Cross-filler

PVC cross-filler, flame retarded formulation. [Data from Jiang, q, KeUer, j,... 

Commercially produced elastic materials have a number of additives. Fillers, such as carbon black, increase tensile strength and elasticity by forming weak cross links between chains. This also makes a material stilfer and increases toughness. Plasticizers may be added to soften the material. Determining the effect of additives is generally done experimentally, although mesoscale methods have the potential to simulate this. 

Alkyds are formulated from polyester resins, cross-linking monomers, and fillers of mineral or glass. The unsaturated polyester resins used for thermosetting alkyds are the reaction products of polyfunctional organic alcohols (glycols) and dibasic organic acids. 

Phenol—formaldehyde (PF) was the first of the synthetic adhesives developed. By combining phenol with formaldehyde, which has exceptional cross-linking abiHties with many chemicals and materials, and a small amount of sodium hydroxide, a resin was obtained. The first resins soHdified as they cooled, and it was discovered that if it was ground to a powder with a small amount of additional formaldehyde and the appHcation of more heat, the mixture would Hquify and then convert to a permanently hard material. Upon combination of the powdered resin mixture with a filler material such as wood flour, the result then being placed in a mold and pressed under heat and pressure, a hard, durable, black plastic material was found to result. For many years these resulting products were called BakeHte, the trade name of the inventor. BakeHte products are still produced today, but this use accounts for only a small portion of the PF resins used. 

Fillers (qv) are occasionally used in flexible slab foams the two most commonly used are calcium carbonate (whiting) and barium sulfate (barytes). Their use level may range up to 150 parts per 100 parts of polyol. Various other ingredients may also be used to modify a flexible foam formulation. Cross-linkers, chain extenders, ignition modifiers, auxiHary blowing agents, etc, are all used to some extent depending on the final product characteristics desired. 

Dicyclopentadiene is also polymerized with tungsten-based catalysts. Because the polymerization reaction produces heavily cross-Unked resins, the polymers are manufactured in a reaction injection mol ding (RIM) process, in which all catalyst components and resin modifiers are slurried in two batches of the monomer. The first batch contains the catalyst (a mixture of WCl and WOCl, nonylphenol, acetylacetone, additives, and fillers the second batch contains the co-catalyst (a combination of an alkyl aluminum compound and a Lewis base such as ether), antioxidants, and elastomeric fillers (qv) for better moldabihty (50). Mixing two Uquids in a mold results in a rapid polymerization reaction. Its rate is controlled by the ratio between the co-catalyst and the Lewis base. Depending on the catalyst composition, solidification time of the reaction mixture can vary from two seconds to an hour. Similar catalyst systems are used for polymerization of norbomene and for norbomene copolymerization with ethyhdenenorbomene. 

In recent years, synthetic polymeric pigments have been promoted as fillers for paper. Pigments that ate based on polystyrene [9003-53-6] latexes and on highly cross-linked urea—formaldehyde resins have been evaluated for this appHcation. These synthetic pigments are less dense than mineral fillers and could be used to produce lightweight grades of paper, but their use has been limited in the United States. 

Fillers. Materials used as fillers (qv) in mbber can also be classified as acidic, basic, or neutral. Furnace blacks, ie, HAF, FEF, or SRF, are somewhat basic. As such, they can have an activating effect on sulfur cure rates. Furthermore, carbon blacks have been found to promote formation of mono/disulfide cross-links thereby helping minimize reversion and enhance aging properties. 

Like HIIR, EPR has a fiiUy saturated backbone and has only unsaturation points available for vulcanization cross-linking in very small percentages of the pendent diene modifier (EPDM). It is an excellent aging compound with high dex fatigue life even when heavily loaded with fillers and is utilized in PCT white sidewalls. 

Moisture-Curing Silicones. The formulation of moisture-curing sHicones includes a sHicone polymer, filler, a moisture-reactive cross-linker, and sometimes a catalyst. The most common sHicone polymer used in sealant formulations is an alternating sHicon—oxygen backbone with methyl groups attached to the sHicon such as the sHicone polymer (1). 

The compression set of sihcone mbber is similar to organic types of mbber at low (0—50°C) temperatures, ranging from 5 to 15% (380). Above 50°C, sihcone mbber is superior, but compression set increases with time and temperature. Sihcone mbber is more tear-sensitive than butyl mbber, and the degree of sensitivity is a function of filler size and dispersion, cross-link density, and curing conditions. The electrical properties of sihcone mbber are generally superior to organic mbbers and are retained over a temperature range from —50 to 250°C (51). Typical electrical values for a heat-cured sihcone mbber are shown in Table 9. 

The Hquid polymer is then compounded with metal oxides or peroxides, as weU as fillers (carbon black) and can undergo cold vulcanization, ie, chain extension and cross-linking iato a soHd matrix. It is largely used as a sealant and gasket material for wiadows, automobile wiadshields, etc. 

As with almost all mbbers, the final properties are deterrnined by compounding and subsequent vulcanization or cross-linking. Various fillers, processing aids, plasticizers, tackifiers, cure systems, and antidegradants are used. 

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