Role-filler property

In PVC coating formulation fillers play a role. Filler choice mostly depends on the way the filler affect viscosity. The filler should not absorb the plasticizers nor interfere with the pseudoplastic behavior of the paste which is determined by the resin properties and by the choice of plasticizers. Fillers must be completely dispersed, since the gaps between the coated substrate and the knife are very small. There must be no lumps. Fillers should not interfere with deaeration which is... 

Data of Figs 8-10 give a simple pattern of yield stress being independent of the viscosity of monodisperse polymers, indicating that yield stress is determined only by the structure of a filler. However, it turned out that if we go over from mono- to poly-disperse polymers of one row, yield stress estimated by a flow curve, changes by tens of times [7]. This result is quite unexpected and can be explained only presumably by some qualitative considerations. Since in case of both mono- and polydisperse polymers yield stress is independent of viscosity, probably, the decisive role is played by more fine effects. Here, possibly, the same qualitative differences of relaxation properties of mono- and polydisperse polymers, which are known as regards their viscosity properties [1]. 

The fact that the appearance of a wall slip at sufficiently high shear rates is a property inwardly inherent in filled polymers or an external manifestation of these properties may be discussed, but obviously, the role of this effect during the flow of compositions with a disperse filler is great. The wall slip, beginning in the region of high shear rates, was marked many times as the effect that must be taken into account in the analysis of rheological properties of filled polymer melts [24, 25], and the appearance of a slip is initiated in the entry (transitional) zone of the channel [26]. It is quite possible that in reality not a true wall slip takes place, but the formation of a low-viscosity wall layer depleted of a filler. This is most characteristic for the systems with low-viscosity binders. From the point of view of hydrodynamics, an exact mechanism of motion of a material near the wall is immaterial, since in any case it appears as a wall slip. 

The role of the matrix is to protect the filler from corrosive action of the enviroment and to ensure interactions between the fibers by mechanical, physical and chemical effects. The mechanical properties of fiber composites are dependent on the mutual position of the fibers in the monolithic materials. 

Cure systems, however, paint only part of the picmre with regard to the manufacture of mbber articles polymers and fillers are equally important in meeting performance requirements. In addition, compound mixing and processing play an important role in achieving final vulcanizate properties. 

The aluminosilicate glass has a dual role it acts as a filler and is also the source of ions required to gel phosphoric add solutions. These glasses act as a source of ions because they are decomposed by adds. This property is dependent on the Al/Si ratio being suflidently high, approaching 1 1. The reasons and criteria for the decomposition of aluminosilicates are examined fully in Section 5.9.2. 

The pigment phase holds potential for manipulation of the paint properties. For example, in antifouling paints, seawater-soluble pigments play an active role in the paint behaviour (see e.g. Kiil et al., 2002 and later sections on mechanisms). Extenders (fillers) are coarse particles (e.g. natural limestone or clay). They are cheap and added for economic reasons, but also provide strength and resistance to the paint. 

The term non-interactive filler means that the filler does not play a role in the crosslinking of the network. Even so fillers can have a marked effect on both elastic properties and wear resistance. Filler particles are usually inorganic or organic particles with a high modulus. For example carbon is used in car tyres. 

The use of inorganic additives as extenders in thermoplastic polymers is a long established practice. In recent years, the role of such additives has changed from that of cost-reducing fillers to property enhancing reinforcing agents. This conversion has come about as a result of the comp tibilization of the additive with the thermoplastic polymer, by interaction at the polymer-filler interface. 

First introduced industrially in the 1930s, thermoplastic polymers are today produced and consumed in vast quantities and play a major role in many aspects of our everyday lives. It is estimated that over 16 million tons were consumed in Western Europe alone in 1991 [1]. Mineral fillers have, since the beginning, made an important contribution to the spectacular growth of thermoplastic polymers. The addition of mineral materials was initially seen mainly as a means of extending or reducing the compound cost but, as the relative cost of the polymers decreased, this became less important and attention was more and more focused on the property improvements that could be achieved. 

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. 

Although a number of filler characteristics influence composite properties, particle size, specific surface area, and surface energetics must again be mentioned here. All three also influence interfacial interactions. In the case of large particles and weak adhesion, the separation of the matrix/ filler interface is easy, debonding takes place under the effect of a small external load. Small particles form aggregates which cause a deterioration in the mechanical properties of the composites. Specific surface area, which depends on the particle size distribution of the filler, determines the size of the contact surface between the polymer and the filler. The size of this surface plays a crucial role in interfacial interactions and the formation of the interphase. 

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. 

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