ZnO nanoparticle-reinforced lignin-phenol-formaldehyde foam: Formulation, optimization and properties

In this work, the formulation of ZnO nanoparticle-reinforced lignin phenol formaldehyde foam (ZnO-LPF) has been optimized and the potential for enhancing its mechanical properties has been evaluated. The insulation material industry is shifting towards a more sustainable future by developing foams through partial replacement of petroleum-resourced raw materials with bio-based alternatives. LPF foams represent one such alternative to phenolic foams synthesized from phenol and formaldehyde. While the partial replacement of phenol with lignin can potentially reduce environmental impacts, some of the key characteristics of phenolic foams, such as mechanical strength, are compromised. In this study, LPF resin was prepared by replacing certain percentages of phenol with lignin, and the various LPF foams were prepared by varying the formulation and measuring the key properties to obtain a formulation with optimal characteristics. Later, the selected formulation was further improved by incorporating ZnO nanoparticles, and the impact of its concentration on enhancing the key properties was analyzed. The resin and foams were characterized using scanning electron microscopy, thermogravimetry analysis, thermal conductivity, and mechanical property analysis. The compressive strength of the 10LPF foams initially increased with ZnO addition and later decreased at higher nanoparticle concentrations. The foam with 0.1 % (w/w) ZnO exhibited excellent compressive strength and thermal conductivity.