Differential Scanning Calorimetry (DSC)
Differential Scanning Calorimetry (DSC) is a thermoanalytical technique used to determine the transition temperatures and enthalpies and other thermal properties of polymers.
DSC typically measure the glass transition temperature and enthalpies to determine the degree of cure and cross-link density of thermosetting polymer, which are relating to the physical/chemical properties of the applied coating products. The cross-link density is a combined result of chemical composition, reacting temperature and proceeding duration. As the thermosetting reaction proceeds, cross-link density and molecular weight increases, and consequently, the free volume of the coating decreases. Decrease in free volume of the coating results in an increase in the glass transition temperature of the coating, which can then be measured by DSC method. Correspondingly, the degree of cure can be calculated via dividing the residual enthalpy of post-crosslinking sample by the enthalpy of pre-crosslinking material, which is usually powder for an FBE system.
The coating system made of thermoplastic polymer is usually characterized by degree of crystallinity instead, which is influenced by the chemical structure and thermal history, such as the cooling conditions during processing or post-thermal treatment. The degree of crystallinity affects significantly on hardness, density, transparency and diffusion, and the higher the degree of crystallization, the stiffer and stronger, but also more brittle. The degree of crystallization is determined through dividing the obtained melting enthalpy by its literature value or a measured value on raw material.