Production of rigid polyurethane foams from biopolyols with optimized synthesis processes and the formulation/structure/property relationships of the foams

Rigid polyurethane foams (RPUFs) are important polymers whose performance properties can be controlled by varying the amount and types of their components in the reaction of polyol which includes a surfactant, catalyst, and blowing agent with diisocyanate. As with most polymers, the production of SPKs from petroleum-based components has become one of the main problems of mankind in terms of environmental, energy, and material sustainability. The increasing concerns of society regarding environmental protection, the depletion of fossil fuels, and the new regulations that have been made by the governments have been forcing researchers and industry to look for renewable energy resources which can replace petroleum-based compounds in order to sustain the production of polyurethanes. In this study, biopolyols were synthesized from two different biomasses -sugar beet pulp and sunflower oil- using the methods of acid-catalyzed solvothermal liquefaction and epoxidation reaction followed by ring-opening, respectively. The synthesis processes of biopolyols were optimized using Response Surface Methodology based on Central Composite Design and the obtained biopolyols were characterized in detail. A multi-series of bio-based RPUFs (bioRPUFs) were fabricated with partial substitution of the biopolyols with petroleum-based polyol and their structure/property relationship was investigated depending on the formulations. The flame retardants such as expandable graphite and dimethyl methyl phosphonate were also added to bioRPUFs in different amounts to improve their flame retardancy. The values of average cell size, closed-cell ratio, apparent density, thermal conductivity, and compressive strength for all the foams were detected. Besides, thermal decomposition properties using thermogravimetric analysis and flame retardant properties using the limiting oxygen index and the cone calorimeter tests were determined. While the compressive strength values of all the foams and their composites were in the range of 61 and 260 kPa, the thermal conductivity values were in the range of 27.5 and 39.3 mW/m.K. In addition, with an increasing amount of flame retardants, the cellular structures were preserved and the limiting oxygen index (LOI) values of APK50/10E/10D and ŞPK/10E/10D foam composites increased to 25.7% and 24.9%, respectively.