Report on optimal conditions for plant oil-based binders (curability, polymerization technology and processability)

The objectives of Task 3.1 were to select a plant oil and find the optimal conditions for cationic polymerization of the epoxidized oil catalysed by either Lewis acids or dicarboxylic acid hardeners working at low temperature; the above options were used as plant oil-based binders for the composites (or wallboards) with ethyl palmitate as bioPCM. Photo-polymerization of the epoxidized oil by UV curing was also studied. Catalysts and hardeners were studied and evaluated based on several criteria, including bio-based content, curing time and temperature, physical-mechanical, thermal properties and cost. It was found that citric and oxalic acids fulfil best the requirements. The two acids were selected as hardeners for producing bioPCM-containing composites at a pilot scale (see Deliverable D4.3 “Demonstration of wallboard production”). Preliminary physical-mechanical results demonstrated that oxalic acid is better hardener than citric acid. Addition of impregnated particles decreases the mechanical properties due to insufficient adhesion between the binder and particles with oily surfaces. Another advantage of using oxalic acid is that the curing temperature is 60°C. Stability of the impregnated ethyl palmitate is good; no leaching was observed after 30 days’ exposure at 50°C temperature. However, crystallization of ethyl palmitate on the board’s surface must be eliminated. Crystallization does not mean leaching of the bioPCM, it is a surface phenomenon that is an aesthetic problem and probably can influence the finishing of the boards by lamination or painting. In order to eliminate crystallization of bioPCM, UV-curable coatings were formulated with ELO and either triarylsulfonium hexafluoroantimonate salts (mixed) or bis(4-methylphenyl)iodonium hexafluorophosphate to enable low-temperature curing. Working temperature of the bioPCM-wood composites with oxalic and a melting enthalpy of ca. 70 J/g justified the use of oxalic acid as hardener to improve the thermal performance of the composite. Additionally, processing the composite at lower curing temperature than citric acid facilitated the technology of the product. Following the laboratory results, SLU prepared the coming work in WP4 where the scale-up of the composite production demands ca. 180 kg ELO binder, provided with guidelines and safety instructions. SLU has collaborated with the project partner BOKU by exchange of experience in analytical analyses and characterization of the composite binders. The results of Task 3.1, presented in Deliverable 3.1, are conveyed and used further in Task 3.4 in WP3 and Tasks 4.1-4.4 in the work of WP4.