Crystalline Filler

Aesthetic dental ceramics are essentially glass-matrix materials with varying volume fractions of crystalline fillers. Crystalline fillers are used in the glass matrix both for dispersion strengthening, usually at volume fractions of 40—70%, and for altering optical properties, usually at low volume fractions. Dental ceramics are generally manufactured from two distinct classes of materials, ie, beneficiated feldspathic minerals and glass—ceramics. 

Transparency. Some applications of plastics require transparency. Amorphous plastics should be able to transmit light. Some factors which prevent transparency include unsatura-tion/light absorption, crystallinity, fillers and reinforcing fibers, and use of rubber particles to increase impact strength. The plastics most often used for their transparency are poly(4-methylpentene-l) (TPX), poly(methyl methacrylate) (almost equal to glass), cellulose acetate, propionate, and butyrate, polycarbonate, and polysulfones (slightly yellow). As a research challenge, it is quite possible that fillers and rubber particles could... 

Thermodynamics of Solubility Mathematics of Diffusion Factors Affecting Solubility and Transport Crystallinity, Fillers, and Morphology Temperature and Transitions Penetrant Size... 

CrystallinitY, Fillers, and Morphology. The solubility of low molecular weight compounds is extremely small in the crystallites of polymers in comparison to that in the amorphous regions of the same polymer (15). Thus, equilibrium sorption in semicrystalline polymers is less than that for corresponding completely amorphous ones. For the same reasons crystalline polymers are more chemical resistant than amorphous ones. As a good approximation for gases, the Henry s law solubility coefficient of a semicrystalline polymer is related to that for the same polymer in the amorphous state, S, by the following ... 

Additional TMDSC study of other vinyl polysiloxane, polyether and polysulfide impression materials is important to verify if the polymer transitions shown in Figures 16 to 19 generally exist in different products and to investigate the effects of other temperature modulation conditions. Complementary research on correlations with clinically relevant mechanical properties of the elastomeric impression materials is needed to verify if these thermal analyses have useful predictive power. Interestingly, when compared at apparently similar viscosities, the reported values of the elastic modulus [3] are highest for the vinyl polysiloxane silicone impression materials, intermediate for the polyether impression materials, and lowest for the polysulfide impression materials, in reverse order to the relative values of Tg fovind in our thermal analyses [45]. Our X-ray diffraction and scanning electron microscopic study [47] of these impression materials has shown that they contain substantial amounts of crystalline filler particles in the micron size range, which are incorporated by manufacturers to achieve the clinically desired viscosity levels. Tliese filler particles should have considerable influence on the mechanical properties of the impression materials. 

The polycarbonate exhibits a typical Newtonian flow behaviour at the low shear rates investigated, while it shows the tendency to continuosly shear thin, if subjected to high shear rates. The same flow behaviour is exhibited by the blends with the lower content of the liquid-crystalline filler. At higher content of liquid-crystalline filler, the rheology of the blend is strongly affected by the presence of the second phase, whose viscosity continuously shear thins over the shear rates investigated. 

While the presence of the LCP inclusion strongly reduces the degree of spring back shrinkage, the recoil kinetics has not been altered of the liquid-crystalline filler. 

Layered double hydroxides (LDHs) are a different kind of layered crystalline filler for nanocomposite formation. Because they combine the flame retardant features of conventional metal hydroxide fillers (magnesium hydroxide and aluminum hydroxide) with those of layered silicate nanofillers (montmorillonite), LDHs are considered to be a new emerging class of nanofillers favorable for the preparation of flame retardant nanocomposites. In the present chapter, recent progress in the study of polymer/LDH flame retardant nanocomposites is reviewed. 

Fillers can be crystalline or amorphous. Examples of crystalline fillers include calcium carbonate and anatase (titanium dioxide) whereas solid glass beads are amorphous. Many, but not all, fillers are extracted from the earth s crust by mining or quarrying operations examples include calcium carbonate, talc, bentonite, wollastonite (calcium metasilicate) and titanium dioxide. Some fillers are extracted along with impurities that can seriously affect the colour, electrical properties and toxicity of plastics unless they are removed. Others, such as wood flour, have organic origins. The use of wood flour itself has been rather limited because of compatibility problems. 

SilverBond ground crystalline silica is the performance standard by which other crystalline fillers are measured. Completely inert, SilverBond provides excellent tint retention in exterior architectural finishes and helps prevent atmospheric degradation at the surface interface. Low oil absorption allows for high loadings, and its neutral pH makes SilverBond the preferred filler in catalyzed two-component systems. A hard filler, SilverBond imparts excellent abrasion and scratch resistance when incorporated into industrial paint and coatings, grouts, elastomeric sealants and high performance epoxies. 

An adequate procedure for the incorporation of fibrous, lamellar, or crystalline fillers and reinforcements must preserve their form and dimensions [44 6]. 

There is a wide variety of both synthetic and natural crystalline fillers that are able, under specific conditions, to influence the properties of PP. In PP nanocomposites, particles are dispersed on the nano-scale. " The incorporation of one-, two- and three-dimensional nanoparticles, e.g. layered clays, nanotubes, nanofibres, metal-containing nanoparticles, carbon black, etc. is used to prepare nanocomposite fibres. However, the preparation of nanofilled fibres offers several possibilities, such as the creation of nanocomposite fibres by dispersing of nanoparticles into polymer solutions, the polymer melt blending of nanoparticles, in situ prepared nanoparticles within a polymeric substrate (e.g. PP/silica nanocomposites prepared in situ via sol-gel reaction), " the intercalative polymerization of the monomer. 

Charnetskaya A G, Pohzos G, Shtompel V I, Privalko E G, Kercha Yu Yu and Pissis P (2003) Phase morphology and molecular dynamics of a polyurethane ionomer reinforced with a liquid crystalline filler, Eur Polym J 39 2167-2174. 

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