Interaction filler/matrix

Studies on filled systems all find that the experimental observations can be explained by matrix-filler interaction. This interaction is a complex process involving  

These proeesses modify surfaee layers of both interacting materials (filler and matrix) and form an interphase which differs in properties from the bulk matrix. The formation of the interphase is responsible for changes in the physical and mechanical properties of filled materials and usually improves material reinforcement.  

These and other phenomena are the subject of discussion in the following sections of this chapter. 

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In the first approximation A(c) should be dependent on the molecular characteristics of the matrix and matrix-filler interaction. 

Even though Eq. (36) was derived on the basis of a simplest model and, as the authors themselves admit, cannot be expected to provide a high degree of agreement with the experiment, it can well be used for obtaining rough estimates of the matrix-filler interaction. 

Keywords aggregation, interfacial interaction, reversible work of adhesion, wettability, matrix-filler interaction, surface treatment, interphase, surfactant, coupling agent, elastomer interlayer... 

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... 

The specific surface area of fillers is closely related to their particle size distribution however, it also has a direct impact on composite properties. Adsorption of both small molecular weight additives, and also that of the polymer is proportional to the size of the matrix/filler interface [14]. Adsorption of additives may change stability, while matrix/filler interaction significantly influences mechanical properties, first of all yield stress, tensile strength and impact resistance [5,6]. 

Particle/particle interactions induce aggregation, while matrix/filler interaction leads to the development of an interphase with properties different from those of both components. Both influence composite properties significantly. Secondary, van der Waals forces play a crucial role in the development of these interactions. Their modiflcation is achieved by surface treatment. Occasionally reactive treatment is also used, although its importance is smaller in thermoplastics than in thermoset matrices. In the following sections of this chapter attention is focused on interfacial interactions, their modification and on their effect on composite properties. 

As was mentioned in the previous section two types of interactions must be considered in particulate filled polymers particle/particle and matrix/filler interaction. The first is often neglected even by compounders, in spite of the fact that its presence may cause composite properties to deteriorate significantly especially under the effect of dynamic loading conditions [18]. Many attempts have been made to change both interactions by the surface treatment of the filler, but the desired effect is often not achieved due to improper use of incorrect ideas. 

In spite of the imperfections of the approach, the reversible work of adhesion can be used for the characterization of matrix/filler interactions in particulate filled polymers. Debonding is one of the dominating micromechanical processes in these materials. Stress analysis has shown that debonding stress (a ) depends on the reversible work of adhesion [8], i.e. ... 

The direct determination of matrix/filler interaction is difficult, indirect techniques are used in most cases. These employ the principles discussed in Sect. 3.2. The surface tension of the components and interfacial tension or ac-id/base interaction parameters must be known in order to determine the reversible work of adhesion. Adsorption-desorption techniques, which use small molecular weight materials having an analogous structure to the polymer, can be used for the estimation of interfacial interaction. 

Any factor that affects the formation of the percolating whisker network, or interferes with it, changes the mechanical performances of the composite [38], Three main parameters were reported to affect the mechanical properties of such materials, viz. the morphology and dimensions of the nanoparticles, the processing method, and the microstructure of the matrix and matrix-filler interactions. 

The mechanical performances of polymer nanocomposites are influenced not only by several factors such as properties and amounts of the constituent phases (matrix and nanofiller), nanoparticle dispersion, morphology, and orientation, the matrix-filler interactions but also by the degree of crystallinity and crystalline phases of the polymer, as described... 

From the tensile tests presented, it appeared that the nanocomposites made by alkyl silane-functionalized sepiolite give the best mechanical performances, in particular for what concerns the yield stress. In fact, the sepiolite surface fimctionalization by silane is a reactive treatment, which decreases the interparticle aggregation (improved dispersion) and, at the same time, increases the matrix-filler interactions. The addition of fimc-tionalized polymers is, instead, a nonreactive surface treatment. It leads to a decrease of the particle-particle interaction but can also reduce the matrix-particle interaction, which leads to lower yield stress and ultimate tensile stress. 

Nonreactive treatment leads to the decrease of particle/particle and matrix filler interaction. The latter leads to decretised strength and increased deformability, occasionally to increased impact resistance. 

Shenoy, A.V. and Saini, D.R. (1986) Quantitative estimation of matrix filler interactions in ferrite-filled styrene-isoprene-slyrene block copolymer systems, Polym. Composites, 7,96-100. 

Effect of filler-matrix affinity can be quantitatively estimated through dynamic viscoelastic data. An interaction parameter has been defined which gives a measure of the postulated matrix immobilization at die interphase of the filler. It has been shown that there is a correlation between the interaction parameter in die melt state and the solid state at comparable frequency of deformation. Thus, it is possible to generate dynamic data in the melt state for quantitatively estimating the matrix-filler interaction and then extrapolating die affiiiity behavior to die solid state. 

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