Alkaline Treatment Research Articles

The hemp-reinforced polypropylene composite: Effect of the alkaline and coupling agents treatment

The hemp-reinforced polypropylene composite was produced by the twin-screw extrusion in the presence of polypropylene-graft-maleic anhydride (PP-g-MA) and silane as coupling agents and subsequence by the compression molding. The hemp fiber was obtained by sodium hydroxide treatment prior to the twin-screw extruder. The PP/Hemp composite was analyzed using a universal testing machine, scanning electron microscope, differential scanning calorimetry, X-ray diffraction, and Fourier transform infrared spectroscopy. The mechanical properties of the PP/MA/Hemp demonstrated a better result than that of PP/Si/Hemp in most hemp contents. The SEM images of the PP/MA/Hemp exhibited excellent interfacial bonding in PP/MA/Hemp30 without fiber pullouts. However, the fiber breakage and some fiber pullout with gaps around the fiber of PP/Si/Hemp indicate the poor bonding of the PP matrix. The functional group of the PP/Hemp composite showed the –OH cellulose result peak of the reaction between hemp fibers and polypropylene.

Characterization Electrospun Nanofibers Based on Cellulose Triacetate Synthesized from Licorice Root Cellulose

Cellulose triacetate (CTA) nanofibers were formed by electrospinning using two binary solvent systems: methylene chloride/ethanol and chloroform/acetone. Previously, licorice root cellulose (LRC) with a degree of polymerization (DP) of 710 was extracted from licorice root waste by alkaline treatment and hydrogen peroxide bleaching at high temperatures. Then CTA with a degree of substitution (DS) of 2.9 and an average molecular weight of 175 kDa was synthesized from LRC using acetic acid and acetic anhydride, sulfuric acid was as a catalyst. The influence of the electrospinning process and various solvent systems on the morphology and structure of nanofibers is studied. The structure and morphology of the nanofibers were characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction, scanning electron microscopy (SEM), thermal gravimetric analysis (TGA), and the sorption characteristics were also investigated. The results showed that the morphology and structure of nanofibers depended on the solvent mixture used. The average diameters of the CTA nanofibers with grooved morphology varied 200-700 nm (solvent methylene chloride/ethanol) and the dumbbell-shaped (flat ribbon) CTA nanofibers in a wide range from 200 nm to 4 mkm (solvent chloroform/acetone).

Alkaline treatment and fractionation of OCC for strength improvement

Abstract The main drawback of recycled fibers is the deterioration of fiber bonding dependent papermaking properties (like tensile, tear and burst indexes) due to the hornification effect, as a results of drying during papermaking. In order to improve the papermaking properties through increasing fiber bonding, an alkaline treatment of Old Corrugated Cardboard (OCC) followed by fractionation were carried out in this investigation. Alkaline treatment dissolved 6.6 % organics (carbohydrates and lignin) and fibers became wider as a results of fiber swelling. The alkali treatment decreased fines from 39.9 % to 28.5 %, consequently, decreased drainage resistance from 26 °SR to 21 °SR. The papermaking properties of OCC pulp increased on alkaline treatment. Fiber fractionation of alkaline treated OCC further increased papermaking properties. At 40 °SR value, the tensile index, burst index and tear index of alkaline treated longer fiber fraction was 49 N m/g, 3.2 kPa m2/g, 7.2 mN m2/g, respectively while it was 40.4 N m/g, 2.1 kPa m2/g and 6.1 kPa m2/g, for non-treated longer fiber fraction, respectively.

Revealing spatial distribution and accessibility of cell wall polymers in bamboo through chemical imaging and mild chemical treatments

Understanding the distribution and accessibility of polymers within plant cell walls is crucial for addressing biomass recalcitrance in lignocellulosic materials. In this work, Imaging Fourier Transform Infrared (FTIR) and Raman spectroscopy, coupled with targeted chemical treatments, were employed to investigate cell wall polymer distribution in two bamboo species at both tissue and cell wall levels. Tissue-level Imaging FTIR revealed significant disparities in the distribution and chemical activity of cell wall polymers between the fibrous sheath and fibrous strand. At the cell wall level, Imaging Raman spectroscopy delineated a distinct difference between the secondary wall and intercellular layer, with the latter containing higher levels of lignin, hydroxycinnamic acid (HCA), and xylan, and lower cellulose. Mild acidified sodium chlorite treatment led to partial removal of lignin, HCA, and xylan from the intercellular layer, albeit to a lesser extent than alkaline treatment, indicating susceptibility of these polymers to chemical treatment. In contrast, lignin in the secondary wall exhibited limited reactivity to acidified sodium chlorite but was slightly removed by alkaline treatment, suggesting stable chemical properties with slight alkaline intolerance. These findings provide valuable insights into the inherent design mechanism of plant cells and their efficient utilization.

Ultrasound-Assisted Alkaline Pretreatment of Biomass to Enhance the Extraction Yield of Valuable Chemicals

As a renewable and sustainable resource, lignocellulosic biomass serves as a crucial raw material for the production of biofuels, biochemicals, and various value-added products. This paper aims to develop and optimize a mild alkaline treatment of sawdust assisted by ultrasound, along with enzymatic hydrolysis of the pretreated material. The alkaline sonochemical pretreatment emerged as the optimal approach to enhance the susceptibility of cellulose to subsequent enzymatic hydrolysis to improve the yield of reducing sugars. A comparative study was performed using various ultrasonic applicators (horn and bath) and conventional assisted alkaline pretreatment. The ultrasonic-assisted pretreatment revealed a higher delignification of 68% (horn) and 57% (bath) compared with conventional pretreatment. Processes were optimized using a statistical analysis based on a 23 factorial design. The ratios between sawdust and alkaline solution (RSL = 0.5–1.5 g/100 mL), US amplitude (A = 20–60%), and working temperature (t = 30–50 °C) were selected as process factors. The optimal operating conditions to maximize the reducing sugar yield (138.15 mg GE/gsubstrate) were found as follows: a solid/liquid ratio of RSL,opt = 1.25 g/100 mL, US amplitude of Aopt = 60%, and pretreatment temperature of topt = 50 °C. The overall outcomes clearly confirmed the intensification of delignification by ultrasound-assisted alkaline pretreatment.

Structural characteristics of organics released from sludge pretreatment and their performance in the synthesis of biomass plastics

The conversion of organics from sludge into high-value added products is essential for achieving circular economy and sustainable development in wastewater treatment processes. Currently, research focuses on promoting the release of organics from sludge, but there is a lack of in-depth understanding of the properties and structures of the released organics. To find out a suitable sludge pretreatment method (ultrasound, alkaline, thermal, ultrasound-alkaline, alkaline-thermal hydrolysis) for biodegradable plastic synthesis, the composition, properties and structures of the released organics from sludge were studied. Alkaline treatment (pH 12) resulted in the highest surface charge with Zeta potential of –23.53 mV. The release concentration and the radius of rotation (17.79 nm) of proteins were maximized after pH 12 + 150 °C pretreatment. Ultrasound treatment disrupted the extracellular polymeric substances of sludge, releasing organics with the highest thermal stability and hydrophobicity indices (20,313). Simultaneously, β-sheets was the main secondary structure of proteins. Random coils were the main proteins secondary structure after the other pretreatments instead. Meanwhile, small-angle scattering calculations showed that the released proteins tended to be discoidal for all pretreatment methods. In addition to proteins, polysaccharides, and humic acids, small organic compounds were also produced, such as amino acids (D-alanine), aromatic compounds (pyridine), alcohols, sugars (pyranose), fatty acids (oleic and palmitic), small molecule acids (acetic), etc. Furthermore, pretreatment with pH 12 + 150 °C was more efficient for the whole process of sludge synthesis into plastics. Correlation analysis shows that the radius of rotation of proteins is the main factor affecting the tensile strength and elongation at break of synthetic plastics. This study conducted an in-depth analysis of the structure and properties of organics after different pretreatments and provided a new pathway for the resource utilization of sludge through the synthesis of plastics using sludge organics.

Enhancing the Electrochemical Performance of ZnO-Co3O4 and Zn-Co-O Supercapacitor Electrodes Due to the In Situ Electrochemical Etching Process and the Formation of Co3O4 Nanoparticles

Zinc oxide (ZnO) and materials based on it are often used to create battery-type supercapacitor electrodes and are considered as promising materials for hybrid asymmetric supercapacitors. However, when creating such electrodes, it is necessary to take into account the instability and degradation of zinc oxide in aggressive environments with a non-neutral pH. To the best of our knowledge, studies of the changes in the properties of ZnO-containing electrodes in alkaline electrolytes have not been carried out. In this work, changes in the structure and properties of these electrodes under alkaline treatment were investigated using the example of ZnO-containing composites, which are often used for the manufacturing of supercapacitor electrodes. Supercapacitor electrodes made of two materials containing ZnO were studied: (i) a heterogeneous ZnO-Co3O4 system, and (ii) a hexagonal h-Zn-Co-O solid solution. A comparison was made between the structure and properties of these materials before and after in situ electrochemical oxidation in the process of measuring cyclic voltammetry and galvanostatic charge/discharge. It has been shown that the structure of both nanoparticles of the heterogeneous ZnO-Co3O4 system and the h-Zn-Co-O solid solution changes due to the dissolution of ZnO in the alkaline electrolyte 3.5 M KOH, with the short-term alkaline treatment producing cobalt and zinc hydroxides, and long-term exposure leading to electrochemical cyclic oxidation–reduction, forming cobalt oxide Co3O4. Since the resulting cobalt oxide nanoparticles are immobilized in the electrode structure, a considerable specific capacity of 446 F g−1 or 74.4 mA h g−1 is achieved at a mass loading of 0.0105 g. The fabricated hybrid capacitor showed a good electrochemical performance, with a series resistance of 0.2 Ohm and a capacitance retention of 87% after 10,000 cycles.

Production and characterization of sustainable biocompatible PLA/walnut shell composite materials

AbstractVarious treatments, such as alkaline and silane treatments, are commonly applied to natural fillers before production to enhance their quality, thermal stability, and water absorption capacity and improve the fiber–matrix interface properties. However, these processes are not environmentally friendly and may escalate the production cost of composites due to the need for additional processing steps in mass production. This study delves into the impact of untreated walnut shell (WS) filler material, employed in varying ratios (ranging from 10 to 40%) as a filler, on the mechanical, thermal, morphological, and physical properties of environmentally friendly polylactic acid (PLA) matrix composites. The experimental results highlight a significant decrease in tensile modulus by 28%, tensile strength ranging from 32 to 65%, a decrease in flexural modulus by 22%, and flexural strength ranging from 24 to 58% with varying WS filler ratios. Time-dependent water absorption and increased density were observed. FT-IR analysis indicates structural similarities, while DSC results show minimal effects on glass transition temperature and crystallinity. TGA results reveal reduced thermal stability with increasing WS content. SEM microstructure imaging demonstrates homogeneous WS particle distribution, but higher WS content leads to increased brittleness and diminished resistance properties. In conclusion, this study underscores the importance of balancing sustainability through WS filler ratios while preserving mechanical performance.

Valorisation of cotton post-industrial textile waste into lactic acid: chemo-mechanical pretreatment, separate hydrolysis and fermentation using engineered yeast

BackgroundThe textile industry has several negative impacts, mainly because it is based on a linear business model that depletes natural resources and produces excessive amounts of waste. Globally, about 75% of textile waste is disposed of in landfills and only 25% is reused or recycled, while less than 1% is recycled back into new garments. In this study, we explored the valorisation of cotton fabric waste from an apparel textile manufacturing company as valuable biomass to produce lactic acid, a versatile chemical building block.ResultsPost-industrial cotton patches were pre-treated with the aim of developing a methodology applicable to the industrial site involved. First, a mechanical shredding machine reduced the fabric into individual fibres of maximum 35 mm in length. Afterwards, an alkaline treatment was performed, using NaOH at different concentrations, including a 16% (w/v) NaOH enriched waste stream from the mercerisation of cotton fabrics. The combination of chemo-mechanical pre-treatment and enzymatic hydrolysis led to the maximum recovery yield of 90.46 ± 3.46%, corresponding to 74.96 ± 2.76 g/L of glucose released, which represents a novel valorisation of two different side products (NaOH enriched wastewater and cotton textile waste) of the textile industry. The Saccharomyces cerevisiae strain CEN.PK m850, engineered for redirecting the natural alcoholic fermentation towards a homolactic fermentation, was then used to valorise the glucose-enriched hydrolysate into lactic acid. Overall, the process produced 53.04 g/L ± 0.34 of l-lactic acid, with a yield of 82.7%, being the first example of second-generation biomass valorised with this yeast strain, to the best of our knowledge. Remarkably, the fermentation performances were comparable with the ones obtained in the control medium.ConclusionThis study validates the exploitation of cotton post–industrial waste as a possible feedstock for the production of commodity chemicals in microbial cell-based biorefineries. The presented strategy demonstrates the possibility of implementing a circular bioeconomy approach in manufacturing textile industries.Graphical

Modification of hordein by gallic acid in ethanol-free environments: Impact of covalent and non-covalent interactions on structure, physicochemical properties and self-assembly

The objectives of this study were to modify hordein with gallic acid (GA) in alcohol-free media and to compare the impact of covalent and non-covalent binding on the properties of hordein. Covalent hordein-GA complexes (H-GA) and non-covalent hordein/GA complexes (H/GA) were distinguished by molecular weight, free sulfhydryl groups and free amino groups. Isothermal titration calorimetry (ITC) demonstrated that physical mixing induced non-covalent binding of GA to hordein via hydrogen bonding and hydrophobic interactions, with a lower binding efficiency than covalent ones. Both complexation types led to a structural shift of hordein toward disorder, while grafting of oligomeric GA and alkaline treatment resulted in lower surface hydrophobicity and higher antioxidant activity of H-GA compared to H/GA. The nanoparticles assembled from H-GA had smaller particle sizes and higher physical stability than those formed from H/GA. The results of this study may provide new insights into the modification of hordein by polyphenols.

Assessment of mechanical and physicochemical properties of palm fiber composites: Effect of alkaline treatment and volume alterations

This study assesses the impact of alkaline treatments and volume fractions on biocomposites composed of a high-density polyethylene (HDPE) matrix reinforced with date palm tree fibers (FPDS). Tensile tests were conducted on both untreated and NaOH-treated biocomposites. Additionally, fiber analysis was performed using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results reveal higher strength and stiffness compared to HDPE, albeit with limited plasticity making the material brittle. The NaOH treatment enhances certain mechanical properties. Further assessments encompassed hardness, density, melt index, and Izod impact tests. Two volume fractions, 20% and 25%, of FPDS were tested. The study establishes a correlation between empirical predictions and artificial neural network (ANN) models. Notably, an ANN architecture consisting of two input factors, 10 hidden nodes, and one output provides the analysis of mechanical properties. This investigation highlights the potential of FPDS-reinforced HDPE biocomposites, emphasizing their mechanical performance under various treatments and fiber levels.

Performance of Flax/Epoxy Composites Made from Fabrics of Different Structures

Flax fibers have been shown to have comparable mechanical properties to some conventional synthetic fibers. Flax fabrics with different textile structures show differences in resistance against mechanical loads mainly rooted in fabric orientation and the resultant resin impregnation. Thus, in this study, flax fabrics with three different textile structures, fine twill weave, coarse twill weave and unidirectional, were used as reinforcements in an epoxy matrix. The surfaces of the fabrics were chemically treated using an alkaline treatment, and the alterations in fabric crystallinity index (CrI) were determined using X-ray diffraction (XRD). Experimental results confirmed that textile structures and CrI had significant effects on the mechanical properties of composites. Although an increment in CrI, resulting from chemical treatment, always enhanced tensile and flexural properties, it adversely affected damage development once composites were exposed to impact load. In terms of textile structures, unidirectional fabric outperformed woven fabrics in tensile and flexural properties while in impact properties, the latter had a better performance inducing less damage development. Finally, the mechanism of damage development in different composites was discussed in detail using Scanning Electron Microscopy (SEM) images. It is envisaged that the results of this study will provide an insight that will lead to the proper choice of the optimal kind of flax fabric for different applications.

Development of Polylactic Acid Films with Alkali- and Acetylation-Treated Flax and Hemp Fillers via Solution Casting Technique.

This study aims to enhance value addition to agricultural byproducts to produce composites by the solution casting technique. It is well known that PLA is moisture-sensitive and deforms at high temperatures, which limits its use in some applications. When blending with plant-based fibers, the weak point is the poor filler-matrix interface. For this reason, surface modification was carried out on hemp and flax fibers via acetylation and alkaline treatments. The fibers were milled to obtain two particle sizes of <75 μm and 149-210 μm and were blended with poly (lactic) acid at different loadings (0, 2.5%, 5%, 10%, 20%, and 30%) to form a composite film The films were characterized for their spectroscopy, physical, and mechanical properties. All the film specimens showed C-O/O-H groups and the π-π interaction in untreated flax fillers showed lignin phenolic rings in the films. It was noticed that the maximum degradation temperature occurred at 362.5 °C. The highest WVPs for untreated, alkali-treated, and acetylation-treated composites were 20 × 10-7 g·m/m2 Pa·s (PLA/hemp30), 7.0 × 10-7 g·m/m2 Pa·s (PLA/hemp30), and 22 × 10-7 g·m/m2 Pa·s (PLA/hemp30), respectively. Increasing the filler content caused an increase in the color difference of the composite film compared with that of the neat PLA. Alkali-treated PLA/flax composites showed significant improvement in their tensile strength, elongation at break, and Young's modulus at a 2.5 or 5% filler loading. An increase in the filler loadings caused a significant increase in the moisture absorbed, whereas the water contact angle decreased with an increasing filler concentration. Flax- and hemp-induced PLA-based composite films with 5 wt.% loadings showed a more stable compromise in all the examined properties and are expected to provide unique industrial applications with satisfactory performance.

Optimization of microalgae protein extraction from Scenedesmus obliquus and investigating its functional properties

The objective of this work was to evaluate alkaline treatment with enzymatic approaches for the optimal extraction of proteins from Scenedesmus obliquus microalgae. The experiments were designed with an emphasis on the alkaline treatment period and the enzyme-to-substrate ratio utilizing response surface methodology (RSM) with central composite design (CCD). Higher enzyme concentrations led to better extraction rates and efficiency, according to the findings. Cellulase demonstrated extraction efficiencies between 16.88% and 21.42%, but the multi-enzyme complex had efficiencies ranging from 15.28% to 27.87%. With an extraction rate of 19.13%, alkaline treatment was less advantageous than enzymatic treatment due to its longer procedure. Microalgal proteins' functional characteristics were also looked at. These proteins demonstrated foaming capacity, oil absorption, and emulsification ability, making them suitable alternatives to animal proteins in food systems such as egg white and soybean. Although microalgal protein powder had lower foam capacity (20%), stability (25%), fat absorption capacity (124%), and emulsification ability compared to egg white powder, it still exhibited favorable functional properties, highlighting its potential for various food applications. Further enhancement of the functional properties can be achieved by optimizing the environmental conditions during extraction.

Development of zein-based complexes and conjugates with enhanced surface hydrophilicity: Structure, emulsifying, foaming, and antioxidant properties

Corn zein is an abundant and inexpensive source of plant proteins. However, it is a strongly hydrophobic molecule with poor water solubility, which limits its range of applications in the food and other industries. In this study, zein-EGCG-alginate ternary conjugates were prepared using an alkaline treatment combined with the Maillard reaction. The nature of the conjugates formed was characterized using a range of analytical methods, including SDS-PAGE, dynamic light scattering, particle electrophoresis, spectroscopy, calorimetry, and electron microscopy. Scanning and transmission electron microscopy showed that the particles in the dispersion of ternary complexes were larger and more irregularly shaped than those in the original protein dispersion. Spectroscopic analyses indicated alterations in the structure of the proteins caused by both the alkaline and Maillard reaction treatments. Ternary conjugates (zein-EGCG-SA) had better emulsification and foaming properties than single protein (zein) or binary conjugates (zein-EGCG). Moreover, the surface hydrophobicity of the ternary complexes was lower, while their thermal stability and antioxidant activity were higher. For instance, the DPPH and ABTS free radical scavenging activity of the ternary conjugates were enhanced to around 67% and 89%, respectively. The alkaline-Maillard treatment also greatly improved the water dispersibility of zein, reaching a solubility level close to 60%. This study may broaden the range of applications of zein as a functional ingredient in the food and other sectors.

Augmenting bamboo strength and thermal stability for sustainable construction

In modern timber structures, the prevalent use of metal fasteners for structural connections introduces concerns related to their high thermal conductivity, which can induce excessive charring of adjacent wood and compromise joints fire resistance. To address this, the exploration of high-strength bio-materials presents a promising alternative. In this study, an eco-friendly methodology was employed to augment the densification of bamboo, resulting in the creation of composite-modified bamboo without the use of organic thermosetting resin. Comprehensive investigations were conducted to evaluate its mechanical properties and high-temperature performance. Microscopic alterations were unveiled through Fourier Transform Infrared spectroscopy (FT-IR) and scanning electron microscopy, complementing each other in revealing substantial changes. The results of chemical constituents and FT-IR analyses corroborated the observed alterations. A noteworthy observation is that the modification of composite materials significantly increased modulus of elasticity, bending, and tensile strengths of bamboo, with a slight improvement in compressive strength. Additionally, it concurrently enhanced ductility. The thermal stability of composite-modified bamboo exhibited an initial increase followed by a subsequent decline over duration. The increased density induced by hot pressing facilitated the formation of a denser charring layer, effectively serving as a protective shield against external heat and oxygen. Consequently, this limited the degradation of bamboo constituents under high-temperature conditions. The optimal alkaline treatment duration for 9 mm thick bamboo was determined as 7 h based on the methodology established in this investigation.

Catalytic pyrolysis of high-density polyethylene (HDPE) over hierarchical ZSM-5 zeolites produced by microwave-assisted chelation-alkaline treatment

A new microwave (MW) assisted chelation-alkaline strategy was developed to produce hierarchical ZSM-5 zeolites (with external surface area of 203 m2/g) in minutes, leading to the formation of heterogeneous structure with a high-silica shell and aluminium-rich core (silicon-to-aluminium ratios of 49.2 and 37.6, respectively). The zeolites were assessed comparatively by catalytic pyrolysis of high-density polyethylene (HDPE). Compared to the mesoporous ZSM-5 zeolite prepared by the conventional alkaline treatment (via desilication by the NaOH aqueous solution), the hierarchical zeolite by the MW-assisted method showed comparable kinetics in catalytic pyrolysis of HDPE, but with the improved stability in the cyclic pyrolysis-regeneration tests. The improved stability could be due to the better-preserved structural integrity thanks to the relatively milder surface etching by the MW-assisted chelation dealumination method. In addition, compared to the parent ZSM-5, the product distribution of HDPE catalytic pyrolysis over the hierarchical ZSM-5 zeolite showed a higher portion of oil products (i.e., 12 wt% vs. 6.9 wt%) and an improved alkane-to-olefin ratio in the oil products (2.22 vs. 1.86, respectively) due to the reduced acidity and improved hydrogen transfer ability. The MW-assisted chelation-alkaline treatment could be a new strategy to regulate the trade-off between stability and activity of zeolites for catalytic applications.

Regulation of acid/basic properties of Zr-Beta zeolite for efficient conversion of furfural to furfuryl alcohol

Zr-Beta zeolites with different acid/basic properties were prepared by hydrothermal and post-synthesis methods and subsequent alkaline treatment. The acid/basic properties of Zr-Beta zeolites were characterized by FT-IR spectra of hydroxyl region and probe molecule adsorption (CD3CN, pyridine and CHCl3). The effects of the acid/basic properties of Zr-Beta zeolites on the conversion of furfural (FUR) to furfuryl alcohol (FAL) via Meerwein-Ponndorf-Verley reduction were investigated and discussed. The results indicate that both Brønsted acid sites, including strong and weak Brønsted acid sites, and Lewis acid sites are effective for conversion of FUR, but high yield of FAL can only be obtained over Zr-Beta with sole Lewis acid sites of framework Zr due to the further conversion of FAL to furfuryl ether, angelica lactone and levulinate ester over Brønsted acid sites. Therefore, Al-free Zr-Beta(h) synthesized in fluoride media is more active and selective than the post-synthesized counterpart. Alkali (earth) metal cations modified Zr-Beta(h) can further eliminate weak Brønsted acid sites of silanols and at the same time generate basic sites. Thus, the activity and selectivity of Zr-Beta(h) are further enhanced. 99.5 % of FAL yield was obtained over Na-Zr-Beta(h) with 99.8 % of FUR conversion at 120 °C for 4 h.

Application of Corn Straw, an Agro-Waste, to Remove Dyes in an Aqueous Medium, Producing Blue or Red Fibers

The contaminant dyes that, even at low concentrations, may cause a series of adverse effects in humans and animals, and their removal by adsorption methods using alternative adsorbents as natural fibers, are regarded as a research topic that has become increasingly relevant. In this study, corn straw (CS), an agro-industrial residue, was used to remove dyes. The samples were characterized by ATR-FTIR, SEM-EDS, zeta potential, diffuse spectra, and colorimetry, before and after dye removal. The analyses allowed us to differentiate the morphology of CS after the treatment’s fiber on the adsorbent surface. The zeta potential showed a negative surface charge, but the acidic or alkaline treatment affected the surface charge of the sample, influencing the adsorption of cationic or anionic dyes. Adsorption data presented an increased removal when alkaline treatment was applied for the methylene blue (MB; qmax = 16.7 mg g−1), and the acid treatment was more effective for the Congo red (CR; qmax = 2.13 mg g−1). After color stability tests, it was observed that the anionic dye CR was more easily desorbed due to the surface charge of the adsorbent. Due to the chemical treatment, corn straw proved to be a good sustainable adsorbent for removing anionic or cationic dyes from aqueous media, contributing directly to the objective of sustainable development (#6—drinking water and sanitation) and with SDG numbers 3, 11, 12, 14, and 17.

Modified rice husk as component in recyclable and biodegradable epoxy thermosets

Rice husk (RH), an abundant agricultural residue, was successfully chemically modified and used as a component in reprocessable and biodegradable epoxy thermosets. First, RH was subjected to alkaline treatment to increase the cellulose content followed by succinylation and curing with trimethylolpropane triglycidyl ether to form the thermoset films. The chemical structure of the different intermediates and thermosets was confirmed by Fourier transform infrared spectroscopy. The developed thermoset films had good solvent resistance against common organic solvents and good thermal stability as measured by thermogravimetry with peak temperatures of 347–387 ℃, char residues of 16–20% and limiting oxygen index values of 24–26%, respectively. The films could be thermally reprocessed by hot-pressing with excellent recovery of the mechanical properties (92–96% recovery of tensile stress). Furthermore, 80–84% biodegradation during 150 days under mesophilic home composting conditions was demonstrated by cumulative CO2 evolution. These results indicate promising potential for the developed RHs thermosets as replacements for petroleum-based plastics in e.g. packaging and agricultural applications.