Other Fillers

In this paragraph are summarized other additives reported in the scientific literature, which affect the thermal stability of polyurethane. In this context, silver nanoparticles have been attracted the attention of the researchers due to their antimicrobial activity. Actually, the antimicrobial properties are so interesting for reinforce PUs giving new multifunctional materials for biomedical applications. It has been reported that the addition of silver nanoparticles provokes an enhancement on the PU thermal stability [131]. Chou et al. reported an increase in the thermal stability for a PU-based coating reinforced with Ag nanoparticles [132], Deka et al. detected an increment on more than 40 °C on the PU thermal stability when Ag nanoparticles have been added to the polymer matrix [133], 

Depending on the geographical area, ground marble fillers, some with surface treatment, are used for PVC-U and PVC-P applications. 

Ground dolomite (calcium magnesium carbonate) and limestone fillers are also used. 

Talc has been used in calendered PVC compounds to increase melt cohesion and modulus of the finished material. 

Cellulose fillers, with and without silane coupling agent treatment, have been investigated at various levels showing an increase in physical properties and viscosity (53). 

Silane coupling agents have also been used for interfacial enhancement of PVC-P/silica composites (440). 

Conductive metals are also advocated. Bekaert Fibre Technologies manufactures stainless steel fibres for vehicle fuel systems and electronic equipment housings in Europe, Bekintex of Belgium markets Beki-Shield GR stainless steel fibres containing a polymeric binder for use in EMI and ESD applications. Very low doses are said to be sufficient. Nickel-coated mica has been suggested as a conductive filler for ABS. Aluminium, copper and silver in the form of either powders or flakes have all been used. 

ABB has developed compounds that change from conductive to non-conductive on heating, as a consequence of the properties of a doped ceramic filler. 

Since many of the newer antistatic agents are expensive and high loadings are sometimes necessary, there is an incentive to use multilayer films, confining the antistat to the outer layer. However, where dust attraction is the only consideration, low dose levels will usually suffice. 

---

Singk-Screw E.xtruders. These iacorporate iagredients such as antioxidants (qv), stabilizers, pigments, and other fillers iato plastics and elastomers (Fig. 

For many electronic and electrical appHcations, electrically conductive resias are required. Most polymeric resias exhibit high levels of electrical resistivity. Conductivity can be improved, however, by the judicious use of fillers eg, in epoxy, silver (in either flake or powdered form) is used as a filler. Sometimes other fillers such as copper are also used, but result in reduced efficiency. The popularity of silver is due to the absence of the oxide layer formation, which imparts electrical insulating characteristics. Consequently, metallic fibers such as aluminum are rarely considered for this appHcation. 

For equivalent particle size the carbon blacks are the most powerful reinforcing fillers. However, fine particle size silicas can be very useful in non-black compounds whilst other fillers such as aluminium hydroxide, zinc oxide and calcium silicate have some reinforcing effect. 

Miscellaneous uses include textile bobbins, guns for hot melt adhesives and bilge pump housings. These materials are normally found in reinforced form. In addition to glass fibres, other fillers such as glass beads, talc and mica are used in conjunction with coupling agents. 

Rubber latex cement Rubber latex cement consists of mixtures of sand and other fillers which are gauged with rubber latex solution. These cements are suitable for dilute acid conditions and are particularly useful in conditions where dilute acid alternates with water or dilute alkalis. They remain very slightly resilient and adhere very well to stoneware. They are not of course... 

Among other fillers of note are aluminium flakes [15], hybrid fillers — a mixture of flakes and fibers (Transmet Corp.) [14], mica coated with a layer of Ni (Martin Marietta) [14], etc. 

Thermosetting resins are combined with fibers and other fillers to form composites.19 Thermosetting resins with low viscosities are necessary to wet fibers or... 

The tire industry is by far the largest consumer for carbon black, so it should not be surprising that a major focus for research and development at carbon black producers has been understanding and improving the performance of carbon black and other fillers in tires. This chapter will describe... 

A typical stress-strain curve for a pure gum natural rubber vulcanizate (i.e., without carbon black or other fillers ) is shown in Fig. 83. The stress rises slowly up to an elongation of about 500 percent (length six times initial length), then rises rapidly to a value at break in the neighborhood of 3000 pounds per square inch based on the... 

Inorganic fillers in plastics compositions are usually in a very finely divided form and, as such, are ideal for powder XRD study. A sample size of a few mg gives a good pattern in 1 or 2 h. Crystalline mineral fillers can usually be observed directly in the complete polymeric formulation, in concentrations exceeding about 1 %. Combined XRD/XRF studies are favoured [326]. A mineral filler is easy to identify in a compound in the absence of other fillers. 

For silica fillers, hydrolytic stability is best when M = Si for other fillers, e.g., calcium carbonate then titanate- or zirconate-coupling agents are preferred. 

The styrenic thermoplastic elastomers are the only type which are fully compounded in the manner of conventional elastomers. In this case, however, the addition of carbon black, or other fillers, does not give reinforcement. Additions of polystyrene, or high impact polystyrene, and oil are used to vary hardness and tear strength, and fillers can be used to cheapen the material. Other added polymers, e g., EVA, can be used to increase ozone resistance. These materials also require antioxidants for protection during processing and service life, and the poor UV stability restricts their use in outdoor applications. 

In order to impregnate paper, wood and other fillers, nearly 10-15 per cent of the phenolic resins is produced as alcoholic solutions. These find use for decorative purposes for counter tops and wall coverings and industrial laminates of electrical parts. 

In this simple form, this expression is a good first approximation to compare the experimental reinforcement achieved upon addition of filler to the matrix, to the theoretical prediction [11]. It provides a measure of how efficiently the properties of the nanofiller are exploited in the composite, but also enables the comparison with the level of reinforcement achieved using other fillers. Note, in addition, that equation (8.2) sets an upper limit between Efl5 = 200 GPa and / = 1000 GPa, depending on whether the nanocarbon is randomly or perfectly oriented (without taking q0 into account). 

The influence of fillers has been studied mostly at hl volume fractions (40-42). However, in addition, it is instructive to study low volume fractions in order to test conformity with theoretical predictions that certain mechanical properties should increase monotonlcally as the volume fraction of filler is Increased (43). For example, Einstein s treatment of fluids predicts a linear increase in viscosity with an increasing volume fraction of rigid spheres. For glassy materials related comparisons can be made by reference to properties which depend mainly on plastic deformation, such as yield stress or, more conveniently, indentation hardness. Measurements of Vickers hardness number were made after photopolymerization of the BIS-GMA recipe, detailed above, containing varying amounts of a sllanted silicate filler with particles of tens of microns. Contrary to expectation, a minimum value was obtained (44.45). for a volume fraction of 0.03-0.05 (Fig. 4). Subsequently, similar results (46) were obtained with all 5 other fillers tested (Table 1). 

Payload. Generally that part of the load which is expandable, deliverable, or ready for use in direct accomplishment of the mission. In a projectile the explosive or other filler. In a guided missile or rocket, the warhead compartment and that which is carried in it (Ref 40a, p 108-L)... 

Composite-based PTC thermistors are potentially more economical. These devices are based on a combination of a conductor in a semicrystalline polymer—for example, carbon black in polyethylene. Other fillers include copper, iron, and silver. Important filler parameters in addition to conductivity include particle size, distribution, morphology, surface energy, oxidation state, and thermal expansion coefficient. Important polymer matrix characteristics in addition to conductivity include the glass transition temperature, Tg, and thermal expansion coefficient. Interfacial effects are extremely important in these materials and can influence the ultimate electrical properties of the composite. 

Both adhesive and hydrodynamic forces depend on the size of the particles. The two forces were calculated for CaC03 fillers of various particle sizes homogenized in a PP matrix. The results are presented in Fig. 3. At a certain particle size adhesion exceeds shear forces, aggregation of the particles takes place in the melt. Since commercial fillers have a relatively broad particle size distribution, most fillers show some degree of aggregation and the exact determination of the particle size, or other filler characteristics where aggregation appears, is difficult. Experiments carried out with 11 different CaC03 showed this limit to be around 6 m /g specific surface area [25]. 

Over 1 million tons each of calcium carbonate and carbon black and over ISO thousand tons of alumina trihydrate (ATH) are used annually as fillers by the U.S. polymer industry. Asbestos continues to be used in moderate amounts (250 thousand tons annually), but it is being displaced by other fillers because of its toxicity. 

---