Optimization of microfibrillated cellulose isolation from cocoa pod husk via mild oxalic acid hydrolysis: A response surface methodology approach

L Fernando Zambrano-Mite; Yanet Villasana; M Lorena Bejarano; Christian Luciani; Dario Niebieskikwiat; Willin Álvarez; Dario F Cueva; Daniel Aguilera-Pesantes; Lourdes M Orejuela-Escobar

doi:10.1016/j.heliyon.2023.e17258

Optimization of microfibrillated cellulose isolation from cocoa pod husk via mild oxalic acid hydrolysis: A response surface methodology approach

Heliyon. 2023 Jun 13;9(6):e17258. doi: 10.1016/j.heliyon.2023.e17258. eCollection 2023 Jun.

Authors

Affiliations

¹ Biomass Laboratory, Biomass to Resources Group, Universidad Regional Amazónica Ikiam, Tena 096975, Ecuador.
² Institute of Energy and Materials, Universidad San Francisco de Quito USFQ, Diego de Robles y Vía Interoceánica, Quito 170901, Ecuador.
³ Departamento de Física, Colegio de Ciencias e Ingenierías, Universidad San Francisco de Quito USFQ, Diego de Robles y Vía Interoceánica, Quito 170901, Ecuador.
⁴ Facultad de Ciencias de La Vida. Universidad Regional Amazónica Ikiam, Tena 096975, Ecuador.
⁵ Applied Circular Engineering & Simulation Group (GICAS), Chemical Engineering Department, Colegio de Ciencias e Ingenierías, Universidad San Francisco de Quito USFQ, Diego de Robles y Vía Interoceánica, Quito 170901, Ecuador.
⁶ CLYDENT S.A, km 4.5 Vía a Taura, Guayaquil, Ecuador.
⁷ Instituto de Investigaciones Biológicas y Ambientales (Biósfera), Universidad San Francisco de Quito USFQ, Diego de Robles y Vía Interoceánica, Quito 170901, Ecuador.
⁸ Instituto de Investigaciones Biomédicas (IBioMed), Universidad San Francisco de Quito USFQ, Diego de Robles y Vía Interoceánica, Quito 170901, Ecuador.
⁹ Geocircular Consulting Group LLC, Temple Terrace, FL 33617, USA.

Abstract

Theobroma cacao L. species, cultivated worldwide for its valuable beans, generates up to 72% weight of the fruit as waste. The lack of reutilization technologies in the cocoa agroindustry has hindered the exploitation of valuable bio-components applicable to the generation of high value added bioproducts. One such bioproduct is microfibrillated cellulose (MFC), a biopolymer that stands out for its desirable mechanical properties and biocompatibility in biomedical, packing, 3D printing, and construction applications. In this study, we isolated microfibrillated cellulose (MFC) from cocoa pod husk (CPH) via oxalic acid hydrolysis combined with a steam explosion. MFC isolation started with the Solid/Liquid extraction via Soxhlet, followed by mild citric acid hydrolysis, diluted alkaline hydrolysis, and bleaching pre-treatments. A Response Surface Methodology (RSM) was used to optimize the hydrolysis reaction at levels between 110 and 125 °C, 30-90 min at 5-10% (w/v) oxalic acid concentration. The cellulose-rich fraction was characterized by Fourier-Transform Infrared Spectroscopy (FTIR), Thermogravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC), X-Ray Diffraction (XRD), and Scanning Electron Microscopy (SEM) analyses. Characterization analyses revealed a cellulose-rich polymer with fibers ranging from 6 to 10 μm, a maximum thermal degradation temperature of 350 °C, and a crystallinity index of 63.4% (peak height method) and 29.0% (amorphous subtraction method). The optimized hydrolysis conditions were 125 °C, 30 min, at 5% w/v oxalic acid: with a 75.7% yield. These results compare with MFC obtained through highly concentrated inorganic acid hydrolysis from different biomass sources. Thus, we show a reliable and greener alternative chemical treatment for the obtention of MFC.

Keywords: Biomass valorization; Cocoa pod husk; Design of experiments; Green hydrolysis; Microfibrillated cellulose.