Thermogravimetric Analysis (TGA) is the analysis of dimensional changes of a material as a function of temperature. ARDL provides testing to measure these changes as they relate to the linear thermal expansion of a material using specific equipment and test methodologies. Measurements are made of the material’s weight loss percentage over a temperature sweep. Analysis of the results can help with understanding the sample’s composition, the amount of highly volatile matter, medium volatile matter, combustible material and ash content, as well as its thermal stability. Test temperatures are usually room temperature to 1,000°C.
Thermogravimetric analysis was used as one of several complementary techniques in the identification of an unknown polymer composite, which microscopy revealed had fiberglass content. XPS identified the composition of the fiberglass and revealed the presence of CaCO3 as residues of a lower temperature TGA run than the high temperature run shown below. FTIR indicated a polymer consisting of polyester and, probably, polystyrene. TGA was then performed on the material to find the weight percent of each material. The sample was heated from room temperature to 900°C at a rate of 5°C/min in air. The TGA curve (below) is labeled in terms of the identity of the components. Here polyester (71% of the polymer), polystyrene (29% of the polymer), fiberglass (22.9% of the whole) and CaCO3 (49.3% of the whole) were easily identified by their different temperatures of combustion or evaporation. The combustion of the styrene polymer component produced enough energy that the temperature momentarily increased more than the programmed rate, which accounts for the unusual shape of the curve due to the cooling that followed the reactive overheating. The remaining material after the TGA analysis was completed was confirmed by XPS to consist only of CaCO3. The results obtained for the polymer matrix match the common blend co-polymer of 70% polyester and 30% polystyrene by weight.
Applications of TGA Analysis or Thermogravimetry
Thermogravimetric Analysis provides the change (multigram samples) in weight of a sample as function of temperature. It is a precise quantitative method of determining combustibles, loss of volatiles, curing times, decomposition of hydrates and carbonates, and weight loss changes. Rates of weight loss or gain are easily determined from the curve. The use of controlled atmospheres allows for the study of solid-gas reactions.