Interface polymer-filler

An intensity factor—the specific activity of the filler-polymer interface causing chemical and/or physical bonding. 

Utracki and Fisa (1982) and Metzner (1985) review the rheology of (asymmetric) fibre-and flake-filled plastics, noting the importance of the filler-polymer interface, filler-filler interactions, filler concentration and filler-particle properties in determining rheological phenomena such as yield-stress, normal-stress and viscosity profiles (thixotropy and rheo-pexy, dilatancy and shear thinning). 

Well-bonded filler-polymer interface and the ignorance of interfacial slip, filler-polymer debonding or matrix cracking. 

Given the overall importance of mechanical properties, this chapter focuses on parameters controlling such properties as related to the filler, the filler/polymer interface, and the method of fabrication. Concepts presented below may also be applicable to the modification ofother polymer properties (e.g., permeability, thermal expansion) through the addition of functional fillers. 

In some cases, it is desirable to increase the permeability of a polymeric material. One example is breathable films. For example, calcium carbonate filled PP films are first made by solvent casting, or extrusion casting or as blown film and subsequently stretched to delaminate the filler - polymer interface [57]. High filler loadings are used to ensure interconnecting voids, giving unimpeded diffusion [58]. 

From surface energy theory, the work of cohesion in a liquid is equal to twice the surface energy. For a polymer this would be approximately 70mjm . It has been shown that for cases when either or both the filler and polymer are non-polar, Wpp, the reversible work necessary to separate unit area of filler-polymer interface is given by ... 

First, it is necessaiy to emphasize that nanocomposite reinforcement comprises several contributions. Above the neat matrix Tg, immobilization of polymer chains becomes the primary effect given by the large nano-filler surface area open for polymer-filler contacts. Thus, the nanocomposite represents a system with high filler-polymer interface area. This is analogous in respect of surface interaction to another system produced by depositing thin polymer layers on solid substrates. 

Lequeux et al. [74] and other authors [43,52] have shown that the nanocomposite contains a phase at the filler-polymer interface exhibiting dynamics substantially slower in comparison to the neat polymer above Tg. Davis and coworkers [43] have shown that the time constant Tj (determined by the NMR method) belonging to the immobilized phase is comparable to the T2 value of the neat matrix below its Tg. Thus, it seems necessary to extend the Langevin effect [71] by the dynamics effects, which are constrained to the diffuse shell of nanometer thickness surrounding each particle. 

If a polar solvent enters the composite, it will tend to cancel out stress-induced charges and lower the sample sensitivity. The filler-polymer interface adhesion may also be reduced, producing the following effects ... 

When applied to partide-reinforced polymer composites, micromechanics models usually follow certain basic assumptions linear elasticity of fillers and polymer matrix the fillers are axisymmetric, identical in shape and size, and can be characterized by parameters such as aspect ratio well-bonded filler-polymer interface, so no interfacial slip is considered filler-matrix debonding and matrix microcraddng. Further details of some important preliminary concepts such as hnear elastidty, average stress and strain, composites average properties, and the strain concentration and stress concentration tensors can be found in preview literature [48-50]. 

These assumptions maximize the distance that the diffusing molecules must travel and thus define the maximum decrease in permeability that geometrically can be expected for the addition of filler to a polymer. In the same article, Nielsen developed a second model for predicting a change in permeability that can be expected when the permeant is partially soluble in the polymer and when the concentration of sorbed molecules at the filler-polymer interface is different from the concentration in the polymer. He proposed that around each filler particle there is an interfacial layer which shows properties different from the bulk polymer saturated with sorbed molecules. In this case the total permeability is divided into two parts (Equation 11.4) ... 

---