Chemical, Thermal and Antioxidant Properties of Lignins Solubilized during Soda/AQ Pulping of Orange and Olive Tree Pruning Residues

Abstract

Some agroforestry residues such as orange and olive tree pruning have been extensively evaluated for their valorization due to its high carbohydrates content. However, lignin-enriched residues generated during carbohydrates valorization are normally incinerated to produce energy. In order to find alternative high added-value applications for these lignins, a depth characterization of them is required. In this study, lignins isolated from the black liquors produced during soda/anthraquinone (soda/AQ) pulping of orange and olive tree pruning residues were analyzed by analytical standard methods and Fourier-transform infrared spectroscopy (FTIR), nuclear magnetic resonance (solid state 13C NMR and 2D NMR) and size exclusion chromatography (SEC). Thermal analysis (thermogravimetric analysis (TGA), differential scanning calorimetry (DSC)) and antioxidant capacity (Trolox equivalent antioxidant capacity) were also evaluated. Both lignins showed a high OH phenolic content as consequence of a wide breakdown of β-aryl ether linkages. This extensive degradation yielded lignins with low molecular weights and polydispersity values. Moreover, both lignins exhibited an enrichment of syringyl units together with different native as well as soda/AQ lignin derived units. Based on these chemical properties, orange and olive lignins showed relatively high thermal stability and good antioxidant activities. These results make them potential additives to enhance the thermo-oxidation stability of synthetic polymers.

Solid-State Fermentation withStreptomycesas an Ecofriendly Route to Tune Lignin Properties and Its Use as a Binder in Adhesive Formulation

“…The spectra corresponding to the aliphatic-oxygenated (δ C /δ H 45.0–95.0/2.5–6.0 ppm) and the aromatic (δ C /δ H 90.0–150.0/5.0–8.0 ppm) regions are also displayed in Figure , for control and fermented barley substrates, and Figure , for control and fermented wheat substrates. The main 13 C– 1 H lignin correlation signals identified in HSQC spectra are shown in Table , assigned according to those described by different studies. − Some of the lignin substructures identified have been displayed in Figure . Furthermore, the quantification of the main lignin substructures and end groups (per 100 aromatic units) as well as the quantification of the aromatic units (molar percentage), p -coumaric acid and ferulic acid, and S/G ratios was performed from the integration of the volume contours of their correlation signals and included in Table .…”

Structural Characterization of the Milled-Wood Lignin Isolated from Sweet Orange Tree (Citrus sinensis) Pruning Residue

“…It is interesting to note that the molecular weight of the OTP-MWL was similar to that of the lignin derived from black liquors after soda/AQ cooking of OTP residue, which exhibited a M w /M n of 6430/4890 (M w /M n of 1.3). Since the lignin obtained from the black liquors after soda/AQ treatment has undergone significant degradation and structural alteration during the alkaline cooking process [11], this fact, therefore, indicates that the soda/AQ cooking process caused a repolymerization of the lignin degradation products.…”

“…This residue is a lignocellulosic material that has also been used for a variety of purposes, such as the production of biofuels and bioproducts, as a soil amendment, for the formation of pellets, and as sustainable reinforcement fibre for biopolyethylene, as well as for the manufacturing of pulp and paper [5][6][7][8][9][10]. However, due to their wide availability and low price, as well as their high lignin and carbohydrate contents, OTPs can be considered excellent candidates for use as feedstocks to produce biofuels and biomaterials in the context of the so-called lignocellulosic biorefineries [7,[11][12][13][14][15].…”

“…However, and despite the high amounts of OTPs available worldwide and their varieties of uses, there are no previous studies addressing the structure of the native lignin in this lignocellulosic material. Only one previous work was published that reported the structural characteristics of the lignin obtained from the black liquors produced after soda/anthraquinone (soda/AQ) cooking of OTPs [11]. However, it is evident that the structure of the lignin in the black liquors was greatly modified during the cooking process and was no longer representative of the native lignin, so the structure of the native lignin of OTPs is still unknown.…”

Wood Waste from Fruit Trees: Biomolecules and Their Applications in Agri-Food Industry

“…A recent study of Italian orange orchards reported that annual pruning generates approximately 1.8 tons of wood biomass/ha, which agrees with the Spanish data [ 149 ]. Eugenio et al [ 150 ] stated that each year Spain generates 2.25 MT of orange tree pruning residues overall, while González et al [ 151 ] estimate that this Iberian country produces 5 MT of orange wood waste. In this sense, as orange production represents 58% of the citrus production, the pruning from citrus fruit in Spain can be estimated at between 4 and 9 MT per year.…”