Objective  This paper aims to explore the effects of surfactant content on the surface wettability for medium density fiberboard (MDF) modified by paraffin emulsion, which can provide theoretical basis and technical supports for the development and application of paraffin-based waterproofing agent.

  Method  Four groups of paraffin emulsions with different mass fractions of surfactant at 2%, 4%, 6% and 8% were prepared by 58# paraffin, Span 80 and Tween 80 as raw materials and the paraffin emulsions were used to treat the medium density fiberboard (MDF) samples by impregnation under normal pressure. Surface wettability of the samples was assessed by contact angle measurement; microstructure and elemental composition of the sample surfaces were characterized and analyzed by field emission scanning electron microscope (FESEM) and X-ray photoelectron spectroscopy (XPS).

  Result  Compared with the untreated samples, the initial contact angle of the treated samples increased, and the declining rate of contact angle and surface droplet volume decreased significantly. With an increase in the mass fraction of surfactant, the initial contact angle of the treated samples decreased, and the decreasing rate of contact angle and surface droplet volume accelerated. FESEM and XPS results showed that increasing mass fraction of surfactant in paraffin emulsion would lead to a smoother sample surface and reduce the C1/C2 value on the treated sample surfaces.

  Conclusion  With an increase in mass fraction of surfactant, paraffin wax particles tend to collide and aggregate and a double layer structure of surfactant molecules is formed on the sample surfaces. The surface wettability of the treated samples is improved due to the reduction in surface roughness as well as the increased amount of hydrophilic groups. Lowering the mass fraction of surfactant could reduce the surface wettability of MDF modified by paraffin emulsion, which provide an insight into the development and application of paraffin-based waterproofing agent.