Aqueous adhesives

The need to ensure environmental and fire safety and labor protection has led to a the creation of a wider range of water-containing adhesive materials and the scope of their applications, as well as to increase the strength of adhesive joints on their basis. The present paper reviews aqueous adhesives produced by the domestic industry.     

Epoxy-foam adhesives

The historical aspects of creation of domestic epoxy-foam adhesives (FA) for sealing radio-engineering equipment are briefly discussed, and the advantages (adhesion, cohesion strength etc.) over FAs based on other polymers are shown. The characteristics of modern FAs of the VKV series that are used in aircraft engineering are presented. The possibility of application of alternative foaming agents (azo compounds) is shown after which evolution of gaseous products form reactive modifying agents that provide an increase in the strength and operational characteristics compared to the known analogs.     

Silicate-based adhesives

The possibility of improving the properties of adhesives based on PVA dispersions by the addition of a fairly cheap and accessible component (liquid glass) is studied. This modification is shown to yield an increase in the adhesive viscosity and improve its technological characteristics and the water resistance of an adhesive joint. A scientific interpretation of the effects observed during modification is given.     

Hot-melt adhesives

The manufacturing and physical properties of hot-melt adhesives are briefly reviewed. The effect of surface roughness on the adhesive properties of hot-melt seals have been studied based on the example of the technique for repairing automotive batteries.     

Natural underwater adhesives

The general topic of this review is protein‐based underwater adhesives produced by aquatic organisms. The focus is on mechanisms of interfacial adhesion to native surfaces and controlled underwater solidification of natural water‐borne adhesives. Four genera that exemplify the broad range of function, general mechanistic features, and unique adaptations are discussed in detail: blue mussels, acorn barnacles, sandcastle worms, and freshwater caddisfly larva. Aquatic surfaces in nature are charged and in equilibrium with their environment, populated by an electrical double layer of ions as well as adsorbed natural polyelectrolytes and microbial biofilms. Surface adsorption of underwater bioadhesives likely occurs by exchange of surface bound ligands by amino acid sidechains, driven primarily by relative affinities and effective concentrations of polymeric functional groups. Most aquatic organisms exploit modified amino acid sidechains, in particular phosphorylated serines and hydroxylated tyrosines (dopa), with high‐surface affinity that form coordinative surface complexes. After delivery to the surfaces as a fluid, permanent natural adhesives solidify to bear sustained loads. Mussel plaques are assembled in a manner superficially reminiscent of in vitro layer‐by‐layer strategies, with sequentially delivered layers associated through Fe(dopa)₃ coordination bonds. The adhesives of sandcastle worms, caddisfly larva, and barnacles may be delivered in a form somewhat similar to in vitro complex coacervation. Marine adhesives are secreted, or excreted, into seawater that has a significantly higher pH and ionic strength than the internal environment. Empirical evidence suggests these environment triggers could provide minimalistic, fail‐safe timing mechanisms to prevent premature solidification (insolubilization) of the glue within the secretory system, yet allow rapid solidification after secretion. Underwater bioadhesives are further strengthened by secondary covalent curing. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Lakroten grade adhesives

An assortment of adhesive materials with permanent tackiness developed by OOO PKF Orgkhimprom is reported. Data on the effect of different factors (viscosity, thickness of the adhesive layer, and content of polymer phase) on the conditions of adhesive processing are discussed. Strength characteristics of adhesives as functions of the polarity of substrate and service temperature of bonded items are considered. Possible uses of suspension copolymers with permanent tackiness as modifying additives controlling the adhesive and cohesive characteristics of adhesive compositions are demonstrated.     

Rheology of adhesives

Summary The development of rigidity in adhesive solutions, viz. gelatin, casein, urea-formaldehyde, resorcinalformaldehyde and tannin formaldehyde, was followed with the help of theSaunders andWard apparatus. The shape of the curves shows that the development of rigidity differs with the type of adhesive. The influence of temperatures was also studied with ureaformaldehyde, the „gelation time“ is almost halved for every 5°C rise of temperature. Finally the compressive strength of the set gels is also reported.

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Zusammenfassung Es wurde mit Hilfe derSaunders undWard-Apparatur das Erstarren von Klebstoffl?sungen, z. B. Gelatine, Kasein, Harnstoff-Formaldehyd, Resorcinal-Formaldehyd, Tannin-Formaldehyd verfolgt. Die Form der Kurven zeigt, da? der Erstarrungsvorgang vom Typ des Klebstoffs abh?ngt. Der Einflu? der Temperatur beim Harnstoff-Formaldehyd zeigt, da? die Gelatinierungszeit für jede 5°C Temperaturerh?hung etwa auf die H?lfte sinkt. Die Druckfestigkeit der verfestigten Gele wurde ebenfalls untersucht.

     

Thermal stability of epoxy adhesives

A study was made of the thermal stability of epoxy compounds which were unfilled or contained metallic fillers such as aluminium dust, aluminium flakes, powdered bronze, powdered brass and silver flakes. The properties of the compounds were modified by the use of various hardeners.

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Zusammenfassung Es wurde die thermische StabilitÄt ungefüllter und gefüllter Epoxidkompositionen untersucht. Als metallische Füllstoffe wurden Aluminiumpulver und -flocken, Messing- und Bronzpulver sowie Silberflocken eingesetzt. Die Eigenschaften dieser Kompositionen wurden mit verschiedenen HÄrtern modifiziert.

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Design and fabrication of gecko-inspired adhesives

Recently, there has been significant interest in developing dry adhesives mimicking the gecko adhesive system, which offers several advantages compared to conventional pressure-sensitive adhesives. Specifically, gecko adhesive pads have anisotropic adhesion properties; the adhesive pads (spatulae) stick strongly when sheared in one direction but are non-adherent when sheared in the opposite direction. This anisotropy property is attributed to the complex topography of the array of fine tilted and curved columnar structures (setae) that bear the spatulae. In this study, we present an easy, scalable method, relying on conventional and unconventional techniques, to incorporate tilt in the fabrication of synthetic polymer-based dry adhesives mimicking the gecko adhesive system, which provides anisotropic adhesion properties. We measured the anisotropic adhesion and friction properties of samples with various tilt angles to test the validity of a nanoscale tape-peeling model of spatular function. Consistent with the peel zone model, samples with lower tilt angles yielded larger adhesion forces. The tribological properties of the synthetic arrays were highly anisotropic, reminiscent of the frictional adhesion behavior of gecko setal arrays. When a 60° tilt sample was actuated in the gripping direction, a static adhesion strength of ~1.4 N/cm(2) and a static friction strength of ~5.4 N/cm(2) were obtained. In contrast, when the dry adhesive was actuated in the releasing direction, we measured an initial repulsive normal force and negligible friction.     

Structure of algal-born phenolic polymeric adhesives

Adhesive materials extracted from the brown alga Fucus serratus are composed of phenolic polymer, alginate, and CaCl2. The phenolic polymer undergoes an oxidation reaction in the presence of bromoperoxidase, KI, and H2O2. The nanostructure of the adhesive was investigated using small angle X-ray scattering, light scattering, and cryo- transmission electron microscopy experiments. These have shown that the phenolic polymer undergoes self-assembly and forms flexible chain-like objects. Oxidation or adding alginate does not alter this structure. However, once calcium ions are added, a rigid network is formed. Presumably, this network is responsible for the cohesive strength of the glue.     

Application of adhesives in instrument engineering

A variety of adhesives produced at the enterprise, including optical, melt, and current-conducting adhesives, is presented. The technical characteristics of these glues and their function in the process of manufacturing quantum electronics instruments are discussed.     

Current-conducting adhesives developed at OAO Kompozit

Requirements for current-conducting adhesives used to assemble electric and radio products are formulated. Current-conducting adhesives presently used in Russian and foreign practice are reviewed. The main characteristics of current-conducting, hot-cured TZK-14s adhesive developed at OAO Kompozit are given. Based on preliminary testing, TZK-14s adhesive has been proposed as a substitute for VK-20 adhesive (which contains silver powder), the components of which are no longer produced in Russia.     

Thermally degradable maleimides for reworkable adhesives

New thermosetting materials were developed for reworkable adhesive applications by introducing acetal ester groups as thermally degradable linkages into maleimide compounds. The synthesis of compounds containing maleimide functionality and acetal ester linkages was conducted by a one‐step neat reaction from commercially available materials. The polymerization process and thermal degradation of the synthesized materials were studied. It was found that the acetal ester linkage degraded rapidly above 225 °C, and introduction of this linkage into the adhesive formulation led to improved reworkability of adhesively bonded substrates. A mechanism for reworkability was proposed based on the insight provided by experimental and modeling work. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1073–1084, 2009     

POSS-modified PEG adhesives for wound closure

PEG-related adhesives are limited in clinical use because they are easy to swell and cannot support the cell growth.In this study,we produced a series of POSS-modified PEG adhesives with high adhesive strength.Introduction of inorganic hydrophobic POSS units decreased the swelling of the adhesives and enhanced cell adhesion and growth.The in vitro cytotoxicity and in vivo inflammatory response experiments clearly demonstrated that the adhesives were nontoxic and possessed excellent biocompatibility.Compared with the sutured wounds,the adhesive-treated wounds showed an accelerated healing process in wounded skin model of the Bama miniature pig,demonstrating that the POSS-modified PEG adhesive is a promising candidate for wound closure.     

Flexible polyfluorinated bis-diazirines as molecular adhesives

Motivated by a desire to develop flexible covalent adhesives that afford some of the same malleability in the adhesive layer as traditional polymer-based adhesives, we designed and synthesized two flexible, highly fluorinated bis-diazirines. Both molecules are shown to function as effective crosslinkers for polymer materials, and to act as strong adhesives when painted between two polymer objects of low surface energy, prior to thermal activation. Data obtained from lap-shear experiments suggests that greater molecular flexibility is correlated with improved mechanical compliance in the adhesive layer.

Flexible, highly fluorinated covalent adhesives are synthesized, and are shown to afford comparable C–H insertion efficiency and adhesion strength relative to a rigid analogue, while providing improved mechanical compliance in the adhesion layer.     

Curing agents of silicate based adhesives

In this work, we report information on modifying silicate based adhesives with substances that increase their curing rate, i.e., curing agents, which can be divided into ten groups. The characteristic features and the chemistry of the curing agents of each group are discussed; their technical and economic assessments are given.     

Structural adhesives with increased deformation resistance

The radiation-resistant cold-setting adhesive compositions with increased elasticity have been developed based on epoxy-diane resin modified by low-molecular two- and three-functional diluents. The presented adhesives can operate in the temperature range of −196 to +150°C, and they yield a high shear strength of the adhesive joint for aluminum alloys (16–23 MPa) and peeling strength for the joint between organic fabrics and aluminum alloys (1.75–2.4 kN/m).