TESTING AND EVALUATION METHODS FOR THERMOPLASTIC COMPOUNDS

As an introduction to the most commonly used tests for thermoplastic compounds, herein we will focus on physical property testing:

Testing agencies
Several national and international agencies establish and publish testing specifications for industrial materials. The most commonly used standards in the United States come from ASTM International.

A major international organization similar to ASTM International is the International Organization for Standardization (ISO). Both agencies have a common goal of developing standards in hopes of facilitating the exchange of quality goods and services and ensuring their safe use.

Physical property testing
Physical property tests measure the molecular structure of the material which can often effect the physical properties. The most important properties for measurement include:

• Specific Gravity (ASTM D792): The ratio of the density of a liquid or solid mass to the density of water at a specific temperature.
• Hardness (ASTM D2240): The resistance of a plastic material to indentation. It is measured on a durometer machine which led to the industry to call hardness “duro.” Normal specification is plus or minus 3 and three scales are used: Shore A for flexible, Shore C for semi rigid and Shore D for rigid. Usually a delayed reading of 10 or 15 seconds is used.
• Tensile Strength (ASTM D638): The maximum nominal stress sustained by a test specimen being pulled from both ends, at a specific temperature and a specific rate of stretching. Specification is a minimum amount in Pascals, (10-6 N/mm2).
• Elongation (ASTM D638): The amount of increased length of a material until breakage. Specification is a minimum percentage.
• Flexural properties (three point bending method) (UNE-EN ISO 178): The three point bending flexural test provides values for the modulus of elasticity in bending, flexural stress, flexural strain and the flexural stress-strain response of the material. The main advantage of a three point flexural test is the ease of the specimen preparation and testing.
• Impact Energy-Charpy ( UNE-EN ISO 179): The Charpy impact test, also known as the Charpy V-notch test, is a standardized high strain-rate test which determines the amount of energy absorbed by a material during fracture. This absorbed energy is a measure of a given material’s notch toughness and acts as a tool to study temperature-dependent ductile-brittle transition.