Filled thermosets

Graham V. Jackson, Michael L. Orton and Howard Taylor 

Crosslinked polymers can be characterised conveniently by defining their crosslink density as branch points per unit volume or average molecular weight between crosslinks. This parameter in conjunction with the molecular nature of the polymer defines whether the material will behave as an elastomer or as a rigid material, which shows either ductile or brittle failure behaviour. Fillers can be used to modify properties further across the whole range of polymer behaviour. Because inorganic fillers are, compared to most polymers, much stiffer and less extensible materials, their incorporation into a polymer will usually produce a composite material of reduced strain to failure and increased stiffness relative to the polymer, i.e., the composite will be less elastomeric or less ductile. Nevertheless, large quantities of fillers are used in polymers that already have low strains to failure and show brittle failure behaviour. This chapter will confine itself to a discussion of the use of fillers in ductile and brittle crosslinked polymers. 

Fillers, through their essentially volumetric and thermal inertness at typical thermoset resin-processing temperatures, offer a valuable means of exotherm and shrinkage control. 

Fillers can modify the properties of the cured polymer in a wide variety of ways. Some examples of properties readily modified by incorporation of fillers are mechanical properties such as stiffness, hardness, strength and toughness, and thermal properties such as expansion, conductivity or thermal decomposition. The latter can have a considerable effect on flammability and smoke generation. Fillers are also an important way of varying and enhancing aesthetics. 

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Mineral hydrates, such as alumina trihydrate and magnesium sulfate heptahydrate, are used in highly filled thermoset resins. 

Inserts are often dedicated to specific plastic materials neat thermoplastics, neat and filled thermosets, reinforced plastics, composites, structural foams. .. 

Thermal and physical properties of plastics (typical values) Thermoplastic 50/c glass-filled thermoset... 

The membrane material used in the past, if a membrane were used at all, was lead. Today membrane materials include rubber, urethanes, fiberglass reinforced thermoset resins, and aggregate filled thermoset resins. The fiberglass reinforced and aggregate filled resins have also found use as linings without brick or tile. 

As discussed earlier, while the scale of the fillers is substantially different, nanocomposite materials concepts and technology are very similar to those of conventional composite materials. This is clearly demonstrated in the case of new thermosets for nonlinear optical (NLO) applications, " " where nanocomposite of liquid crystalline thermosets, IPNs, and simple filled thermosets are evaluated. Tripathy et al. discussed four different ways to prepare nonlinear optical polymers. (1) The polymer matrix is doped with NLO moieties in a guest/host system (2) In side-chain polymer systems, NLO polymers with active moieties are covalently bonded as pendant groups (3) In the main chain polymer, the chromo-phores are incorporated as parts of the main polymer backbone to enhance the temporal stability of the NLO properties and (4) Stability of the optical noninearity in sol-gel-based thermosets is related to... 

The filler effects on the chemoviscosity of thermosetting resins have not been studied extensively, but are vital to understanding the rheology of filled thermosets. For example, the effects of filler concentration on viscosity can be used in process control to monitor batch-to-batch variations or to provide essential information for research into alternative filler/resin batches. Ng and Manas-Zloczower (1993) examined an epoxy-resin system with silica filler and established that the elastic modulus of the resin can be expressed in terms of... 

The measurement of yield stress at low shear rates may be necessary for highly filled resins. Doraiswamy et al. (1991) developed the modified Cox-Merz rule and a viscosity model for concentrated suspensions and other materials that exhibit yield stresses. Barnes and Camali (1990) measured yield stress in a Carboxymethylcellulose (CMC) solution and a clay suspension via the use of a vane rheometer, which is treated as a cylindrical bob to monitor steady-shear stress as a function of shear rate. The effects of yield stresses on the rheology of filled polymer systems have been discussed in detail by Metzner (1985) and Malkin and Kulichikin (1991). The appearance of yield stresses in filled thermosets has not been studied extensively. A summary of yield-stress measurements is included in Table 4.6. 

It is evident that strict control over the composition of a filled thermoset system is vital to establishing the chemoviscosity of the system. Also, the measurement of samples with various filler loadings, filler types, surface treatments and filler dimensions would aid in fully describing the effect of fillers and enable better characterization of filled samples. 

Durez . [OxyQiem/Durez] Phenolic, alkyd, or phthalate resins, some glass or mineral filled thermosets for tqpplics. incl. automrxive transmission parts and braking systems, communication products for compr., transfer, and inj. molding applies. 

Gama-FIL [Georgia Marble] Calcium carbonate filler for use in plastics, BMC/SMC, paint, caulks, sealants, adhesives, paper, foam urbane, niodi-fied acrylics, filled thermosets/thermo-plastics, and rubber. 

Gama-Sperse . [Georgia Marble] Calcium carboiate filler fw paint plastics, caulks, sesdants, adhesives, foam urediane, filled thermosets/tbermqplas-tics, BMC, and rubber q lks. 

Chem. Descrip. Calcium carbonate CAS 471-34-1 EINECS/ELINCS 207439-9 Uses Filler for plastics, PVC, polyolefins, polyesters, BMC/SMC, paint, caulks, sealants, adhesives, paper, foam urethane, modified acrylics, filled thermosets/thermoplastics, and rubber Features Improves impact str., dimensional stability Regulatory NSF approved for potable water materials Properties Wh. powd. 2 avg. particle diam. 99.9% finer than 8 0.15% sol. in water sp.gr. 2.70-2.71 dens. 22.57 Ib/gal bulk dens. 38 Ib/tP (loose) oil absorp. 23 01 cc/100 g brightness (Hunter) 95 ref. index 1.6 pH 9.5 (sat.) hardness (Mohs) 3.0 Toxicobgy Nontoxic Camel-TEX [IMERYS]... 

Chem. Descrip. y-Methacryloxypropyltrimethoxysilane CAS 2530-85-0 EINECS/ELINCS 219-785-8 Uses Adhesion promoter for adhesives and coatings coupling agent for glass-reinforced and min.-filled thermosetting resins blend additive in resin systems (polyester, acrylic), and filled or reinforced thermoplastic polymers (polyolefins, polyurethanes)... 

Fiberite SI Filled thermoset silica compounds Fiberite/ICI... 

Plastic tooling ru A term designating structures composed of plastics that are used as tools in the fabrication of metals or other materials including plastics. While they are usually made of reinforced and/or filled thermosets, flexible silicone or polyurethane tools are often used for casting plastics. Common applications of rigid plastics... 

Titanates are currently used with calcium carbonate to reduce the viscosity of filled thermosetting polymer systems. 

Quadrini F, Santo L, Squeo EA (2012) Solid-state foaming of nano-clay-filled thermoset foams with shape memory properties. Polym Plast Technol Eng 51(6) 560-567... 

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