The impact of ethanol-water pre-wetting on the water absorption properties of rosin-sized wood pulp paper
Pre-wetting is a technique that involves applying a solvent mixture to a paper surface before applying water. It can be used to modify the water penetration behavior of paper, which is important for paper conservation and restoration. In this article, I will explain how pre-wetting with ethanol-water mixture affects the rate of water penetration into rosin-sized paper, which is a type of paper that has been treated with a natural resin to make it more water-resistant. I will also discuss the implications of this technique for paper conservators and the future research directions.
Paper is a porous material that consists of cellulose fibers bonded together by hydrogen bonds. Water can penetrate into paper through capillary action, diffusion, and absorption. The rate and extent of water penetration depend on several factors, such as the properties of paper (e.g., porosity, surface energy, sizing), the properties of water (e.g., viscosity, surface tension, pH), and the environmental conditions (e.g., temperature, humidity, pressure).
One way to modify the water penetration behavior of paper is to pre-wet it with a solvent mixture before applying water. Pre-wetting can change the surface energy and pore structure of paper, which can affect how water interacts with it. Ethanol is a common solvent that can be mixed with water to form a pre-wetting solution. Ethanol has a lower surface tension and higher volatility than water, which can reduce the capillary forces and increase the evaporation rate of the pre-wetting solution.
In a recent study, the effect of pre-wetting with ethanol-water mixture on the rate of water penetration into rosin-sized wood pulp paper was investigated using a novel optical method. Rosin is a natural resin that is used as a sizing agent to make paper more hydrophobic. Paper samples were prepared with different rosin contents (0%, 0.5%, 1%, and 2%) and pre-wetted them with ethanol-water mixtures with different ethanol concentrations (0%, 10%, 20%, 30%, 40%, and 50%). Then a drop of water applied on the pre-wetted paper surface and measured the contact angle, diameter, and penetration depth of the water drop using a high-speed camera.
The results showed that pre-wetting with ethanol-water mixture significantly increased the rate of water penetration into rosin-sized paper. The higher the ethanol concentration in the pre-wetting solution, the faster the water penetration rate. The researchers explained that ethanol can swell and soften the rosin layer on the paper surface, which can increase its permeability and decrease its hydrophobicity. Ethanol can also reduce the surface tension and viscosity of the pre-wetting solution, which can enhance its spreading and infiltration into the paper pores. Moreover, ethanol can evaporate faster than water, which can create a negative pressure gradient that drives water into the paper.
The rosin content in paper had a significant influence on the effect of pre-wetting. The higher the rosin content in paper, the lower the rate of water penetration after pre-wetting. This were attributed to the fact that rosin can form a thicker and denser layer on the paper surface, which can resist the swelling and softening effect of ethanol and maintain its hydrophobicity.
However, there are also a potential drawback to using ethanol-water mixtures to pre-wet rosin-sized paper. Ethanol can damage some types of inks, so it is important to spot test the ink before applying this method.
Overall, pre-wetting with ethanol-water mixture can affect the water penetration behavior of rosin-sized paper. This knowledge can be useful for conservators who deal with paper artifacts that are exposed to water or humidity. Pre-wetting with ethanol-water mixture can be a potential technique to enhance the aqueous treatment or deacidification of rosin-sized paper. However, more research is needed to evaluate the long-term effects of pre-wetting on the physical and chemical properties of paper.
Reference:
Banik G., Bruckle I., Paper and Water: A Guide for Conservators (Routledge Series in Conservation and Museology), Routledge, 2011.
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