Analytical Tools to Aid in Coating Formulation Development

04 Oct 2019

Reactive Chemistries

Coatings are a large and important industry, enhancing the protective, aesthetic and mechanical properties of metals and other substances. When it comes to analyzing coatings, much attention is placed on characterizing the raw materials and final coating; however, relatively little is devoted to understanding property changes during coating formation. In this regard, coatings pose a significant analytical challenge because of the large property changes and simultaneous generation of volatiles.

Analytical characterization during the coating process provides valuable information about coatings and how they change over time. Understanding this will help ensure proper application and utility of the coating for the material and product. There are several approaches that can provide these analytical insights, including spectroscopic, dielectric, thermal and mechanical.  Examples of thermal approaches include Thermogravimetric Analysis (TGA), Thermomechanical Analysis (TMA) and Differential Scanning Calorimetry (DSC).  One example of mechanical assessment is Dynamic Mechanical Analysis (DMA).

DSC and DMA provide thermal and rheological insight for several systems.  Below is a description of the kind of information that can be generated for coatings.

1. Differential Scanning Calorimetry (DSC) is a thermal test that compares heat flow into or out of a sample compared to an empty reference cell. For polymers, DSC can identify Tg, melting, crystallization, cure and more. For curing systems, the DSC curve provides useful information on reactivity and a basis for calculating degree of cure. It also provides important information regarding the development of Tg over time. Depending on the system, these data can often show whether vitrification is occurring.
2. Dynamic Mechanical Analysis (DMA) measures mechanical properties of a material.  It can be used to assess a variety of coatings. The technique applies a small-strain, sinusoidal deformation and measures the force response to assess rheological properties of films. Typically these data can be collected as a function of temperature or frequency. As a complement to DSC, DMA also provides information on Tg, secondary transitions, and degree of cure.

Understanding the development of coating properties is important for improved formulations.  While aqueous- or solvent-based systems present analytical challenges, DSC and DMA can be used to provide thermal and rheological insights for coatings.  For more discussion on assessing coating formulations, including case studies and their outcomes, download our webinar recording.