Defence of doctoral thesis: Andrea Träger – Strategies for Molecular Engineering of Macroscopic Adhesion and Integrity Focusing on Cellulose Based Materials

Abstract

Many aspects of modern human life pose a strain on the delicate ecosystems around us. One example is marine litter – mainly various plastic items – which accumulate in the marine environment, where they cause problems for the fauna, such as ingestion and entanglement.The widely used plastics offer many advantages for packaging, such as low cost and easy processing into many shapes. However, in addition to their low biodegradability leading to their persistence and accumulation in nature, they are largely manufactured from petroleum,a non‐renewable resource. Clearly, it would be highly desirable to exchange the petroleum‐based materials for biodegradable ones from renewable resources. Cellulose, as the most abundant biopolymer, is one choice. There are however challenges in terms of replacing currently used plastics with cellulosic materials. One is the low ductility and formability of cellulose. Various efforts are undertaken to increase the formability of cellulose. One approach to increase the renewable fraction within a material is to utilise the intrinsic stiffness and strength of cellulose to increase the structural integrity of a composite. To fully optimise these types of materials, a fundamental understanding of the interaction across interfaces within the material is essential. The main objective in this thesis was to elucidate strategies to measure, to tune and to control the interaction across interfaces. Specific polymers were designed and synthesised which could be used to modify surfaces to achieve a wet adhesion as high as that of mussel foot protein. Many properties of the joint were tuneable by varying length and structure of the polymer and amount of polymer deposited on the surfaces. A method to accurately evaluate interfacial adhesion between a chemically modified cellulose material and another surface was successfully developed, using nanometre smooth cellulose probes exhibiting bulk material properties. Two composite materials containing cellulose as reinforcing element were successfully prepared,utilising different strategies to control and enhance the interaction between the composite constituents. Together, these findings contribute to the knowledge of how to evaluate and control the interaction across an interface.