Лако-красочные материалы — производство

In the case of the formulation of mixed resins for adhesives for which extensive formula­tion experience does not exist, the gel theory approach is also particularly useful. Le us examine, as an example, what would be the degree of conversion at the gel point of a resin based on the reaction of resorcinol (R) with […]

A. Formulation of Phenol-Resorcinol-Formaldehyde Cold-Set Adhesives 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, […]

The branching coefficient as defined by Flory is a = the probability that a certain branched unit will be joined to a second branched unit rather than to a terminal group. For example, for a trifunctional monomer if a = 1/2 the molecule is a continuous chain equivalent in theory to a gel. In this […]

Kinetic or coagulation theories develop all chemical species by the use of an infinite set of kinetic differential equations [1]. The resulting chemical species distribution can be obtained analytically only in the simplest case of random reactions; in some other cases distributions can be obtained numerically; and lastly the solution of the set of equa­tions […]

These methods generate structures by random combinations of reacting functional groups. This approach is thorough and the results are good when dealing with equilibrium — controlled reactions. The results are often a good approximation in kinetic-controlled reactions. Most of the formaldehyde-based polycondensations are equilibrium-controlled reactions, this being particularly true for urea-formaldehyde, melamine-urea — formaldehyde, phenol-formaldehyde […]

Several theories and methods defining and modeling the formation of polymer networks exist [1-3]. The most useful of such theories, purely from an applied everyday use, are often the simpler and older ones [4,5]. More complex theories, although often excellent at describing to a much greater and thorough extent the molecular reality of gelation, suffer […]

A. Pizzi Ecole Nationale Superieure des Technologies et Industries du Bois, Universite de Nancy I, Epinal, France I. INTRODUCTION The study of adhesion and adhesives involves many scientific approaches and in parti­cular many different scientific disciplines. From physics to applied engineering, from surface science to chemistry, be it analytical, organic, or physical, all have, and […]

The molecular mechanics approach just described functions well, but the manner in which it has been used in the previous section is rather limited to static situations: dynamic situations can also be described well, although by a series of finite steps of ‘‘before and after’’ static calculations to ascertain the changes which have occurred or […]

Contrary to the generalized approach already presented, models describing the adhesion between a polymer well defined at a molecular level and another, equally molecularly well-defined substrate also exist. These are models in which molecular mechanics and dynamics are applied in their more accepted role described in the Introduction. It must be realized that such models […]

The mechanics of particle adhesion and the deformations resulting from the stresses generated by adhesion forces have now been studied both experimentally and theoreticallyfor a long time. Most of the approaches taken on the subject stem from a thermodynamic rather than a molecular viewpoint, such as the use of the so-called Johnson-Kendall — Roberts (JKR) […]