Polyurethane rigid foams are widely used as thermal insulation materials. The general route to make polyurethane is through the reaction between polyol and isocyanate. Blowing agents are added to generate cell structure for foam applications. As people are becoming much more environmentally conscious, green products are becoming increasingly more mainstream. According to a life cycle comparison of soy-based polyol and petroleum-based polyol, the soy-based feedstocks showed 75% less total environmental impact than petroleum-based feedstocks with significant global warming reductions. Though some studies have shown that soy-based polyol has potential to replace petro polyol in rigid foam application, a systematic study is still needed. The goal of the thesis is to formulate polyurethane rigid foam from soy-based polyol, understand the mechanism behind the property deficiencies, and develop strategies to improve them.
Initially, a petroleum-based polyol with functionality of 4.4 and molecular weight of 690 g/mol was chosen as the control polyol. This was compared to a soy-based polyol (SBOP) with functionality of 4.4 and molecular weight of 1100 g/mol. It was found that soy-based foams had much higher density, k value (thermal conductivity), and poorer cell morphology. By adding glycerol, which can help to balance the gelling and blowing reaction, foam properties of density, k value, and cell morphology were greatly improved. Moreover, soy-based foams had a similar k value and k value aged with time, as control foams. Measurements of foam kinetic had shown that glycerol not only generated more heat for pentane evaporation to form cell structure, but also accelerated the build-up of crosslinks to support the cell structure. Considering the structure difference between SBOP and petroleum-based polyol, the effect of surfactant on foam properties especially k value and its aging was investigated. Though soy-based foams from different surfactants did show different k value, only a small correlation between surfactant hydrophobicity and foam properties was observed. The average cell size increased slightly with increasing surfactant hydrophobicity.
Although glycerol improved foam properties significantly, foams with high glycerol addition had high flammability which was not favorable in industry. Additionally, due to the high polarity of glycerol, the reactive nature of soy foaming system was largely changed. Thus, a new formulation was highly desired in order to study the effect by solely replacing petroleum-based polyol with SBOP.
The second control polyol selected had lower molecular weight and lower functionality than SBOP, a glycerol free formulation was developed. In this formulation, exactly same type and amount of chemicals were used for both control polyol and SBOP. Soy-based foams had comparable density, initial k value, cell morphology, higher Tg, and compressive strength than petroleum-based foams. However, they showed much faster k value aging. The effect of solely replacing SBOP on foam k value aging was further studied. Foam k value aging was related to the permeability of CO2, air and physical blowing agents. Permeability was measured through polyurethane thin films. Soy-based polyurethane thin films had much higher N2 permeation than petroleum-based films, and N2 had much higher k value than physical blowing agent pentane. Three different approaches were discussed to reduce N2 permeation. They focused on the effect of polymer intrinsic property (cohesive energy), polymer Tg (free volume theory) and the addition of physical gas barrier respectively.