Bio-based Adhesives Research Articles

Nanocellulose in Heterogeneous Water-Based Polymerization for Wood Adhesives

The interest in the development of biobased adhesives has increased due to environmental concerns. Moreover, as the production of engineered wood products (EWPs) is expected to grow, the wood adhesives market needs to transit toward formaldehyde-free products. Cellulose nanoparticles (CNPs) are a material with unique properties and advantages for producing hybrid materials as biobased wood adhesives. Besides their traditional use as reinforcing additives, CNPs can be incorporated at the beginning of the polymerization reaction to form in situ polymerized hybrid adhesives with better mechanical and physicochemical properties than the neat adhesive. Despite their outstanding characteristics, CNPs are still an emerging nanomaterial in the wood adhesive field, and the studies are incipient. This review explores the utilization of CNPs in heterogeneous polymerization for the production of polyvinyl acetate, polymeric isocyanates, waterborne polyurethane systems, and other waterborne polymer latexes. The main challenges are discussed, and some recommendations are set down for the manufacture of these novel hybrid nanocomposites.

Tough protein based adhesive reinforced by molecular spring strengthening strategy

It is of great importance but still a great challenge to develop bio-based environmental adhesives for industrial applications. In this study, inspired by the adhesion structure of lignin and spring mechanics, a new biomimetic strategy was proposed to prepare high bonding strength, formaldehyde-free and petroleum resource-independent adhesive from biomass. Through Schiff base and Michael addition reaction between the quinone of oxidized demethylated lignin (DL) and the amino and sulfhydryl groups of soybean protein isolate (SPI) with helix chain, SPI was grafted onto DL to form reinforcement structure and crosslinker with molecular spring structure (namely SDL). Cleavage of the disulfide bonds of keratin and introduction of SDL reconstituted a strong cohesive crosslinking network (KPT-SDL), in which the α-helical peptide chain in SDL was stretched and the intramolecular hydrogen bonds were broken under tensile force, thus achieving energy dissipation and significantly improving the shear strength and toughness of the keratin-based adhesives. The maximum wet strength of the wood-based panel prepared by KPT-SDL adhesive reached to 1.22 MPa, which was comparable to the level of industrial adhesives and 197.56% higher than the original keratin-based adhesive. In addition, KPT-SDL presented high adhesion to numerous types of substrates, including steel and ceramic. This study provided a green and effective biomimetic strategy for high value-added keratin to promote the development of strong and tough composites, which had a good value of frontier research and industrial development.

A Critical Review on Wood-Based Polymer Composites: Processing, Properties, and Prospects.

Waste recycling is one of the key aspects in current day studies to boost the country’s circular economy. Recycling wood from construction and demolished structures and combining it with plastics forms wood-polymer composites (WPC) which have a very wide scope of usage. Such recycled composites have very low environmental impact in terms of abiotic potential, global warming potential, and greenhouse potential. Processing of WPCs can be easily done with predetermined strength values that correspond to its end application. Yet, the usage of conventional polymer composite manufacturing techniques such as injection molding and extrusion has very limited scope. Many rheological characterization techniques are being followed to evaluate the influence of formulation and process parameters over the quality of final WPCs. It will be very much interesting to carry out a review on the material formulation of WPCs and additives used. Manufacturing of wood composites can also be made by using bio-based adhesives such as lignin, tannin, and so on. Nuances in complete replacement of synthetic adhesives as bio-based adhesives are also discussed by various researchers which can be done only by complete understanding of formulating factors of bio-based adhesives. Wood composites play a significant role in many non-structural and structural applications such as construction, floorings, windows, and door panels. The current review focuses on the processing of WPCs along with additives such as wood flour and various properties of WPCs such as mechanical, structural, and morphological properties. Applications of wood-based composites in various sectors such as automotive, marine, defense, and structural applications are also highlighted in this review.

Life-Cycle Analysis and Evaluation of Mechanical Properties of a Bio-Based Structural Adhesive

For this present paper, we performed a life-cycle analysis and an evaluation of the mechanical properties of an epichlorohydrin/cardanol adhesive in a neat and a nano-filled form. Six different potentials and the cost of the adhesives were derived and compared with those of a commercial epoxy resin. Overall, the neat adhesive was found to be more environmentally friendly and to have a lower production cost. However, the addition of carbon nanotubes increased both the environmental footprint and the cost. The evaluation with regards to the mechanical properties was performed through a comparison of bulk properties and joint properties with the respective average values of commonly used structural and nonstructural adhesives from the literature. It was found that for all properties except for the Young’s modulus the novel adhesive had values greater than the average values of the cosmetic adhesives and for most properties it had values close to the average values of the structural adhesives. Moreover, the presence of the carbon nanotubes enhanced the mechanical properties of the adhesive except for the tensile strength.

An overview of different types and potential of bio-based adhesives used for wood products

Bio-based adhesives have shown promise in the engineered wood products industry, and there is a substantial growth of research on bio-based bonding agents. Wood is a renewable resource, and most of the engineered wood products are synthetic adhesive-bonded composites and laminates. Environmental concerns exist for the use of adhesives made from fossil fuels lowering the bio-content of the bonded wood products. Bio-based adhesives are getting more attention since they are environmentally friendly green products without any adverse effects on the environment. However, there is a remaining challenge for the industry to make them more effective than synthetic ones in terms of their mechanical properties and long-term durability. These adhesives, with different components such as cellulose, proteins, lignins, and tannins are adhesives which exhibit great potential for the bonding of specially engineered wood products. The modification of bio-based adhesives with different dispersing agents and cross-linkers can improve their strength and water resistance properties to compete with synthetic adhesives. The blending of proteins and carbohydrates can yield good bio-adhesives with acceptable adhesive properties. All these improvements of bio-based adhesives help us move towards ‘sustainable’ products where clean synthesis, biomass and water-based processing are highly desirable. Based on studies conducted in recent decades, the objective of this article is to review the production processes of adhesives from different bio-resources, their necessary modification for improving properties and their utilization in the wood-based industries. Finding the research gaps would also help to hasten the research activities for applying these bio-based adhesives at the industrial scale.

A Review of Bio-Based Adhesives from Primary and Secondary Biomass for Wood Composite Applications

Abstract Today there is a great demand in the market of wood-based panels like medium density fibreboard (MDF), plywood and oriented strand board (OSB). These boards provide functionality in various industrial fields from building to furniture production. All are produced from timber and some type of binding resin, the most often used in Europe are phenol formaldehyde (FF), isocyanate (MDI) and melamine urea formaldehyde (MUF). These resins guarantee sturdiness of the material but are toxic to humans and makes recycling of the wood-based panels very difficult. There are attempts of wood-based panels industry to transition away from fossil-based adhesives. Various resins have been developed using lignin and tannin or protein. Soy based adhesive SOYAD™ has already reached the market, other soy protein-based adhesives are integrated into ultra-low formaldehyde emission particle boards like Nu green 2® and Transform™. This paper gives an overview on bio-based adhesives that are used or have the potential to be used for wood-based panel production.

Curing Kinetics of Tannin and Lignin Biobased Adhesives Determined by DSC and ABES

The curing process of two biobased adhesives: pine tanninhexamine (TH) and organosolv lignin non-isocyanate polyurethane (NIPU), suitable for interior nonstructural use, were compared with commercial urea-formaldehyde (UF) adhesive. Changes in chemical structure before and after the curing process were observed with Fouriertransform infrared spectroscopy (FTIR). The process of adhesive curing was monitored with differential scanning calorimetry (DSC) and the automated bonding evaluation system (ABES). Both DSC and ABES measurements confirmed UF as the fastest and NIPU as the slowest curing adhesive observed. Taking into account the ABES results, the optimal pressing parameters for the TH adhesive would be 4 min at 175°C, for the NIPU adhesive 7 min at 200°C and for the UF 1.5 min at 100°C. Strong linear correlation was observed between mechanical and chemical curing for the UF and NIPU adhesives, whereas lower correlation was observed for the TH adhesive. At all observed adhesives, the DSC measurements were underestimating the curing process determined by ABES in the first part and overestimating it at the end. The underestimation was the most evident with the TH adhesive and the less with the UF adhesive. When comparing the uncured and cured FTIR spectra of all three types of adhesives, a drastic decrease in the characteristic band of -OH groups at 3330–3400 cm−1 and an increase in the signal intensity at 2920 cm−1 of aliphatic -CH2-groups were observed. For the UF adhesive, the C=O stretching frequency has shifted from 1632 cm−1 for uncured to three different bands at 1766, 1701, and 1655 cm−1 for cured UF. The sharp band for phenolic alcohols at 1236 cm−1 of C–O stretch and hydroxyl O–H functional group at 1009 cm−1 and at 684 cm−1 of uncured TH adhesive diminished during curing, which indicates that a crosslinking reaction occurs via -OH groups. The peak of the C=O group of urethane bridges at 1697 cm−1 for uncured NIPU shifted to lower wavenumber at 1633 cm−1 for cured NIPU.

Manufacturing and Evaluation of Mechanical Properties for Rice Husk Particle Board Using IoT

In recent times, different types of particleboards are being preferred in the construction of houses, partitions, furnitureetc. The production of such materials can be manufactured using rice husk, which has been obtained as waste produced inrice millers. Adhesive such as formaldehyde, when exposed to fire, causes toxic flames which are fatal in nature. The basiccondition for production of particleboards is to check the temperature and humidity content in the rice husk which has beendone by using DHT 11 sensors i.e., application of Internet of Thing (IoT) erected method. This identification helps infinding the suitable temperature through which bio-based adhesives have been prepared. In present study, two differenttypes of bio-adhesives namely tamarind with formalin and tamarind with boric acid has been used in manufacturing process.The application of IoT erected method follows a complex preparation method but will partially fulfil the job and reduceshuman involvement. Finally, when the proper temperature and moisture level has been measured, the preparation becomeseasy. After manufacturing the particleboard, the strength has been tested by a three-point bend test and have been comparedwith commercially available boards with formaldehyde base adhesive.

Bio-based and bio-inspired adhesives from animals and plants for biomedical applications.

With the “many-headed” slime mold Physarum polycelphalum having been voted the unicellular organism of the year 2021 by the German Society of Protozoology, we are reminded that a large part of nature's huge variety of life forms is easily overlooked – both by the general public and researchers alike. Indeed, whereas several animals such as mussels or spiders have already inspired many scientists to create novel materials with glue-like properties, there is much more to discover in the flora and fauna. Here, we provide an overview of naturally occurring slimy substances with adhesive properties and categorize them in terms of the main chemical motifs that convey their stickiness, i.e., carbohydrate-, protein-, and glycoprotein-based biological glues. Furthermore, we highlight selected recent developments in the area of material design and functionalization that aim at making use of such biological compounds for novel applications in medicine – either by conjugating adhesive motifs found in nature to biological or synthetic macromolecules or by synthetically creating (multi-)functional materials, which combine adhesive properties with additional, problem-specific (and sometimes tunable) features.

Influence of the Macromolecular architecture on the properties of biobased polyurethane tissue adhesives

Polyurethanes (PU) have recently emerged as promising biomaterials for tissue adhesive applications. Compared to other tissue adhesives, they offer substantial advantages such as the possibility to tailor adhesive strengths and curing times, for instance. All these properties are directly affected by the composition and final architecture. In this work, biobased two-components PU sealants were prepared, based on (i) an isocyanate-terminated prepolymer and (ii) a chain extender. Here, an exhaustive evaluation of the oligoester-diols and chain extenders influence on the sealants properties has been performed. In order to bring controlled variations on the final macromolecular architectures, three different prepolymers were prepared: two are based on poly(3-hydroxybutyrate) diol oligomers and another one on poly(lactic acid) diol oligomers, with a 50/50 isocyanate molar ratio of hexamethylene diisocyanate and biobased dimeryl diisocyanate. To study the chain extenders influence, five different aliphatic and linear bifunctional molecules were assessed, with varying length and functional groups reactivity. Ultimately, PUs obtained after the two-component systems curing were also fully characterized. They exhibited an overall good biocompatibility around 80%, with limited cytotoxicity. A wide range of physico-chemical and mechanical properties were also obtained, evidencing the importance of the macromolecular architecture on the systems final properties.

Synthesis and characterization of novel eco-epoxy adhesives based on the modified tannic acid for self-healing joints

The aim of this research was to investigate the self-healing potential of damaged Al joints when bonded using novel eco-epoxide adhesives derived from tannic acid (TA). Two eco-epoxy components based on TA, (A) glycidyl ether and (B) glycidyl phosphate ester of TA, were produced. The effect of the eco-epoxy components on the self-healing ability was assessed in terms of the energy dissipation recovery after partial failure in a double cantilever beam (DCB) test, which was compared to the reference epoxy (R). The self-healing process required 2 h and 2 bars in an autoclave at 180 °C. Techniques such as DSC, FTIR and DMA showed residual activity and potential self-healing capability of the used adhesives. A combination of two monitoring techniques, Digital Image Correlation (DIC) and Acoustic Emission (AE), was used to monitor the strain distribution and damage propagation in the DCB specimens. The healing index for adhesives R, B and A was found to be 8.9%, 3.0%, and 82.5% respectively. The findings of this work highlighted the potential of using bio-based epoxy adhesives in structural adhesive bonding, as well as the prospect of utilizing their self-healing ability to restore the strength of such bonded parts.

Strong and recyclable soybean oil-based epoxy adhesives based on dynamic borate

Biobased and recyclable epoxy vitrimer adhesives (ESOBV) containing dynamic borate ester bonds were formulated from epoxidized soybean oil (ESO) and a dithiol borate ester curing agent (BDB) via a thermally-induced “thiol-epoxy” click reaction. The cross-linked ESOBV adhesives showed superior adhesion strength (3.84–9.61 MPa) on various substrates including steel, glass, wood, and bamboo plates. The reaction between the epoxy groups from ESO and the sulfhydryl groups from BDB generates a large number of hydroxyl groups, which could form hydrogen bonds with substrates. The cured ESOBV adhesives had high tensile strength (18.74–25.14 MPa) and superior thermal stability. The dynamic borate ester bonds in the network undergo topological rearrangement at evaluated temperature, enabling the ESOBV good reprocessability and reusability. The adhesives could be recycled via molecular rearrangement, and the recycled solid ESOBV had comparable lap-shear strength on substrates to the original liquid ESOBV. This study provides a simple method for preparing strong and recyclable vegetable oil-based adhesives.

Alkali-treated Wheat Gluten Cross-linked with Sodium Alginate as a Bio-based Wood Adhesive for Interior Grade Particleboard

Alkali-treated Wheat Gluten Cross-linked with Sodium Alginate as a Bio-based Wood Adhesive for Interior Grade Particleboard

Non-Formaldehyde, Bio-Based Adhesives for Use in Wood-Based Panel Manufacturing Industry-A Review.

There is a strong need to develop and implement appropriate alternatives to replace formaldehyde-based adhesive systems, such as phenol–formaldehyde, in the industry of wood-based panels (WBPs). This is due to the toxicity and volatility of formaldehyde and restrictions on its use associated with some formaldehyde-based adhesives. Additionally, the current pressure to reduce the dependence on polymeric materials, including adhesives, from petrochemical-based sources has led to increased interest in bio-based adhesives, which, in some cases, already provide acceptable properties to the end-product. Among the potential raw materials for good-quality, renewable-based adhesive formulations, this paper highlights tannins, lignin, and protein sources. However, regarding renewable sources, specific features must be considered, such as their lower reactivity than certain petrochemical-based sources and, therefore, higher production costs, resource availability issues, and the need for toxicological investigations on alternative systems, to compare them to conventional systems. As a result, further research is highly encouraged to develop viable formaldehyde-free adhesive systems based on renewable sources, either at the technical or economical level. Moreover, herein, we also showcase the present market of WBPs, highlighting the obstacles that the alternative and new bio-based adhesives must overcome.

Bio-Based Epoxy Adhesives with Lignin-Based Aromatic Monophenols Replacing Bisphenol A.

A bio-epoxy surface adhesive for adherence of the metal component species to glass substrate with desirable adhesion strength, converted controlled removal upon request, and bio-based resource inclusion was developed. For the development of resin, three different lignin-based aromatic monophenols, guaiacol, cresol, and vanillin, were used in the chemical epoxidation reaction with epichlorohydrin. The forming transformation process was studied by viscoelasticity, in situ FTIR monitoring, and Raman. Unlike other hydroxyl phenyls, guaiacol showed successful epoxide production, and stability at room temperature. Optimization of epoxide synthesis was conducted by varying NaOH concentration or reaction time. The obtained product was characterized by nuclear magnetic resonance and viscosity measurements. For the production of adhesive, environmentally problematic bisphenol A (BPA) epoxy was partially substituted with the environmentally acceptable, optimized guaiacol-based epoxy at 20, 50, and 80 wt.%. Mechanics, rheological properties, and the possibility of adhered phase de-application were assessed on the bio-substitutes and compared to commercially available polyepoxides or polyurethanes. Considering our aim, the sample composed of 80 wt.% bio-based epoxy/20 wt.% BPA thermoset was demonstrated to be the most suitable among those analyzed, as it was characterized by low BPA, desired boundary area and recoverability using a 10 wt.% acetic acid solution under ultrasound.

Development of Bio-based Polyurethane Wood Adhesives from Agroindustrial Waste

Development of Bio-based Polyurethane Wood Adhesives from Agroindustrial Waste

Influence of a hydrocarbon side chain on the performance of Physaria fendleri-Castor oil polyurethane packaging adhesives

Polyurethanes (PU) are an important class of materials used in various applications across industries. With increased global interest in sustainable and environmentally benign packaging, there is high demand to replace traditional petroleum-based materials with renewable, bio-derived sources. This research developed PU adhesives for multilayer flexible food packaging using Physaria fendleri oil (formerly Lesquerella fendleri) and Ricinus communis (Castor oil), each possessing naturally occurring hydroxyl functional groups. Physaria oil has, on average, hydroxyl functionality on two of the three fatty acids compared to all three for Castor oil; therefore systematically varying the concentration of each oil and maintaining a constant crosslink density for each adhesive facilitates an understanding of the effect of Physaria oil's unreacted hydrocarbon sidechain on physical properties in biobased adhesives. The results of this study determined that the peel resistance of polyethylene and polyethylene terephthalate substrates adhered with adhesives containing varying amounts of Physaria and castor oils possessed average peel strengths of 6–8 N relatively independent of composition. Furthermore, the glass transition temperatures were measured to be within the range of −25 to −44 °C with higher concentrations of the hydrocarbon sidechain resulting in lower T g s. These physical properties indicate their use in multilayer food packaging adhesive applications where isocyanate PU adhesives are still commonplace. Understanding the PU adhesive network structure-property relationships will help develop the next generation of bio-derived PU adhesives with additional sources of renewable feedstocks for food packaging applications. • Hydroxyl functional oils (f~2; f~3) were used to synthesize polyurethane adhesives. • The oils were varied to understand the influence of a C18 side chain on adhesive properties. • The C18 side chain did not influence peel strength (6–8 N). • The C18 side chain decreased glass transition temperatures (−25 to −44 °C). • Physaria fendleri is a domestic oil that can be used for packaging adhesives.

Green Wood Adhesives from One-Pot Coacervation of Folic Acid and Branched Poly(ethylene imine).

Adhesives are extensively used in furniture manufacture, and most currently utilized furniture glues are formaldehyde-based chemicals, which emit formaldehyde throughout the entire life of the furniture. With increasing concerns about formaldehyde emission effects on human health, formaldehyde-free and environmentally friendly wood adhesives from bio-based resources are highly desired. In this study, we developed an eco-friendly, high-strength, and water-based wood adhesive from one-pot coacervation of the hierarchical self-assembly of folic acid (FA, a biomolecule, vitamin B9) with a commercially available biocompatible polymer-branched poly(ethylene imine) (b-PEI). The coacervation is caused by multiple hydrogen bonds between b-PEI and the stacks of FA quartets, which demonstrates a continuous robust 3D network, thus realizing adhesion and cohesion behaviors. This coacervate has the strongest adhesion toward wood compared with other substrates. The long-lasting shear bonding strength is up to 3.68 MPa, which is much higher than that of commercial super glue, but without releasing any toxic components. Since all the fabrication and application processes are under ambient conditions without any heating and high-pressure procedures, this work provides a facile yet powerful strategy to develop formaldehyde-free, eco-friendly, and high-performance bio-based waterborne adhesives for wood bonding.

Honeycomb Organization of Chitin Nanocrystals (ChNCs) in Nanocomposite Films of UV-Cured Waterborne Acrylated Epoxidized Soybean Oil Emulsified with ChNCs.

Stable biobased waterborne Pickering dispersions of acrylated epoxidized soybean oil (AESO) were developed using chitin nanocrystals (ChNCs) as sole emulsifier without any additives. Thin AESO-ChNC nanocomposite films were produced by UV-curing thin-coated layers of the AESO emulsion after water evaporation. The kinetics of photopolymerization were assessed by monitoring the consumption of the AESO acrylate groups by infrared spectroscopy (Fourier transform infrared (FTIR)). The curing was faster in the presence of ChNCs, with a disappearance of the induction period observed for neat AESO. The coating of AESO droplets with a thin layer of ChNCs was confirmed by scanning electron microscopy (SEM) observation. SEM and transmission electron microscopy (TEM) images revealed the honeycomb organization of ChNCs inside the cured AESO-ChNC films. The mechanical, thermal, and optical properties of the nanocomposite films were studied by dynamic mechanical analysis (DMA), tensile testing, differential scanning calorimetry (DSC), and transmittance measurement, as a function of ChNC content. The inclusion of ChNCs is strongly beneficial to increase the stiffness and strength of the cured films, without compromising its optical transparency. The ability of ChNCs to act as an emulsifier for AESO in replacement of synthetic surfactants and their strong reinforcing effect in UV-cured films offer new opportunities to produce waterborne stable dispersions from AESO for application in biobased coatings and adhesives.

Toward UV-Triggered Curing of Solvent-Free Polyurethane Adhesives Based on Castor Oil

An o-nitrobenzyl-protected precursor was used as a phototrigger for the release of the diamine cadaverine in polyurethane adhesives based on castor oil as a renewable source of polyol and organic diisocyanates. This resulted in formulations with suitably controlled curing by photoactivation. This material shows faster curing when UV light is applied as compared to curing in the absence of irradiation, which was in situ monitored by rheological measurements. In addition, the adhesion performance is superior, reaching lap shear strength values of up to 4600 kPa, which is unprecedented for bio-based adhesives. On one hand, the in-depth chemical characterization with FTIR spectroscopy revealed that the slow release of cadaverine yields a well-balanced urethane/urea composition with direct impact on adhesion properties. The photocured bioadhesive was shown to bond a variety of surfaces, such as polyethylene or even wood. On the other hand, the direct one-time addition of cadaverine yields a material with approximately the same viscoelastic properties, which were achieved almost immediately as a consequence of the favored fast formation of urea bonds in detriment of urethanes, however, lacking adhesion properties.