Progress in Bio‐Based Phenolic Foams: Synthesis, Properties, and Applications

Preparation and Characterization of Date Palm Bio-Oil Modified Phenolic Foam

In this work, the potential of biomass-derived date palm bio-oil as a partial substitute for phenol in the phenolic resin was evaluated. Date palm bio-oils derived from date palm were used for the partial substitution of phenol in the preparation of phenolic foam (PF) insulation materials. Date palm waste material was processed using pyrolysis at 525 °C to produce bio-oil rich in phenolic compounds. The bio-oil was used to partially replace phenol in the synthesis of phenolic resin, which was subsequently used to prepare foams. The resulting changes in the physical, mechanical, and thermal properties of the foams were studied. The substituted foams exhibited 93%, 181%, and 40% improvement in compressive strength with 10%, 15%, and 20% bio-oil substitution, respectively. Due to the incorporation of biomass waste material, the partial reduction in phenol uses, and the favorable properties, the date palm bio-oil substituted phenolic foams are considered more environmentally benign alternatives to traditional phenolic foams.

Comparison of Toughening Effects of Various Additives on Phenolic Foam

Phenolic foams (PFs) are considered excellent insulation materials owing to their flame retardancy and low thermal conductivity. However, their mechanical properties often lag behind those of other polymeric insulation materials. To fully exploit their properties and broaden end-use applications, the mechanical properties of PFs must be enhanced. In this study, various modifications were introduced into the PF matrix with the aim of enhancing its properties. The toughening effects of four additives: urea (U), nano clay (NC), sodium silicate (SS), and lignin (Li) were studied and compared. Changes that occurred in the density, cell morphology, thermal conductivity, compressive strength, and thermal stability after the addition of these fillers were analyzed. Both compressive strength and thermal stability increased with the inclusion of all additives, and the SS-toughened foam shows the biggest improvement. Li and NC addition resulted in a 34% improvement in compressive strength, while SS and U addition displayed increases of 52 and 11%, respectively. SS-toughened PF shows greater improvements in all of the important properties compared with those of the other toughened foams. Several PFs were prepared by changing the SS concentration to optimize the formulation, which yielded improvements in properties. The effects of SS concentration on density, thermal conductivity, and compressive strength were studied. The formulation with 0.37% sodium silicate concentration (PF-SS1) shows a 15% improvement in mechanical properties.

Engineering novel phenolic foams with lignin extracted from pine wood residues via a new levulinic-acid assisted process

Phenolic foams are typically produced from phenolic resins, using phenol and formaldehyde precursors. Therefore, common phenolic foams are non-sustainable, comprising growing environmental, health, and economic concerns. In this work, lignin extracted from pine wood residues using a "green" levulinic acid-based solvent, was used to partially substitute non-sustainable phenol. The novel engineered foams were systematically compared to foams composed of different types of commercially available technical lignins. Different features were analyzed, such as foam density, microstructure (electron microscopy), surface hydrophilicity (contact angle), chemical grafting (infrared spectroscopy) and mechanical and thermal features. Overall, it was observed that up to 30 wt% of phenol can be substituted by the new type of lignin, without compromising the foam properties. This work provides a new insights on the development of novel lignin-based foams as a very promising sustainable and renewable alternative to petrol-based counterparts.

A mini-review on building insulation materials from perspective of plastic pollution: Current issues and natural fibres as a possible solution

As plastic pollution is eroding our ecological environment at an alarming rate around the world, tracking the origins is a necessity for putting forward effective measures to prevent it. The building industry, as an important sector consuming plastic products and producing plastic wastes, is increasing application of thermal insulations to improve energy efficiency. However, most insulation materials have negative impact on the environment. With the strategies to boost sustainability of buildings, natural fibres have occurred in the market as promising raw materials for thermal insulations. This mini-review aims to describe the extent building insulations contributed to plastic pollution, and a possible solution to plastic pollution from natural fibres and their current shortcomings. Hopefully, the mini-review could advance the current knowledge on contribution of building materials, especially thermal insulations to the ubiquitous plastic pollution, and the potential of natural fibres for replacing the plastic insulations, which could accordingly help future development of sustainable green insulations.