Kraft Pulping of Mango Seed Husk: Lignin Yield Optimization and Potential Resin Application

Abstract:

Growing concerns on environmental deterioration is driving the research towards the use of renewable resources in the production of various materials. Biomass feedstocks, such as agricultural and food industry residues, present many advantages as these are widely available, can be inexpensive resources for commercial biorefineries, and can help in the waste reduction in most industries. In the Philippines, ample mango waste is generated due to its flourishing mango processing industry. Mango wastes have already shown valorization potential in numerous studies, however, studies on mango seed husk (MSH) are still limited. This study characterized the lignin found in MSH derived from kraft pulping as phenol substitute in the phenol-formaldehyde (PF) resin synthesis. During kraft delignification, the effects of alkali charge (7.3-20.7% Na₂O), temperature (130-180°C), and liquid-to-solid ratio (LSR) (6.59-23.41 w/w) on the lignin yield were examined using central composite design. The model obtained showed that lignin yield is influenced by the process variables in the following order of decreasing significance: alkali charge, LSR, and temperature. Moreover, low R² values are observed suggesting that there may be other factors affecting the response not considered in this study and that the model has low predictive power. In addition, MSH lignin was isolated from the black liquor by single-step acid precipitation at pH 2 with 20 wt% H₂SO₄. Characterization using FT-IR and difference UV spectroscopy showed that kraft MSH lignin could be a great potential as phenol substitute in PF resin production as it is mostly represented by guaiacyl units and has high total phenolic hydroxyl groups content (3.38 mmol/g). MSH lignin, with its high phenolic hydroxyl content and guaiacyl structure, has diverse industrial applications beyond resin synthesis. It can be used as a natural antioxidant in polymers, a bio-based adhesive for wood products, a UV-absorbing agent in coatings, a precursor for carbon fibers, and a surfactant in concrete and agricultural formulations. Additionally, its antimicrobial properties make it suitable for pharmaceuticals and cosmetics.

• Periodical: Advanced Materials Research (Volume 1186)
• Pages: 61-90
• DOI: https://doi.org/10.4028/p-6NUeTD
• Online since: January 2026
• Authors: Ian Dominic F. Tabañag*, Licca May Katrina N. Camay, Richmond C. Pepito, Christine R. Reguya
• Keywords: Central Composite Design, Kraft Pulping, Lignin, Mango Seed Husk, Phenol-Formaldehyde Resin

References

[1] E. De Jong, A. Higson, P. Walsh, M. Wellisch, and others, "Bio-based chemicals value added products from biorefineries," IEA Bioenergy, Task 42 Biorefinery, vol. 34, p.1–36, 2012.

[2] J. Speight, "Synthetic fuels handbook: properties, process and performance," 2008.

[3] K. Kohli, R. Prajapati, and B. K. Sharma, "Bio-based chemicals from renewable biomass for integrated biorefineries," Energies, vol. 12, no. 2, p.233, 2019.

DOI: 10.3390/en12020233

[4] L. Mopera, "Food Loss in the Food Value Chain: The Philippine Agriculture Scenario," J. Dev. Sustain. Agric., vol. 11, no. 1, p.8–16, 2016.

[5] Food and Agriculture Organization of the United Nations, "Major Tropical Fruits- Statistical compendium 2018," 2019.

[6] Philippine Statistics Authority, "2015-2019 Crop Statistics of the Philippines," 2020.

[7] N. A. Sagar, S. Pareek, S. Sharma, E. M. Yahia, and M. G. Lobo, "Fruit and Vegetable Waste: Bioactive Compounds, Their Extraction, and Possible Utilization," Compr. Rev. Food Sci. Food Saf., vol. 17, no. 3, p.512–531, 2018.

DOI: 10.1111/1541-4337.12330

[8] M. A. Henrique, H. A. Silvério, W. P. F. Neto, and D. Pasquini, "Valorization of an agro-industrial waste, mango seed, by the extraction and characterization of its cellulose nanocrystals," J. Environ. Manage., vol. 121, p.202–209, 2013.

DOI: 10.1016/j.jenvman.2013.02.054

[9] R. K. Muthu, T. Anand, R. Vidyalakshmi, and S. Anandakumar, "Fabrication and Property Evaluation of Biodegradable Tableware (Plate) Made from Mango Seed Shell," Int. J. Pure App. Biosci, vol. 7, no. 1, p.448–454, 2019.

DOI: 10.18782/2320-7051.7443

[10] A. S. Franca, L. S. Oliveira, S. A. Saldanha, P. I. A. Santos, and S. S. Salum, "Malachite green adsorption by mango (Mangifera indica L.) seed husks: Kinetic, equilibrium and thermodynamic studies," Desalin. Water Treat., vol. 19, no. 1–3, p.241–248, 2010.

DOI: 10.5004/dwt.2010.1105

[11] A. Abolaji, O. Adeyinka, and A. Olaitan, "Suitability of Mango Seed Shell Particles and Recycled High Density Polyethylene (RHDPE) Composites for Production of Particleboard," Am. J. Eng. Res, vol. 6, no. 8, p.314–325, 2017.

[12] A. A. Odunsi, "Response of laying hens and growing broilers to the dietary inclusion of mango (Mangifera indica L.) seed kernel meal," Trop. Anim. Health Prod., vol. 37, no. 2, p.139–150, 2005.

DOI: 10.1023/b:trop.0000048455.96694.85

[13] G. D. Akpen, I. L. Nwaogazie, and T. G. Leton, "Kinetic studies of colour and phenol removal from wastewater using mango seed shell activated carbon," Glob. J. Eng. Res., vol. 11, no. 1, p.35–46, 2012.

DOI: 10.4314/gjer.v11i1.4

[14] J. G. Vieira et al., "Synthesis and characterization of methylcellulose from cellulose extracted from mango seeds for use as a mortar additive," Polímeros, vol. 22, no. 1, p.80–87, 2012.

DOI: 10.1590/s0104-14282012005000011

[15] L. A. Andrade, M. A. S. Barrozo, and L. G. M. Vieira, "Thermo-chemical behavior and product formation during pyrolysis of mango seed shell," Ind. Crops Prod., vol. 85, p.174–180, 2016.

DOI: 10.1016/j.indcrop.2016.03.004

[16] C. A. Rezende, M. A. de Lima, P. Maziero, E. R. DeAzevedo, W. Garcia, and I. Polikarpov, "Chemical and morphological characterization of sugarcane bagasse submitted to a delignification process for enhanced enzymatic digestibility," Biotechnol. Biofuels, vol. 4, no. 1, p.54, 2011.

DOI: 10.1186/1754-6834-4-54

[17] P. S. nee' Nigam, N. Gupta, and A. Anthwal, "Pre-treatment of agro-industrial residues," in Biotechnology for agro-industrial residues utilisation, Springer, 2009, p.13–33.

DOI: 10.1007/978-1-4020-9942-7_2

[18] L. F. Ballesteros, J. A. Teixeira, and S. I. Mussatto, "Chemical, functional, and structural properties of spent coffee grounds and coffee silverskin," Food bioprocess Technol., vol. 7, no. 12, p.3493–3503, 2014.

DOI: 10.1007/s11947-014-1349-z

[19] N. Mandlekar et al., "An Overview on the Use of Lignin and Its Derivatives in Fire Retardant Polymer Systems," Lignin - Trends Appl., 2018.

DOI: 10.5772/intechopen.72963

[20] R. Martín-sampedro, J. I. Santos, Ú. Fillat, B. Wicklein, M. E. Eugenio, and D. Ibarra, "Characterization of lignins from Populus alba L. generated as by-products in different transformation processes: Kraft pulping, organosolv and acid hydrolysis," Int. J. Biol. Macromol., vol. 126, p.18–29, 2019.

DOI: 10.1016/j.ijbiomac.2018.12.158

[21] N. E. El Mansouri and J. Salvadó, "Structural characterization of technical lignins for the production of adhesives: Application to lignosulfonate, kraft, soda-anthraquinone, organosolv and ethanol process lignins," Ind. Crops Prod., vol. 24, no. 1, p.8–16, 2006.

DOI: 10.1016/j.indcrop.2005.10.002

[22] C. Xu and F. Ferdosian, Degradation of Lignin by Depolymerization. 2017.

[23] E. Ahmad and K. K. Pant, Lignin Conversion: A Key to the Concept of Lignocellulosic Biomass-Based Integrated Biorefinery. Elsevier B.V., 2018.

DOI: 10.1016/b978-0-444-63992-9.00014-8

[24] R. B. Santos, P. W. Hart, H. Jameel, and H.-M. Chang, "Important reactions of lignin," BioResources, vol. 8, no. 1, p.1456–1477, 2013.

[25] C. Xu and F. Ferdosian, Conversion of Lignin into Bio-based Chemicals and Materials. Germany: Springer, 2017.

[26] M. Belgacem and A. Gandini, Monomers, Polymers and Composites from Renewable Resources. 2008.

[27] E. Brännvall, "The Limits of Delignification in Kraft Cooking," BioResources, vol. 12, no. 1, p.2081–2107, 2017.

DOI: 10.15376/biores.12.1.brannvall

[28] A. Mukherjee, S. Banerjee, and G. Halder, "Parametric optimization of delignification of rice straw through central composite design approach towards application in grafting," J. Adv. Res., vol. 14, p.11–23, 2018.

DOI: 10.1016/j.jare.2018.05.004

[29] W. D. Wan Rosli, I. Mazlan, and K. N. Law, "Effects of kraft pulping variables on pulp and paper properties of acacia mangiumkraft pulp," Cellul. Chem. Technol., vol. 43, no. 1–3, p.9–15, 2009.

[30] P. Maan, A. Kadam, A. Kumar, S. Kumar, and D. Dutt, "com Process Parameters Optimization of Casuarina equisetifolia for Enhanced Production of Bleachable Grade Kraft Pulp through RSM," vol. 13, no. 4, p.8802–8813, 2018.

DOI: 10.15376/biores.13.4.8802-8813

[31] M. S. Jahan, "Pulping of Bangladeshi Cotton Stalks," vol. 39, p.147–154, 2004.

[32] G. Engida, "Kraft Pulping of Wheat Straw," Addis Ababa University, 2017.

[33] K. L. Hii and M. D. Mashitah, "Optimisation of pressed pericarp fibre delignification for glucose recovery using response surface methodology," Int. J. Environ. Eng., vol. 6, no. 2, p.220–238, 2014.

DOI: 10.1504/ijee.2014.062157

[34] B. O. Ogunsile, "Effects of Operational Variables on the Pulp Yield and Lignin Dissolution of C Yperus Articulatus," vol. 30, no. 1, p.95–101, 2010.

[35] C. G. Yoo and A. J. Ragauskas, "Opportunities and Challenges of Lignin Utilization," ACS Symp. Ser., vol. 1377, p.1–12, 2021.

[36] M. Cardoso, É. D. de Oliveira, and M. L. Passos, "Chemical composition and physical properties of black liquors and their effects on liquor recovery operation in Brazilian pulp mills," Fuel, vol. 88, no. 4, p.756–763, 2009.

DOI: 10.1016/j.fuel.2008.10.016

[37] J. Domínguez-robles, E. Espinosa, D. Savy, and A. Rosal, "Selective Lignin Precipitation using Mineral Acids," BioResources, vol. 11, no. 3, p.7061–7077, 2016.

DOI: 10.15376/biores.11.3.7061-7077

[38] A. S. Klett, "Purification, Fractionation, and Characterization of Lignin from Kraft Black Liquor for Use as a Renewable Biomaterial," Clemson University, 2017.

[39] Y. Mardiyati, E. Y. Tarigan, P. Prawisudha, S. M. Shoimah, R. R. Rizkiansyah, and S. Steven, "Binderless, all-lignin briquette from black liquor waste: Isolation, purification, and characterization," Molecules, vol. 26, no. 3, 2021.

DOI: 10.3390/molecules26030650

[40] A. L. Macfarlane, M. Mai, and J. F. Kadla, Bio-based chemicals from biorefining: Lignin conversion and utilisation. 2014.

DOI: 10.1533/9780857097385.2.659

[41] J. M. Jardim, P. W. Hart, L. Lucia, and H. Jameel, "Insights into the potential of hardwood kraft lignin to be a green platform material for emergence of the biorefinery," Polymers (Basel)., vol. 12, no. 8, 2020.

DOI: 10.3390/polym12081795

[42] W. Yang et al., "Preparation and properties of adhesives based on phenolic resin containing lignin micro and nanoparticles: A comparative study," Mater. Des., vol. 161, p.55–63, 2019.

DOI: 10.1016/j.matdes.2018.11.032

[43] A. Tejado, C. Peña, J. Labidi, J. M. Echeverria, and I. Mondragon, "Physico-chemical characterization of lignins from different sources for use in phenol-formaldehyde resin synthesis," Bioresour. Technol., vol. 98, no. 8, p.1655–1663, 2007.

DOI: 10.1016/j.biortech.2006.05.042

[44] S. Yang, J. L. Wen, T. Q. Yuan, and R. C. Sun, "Characterization and phenolation of biorefinery technical lignins for lignin-phenol-formaldehyde resin adhesive synthesis," RSC Adv., vol. 4, no. 101, p.57996–58004, 2014.

DOI: 10.1039/c4ra09595b

[45] B. M. Upton and A. M. Kasko, "Strategies for the conversion of lignin to high-value polymeric materials: review and perspective," Chem. Rev., vol. 116, no. 4, p.2275–2306, 2015.

DOI: 10.1021/acs.chemrev.5b00345

[46] Y. Xu, L. Guo, H. Zhang, H. Zhai, and H. Ren, "Research status, industrial application demand and prospects of phenolic resin," RSC Adv., vol. 9, no. 50, p.28924–28935, 2019.

DOI: 10.1039/c9ra06487g

[47] L. Pilato, Phenolic Resins: A Century of Progress. Springer, 2010.

[48] S. A. Shahid, M. Ali, and Z. I. Zafar, "Characterization of phenol-formaldehyde resins modified with crude bio-oil prepared from Ziziphus mauritiana endocarps," BioResources, vol. 9, no. 3, p.5362–5384, 2014.

DOI: 10.15376/biores.9.3.5362-5384

[49] A. Sluiter, R. Ruiz, C. Scarlata, J. Sluiter, and D. Templeton, "Determination of Extractives in Biomass—NREL TP-510-42619," 2008.

[50] W. G. Trindade et al., "Thermoset Phenolic Matrices Reinforced with Unmodified and Surface-Grafted Furfuryl Alcohol Sugar Cane Bagasse and Curaua Fibers : Properties of Fibers and Composites," p.2485–2496, 2005.

DOI: 10.1021/bm058006+

[51] D. M. Neiva, J. Gominho, and H. Pereira, "Modeling and optimization of Eucalyptus globulus bark and wood delignification using response surface methodology," BioResources, vol. 9, no. 2, p.2907–2921, 2014.

DOI: 10.15376/biores.9.2.2907-2921

[52] G. E. P. Box, J. S. Hunter, and W. G. Hunter, "Statistics for experimenters," in Wiley Series in Probability and Statistics, Wiley Hoboken, NJ, USA, 2005.

[53] A. Gärtner, G. Gellerstedt, and T. Tamminen, "Determination of phenolic hydroxyl groups in residual lignin using a modified UV-method," Nord. Pulp Pap. Res. J., vol. 14, no. 2, p.163–170, 1999.

DOI: 10.3183/npprj-1999-14-02-p163-170

[54] E. Maekawa, T. Ichizawa, and T. Koshijima, "An evaluation of the acid-soluble lignin determination in analyses of lignin by the sulfuric acid method," J. Wood Chem. Technol., vol. 9, no. 4, p.549–567, 1989.

DOI: 10.1080/02773818908050315

[55] J. Baruah et al., "Recent trends in the pretreatment of lignocellulosic biomass for value-added products," Front. Energy Res., vol. 6, no. DEC, p.1–19, 2018.

DOI: 10.3389/fenrg.2018.00141

[56] M. E. Eugenio, D. Ibarra, R. Martin-Sampedro, E. Espinosa, I. Bascon, and A. Rodríguez, "Alternative Raw Materials for Pulp and Paper Production in the Concept of a Lignocellulosic Biorefinery," IntechOpen, 2019.

DOI: 10.5772/intechopen.90041

[57] F. I. Oyeleke, A. Olaniyan, M. O. Sunmonu, and S. K. Oyeniyi, "Development of a Fruit Washing Machine," J. Agric. Eng. Technol., vol. 22, no. 1, p.29–36, 2014.

[58] M. Ekpenyong, S. Antai, A. Asitok, and B. Ekpo, "Response surface modeling and optimization of major medium variables for glycolipopeptide production," Biocatal. Agric. Biotechnol., vol. 10, p.113–121, 2017.

DOI: 10.1016/j.bcab.2017.02.015

[59] J. Frost, "Multiple regression analysis: Use adjusted R-squared and predicted R-squared to include the correct number of variables," Minitab Blog, vol. 13, no. 6, 2013.

[60] Minitab Blog Editor, "Multiple Regression Analysis: Use Adjusted R-Squared and Predicted R-Squared to Include the Correct Number of Variables," 2013. [Online]. Available: https://blog.minitab.com/en/adventures-in-statistics-2/multiple-regession-analysis-use-adjusted-r-squared-and-predicted-r-squared-to-include-the-correct-number-of-variables.

DOI: 10.1002/9781118445112.stat06627

[61] F. Moksony and R. Heged, "Small is beautiful. The use and interpretation of R2 in social research," Szociológiai Szemle, Spec. issue, p.130–138, 1990.

[62] J. Frost, "How to interpret a regression model with low R-squared and low P values," Minitab Inc.(ed) Get. started with minitab, vol. 17, 2014.

[63] J. Frost, "Regression analysis: How do I interpret R-squared and assess the goodness-of-fit," Minitab Blog, vol. 30, 2013.

[64] D. Bacs and I. H. Boyaci, "Modeling and optimization I: Usability of response surface methodology," J. Food Eng., vol. 78, no. 3, p.836–845, 2007.

[65] D. C. Montgomery, Design and Analysis of Experiments, 8th ed. John Wiley & Sons, Inc., 2019.

[66] M. Lal, D. Dutt, C. H. Tyagi, J. S. Upadhyay, and S. Upadhyay, "Characterization of Anthocephalus cadamba and its delignification by kraft pulping," Tappi J., vol. 9, no. 3, p.30–37, 2010.

DOI: 10.32964/tj9.3.30

[67] J. Gierer, "Wood Science and Technology," vol. 266, p.241–266, 1980.

[68] M. Gustavsson, "The Significance of Liquor-to-Wood Ratio on the Reaction Kinetics of Spruce Sulphate Pulping," no. April, 2007.

[69] Minitab 18 Support, "Contour plots and 3D surface plots," 2019.

[70] M. Bassiouni and M. Ghazy, "Effect of Temperature and Time on the Kraft Pulping of Egyptian Bagasse," Int. J. Sci. Res., vol. 5, no. 2, p.179–184, 2016.

[71] H. Li, J. Zhou, J. Zhang, G. Sun, Y. Yang, and F. Liang, "The optimum delignification conditions and delignification course during the pretreatment process of poplar kraft pluping with green liquor pretreatment," ICMREE 2013 - Proc. 2013 Int. Conf. Mater. Renew. Energy Environ., vol. 1, p.345–350, 2013.

DOI: 10.1109/icmree.2013.6893680

[72] H. Chen, Lignocellulose Biorefinery Feedstock Engineering, 1st ed. China: Woodhead Publishing, 2015.

[73] D. Fengel and G. Wegener, Wood: Chemistry, Ultrastructure, Reactions, 2nd ed. Berlin and New York: Walter de Gruyter, 1983.

[74] A. García et al., "Characterization of lignins obtained by selective precipitation," Sep. Purif. Technol., vol. 68, no. 2, p.193–198, 2009.

[75] O. Ajao, J. Jeaidi, M. Benali, A. M. Restrepo, N. El Mehdi, and Y. Boumghar, "Quantification and variability analysis of lignin optical properties for colour-dependent industrial applications," Molecules, vol. 23, no. 2, 2018.

DOI: 10.3390/molecules23020377

[76] S. I. Mussatto, M. Fernandes, and I. C. Roberto, "Lignin recovery from brewer's spent grain black liquor," Carbohydr. Polym., vol. 70, no. 2, p.218–223, 2007.

DOI: 10.1016/j.carbpol.2007.03.021

[77] H. Zhang, S. Fu, and Y. Chen, "Basic understanding of the color distinction of lignin and the proper selection of lignin in color-depended utilizations," Int. J. Biol. Macromol., vol. 147, p.607–615, 2020.

DOI: 10.1016/j.ijbiomac.2020.01.105

[78] A. Vishtal and A. Kraslawski, "Challenges in industrial applications of technical lignins," BioResources, vol. 6, no. 3, p.3547–3568, 2011.

DOI: 10.15376/biores.6.3.vishtal

[79] E. Hermiati, L. Risanto, M. A. R. Lubis, R. P. B. Laksana, and A. R. Dewi, "Chemical characterization of lignin from kraft pulping black liquor of Acacia mangium," AIP Conf. Proc., vol. 1803, 2017.

DOI: 10.1063/1.4973132

[80] M. N. Mohamad Ibrahim, N. Zakaria, C. S. Sipaut, O. Sulaiman, and R. Hashim, "Chemical and thermal properties of lignins from oil palm biomass as a substitute for phenol in a phenol formaldehyde resin production," Carbohydr. Polym., vol. 86, no. 1, p.112–119, 2011.

DOI: 10.1016/j.carbpol.2011.04.018

[81] O. Faix, "Classification of Lignins from Different Botanical Origins by FT-IR Spectroscopy," Holzforschung, vol. 45, no. s1, p.21–28, 1991.

DOI: 10.1515/hfsg.1991.45.s1.21

[82] K. Minu, K. K. Jiby, and V. V. N. Kishore, "Isolation and purification of lignin and silica from the black liquor generated during the production of bioethanol from rice straw," Biomass and Bioenergy, vol. 39, p.210–217, 2012.

DOI: 10.1016/j.biombioe.2012.01.007

[83] F. Bello and A. Chimphango, "Optimization of lignin extraction from alkaline treated mango seed husk by high shear homogenization-assisted organosolv process using response surface methodology," Int. J. Biol. Macromol., vol. 167, no. xxxx, p.1379–1392, 2021.

DOI: 10.1016/j.ijbiomac.2020.11.092

[84] N. E. El Mansouri, Q. Yuan, and F. Huang, "Characterization of alkaline lignins for use in phenol-formaldehyde and epoxy resins," BioResources, vol. 6, no. 3, p.2647–2662, 2011.

DOI: 10.15376/biores.6.3.2647-2662

[85] N. H. Do et al., "The novel method to reduce the silica content in lignin recovered from black liquor originating from rice straw," Sci. Rep., vol. 10, no. 1, p.1–10, 2020.

DOI: 10.1038/s41598-020-77867-5

[86] C. A. Vega-Aguilar, G. Lutz, and J. F. Mata-Segreda, "Phenolic resin derived from Jatropha curcas seed-husk lignin as phenol substitute," UNED Res. J., vol. 7, no. 2, p.217–223, 1969.

DOI: 10.22458/urj.v7i2.1148

[87] S. Y. Lin and C. W. Dence, Methods in Lignin Chemistry. Springer Series in Wood Science, 1992.

[88] A. Alzagameem et al., "Lignocellulosic biomass as source for lignin-based environmentally benign antioxidants," Molecules, vol. 23, no. 10, p.1–19, 2018.

DOI: 10.3390/molecules23102664

[89] N. M. Stark, D. J. Yelle, and U. P. Agarwal, "Techniques for Characterizing Lignin," Lignin Polym. Compos., p.49–66, 2015.

DOI: 10.1016/b978-0-323-35565-0.00004-7

[90] I. Šurina et al., "Characterization of non-wood lignin precipitated with sulphuric acid of various concentrations," BioResources, vol. 10, no. 1, p.1408–1423, 2015.

DOI: 10.15376/biores.10.1.1408-1423

[91] M. Jablonský, J. Kočiš, A. Ház, and J. Šima, "Characterization and comparison by UV spectroscopy of precipitated lignins and commercial lignosulfonates," Cellul. Chem. Technol., vol. 49, no. 3–4, p.267–274, 2015.

[92] X. Pan and J. N. Saddler, "Effect of replacing polyol by organosolv and kraft lignin on the property and structure of rigid polyurethane foam," Biotechnol. Biofuels, vol. 6, no. 1, p.1–10, 2013.

DOI: 10.1186/1754-6834-6-12

[93] C. Huang, J. He, R. Narron, Y. Wang, and Q. Yong, "Characterization of Kraft Lignin Fractions Obtained by Sequential Ultrafiltration and Their Potential Application as a Biobased Component in Blends with Polyethylene," ACS Sustain. Chem. Eng., vol. 5, no. 12, p.11770–11779, 2017.

DOI: 10.1021/acssuschemeng.7b03415

[94] F. E. Brauns and D. A. Brauns, The Chemistry of Lignin, 1st ed. Academic Press, 1960.

[95] M. Zhao, J. Jing, Y. Zhu, X. Yang, X. Wang, and Z. Wang, "Preparation and performance of lignin – phenol – formaldehyde adhesives," Int. J. Adhes. Adhes., vol. 64, p.163–167, 2016.

DOI: 10.1016/j.ijadhadh.2015.10.010

[96] W. Zhang, Y. Ma, Y. Xu, C. Wang, and F. Chu, "Lignocellulosic ethanol residue-based lignin-phenol-formaldehyde resin adhesive," Int. J. Adhes. Adhes., vol. 40, p.11–18, 2013.

DOI: 10.1016/j.ijadhadh.2012.08.004

[97] S. Yang, J.-Q. Wu, Y. Zhang, T.-Q. Yuan, and R.-C. Sun, "Preparation of Lignin-Phenol-Formaldehyde Resin Adhesive Based on Active Sites of Technical Lignin," J. Biobased Mater. Bioenergy, vol. 9, p.266–272, 2015.

DOI: 10.1166/jbmb.2015.1514

[98] S. Kalami, M. Arefmanesh, E. Master, and M. Nejad, "Replacing 100% of phenol in phenolic adhesive formulations with lignin," J. Appl. Polym. Sci., vol. 134, no. 30, p.45124, 2017.

DOI: 10.1002/app.45124

[99] N. Tachon, B. Benjelloun-Mlayah, and M. Delmas, "Organosolv wheat straw lignin as a phenol substitute for green phenolic resins," BioResources, vol. 11, no. 3, p.5797–5815, 2016.

DOI: 10.15376/biores.11.3.5797-5815

[100] Minitab 18 Support, "Lack-of-fit and lack-of-fit tests," 2019.

[101] Khan, M. A., Ashraf, S. M., & Malhotra, V. P. (2004). Development and characterization of a wood adhesive using bagasse lignin. International Journal of Adhesion and Adhesives, 24(6), 485–493.

DOI: 10.1016/j.ijadhadh.2004.01.003

[102] Danielson, B., & Simonson, R. (1998). Kraft lignin in phenol formaldehyde resin. Part 1. Partial replacement of phenol by kraft lignin in phenol formaldehyde adhesives for plywood. Journal of Adhesion Science and Technology, 12(9), 923–939.

DOI: 10.1163/156856198X00542

[103] Abdelwahab, N. A., & Nassar, M. A. (2011). Preparation, optimisation and characterisation of lignin phenol formaldehyde resin as wood adhesive. Pigment & Resin Technology, 40(3), 169–174.

DOI: 10.1108/03699421111130432