Adhesive Formulations Research Articles

Optimizing a canola-gelatine-urea bio-adhesive: effects of crosslinker and incubation time on the bonding performance

The importance of creating eco-friendly and health-conscious materials has become paramount in striving to attain long-term development goals. For the past decades, constant efforts have been made to tackle the issue of formaldehyde release from wood-based panels which, to date, are still mainly produced from unsustainable synthetic adhesives. In the pursuit of sustainable and environmentally responsible adhesive solutions for the wood industry, sodium bisulfate, sodium bisulfite, and sodium nitrite were used under different heat treatment conditions as crosslinkers for canola protein-based bio-adhesive formulations. The developed adhesive formulations showed outstanding mechanical properties, with a viscosity below 4000 mPa/s despite the relatively high solid content, as well as excellent bonding performances. The one-layer particleboards bonded with the canola-based adhesive demonstrated outstanding mechanical properties, with the internal bonding and the bending strength values surpassing 0.60 N/mm2 and 10 N/mm2, respectively. Notably, the sodium nitrite-crosslinked variants exhibited significantly superior performance compared to the UF-bonded control boards. Longer incubation times generally improve bonding strength, with sodium nitrite showing the most pronounced effects. The results of this research showcase not only the possibility of developing a plant protein-based wood adhesive with high solid content, but also the potential superiority of canola protein-based wood adhesives when compared to conventional, synthetic counterparts. These findings offer valuable insights for optimizing bio-based adhesives in wood composite manufacturing, highlighting sodium nitrite as a promising crosslinker for enhancing the adhesive’s performance.

Kinetic Study of Anaerobic Adhesive Curing on Copper and Iron Base Substrates.

Anaerobic adhesives (AAs) cure at room temperature in oxygen-deprived spaces between metal substrates. The curing process is significantly influenced by the type of metal ions present. This study investigates the curing kinetics of a high-strength AA on iron and copper substrates using differential scanning calorimetry (DSC). The activation energy and kinetic parameters were determined with different empiric models, revealing that curing on copper is faster and more complete compared to iron. The findings suggest that copper ions lower the activation energy required for curing, enhancing the adhesive's performance. This research addresses the gap in understanding how metal ions affect AA curing kinetics, offering valuable insights for optimizing adhesive formulations for industrial applications.

Eco-Friendly and High-Performance Bio-Polyurethane Adhesives from Vegetable Oils: A Review.

Current petrochemical-based adhesives adversely affect the environment through substantial volatile organic compound (VOC) emissions during production, contributing to air pollution and climate change. In contrast, vegetable oils extracted from bio-resources provide a compelling alternative owing to their renewability, abundance, and compatibility with adhesive formulation chemistry. This review aimed to critically examine and synthesize the existing scholarly literature on environmentally friendly, sustainable, and high-performance polyurethane adhesives (PUAs) developed from vegetable oils. The use of PUAs derived from vegetable oils promises to provide a long-term replacement while simultaneously maintaining or improving adhesive properties. This quality renders these adhesives appropriate for widespread use in various sectors, including construction, automotive manufacturing, packaging, textile, and footwear industries. This review intended to perform a comprehensive assessment and integration of the existing research, thereby identifying the raw materials, strengths, weaknesses, and gaps in knowledge concerning vegetable oil-based PUAs. In doing so, it responded to these gaps and proposes potential avenues for future research. Therefore, this review accomplishes more than merely evaluating the existing research; it fosters the advancement of greener PUA technologies by identifying areas for improvement and innovation towards more sustainable industrial practices by showcasing vegetable oil-based PUAs as viable, high-performance alternatives to their petroleum-based counterparts.

Research and improvement of cyanoacrylate on bonding properties of silicone adhesive material

Cyanoacrylate adhesives represent the earliest discovered and most widely utilized adhesives known to date, boasting exceptional bonding properties such as the ability to cure at room temperature, rapid curing rates, and strong adhesion. However, shortcomings persist in practical applications, notably in addressing inert materials like silicone that pose challenges for ideal adhesion. To enhance the bonding performance of cyanate ester adhesives with silicone materials, this study delves into two aspects: modifying cyanate esters and pre-treating silicone surfaces to reduce surface energy. Following internal modifications, the maximum bonding strength to silicone sheets reached 2.33 MPa, while pre-treating the silicone substrate surface enabled a maximum bonding strength of 6.10 MPa. Utilizing SEM, ATR, EDS, and other analytical techniques, the mechanisms behind the improvement in silicone substrate bonding strength are characterized, revealing changes in properties pre- and post-treatment. This research paves a novel path and direction for future scientific investigations and advancements in adhesive formulation and enhancement.

Microcapsules of Poly(butylene adipate-co-terephthalate) (PBAT) Loaded with Aliphatic Isocyanates for Adhesive Applications.

This work introduces the encapsulation of hexamethylene diisocyanate derivatives (HDI, TriHDI, and PHDI) with the biodegradable polymer poly(butylene adipate-co-terephthalate) (PBAT) through a solvent evaporation method. These microcapsules (MCs) were then employed in adhesive formulations for footwear. Moreover, MCs containing PHDI were produced in a closed vessel, demonstrating the potential for recovering and reusing organic solvents for the first time. The MCs were achieved with an isocyanate payload reaching up to 68 wt %, displaying a spherical shape, a core-shell structure, and thin walls without holes or cracks. The application of MCs as cross-linking agents for adhesives was evaluated following industry standards. The adhesives' strength surpassed the minimum requirement by a significant margin. Creep tests demonstrated that the formulation with MCs exhibits superior thermostability. Furthermore, the formulation with MCs-PHDI presented the best results reported to date for this type of system, as no displacement was observed in the bonded substrates. Environmental assessment indicates that adhesives with MCs have higher global warming potential (+16.2%) and energy consumption (+10.8%) than the standard commercial adhesives, but under alternative realistic scenarios, the differences can be insignificant. Therefore, adhesive formulations incorporating MCs promise to be on par with traditional adhesive systems regarding environmental impacts while providing benefits such as improved and safe handling of isocyanates and excellent bonding effectiveness.

Synergistic enhancement of hydrophobic dental adhesives: autonomous strengthening, polymerization kinetics, and hydrolytic resistance

The leading cause of composite restoration failure is recurrent marginal decay. The margin between the composite and tooth is initially sealed by a low-viscosity adhesive, but chemical, physical, and mechanical stresses work synergistically and simultaneously to degrade the adhesive, destroying the interfacial seal and providing an ideal environment for bacteria to proliferate. Our group has been developing self-strengthening adhesives with improved chemical and mechanical characteristics. This paper reports a self-strengthening adhesive formulation that resists hydrolysis-mediated degradation by providing intrinsic reinforcement of the polymer network through synergistic stimulation of free-radical polymerization, sol-gel reaction, and hydrophobicity. Hydrophobic resin formulation (NE1) was developed using HEMA/BisGMA 28/55w/w and 15 wt% MPS. Control (NC1) contained HEMA/BisGMA 28/55 w/w and 15 wt% MES. The polymerization kinetics, water sorption, leachates, and dynamic mechanical properties of the resin samples were investigated. The NC1 and NE1 samples showed comparable polymerization kinetics, degrees of conversion and water sorption. In contrast, NC1 showed significantly higher levels of HEMA and BisGMA leachate, indicating faster degradation in ethanol. At day 3, cumulative HEMA leachate for NC1 was ten times greater than NE1 (p < 0.05). Dynamic mechanical properties were measured at 37 and 70°C in both dry and wet conditions. Under dry conditions, the storage moduli of NC1 and NE1 were comparable and the glass transition temperature (Tg) of NC1 was statistically significantly lower (p < 0.001) than NE1. Under wet conditions, the storage modulus of NC1 was lower than NE1 and at 70°C there was a threefold difference in storage modulus. At this temperature and under wet conditions, the storage modulus of NC1 is statistically significantly lower (p < 0.001) than NE1. The results indicated that in the wet environment, NE1 provided lower chain mobility, higher crosslink density, and more hydrogen bonds. The newly formulated methacrylate-based adhesive capitalizes on free-radical polymerization, sol-gel reactions, and hydrophobicity to provide enhanced mechanical properties at elevated temperatures in wet environments and hydrolytic stability under aggressive aging conditions.

The Effect of Cellulose Nanocrystal Reassembly on Latex-Based Pressure-Sensitive Adhesive Performance.

Different cellulose nanocrystal (CNC) forms (dried vs never-dried) can lead to different degrees of CNC reassembly, the formation of nanofibril-like structures, in nanocomposite latex-based pressure-sensitive adhesive (PSA) formulations. CNC reassembly is also affected by CNC sonication and loading as well as the protocol used for CNC addition to the polymerization. In this study, carboxylated CNCs (cCNCs) were incorporated into a seeded, semibatch, 2-ethylhexyl acrylate/methyl methacrylate/styrene emulsion polymerization and cast as pressure-sensitive adhesive (PSA) films. The addition of CNCs led to a simultaneous increase in tack strength, peel strength, and shear adhesion, avoiding the typical trade-off between the adhesive and cohesive strength. Increased CNC reassembly resulted from the use of dried, redispersed, and sonicated cCNCs, along with increased cCNC loading and addition of the cCNCs at the seed stage of the polymerization. The increased degree of CNC reassembly was shown to significantly increase the shear adhesion by enhancing the elastic modulus of the PSA films.

Thermophysical and adhesive properties of functional polymer materials based on epoxy resin and silicon-containing component

The work was aimed at developing an adhesive formulation with increased adhesive strength for metals. It contains an epoxy resin of the bisphenol type СHS-TROXY 520 (an analogue of ED-20), an amine hardener triethanolamine (TEA) and a silicon-containing component (3-isocyanatopropyl)triethoxysilane, designated as NCO-Si, with an optimal ratio of components. The content of NCO-Si in the formulations was 0.5, 1.0, 3.0 and 5.0 wt. %, respectively. The gradual transformation of the epoxy system into a three-dimensional network with the formation of ester and urethane groups was shown by IR spectroscopy method. Tensile and shear strength were determined using the tearing machine R-50 in accordance with current standards. It was found that the maximum values of physical and mechanical parameters were obtained when the amount of NCO-Si was 3 wt. %. The maximum values of adhesion strength to steel substrates δst. = 58.5 MPa significantly exceed those for neat epoxy formulations. The shear strength values for steel plates τst. = 21 MPa increase by 60 %, for aluminium plates they are δAl =14.5 MPa and increase by 48 %. The morphology of the samples has been studied by means of optical microscopy. It is shown that the modified NCO-Si samples are characterised by a phase-separated structure. At a minimum amount of NCO-Si (0.5 wt. %), structurally disordered spherical domains with a size of ~1÷3 μm are observed, an increase in the content of the organosilicon component leads to the formation of interconnected regular structures, which are less pronounced at 1.0 wt. % of NCO-Si and clear at 3.0 and 5.0 wt. % of NCO-Si. Thermogravimetric analysis (TGA) was performed as well. It is shown that the modification of epoxy resin by a silicon-containing component with NCO-Si groups leads to an improvement in thermophysical parameters, a decrease in internal stresses and the formation of a material with a structure close to equilibrium.

Multiaxial stress effects on bonding strength in adhesively bonded joints

ABSTRACT This study investigates adhesive bonding as a crucial engineering technique for joining materials, with a focus on load distribution, structural enhancement, and weight reduction. Advances in adhesive formulations, surface preparation, and application techniques continue to expand its capabilities. The research addresses stresses in hybrid joints resulting from pre-tensioning bolts and subsequent axial loading, emphasizing the influence of normal stresses on the critical adhesive-steel interface. Off-axis samples are bonded to mild steel using four different adhesives: SW7240, S370, DP460 (2K-epoxies), and SF479 (2K polyurethane). The choice of adhesive significantly influences shear strength under various loading conditions. Formulating this interaction in terms of maximum shear or von Mises stresses leads to relatively complex failure criteria that make the further analysis dependent on each adhesive. On the other hand, expressing strength at maximum principal stress significantly simplifies comparative analysis, as it consistently exhibits an almost linear trend, indicating strength reduction with increasing hydrostatic pressure for all adhesives, potentially simplifying subsequent strength predictions of hybrid joints.

Antimicrobial properties and bonding durability of pH-responsive dentin adhesives with chlorhexidine-load mesoporous silica nanoparticles

In this study, we synthesized pH-sensitive CHX@SBA-PDA nanoparticles and characterized their structure. These nanoparticles were then incorporated into Single Bond 2 commercial dentin adhesive. Subsequently, timely and long-term antibacterial evaluation, cytotoxicity evaluation and bonding properties were conducted. The results demonstrated the successful synthesis of CHX@SBA-PDA nanoparticles. Moreover, CHX@SBA-PDA exhibited excellent pH sensitivity and maintained a high release rate of chlorhexidine (CHX) under cariogenic low pH conditions. At pH 5.0, the release rate could reach up to 71.1% after 24 h of incubation with CHX@SBA-PDA nanoparticles. Among the different adhesive formulations tested, the 2% wt adhesive displayed the strongest immediate and 30 days bacterial inhibition ability (p < 0.05). No significant difference was observed in immediate shear strength among the four groups (p > 0.05). After undergoing pH cycling, all functional adhesive groups exhibited higher shear strength compared to the control group (p < 0.05). Furthermore, there was no significant difference in cell proliferation activity between the experimental group and control group (p > 0.05). In conclusion, our functional dentin adhesive containing CHX@SBA-PDA nanoparticles demonstrated long-term antibacterial properties as well as improved bond strength characteristics, thus, offering a promising approach to enhance durability of bonded restorations.

Compatibility versus reaction diffusion: Factors that determine the heterogeneity of polymerized adhesive networks

ObjectivesHeterogeneity and phase separation during network polymerization is a major issue contributing to the failure of dental adhesives. This study investigates how the ratio of hydrophobic crosslinkers to hydrophilic comonomer (C/H ratio), as well as cosolvent fraction (ethanol/water) influences the degree of heterogeneity and proclivity for phase separation in a series of model adhesive formulations. MethodsTwelve formulations were investigated, with 4 different C/H ratios (7:1, 2.2:1, 1:1, 0.5:1) and 3 different overall cosolvent fractions (0, 10 and 20 wt%). The heterogeneity and phase behavior were characterized using Fourier Transform Infrared Spectroscopy (FT-IR), dynamic mechanical analysis (DMA), small-angle x-ray scattering (SAXS) and atomic force microscopy (AFM). ResultsIn resins without cosolvent, all characterizations confirm reduced heterogeneity as C/H ratio decreases. However, when 10 or 20 wt% of cosolvent is included in the adhesive formulation, a higher degree of heterogeneity and even distinct phase separation with domains ranging from a few hundreds of nanometers to a few micrometers in size form. This is particularly noticeable at lower C/H ratios, which is surprising as HEMA is commonly considered a compatibilizer between hydrophobic crosslinkers and aqueous (co)solvents. SignificanceOur experiments demonstrate that formulations with lower C/H ratio and thus a lower viscosity experience later onsets of diffusion limitations during polymerization, which favors thermodynamically driven phase separation. Therefore, to determine or predict the resulting phase structure of adhesive materials, it is necessary to consider the kinetics and diffusion constraints during the formation of the polymer network and not just the compatibility of resin constituents.

A new platform for designing high‐performance epoxy film adhesive with poly (butyl acrylate‐block‐styrene) block copolymer and alumina nano particles in aluminum–aluminum bonded joints: Preparation and analysis of the mechanical, adhesion, and thermal properties

AbstractEpoxy film adhesives are typically used in different industries. However, these adhesives suffer from brittleness, low flexibility, and thermal stability problems. In this research, phenolic resin (Novolac) and poly (butyl acrylate‐block‐styrene) were used in the formulation of epoxy film adhesive (Diglycidyl ether bisphenol A) to increase thermal stability and adhesion strength and as the toughening agent, respectively. Alumina nanoparticles were also employed to enhance the mechanical properties. The influence of block copolymer and alumina nano particles was also assessed on the mechanical and thermal properties of epoxy‐based film adhesives. The investigation of the mechanical properties of dumbbell‐shaped samples and adhesion strength of the Al‐Al bonded joints were evaluated by tensile, lap shear, and T‐peel tests. The thermal stability of the optimal samples was assessed by thermogravimetry analysis (TGA). SEM analysis was also utilized to study the toughening mechanism. Tensile test of the dumbbell‐shaped samples indicated that the incorporation of 2.5 phr block copolymer and 2 phr alumina nanoparticles enhanced the toughness to 250%. The shear and peel strengths of this sample also exhibited 51% and 76% increase, respectively, showing a remarkable synergistic effect. On the other hand, TGA results revealed that the incorporation of block copolymer improved the thermal stability of the adhesive matrix. The copresence of these two materials also showed a considerable synergistic effect on the thermal stability. The SEM results were also in line with the results of mechanical tests as the crack deviation, crack pinning, and debonding were the most important mechanisms of toughening.Highlights A new platform was developed for designing epoxy films adhesives with high mechanical, adhesion, and thermal properties. The hybrid of butyl acrylate block styrene copolymer, phenolic resin, and alumina nanoparticles showed synergistic effects on the lap shear and T‐peel strength. The greatest improvement in toughness was related to the epoxy adhesive containing 2.5 phr block copolymer and 2 phr alumina nanoparticles. Analysis of the fracture surface showed that by using hybrid of nanoparticles and block copolymers in the epoxy film adhesive formulation, the cohesive failure occurred. The use of hybrid additives in film adhesive formulations enlightened manufacture of adhesives for future studies on adhesive formulations.

High-Performance Bioinspired Microspheres for Boosting Dental Adhesion.

Dental adhesives are widely used in daily practice for minimally invasive restorative dentistry but suffer from bond degradation and biofilm attack. Bio-inspired by marine mussels having excellent surface-adhesion capability and high chemical affinity of polydopamine (PDA) to metal ions, herein, experimental zinc (Zn)-containing polydopamine-based adhesive formulation, further being referred to as "Zn-PDA@SiO2"-incorporated adhesive is proposed as a novel dental adhesive. Different Zn contents (5 and 10mm) of Zn-PDA@SiO2 are prepared. Considering the synergistic effect of Zn and PDA, Zn-PDA@SiO2 not only presents excellent antibacterial potential and notably inhibits enzymatic activity (soluble and matrix-bound proteases), but also exhibits superior biocompatibility and biosafety in vitro/vivo. The long-term bond stability is substantially improved by adding 5wt% 5mm Zn-PDA@SiO2 to the primer. The aged bond strength of the experimentally formulated dental adhesives applied in self-etch (SE) bonding mode is 1.9 times higher than that of the SE gold-standard adhesive. Molecular dynamics calculations indicate the stable formation of covalent bonds, Zn-assisted coordinative bonds, and hydrogen bonds between PDA and collagen. Overall, this bioinspired dental adhesive provides an avenue technology for innovative biomedical applications and has already revealed promising perspectives for dental restorative dentistry.

Enhanced curing process of eco-friendly oxidized cornstarch adhesive with Nano-CeO2

ABSTRACT This paper investigates the development of an eco-friendly adhesive fortified with cerium dioxide nanoparticles (nano-CeO2), incorporating oxidized corn starch (OCS) and a Polyvinyl acetate (PVAc) emulsion. Initially, OCS was prepared through an oxidation reaction, and its chemical structural attributes were explored using FT-IR, XRD, DSC, viscosity, and carboxyl value analysis. Subsequently, the adhesive formulation (OCS-PVAc-CeO2) was synthesized, demonstrating substantial improvements in both strength and curing kinetics due to the inclusion of nano-CeO2, as confirmed by SEM surface morphology analysis. Laboratory-scale evaluations of this adhesive confirmed its suitability for the packaging industry due to its rapid curing process and enhanced mechanical properties.

Exploring the potential of chitin and chitosan extracted from shrimp shell waste in enhancing urea-formaldehyde wood adhesives

This work aims to investigate the properties of both chitin (CT), and chitosan (CS) extracted from shrimp shell waste (SSW) and its potential use for the improvement of urea-formaldehyde (UF) based adhesives in particleboards manufacturing. For this purpose, characterization techniques (SEM, ATR-FTIR, XRD, and TGA/DTG) were used to confirm the successful extraction of CT and CS. The effect of different ratios of 4, 6, 8, and 10 wt% of CT and CS, on the ultimate particleboard’s mechanical properties (dry internal bond (IB), modulus of rupture (MOR), modulus of elasticity (MOE) and surface soundness (SS)) was investigated, and compared to the European Standards. It was evidenced that the optimal formulation of adhesives is (92:8; w:w) for both UF:CT and UF:CS leading to higher mechanical performance. For instance, MOE was uplifted to 3478 and 3568 MPa, and MOR was uplifted to 21 and 22 MPa, with the loading of CT and CS respectively, compared to MOE = 2579 MPa and MOR = 16 MPa for the particleboard glued with only UF adhesive. Moreover, when 8 wt% of CT and CS are formulated with UF adhesive, the formaldehyde emission from particleboard was reduced significantly about 36.11 and 37.18%, respectively. The addition of 8 wt% CT and CS exhibited a decrease in the values Thickness Swelling (TS) and Water Adsorption (WA) of the particleboards, highlighting the improvement of the physical properties of the final products. This study aims to promote the use of shrimp shell waste in the development of high added value products in wood urea-formaldehyde based adhesives.

Multifunctional Dental Adhesives Formulated with Silane-Coated Magnetic Fe3O4@m-SiO2 Core-Shell Particles to Counteract Adhesive Interfacial Breakdown.

The process of bonding to dentin is complex and dynamic, greatly impacting the longevity of dental restorations. The tooth/dental material interface is degraded by bacterial acids, matrix metalloproteinases (MMPs), and hydrolysis. As a result, bonded dental restorations face reduced longevity due to adhesive interfacial breakdown, leading to leakage, tooth pain, recurrent caries, and costly restoration replacements. To address this issue, we synthesized and characterized a multifunctional magnetic platform, CHX@SiQuac@Fe3O4@m-SiO2, to provide several beneficial functions. The platform comprises Fe3O4 microparticles and chlorhexidine (CHX) encapsulated within mesoporous silica, which was silanized by an antibacterial quaternary ammonium silane (SiQuac). This platform simultaneously targets bacterial inhibition, stability of the hybrid layer, and enhanced filler infiltration by magnetic motion. Comprehensive experiments include X-ray diffraction, FT-IR, VSM, EDS, N2 adsorption-desorption (BET), transmission electron microscopy, scanning electron microscopy, thermogravimetric analysis, and UV-vis spectroscopy. Then, CHX@SiQuac@Fe3O4@m-SiO2 was incorporated into an experimental adhesive resin for dental bonding restorations, followed by immediate and long-term antibacterial assessment, cytotoxicity evaluation, and mechanical and bonding performance. The results confirmed the multifunctional nature of CHX@SiQuac@Fe3O4@m-SiO2. This work outlined a roadmap for (1) designing and tuning an adhesive formulation containing the new platform CHX@SiQuac@Fe3O4@m-SiO2; (2) assessing microtensile bond strength to dentin using a clinically relevant model of simulated hydrostatic pulpal pressure; and (3) investigating the antibacterial outcome performance of the particles when embedded into the formulated adhesives over time. The results showed that at 4 wt % of CHX@SiQuac@Fe3O4@m-SiO2-doped adhesive under the guided magnetic field, the bond strength increased by 28%. CHX@SiQuac@Fe3O4@m-SiO2 enhanced dentin adhesion in the magnetic guide bonding process without altering adhesive properties or causing cytotoxicity. This finding presents a promising method for strengthening the tooth/dental material interface's stability and extending the bonded restorations' lifespan.

Upcycling of protein concentrates from industrial byproducts into polyurethane wood adhesives

Wood structures generally rely on synthetic adhesives for their strength and versatility. However, environmental concerns linked to the chemical composition of these adhesives have stimulated the search for more environmentally friendly adhesives. Researchers have explored replacing petroleum-based constituents with natural raw materials such as lignins, tannins, and proteins. Of these alternatives, proteins, being biological macromolecules, are recognized for their capacity to enhance adhesion to wood substrates. This study considered the development of protein-based adhesives derived from diverse sources, including soybean meal, microbrewery spent grains, shrimp shells, and skim milk powder. These raw materials were subjected to mild alkaline conditions to yield protein concentrates. The resulting adhesives were formulated at various protein content levels: 5%, 10%, 15%, and 20%. The study’s findings showed that the incorporation of proteins into the polyurethane adhesive system not only can preserve but also augment adhesive performance. This enhancement encompasses deeper penetration into wood substrates and an overall improvement in mechanical strength. These results underscore the promise of proteins as a sustainable alternative to petroleum-based polyols in adhesive formulations.

A review of the chemical modification and applications of starch

The modification of starch using esterification, etherification, oxidation, and Schiff base formation has garnered significant interest owing to its wide-ranging applications in different sectors. This overview delves into the various techniques utilized for modifying starch molecules and examines their utilization in adsorption, adhesive formulations, pharmaceuticals, nanoparticle synthesis, and film manufacturing. The article delves into the synthesis pathways associated with esterification, etherification, oxidation, and Schiff base formation, underscoring their influence on the physicochemical characteristics of starch. Furthermore, it thoroughly examines the application of modified starch in pollutant adsorption processes, as adhesive agents in industries, as excipients in pharmaceutical formulations, and as crucial elements in the creation of starch-based nanoparticles and films.

Salicylhydroxamic acid containing structural adhesive.

The feasibility of utilizing salicylhydroxamic acid (SHAM) as a new adhesive molecule for designing structural adhesives is investigated in this study. SHAM-containing polymers were prepared with a hydroxyethyl methacrylate (HEMA) or methoxyethyl acrylate (MEA) backbone and mixed with polyvinylidene fluoride (PVDF). PVDF was included to increase the cohesive property of the adhesive through hydrogen bond (H-bond) formation with the adhesive polymers. SHAM-containing adhesive demonstrated lap shear adhesion strength (S adh) greater than 0.9 MPa to glass, metal, and polymeric surfaces. Adhesive formulations with elevated SHAM-content also demonstrated increased adhesive properties with S adh values reaching as high as 4.8 MPa. Due to the physically crosslinked nature of these adhesives, formulations with extensive H-bonding resulted in strong adhesion and stability. HEMA consists of a terminal hydroxyl group with both H-bond donor and acceptor, which enabled HEMA-containing adhesives to demonstrate strong adhesion even without PVDF. On the other hand, MEA contains a methoxy group that lacks H-bond donors for forming H-bonding and MEA-containing adhesives required PVDF to provide H-bond acceptors to increase its cohesive property. An aging study was performed on the bonded joints. While the adhesive joints did not demonstrate any reduction in S adh values over 25 days when incubated in a dry condition, S adh values decreased by 80% over 48 h when incubated in water. This is potentially due to the hydrophilic and physically crosslinked nature of the adhesive. Nevertheless, the SHAM-containing adhesive outperformed a catechol-containing adhesive and epoxy glue and is a promising new adhesive molecule for designing structural adhesives.

Molecular behavior of silicone adhesive at buried polymer interface studied by molecular dynamics simulation and sum frequency generation vibrational spectroscopy.

Silicones have excellent material properties and are used extensively in many applications, ranging from adhesives and lubricants to electrical insulation. To ensure strong adhesion of silicone adhesives to a wide variety of substrates, silane-based adhesion promotors are typically blended into the silicone adhesive formulation. However, little is known at the molecular level about the true silane adhesion promotion mechanism, which limits the ability to develop even more effective adhesion promoters. To understand the adhesion promotion mechanism of silane molecules at the molecular level, this study has used sum frequency generation vibrational spectroscopy (SFG) to determine the behavior of (3-glycidoxypropyl)trimethoxy silane (γ-GPS) at the buried interface between poly(ethylene terephthalate) (PET) and a bulk silicone adhesive. To complement and extend the SFG results, atomistic molecular dynamics (MD) simulations were applied to investigate molecular behavior and interfacial interaction of γ-GPS at the silicone/PET interface. Free energy computations were used to study the γ-GPS interaction in the sample system and determine the γ-GPS interfacial segregation mechanism. Both experiments and simulations consistently show that γ-GPS molecules prefer to segregate at the interface between PET and PDMS. The methoxy groups on γ-GPS molecules orient toward the PDMS polymer phase. The consistent picture of interfacial structure emerging from both simulation and experiment provides enhanced insight on how γ-GPS behaves in the silicone - PET system and illustrates why γ-GPS could improve the adhesion of silicone adhesive, leading to further understanding of silicone adhesion mechanisms useful in the design of silicone adhesives with improved performance.