Properties of Adhesives Based on Polymeric Mixtures

In the course of blending polymers, the following systems can be formed one-phase systems, two-phase (colloid) systems, or systems in a metastable state of transition from a one-phase into a two-phase system. The properties of polymer mixtures are determined to a great extent by the phase equilibrium in the system formed and their properties can be changed by controlling the processes of phase separation, which occur by two mechanisms by nucleation and growth or by the spinodal mechanism. 

Two-phase mixtures of polymers differ from classic ll colloid systems mainly by a transition layer that exists between the system components and is of special significance. The formation of such a layer in mixtures of linear polymers is governed by the kinetic factors of the retarded process of phase sep u ation, by the collid-chemic ll mechanism of formation, or by the adsorption interaction as well as by the segmental solubility [103,104], In mixtures of crosslinked polymers its formation is governed also by the conditions of synthesis. Note also that in the thermodynamic llly nonequilibrium mixtures of polymers in the two-phase systems, the processes of segmental solubility usually have time to reach completion while the macromolecules do not move inside the high-viscosity medium, which ensures the stability of the structure and its mechanical properties [103]. 

The most promising method of obtaining polymeric materials is by the use of so-called hybrid binders. These constitute polymeric composite materials in which crosslinking indicates the heterogeneity of the distribution of the system components determined by thermodynamic 

Surface physic d-chemic d phenomena are involved in all heterogeneous polymeric systems with a developed interphase surface. These include wetting and dl kinds of adhesion (friction, fracture, dispersion, homogenization, structuring). The development of the idea of the interrelation of the dispersion state and sxmface phenomena, due to P.A. Rebinder, leads to the necessity for the addition of surfactant in small amounts. The mechanism of the action of these additives on different interphase hound u ies is considered in detail in [105]. 

Integration of surfactant in small quantities facilitates the dispersion of the structur d elements of dispersions, solutions, and melts of the polymers. In the case of surfactant with groups that can he involved in the formation of hydrogen bonds between the structural elements, the effect of p u ticle dispersion increases with increase of the length of the surfactant hydrocarbon radical and with increase of the polymer polarity. To improve the properties of the polymer mixture, a third component is sometimes added. A rather promising method of controlling the properties is to combine polymer mixtures with their block polymers. The latter in sm dl quantities tend to concentrate on the interphase boundary, thus improving the interaction of the mixture components they seem also to serve as emulsifiers. 

---