Лако-красочные материалы — производство

Thermal analysis provides a rapid method for measuring transitions due to mor­phological or chemical changes (or both) in a polymer as it is heated/cooled through a specified temperature range.

For dynamic mechanical thermoanalysis (DMTA; e. g. ASTM D4065), a specimen of known geometry is subjected to mechanical oscillations at fixed or natural resonant frequencies.

The elastic or loss moduli (or both) ofthe specimen are measured while varying the time, temperature of the specimen or frequency, or both, of the oscillation. Plots of the elastic (E’, G’) or loss moduli (E”, G”), or both, are indicative of viscoelastic characteristics of the tested material. Rapid changes in viscoelastic properties at particular temperatures, times or frequency are normally referred to as ‘transition regions’. A plot of the elastic modulus and loss modulus of material versus temperature provides a graphical representation of elasticity and damping as a function of temperature or frequency.

By using differential scanning calorimetry (DSC; e. g. ASTM D3418), changes in specific heat capacity, heat flow (in conjunction with Test Method D 3417) and temperature values can be determined for the polymer transitions mentioned above. The test methods consist of heating or cooling the material at a controlled rate in a specified purge gas at a controlled flow rate, and continuously monitoring the

difference in temperature or the difference in heat input between a reference material and a test material due to energy changes in the material.

DSC can be used to assist in identifying specific polymers, polymer alloys and certain polymeradditives, whichexhibitthermaltransitions. Chemicalreactionswhichcauseor affect certain transitions that can be measured using this technique include oxidation, crystallization, the curing ofthermosetting resins, or thermal decompositions marked by absorption or release of energy by the specimen resulting in a corresponding endothermic or exothermic peak or baseline shift in the heating or cooling curve.

7.1.3