【Basic Knowledge of Terminology Explanations for “Polymers and Materials”-023】Terminology explanations related to polymers
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1. Viscous flow temperature: The transition temperature between the elastomeric state and the viscous flow state. 2. Glassy state: Amorphous polymers are in a state with general elasticity. 3. Heat distortion temperature: It refers to the temperature at which, with a heating rate of 2°C per minute and a load of 18.5 Kg/cm2 or 4.6 Kg/cm2 applied to the surface of the plastic (with the sample being 120 mm long and 15 mm wide), the sample undergoes bending deformation; this temperature is reached when the bending deflection at the midpoint of the sample reaches 0.21 mm. 4. Shear-thinning: The viscosity of pseudoplastic fluids decreases as the shear rate increases. 5. Mechanical relaxation: The mechanical properties of polymers change over time.
The heat deformation temperature is also a crucial parameter; so how can this temperature be increased?
The heat deformation temperature is a parameter that indicates the relationship between heating and deformation of the material being tested. It is the temperature corresponding to a specified deformation, achieved by applying a certain load to a polymer material or polymer and raising its temperature at a specific rate. It is a measure used to assess the heat resistance of polymers or polymer materials. Vicat softening temperature (abbreviated as VST) – the temperature at which a specimen of engineering plastics, general-purpose plastics, or other polymers is pressed 1 mm deep by a 1 m² pressure pin in a liquid heat transfer medium, under a certain load and at a constant heating rate. Heat deformation temperature – determined by following standard procedures, giving the temperature at a specified load and degree of deformation; for engineering plastics, a load of 1.82 MPa is generally used, such as for nylon, PET, PBT, etc., while plastics with low heat deformation resistance typically use a load of 0.45 MPa, such as for PP, PE, PS, etc. Martens test – a method used to determine the heat resistance of plastics. It involves placing a specimen of specified dimensions in an environment with a constant heating rate of 50°C/h, subjecting it to a bending stress of 4.9 MPa; the test is stopped at the temperature at which the bending deformation reaches a specified value. This temperature is known as the Marten heat resistance temperature. The high bending stress it experiences limits the scope of application for this testing method. It is usually used only for materials such as fiber-reinforced plastics in situations where the load heat deformation temperature cannot be measured. So what is the relationship between Vicat temperature and heat distortion temperature, or what are the differences between them?