Production and characterization of cellulose acetate using olive tree pruning biomass as feedstock

Abstract

Olive tree pruning (OTP) is one of the most abundant sources of biomass waste in the Mediterranean basin. This is especially relevant in southern Spain where olive oil production represents a large part of the economy. Olive tree prunings are mostly either burned or are spread in olive orchards as an organic amendment, or used for heat generation on a domestic scale. However, the lignocellulosic composition of OTP makes it a potential source of biopolymers, thus providing an excellent economic alternative for the olive oil sector. In this work, pretreated OTP fibers were subjected to an optimized alkaline treatment followed by a single‐step bleaching reaction with H2O2. Afterwards, the cellulose pulp was transformed chemically to obtain cellulose acetate. Noncellulosic components were removed effectively from OTP, thus obtaining a pulp highly purified in cellulose with 71% crystallinity and 355 °C maximum degradation temperature. Nevertheless, a very large amount of cellulose (ca. 50%) was eliminated throughout the process, especially during acid pretreatment, which was responsible for 38% solubilization. A similar level of acetylation and degree of substitution was obtained by using acetylation times in the range of 1 to 6 h. No large differences were observed in the infrared spectra and X‐ray diffractograms of the synthesized acetates. However, their thermal stability varied significantly with reaction time, evolving from a multistep degradation pattern to a single and sharp peak between 300 and 400 °C with increasing time. Thermogravimetric curves revealed that at least 5 h (preferably 6 h) were needed to obtain cellulose acetate from OTP with adequate thermal stability for further processing.

Characterization of Cellulosic Pulps Isolated from Two Widespread Agricultural Wastes: Cotton and Sunflower Stalks

“…However, it should also consider the contribution of other volatiles different from water, such as low-molecular weight compounds and extractives [ 31 , 44 ]. This is consistent with the fact that untreated CS and SFS exhibited higher initial weight loss than their corresponding cellulose counterparts, as found previously [ 34 ], since the extractives and low-molecular-weight compounds are removed with the chemical treatment. Following this initial loss, rapid decomposition of both untreated and bleached fibers occurred up to approximately 400 °C.…”

“…Yield WHOLE , calculated as in Equation ( 4), were 20.1% and 32.0% for CS and SFS wastes, respectively, with the major contribution of acid pre-treatment, especially for CS, followed by alkaline hydrolysis (yields 75.5% for CS-BH and 70.2% for SFS-BH) and bleaching, which reached yields of about 90% for both CS-BL and SFS-BL fibers. Similar results were found for the extraction of cellulose from other widespread lignocellulosic wastes such as sugarcane straw [41], brewer's spent grains [33], or olive tree pruning [34].…”

“…The effect of either t , T, or c on the response variables is reflected in the linear, quadratic, and interactive coefficients of the model equations. Regarding CS (Equations (8)–(10)), the analysis of these coefficients showed that the three linear terms contributed to enhanced hydrolysis of hemicellulose and lignin, but also that T and c affected cellulose solubilization as expected [ 32 , 34 ]. These effects were more pronounced for T and especially c , thus confirming the lower influence of reaction time on the hydrolysis of lignocellulosic biomass found in other studies [ 32 , 40 ].…”

“…The extraction of cellulose from CS and SFS fibers was conducted by a chemical procedure based on our previous works with other lignocellulosic residues [ 32 , 33 , 34 ] consisting of an acid pre-treatment (AH), followed by alkaline hydrolysis (BH) and a bleaching reaction (BL). As described below, the experimental conditions for the acid pre-treatment were optimized to maximize the removal of non-cellulosic compounds [ 32 ].…”