Testing And Evaluation Methods For Thermoplastics Compounds

A thermoplastic, or thermosoftening plastic, is a plastic polymer material that becomes pliable or moldable at a certain elevated temperature and solidifies upon cooling. Most thermoplastics have a high molecular weight. The polymer chains associate by intermolecular forces, which weaken rapidly with increased temperature, yielding a viscous liquid.

Mechanical Testing of Thermoplastics Materials

Physical testing of Thermoplastics measures the strength, elongation, toughness and other important properties. The most important properties for measurement are;

1) Hardness (ASTM D2240): The resistance of a plastic material to indentation. It is measured on a durometer machine. Normal specificationa is plus or minus 5 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.

2) 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 MegaPascals, (N/mm2).

3) Elongation (ASTM D638): The amount of increased length of a material until breakage. Specification is a minimum percentage.

4) Flexural properties (three point bending method): 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.

5) Creep and Stress Relaxation: Creep is the property of a material to expand or deform continuously over a period of time under the application of a constant force. Creep is one of the most widespread failure mechanism of thermoplastic materials.