Plastics surface preparation description

The combination of properties that makes fluorocarbons highly desirable engineering plastics also makes them nearly impossible to heat or solvent weld and very difficult to bond with adhesives without proper surface treatment. The most common surface preparation for fluorocarbons is a sodium naphthalene etch, which is believed to remove fluorine atoms from the surface to provide better wetting properties. A formulation and description of the sodium naphthalene process can be found in another chapter. Commercial chemical products for etching fluorocarbons are also listed. 

Lord Corporation introduced adhesives containing methacrylated phosphate monomers that gave much-improved thermal and atmospheric durability, and Dymax Corporation introduced their aerobic acrylics that were less sensitive to inhibition by atmospheric oxygen. Dow Automotive, 3M, and Loctite recently introduced two-part acrylic-based adhesives that can bond many low-surface-energy plastics, including many grades of polypropylene, polyethylene, and thermoplastic polyolefins without special surface preparation (see Section 4.2.2 for a description of this technology). 

The stresses in joints are discussed extensively so that the engineer can get sufficient philosophy or feel for them, or can delve more deeply into the mathematics to obtain quantitative solutions even with elasto-plastic behaviour. A critical description is given of standard methods of testing adhesives, both destructively and non-destructively. The essential chemistry of adhesives and the importance of surface preparation are described and guidance is given for adhesive selection by means of check lists. For many applications, there will not be a unique adhesive which alone is suitable, and factors such as cost, convenience, production considerations or familiarity may be decisive. A list of applications is given as examples. 

Two major techniques have been used to study the dimension of chromosome fibers by electron microscopy. The first is the surface spreading method, in which the cells are spread on a water-air interphase, and all the intracellular components are dispersed. But the chromatin and the spindle remain close together and can be picked up on a grid, which can then be prepared for electron microscopic examination. The second technique is the thin-sectioning method. After fixation the tissue is embedded in plastic and cut less than 1000 A thick. Refer to specialized texts for descriptions of these techniques [119]. The important finding is that with the first method, the dimension of the fibers diameter is estimated to be 200-300 A, whereas it is only 80-180 A with the second. 

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