Lignin particle- and wood flour-reinforced phenolic foams: Friability, thermal stability and effect of hygrothermal aging on mechanical properties and morphology

In the present work, the effect of lignin particles and wood flour weight fractions incorporated on friability and thermal stability of a phenolic foam was determined. In addition, the effect of hygrothermal aging on compressive mechanical properties and cell size of the materials was studied. The incorporation of lignin particles decreased friability of the phenolic foam; whereas, wood flour increased it. The influence of both reinforcements on thermal stability of the material was very low. Although the reduction in mechanical properties of reinforced foams was higher than for the unreinforced material after hygrothermal aging, modulus and strength of the reinforced foams were still superior to those of the unreinforced material. Hygrothermal aging did not influence cell size of the foams studied. The material which exhibits the best combination of features was 8.5 wt.% lignin particle-reinforced phenolic foam.