Bond Performance

Once a process is being used, recognize that if the compound additives or fillers are changed or added, bond performance can change or even not exist. As an example an unreinforced plastic can be welded to itself however with a certain amount of glass fiber fillers (they do not melt) added to the plastic, action in weld strength can be reduced or even eliminated. 

Bond Durability. Because we lack an adequate theoretical basis for predicting adhesion, many empirical studies of bond performance have been reported. Some most interesting and potentially applicable studies of adhesive durability have been reported recently (40, 41, 42, 43, 44) but are mentioned only in passing because the thrust of this review is adhesion, not adhesives. 

Wood Extractives. Glue bonds can be affected in many ways by extraneous components on or near the surface of wood. Chen (56) showed that extractive removal did improve bond performance and that the extractives, in part, reduce wettability. This effect is reflected also in Figure 2 from Jordan and Wellons (29). Hergt and Christensen (57) also showed that extractives can slow water adsorption from the adhesive into the wood, thus slowing development of cohesion in the adhesive. 

The choice of solvent or diluent is made with regard to the solubility of individual components and to the viscosity, drying times, and wetting characteristics required of the final product. All these properties affect the bond performance of the resulting epoxy adhesive formulation. 

Maximum bond performance and minimal internal stresses are sometimes achieved if the substrate has a moisture content during bonding that is close to the average moisture content anticipated during service—provided, of course, that the moisture retained in the substrate does not adversely affect the initial bond strength. This may require preconditioning of the substrates in a controlled environment before bonding. 

E 1512 E 1555 E 1793 Test Methods for Testing Bond Performance of Adhesive Bonded Anchors Specification for Structural Paste Adhesive for Sandwich Panel Repair Standard Practice for Preparation of Aluminum Alloy for Bonding in Foam and Beam Type Transportable Shelters... 

C-2H bond performs rotational random jumps on the surface of a cone with a full opening angle X = 6° (from Ref. 93). (b) Experimental 2H NMR spectra of chlorobenzene-ds in a mixture with cis-decalin at various temperatures T < Tg and at a long solid-echo delay tp [429]. 

The bond performances of lignin-phenolic resin systems were studied through a series of experiments, each designed to elucidate a facet of the problem. The resin preparation and panel fabrication procedures were, however, maintained as uniformly as possible. Thus, unless otherwise specified, the experimental procedures described below were used in the study. 

Fig. 15. Effects of small-amplitude reorientation on 2H NMR stimulated-echo experiments, as calculated by means of RW simulations. The C-2H bonds perform rotational random jumps on the surface of a cone with a full opening angle % = 6°, which are governed by a broad logarithmic Gaussian distribution of correlation times G(lgr) (a = 2.3). (a) Correlation functions m tp — 30 is) for the indicated mean logarithmic time constants lgr 1. The calculated data are damped by an exponential decay, exp[—(tm/rso)] with rSD = 1 s, so as to mimic effects due to spin diffusion. The dotted lines are fits with Fcos(tm tp) = (1—C) expHtm/t/l + Qexp[—Om/rso)]- (b) Amplitude of the decays, 1-C,p, for various t resulting from these fits. The dotted line is the value of the integral in Eq. (12) as a function of rm. (Adapted from Ref. 76).

In this model,110 it was assumed that all C 2H bonds perform thermally activated rotational jumps within energy landscapes on the surface of a cone. Specifically, six basins were supposed to be separated by six energy barriers at positions 0, 60,..., 300° around the axis of the cone. For each cone, the barriers were drawn anew from the distribution of activation energies determined for TOL in DS.12,19 Further, it was assumed that all positions on the surface of the cone, except for the barriers, have the same energy, i.e., a random-barrier model was considered. The thermally activated jumps lead to a random new position in one of the two neighboring basins. This means that several back-and-forth jumps occur over relatively low energy barriers until relatively high barriers are crossed. In other words, many... 

Summary Thermoanalytical and spectroscopic ( Si NMR and IR) methods were used to characterize the changes of structure of silicon resins when heated up to 700 °C. Building groups with unreacted Si-OH bonds perform a postcondensation to Si-O-Si bonds at 250 °C. At about 500 °C, Si-C bonds cleave by an oxidative conversion to Si-OH. At the end the silicon resin is converted to an aerosil like material. 

A useful transformation of 3,6-dihydrO-2TM,2-oxa7ines 1 is the diastereoselective ew-hydrox-ylation of the double bond, performed with osmium tetrOxide, followed by cleavage of the N-0 bond to obtain key intermediates for aminocyclitols with biological activity22. 

The regio- and stereochemistry of the cycloadduct was determined by H-NMR spectroscopy68. Further transformations, involving cis hydroxylation with osmium tetroxide and reductive cleavage of the N-O bond, performed with Raney nickel at 40 °C, lead after acetylation, to an ( )-aminoallose derivative67,127. 

Wool oxidized with peracetic acid contains 14 % less histidine, 6 % less phenylalanine, and 1 % less tyrosine than the original wool (Corfield et al., 1958), and large amounts of dialyzable nitrogen have been detected in y-keratose (Alexander and Smith, 1956). Thompson and O Donnell (1959a) found that peracetic acid not only ruptures peptide bonds in the wool proteins, but also fails to oxidize all the disulfide bonds. Performic acid suffers neither of these disadvantages and is therefore preferable. 

Impermeable silicon carbides of both types, sintered and reaction bonded, perform generally better than the permeable refractories as shown in Table 19-3 Both reaction bonded and sintered products can be exposed to higher temperature for longer periods of time with lower weight loss than the oxide, Si3N4 or Si20N2 bonded refractories. This is due to the lower surface area available for reaction and to the greater relative inertness of their bond phases. 

The rubber and resin are coreacted by heating the mixture at around 100 °C in the presence of a Lewis base. Most commonly tertiary amines are used for this purpose. The morphology of the rubber dispersion is important to bond performance and is governed by the coreaction procedure. This material may be formulated into a useful aerospace paste adhesive by the following combination of materials (pbw) ... 

Another mutant, GA, containing chloro-xan thin, a neurosporene analog with nine conjugated double bonds performs efficient triplet energy transfer at room temperature in both RC (Cogdell et al.,... 

Although many techniques have been used to examine how adhesives interact with wood [6], the observations generally have not been related to bond performance. Does penetration into lumens result in better strength, or is penetration into the cell walls more important, especially for durable exterior bonds ... 

Resorcinol-based adhesives are used extensively to bond structural grade, exterior laminated beams for building construction (see Chap. 29 on Resorcinol Adhesives). The coldsetting adhesives which dominate this field are based on phenol-resorcinol-formaldehyde (PRF) resins. The adhesive itself is composed of the PRF resin and a hardener that includes formaldehyde, often in the form of paraformaldehyde mixed with inert fillers. The performance of the resin is resorcinol dependent. The cost of the resin is also resorcinol dependent as this is a very expensive chemical produced industrially in only three locations in the world. The research work on these resins from their inception has then been based on the optimization of their bonding performance coupled with the decrease in the relative percentages of resorcinol used. It has the been a long and successful work of empirical research and development which still continues. 

Another means of providing a hydration-resistant surface is its treatment with a hydration inhibitor [37]. Figure 4 shows wedge tests results for a Forest Product Laboratory (FPL) bond, [38] an FPL bond pretreated with nitrilotrismethylenephos-phonic (NTMP) acid [39-41], and a PAA bond. The monolayer coverage of NTMP stabilizes the surface against hydration and provides wedge test bond performance similar to that of PAA-treated adherends. 

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