Highly porous biochar from spent coffee ground for fully green thermal insulating composites with thermal conductivity of 0.04 W m⁻¹ K⁻¹

Abstract

Biomass materials offer the advantages of low cost, abundant availability, and renewability, making them sustainable and environmentally friendly alternatives to petroleum-based thermal insulation materials. Spent coffee ground (SCG), a type of biomass generated after brewing coffee, has been used as a filler for thermal insulation composites. However, developing SCG-based composites with superior thermal insulation performance remains a significant challenge due to the low porosity of SCG. Herein, a highly porous SCG biochar (SB) was fabricated by a simple carbonization process optimized for temperature and atmosphere. SB-based thermal insulation polymer composites were designed and fabricated for the first time, employing the SB as the filler and biodegradable ethyl cellulose (EC) as the matrix. Meanwhile, the SB was pre-mixed with environmentally friendly solvents (water, ethanol, and propylene glycol) selected based on the chemical interaction within the material system to prevent the impregnation of SB pores with the EC. The chemical and morphological properties of the SB were discussed in terms of their influence on the thermal insulation properties of the fabricated composite. The thermal conductivity and heat transfer mechanism of the SB-based composites were systematically verified using steady-state heat transfer theory. The biodegradable SB-based composite demonstrated outstanding thermal insulation property (0.04 W m⁻¹ K⁻¹) comparable to commercial expanded polystyrene. More importantly, the thermal insulation composites developed in this work consisted of environmentally friendly and sustainable materials, free from hazardous or toxic substances. These thermally insulating and biodegradable SB-based polymer composites are expected to be widely utilized in various thermal insulation applications.

Keywords

Spent coffee ground / Biochar / Green material / Thermal insulation composite / Biodegradability

References

[1] Abu-Jdayil B, Barkhad MS, Mourad A-HI, Iqbal MZ. Date palm wood waste-based composites for green thermal insulation boards. J Build Eng. 2021, 43. 103224

[2] Adam R, Pollex A, Zeng Tet al. . Systematic homogenization of heterogenous biomass batches–industrial-scale production of solid biofuels in two case studies. Biomass Bioenerg. 2023, 173. 106808

[3] AlMallahi MN, Al Abdallah H, Abu-Jdayil B, Elgendi M. Enhancing evaporation using proposed biomass-derived insulation with holistic decision-making. Appl Therm Eng. 2024, 253. 123662

[4] Andrade TS, Vakros J, Mantzavinos D, Lianos P. Biochar obtained by carbonization of spent coffee grounds and its application in the construction of an energy storage device. Chem Eng J Adv. 2020, 4. 100061

[5] Atinafu DG, Choi JY, Nam J, Kang Y, Kim S. Insights into the effects of biomass feedstock and pyrolysis conditions on the energy storage capacity and durability of standard biochar-based phase-change composites. Biochar. 2025, 7. 18

[6] Batista MJ, Ávila AF, Franca AS, Oliveira LS. Polysaccharide-rich fraction of spent coffee grounds as promising biomaterial for films fabrication. Carbohydr Polym. 2020, 233. 115851

[7] Bejenari V, Marcu A, Ipate A-Met al. . Physicochemical characterization and energy recovery of spent coffee grounds. J Mater Res Technol. 2021, 15: 4437-4451.

[8] Boafo FE, Kim J-H, Ahn J-G, Kim S-M, Kim J-T, Zhang L. Study on thermal characteristics and electrical performance of a hybrid building integrated photovoltaic (BIPV) system combined with vacuum insulation panel (VIP). Energy Build. 2022, 277. 112574

[9] Boonrawd C, Yodyingyong S, Benyahia L, Triampo D. Novel solvent–latex mixing: thermal insulation performance of silica aerogel/natural rubber composite. Gels. 2022, 8(1. 7

[10] Brown KR, Xue Z, Cordier Ret al. . 1, 4-cineole: a bio-derived solvent for highly stable graphene nanoplatelet suspensions and well-dispersed UHMWPE nanocomposite fibers. Adv Compos Hybrid Mater. 2024, 75. 160

[11] Buratti C, Belloni E, Lascaro E, Merli F, Ricciardi P. Rice husk panels for building applications: thermal, acoustic and environmental characterization and comparison with other innovative recycled waste materials. Constr Build Mater. 2018, 171: 338-349.

[12] Chan H, Shi C, Wu Zet al. . Superhydrophilic three-dimensional porous spent coffee ground reduced palladium nanoparticles for efficient catalytic reduction. J Colloid Interface Sci. 2022, 608: 1414-1421.

[13] Chen C, Zhou Y, Xie Wet al. . Lightweight, thermally insulating, fire‐proof graphite‐cellulose foam. Adv Funct Mater. 2023, 336. 2204219

[14] Cho J, Jang HG, Kim SY, Yang B. Flexible and coatable insulating silica aerogel/polyurethane composites via soft segment control. Compos Sci Technol. 2019, 171: 244-251.

[15] Choi JY, Yun BY, Kim YU, Kang Y, Lee SC, Kim S. Evaluation of thermal/acoustic performance to confirm the possibility of coffee waste in building materials in using bio-based microencapsulated PCM. Environ Pollut. 2022, 294. 118616

[16] De Rosa M, Bianco V. Optimal insulation layer for heated water pipes under technical, economic and carbon emission constraints. Energy. 2023, 270. 126961

[17] Dell’Orso M, Mangialardi T, Paolini AE, Piga L. Evaluation of the leachability of heavy metals from cement-based materials. J Hazard Mater. 2012, 227–228: 1-8.

[18] Desole MP, Gisario A, Fedele L, Aversa C, Barletta M. Life cycle assessment of secondary packaging. expanded polystyrene versus bioplastic-coated corrugated cardboard. Sustain Prod Consum. 2024, 46: 11-28.

[19] Di Canto JAT, Malfait WJ, Wernery J. Turning waste into insulation—a new sustainable thermal insulation board based on wheat bran and banana peels. Build Environ. 2023, 244. 110740

[20] Dixit A, Dai Pang S, Kang S-H, Moon J. Lightweight structural cement composites with expanded polystyrene (EPS) for enhanced thermal insulation. Cem Concr Compos. 2019, 102: 185-197.

[21] Feng W, Qin M, Feng Y. Toward highly thermally conductive all-carbon composites: structure control. Carbon. 2016, 109: 575-597.

[22] García-García D, Carbonell A, Samper M, García-Sanoguera D, Balart R. Green composites based on polypropylene matrix and hydrophobized spend coffee ground (SCG) powder. Compos Part B Eng. 2015, 78: 256-265.

[23] Ghorbani M, Konvalina P, Neugschwandtner RWet al. . How do different feedstocks and pyrolysis conditions effectively change biochar modification scenarios? A critical analysis of engineered biochars under H2O2 oxidation. Energy Convers Manag. 2024, 300. 117924

[24] Hansen CM (1967) The three dimensional solubility parameter. Danish Technical: Copenhagen 14

[25] Hýsek Š, Podlena M, Bartsch H, Wenderdel C, Böhm M. Effect of wheat husk surface pre-treatment on the properties of husk-based composite materials. Ind Crops Prod. 2018, 125: 105-113.

[26] Kadhim MA, Yan X, Han Ret al. . High-performance biodegradable dielectric composite: towards minimizing electronic waste. Compos Part A Appl Sci Manuf. 2025, 188. 108583

[27] Kataya G, Cornu D, Bechelany M, Hijazi A, Issa M. Biomass waste conversion technologies and its application for sustainable environmental development—a review. Agronomy. 2023, 1311. 2833

[28] Kato Y, Osawa T, Yoshihara M, Fujii H, Tsutsumi S, Yamamoto H. Evaluation of the antifoaming effect using Hansen solubility parameters. ACS Omega. 2020, 511): 5684-5690.

[29] Kim HM, Noh YJ, Yu J, Kim SY, Youn JR. Silica aerogel/polyvinyl alcohol (PVA) insulation composites with preserved aerogel pores using interfaces between the superhydrophobic aerogel and hydrophilic PVA solution. Compos Part A Appl Sci Manuf. 2015, 75: 39-45.

[30] Kim Y-G, Kim HS, Jo SMet al. . Thermally insulating, fire-retardant, smokeless and flexible polyvinylidene fluoride nanofibers filled with silica aerogels. Chem Eng J. 2018, 351: 473-481.

[31] Kim M-J, Choi SW, Kim H, Mun S, Lee KB. Simple synthesis of spent coffee ground-based microporous carbons using K2CO3 as an activation agent and their application to CO2 capture. Chem Eng J. 2020, 397. 125404

[32] Kim SJ, Nam HE, Lee H, Kim SH, Jang J-u, Kim SY. Ethyl cellulose/carbonized spent coffee ground-based biocomposites for superior hydrophobicity and electric protection performance. Compos Part A Appl Sci Manuf. 2024, 177. 107964

[33] Kim J, Lee J, Lee S, Kwon O, Lee J, Kim J. Enhanced biodegradability and thermal insulation capability of polylactic acid reinforced with calcium-crosslinked orange peel biochar. Ind Crops Prod. 2025, 226. 120666

[34] Lachheb A, Allouhi A, El Marhoune Met al. . Thermal insulation improvement in construction materials by adding spent coffee grounds: an experimental and simulation study. J Clean Prod. 2019, 209: 1411-1419.

[35] Lacoste C, El Hage R, Bergeret A, Corn S, Lacroix P. Sodium alginate adhesives as binders in wood fibers/textile waste fibers biocomposites for building insulation. Carbohydr Polym. 2018, 184: 1-8.

[36] Lee H, Lee D, Cho Jet al. . Super-insulating, flame-retardant, and flexible poly (dimethylsiloxane) composites based on silica aerogel. Compos Part A Appl Sci Manuf. 2019, 123: 108-113.

[37] Lee K-T, Cheng C-L, Lee D-Set al. . Spent coffee grounds biochar from torrefaction as a potential adsorbent for spilled diesel oil recovery and as an alternative fuel. Energy. 2022, 239. 122467

[38] Li M, Ren T, Sun Yet al. . New parameter derived from the hansen solubility parameter used to evaluate the solubility of asphaltene in solvent. ACS Omega. 2022, 7(16): 13801-13807.

[39] Li W, Yan D, Li Let al. . Review of thermal treatments for the degradation of dioxins in municipal solid waste incineration fly ash: proposing a suitable method for large-scale processing. Sci Total Environ. 2023, 875. 162565

[40] Li B, Li J, Guo M. Preparation of low internal resistance electrode material with multistage interconnected pores from coffee grounds. Adv Compos Hybrid Mater. 2024, 7(2. 48

[41] Liu S-H, Huang Y-Y. Valorization of coffee grounds to biochar-derived adsorbents for CO2 adsorption. J Clean Prod. 2018, 175: 354-360.

[42] MacLeod M, Arp HPH, Tekman MB, Jahnke A. The global threat from plastic pollution. Science. 2021, 3736550): 61-65.

[43] Martín-Chivelet N, Kapsis K, Wilson HRet al. . Building-integrated photovoltaic (BIPV) products and systems: a review of energy-related behavior. Energy Build. 2022, 262. 111998

[44] Martinez CLM, Saari J, Melo Y, Cardoso M, de Almeida GM, Vakkilainen E. Evaluation of thermochemical routes for the valorization of solid coffee residues to produce biofuels: a Brazilian case. Renew Sustain Energy Rev. 2021, 137. 110585

[45] Mati-Baouche N, De Baynast H, Lebert Aet al. . Mechanical, thermal and acoustical characterizations of an insulating bio-based composite made from sunflower stalks particles and chitosan. Ind Crops Prod. 2014, 58: 244-250.

[46] Mawardi I, Aprilia S, Faisal M, Rizal S. Characterization of thermal bio-insulation materials based on oil palm wood: the effect of hybridization and particle size. Polymers. 2021, 13(19): 3287.

[47] Mawardi I, Aprilia S, Faisal M, Rizal S. Investigation of thermal conductivity and physical properties of oil palm trunks/ramie fiber reinforced biopolymer hybrid composites as building bio-insulation. Mater Today Proc. 2022, 60: 373-377.

[48] McNutt J, He QS. Spent coffee grounds: a review on current utilization. J Ind Eng Chem. 2019, 71: 78-88.

[49] Mengesha DN, Abebe MW, Appiah-Ntiamoah R, Kim H. Ground coffee waste-derived carbon for adsorptive removal of caffeine: effect of surface chemistry and porous structure. Sci Total Environ. 2022, 818. 151669

[50] Mort R, Vorst K, Curtzwiler G, Jiang S. Biobased foams for thermal insulation: material selection, processing, modelling, and performance. RSC Adv. 2021, 1184375-4394.

[51] Muthuraj R, Lacoste C, Lacroix P, Bergeret A. Sustainable thermal insulation biocomposites from rice husk, wheat husk, wood fibers and textile waste fibers: elaboration and performances evaluation. Ind Crops Prod. 2019, 135: 238-245.

[52] Oh W-D, Veksha A, Chen Xet al. . Catalytically active nitrogen-doped porous carbon derived from biowastes for organics removal via peroxymonosulfate activation. Chem Eng J. 2019, 374: 947-957.

[53] Oprea M, Voicu SI. Recent advances in composites based on cellulose derivatives for biomedical applications. Carbohydr Polym. 2020, 247. 116683

[54] Park JH, Kim YU, Jeon J, Yun BY, Kang Y, Kim S. Analysis of biochar-mortar composite as a humidity control material to improve the building energy and hygrothermal performance. Sci Total Environ. 2021, 775. 145552

[55] Qi Y, Xue X, Dong Xet al. . Ameliorating the comprehensive performance of rigid polyurethane foam insulating materials by green cork for building energy conservation. Compos Commun. 2024, 52. 102132

[56] Qiu L, Zou H, Tang D, Wen D, Feng Y, Zhang X. Inhomogeneity in pore size appreciably lowering thermal conductivity for porous thermal insulators. Appl Therm Eng. 2018, 130: 1004-1011.

[57] Rodier L, Bilba K, Onésippe C, Arsène M-A. Utilization of bio-chars from sugarcane bagasse pyrolysis in cement-based composites. Ind Crops Prod. 2019, 141. 111731

[58] Seo J, Kearney LT, Toomey MD, Keum JK, Naskar AK. Polyester-based epoxy vitrimer integrating spent coffee ground as a natural filler. Compos Part B Eng. 2023, 260. 110756

[59] Shakeel F, Haq N, Alanazi FK, Alsarra IA. Measurement and correlation of solubility of olmesartan medoxomil in six green solvents at 295.15–330.15 K. Ind Eng Chem Res. 2014, 53(7): 2846-2849.

[60] She D, Dong J, Zhang Jet al. . Development of black and biodegradable biochar/gutta percha composite films with high stretchability and barrier properties. Compos Sci Technol. 2019, 175: 1-5.

[61] Shi C, Zhang X, Nilghaz Aet al. . Large-scale production of spent coffee ground-based photothermal materials for high-efficiency solar-driven interfacial evaporation. Chem Eng J. 2023, 455. 140361

[62] Singh D, Chaudhary R. Performance evaluation of thermally insulated building integrated photovoltaic roof. Mater Today Proc. 2022, 52: 888-892.

[63] Sun Z, Dai L, Lai P, Shen F, Shen F, Zhu W. Air oxidation in surface engineering of biochar‑based materials: a critical review. Carbon Res. 2022, 1. 32

[64] Tan Z, Yoo CG, Yang D, Liu W, Qiu X, Zheng D. “Rigid-Flexible” anisotropic biomass-derived aerogels with superior mechanical properties for oil recovery and thermal insulation. ACS Appl Mater Interfaces. 2023, 15(35): 42080-42903.

[65] Varamesh A, Zhu Y, Hu Get al. . Fully biobased thermal insulating aerogels with superior fire-retardant and mechanical properties. Chem Eng J. 2024, 495. 153587

[66] Viel M, Collet F, Lanos C. Development and characterization of thermal insulation materials from renewable resources. Constr Build Mater. 2019, 214: 685-697.

[67] Wan Z, Sun Y, Tsang DCet al. . Customised fabrication of nitrogen-doped biochar for environmental and energy applications. Chem Eng J. 2020, 401. 126136

[68] Wasilewska K, Winnicka K. Ethylcellulose–a pharmaceutical excipient with multidirectional application in drug dosage forms development. Materials. 2019, 12(20): 3386.

[69] Woo D-G, Kim SH, Kim TH. Solid fuel characteristics of pellets comprising spent coffee grounds and wood powder. Energies. 2021, 142371.

[70] Xia C, Shi QS. Self-activation for activated carbon from biomass: theory and parameters. Green Chem. 2016, 18: 2063.

[71] Xu Q, Townsend T, Bitton G. Inhibition of hydrogen sulfide generation from disposed gypsum drywall using chemical inhibitors. J Hazard Mater. 2011, 191204-211.

[72] Xu X, Hu R, Chen Met al. . 3D boron nitride foam filled epoxy composites with significantly enhanced thermal conductivity by a facial and scalable approach. Chem Eng J. 2020, 397. 125447

[73] Xu C, Tong S, Sun L, Gu X. Cellulase immobilization to enhance enzymatic hydrolysis of lignocellulosic biomass: an all-inclusive review. Carbohydr Polym. 2023, 321. 121319

[74] Yin Y, Gao Y, Li A. Self-activation of biochar from furfural residues by recycled pyrolysis gas. Waste Manag. 2018, 77: 312-321.

[75] Zhang M, Zhang Z, Zhang R, Peng Y, Wang M, Cao J. Lightweight, thermal insulation, hydrophobic mycelium composites with hierarchical porous structure: design, manufacture and applications. Compos Part B Eng. 2023, 266. 111003

[76] Zhang J, Han Y, Zhang Let al. . Silica aerogel-PVA dough: a high internal phase composite with superior thermal insulation and gas barrier. Compos Sci Technol. 2024, 251. 110553

[77] Zhang X, Gao Y, Wang Xet al. . A flexible, thermal-insulating, and fire-resistant bagasse-derived cellulose aerogel prepared via a refrigerator freezing combined ambient pressure drying technique. Chem Eng J. 2024, 498. 155466

[78] Zhang Y, Li M, Zhu X, Wang L, Mašek O, Sarmah AK, Tsang DCW. Enhanced thermal insulation of biochar-gypsum composites. Cem Concr Compos. 2025, 159. 106013

[79] Zhou S, Tang Z, Pan Zet al. . Regulating closed pore structure enables significantly improved sodium storage for hard carbon pyrolyzing at relatively low temperature. SusMat. 2022, 23357-367.

Funding

Ministry of Trade, Industry and Energy(RS-2024-00420431)

RIGHTS & PERMISSIONS

The Author(s)