All-lignocellulosic Fiberboard from Steam Exploded Arundo Donax L

Extraction and Depolymerization of Lignin from Different Agricultural and Forestry Wastes to Obtain Building Blocks in a Circular Economy Framework

Large amounts of agri-food waste are generated and discarded annually, but they have the potential to become highly profitable sources of value-added compounds. Many of these are lignin-rich residues. Lignin, one of the most abundant biopolymers in nature, offers numerous possibilities as a raw material or renewable resource for the production of chemical products. This study aims to explore the potential revalorization of agricultural by-products through the extraction of lignin and subsequent depolymerization. Different residues were studied; river cane, rice husks, broccoli stems, wheat straw, and olive stone are investigated (all local wastes that are typically incinerated). Traditional soda extraction, enhanced by ultrasound, is applied, comparing two different sonication methods. The extraction yields from different residues were as follows: river cane (28.21%), rice husks (24.27%), broccoli (6.48%), wheat straw (17.66%), and olive stones (24.29%). Once lignin is extracted, depolymerization is performed by three different methods: high-pressure reactor, ultrasound-assisted solvent depolymerization, and microwave solvolysis. As a result, a new microwave depolymerization method has been developed and patented, using for the first time graphene nanoplatelets (GNPs) as new promising carbonaceous catalyst, achieving a 90.89% depolymerization rate of river cane lignin and yielding several building blocks, including guaiacol, vanillin, ferulic acid, or acetovanillone.

Approaching Self-Bonded Medium Density Fiberboards Made by Mixing Steam Exploded Arundo donax L. and Wood Fibers: A Comparison with pMDI-Bonded Fiberboards on the Primary Properties of the Boards

This study presents an unexplored method to produce formaldehyde-free MDF. Steam exploded Arundo donax L. (STEX-AD) and untreated wood fibers (WF) were mixed at different mixing rates (0/100, 50/50, and 100/0, respectively) and two series of boards were manufactured, with 4 wt% of pMDI, based on dry fibers, and self-bonded. The mechanical and physical performance of the boards was analyzed as a function of the adhesive content and the density. The mechanical performance and dimensional stability were determined by following European standards. The material formulation and the density of the boards had a significant effect on both mechanical and physical properties. The boards made solely of STEX-AD were comparable to those made with pMDI, while the panels made of WF without adhesive were those that performed the worst. The STEX-AD showed the ability to reduce the TS for both pMDI-bonded and self-bonded boards, although leading to a high WA and a higher short-term absorption for the latter. The results presented show the feasibility of using STEX-AD in the manufacturing of self-bonded MDF and the improvement of dimensional stability. Nonetheless, further studies are needed especially to address the enhancement of the internal bond (IB).

Optimization of the Production Factors of Boards Obtained from Arundo donax L. Fibers Without Added Adhesives

The main objective of this work was to further analyze the optimization of the production factors of Arundo donax L. fiberboards obtained without adhesives. The production of boards derived from Arundo donax L. without added adhesives and with high mechanical performance has already been demonstrated. This present study explored a modification in the production process through a final curing thermal treatment (final heat treatment, FHT). Since pressing time is an influential factor in the production cost, it is expected that curing allows a reduction of this time. This study compared the results obtained by three panel-production alternatives: long pressing time (tp) without curing and long and short tp with FHT. Of the two factors analyzed, pressing pressure (Pp) was the most important production factor in both the modulus of elasticity (MOE) and modulus of rupture (MOR), while curing was the most important factor for the internal bond (IB). The study shows that a FHT facilitates the distribution of lignin and a possible improvement in the quantity and quality of bonds between lignin and cellulosic fibers. As a consequence, it improves the IB, produces boards with more homogeneous physical and mechanical properties and thereby makes them more hydrophobic. The curing thermal treatment allows high performance panels to be obtained in a manner which is more ecological, quicker, and cheaper.

Effects of Heating Temperature on the Properties of Bio-Board Manufactured by Using Soybean Straw

The objective of this paper is to effectively use soybean straw biomass resources and decrease the negative effects of using synthetic resin. Soybean straw was ground through a wet process then hot-pressed to make biodegradable fiberboard (bio-board) without any binder. The effect of heating temperature on mechanical properties and dimensional stability performance of produced bio-board was investigated. Bonding quality and chemical changes of the bio-board were also evaluated using scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy. The moisture content decreased from 12.5% to 3.4% with the increase of heating temperature. Meanwhile, most mechanical properties of bio-board improved. However, an excessive heating temperature, especially at 230 °C, did not significantly promote the improvement of most mechanical properties. However, the dimensional stability performance of the bio-board was greatly improved from 140 °C to 230 °C. Overall, the results showed that bio-board could be made by using soybean straw without any synthetic resin. Heating temperature plays a significant role in affecting the properties of bio-board. The refined bio-board is expected to be used as a packaging material, heat insulation in architecture, and mulch film for agricultural purposes.

Rice Husk Hydrolytic Lignin Transformation in Carbonization Process

Lignin processing products have an extensive using range. Because products properties depend on lignin precursor quality it was interesting to study lignin isolated from rice husk being a large tonnage waste of rice production and its structural transformations during carbonization. Lignin isolated by the thermal hydrolysis method with H₂SO₄ 1 wt % solution and its carbonized products prepared under different carbonization conditions were characterized using elemental analysis, IR, TPD-MS, XRD, TEM, and EPR. It was shown lignin degradation takes place over the wide (220–520 °C) temperature range. Silica presenting in lignin affects the thermal destruction of this polymer. Due to the strong chemical bond with phenolic hydroxylic group it decreases an evaporation of volatile compounds and as a result increases the temperature range of the lignin degradation. Rice husk hydrolytic lignin transformations during carbonization occur with generation of free radicals. Their concentration is decreased after condensation of aromatic rings with carbon polycycles formation, i.e., the graphite-like structure. Quantity and X-ray diffraction characteristics of the graphite-like phase depend on carbonization conditions. Morphology of the lignin-based carbonized products is represented by carbon fibers, carbon and silica nanoparticles, and together with another structure characteristics provides prospective performance properties of lignin-based end products.