Adhesive mixture

Figure 3.3. Scanning electron microscopy images of spherical pellets of budesonide (upper photograph) and of an adhesive mixture of lactose and micronized salbutamol (lower photograph).

Adhesive mixtures require large carrier crystals to improve the handhng properties of the powders. Dispersion of the small drng particles over the larger carrier material should assure dose uniformity. However, the small dmg particles shonld be removed from the carrier material dnring inhalation, to render an aerosol clond of respirable particles. If the particles remain on the carrier, month or throat deposition of the drng will occur, which might decrease therapeutic efficacy or cause serious side-effects. 

Small amounts of surfactants may be used to prevent aggregation of proteins and may enhance the refolding process when the dried protein dissolves. Buffers may also help to prevent aggregation of the dissolved drug. Similarly, polymers may be used as aggregation inhibitors or to form matrices. Chan et al. [86] prepared crystalline powders of recombinant human deoxyribonuclease with high fractions of sodium chloride. These powders were formulated as adhesive mixtures on lactose and mannitol and showed improved aerosolization behaviour compared to the pure protein. 

Laser diffraction is a fast alternative for analysis of the size distribution of particles in an aerosol cloud. The theory of laser diffraction is well understood [124,125]) but this technique requires special measures to test inhalation devices and to interpret the results correctly. One of the major problems is that flow adjustment through the inhaler is not possible. Furthermore, the presence of carrier particles from adhesive mixtures may disturb the measurement of the fine drug particles and the size distribution obtained is of an unknown dehvered mass fraction of the dose. These practical problems and limitations have been solved by the design of a new modular inhaler adapter for the Sympatec laser diffraction apparatus (Figure 3.6). 

Air can also be eliminated from an adhesive mixture by using a centrifuge. This process is generally employed only with low-viscosity, unfilled adhesives. The centrifuging process consists of rotating the materials at 1000 to 3000 rpm for 1 to 2 min. This is generally sufficient to remove any entrapped air from liquid adhesive systems. 

The results presented in Table III show that only the treatment with cotton fibrils (3.5% add-on) improved the tensile strength (13% increase), whereas the other treatments weakened the fabrics. Add-ons obtained with the CMC and fibril-adhesive mixtures were extremely high, ranging from 24.5 to 72.0%. The affinity between substrate and consolidant in these cases was very poor. 

Best understood of the invertebrate adhesive-mediated attachment mechanisms is that of the common blue mussel, Myiilus edulis, and its close relative, Mytilus californianus L. The mechanism includes the byssus, an acellular proteinaceous organ produced by glands inside the mussel, combined with a delivery system that secretes the byssus efficiently underwater. The protein that is the functional unit of the adhesive mixture was first purified from the gland where it originates and characterized by Waite and Tanzer (i). Called mussel adhesive protein (MAP), it is a high molecular weight (120,000 10,000 MW) basic protein,... 

Use Plasma is used to restore liquid volume and thus osmotic pressure in the body where blood loss has been extensive. Animal blood is used as a component of adhesive mixtures. In dried or powder form it... 

Since the chemical reaction of the two components A and B begins in a pot immediately after mixing, this ready-made adhesive mixture requires speedy application. Otherwise the reaction for the formation of the AB polymer (the adhesive layer) will have developed to such an extent already prior to the application to the adherends that the expected strength of the bonded joint is impaired. Between the mixing of the adhesive mix and its application to the adherends and their fixing only a certain time span is allowed - which may vary for the individual reactive adhesives. This time is called the pot life. Depending on the reactivity of the A and B monomers, pot life can lie in the range of minutes or even hours. 

How to explain the influence of time Let us follow the time-related course of curing in an adhesive mixture of the components A and B, as schematically shown in Figure 3.3 ... 

Inhomogeneous adhesive mixture (in the case of filler-containing adhesives)... 

Microencapsulated adhesive Reactive adhesive mixture, with the (liquid) components encapsulated by a protective skin in the form of finest drops, preventing a reaction during storage. Only after the destruction of the capsule wall, for example, by screwing a nut onto a suchlike coated screw, does a chemical reaction set in and an adhesive layer develop. 

Because of their carcinogenicity, amines have to be monitored. For example, primary aromatic amines (PAAs) are substances that can be transferred from food packaging materials into foodstuffs. In the production of multilayer plastic materials it is common to use reactive adhesive mixtures containing aromatic isocyanate monomers. In cases of incomplete curing, residues of the aromatic isocyanates react with water to produce PAAs. Some of these amines, including... 

For the monomer polymerization at room temperature, the adhesive was augmented with a redox system of 3% BP and 0.75% DMA. To study, explain, and predict the development of the elastic failure of the polymer in the adhesive interlayer, an improved method of investigating adhesive layer crack resistance with modeling of the formation and growth of a crack at the adhesive-honded joint loading was used [119]. Five adhesive-bonded joints with the adhesive mixture compositions shown in Table 3.1 were subjected to static tests for crack resistance at room temperature. The characteristics of the static crack resistance of the adhesive-bonded joint Kic is the coefficient of the stresses intensity Gic is the intensity of the elastic energy release ic is the opening in the crack tip) were determined at the moment of onset of the crack in double-cantilever specimens DCB (Fig. 3.5). The specimen cantilevers were made of PMMA of TOCH type. 

The objective of the work reported here was to expand the investigations of several of the authors [3] concerning the influence of the degree of condensation of UF adhesive resins on the penetration behavior into beech. Since this hardwood species exhibits a completely different wood structure compared to softwood (like fir), it can be expected that penetration of adhesives will occur to a different extent. The structure of beech is characterized mainly by big vessels instead of the rather narrow tracheid cells as it is the case with fir. The resins and adhesive mixtures used in the study reported here were the same as before [3]. The investigation of the... 

The main problem encountered in this study was the development of the new adhesives. Whilst the adhesive manufacturer was able to produce the load-bearing behaviour required by the elastic model, he was not quite able to fully attain the conditions required for the plastic model. The creep tests with small specimens as well as the delamination tests revealed many weaknesses. The final tests revealed that the new adhesive mixtures produced in small quantities in the laboratory could not yet be successfully reproduced in large quantities in factory conditions. Much work needs to be done before the new family of adhesives will attain the stability and reliability required for practical applications. 

The OPS veneers were then segregated by outer and inner layers. The adhesive mixture was composed of a commercially available urea-formaldehyde (UF) resin (42.5% solid) mixed with industrial wheat flour and hardener (ammonium chloride). The adhesive mixture was spread onto the veneers at different spread amounts 200 g/m and 250 g/m (double glueline). The assembled veneers were then cold pressed for 10 min and hot pressed at 130°C for 15 minutes. Two types (Type 1 comprised of 100% outer layer veneers and Type 2 comprised of 100% inner layer veneers) of 5-ply, 450 mm x 450 mm x 13 mm plywoods were produced. Then, the plywoods produced were conditioned at RH of 65% and temperature of 22°C for a week prior to cutting into test specimens. 

Due to the large number of competing reactions between components of widely different concentrations, it is difficult to predict to what extent the different reactions occur in an EPI adhesive mixture. Due to the large amount of water in the adhesive mix, it is clear, however, that there is extensive reaction between the isocyanate and water. 

Both tannin solution and LmwPF resin were prepared at 40% solids. The viscosities of LmwPF and the adhesive mixture of tannin and LmwPF were determined using a Brookfield viscometer Model LVT, CP51 at 25°C. 

A simple joint test sample is subjected to temperature and humidity cycles before transverse tensile loading at a constant loading rate of (10 1) kN/min up to failure (Fig. 3). The objective is to evaluate the effect on bond strength of the damage to wood hbres caused by the action of acids from the adhesive during the climatic cycle. Thus, it must be achieved only if either the adhesive mixture or one of the adhesive components when apphed separately, show an acid pH value lower than 4.0. 

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