Gluing

The mean airborne concentration of n-hexane was 38 ppm (range 4-90 ppm) in the Finnish shoe industry in the 1980 s. The mean concentrations of acetone and toluene were 131 ppm and 14 ppm. The mean exposure levels in two US shoe manufacturing plants in the late 1970 s were toluene 22-50 ppm, methyl ethyl ketone 133-153 ppm, acetone46-223 ppm, and n-hexane 22-55 ppm. The exposure is, however, easy to control by doing the gluing in enclosure hoods. 

In the production of viscose, the workers are exposed to carbon disulfide. In addition to inhalation exposure, absorption through the skin may be important. It is Strongly neurotoxic. Its TLV is 10 ppm and the Finnish OEL 5 ppm. Both cany the skin notation. Urinary 2-thiothiazolidine-4-carhoxylic acid concentration can he used for biological monitoring of exposure to carhon disulfide. Its ACGIH BEI is 5 mg/g creatinine (4 mmol/mol creatinine) and the BEI given hy the FIOH 2.0 mmol/mol creatinine. 

Airborne concentrations from less than 0.2 to 65.7 ppm were detected in measurements conducted in a German plant in the 1990 s. The urinary 2-thiothiazolidine-4-carboxyhc acid levels ranged from less than 0.16 to 11.6 mg/g creatinine. A long time average of about 8 ppm has been reported in a utch factory.  

In acetate fiber plants, the workers are exposed to acetone. The mean concentration in the air of three Japanese factories was 372 ppm. Some workers exposure levels exceeded 1000 ppm.  

Exposrrre to variorrs solvents takes place in pharmaceutical industry. The airborne 8-h TWA concentrations of methylene chloride were 16-167 ppm in a Finnish factory in the 1980 s.  

To achieve a good glue joint, the surfaces to be glued must be well wetted. The glue in the joint must then solidify. Finally, the glue joint must be sufficiently deformable so that stresses can equilibrate. 

For the following discussion it will be assumed that the glue layer deforms more readily than the material to be glued. It must also be assumed that there are no chemical bonds between the material and the glue. The adhesion which is thus to be discussed depends mainly on adsorption and diffusion. The adhesive should be a clean material, and also it should be above its glass-transition temperature (if amorphous) or above its melting point (if partly crystalline). The lower the molecular weight of the adhesive, the more rapidly it can diffuse into the material to be bonded. 

Adsorption, on the other hand, increases with an increasing number of contact points per adhesive molecule, i.e., with higher molecular weight. The adhesion should therefore exhibit an optimum value at a given molecular weight of the melt glue. A small number of branches per molecule of 

Melt glues are used above their melting or glass-transition temperatures. They are used, for example, in the textile industry to bond cover and support materials. Poly(ethylene), poly(ethylene-co-vinyl acetate), and terpolyamides are typical melt glues. 

Danielli, K. G. A. Parthurst, and A. C. Biddiford, Surface Phenomena in Chemistry and Biology, Pergamon Press, New York, 1958. 

When devices are glued with electrically conductive or nonconductive adhesive, the mechanical strength of the bond is the result of thermal curing of the adhesive. Considerably lower than process temperatures for soldering, adhesive curing temperatures have to be chosen to suit the adhesive system, the substrate material, and required process time. 

Adhesives do not have wetting properties. The self-centering effect familiar from soldering does not occur, and, consequently, positioning has to be considerably more accurate. An advantage from the MID point of view is that overspread wetting without solder-stop paint does not occur in gluing. 

The mechanical strength of conductive-adhesive gluing is achieved by thermal curing, while the electrical connection is established by the three-dimensional mesh of touching particles embedded in the polymer matrix (Fig. 5.13). Silver is the most common filler, on account of its good electrical conductivity and high thermal conductivity [109]. Curing temperatures are low (80 to 150 °C), so this process can be used on thermally sensitive materials. 

FIGURE 5.13 Principles of electrically conductive adhesives and adhesives without fillers [48] 

Connections made with insulating adhesives free of fillers are electrically conductive if the partners are in contact with each other in adhesive no thicker than the surface roughness ( 10 pm). In principle the process is very similar to that of anisotropic adhesive gluing. The glue is applied by a dispenser or by print application of a paste. The electrically nonconductive adhesive can be applied allover across multiple connections. This implies low requirements for the process as such and therefore good affinity for fine-pitch applications. Once the partners to be joined have been positioned, the adhesive cures under pressure and temperature within a matter of seconds. 

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The analysis of the test results shows that non-defect adhesive joints of the carbon plastic are acoustically less active than the glued main material. This can be explained by absence of plasticization effect of the die (adhesive layer). The value of the breaking point ("C ) at the adhesive joints shift is 9,6 M Pa. 

In this preliminary work we have investigated composite objects with a simple geometry. In future work the proposed approach will be applied to more complicated objects, in particular glued structures. Since we for such objects expect to have a less distinct back wall echo, we have reason to believe that the preprocessing method that was used in this work has to be somewhat modified. 

The data led to tire cycle shown in figure C2.7.8. Here, only tire active site on tire interior enzyme surface (section C2.6) is depicted, consisting of R groups including aspartic acid, glutamic acid and otliers, represented witli tire shortliand Asp, Glu etc tire subscripts represent tlie positions on tlie polypeptide chain. 

Fig. 3. Some representative pair potentials Uy(r), sealed to move their interesting range to [0,5]. The numbers above each potential denote the class label 7 and the iiinnber of data points available for the fit. (For example, elass 63 gives distanee 3 potentials for the amino acid pairs Lys-Asp, Arg-Lys and Glu-Tyr.) The spectrum below each potential consists of 50 lines pieked uniformly from the data.

You may have noticed that most soft drinks contain high fructose corn syrup Corn starch is hy drolyzed to glucose which is then treated with glu cose isomeraseto produce a fructose rich mixture The... 

The shape of a large protein is influenced by many factors including of course Its primary and secondary structure The disulfide bond shown m Figure 27 18 links Cys 138 of carboxypeptidase A to Cys 161 and contributes to the tertiary structure Car boxypeptidase A contains a Zn " ion which is essential to the catalytic activity of the enzyme and its presence influences the tertiary structure The Zn ion lies near the cen ter of the enzyme where it is coordinated to the imidazole nitrogens of two histidine residues (His 69 His 196) and to the carboxylate side chain of Glu 72... 

Cation (Section 1 2) Positively charged ion Cellobiose (Section 25 14) A disacchande in which two glu cose units are joined by a 3(1 4) linkage Cellobiose is oh tamed by the hydrolysis of cellulose Cellulose (Section 25 15) A polysaccharide in which thou sands of glucose units are joined by 3(1 4) linkages Center of symmetry (Section 7 3) A point in the center of a structure located so that a line drawn from it to any element of the structure when extended an equal distance in the op posite direction encounters an identical element Benzene for example has a center of symmetry Cham reaction (Section 4 17) Reaction mechanism m which a sequence of individual steps repeats itself many times usu ally because a reactive intermediate consumed m one step is regenerated m a subsequent step The halogenation of alkanes is a chain reaction proceeding via free radical intermediates... 

Pentanedioyl, see Glu-taryl CH2—CH2— pynyl Propenoyl, see Acryloyl 1-Propenyl CH3—CH=CH—... 

Four other groups of synthetic adhesives find uses in secondary processing, ie, overlaying, assembly gluing, etc, and in furniture and cabinet manufacture. Poly(vinyl acetate) (PVA) adhesives are widely used in appHcation of veneers and other overlays to panel substrates and in some unit-assembly operations. PVA adhesives are an emulsion of polyvinyl acetate in water and cure by loss of water. The PVA adhesives are somewhat... 

Lumber core is a five-ply panel, usually about 19 mm (3/4 in.) thick, in which the bulk of the thickness, about 16 mm (5/8 in.) is edge-glued lumber. Yellow poplar and red gum are desired species for lumber core. Cross-pHes of lower value wood veneers are laid at right angles to the core grain direction, followed by two thin surface pHes of the decorative face veneer in a parallel direction to the core. This assembly is pressed and bonded to form a panel of exceptional quaHty, provided all steps are accompHshed in a desirable manner. 

Plywood furniture core panels, also about 19 mm (3/4 in.) thick, were normally made of a number of layers of relatively thick, 1.5—3.0 mm (1 /16—1 /8 in.) lower value wood veneers combined with thin surface pHes of the decorative veneer. These assembhes were laid-up from glued veneers and then pressed while the bonding occurred. Both lumber core and plywood core have been almost totally displaced in recent years by particleboard or medium-density fiberboard, both discussed herein. This change resulted from the increasing availabiHty and improved finishing characteristics of composites and from decreasing suppHes of core lumber or veneer of suitable quaHty. 

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