Implementing water resistance properties to recyclable bio-foam.

Abstract

The growing environmental and social concerns about the pollution caused by the manufacture and waste of traditional plastic-based foams used for single-use packaging generate global societal demand for bio-based alternatives produced from natural resources. Forest biomass, the primary source of cellulose, lignin, and wood fibers, holds enormous promise in the future of packaging materials while being more environmentally friendly. The foundation of the current thesis work lies under the recent innovation of new bio-based foam material that was conducted by the Complex Systems and Materials research group of the Applied Physics Department at Aalto University. Such material named "FoamWood" is an example of a cellulose-based foam that can be both more sustainable and less expensive than its oil-based equivalents. However, such bio-foams are easily degradable in water which puts limits to their potential applications.

This thesis work aims to review the effect of adding organic polymer additives such as extracted lignin in order to enhance water resistance properties. The examination shows potential changes in the foam’s biodegradability and ability to resist humidity and moisture exposure. Contact angle measurements of samples prepared with different material compositions are used to examine the effect of lignin on wetting properties. The contact angle test shows a significant increase in the foam’s surface tension, which results in a bigger contact angle after adding lignin. These results were supported by scanning electron microscope (SEM) images to study the water repellent part of the different lignin samples. Later on, Cassie–Baxter wetting model for heterogeneous surfaces explains lignin’s water hydrophobic properties. The results show that lignin produces rough surfaces, as the hydrophobic side of the particles faces the air phase which eventually carries a connection to water resistivity and wetting advantages.