Processing, thermosets lead forming

Consider first the important class of fibre-reinforced thermosets. Figure 6.8 shows the range of common fibre arrangements, and Table 6.2 indicates the forming processes which lead to them. The salient features ol the processes are as follows. 

The metathesis polymerisation of dicyclopentadiene, an inexpensive monomer (commercially available cyclopentadiene dimer produced by a Diels-Alder addition reaction containing ca 95 % endo and ca 5 % exo form), leads to a polymer that may be transformed into a technically useful elastomer [144-146, 179] and thermosetting resin [180,181]. The polymerisation has characteristics that make it readily adaptable to the reaction injection moulding ( rim ) process [182], The main feature of this process comes from the fact that the polymerisation is carried out directly in the mould of the desired final product. The active metathesis catalyst is formed when two separate reactants, a precatalyst (tungsten-based) component and an activator (aluminium-based) component, are combined. Monomer streams containing one respective component are mixed directly just before entering the mould, and the polymerisation into a partly crosslinked material takes place directly in this mould (Figure 6.5) [147,168,183-186],... 

Thermosetting phenolic resins include a number of polymers, the most common being obtained from the condensation of phenol with formaldehyde. The OH group on the benzene ring increases the reactivity in the o- and p- positions leading to three reactive centers for the phenolic component, while formaldehyde acts as having two active centers that can lead to a fully crosslinked polymer. The process may take place in neutral or alkaline conditions when in the first stage of the reaction, compounds known as methylol derivatives are formed. The condensation of phenol with formaldehyde occurs randomly at ortho- or para- position of the phenol, as shown below ... 

Thermosetting polymers (also called thermosets) are a family of plastics characterized by the fact that they are formed starting from a liquid solution that irreversibly leads to a solid material during a heating step. In this sense, they exhibit an opposite behavior than the one of thermoplastic polymers that, with some exceptions, show a reversible solid-to-liquid transition when heated to a convenient temperature. Although the irreversible liquid-to-solid transition can be also produced by other means such as UV or electron beam irradiation, the resulting products are also called thermosetting polymers. The process by which the initial liquid solution is transformed into a solid is usually known as the cure of the material. 

Misra et al. discovered that chicken feather fibers can be nsed as filters to remove heavy metals through the process of biosorption. They reported that the fibers could remove gold, platinum, lead, copper, and several other heavy metals from solutions. Several researchers have incorporated feather fibers into composites. Schmidt blended feather fibers with polyethylene fibers, and then melted them together, while others have used thermoset matrices, to form composites for potential use as air filters, automotive panels, and shaped plastic parts, where the feather fiber can replace glass fibers as material reinforcement. Others are evaluating the feather fibers for use in resin transfer molding."... 

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