Particulate-filled polymer composites adhesion

The interaction of two substrates, the bond strength of adhesives are frequently measured by the peel test [76]. The results can often be related to the reversible work of adhesion. Due to its physical nature such a measurement is impossible to carry out for particulate filled polymers. Even interfacial shear strength widely applied for the characterization of matrix/fiber adhesion cannot be used in particulate filled polymers. Interfacial adhesion of the components is usually deduced indirectly from the mechanical properties of composites with the help of models describing composition dependence. Such models must also take into account interfacial interactions. 

Structural Aspects of Adhesion in Particulate-Filled Polymer Composites... 

Kozlov, G. V. Lipatov, Yu. S. Fractal and structural aspects of adhesion in particulate-filled polymer composites. Composite Interfaces, 2002,9(6), 509-527. 

It is well-known that the interface adhesion markedly influences the mechanical behavior of particulate filled polymer composites [7-11]. The present irradiation grafting pre-treatment provides possibilities for interfacial design,... 

The characteristics of particulate filled polymers are determined by the properties of their components, composition, structure and interactions [2]. These four factors are equally important and their effects are interconnected. The specific surface area of the filler, for example, determines the size of the contact surface between the filler and the polymer, thus the amount of the interphase formed. Surface energetics influence structure, and also the effect of composition on properties, as well as the mode of deformation. A relevant discussion of adhesion and interaction in particulate filled polymers cannot be carried out without defining the role of all factors which influence the properties of the composite and the interrelation among them. 

This chapter focuses its attention on the discussion of the most relevant questions of interfacial adhesion and its modification in particulate filled polymers. However, because of the reasons mentioned in the previous paragraph, the four factors determining the properties of particulate filled polymers will be discussed in the first section. Interactions can be divided into two groups, parti-cle/particle and matrix/filler interactions. The first is often neglected although it may determine the properties of the composite and often the only reason for surface modification is to hinder its occurrence. Similarly important, but a very contradictory question is the formation and properties of the interphase a separate section will address this question. The importance of interfacial adhesion... 

A more strict approach to the characterisation of the effect under consideration is the concept of the unscreened perimeter of any object introduced in [34], for a filler. This perimeter is a measure of the accessibility for the formation of adhesion bonds [34]. The particulate-filled polymers at a definite values of (pf may be considered as percolation clusters with the first percolation threshold (pf = 0.15-0.17 [35]. Because the maximum value of (pf for the composites considered in this paper is equal to 0.176, one can believe these systems are below the percolation threshold and from them the following relationship is valid [34] ... 

In most cases the strength of the adhesive bond is characterized acceptably by Wab values derived from the above presented theory. Often, especially in apolar systems, a close correlation exists between W b the macroscopic properties of the composite in particulate filled polymers, also shown, for example, by the dependence of composite strength on Wab presented in Fig. 9 for PP/CaC03 composites. However, the bond strengths determined with various mechanical tests are usually much lower than the values derived from... 

Adhesion at the interface of the polymer-solid is a determining factor for the physical and mechanical properties of polymer composites. Many properties of particulate-filled composites are determined by the adhesion level at the filler-matrix interface. The problems involved in adhesion are very complicated and adhesion cannot be described by any single theory [1]. Many properties of particulate-filled composites are determined by the adhesion level at the filler-matrix interface [2]. However, no theory allows calculation of the adhesion strength of joints from the data on the nature of substrate and polymer or reliable calculation of the energy of the adhesive interaction. The reason for it is the number of factors that influence adhesion [3-9]. 

Adhesion between the polymer matrix and filler at the interface in the particulate-filled composites is of a key importance for the composite morphology, mechanisms of failure and the composite mechanical and other properties. 

A decrease in radius of filler particles in the composite will result in an increased value of stresses needed to initiate the composite failure. Mechanisms of failure in a composite could take place in the polymer matrix by shear yielding and/or crazing, inside the aggregates of filler particles and/or at the interface matrix/filler by mechanism of dewetting. In particulate-filled composites, yielding and crazing do not depend on the work of adhesion between matrix and filler, VFmf, or thermal stresses, but these influence the dewetting phenomenon, considerably, (Eqn. 5) ... 

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