Effects of Hydrolysis and Bleaching Conditions on the Efficiency of Cellulose Microribbons Extraction from Coffee Parchment Through a Design of Experiments

Abstract

Cellulose microribbons were isolated from coffee parchment through acid hydrolysis, alkaline hydrolysis, and bleaching. Factorial design experiments allowed studying the influence of the chemical precursor concentrations and reaction times on the mass losses. TGA, SEM, XRD, and FT-IR techniques allowed characterized the coffee parchment hydrolyzed and bleached. Obtained results suggest that after acid hydrolysis, hemicellulose was the main fraction released from the coffee parchment, and after alkaline hydrolysis, lignin. Lignocellulosic compound dissolution produces a reduction/disappearance of some vibrational bands. This dissolution enhances the crystalline index and decreases the microrribons diameter. However, in coffee parchment, the microrribons are twisted giving the appearance of fibers with a minor diameter. The design of the experiment results suggests that the main factors during acid and alkaline hydrolysis are the concentration of the chemical precursors. In the bleaching process, a variation in the factors does not significantly influence the response variable. However, for brightness, the precursor concentration affects the cellulose quality. The optimal conditions for cellulose extraction from coffee parchment are 5% (v/v) of HNO3 by 2 h, 3%(m/v) NaOH by 1 h, and a 1:1 ratio of NaClO: CH3COOH by 45 min for bleaching.