Production of Bio-Based Phenol Formaldehyde Resin

Bio-Based Phenol Formaldehyde Resin Production: Current Solutions Phenolic resins obtained through condensation of phenol and formaldehyde have maintained their importance in the thermoset polymer industry since their first commercial production in 1909. Due to their advanced mechanical properties, flame-retardant character, flexibility, low cost, high thermal stability, and resistance to water and chemicals, they have broad application areas across various sectors including aviation and space, automotive, wood-based panels, electrical, paints and coatings [1-3]. Since the early 20th century, phenolic resins have found applications in numerous sectors and have undergone various modifications for end-use applications. Modification work for value-added applications remains on the agenda of both academic and industrial researchers. In addition to these efforts, part of the research focus on phenolic resins involves replacing petroleum-based phenol and formaldehyde, either partially or completely, with naturally derived materials. The primary motivations for these efforts can be examined as: utilizing sustainable bio-based sources in formulations, reducing exposure during production and end use, and enhancing phenolic resin performance. Due to the long-term infeasibility of using chemicals derived from petroleum, many researchers in both academia and industry have focused on using renewable sources in existing chemical technologies. As a result of these efforts, advances in developing chemical technology will enable the conversion of biomass into valuable chemicals and biofuels in biorefineries [4]. Biorefineries play an important role in converting biomass into value-added products. As an example, lignocellulose, a bio-based material with advantages such as accessibility, low cost, and being waste from another sector, is the primary source in the production of bio-based materials. Phenolic compounds, alcohols, and furan-based compounds are valuable chemical types obtained through processing lignocellulose in biorefineries [5-7]. Due to its phenolic structure, lignin is the environmentally friendly material with the highest potential to replace phenol. Cardanol, tannin, gallic acid, and biooils are other bio-based sources used in phenolic resin production [8-13]. In addition to phenol, it is also possible to replace formaldehyde, another component of phenolic resins, with natural sources. Hydroxymethylfurfural (5-HMF), furfural, terephthalaldehyde, and glyoxal are potential alternatives established in the literature [14-16].

1. Bio-Based Phenol Substitutes

1.1. Lignin-Based PF Resins

Lignin is an interesting material obtained from lignocellulosic biomass and capable of substituting petroleum-based raw materials. Lignocellulose consists of three polymers: lignin, cellulose, and hemicellulose, and the composition ratio varies depending on the type of natural source. Various processes have been developed to separate lignocellulose into the mentioned components, including extraction of lignin at high temperature and pressure, lignocellulose depolymerization at high temperatures in the presence of mineral acids, dissolution and precipitation of cellulose, steam/ethanol process, hydrolysis and extraction, organosolv and ultrafiltration process, catalytic conversion, and enzymatic process. Lignin derivatives obtained from the paper industry, such as kraft lignin and lignosulfonate, show promise for phenolic resin production due to their high hydroxyl numbers and phenolic structure. Lignin used in phenolic resin production can be utilized in three forms: crude lignin, purified lignin, and chemically modified lignin. Crude lignin, which has low reactivity toward formaldehyde, is obtained from biorefineries. Purified lignin is used at higher substitution rates compared to crude lignin in obtaining lignin-modified phenolic resins. Modified lignin derivatives whose reactivity is increased through methylolation, phenolation, and demethylation methods can be incorporated in phenolic resins at higher substitution rates. Like other biopolymers, lignin derivatives have different reactivity and consequently different substitution rates in formulation due to their irregular chemical structure and unstable chemical composition [17].

1.2. Tannin-Based PF Resins

Another green source used in phenolic resin synthesis is tannin, a polyphenolic macromolecule obtained from tree bark. Tannins isolated with water at different temperatures from tree bark are generally used in leather production. They are examined in two groups: hydrolyzable tannin and condensed tannin. Hydrolyzable tannins, which are rich in phenolic groups, convert to phenolic acids and carbohydrates in the presence of weak acids or bases. Although they have low reactivity due to their complex structure, they are preferred less frequently in phenolic resin formulations compared to condensed tannins.

1.3. Cardanol-Based PF Resins

Cashew nutshell liquid (CNSL), a byproduct of the cashew nut processing industry, serves as a natural source alternative to phenol due to the phenolic structures it contains, such as anacardic acid (71.7%), cardanol (4.7%), and cardol (18.7%). Cardanol, purified through various methods such as pyrolysis and solvent extraction, has been used both in its raw form and modified versions in the production of novolac and resol-type phenolic resins, with products finding application in various sectors.

2. Bio-Based Formaldehyde Substitutes

As mentioned in our previous articles, formaldehyde is a widely used raw material in many various industries and production areas. Its main applications are wood industry, flooring materials, lubricants, cosmetics, pharmaceuticals, insulation materials, disinfectants and cleaning products, preservatives, paper and photo processing. It is widely used in indoor and outdoor applications, and people are exposed to formaldehyde in some way in every aspect of life. Due to environmental and occupational concerns regarding formaldehyde, a series of regulations and recommendations have been established to limit exposure levels. Occupational exposure limits for formaldehyde vary between countries [18]. Although formaldehyde is an important source in many industries, its negative effects on human health have driven industries and researchers to find safer and more environmentally benign alternatives. Bio-based alternatives will be the most important substitution option for formaldehyde. Hydroxymethylfurfural, furfural, furfuryl alcohol, glyoxal, and vanillin are among the bio-based molecules being investigated to replace formaldehyde in PF resin synthesis.

2.1. 5-HMF-Based PF Resins

Hydroxymethylfurfural (5-HMF) is considered by many to be the best alternative to formaldehyde because it can serve as a source for the production of other different chemicals and can be used as a liquid fuel. It is an organic compound composed of a furan ring with aldehyde and alcohol functional groups. HMF is highly reactive and soluble in aqueous environments due to the presence of aldehyde and alcohol functional groups. It can be used for the production of dimethylfuran (DMF) and ethoxymethylfurfural (EMF), which are biofuel candidates for automobiles [19, 20]. Other chemicals including levulinic acid (LA), succinic acid, and 2,5-furandicarboxylic acid can also be synthesized from HMF through various chemical reactions [21-23]. HMF can be synthesized from lignocellulose and cellulose with the aid of organic solvents and ionic liquids [24]. It is an aromatic aldehyde found in dried fruits, honey, coffee, and flavoring agents. Catalytic dehydration is commonly used to extract HMF from biological sources [25]. The main biological sources used in HMF production are carbohydrates such as simple sugars and their derivatives, or carbohydrate polymers such as lignocellulose, cellulose, lignin, inulin, and starch. Zhang and colleagues developed a series of PF resins by replacing formaldehyde with HMF. The group converted glucose to HMF in the presence of CrCl2/CrCl3 and tetraethylammonium chloride (TEAC) catalysts, subjected it to reaction with phenol, and cured with hexamethylenetetramine (HMTA) to obtain glass fiber-reinforced composite. This study demonstrated that HMF-modified PF resins can be used to produce temperature-resistant green composites [26].

2.2. Furfural-Based PF Resins

Furfural is an organic compound containing an aldehyde functional group in the furan ring. Furfural has industrial value as a lubricant in resin production and in the synthesis of organic compounds such as tetrahydrofuran, furfuryl alcohol (FFA), tetrahydrofurfuryl alcohol (THFA), methyltetrahydrofuran (MTHF), furfurylamine, furoic acid, and methylfuran. Furfural is produced industrially from non-food residues of wood waste. Companies in China, Australia, and the Netherlands have been able to produce furfural from lignocellulosic biomass with high yields. Ionic liquids have also been used to produce furfural from lignocellulose materials [7]. Pizzi and colleagues developed phenol-furfural resin and investigated their flow properties and electrical properties [27,28]. Ahuja and colleagues investigated the kinetics of phenol-furfural novalac resins in the presence of potassium carbonate catalyst over a wide range of furfural-phenol (F/P) molar ratios [29].

2.3. Glyoxal-Based PF Resins

Glyoxal is a non-toxic reactive organic compound with two aldehyde groups in its structure. Its non-volatility, low cost, and ease of biodegradability make it a suitable candidate for formaldehyde substitution in phenolic adhesive production. Glyoxal is found in products such as wine, beer, tea, coffee, yogurt, bread, rice, soybeans, soy sauce, and oils. It can be prepared directly from glucose through retroaldol condensation and from a glykoaldehyde intermediate through autoxidation [30]. Formaldehyde substitutes used in phenolic resin synthesis are summarized in Table 4.

Conclusion

Comprehensive research on phenolic resins obtained using bio-based sources has been conducted over the past 20 years, and industrial products have been developed. Despite all these efforts, industrial production and applications are in relatively early stages. While showing promise in terms of substituting chemicals currently established in industry, technical and economic challenges must be overcome for widespread industrial application of bio-based materials [31]. Bio-based materials containing phenolic groups such as lignin, tannin, and cardanol must be competitive in terms of performance to replace their petroleum-based counterparts. Additionally, if high purification costs for bio-based materials can be overcome, significant obstacles to commercialization of the technology would be removed. Fluctuations in oil prices, energy crises likely to occur worldwide, and health and environmental concerns during phenolic resin production and application have been driving forces in safe and sustainable source usage for phenolic resin synthesis. The literature information presented in the article has been compiled from current articles on obtaining PF resins using bio-based raw materials, and was created to convey the current state of the technology to limited Turkish-language literature in sectors where PF resins are used, particularly the wood-based panel sector.   References [1] Xu, Y., Guo, L., Zhang, H., Zhai, H., & Ren, H. (2019). Research status, industrial application demand and prospects of phenolic resin. RSC Advances, 9(50), 28924-28935. [2] Xue, B., & Zhang, X. L. (2007). Application and development trend of phenolic resin. Thermosetting Resin(China), 22(4), 47-50. [3] Hirano, K., & Asami, M. (2013). Phenolic resins—100 years of progress and their future. Reactive and functional polymers, 73(2), 256-269. [4] Kamm, B. (2007). Production of platform chemicals and synthesis gas from biomass. Angewandte Chemie International Edition, 46(27), 5056-5058. [5] Dashtban, M., Gilbert, A., & Fatehi, P. (2012). Production of furfural: overview and challenges. J. Sci. Technol. For. Prod. Process, 2(4), 44-53. [6] Cherubini, F. (2010). The biorefinery concept: using biomass instead of oil for producing energy and chemicals. Energy conversion and management, 51(7), 1412-1421. [7] FitzPatrick, M., Champagne, P., Cunningham, M. F., & Whitney, R. A. (2010). A biorefinery processing perspective: treatment of lignocellulosic materials for the production of value-added products. Bioresource technology, 101(23), 8915-8922. [8] Manjula, S., Pavithran, C., Pillai, C. K. S., & Kumar, V. G. (1991). Synthesis and mechanical properties of cardanol-formaldehyde (CF) resins and CF-poly (methylmethacrylate) semi-interpenetrating polymer networks. Journal of materials science, 26(15), 4001-4007. [9] Li, J., Zhu, W., Zhang, S., Gao, Q., Xia, C., Zhang, W., & Li, J. (2019). Depolymerization and characterization of Acacia mangium tannin for the preparation of mussel-inspired fast-curing tanninbased phenolic resins. Chemical Engineering Journal, 370, 420-431. [10] Tahir, P. M., Halip, J. A., & Lee, S. H. (2019). Tannin-based bioresin as adhesives. In Lignocellulose for future bioeconomy (pp. 109-133). Elsevier. [11] Shukor, N. F. (2019). Gallic Acid as a Potential Substitution for Phenol in Phenol-formaldehyde Resin for Biocomposite Matrices (Doctoral dissertation, University of Sheffield). [12 ] Dong, F., Wang, M., & Wang, Z. (2018). Bio-oil as substitute of phenol for synthesis of resol-type phenolic resin as wood adhesive. International Journal of Chemical Reactor Engineering, 16(3). [13] Cui, Y., Hou, X., Wang, W., & Chang, J. (2017). Synthesis and characterization of bio-oil phenol formaldehyde resin used to fabricate phenolic based materials. Materials, 10(6), 668. [14] Sui, G., Cheng, Y., Yang, X., Wang, X., & Wang, Z. (2019). Use of sustainable glucose and furfural in the synthesis of formaldehyde-free phenolic resole resins. Journal of Applied Polymer Science, 136(28), 47733. [15] Foyer, G., Chanfi, B. H., Virieux, D., David, G., & Caillol, S. (2016). Aromatic dialdehyde precursors from lignin derivatives for the synthesis of formaldehyde-free and high char yield phenolic resins. European Polymer Journal, 77, 65-74. [16] Ballerini, A., Despres, A., & Pizzi, A. (2005). Non-toxic, zero emission tannin-glyoxal adhesives for wood panels. Holz als Roh-und Werkstoff, 63(6), 477-478. [17] Sarika, P. R., Nancarrow, P., Khansaheb, A., & Ibrahim, T. (2020). Bio-based alternatives to phenol and formaldehyde for the production of resins. Polymers, 12(10), 2237. [18] Demiralp, B., & Kapti T. (2020). Formaldehyde and emission regulations. Adhesive & Bonding, 1, 6-12. [19] Liu, X., & Wang, R. (2018). Upgrading of carbohydrates to the biofuel candidate 5-ethoxymethylfurfural (EMF). International Journal of Chemical Engineering, 2018. [20] Wang, X., Liang, X., Li, J., & Li, Q. (2019). Catalytic hydrogenolysis of biomass-derived 5-hydroxymethylfurfural to biofuel 2, 5-dimethylfuran. Applied Catalysis A: General, 576, 85-95. [21] Girisuta, B., & Heeres, H. J. (2017). Levulinic acid from biomass: Synthesis and applications. In Production of platform chemicals from sustainable resources (pp. 143-169). Springer, Singapore. [22] Li, Q., & Xing, J. (2017). Production of 1, 4-diacids (succinic, fumaric, and malic) from biomass. Production of platform chemicals from sustainable resources, 231-262. [23] Sajid, M., Zhao, X., & Liu, D. (2018). Production of 2, 5-furandicarboxylic acid (FDCA) from 5-hydroxymethylfurfural (HMF): recent progress focusing on the chemical-catalytic routes. Green chemistry, 20(24), 5427-5453. [24] Ståhlberg, T., Fu, W., Woodley, J. M., & Riisager, A. (2011). Synthesis of 5-(Hydroxymethyl) furfural in ionic liquids: paving the way to renewable chemicals. ChemSusChem, 4(4), 451-458. [25] Kuster, B. F. M. (1990). 5-Hydroxymethylfurfural (HMF). A review focussing on its manufacture. Starch-Stärke, 42(8), 314-321. [26] Zhang, Y., Nanda, M., Tymchyshyn, M., Yuan, Z., & Xu, C. (2016). Mechanical, thermal, and curing characteristics of renewable phenol-hydroxymethylfurfural resin for application in bio-composites. Journal of materials science, 51(2), 732-738. [27] Pizzi, A., Orovan, E., & Cameron, F. A. (1984). The development of weather-and boil-proof phenol-resorcinol-furfural cold-setting adhesives. Holz als Roh-und Werkstoff, 42(12), 467-472. [28] Patel, R. D., Patel, R. G., Patel, V. S., & Pearce, E. M. (1987). Kinetic investigation on the curing of phenol-furfural resin by differential scanning calorimetry. Journal of Applied Polymer Science, 34(7), 2583-2589. [29] Ahuja, S., & Singh, D. (2011). A kinetic model of alkali catalyzed phenol-furfural novalac resinification. Polymers and Polymer Composites, 19(7), 581-586. [30] Thornalley, P. J., Langborg, A., & Minhas, H. S. (1999). Formation of glyoxal, methylglyoxal and 3-deoxyglucosone in the glycation of proteins by glucose. Biochemical Journal, 344(1), 109-116. [31] Vishtal, A. G., & Kraslawski, A. (2011). Challenges in industrial applications of technical lignins. BioResources, 6(3), 3547-3568.   Berkay Demiralp - R&D Manager Polisan Kimya R&D Center Tolga Kaptı - R&D Director Polisan Kimya R&D Center