Surface characteristics of phenol–formaldehyde–lignin resin determined by contact angle measurement and inverse gas chromatography

It is very valuable to know the surface characteristics of phenol–formaldehyde (PF) resin with lignin to promote the utilization of lignin that is sustainable organic materials. The surface characteristics of PF resin with lignosulfonate and kraft lignin were determined by contact angle measurement and inverse gas chromatography (IGC). In the contact angle measurement, the three-liquid method was utilized to determine the Lifshitz–van der Waals components (γLW), electron-acceptor (γ+), and electron-donor parameter (γ−) of the prepared resins. It was found that the γSLW and γS− of the prepared resin increased with the substitution of lignin for phenol. This may be due to the chemical component change, e.g. introduction of side chains of the lignin and sulfonic acid group. The acid–base component of the work of adhesion between water and the resins increased with the amount of lignosulfonate substituted. This agreed well with the fact that phenol–formaldehyde–lignosulfonate resin has lower resistance to water than phenol–formaldehyde resin. In IGC, the same γLW trends were obtained from the contact angle measurement. However, the absolute values of γLW obtained from the two methods were quite different. This may be due to the fact that IGC measures the surface energy by means of zero coverage adsorption, whereas a multilayer adsorption is utilized in contact angle measurement.