Foaming of Some Cellulose Derivatives - Initial Studies
Fossil-based polymeric foams, based on polymers such as polystyrene and polyurethane, are important and widely employed materials due to their good mechanical properties relative their low density, the low price and the possibility for large-scale production. 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.
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 were chosen as possible and interesting candidates; hydroxypropyl methylcellulose (HPMC) and ethyl hydroxyethyl cellulose (EHEC). The foaming ability of nine different grades of the two cellulose derivatives, five HPMCs and four EHECs, was initially evaluated using a hot-mould process with water as the only blowing agent and plasticiser. The rheological properties of the derivative-water mixtures during a simulated foaming process was assessed using dynamical mechanical thermal analysis (DMTA). The final foams were characterised with regard to their apparent density. Overall, the HPMC derivatives performed significantly better than the EHECs and a few of the former were therefore selected for extrusion experiments. Three of the HPMC derivatives were evaluated in a small-scale batch extrusion experiment using a capillary viscometer. The results pointed towards the existence of a possible processing window for foaming and one of the derivatives were selected for continuous extrusion trials with water as the only added plasticiser and blowing agent. Foams could be produced using a single-screw extruder and the density of the final foams was assessed. Although some instabilities seemed to exist in the extrusion process, processing conditions giving the best results could be found.
In conclusion, HPMC cellulose derivatives could be suitable candidates for production of lightweight, foamed packaging material originating from non-fossil, renewable resources. The material could be processed in a continuous extrusion process, with only water as plasticiser and blowing agent. However, some additional experiments would be needed to finalise the processing operation and tailor the properties of the foams.
hydroxypropyl methylcellulose (HPMC)
ethyl hydroxyethyl cellulose (EHEC)