Thermosetting filler systems

Two or more different filler types are utilized in the case of multi-component compounding, which produces very famous hybrid structures where effects of the different materials or components are combined. " Recent investigations on composites having multi-component filler systems have focused mainly on thermoplastic and thermoset polymers and not so familiar with rubbery materials. In most of the applications, CB and silica have been used... 

Surfactants are added to a thermoset resin system to promote the dispersion of fillers in the resin matrix. Recently, surfactants have been used to disperse carbon nanotubes in polymer matrices [48-50]. Surfactants are of two types neutral and ionic. Surfactants have many applications in coating industries for the development of a water-based resin system [51]. Surfactants are added to phenolic or polyurethane foam formulation in which they facilitate formation of small bubbles. The size and uniformity of bubble formation results in a fine cell structure. A surfactant reduces the surface tension of resin formulations and provides an interface between the highly polar resin and the non-polar blowing agent. The surfactant for a particular resin system must be selected carefully so that it is compatible with the resin and resistant... 

With most thermosetting resin systems additives such as catalysts and hardeners have to be added to the resins to cause polymerisation to occur. Many other additives are also used with thermosetting systems and these include inorganic fillers, internal release agents, pigments, etc. These were dealt with in detail in Chapter 2. 

Coated fillers have been evaluated in a range of halogen-containing polymer systems, including rigid and flexible polychloroprene (Neoprene), and in thermoplastic and thermosetting materials... 

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... 

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. 

The effect of fillers on the gel point of thermosets has not been studied extensively. Ng and Manas-Zloczower (1993) used isothermal dynamic time tests to measure the crossover point for a silica-filled epoxy resin. They noted a decrease in gel time with increasing filler loading. Metzner (1985) also noted that the storage modulus and loss modulus increased by different amounts with filler loading. Therefore, the gel-point tests for highly filled systems must involve knowledge of the effect of filler characteristics at various levels. 

Typical systems are unsaturated polyesters, usually filled with mineral fillers and/or fibres. Newer systems such as thermoset-thermoplastics using reactive solvents for processing high-performance engineering polymers are being researched. 

This year s U.S. production of thermoplastics, thermosets, and synthetic rubber is expected to be 29 billion pounds. About 80% of this is based on only a few common monomers. To improve performance, the polymer industry rarely changes to a new, probably more expensive polymer, but instead it shifts from mere homopolymers to copolymers, polyblends, or composites. These three types of multicomponent polymer systems are closely inter-related. They are intended to toughen brittle polymers with elastomers, to reinforce rubbers with active fillers, or to strengthen or stiffen plastics with fibers or minerals. 

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