values.

ASTM D787 Testing Process and Data Collection

Technicians sample the lot, dry the pellets, and mold the test specimens. They condition the specimens and run the hardness, specific gravity, tensile, impact, deflection temperature, water absorption, and heating weight loss tests. The laboratory records the type and grade, the drying and molding conditions, the specimen thickness, the test methods, and the results of each test. It then compares the results with Table 1 and reports whether the lot conforms.

Common Challenges and Troubleshooting

Moisture in the pellets is the most common problem, so technicians dry the material to 0.2% moisture content or less before molding. A material temperature that sits too close to the discoloration level darkens the specimens, and the standard calls for a temperature 10 to 25 °C below it. Thin sections and higher-molecular-weight compounds need a higher mold temperature, so a mold that runs too cool produces poor specimens. Specimens machined from compression-molded blanks or extruded strips can replace molded ones only when the results prove comparable. A sample that does not represent the whole lot misleads, so technicians follow a statistically adequate sampling plan and remember that a lot can blend several production runs. Conditioning and test atmosphere also matter, so technicians follow Practice D618 for both.

• Laboratory reports each property result against the requirement for the stated type and grade and states whether the lot conforms.
• Technicians record the drying conditions, molding conditions, specimen thickness, conditioning, and test methods, so others can repeat and review the test.
• The analyst compares each result with the Table 1 limit. Specific gravity, water absorption, and weight loss on heating must stay at or below the maximum, and hardness, tensile strength, impact strength, and deflection temperature must reach the minimum.
• Engineers read Type I grades as general purpose and Type II grades as the choice where impact resistance matters, especially at low temperatures. Grade 1 sets the highest hardness and tensile strength, and Grade 11 the highest impact strength at 23 °C.
• Manufacturers or purchasers use the conformance result to accept or reject a lot, because routine testing of each lot covers the Table 1 properties.

Link to ASTM D787 Standard