Particulate fillers, reinforcement

The resulting empirical expression for particulate filler reinforcement for the Lipatov model can be used to calculate the effective interphase thickness Ar, using given values of filler volume fraction, filler particle radius, and measured calorimetric evaluation of X ... 

Particulate fillers are divided into two types, inert fillers and reinforcing fillers. The term inert filler is something of a misnomer as many properties may be affected by incorporation of such a filler. For example, in a plasticised PVC compound the addition of an inert filler will reduce die swell on extrusion, increase modulus and hardness, may provide a white base for colouring, improve electrical insulation properties and reduce tackiness. Inert fillers will also usually substantially reduce the cost of the compound. Amongst the fillers used are calcium carbonates, china clay, talc, and barium sulphate. For normal uses such fillers should be quite insoluble in any liquids with which the polymer compound is liable to come into contact. 

Particulate fillers provide better creep resistance than unfilled plastics but are less effective than fibrous reinforcements. 

In general adding reinforcing fibers significantly increases mechanical properties. Particulate fillers of various types usually increase the modulus, plasticizers generally decrease the modulus but enhance flexibility, and so on. These RPs can also be called composites. However the name composites Utterly identifies thousands of different combinations with very few that include the use of plastics (Table 6-18). In using the term com-... 

The surface tension of two thermoplastics and three fillers are listed in Table 2. Large differences can be observed both in the dispersion, but especially in the polar component. The surface tension of the majority of polymers is in the same range, in fact between that of PP and PMMA. Those listed in Table 2 represent the most important particulate fillers, and also reinforcements used in practice, since clean glass fibers possess similar surface tensions to Si02. Surface treatment lowers the surface tension of fillers significantly (see Sect. 6.1). 

Talc is a hydrated magnesium silicate that is composed of thin platelets primarily white in color. Talc is useful for lowering the cost of the formulation with minimal effect on physical properties. Because of its platy structure and aspect ratio, these extenders are considered reinforcement. Polymers filled with platy talc exhibit higher stiffness, tensile strength, and creep resistance, at ambient as well as elevated temperatures, than do polymers filled with particulate fillers. Talc is inert to most chemical reagents and acids. The actual chemical composition for commercial talc varies and is highly dependent on the location of its mining site. 

Polymers, as well as elastomers, are reinforced by the addition of small filler particles. The performance of rubber compounds (e.g. strength, wear resistance, energy loss, and resilience) can be improved by loading the rubber with particulate fillers. Among the important characteristics of the fillers, several aspects can be successfully interrogated by AFM approaches. For instance, the particle and aggregate size, the morphology, and in some cases the surface characteristics of the filler can be assessed. 

Table 8.4 shows that substantial gains can be obtained by filling crystalline polymers but amoiphous polymers are not much affected by reinforcement. Also, particulate fillers are substantially less effective than fibrous fillers. Glass fiber is the most useful filler in this application. Figure 8.55 shows the effect of two grades of particulate fillers on the heat deflection temperature of polypropylene." Small changes are obseiwed at smaller additions followed by a rapid increase in HDT above a 30% filler content. The particle size has only small difference. 

Sheet molding uses three groups of fillers for different purposes metal oxides for curing, fibers for reinforcement, particulate fillers for variety of other purposes such as improvements in mechanical properties, chemical resistance and surface appearance. The technology is very well documented." ... 

Asbestos-free fiber-reinforced brake linings are being improved through a continuous development effort. A review of problems and achievements was recently published. " Two types of fillers are used in brake pads particulate fillers and reinforcing fibers. Low cost materials are used as particulate fillers, such as calcium carbonate and barite. Their role is to decrease cost without detracting from the per-foimance of the product. 

The reinforcement of elastomers with particulate fillers is a process of great practical and technological importance. Most finished rubber articles are made from filled elastomers and, with a few exceptions, all amorphous rubbers which are incapable of crystallizing under strain require fillers to impart to them technologically useful mechanical properties. 

Reinforcement by particulate fillers is primarily a phenomenon of the rubbery state of viscoelastic response. Fillers which produce dramatic increases in the strength of a polymer 100° C above Tg, often give little or no reinforcement below Tg. 

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