Synthetic Adhesives Research Articles

Properties of adhesive films used in cultural assets

ABSTRACT The hygroscopic nature of wood leads to large moisture fluctuations in the material that may influence the mechanical performance of glued wood products. Adhesives based on bone, fish and hide have a long tradition for the gluing of wood and can be found in wooden structures in our cultural heritage. In this study, selected sorptive and mechanical properties of animal adhesives have been compiled and compared to those of synthetic polyurethane adhesives. Bone, fish and hide adhesives show a high moisture uptake at high relative humidity, which confirms the low moisture resistance of such adhesives. The modulus of elasticity and ultimate tensile strength of the films based on animal adhesives are considerably reduced when the moisture content is increased.

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.

Bioinspired super-strong aqueous synthetic tissue adhesives

Existing tissue adhesives and sealants are far from satisfactory when applied on wet and dynamic tissues. Herein, we report a strategy for designing biodegradable super-strong aqueous glue (B-Seal) for surgical uses inspired by an English ivy adhesion strategy and a cement particle packing theory. B-Seal is a fast-gelling, super-strong, and elastic adhesive sealant composed of injectable water-borne biodegradable polyurethane (WPU) nanodispersions with mismatched particle sizes and counterions in its A-B formulation. B-Seal showed 24-fold greater burst pressure than DuraSeal®, 138-fold greater T-pull adhesive strength than fibrin glue, and 16-fold greater lap shear strength than fibrin glue. In vivo evaluation on a rat cerebrospinal fluid (CSF) rhinorrhea model and a porcine craniotomy model validated the safety and efficacy of B-Seal for effective CSF leak prevention and dura repair. The plant-inspired adhesion strategy combined with particle packing theory represents a new direction of designing the next-generation wet tissue adhesives for surgeries.

Surface Force Measurements of Mussel-Inspired Pressure-Sensitive Adhesives.

Translating fundamental studies of marine mussel adhesion into practical mussel-inspired wet adhesives remains an important technological challenge. To adhere, mussels secrete adhesive proteins rich in the catecholic amino acid 3,4-dihydroxyphenylalanine (Dopa) and positively charged lysine. Consequently, numerous synthetic adhesives incorporating catecholic and cationic functionalities have been designed. However, despite widespread research, uncertainties remain about the optimal design of synthetic mussel-inspired adhesives. Here, we present a study of the adhesion of mussel-inspired pressure-sensitive adhesives. We explore the effects of catechol content, molecular architecture, and solvent quality on pressure-sensitive adhesive (PSA) adhesion and cohesion measured in a surface forces apparatus. Our findings demonstrate that the influence of catechol content depends on the choice of solvent and that adhesive performance is dictated by film composition rather than molecular architecture. Our results also highlight the importance of electrostatic and hydrophobic interactions for adhesion and cohesion in aqueous environments. Together, our findings contribute to an improved understanding of the interplay between materials chemistry, environmental conditions, and adhesive performance to facilitate the design of bioinspired wet adhesives.

Synergetic adhesion in highly adaptable bio-inspired adhesive

Biologically inspired adhesives microstructure requires enough flexibility to make a conformal attachment to the surface as well as high rigidity to maintain the mechanical stability of structure against buckling. To tackle these conflicting factors for the synthetic adhesives is a challenge towards large-scale production and utilizing in practical applications. Addressing this problem, we have fabricated a honeycomb structure with a soft elastic film, partially covering the cavity of the honeycomb pattern. Honeycomb structure provides enough support to maintain the structural stability of the microstructure and soft PDMS film over the pattern provides sufficient flexibility to form a strong attachment with the target surface. Meanwhile, the resemblance of the designed structure to the octopi’s sucker generates a negative pressure resulting in suction forces. To justify this suction effect, we compared our results with other controlled honeycomb microstructures (1) without any elastic film (2) with elastic film covering the whole cavity of the honeycomb pattern. Experimental results and theoretical prediction demonstrate the synergistic role of van der Waals and suction forces in the proposed partial-film honeycomb microstructure. The synergistic role of adhesive forces makes this structure a stronger, durable, and surface adaptable adhesive. We also investigated the critical role of the viscous forces for our proposed microstructure in water and silicon oil wetting conditions which signify the contribution of capillary forces.

The Ultimate Bond

Being introduced in India in 1956 as an easy –to-use white glue for carpenters in replacement of Saresh (fat-based adhesives), the ULTIBOND company started its journey and never looked back. As The ULTIBOND Company was well known to recognize the need of their product and convert it into a marvelous opportunity, the company started manufacturing AI glue products for students as well as for professional and educational institutes. In order to shift end-users from natural glues and other synthetic adhesives available at the time, AI glue embarked on a bold marketing game plan. Instead of selling through stores, AI glue approached carpenters directly. This direct marketing initiative was one of the most successful strategies employed by the company and helped the brand gain a strong foothold in the white glue market. By 1965, the brand was big enough to develop its own manufacturing plant in Maharashtra. Primarily the company decided to enter into the retail market with a packaging of 33 grams collapsible tube in early 1970’s, later came up with many other unique packaging styles to cater the need and requirements of different segments of its customer base.

Mechanical property study of plywood bonded with dimethylol dihydroxy ethylene urea crosslinked rice starch- natural rubber latex-based adhesive

There has been an increase in the demand for adhesives due to the increasing applications of plywood panels in the home furnishings and decorative items industries around the world. Most of the wood-based panels industry depends on synthetic adhesives due to its low cost and high performance. However, because synthetic adhesives emit the carcinogenic gas formaldehyde and increase the risk of human health, there is a growing interest in developing non-toxic and eco-friendly wood adhesives made from renewable materials. The present research aims to develop a bio-adhesive for plywood bonding based on two biopolymers: natural rubber latex (NRL) and dimethylol dihydroxy ethylene urea (DMDHEU) crosslinked rice starch. A bio-adhesive was ultimately formulated with varying weight ratio of NRL and DMDHEU crosslinked rice starch at 1:3, 1:1 and 3:1 respectively. Mechanical characteristics of plywood samples fabricated with the formulated bio-adhesive were measured using IS 17,304 and ISO 12466–1-2007 via hot press at 120 °C. The modulus of rupture (MOR) of plywood glued with Dm-B was 63 MPa, the modulus of elasticity (MOE) was 6480 MPa, and the internal bonding (IB) was 1.48 MPa, each of which met the ISO 12466–2-2007 and IS 303 standards. According to the findings, Dm-B had a profound impact on the performance of adhesion properties and contributed to the elimination of the use of hazardous synthetic adhesives.

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 waste-derived nanocomposite sealant for repairing micro-cracks in concrete

The use of renewable resources has been gaining interest due to their high economic benefits. They are attractive as a sustainable alternative to conventional resources for producing useful and valuable materials. The paper focuses on using a composite of graphene-oxide and chitosan, an aquaculture waste-derived material, as a renewable feedstock for producing a sealant for healing micro-cracks in concrete. The sealant named Eco-Nanoseal is well characterised, and its interaction with concrete is studied. A possible binding mechanism of Eco-Nanoseal with concrete is proposed. The nanofibrous film-forming composite can quickly solidify in the concrete environment without any external polymerising agent. The quick ability to form a solid plug and strong bonding with the concrete surface makes Eco-Nanoseal a potential candidate for healing micro-cracks in concrete. The novel application is demonstrated well in M25 grade concrete cube specimens. With low environmental factor (E-factor) and process mass intensity (PMI) values of 0.05 and nearly 1, respectively, the Eco-Nanoseal complies the critical parameters of materials' sustainability indices. The Eco-Nanoseal is a promising and environmentally-friendly alternative to synthetic polymer-based adhesives.

State of Research and Trends in the Development of Polyvinyl Acetate-Based Wood Adhesive

Synthetic wood adhesives, consisting of urea-formaldehyde resins (UF), phenol-formaldehyde resins (PF), melamine-formaldehyde resins (MF), and polyurethane resins, are widely used. For UF and MF, most investigations are concerned with reducing free formaldehyde content; for PF, most studies focused on finding new alternative chemicals to replace phenol. These adhesives come under the Carcinogenic, Mutagenic, and Reprotoxic chemicals (CMR) category. Due to global energy issues and dependency on petroleum sources, the focus has shifted to look for alternative and renewable raw material sources for wood adhesives. Conventionally available wood adhesives are polyvinyl alcohol (PVA) stabilized, with drawbacks like poor water resistance, poor heat resistance, low-temperature workability, and it’s based on petroleum resources. Polyvinyl acetate (PVAc) is non-resistant to moisture polymer, and if such adhesive joints are exploited in a moist environment, its strength substantially decreases. Sufficiently moisture-resistant adhesive joints are obtained by modifying PVAc dispersion with special compounds like reactive comonomer, Silanes, and modified PVA. To improve the workability at low temperature, Vinyl acetate (VAc) is copolymerized with specific comonomers like butyl acetate without affecting the performance properties. Here, we aim to present an overview of the research trend of PVAc-based adhesives in the wood industry. The review summarizes the current state of research PVAc-based adhesives.

Making Protein-Based Adhesives Water Resistant: Role of Protein Water Solubility, Galloyl Modification, and Complexation

There has been an ongoing interest in using proteins as more environmentally friendly substitutes for the existing synthetic adhesives. Poor water resistance is a particular shortcoming of protein-based adhesives, which negatively affects their outdoor functionality. In this study, we systematically investigated if water solubility of the protein, addition of a phenolic compound such as tannic acid, and protein–polyphenol complexation could improve the water resistance of protein-based adhesives. It was found that the synergetic effects of these parameters can yield commercial-level water resistance.

Tannin‐based bio‐adhesives for the wood panel industry as sustainable alternatives to petrochemical resins

AbstractThe development of natural‐based adhesives is a key aspect in reducing the consumption of fossil resources, in adapting to legislation on the use of formaldehyde and in ensuring the sustainability of the wood panel industry. This study focuses on five alternatives for tannin‐based adhesives (tannin‐paraformaldehyde, tannin‐glyoxal, tannin‐hexamine, tannin non‐isocyanate polyurethane (NIPU) with ammonium hydroxide and tannin NIPU with HDMA bio‐adhesives) as potential proposals for the substitution of synthetic adhesives currently used: Urea‐formaldehyde (UF), Phenol‐formaldehyde (PF) and melamine urea formaldehyde (MUF). Modeling and simulation tools were used for the conceptual design of the reaction stage of the bio‐adhesives due to the lack of real data from industrial scale production systems. The life cycle assessment methodology was used to identify the environmental impacts associated with the production processes of these bio‐adhesives. The results obtained showed that tannin NIPU bio‐adhesive with ammonium hydroxide has the best environmental profile, although the other alternative bio‐adhesives also show good environmental profiles compared to synthetic adhesives. Sensitivity analyses have been carried out after evaluating the main hot spots in the production processes. In all of them, reductions of the environmental impacts have been observed, with the replacement of DMC by EC and the reduction of energy consumption being the options that showed the greatest improvements.

Bioengineered Protein-based Adhesives for Biomedical Applications.

Protein-based adhesives with their robust adhesion performance and excellent biocompatibility have been extensively explored over years. In particular, the unique adhesion behaviours of mussel and sandcastle worm inspired the development of synthetic adhesives. However, the chemical synthesized adhesives often demonstrate weak underwater adhesion performance and poor biocompatibility/biodegradability, limiting their further biomedical applications. In sharp contrast, genetically engineering endows the protein-based adhesives the ability to maintain underwater adhesion property as well as biocompatibility/biodegradability. Herein, we outline recent advances in the design and development of protein-based adhesives by genetic engineering. We summarize the fabrication and adhesion performance of elastin-like polypeptide-based adhesives, followed by mussel foot protein (mfp) based adhesives and other sources protein-based adhesives, such as, spider silk spidroin and suckerin. In addition, the biomedical applications of these bioengineered protein-based adhesives are presented. Finally, we give a brief summary and perspective on the future development of bioengineered protein-based adhesives.

A bio-inspired exploration of eco-friendly bael gum and guar gum-based bioadhesive as tackifiers for packaging applications

The potential opportunities for synthetic adhesives have increased abruptly due to the variety of strengths provided by them. These adhesives release toxic fumes, such as formaldehyde which is a serious predicament. To annihilate this issue, the stipulation for the burgeoning of biodegradable packaging materials has come into account. The objective of this work is to prepare a biobased, biorenewable, and biodegradable cloth-to-cloth, cloth-to-paper, and paper-to-paper adhesive using natural ingredients. The effects of guar gum and bael gums as tackifiers were studied individually as well as synergistically. Neem and olive oil were used as preservatives to impart antimicrobial properties. The performance and stability of adhesive have been determined at ambient as well as extended conditions. The mechanical peel strength and biodegradation analysis have been carried out. The effect of time and temperature on viscosity of guar gum (18%) has been found highest in contrary to other samples. The mechanical peel strength of adhesives by immersing resultant samples in different solvent media has been investigated. The resultant adhesive has been found superior to be utilized in multilayered films, paper binding and cloth reinforced paper bags.

Effect of enzymatic treatment (endo-glucanases) of fiber and mechanical lignocellulose nanofibers addition on physical and mechanical properties of binderless high-density fiberboards made from wheat straw

Fiberboards are used in a variety of applications that can be for interior as well as for exterior. However, their production involves the consumption of virgin wood fibers and the use and production of formaldehyde-based adhesives, with the consequent impact on the environment and health. The removal of these adhesives results in a significant loss of physico-mechanical properties. To confront these major problems, the use of wheat straw, an agricultural waste, as raw material for the production of binderless fiberboards has been explored. As an alternative to synthetic adhesive, enzymatic treatment of fiber and lignocellulose nanofibers (LCNFs) addition, as well as their combination, have been studied. The different treatments produce an important increase in the mechanical properties in front of the untreated fiber and commercial fiberboard, being the combination of both which presents the best results. Separately, the enzymatic treatment produces a greater strengthening effect than the addition of LCNF. In terms of structural stability, the addition of LCNFs and treatment combinations shows the best results for water absorption and thickness swelling. The results obtained show the possibility to obtain fiberboards without synthetic adhesives with mechanical properties far superior to commercial fiberboardsas as such as bending strengths higher than 100 MPa, flexural modulus 5.5 GPa, internal bond 1.6 MPa, and 122.52 kJ/m2 of impact strength with an estimated added cost of 1 €/m3.

Experimental characterisation of the moment-rotation behaviour of beam-beam connections using compressed wood connectors

The widespread use of energy-intensive metallic connectors and synthetic adhesives in modern timber construction has negative implications for the end-of-life disposal or re-use of the structural timber components. Therefore, it is favourable to substitute metallic connectors and synthetic adhesives with bio-based alternatives such as wood-based connectors. Recent studies have shown that densified or compressed wood (CW) with superior mechanical properties could be suitable for the manufacture of wood-based connectors in the form of CW dowels and CW plates. This study experimentally examines the moment-rotation behaviour of semi-rigid type timber-CW beam-beam connections under pure bending. The study also assesses the suitability of current design rules to predict the moment capacity of timber-CW connections. The comparative study has shown that the moment capacity of the timber-CW connection can be conservatively predicted from the characteristic load-carrying capacity of the connections calculated using the EC 5 strength equations.

Molecular Context of Dopa Influences Adhesion of Mussel-Inspired Peptides.

Improving adhesives for wet surfaces is an ongoing challenge. While the adhesive proteins of marine mussels have inspired many synthetic wet adhesives, the mechanisms of mussel adhesion are still not fully understood. Using surface forces apparatus (SFA) measurements and replica-exchange and umbrella-sampling molecular dynamics simulations, we probed the relationships between the sequence, structure, and adhesion of mussel-inspired peptides. Experimental and computational results reveal that peptides derived from mussel foot protein 3 slow (mfp-3s) containing 3,4-dihydroxyphenylalanine (Dopa), a post-translationally modified variant of tyrosine commonly found in mussel foot proteins, form adhesive monolayers on mica. In contrast, peptides with tyrosine adsorb as weakly adhesive clusters. We further considered simulations of mfp-3s derivatives on a range of hydrophobic and hydrophilic organic and inorganic surfaces (including silica, self-assembled monolayers, and a lipid bilayer) and demonstrated that the chemical character of the target surface and proximity of cationic and hydrophobic residues to Dopa affect peptide adsorption and adhesion. Collectively, our results suggest that conversion of tyrosine to Dopa in hydrophobic, sparsely charged peptides influences peptide self-association and ultimately dictates their adhesive performance.

Machine Learning-Based and Experimentally Validated Optimal Adhesive Fibril Designs.

Setae, fibrils located on a gecko's feet, have been an inspiration of synthetic dry microfibrillar adhesives in the last two decades for a wide range of applications due to unique properties: residue-free, repeatable, tunable, controllable and silent adhesion; self-cleaning; and breathability. However, designing dry fibrillar adhesives is limited by a template-based-design-approach using a pre-determined bioinspired T- or wedge-shaped mushroom tip. Here, a machine learning-based computational approach to optimize designs of adhesive fibrils is shown, exploring a much broader design space. A combination of Bayesian optimization and finite element methods creates novel optimal designs of adhesive fibrils, which are fabricated by two-photon-polymerization-based 3D microprinting and double-molding-based replication out of polydimethylsiloxane. Such optimal elastomeric fibril designs outperform previously proposed designs by maximum 77% in the experiments of dry adhesion performance on smooth surfaces. Furthermore, finite-element-analyses reveal that the adhesion of the fibrils is sensitive to the 3D fibril stem shape, tensile deformation, and fibril microfabrication limits, which contrast with the previous assumptions that mostly neglect the deformation of the fibril tip and stem, and focus only on the fibril tip geometry. The proposed computational fibril design could help design future optimal fibrils with less help from human intuition.

Pengaruh Variasi Bio Based Adhesive terhadap Kekuatan Peeling dan Shearing Kayu Pinus pada Adhesive Joint

The methods of joining engineering materials using adhesives is mostly implemented by using synthetic adhesives from non-renewable sources. Even though it has good joining performance, its poisonous nature and difficult to decompose naturally makes the adhesive needs to seek alternatives that are more environmentally friendly. Another reason is to support FAO campaigns for the use of environmentally friendly and biodegradable materials. One that has the potential to replace synthetic one is adhesives from natural sources such as gum rubber, jackfruit, and breadfruit. Because each natural sap has a different composition, the adhesive strength will also be different. Therefore it is necessary to examine the adhesive strength of each of these natural gums. In this research, natural adhesives (gums) and synthetic adhesives were used to joint pine wood as a test specimen. After joining, peeling and shearing tests on the specimens were carried out so that the mechanical strength of the joints for each adhesive variation was recognized. Fracture analysis was then performed to analyze the mechanism of joint failure for each adhesive variation. From this research, the highest peeling strength was obtained from rubber tree sap of 0.15 MPa, while the highest shearing strength was also obtained for rubber sap of 0.68 MPa.

Self-Cleaning Performance of the Micropillar-Arrayed Surface and Its Micro-Scale Mechanical Mechanism

The exceptional adhesive ability of geckos remains almost uninfluenced by contaminated surfaces, showing that the adhesion system of geckos has self-cleaning properties. Although there have been several studies on the self-cleaning performance of geckos and gecko-inspired synthetic adhesives, the microscale mechanical mechanism of self-cleaning is still unclear. In the present study, a micropillar-arrayed surface is fabricated using a template molding method to investigate its self-cleaning performance in a load-pull contact process. The effects of preload, microparticle size on self-cleaning properties are studied. The self-cleaning efficiency of the micropillar-arrayed surface is found to increase with an increase in the microparticle size. For large and small microparticles, self-cleaning efficiency increases with an increase in the preload. For medium microparticles, self-cleaning efficiency first increases and then decreases as the preload increases. The mechanical mechanism underlying such self-cleaning performance is further elucidated; it is mainly attributed to the competition among the elastic energy stored in the micropillars induced by the bending deformation, the interfacial adhesion energy between the microparticles and the deformed micropillars, and the interfacial adhesion energy between the microparticles and substrate, as well as the varying contact states between the microparticles and the deformed micropillars. The preload can not only change the contact states between the microparticles and the micropillar-arrayed surface but also influence the bending elastic energy stored in the micropillars. The results obtained in the present study can help deeply understand the self-cleaning mechanism of micropillar-arrayed surfaces as well as provide a guideline for designing functional surfaces with high self-cleaning efficiency.