Foaming of cellulose derivatives and hemicellulose-containing materials

Abstract: Fossil-based polymeric foams are important materials due to their good mechanical properties relative their low density, the low price and the possibility for large-scale production. They are widely used in cushioning, absorbing and insulation applications. There are however a few disadvantages with these foamed products. The raw-material originates from a non-renewable resource. In the foaming process some possible less environmentally friendly additives/blowing agents are used. Also, the relatively low price of these foamed articles makes them ideal for single-use packaging and, unfortunately, they often end up in nature where the slow degradation will ensure that they stay for a long time, causing problems for marine living and other species. One possible way to solve at least some of the issues relating to fossil-based foamed products would be to use a renewable, non-fossil, raw material. There are several polymers of a non-fossil origin which could serve a primary material for foams and in this thesis two different types of cellulose derivatives (hydroxypropyl methylcellulose (HPMC) and ethyl hydroxyethyl cellulose (EHEC)) as well as a number of different hemicelluloses (xylan, arabinoxylan (AX), β-glucan concentrate and galactoglucomannan (GGM)) were studied as possible and interesting candidates. The foaming ability of some different grades of the two cellulose derivatives, xylan, AX and GGM, was initially evaluated using a hot-mould process with water as the only blowing agent and plasticiser. A simulated foaming process was assessed using dynamical mechanical thermal analysis (DMTA) for HPMC and the rheological properties of the polymer-water mixtures were determined. Three grades of the HPMC derivatives were evaluated in a small-scale batch extrusion experiment using a capillary viscometer. Also, the β-glucan concentrate (mixed with water) was foamed in the capillary viscometer and its shear and extensional viscosities were evaluated. The results pointed towards the existence of a possible processing window for foaming and extrusion experiments were therefore performed with the HPMC and the β-glucan polymers. For HPMC, water was the only added plasticiser and blowing agent and for the β-glucan concentrate also sodium bicarbonate and citric acid were used along with the water. The final foams from both foaming techniques were characterised with regard to their apparent density and foam structure. In conclusion, cellulose derivatives and hemicelluloses could be suitable candidates for production of lightweight, foamed material originating from non-fossil, renewable resources.