Crosslinking Mechanism of Soy Protein-based Adhesives based on Glyoxal and a Compound of Protein Model

The crosslinking mechanism of glyoxal and asparagine was analyzed,and the relationship between the mechanism and practical performances of soy protein-based adhesives was also discussed.It is shown that when pH=1 and 3,glyoxal reacted with asparagine in the form of major cyclic ether compounds.When pH=5,glyoxal reacted with asparagine in two structural forms of sodium glycollate and cyclic ether compounds.However,amidogens of asparagine were easy to develop protonation under acid conditions.Supplemented by the instability of cyclic ether compounds,the reaction activity and reaction degree between glyoxal and asparagine were relatively small.Under alkaline conditions,glyoxal mainly reacted with asparagine in the form of sodium glycollate.With the increase of pH,the polycondensation was more sufficient and the produced polycondensation products were more stable.The reaction mechanism between glyoxal and asparagine had strong correspondence to the practical performances of the adhesives.Glyoxal solution could develop crosslinking reactions with soy protein under both acid and alkaline conditions.Bonding strength and water resistance of the prepared soy protein-based adhesives were increased significantly.When pH>7,glyoxal had relatively high reaction activity and reaction intensity with soy protein,and the prepared adhesives had high crosslinking density and cohesion strength,showing relatively high bonding strength,water resistance and thermal stability.

Study on the Soy Protein-Based Adhesive Cross-Linked by Glyoxal

Based on the ESI-MS and ^(13)C-NMR analysis of the forms of glyoxal in acidic and alkaline solutions,the soy-based adhesive cross-linked by glyoxal was prepared in this work.The results showed that glyoxal existed in water in different forms at different pH levels.Under alkaline conditions,glyoxal transformed to glycolate through the intramolecular disproportionation reaction.Under acidic conditions,although some of glyoxal transformed to glycolate as what happened under alkaline conditions,most of glyoxal molecules existed in the form of fiveor six-membered cyclic ether structure.No ethylene tetraol or free aldehyde group was actually detected under these conditions.Although glyoxal reacted with soy protein under both acidic and alkaline conditions,alkaline conditions were more favorable for the improvement of mechanical performance and water resistance of soybased adhesives than acid conditions.

Adhesion of Technical Lignin-Based Non-Isocyanate Polyurethane Adhesives for Wood Bonding

Lignin is the most abundant aromatic natural polymer,and receiving great attention in replacing various petro-leum-based polymers.The aim of this study is to investigate the feasibility of technical lignin as a polyol for the synthesis of non-isocyanate polyurethane(NIPU)adhesives to substitute current polyurethane(PU)adhesives that have been synthesized with toxic isocyanate and polyols.Crude hardwood kraft lignin(C-HKL)was extracted from black liquor from a pulp mill followed by acetone fractionation to obtain acetone soluble-HKL(AS-HKL).Then,C-HKL,AS-HKL,and softwood sodium lignosulfonate(LS)were used for the synthesis of technical lignin-based NIPU adhesives through carbonation and polyamination and silane as a cross-linker.Their adhesion per-formance was determined for plywood.FTIR spectra showed the formation of urethane bonds and the reaction between lignin and silane.The NIPU adhesives prepared with C-HKL showed the highest adhesion strength among the three lignin-based NIPU adhesives.As the silane addition level increased,the adhesion strength of NIPU adhesives increased whereas formaldehyde emission decreased for all NIPU adhesives prepared.These results indicate that NIPU adhesives based on technical kraft lignin have a great potential as polyol for the synth-esis of bio-based NIPU adhesives for wood bonding.

Theoretical optimization of micropillar arrays for structurally stable bioinspired dry adhesives

Inspired by the excellent adhesion performances of setae structure from organisms,micro/nano-pillar array has become one of the paradigms for adhesive surfaces.The micropillar arrays are composed of the resin pillars for adhesion and the substrate with different elastic modulus for supporting.The stress singularity at the bi-material corner between the pillars and the substrate can induce the failure of the micropillar-substrate corner and further hinder the fabrication and application of micropillar arrays,yet the design for the stability of the micropillar array lacks systematical and quantitative guides.In this work,we develop a semi-analytical method to provide the full expressions for the stress distribution within the bi-material corner combining analytical derivations and numerical calculations.The predictions for the stress within the singularity field can be obtained based on the full expressions of the stress.The good agreement between the predictions and the FEM results demonstrates the high reliability of our method.By adopting the strain energy density factor approach,the stability of the pillar-substrate corner is assessed by predicting the failure at the corner.For the elastic mismatch between the pillar and substrate given in this paper,the stability can be improved by increasing the ratio of the shear modulus of the substrate to that of the micropillar.Our study provides accurate predictions for the stress distribution at the bi-material corner and can guide the optimization of material combinations of the pillars and the substrate for more stable bioinspired dry adhesives.

Properties of Bark Particleboard Bonded with Demethylated Lignin Adhesives Derived from Leucaena leucocephala Bark

Lignin extraction from bark can maximize the utilization of biomass waste,offer cost-effectiveness,and promote environmental friendliness when employed as an adhesive material in bark particleboard production.Particles of fine(0.2 to 1.0 mm),medium(1.0 to 2.5 mm),and coarse(2.5 to 12.0 mm)sizes,derived from the bark of Leucaena leucocephala,were hot-pressed using a heating plate at 175℃for 7 min to create single-layer particleboards measuring 320 mm×320 mm×10 mm,targeting a density of 700 kg/m^(3).Subsequently,the samples were trimmed and conditioned at 20℃and 65%relative humidity.In this study,we compared bark particleboard bonded with urea formaldehyde(UF)adhesive to fine-sized particleboard bonded with demethylated lignin adhesive.The results indicated that bark particleboards utilizing demethylated lignin and UF adhesives exhibited similar qualities.Coarse particleboard showed differences in modulus of elasticity(MOE)and modulus of rupture(MOR),while medium-sized particles exhibited significant variations in moisture content(MC)and water absorption(WA).Furthermore,the thickness swelling of coarse and medium-sized particles under wet and oven-dried conditions exhibited notable distinctions.Overall,the demethylated lignin adhesive extracted from L.leucocephala bark demonstrated similar quality to UF adhesive,with particle size correlating inversely to the strength of the bark particleboard.

Reinforcing Effect of Graphene in Epoxy Adhesives: Review

Due to its great strength, hardness, and chemical resistance, epoxy adhesives are becoming more and more used. They continue to have drawbacks, nevertheless, such as poor thermal stability, and poor electrical conductivity. Two-dimensional graphene is a wonderful substance with exceptional qualities including high strength, high electrical conductivity, and large surface area. Because of these characteristics, graphene has been thoroughly researched for its prospective uses in a variety of industries, including electronics, energy storage, and biomedical engineering. The use of graphene as an additive in epoxy adhesives to enhance the characteristics of such materials is one of its promising uses. This paper reviewed the latest findings about graphene’s effects on epoxy adhesives. The various methods to produce graphene-epoxy composites and their improvements are discussed. This research additionally discusses the challenges associated with the production and processing of graphene-epoxy composites, as well as the mechanisms behind the improvements in mechanical, electrical, and thermal characteristics. The final section of this review discusses the challenges and prospective uses of graphene in epoxy adhesives in the future.

RGS4 promotes the progression of gastric cancer through the focal adhesion kinase/phosphatidyl-inositol-3-kinase/protein kinase B pathway and epithelial-mesenchymal transition

BACKGROUND Regulator of G protein signaling(RGS)proteins participate in tumor formation and metastasis by acting on theα-subunit of heterotrimeric G proteins.The speci-fic effect of RGS,particularly RGS4,on the progression of gastric cancer(GC)is not yet clear.AIM To explore the role and underlying mechanisms of action of RGS4 in GC develop-ment.METHODS The prognostic significance of RGS4 in GC was analyzed using bioinformatics based public databases and verified by immunohistochemistry and quantitative polymerase chain reaction in 90 patients with GC.Function assays were employed to assess the carcinogenic impact of RGS4,and the mechanism of its possible influence was detected by western blot analysis.A nude mouse xenograft model was established to study the effects of RGS4 on GC growth in vitro.RESULTS RGS4 was highly expressed in GC tissues compared with matched adjacent normal tissues.Elevated RGS4 expression was correlated with increased tumor-node-metastasis stage,increased tumor grade as well as poorer overall survival in patients with GC.Cell experiments demonstrated that RGS4 knockdown suppressed GC cell proliferation,migration and invasion.Similarly,xenograft experiments confirmed that RGS4 silencing significantly inhibited tumor growth.Moreover,RGS4 knockdown resulted in reduced phosphorylation levels of focal adhesion kinase,phosphatidyl-inositol-3-kinase,and protein kinase B,decreased vimentin and N-cadherin,and elevated E-cadherin.CONCLUSION High RGS4 expression in GC indicates a worse prognosis and RGS4 is a prognostic marker.RGS4 influences tumor progression via the focal adhesion kinase/phosphatidyl-inositol-3-kinase/protein kinase B pathway and epithelial-mesenchymal transition.

Application of face centred cubic TiB powder as conductive filler for electrically conductive adhesives

Face centred cubic（FCC） TiB ceramic powder synthesized by Ti-boronizing method was used as conductive filler to make ceramic electrically conductive adhesives（ECAs） with the polymer matrix.Electrically conductive properties of the ceramic ECAs were studied.The bulk electrical resistivity varied with the powder content of the FCC-TiB in ECAs.The FCC-TiB filled ECAs also showed the percolation behavior that usually occurred for the metal-filled ECAs,the percolation threshold was located at the content of 60%FCC-TiB.A minimum value of 0.1 Ω·cm was obtained at a content of 75%FCC-TiB.In order to check the reliability of mechanical property,tensile test was done to measure the shear strength,and the shear strength dropped with increasing the content of FCC-TiB powders.It is about 12.26 MPa at the content of 70%TiB powders.The Cu filled ECAs were also prepared for comparison.The properties of the oxidation resistance of the two ECAs were evaluated.The results show that the ceramic ECAs have excellent oxidation resistance and better stability compared with the Cu filled ECAs.

Effects of medical adhesives in prevention of complications after endoscopic submucosal dissection

AIM:To evaluate the use of medical adhesive spray in endoscopic submucosal dissection (ESD). METHODS:Patients who underwent ESD between January 2009 and June 2012 (n = 173) were enrolled in the prospective randomized study. Two patients undergoing surgery due to severe intraoperative hemorrhage and failed hemostasis were excluded, and the remaining 171 patients were randomly divided into two groups:group A (medical adhesive group, n = 89) and group B (control group, n = 82). In group A, a medical adhesive spray was evenly applied after routine electrocoagulation and hemostasis using hemostatic clip after ESD. Patients in group B only treated with routine wound management. Intraoperative and postoperative data were collected and compared. RESULTS:In all 171 patients, ESD was successfully completed. There was no significant difference in the average treatment time between groups A and B (59.4 min vs 55.0 min, respectively). The average length of hospital stay was significantly different between group A and B (8.89 d vs 9.90 d, respectively). The incidence of intraoperative perforation was 10.1% in group A and 9.8% in group B, and was not significantly different between the two groups. In all cases, perforations were successfully managed endoscopically and with conservative treatment. The incidence of postoperative delayed bleeding in group A was significantly lower than that in group B (0.00% vs 4.88%, respectively). CONCLUSION:ESD is an effective minimally invasive treatment for gastrointestinal precancerous lesions or early-stage gastrointestinal cancer. Medical adhesive spray is effective in preventing delayed bleeding after ESD, and can thus reduce the average length of hospital stay.

State of research and trends in development of wood adhesives

We aim to present an overview of the status of adhesives in the wood industry, especially in the area of wood-based panels. The review summarizes the current state of research of two kinds of adhesives, i.e., synthetic adhesives and natural adhesives. Synthetic adhesives, consisting of urea-formaldehyde resins （UF）, phenol-formaldehyde resins （PF）, polyvinyl acetate emulsion （PVAc） and isocyanates, are widely used. For UF, most investigations are concerned with the reduction of free formaldehyde; for PF, most studies focus on finding new chemicals to replace phenol. PVAc has poor properties, but these can be improved by a blending reactions and copolymerization with other chemicals. Isocyanate is an environmentally friendly synthetic adhesive, but also suffers from inadequate properties. Natural adhesives, such as protein/starch, lignin and tannins, have poor bonding effect that limits their level of use, but their main advantages are that they are environmentally friendly and a renewable resource. Studies of modification can improve the bonding performances and gradually cause natural adhesives to become applied in industrial production. Some proposals for future development and the importance of environmentally friendly adhesives are provided, which will be helpful in future theoretical and experimental research.

Finite element analysis of multi-piece post-crown restoration using different types of adhesives

The multi-piece post-crown technique is more effective in restoring residual root than other restoration techniques.Various types of adhesives have different material properties that affect restoration.Therefore,the choice of adhesive is particularly important for patients.However,the effect of different kinds of adhesives was not too precise by experimental methods when concerning about individual differences of teeth.One tooth root can only be restored with one type of adhesive in experiment.After the mechanical test,this tooth root cannot be restored with other adhesives.With the help of medical imaging technology,reverse engineering and finite element analysis,a molar model can be reconstructed precisely and restored using different types of adhesives.The same occlusal and chewing loads were exerted on the same restored residual root models with different types of adhesives separately.Results of von Mises stress analysis showed that the adhesives with low Young’s modulus can protect the root canal effectively.However,a root canal concentration is apparently produced around the root canal orifice when chewing.Adhesives with large Young’s modulus can buffer the stress concentration of the root canal orifice.However,the root canal tissue may be destroyed because the adhesive is too hard to buffer the load.

No-Aldehydes Glucose/Sucrose-Triacetin-Diamine Wood Adhesives for Particleboard

A three reagents adhesive system for wood particleboards not containing any aldehyde was developed by the reaction of glucose or sucrose with triacetin(glycerin triacetate)and with hexamethylene diamine.The system was found to be based on the mix of three reactions,namely the reaction of(i)glucose with triacetin,(ii)of the diamine with triacetin,and(iii)of glucose with the diamine.The chemical species formed were identified by Matrix Assisted Laser Desorption Ionization Time of Flight(MALDI-ToF)mass spectrometry.Wood particleboard panels were prepared with this adhesive system and gave good internal bond(IB)strength results suitable for interior grade panels and with extremely low formaldehyde emission.

Starch-Based Adhesives for Wood/Wood Composite Bonding: Review

Increasing global energy crisis and scarcity of petroleum resources has shifted focus of chemical industries to look for alternative raw material resources. The main focus of raw materials in wood adhesives, such as petroleum and natural gas [1] [2], would be gradually replaced by renewable biopolymers. Starch is a relatively inexpensive and renewable product from abundant plants, easy processing and it has been extensively used as binders, sizing materials, glues and pastes [3], but its bonding capacity is not strong enough to glue wood [4]. Extensive research has been carried out on improving the cohesive properties, especially water resistance, of starch-based adhesives. In starch-based wood adhesive many new approaches have come forward for effective use it in wood/wood composite adhesive giving comparable performance as synthetic adhesives. This review of starch-based adhesives is made with the focus on starch modification methods for improving properties of starch-based adhesives.

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℃,for the NIPU adhesive 7 min at 200℃and for the UF 1.5 min at 100℃.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.

Passive smart self-repairing concrete beams by using shape memory alloy wires and fibers containing adhesives

An innovative approach to increase structural survivability of concrete and maintain structural durability of concrete was developed in case of earthquakes and typhoons. This approach takes advantage of the superelastic effect of shape memory alloy(SMA) and the cohering characteristic of repairing adhesive. These SMA wires and brittle fibers containing adhesives were embedded into concrete beams during concrete casting to form smart reinforced concrete beams. The self-repairing capacity of smart concrete beams was investigated by three-point bending tests. The experimental results show that SMA wires add self-restoration capacity,the concrete beams recover almost completely after incurring an extremely large deflection and the cracks are closed almost completely by the recovery forces of SMA wires. The number or areas of SMA wires has no influence on the tendency of deformation during loading and the tendency of reversion by the superelasticity. The adhesives released from the broken-open fibers fill voids and cracks. The repaired damage enables continued function and prevents further degradation.

Reliability aspects of electronics packaging technology using anisotropic conductive adhesives

Anisotropic conductive adhesive technology for electronics packaging and interconnect application has significantly been developed during the last few years. It is time to make a summary of what has been done in this field. The present paper reviews the technology development, especially from the reliability point of view. It is pointed out that anisotropic conductive adhesives are now widely used in many applications and the reliability data and models have been developed to a large extent for anisotropic conductive adhesives in various applications.

Nanocellulose Applications in Wood Adhesives—Review

Bio-based materials open a new world of possibilities in every field due to its independence from the petrochemical origin. Moreover, concerns on environmental footprints and toxicity of synthetic adhesives made scientists investigate the utilization of biomaterials for wood adhesives. In this perspective, nanocellulose as a sustainable and cheap bio-nanomaterial provides a better alternative to conventional adhesive based on formaldehyde-containing condensation resins. Property of nanocellulose to act as both binders and as structural reinforcement in various adhesive systems adds to its potential. Besides by reducing the harmful emission of formaldehyde, it also can improve the mechanical properties and enhance performance of adhesives. This review paper aims to point out the potential application of nanocellulose based wood adhesives compared to petroleum-based conventional systems beyond renewability. New functionalities through structural modification in nanocellulose could bring a replacement with the synthetic adhesive systems which will play a significant role in future bio-economy.

PVC gel bio-inspired adhesives with variable modulus and its application in a gripper

Inspired by the microstructure of gecko’s toe,two kinds of polyvinyl chloride(PVC)gels with different modulus were poured on a silicon mold with micropillars,and then a bio-inspired adhesive with variable modulus was manufactured in this study.The adhesions of variable modulus and fixed modulus bio-inspired adhesives were tested,respectively,on a smooth glass and a printed circuit board(PCB)with different surface structures.The results show that PVC gel bio-inspired adhesives with variable modulus have many advantages compared with the fixed modulus bioinspired adhesives.The adhesion of variable modulus bio-inspired adhesives on the rough PCB surface increased by 2−5 times,and due to the use of variable modulus of PVC gel,the surface micropillars can maintain high aspect ratio and flexible tips at the same time.Moreover,the use of PVC gel makes it easier to demold during the bio-inspired adhesives preparation.An adhesion-desorption device was made according to the movement of the gecko toes,and the PCB was successfully grasped.

A Soy Protein-Based Composite Film with a Hierarchical Structure Inspired by Nacre

Soy protein-based composite film is a potential replacement for petroleum-based film with multipurpose applica-tions and cleaner production.It is difficult to improve both the tensile strength and toughness of a protein-based film without sacrificing its elongation.In this study,inspired by the hierarchical structure of nacre,a facile yet delicate strategy was developed to fabricate a novel bio-based film with excellent toughness and high strength.Triglycidylamine(TGA)crosslinked soy protein(SPI)as hard phase and thermoplastic polyurethane elastomer(TPU)as soft phase comprise an alternative lay-up hierarchical structure.The interface of these two phases is enhanced using triglycidylamine(TGA)surface-modified TPU(MTPU).The tensile strength of SPI/MTPU/TGA films increases by 392%to 7.78 MPa and their toughness increases by 391%to 8.50 MJ/m^(3) compared to soy protein/glycerol film.The proposed hierarchical structure can also be extended to other high-performance materials and polymers.

Sustainable Raw Materials in Hot Melt Adhesives: A Review

Hot-melt (HM) adhesives offer advantages over their contemporary water-based and solvent-based adhesives like low volatile organic compounds (VOCs), 100% solid, fast drying, setting etc. In recent years, to reduce their dependence on dwindling petroleum resources and due to the enormous use of HM adhesives in packaging areas that demand 100% recyclability, efforts have been devoted to making these formulations completely bio-based, sustainable and biodegradable. In this attempt, research and developments have been focused on using starch, modified starch, soy protein, polylactides, polyamides, lignin and vegetable oils as a partial/fully replacement to the petrochemical-based polymers. The huge amount of research going on in the field of bio-based polymers has still not reached its complete potential in the field of HM adhesives. In this review paper, HM adhesives based on sustainable raw materials namely starch, modified starch, polyamides, poly (lactic acid), soy protein and lignin are discussed.