Meaning
Heating a material often causes the release of absorbed moisture, residual solvents or reaction byproducts into the surrounding environment. Volatile mass loss is the reduction in the total weight of a sample as these components evaporate or outgas. It is the primary measurement taken during thermogravimetric analysis to determine the composition and stability of a substance.
Stoichiometric Change
Removal of components from a reacting mixture can alter the properties of the polymer. Significant volatile mass loss during a cure cycle can lead to the formation of voids or bubbles in a finished part. This outgassing is common in materials like phenolics or polyimides that produce water as part of the condensation reaction.
Controlling the rate of this loss is necessary to ensure the structural integrity of the product.
Signal Interference
Heat flow measurements in a calorimeter are often disrupted by the energy required for evaporation. Because evaporation is an endothermic process, volatile mass loss can create a negative peak that overlaps with exothermic reaction peaks. This overlap makes it difficult to calculate the true enthalpy of a reaction or to identify the onset of a transition.
Precise kinetic analysis requires the suppression of this loss or the use of simultaneous mass and heat measurements.
Analysis Mitigation
Specialized equipment and techniques are used to manage the escape of gases. Hermetically sealed pans or high-pressure crucibles prevent volatile mass loss by keeping the components contained. If the loss must be measured, a thermogravimetric analyzer provides a continuous record of the sample weight.
Comparing the results from sealed and open tests allows researchers to isolate the effects of evaporation from the chemical reactions.
