Production of Bio-Based Phenol Formaldehyde Foams

Considering the declining non-renewable fossil resources, there is increasing interest in the development of more environmentally conscious, sustainable and cost-effective substitutes for chemical production. Lignin, a main component in lignocellulosic biomass, has been considered to be a potential substitute for petroleum-based phenol due to its phenolic structure.\nThis PhD dissertation aimed at producing bio-based phenol formaldehyde (BPF) foams using bio-phenols, including but not limited to, kraft lignin (KL), organosolv lignin (OL), hydrolysis lignin (HL), and bio-crude oil from white birth bark. The challenge of the existing process of producing BPF foams is that a low phenol substitution ratio, generally less than 30%, can be achieved due to much lower reactivity of bio-phenols compared with phenol. The use of conventional foaming technology was considered as the main reason for the low phenol substitution ratio in the production of BPF foams. Therefore, a novel foaming technology was developed for the production of BPF foams with high phenol substitution ratios of up to 50%, taking into account both fundamental foaming principle and characteristics of BPF resoles.\nKL and OL were used as petroleum-based phenol substitutes without any pretreatments for BPF foam production. The optimal composition of the blowing agent was found to be (5 wt.% hexanes + 5 wt.% pentane) for the 50% BPF foams, (7.5 wt.% hexanes + 2.5 wt.% pentane) for the 40% BPF foams, 10 wt.% hexanes for the 30% BPF foams. The results of cone calorimeter and limiting oxygen index (LOI) tests suggested that substituting phenol with lignin does not impact significantly on the combustion properties of the PF foams. Being even better, the introduction of KL in the PF foam could reduce the emission of toxic CO during the combustion.\nHL was de-polymerized by a proprietary low-temperature/no pressure de-polymerization process for the preparation of de-polymerized hydrolysis lignin (DHL) with Mn of 638 g/mol, Mw of 1910 g/mol, and PDI of 2.99. Then the DHL was utilized as a phenol substitute for the synthesis of foamable BPF resole resins, followed by employing the above mentioned new modified foaming technology for BPF foam production. White birch bark was hydrothermally liquefied in ethanol-water (1:1, w/w) mixture into phenolic bio-crude oil, followed by production of foamable BPF resoles and then BPF foams.\nAll BPF foams produced exhibited low apparent density, strong compressive strength, low thermal conductivity, and satisfactory closed cell structure, all of which were comparable to conventional PF foams. The new foaming technology demonstrated to be promising for industrial applications, which reduced the use of both petroleum-based phenol and toxic formaldehyde by up to 50% in the preparation of BPF foams. The utilization of lignin for manufacturing of value-added bio-based materials could not only produce high-value bio-based PF foams as promising insulation and fire-retarding materials, but also greatly benefit the forestry and agriculture sectors with additional revenue streams.

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