Adhesive Bonding to Galvanized Steel: II. Substrate Chemistry, Morphology and Bond Failure Analysis

Galvanized substrate morphology, oxide layer chemistry, bond failure modes, failure loci, and bondline corrosion have been investigated for adhesive bonds to galvanized steel. Significant differences in surface morphology were observed between the relatively smooth surfaces of “hot-dipped” substrates and the considerably rougher texture of “electroplated” substrates. The hot-dipped substrates were also chemically heterogeneous, with significant amounts of Al, Mg, Ca, and Pb, in addition to Zn, constituting the surface layer. For electroplated substrates, on the other hand, Zn was the major constituent. It was concluded that, for a given adhesive, low strengths and poor bond durability generally correlated with the minimum surface roughness and maximum chemical heterogeneity of the hot-dipped substrates. Higher strengths, and better durability, on the other hand, were observed for electroplated substrates, which showed the greater roughness, as well as chemically the more uniform surface.

Significantly, ESCA spectroscopy of fracture surfaces of unaged samples established that failure loci for both one and two-part epoxy adhesives included the oxide layer of the substrate. This was true for both hot-dipped, as well as electroplated substrates. For aged samples, scanning electron microscopy and X-ray diffraction analysis of failure surface identified zinc-based corrosion products present in the original bond area.     

建筑结构粘结剂的研究进展

在综合分析国内外文献的基础上,本文简述了粘结剂的发展历史,它在建筑业中的应用现状及在现代建筑业中的地位;研究了建筑结构粘结剂的主要性能指标,粘结剂连接的优点和主要技术检验指标等.此外,对目前广受关注的粘结剂耐久性研究的试验方法做了总结,列举了最新研究进展.在此基础上,指出了目前研究的不足,提出了对研究方向的建议.     

Effect of adhesive‐coated glass fiber in natural rubber (NR), acrylonitrile rubber (NBR), and ethylene–propylene–diene rubber (EPDM) formulations. II. Effect of cyclic loading,abrasion, and accelerated aging

Treated glass fibers (RICS, 3 and 6 mm in length) were added at a concentrations of 10, 20, and 30 phr in natural rubber (NR), nitrile rubber (NBR), and ethylene–propylene–diene comonomer (EPDM) formulations, in both plain and carbon black mixes. The compounds were mixed in two‐roll mill and were evaluated for their resistance to hot‐air aging, abrasion, compression set, Goodrich heat buildup, De Mattia fatigue, and for NR mixes, adhesion in the tensile mode. The vulcanizates of the three rubbers showed resistance to hot‐air aging. Abrasion resistance was poor for NR, and it improved with carbon black addition in the presence of treated glass fiber in NBR. In carbon‐black‐added EPDM vulcanizates, the abrasion resistance and fatigue resistance were better. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1124–1135, 2004     

Water‐soluble/dispersible cationic pressure‐sensitive adhesives. I. Adhesives from solution polymerization

Pressure‐sensitive adhesives (PSAs) have long been a problem as sticky contaminants for paper recycling mills. The main problem associated with such stickies is that the PSAs in the waste papers deposit on the felts, press rolls, and drying cylinders of paper machines, and this creates problems with paper formation, reducing the paper quality and paper machine runnability. The annual cost of stickies to the U.S. paper industry is estimated to be about $600,000,000–650,000,000. To solve this problem, a series of cationic water‐soluble/dispersible PSAs have been synthesized by the free‐radical solution polymerization of butyl acrylate and [3‐(methacryloylamino)propyl]trimethylammonium chloride in ethanol. The PSA end‐use properties, repulpability in paper recycling, and the effects on the properties of recycled paper products have been studied. The cationic PSAs can be dissolved or dispersed in water if the cationic charge density in the PSA backbone is controlled, and so they do not deposit as stickies during recycling and papermaking processes. Because the PSAs are cationically charged, they can easily be removed from the papermaking system by adsorption onto the negatively charged fibers and fine surfaces. Furthermore, the adsorbed colloidal or dissolved PSAs have little effect on the final paper properties. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1624–1630, 2003     

An NMR‐MOUSE® for Analysis of Thin Objects

A special unilateral NMR sensor has been designed for investigations of thin samples with a thickness of less than 1 mm and of surface effects of polymers. For use with the bar‐magnet NMR‐MOUSE®, the so‐called “crazy coil” is introduced with a low penetration depth. It is a flat meander coil etched on a printed circuit board with wiggles in the conductors. The design of the new coil and FEM simulations of the B ₁ field are presented. Different applications are discussed by means of illustrative examples. They are the detection of surface damage in rubber samples, the swelling and drying of a latex membrane exposed to cyclohexane vapor mimicking a chemical sensor, and the drying of a thin sprayed adhesive layer.

Bar‐magnet NMR‐MOUSE® with crazy coil.     

Reactivity,chemical structure,and molecular mobility of urea–formaldehyde adhesives synthesized under different conditions using FTIR and solid‐state 13C CP/MAS NMR spectroscopy

This study was conducted to investigate the effects of reaction pH condition and hardener type on the reactivity, chemical structure, and molecular mobility of urea–formaldehyde (UF) resins. Three different reaction pH conditions, such as alkaline (7.5), weak acid (4.5), and strong acid (1.0), were used to synthesize UF resins, which were cured by adding four different hardeners (ammonium chloride, ammonium sulfate, ammonium citrate, and zinc nitrate) to measure gel time as the reactivity. FTIR and ¹³C‐NMR spectroscopies were used to study the chemical structure of the resin prepared under three different reaction pH conditions. The gel time of UF resins decreased with an increase in the amount of ammonium chloride, ammonium sulfate, and ammonium citrate added in the resins, whereas the gel time increased when zinc nitrate was added. Both FTIR and ¹³C‐NMR spectroscopies showed that the strong reaction pH condition produced uronic structures in UF resin, whereas both alkaline and weak‐acid conditions produced quite similar chemical species in the resins. The proton rotating‐frame spin–lattice relaxation time (T_1ρH) decreased with a decrease in the reaction pH of UF resin. This result indicates that the molecular mobility of UF resin increases with a decrease in the reaction pH used during its synthesis. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2677–2687, 2003     

Crosslinked acrylic pressure‐sensitive adhesives. II. Effect of humidity on the crosslinking reaction

The effect of humidity during storage on the crosslinking reactions of isocyanate groups was investigated with attenuated total reflectance Fourier transform infrared spectroscopy with pressure‐sensitive adhesives composed of poly[ethyl acrylate‐co‐(2‐ethylhexyl acrylate)‐co‐(2‐hydroxyethyl methacrylate)] as a base resin and polyisocyanate as a crosslinker. A peak‐resolving analysis of the amide II region revealed four bands. According to an analysis of the Fourier transform infrared spectra of the model compounds, these four bands were assigned to free urethane linkages, hydrogen‐bonded urethane linkages, free urea linkages, and hydrogen‐bonded urea linkages. As expected, storage under humid conditions led to the formation of free and hydrogen‐bonded urea linkages corresponding to the promotion of isocyanate consumption. Peak resolution of the amide II region was found to be a reasonable way of monitoring urethane and urea linkages during crosslinking reactions. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3039–3045, 2003     

Thiol-ene emulsion polymerization using a semi-continuous approach

The thermally initiated thiol-ene emulsion polymerization of diallyl phthalate (DAP) diene and ethylenedioxy diethanthiol (EDDT) dithiol monomers in batch and semibatch emulsion polymerization is investigated. The batch process leads to larger and broader particle sizes than when the polymerization is carried out in semibatch. The evolution of the particle size and the final particle size distribution indicate that the stability of the latexes is limited and, hence, aggregation phenomena occurred in both processes. In particular, the evolution of the particle size distribution (PSD) in the semibatch process indicates nucleation, growth, and aggregation occurring simultaneously that produced a bimodal particle size. When the diene monomer was changed to diallyl terephthalate (DATP), the semibatch polymerization yielded smaller particles and narrow distribution without any indication of aggregation. The partial substitution of the dithiol by a trithiol monomer that is substantially more water insoluble affected nucleation of the particles, yielding for both systems smaller particles. The polythioether polymers synthesized present low glass transition temperatures (~ −30/−40°C) and those containing the therephthalate yield crystalline films. The potential application of the polymers as pressure sensitive adhesives (PSAs) was preliminarily assessed.     

The comparative study of biocomposites based on hydrochar and chitosan-modified urea-formaldehyde resins

To provide new insight into the field of urea-formaldehyde (UF) adhesives science, in this work, for the first time, UF resin was modified with hydrochar of spent mushroom substrate (HCUF) and chitosan (CHUF) to investigate the effect of these bio-fillers on the hydrolytic and thermal stability of in situ prepared UF resins. The characterization of the modified UF biocomposites was performed using X-ray diffraction analysis (XRD), Fourier transforms infrared spectroscopy (FTIR), non-isothermal thermogravimetric analysis (TG), differential thermal gravimetry (DTG), and differential thermal analysis (DTA). Scanning electron micrographs (SEM) of the CHUF and HCUF biocomposites show a spherical structure that differs from each other because the surface of the CHUF biocomposite has pronounced pores that form a network structure. With its hydroxyl and amino groups, chitosan bonding to UF resin through hydrogen bonds, which is confirmed by FTIR analysis. The content of free FA in CHUF biocomposite is 0.06%, while that of HCUF is higher and amounts to 0.48%. The content of released FA in both modified UF biocomposites was similar (2.5% and 2.8% for CHUF and HCUF, respectively). The hydrolytic stability of CHUF is slightly higher compared to the HCUF biocomposite. Thermal analysis shows that the CHUF is thermally more stable because it starts to decompose at a slightly higher temperature than the HCUF biocomposite.     

Effect of hydrolysis and denaturation of wheat gluten on adhesive bond strength of wood joints

In this study the adhesive bond strength of different wheat gluten modifications and the relationship between molecular weight and adhesive strength was examined. Guanidine hydrochloride and sodium hydroxide were used as denaturation and dispersing agent. Additionally wheat proteins were hydrolyzed by alkaline conditions and enzymes. Effects of different treatments were observed by viscosity measurements and gel electrophoresis. Wood lap joints were prepared with modified proteins and tensile shear strength was tested under dry and wet conditions. In situ hardening of different formulations was analyzed by means of DMA with two‐layered specimens in a three‐point bending test set‐up. Higher solubility had no positive effect on dry bonding strength and wet bonding strength was even reduced. Depending on the degree of hydrolysis, significant improvement of adhesive bond strength was observed. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013