Formulation optimization of unreinforced and lignin nanoparticle-reinforced phenolic foams using an analysis of variance approach

Formulations of unreinforced and lignin nanoparticle-reinforced phenolic foams were optimized using an analysis of variance approach. The variables studied in the formulation of phenolic foams were stirring speed (650–850 rpm) and blowing agent amount (1.5–3.5 wt.%). For lignin nanoparticle-reinforced phenolic foams, the variables were lignin nanoparticle weight fraction (1.5–8.5 wt.%) and blowing agent amount (1.5–3.5 wt.%). The responses measured for both foams were density, compressive modulus, and compressive strength. In addition, the morphology of the foams was observed using scanning electron microscopy (SEM) to determine cell size distributions. The results showed that the variables studied exhibited a strong influence on the responses and the cell size distribution of the foams. Statistical models allowed for prediction of the properties of the foams and for comparison of the properties of unreinforced and lignin nanoparticle-reinforced phenolic foams. The incorporation of lignin nanoparticles in phenolic foams results in a compressive modulus and compressive strength that has up to 128% and 174%, respectively, of the values for unreinforced foams. The amount of blowing agent saved to produce a reinforced foam was up to 31% of the amount necessary to produce an unreinforced foam of the same density.