Mass Transport Through Polymer Films: The Importance of Interfaces and Compatibility
Different types of barriers are used in packaging to keep and protect products from the surrounding environment and are often essential for storing and transportation. Today, many barriers are made of different types of polymers, but since most polymers do not exhibit desired barrier properties on their own, combinations must be used. One way to combine materials is to create composites by adding a filler to a matrix material. Another way is to combine numerous layers to form laminates. When two materials are combined, interfaces are formed between these materials. These interfaces can exhibit other properties than those of the bulks. For example, a filler can induce crystallinity in a matrix material, which will decrease its barrier properties. It is therefore important to understand the impact of interfaces on barrier properties for the production of functional barriers.
The major focus of this project was to study the mass transport of water and carboxylic acids in composites and laminates, respectively. To increase the compatibility between the matrix and the filler in a composite material, several surface modifications were used. It was shown that good dispersion of the filler was important for the production of homogenous films, but also that a rod-like nano-filler can cause pores in a composite material, resulting in increased water permeability. A simple and straightforward method was suggested to predict the dispersability of a filler in a polymeric matrix. The transport of carboxylic acids was studied in laminates with varying numbers of layers. It was found that laminates resulted in stronger barrier properties than single-layered films, likely because of the ordering of chains close to the interface. The results obtained in this thesis will contribute to the production of functional barriers.