Sulfur Versus Non-Sulfur Containing Polyimide Adhesives for Bonding Steel

Due to their superior thermal and chemical stability, polyimides are often used as adhesives in harsh environments. This study examines the effect on bond strength of thioether sulfur in the polyimide backbone. Bonds were made using steel that was believed to catalyze the oxidation of sulfur. In addition, non-sulfur containing polyimides with similar T_g were also studied for comparison. The polymer/metal interface was studied using both the T-peel and wedge tests. No apparent effect was observed in the T-peel test with steel where the T-peel strengths of non-sulfur and sulfur containing polyimides were similar. In the wedge test, however, the sulfur-containing BDSDA/ODA bonded to steel had the smallest initial crack length of 34 mm. However, the BTDA/APB bonds tested in a dry environment had the smallest crack growth. The sulfur-containing BTDA/ASD performed best of the bonds tested in a wet environment. Metal-catalyzed oxidation of sulfur was observed to take place in the steel case, but not to an extent to have a noticeable effect on peel strength.     

纳米技术在聚氨酯胶粘剂中的应用及发展

概述了纳米复合聚氨酯胶粘剂的制备方法,综述了纳米技术在聚氨酯胶粘剂中的应用,并指出发展纳米技术的重要性。     

Structure of resorcinol,phenol, and furan resins by MALDI‐TOF mass spectrometry and 13C NMR

The structure of traditional, linear phenol–resorcinol–formaldehyde (PRF) resins, urea‐branched PRF resins, and phenol–resorcinol–furfural (PRFuran) resins has been investigated in depth by both matrix‐assisted laser desorption/ionization time of flight (MALDI‐TOF) mass spectroscopy and ¹³C NMR. The structure of a variety of oligomers has been obtained, and the structures present in each of the three types of resins related to the very different percentages of resorcinol needed for their equal performance as adhesives. The oligomers type and species distribution appeared very different for each case. PRF resins performance is improved by maximizing either the proportion of resorcinol‐containing oligomers or methylol‐groups containing oligomers, even without any resorcinol, or both. It is equally obtained by the minimization of the relative proportion of the low reactivity Phenol (CH₂ Phenol) species in which resorcinol is not present, this being the most important parameter. This can be obtained by more effective use of the resorcinol by just modifying the resin manufacturing procedure. This parameter instead does not appear to be determinant in PRFuran resins. In these, it is the higher molecular weight of furfural in relation to formaldehyde that engenders for the same manufacturing procedure a correspondingly lower proportion of resorcinol in the resin. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2665–2674, 2004     

Rheology,structure, and properties of ethylene–vinyl acetate/metallocene‐catalyzed ethylene–α‐olefin copolymer blends

The rheology, morphology, thermal, mechanical, and adhesive properties of blends containing ethylene–vinyl acetate and metallocene‐catalyzed ethylene–α‐olefin copolymers, containing butene and octene comonomers, were investigated. On the basis of the thermal and rheological properties and scanning electron microscopy observations, we deduced that these blends were immiscible, both in the solid and melt states over the whole range of compositions. Rheological properties were correlated to blend morphology with the Palierne emulsion model. The butene‐based blends had better mechanical properties, which was attributed to their finer morphology, lower interfacial tension, and better adhesive properties. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 881–889, 2004     

环氧胶粘剂增韧改性研究进展

概述了关于近些年环氧树脂以及环氧树脂胶粘剂增韧改性的研究进展情况,简单地介绍了以无机刚性填料(颗粒)增韧改性环氧胶粘剂的情况,比较详细地叙述了以橡胶弹性体和热塑性树脂增韧改性环氧胶粘剂的一些重要研究情况及相关的增韧机理,指出了国内外之间环氧胶粘剂发展的差距,同时提出了环氧胶粘剂将来的重点和发展趋势。     

Effect of poly(ethylene glycol) on the hydrophobic interactions and rheology of proanthocyanidin biopolymers from Pinus radiata

The rheology of solutions of extracts from the bark of Pinus radiata was investigated in the presence of poly(ethylene glycol)s (PEGs) of different molecular weights. PEG with a molecular weight of 4600 (1% w/w) was sufficient to reduce the viscosity of a concentrated (40% w/w) pine tannin extract by one order of magnitude. The reduction of the viscosity was due to the inhibition of molecular association via hydrogen bonding and hydrophobic interactions between tannin and PEG and depended on the molecular weight of PEG. PEG effectively reduced the viscosity of polyphenolic tannins but retained high reactivity toward paraformaldehyde for adhesive formulations. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1254–1260, 2005     

Use of organosolv lignin in phenol-formaldehyde resins for particleboard production: II. Particleboard production and properties

The objective of this work was to demonstrate the utility of lignin-based resins designed for application as an adhesive in the production of particleboard. Bond qualities of lignin-phenol-formaldehyde resins, phenolated-lignin-formaldehyde resins and commercial phenol-formaldehyde (PF-com) resin were assessed by using an automatic bonding evaluation system, prior to production of particleboards. In order to evaluate the quality of lignin-based resins, particleboards were produced and physical and mechanical properties were investigated. These physical properties included internal bond, modules of rupture and modulus of elasticity. Thickness swell and water absorption properties of particleboards bonded with lignin-based resins were also determined. The lignin-based resins have been reported previously in Part I of this study. The results showed that particleboards bonded with phenolated-lignin formaldehyde resins (up to 30% lignin content) exhibited similar physical and mechanical properties when compared to particleboards bonded with PF-com. The work has indicated that phenolated-lignin formaldehyde resins (up to 30% substitution level) can be used successfully as a wood adhesive for constructing particleboard. The performance of these panels is comparable to those of boards made using PF-com resin.     

The Effect of Moisture Content in Epoxy Film Adhesives on their Performance. III: Bulk Properties

Humidity absorbed by epoxy film adhesives during low temperature storage or exposure to atmosphere may result in reversible changes and irreversible modifications. Vacuum treatment may partially remedy the reversible changes. The consequences of vacuum drying are manifested in enhancement of both the peel and shear properties of bonded joints (Part I and Part II of this series of papers) and the thermal, physical and mechanical properties of the bulk adhesive, characterized in the present study.

Experimental results have shown that the bulk properties of structural epoxy based adhesives are highly correlated with the aging processes caused by water absorption in the prepolymerized adhesive. Applying the vacuum process is harmful to fresh unaged adhesive due to devolatization of low molecular species of the film adhesive.

The characterization of bulk properties for the purpose of following the aging and recovery processes is advantageous, since the bulk is independent of geometrical and interfacial effects which dominate in the case of property evaluation of the adhesive in a bonded joint.     

Adhesives in construction: A contractor's viewpoint

The development of epoxy- and polyester-based adhesives has dramatically widened the scope of adhesive bonding in the civil engineering industry but the technology of the adhesives used has often been more appropriate to the workshop than to the construction site. There is a need for the suppliers of structural adhesives to recognize this and to develop compositions and application techniques more amenable to site use. It is equally necessary for the construction industry to make more effort to understand these materials, to take advantage of their outstanding properties, and hence to use them successfully for the construction and repair of concrete structures.     

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