Defence of doctoral thesis: Adrian Eliasson – Ductile wood fiber-based materials through sonication and plasticization

Today’s society is highly dependent on plastic materials having essential qualities such as formability, but they have severe drawbacks like limited recyclability. Thus, it is highly desirable to find alternatives to these materials, especially for single-use applications as in the packaging industry. In recent years, biopolymers such as cellulose have been of significant interest as alternatives for plastic. However, biopolymers are challenging as they are extracted from nature as polymers with predefined length and chemical structure that are difficult to modify. To improve moldability among other properties, biopolymers need multi-step modifications, often requiring large quantities of chemicals and loss of desired inherent properties. Here, ultrasonication is used to increase the sorption of plasticizers, e.g., glycerol or urea, onto cellulose to increase the ductility of the materials. The ductility increases from 10% achieved for only sonicated materials to 40% for materials sonicated with glycerol. This is due to glycerol on the fiber’s surface which reduces the capacity of forming strong fiber joints and causes slippage. This is evidenced by the stress-strain curves of the glycerol-plasticized materials, which exhibit a region of plastic deformation not usually seen in paper-like materials. Furthermore, the effects of glycerol on fiber wall levels are observed through both scattering experiments and DMA. The scattering shows that the fiber in a water-free glycerol swollen state retains a state typical for water-swollen fibers. The trend is proportional to the glycerol content. The DMA shows a thermal transition for the fiber wall level related to glycerol content. This thesis demonstrates that ultrasonication of pulp in the presence of plasticizer imparts ductility to the corresponding material which may hold promise for the future. The concept is reliant on the combinations of ultrasonication, plasticizer and theunique fines formed during ultrasonication.

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