Preparation and characterization of the bonding performance of a starch-based water resistance adhesive by Schiff base reaction

Facile fabrication of a starch-based wood adhesive showcasing water resistance, flame retardancy, and antibacterial properties via a dual crosslinking strategy

The demand for non-toxic, environmentally friendly, easily processable, water-resistant, flame-retardant and antimicrobial adhesives in the wood processing industry is becoming increasingly urgent. Few adhesives can possess these functions altogether while being synthesized easily. This paper presents a one-pot process utilizing corn starch, sodium hypochlorite, itaconic acid, and borax to synthesize a starch-based adhesive with dual crosslinking. Initial crosslinking takes place between the carboxyl groups of itaconic acid and hydroxyl groups on oxidized starch due to the formation of ester bonds. Secondary crosslinking by borate ester bonds occurs between starch hydroxyl groups and boric acid. The entire reaction process is environmentally benign, generating no waste, with all reactants converted into final products, aligning with "green" chemistry principles. When used to bond wooden boards, this adhesive achieved a dry shear strength of 5.34 ± 0.24 MPa, and a wet shear strength of 1.22 ± 0.06 MPa after soaking in water. Additionally, this starch-based adhesive exhibited antibacterial properties against Escherichia coli (ATCC 8739) and Staphylococcus aureus. Moreover, with borax incorporated, the adhesive demonstrated flame-retardancy. The limiting oxygen index for bonded wooden boards was 30.9 %, qualifying it as a flame-retardant material. These multiple functions render it promising for applications in the wood processing industry.

Preparation and properties of room temperature foaming lignin-based non-isocyanate polyurethane foams

The preparation and application of biomass-based non-isocyanate polyurethane (NIPU) is an essential and meaningful hot topic research work in the field of polyurethane industry, due to its advantages of sustainability of raw materials and no highly toxic isocyanate used in the synthesis. Lignin, as the second most renewable natural polymer on earth, was used in this paper to synthesize lignin-based non-isocyanate polyurethane (L-NIPU) resins. Subsequently, L-NIPU foams were prepared by self-foaming at room temperature with the addition of maleic acid as an initiator and glutaraldehyde as a cross-linker, and their properties were investigated. Results show that L-NIPU foams are lightweight (0.11-0.18 g/cm3), have low thermal conductivity (0.033-0.04 W/m·K), and have excellent compressive strength. When the addition of maleic acid and glutaraldehyde is respectively 18 % and 25 % (based on L-NIPU resin quality), the compressive strength can be as high as 0.5 MPa, and the thermal conductivity is only 0.03559 W/m·K, so it can be used as an insulating board in buildings. In addition, FT-IR and XPS analyses showed that maleic acid and glutaraldehyde can react with the amino group in L-NIPU to form a cross-linked network structure, which ensures the favorable mechanical properties of the foam.

Preparation of natural adhesives with high-strength and low temperature fast-curing properties

The development of natural adhesives to substitute petroleum-based products is crucial for sustainable progress. However, the bond strength of most existing natural adhesives still falls short of that of commercially available adhesives and the curing process often demands prolonged high-temperature treatment. Herein, we prepared pure natural adhesives using gelatin (GE), tung oil (TO), and dopamine (DA) as the main raw materials. The shear strength of the adhesive to wood reached up to 6.35 MPa, a significant improvement over most natural wood adhesives reported. Additionally, the tensile strength of the adhesive to wood reached 10.50 MPa, which is comparable to commercially available neoprene-phenolic wood adhesives (9.99 MPa) and cyanoacrylate instant adhesives (9.48 MPa). In addition, the natural adhesive prepared by us exhibits fast curing performance at room temperature and can be fully cured in only 12 min, which is significantly better than the commercially available adhesive. The adhesives prepared in this study also possessed excellent reversible curing properties, antimicrobial properties, low toxicity, and degradability. These characteristics offer new insights for the advancement and dissemination of natural adhesives.

Effect of different initiators on the properties of diacetone acrylamide grafted starch-based adhesive

Environmentally friendly and non-toxic bio-based adhesives are emerging as the most promising substitutes for petroleum-based adhesives, attracting increasing attention. This work involved the synthesis of a starch-based adhesive for particleboards by grafting diacetone acrylamide (DAAM) onto starch. The graft polymerization was initiated using three different initiators: ammonium persulfate (APS), hydrogen peroxide (H2O2)/ammonium ferrous sulfate system, and ceric ammonium nitrate (CAN). A comparative study was conducted to assess the varying effects of these initiators. The results showed that in the graft copolymerization of starch with DAAM, different initiators produced different types of free radicals, and CAN initiation produced alkyl radicals and long-chain alkyl radicals with a peak total spin value of 3.96 × 1015, and thus had the highest grafting efficiency and grafting rate of 72.59 % and 16.75 %, respectively. From the comparison of the total number of spins, it can be seen that CAN is more targeted for starch initiation. In addition, characterization results from Fourier transform infrared spectroscopy and confocal Raman spectroscopy showed that DAAM underwent a graft copolymerization reaction with starch. Notably, the adhesive initiated by CAN demonstrated the highest water resistance and mechanical strength, with an absorption thickness expansion and static bending strength of 8.52 % and 10.56 MPa, respectively.

Development of environmentally friendly glyoxal-based adhesives with outstanding water repellency utilizing wheat gluten protein

To reduce the release of volatile organic compounds (VOCs) from formaldehyde-based adhesives at the source, the use of low-toxicity and biodegradable glyoxal instead of formaldehyde for the preparation of novel urea-glyoxal resins is a simple and promising strategy. The limited water resistance and adhesive strength of the new urea-glyoxal resins (UG) restrict their extensive application. This study prepared a high-performance, water-resistant WP-UG wood adhesive by combining UG prepolymer with wheat gluten protein (WP). FTIR, XRD, and XPS confirmed the existence of a chemical reaction between the two components, and thermal analysis showed that WP-UG plywood had better thermal stability. Evaluation of the gluing properties revealed that the dry and wet strengths of WP-UG adhesive bonded plywood reached 1.39 and 0.87 MPa, respectively, which were significantly higher than those of UG resin by 35 % and 314 %. The bond strength increased from 0 to 0.89 MPa after immersion in water at 63 °C for 3 h. The results indicated that the introduction of WP promoted the formation of a more complex and tightly packed crosslinking network and developed a glyoxal-based adhesive with high bond strength and water resistance. This study provides a new green pathway for novel urea-formaldehyde binders to replace harmful formaldehyde-based binders, which helps to increase their potential application value in the wood industry.

Preparation and characterization on the eco-friendly corn starch based adhesive of with salient water resistance, mildew resistance

Starch adhesive is a commonly used bonding glue that is sustainable, formaldehyde-free and biodegradable. However, there are obviously some problems related to its high viscosity, poor water and mildew resistance. Hence, exploring a starch-based adhesive with good properties that satisfies the requirements of wood processing presents the context of the current research. Thus, corn starch was used as raw material to form oxidized starch (OCS) via oxidation using sodium periodate, it was reacted with a synthesis polyurea compound that prepared from hexanediamine-urea (HU) obtained by deamination to yield a oxidized starch-hexanediamine-urea adhesive (denoted hereafter as OCSHU). The oxidation process was optimized in terms of oxidant concentration, reaction time and temperature. Furthermore, the impact of HU addition on the mechanical properties of the adhesive was explored. Results indicate adhesive exhibited outstanding shear strength, when 13 % of NaIO4 was used as an oxidant to treat starch at 55 °C for 24 h, and involved in a subsequent reaction with 40 % of HU. The dry shear strength, 24 h cold water strength, 3 h hot water strength and 3 h boiling water strength are 1.84, 1.50, 1.32, and 1.31 MPa. Meantime, OCSHU adhesive solution revealed good storage stability whereas cured resin exhibited mildew resistance. The developed adhesive is a simple and green biomass wood adhesive.

Synthesis of carbon dot based Schiff bases and selective anticancer activity in glioma cells

Schiff bases have remarkable anticancer activity and are used for glioma therapy. However, the poor water solubility/dispersibility limits their therapeutic potential in biological systems. To address this issue, carbon dots (CDs) have been utilized to enhance the dispersibility in water and biological efficacy of Schiff bases. The amino groups on the surface of CDs were conjugated effectively with the aldehyde group of terephthalaldehyde to form novel CD-based Schiff bases (CDSBs). The results of the MTT assays demonstrate that CDSBs have significant anticancer activity in glioma GL261 cells and U251 cells, with IC50 values of 17.9 μg mL-1 and 14.9 μg mL-1, respectively. CDSBs have also been found to have good biocompatibility with normal glial cells. The production of reactive oxygen species (ROS) in GL261 glioma cells showed that CDSBs, at a concentration of 44 μg mL-1, resulted in approximately 13 times higher intracellular ROS production than in the control group. These experiments offer evidence that CDSBs induce mitochondrial damage, leading to a reduction in mitochondrial membrane potential in GL261 cells. In particular, in this work, CDs serve not as carriers, but as an integral part of the anticancer drugs, which can expand the role of CDs in cancer treatment.

Boiling water resistant fully bio-based adhesive made from maleated chitosan and glucose with excellent performance

Biomass resources are widely considered potential alternatives to formaldehyde-based wood adhesives because of their abundance. In this study, an environmentally friendly biomass adhesive, carboxylated chitosan-glucose (CSC-G), was prepared using chitosan, maleic anhydride, and glucose. The structure and water resistance of the adhesive were analyzed in detail. Maleic anhydride act as a bridge connecting chitosan and glucose, giving the adhesive good water solubility and resistance. The improved water resistance of the CSC-G adhesive was attributed to the formation of covalent cross-linked structures and an increased degree of system cross-linking. Additionally, the curing temperature of the CSC-G adhesive was superior to those of previously reported polyester adhesives. This study not only expands the application scope of fishery waste, but also demonstrates its great potential for the preparation of high-performance plywood.