Dynamic vapor sorption (DVS) measurements are widely used to collect water vapor sorption isotherms for wood and other cellulosic materials. Equilibrium moisture content (EMC) is typically assumed to have been reached when the rate of change in moisture content with time (\({\text{d}}M/{\text{d}}t\)) drops below a certain value. However, the errors associated with determining EMC in this manner have never been characterized. Here, an operational definition of equilibrium for DVS measurements is provided, and twenty test cases over four cellulosic materials are presented where the relative humidity was stepped up or down and then held constant until equilibrium was reached. Then, both the time to reach various \({\text{d}}M/{\text{d}}t\) “stop criteria” and the errors in EMC associated with those stop criteria are quantified. The errors in the EMC from the widely used 0.002% min⁻¹ stop criterion are found to be as large as 1.2% MC, and the average error for 20 test cases is 0.5% MC, which are much larger than the 0.1% MC error claimed in the literature. Longer data collection times are recommended, and a more stringent \({\text{d}}M/{\text{d}}t\) criterion (0.0003% min⁻¹, using a 2-h window) for cellulosic materials is proposed. The errors with this criterion are less than 0.75% MC, and the average error is 0.3% MC. Furthermore, it is shown that the errors for a given stop criterion are systematic and can be fairly well characterized with a simple linear regression. Finally, a correction for systematic error is proposed that results in more accurate EMC values with shorter hold times.

Sustainable, non-halogenated flame retardants are desired for a variety of industry applications. Lignin, an industrially processed wood derivative, has been examined as a potential sustainable flame retardant additive to polymer systems. Here, the lignin is phosphorylated using a pyridine-catalysed esterification reaction with diphenyl phosphoryl chloride to improve its char-forming abilities. The chemical modification of the lignin was characterised by nuclear magnetic resonance spectroscopy and showed the formation of phosphorylated structures on the lignin. The thermal decomposition profile and char-forming characteristics of the modified lignin and modified lignin–epoxy composites were investigated using thermogravimetry. The flammability performance of modified lignin–epoxy composites was tested using mass loss calorimetry. With the addition of 10% modified lignin, the peak heat release rate decreased by 40% and the total heat of combustion decreased by 20%. Scanning electron microscopy was used to investigate the char morphology of the post-flame test samples and showed closed cell foam structures.