Preparation of Environmentally Friendly Urea-Hexanediamine-Glyoxal(HUG)Resin Wood Adhesive

Using non-toxic,low-volatile glyoxal to completely replace formaldehyde for preparing urea-glyoxal(UG)resin adhesive is a hot research topic that could be of great interest for the wood industry.However,urea-glyoxal(UG)resins prepared by just using glyoxal instead of formaldehyde usually yields a lower degree of polymerization.This results in a poorer bonding performance and water resistance of UG resins.A good solution is to pre-react urea to preform polyurea molecules presenting already a certain degree of polymerization,and then to condense these with glyoxal to obtain a novel UG resin.Therefore,in this present work,the urea was reacted with hexamethylene diamine to form a polyurea named HU,and then this was used to react it with different amounts of glyoxal to synthesize hexamethylenediamine-urea-glyoxal(HUG)polycondensation resins,and to use this for bonding plywood.The results show that the glyoxal can well react with HU polyuria via addition and schiff base reaction,and also the HUG resin exhibits excellent bonding strength and water resistance.The shear strength of the plywood bonded with this HUG at 160°C hot press temperature as high as 1.93 MPa,2.16 MPa and 1.61 MPa,respectively,which meets the requirement of the China national standard GB/T 9846-2015(≥0.7 MPa),and can be a good choice as a wood adhesive for industrial application.

MUF Resins Improved by Citric Acid as Adhesives for Wood Veneer Panels

This article presents the first applied results of using citric acid in combinations with a melamine-urea-formal-dehyde(MUF)resin for bonding wood veneers.The chemical reactions involved are shown based on a MALDI ToF analysis of the reaction of the MUF resin with citric acid.The preliminary results of the physical and mechanical properties of the LVL prepared are also presented.Veneers from Populus sp were used to manufacture 5-layer laminated veneer lumber(LVL)of small dimensions.Five combinations of the amount of citric acid,MUF spread rate and pressing parameters were tested.LVL bonded with 20%of citric acid+100 g/m^(2)of MUF,hot-pressed using a 3-step process with maximum 1.5 MPa of pressure yielded the board with better dimensional stability and mechanical properties.It could be concluded that citric acid in combination with MUF can be used for bonding wood veneer and the research should be continued to study further the parameters involved and to enhance the results.

Study on Camellia Oleifera Protein based Wood Adhesive by Epoxy Resin and Its Crosslinking Mechanism

Epoxy resin (EPR) was used to crosslink with Camellia oleifera Abel.protein to prepare wood adhesive,and the bonding performance and curing characteristics of which were mainly investigated,and the synthesis mechanism was also discussed by using model compounds.The experimental results show that EPR can significantly improve the bonding performance of Camellia oleifera Abel.protein-based adhesive,and the maximum of which reaches 0.72 MPa satisfies the strength requirement of Type II plywood in GB/T 17657-2013.After alkali treatment,the protein can more easily crosslink with EPR at low curing temperature,and the adhesive has high degree of crystallinity of curing products,high degree of crosslinking reaction,and high bonding strength.The reaction mechanism of EPR-modified Camellia oleifera Abel.protein adhesive can be divided into resinification phase and curing phase.

Determination of Water Diffusion Coefficients and Dynamics in Adhesive/Carbon Fiber Reinforced Epoxy Resin Composite Joints

To determinate the water diffusion coefficients and dynamics in adhesive/carben fiber reinforced epoxy resin composite joints, energy dispersive X-ray spectroscopy analysis（EDX） is used to establish the content change of oxy- gen in the adhesive in adhesive/carbon fther reinforced epoxy resin composite joints. As water is made up of oxygen and hydrogen, the water diffusion coefficients and dynamics in adhesive/carben fiber reinforced epoxy resin composite joints can be obtained from the change in the content of oxygen in the adhesive during humidity aging, via EDX analy-sis. The authors have calculated the water diffusion coefficients and dynamics in the adhesive/carbon fiber reinforced epoxy resin composite joints with the aid of beth energy dispersive X-ray spectroscopy and elemental analysis. The de- termined results with EDX analysis are almost the same as those determined with elemental analysis and the results al- so show that the durability of the adhesive/carbon fther reinforced epoxy resin composite joints subjected to silane cou- pling agent treatment is better than those subjected to sand paper burnishing treatment and chemical oxidation treat- ment.

SEM Comparison of Penetration in Artificial White Spots Lesion between an Infiltrant Resin and Two Adhesive Systems

White spot infiltration emerged as an alternative of non-invasive treatment to halt progression of the lesion, through the use of low viscosity resins that would permeate the porous enamel and form a physical barrier that would prevent the acid diffusion produced by micro-organisms. Purpose: To compare penetration levels in artificial white spot lesions, of infiltrant resin ICON™and 2 conventional adhesives systems, XP-Bond™and Single Bond 2™. Methodology: White spot lesions (ICDAS code 2) were caused in 75 premolars or third molars were extracted in good conditions, by immersion in a 0.1 M lactic acid solution (pH 4.5) at 37℃ for 8 weeks. They were divided randomly into 3 groups of 25 samples and applied the following resins, Group A: ICON™, B: XP-Bond™and C: Single Bond 2™. Subsequently, the enamel was removed with hydrochloric acid to expose resin saturated area and the samples were metalized with Au-Pd for SEM observation. The resin tags lengths were measured on microphotographs through software, and the values were analyzed with the statistics ANOVA and Scheffé post-test. Results: There were significant differences (p ™(82.7 μm ± 26.8 μm) compared to adhesive systems XP-Bond™(58.5 μm ± 29.3 μm) and Single Bond 2™(44.8 μm ± 32.5 μm). We found no significant differences between the two adhesive systems (p > 0.05). Conclusion: Under the conditions tested, the penetration of infiltrant ICON was significantly higher than the adhesive systems;however, it removes the surface layer of the enamel.

A Boron-based Adhesion Aid for Efficient Bonding of Silicone Rubber and Epoxy Resin

We improved the adhesion between silicon based insulating materials and epoxy resin composites by adding the adhesion promoter cycloborosiloxane(BSi,cyclo-1,3,3,5,7,7-hexaphenyl-1,5-diboro-3,7-disiloxane).The experimental results show that the addition of BSi in the silicone rubber(SR)system significantly increases the tensile shear strength between BSi and epoxy resin(EP),reaching 309%of the original value.On this basis,the mechanism of BSi to enhance the adhesion effect was discussed.The electron deficient B in BSi attracted the electron rich N and O in EP to enhance the chemical interaction,combined with the interfacial migration behavior in the curing process,to improve the adhesion strength.This study provides the design and synthesis ideas of adhesive aids,and a reference for further exploring the interface mechanism of epoxy resin matrix composites.

New composite grouting materials:Modified urea-formaldehyde resin with cement

A new composite two component grout comprised of modified urea-formaldehyde resin and cement was formulated to take account of the advantages and disadvantages of both the cement grout and the chem- ical grout. The new grout is designed for water blocking by reinforcing as well as seepage control by bore grouting. The A component consists of a modified urea-formaldehyde resin A component, some cement, and some water. The B component is an alkaline coagulant. An orthogonal test of four factors at three lev- els showed that gel time increased with increased water content and with urea-formaldehyde resin con- tent. Gel time decreased at increased levels of alkaline coagulant. The A component of this new composite grout is stable over time. A mixed cross-over test showed that as the volume ratio of A to B increases the gel time falls at first but then increases. The solid strength decreases with increasing levels of the B com- ponent. The solid strength increases over time and becomes stable by the 28th day after mixing. The vis- cosity increases with increasing levels of resin A component. The increase is exponential and may be fit to： μ = 8.162e0.0286x.

Effect of Self-adhesive Resin Cement and Tribochemical Treatment on Bond Strength to Zirconia

Aim To evaluate the interactive effects of different self- adhesive resin cements and tribochemical treatment on bond strength to zirconia. Methodology The following self-adhesive resin cements for bonding two zirconia blocks were evaluated： Maxcem （MA）, Smartcem （SM）, Rely X Unicem Aplicap （UN）, Breeze （BR）, Biscem （BI）, Set （SE）, and Clearfil SA luting （CL）. The specimens were grouped according to conditioning as follows： Group 1, polishing with 600 grit polishing paper; Group 2, silica coating with 110 μm Al2O3 particles which modified with silica; and, Group 3, tribochemical treatment - silica coating ＋ silanization. Specimens were stored in distilled water at 37℃ for 24 hours before testing shear bond strength. Results Silica coating and tribochemical treatment significantly increased the bond strength of the MA, UN, BR, B1, SE and CL to zirconia compared to #600 polishing. For both #600 polished and silica coating treatments, MDP- containing self-adhesive resin cement CL had the highest bond strengths to zirconia. Conclusion Applying silica coating and tribochemical treatment improved the bond strength of self-adhesive resin cement to zirconia, especially for CL.

YbF_3/SiO_2 Fillers as Radiopacifiers in a Dental Adhesive Resin

The objective of this study was to evaluate the effect of functionalizing a dental adhesive resin with YbF_3/SiO_2 fillers for use as radiopacifiers.Particles of YbF_3/SiO_2 were obtained with the high-energy mechanical milling method and characterized by both physical and chemical methods.After characterization,the particles were sieved and silanized prior to being incorporated into an adhesive resin.The stability of the particle suspension was then evaluated.After light activation,the radiopacity,degree of conversion,flexural strength and elastic modulus were determined.The dental adhesive resins with 10 and 15 wt% of filler provided satisfactory radiopacity,while flexural strength and elastic modulus were not affected.The degree of conversion was statistically lower than that of the control(p<0.05).The method used for incorporating the tested ytterbium fluoride/silicon dioxide particles at concentrations of 10 and 15 wt% was shown to be feasible for the development of a radiopaque dental adhesive system.

STUDIES ON IPE OF POLYACRYLAMIDE INVERSE EMULSION AND MODIFIDE UREA-FORMALDEHYDE RESIN

The selective water plugging agent was prepared by heating the blends of the polyacry-lamide inverse latex, modified urea formaldehyde resin, crosslinking agent and catalysts.The results show that using different types of polymers and additives or changing in theirproportion of the blends, the gelling viscosity, starting point of gelling and other propertiesof the IPN can be controlled.

Short Communication—A Novel Sample Preparation Method That Enables Ultrathin Sectioning of Urea-Formaldehyde Resin for Imaging by Transmission Electron Microscopy

Urea-formaldehyde (UF) resin is widely used as an adhesive for the manufacture of a range of wood and fiber based products. Although the microstructure of this resin has been examined at high resolution by field-emission scanning electron microscopy and atomic force microscopy, transmission electron microscopy (TEM) has thus far not been used, perhaps because of difficulties in ultrathin sectioning this resin in cured (polymerized) state. In the technical note presented here, a novel sample preparation method is described which enabled us to examine the microstructural morphology of UF resin by transmission electron microscopy in ultrathin sections, revealing the presence of spherical particles within the resin. Our initial attempt to ultrathin section the resin directly was not successful as it was too brittle to trim blocks for sectioning. Then, we developed a sample preparation technique that involved impregnation ofPinus radiatawood tissues with the UF resin, and then embedding of resin impregnated wood tissues with Spurr’s low viscosity embedding medium, which has been widely employed in plant and wood ultrastructure work. The TEM images illustrated and the information on the microstructural morphology of the UF resin presented are based on this novel sample preparation approach.

Enhancing adhesive bond strength of CFRP/titanium joints through NaOH anodising and resin pre-coating treatments with optimised anodising conditions

Adhesively Bonded Carbon Fibre Reinforced Plastic(CFRP)and titanium alloy have been extensively used as a hybrid structure in modern aircrafts due to their excellent combination of mechanical properties and chemical stabilities.This study utilised NaOH anodising method to create micro-rough titanium surfaces for enhancing adhesive bonding between titanium alloy and CFRP laminates.A special and simple technique named Resin Pre-Coating(RPC)was also employed to improve the surface wetting of anodised titanium and grinded CFRP substrates.The influences of anodising temperature and duration on the surface morphology,wettability and adhesive bond strength were investigated.The single lap shear test results showed that the bond strength of specimens anodised at 20℃for 15 min improved by 135.9%and 95.4%,respectively,in comparison with that of acid pickled and grinded specimens(without RPC treatment).Although increasing the anodising temperature and duration produced rougher titanium surfaces,the adhesively bonded joints were not strong enough due to relatively friable titanium oxide layers.

Synthetic Process of Bio-Based Phenol Formaldehyde Adhesive Derived from Demethylated Wheat Straw Alkali Lignin and Its Curing Behavior

Lignin is a natural biopolymer with a complex three-dimensional network, commercially obtained from wasteliquid of paper pulp and bioethanol production, and could be a candidate for preparation of environment-friendlybio-based polyphenol material. In the present work, the demethylated wheat straw alkali lignin (D-Lig), preparedby demethylation of wheat straw alkali lignin (Lig) using an in-situ generated Lewis acid, was used to synthesizebio-based phenol formaldehyde resin adhesive (D-LPF) applied in plywood. Effects of synthetic process’s factors,including lignin substitution for phenol, NaOH concentration and molar ratio of formaldehyde to phenol, on thebonding strength and free formaldehyde content of D-LPF were investigated in detail, and the optimum syntheticprocess of D-LPF was obtained as following: Lignin substitution for phenol 60%, NaOH concentration 5.0% andmolar ratio of formaldehyde to phenol 2.0, and under the optimum reaction condition, the D-LPF presented lower free formaldehyde content (0.18%) and higher bonding strength (2.19 MPa), which was better than those ofcontaining-lignin phenol formaldehyde resin adhesive (LPF). Additionally, the curing behavior of the adhesivewas studied by differential scanning calorimetry (DSC) combined with gel time. It can be obtained that D-LPFresin adhesive had the shortest gel time, and fastest curing rate, compared with those of PF and L-PF resin adhesives. The curing kinetics data was fitted well by Kissinger model using non-isothermal DSC method, and theaverage activation energy value was 85.3 kJ/mol, slightly higher than that of commercial PF resin, while lowerthan that of LPF (90.2 kJ/mol). Finally, based on the analytical results of high temperature fourier transform infrared spectroscopy (FTIR), a possible curing mechanism of D-LPF was proposed.

Preparation of the Heat Resistant Adhesive of NBR Modified BMI

A Kind of homogeneous resin , which can be used as thermal resistant adhesive and matrix for composite, was prepared by bis (4-maleimidophenyl) methane ( BMI), 4,4’ -diaminodiphenylmethane( DDM), aniline (An), phenol type epoxy resin ( F-51 ) and nitrile -butadiene rubber ( NRR) through solution copolymer-ization . The reaction from prepolymerization to curing of the resin system was studied. And the factors such as raw material ratio and curing temperature, which affect thermal resistance and adhesives of cured product, were also analyzed. SEM and IR spectra were utilized to discuss the mechanisms of toughness and reaction of modified BMI.

Synthesis of Green Adhesive with Tannin Extracted from Eucalyptus Bark for Potential Use in Wood Composites

Recently,the exploitation of renewable plant resources in the formulation of adhesives is very promising for their availability at low coast,as well as their richness in biomolecules such as polyphenols.In this way,many research studies tannins extracted from different sources such as mimosa,quebracho,and pine have been the subject of very satisfactory recent studies.In this paper,a new complete characterization of the tannins extracted from the bark of eucalyptus globulus harvested from two regions in Algeria was achieved.The structural characterization enabled us to confirm the richness in condensed tannins,particularly in procyanidin and prodelphinidin units.The most reactive tannins obtained during extraction at 70℃(yield:27.1%)have a Stiasny number of 75.92%.This extract was used for the formulation of adhesives(tannin/hexamine).The thermal characterizaction of the adhesives showed higher stability for the tannin formulation of eucalyptus/hexamine as well as an excellent mechanical performance with a MOE of 2807 MPa at 180℃and shear strength of 689.4 N/mm^(2).

In vitro analysis of riboflavin-modified,experimental,two-step etch-and-rinse dentin adhesive:Fourier transform infrared spectroscopy and micro-Raman studies

To modify two-step experimental etch-and-rinse dentin adhesive with different concentrations of riboflavin and to study its effect on the bond strength,degree of conversion,along with resin infiltration within the demineralized dentin substrate,an experimental adhesive-system was modified with different concentrations of riboflavin（mlm,0,1%,3%,5%and 10%）.Dentin surfaces were etched with 37%phosphoric acid,bonded with respective adhesives,restored with restorative composite-resin,and sectioned into resin-dentin slabs and beams to be stored for 24 h or 9 months in artificial saliva.Micro-tensile bond testing was performed with scanning electron microscopy to analyse the failure of debonded beams.The degree of conversion was evaluated with Fourier transform infrared spectroscopy（FTIR） at different time points along with micro-Raman spectroscopy analysis.Data was analyzed with one-way and two-way analysis of variance followed by Tukey＇s for pair-wise comparison.Modification with 1%and 3%riboflavin increased the micro-tensile bond strength compared to the control at 24 h and 9-month storage with no significant differences in degree of conversion（P〈0.05）.The most predominant failure mode was the mixed fracture among all specimens except 10%riboflavin-modified adhesive specimens where cohesive failure was predominant.Raman analysis revealed that 1%and 3%riboflavin adhesives specimens showed relatively higher resin infiltration.The incorporation of riboflavin in the experimental two-step etch-and-rinse adhesive at 3%（mlm） improved the immediate bond strengths and bond durability after 9-month storage in artificial saliva without adversely affecting the degree of conversion of the adhesive monomers and resin infiltration.

600 Mesh Silicon Carbide Corona Protection Varnish with EPOXY/OMMT Nano-composite Adhesive

A new corona protection varnish was prepared by using epoxy/montmorillonite nanocomposite and pure epoxy resin as adhesives respectively.The adhesive with different amounts of organic montmorillonite（OMMT） was mixed with 1200 mesh silicon carbide（Si C） by different weight ratios.The surface states of the varnishes with various adhesives were observed by powerful optical microscope.Some properties of the varnishes were analyzed during the enduring time under 5kV/cm DC,such as the relation of change in nonlinear coefficient,natural surface resistivity,and surface temperature variation.The results showed that the amounts of OMMT had little effect on the natural surface resistance of the varnish but had important influence on the nonlinear property of the varnish.When the range of the OMMT content was 2wt% to 6wt%,the nonlinear coefficient of all materials with epoxy/OMMT nano-composite adhesive was higher than that with pure epoxy resin adhesive.The surface temperature of the varnish with epoxy/OMMT nanocomposite adhesive was all lower than that with the pure epoxy resin adhesive under high electrical field strength.

Effect of enamel-grinding on adhesionstrength of enamel-resin junction

In this paper,we have tested the normal and mottled enamel in order to get some instructive information for the clinical treatment. As demonstrated by the results of our experiments, the grinding treatment of the enamel superficial layer has no significant improvement on the adhesional strength of the junction between the normally developed teeth and the resin. However, it does exhibit evident effect on the adhesional strength of the junction between the fluorosis teeth and the repairing resin.

水利工程用环氧树脂改性聚氨酯丙烯酸酯性能研究

水利工程金属结构和水工建筑物常遭受腐蚀、高速含沙水流磨蚀破坏,需对其进行便捷有效的防护。利用环氧树脂对聚氨酯丙烯酸酯(PUA)进行改性提高PUA与基体黏结性能,采用紫外光(UV)固化技术制备PUA涂层。研究了环氧树脂改性PUA的化学结构及环氧树脂用量对PUA的力学性能、热稳定性能、耐溶剂性能和抗冲磨性能的影响。结果表明,环氧树脂改性PUA的拉伸强度随着环氧树脂用量增加,呈下降趋势,当加入5%时,PUA拉伸强度为103.0 MPa,材料呈强而脆的特性。环氧树脂加入提升了PUA的拉伸剪切强度,由0.25 MPa增至1.60 MPa。同时,环氧树脂改性PUA具有良好的耐水性能、耐溶剂性能、抗冲磨性能,5%环氧树脂改性PUA抗冲磨强度为800 h/(kg·m^(2))。

石墨烯增强环氧树脂胶黏剂的研究进展

环氧树脂胶黏剂具有较高的强度、硬度和耐化学腐蚀性,故其应用越来越广泛。但它也存在一些缺点,如热稳定性差、导电性差等。二维石墨烯是一种具有高强度、高导电性、大比表面积等优异性能的材料,在环氧树脂胶黏剂中添加石墨烯可增强其性能。综述了石墨烯-环氧复合材料的制备及石墨烯对环氧胶黏剂的影响,展望了石墨烯-环氧复合材料的应用前景。未来,在石墨烯-环氧复合材料合成与加工过程中还需解决石墨烯的均匀分散、生产的可扩展性、与环氧树脂及固化剂的相容性等问题。