Polyester Moulding Compositions

Diallyl phthalate (see also Section 25.3) has also been used as a laminating resin but because of its higher price it has been largely replaced by the glycol-saturated acid-unsaturated acid polyesters. 

Other allyl compounds described in the literature include diallyl carbonate, diallyl isophthalate and diallyl benzene phosphonate. 

Although phenolic and amino moulding powders remain by far the most important of the thermosetting moulding compositions a number of new materials have been introduced over the last 30 years based on polyester, epoxide and silicone resins. 

The dough moulding compounds were originally developed in an attempt to combine the mechanical properties of polyester-glass laminates with the speed of cure of conventional moulding powder. In spite of their somewhat high cost they have now established themselves in a number of applications where a mechanically strong electrical insulant is required. 

Formulations for the three typical DMC grades are given in Table 25.2. 

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Allyl resins Polyester Moulding Compositions Fibre-forming and Film-forming Polyesters Polyfethylene terephthalate) Moulding Materials... 

Heitz, T Heym, M., Muhlbach, K. and Plachetta, C., Stabilized polyester moulding compositions, US Patent 5 733 959 (to BASF, Ludwigshafen, Germany), 1998. 

Akkapeddi, M. K., Van Buskirk, B., and Chun, S., Polyester moulding compositions and articles exhibiting good impact, heat and solvent resistance, US Patent 5 723 520 (to Allied Signal Inc., Morristown, NJ), 1998. 

Polyesters are eneountered in many forms. They are important as laminating resins, moulding compositions, fibres, films, surface coating resins, rubbers and plasticisers. The common factor in these widely different materials is that they all contain a number of ester linkages in the main chain. (There are also a number of polymers such as poly(vinyl acetate) which contain a number of ester groups in side chains but these are not generally considered within the term polyester resins.)... 

The polyester alkyd moulding compositions are also based on a resin similar to those used for laminating. They are prepared by blending the resin with cellulose pulp, mineral filler, lubricants, pigments and peroxide curing agents on... 

This monomer has been used as the basis of a laminating resin and as a reactive diluent in polyester laminating resins, but at the present time its principal value is in moulding compositions. It is possible to heat the monomer under carefully controlled conditions to give a soluble and stable partial polymer in the form of a white powder. The powder may then be blended with fillers, peroxide catalysts and other ingredients in the same manner as the polyester alkyds to form a moulding powder. Similar materials may be obtained from diallyl isophthalate. 

The use of these sensors is not restricted to high-performance composites, but can be extended to on-line monitoring of resin-transfer moulding (McIUiagger et al, 2000) and glass-polyester prepreg composite cure (Kim and Lee, 2002). 

Phosphorus compounds are often combined with silicon rather than nitrogen, as in European Patent 899301 from General Electric, in which a polyester moulding compound is flame retarded with an organoclay, a polymeric siloxane composition and a boron and phosphorus containing material. 

Several recent patents concern thermoplastic polyesters for electrical goods. DuPont has disclosed a moulding composition for PBT, to which is added a reinforcement and a mixture of melamine pyrophosphate with an aromatic phosphate oligomer. The physical properties are reported to be good (EP 903370). 

The processing of polyester matrix composites has also been modelled (3). In reference (3) the resin transfer moulding process (RTM) was modelled and the predictions were experimentally verified. Different m epoxy based materials, in this case the polyester resin gelled fi om the skin to the core as shown in Figure 25. 

As a class the polyesters find wide application as fibres, as laminating resins for glass-fibre reinforced cars and boats, in moulding compositions, in surface coatings, as adhesives and as plasticizers for PVC. Elastomeric polyesters may also be prepared. Providing that the molecule is flexible (for example by primarily consisting of a carbon-carbon aliphatic backbone with small substituents on the carbon atoms, does not crystallize or has a very low melting point) then the presence of a few ester links, which increase interchain attraction and reduce rubberiness, is not too adverse on the rubbery properties of the polymer. 

The most important initiators used at elevated temperatures are peroxides, which liberate free radicals as a result of thermal decomposition. A peroxide which is widely used in this way is benzoyl peroxide (XII), the decomposition of which is discussed in section 1.4.2(a). Other peroxides which find application in the cross-linking of unsaturated polyesters are 2,4-dichlorobenzoyl peroxide (XIII), di-tert-butyl peroxide (XIV) and lauroyl peroxide (XV). Mixtures of polyester resin and this type of peroxide are comparatively stable at room temperature but rapidly cross-link at temperatures ranging from about 70 to 150°C, depending on the choice of peroxide. Such peroxides are used principally in processes employing moulding compositions, when short curing times are required. 

Polymer-matrix composites for aerospace and transport are made by laying up glass, carbon or Kevlar fibres (Table 25.1) in an uncured mixture of resin and hardener. The resin cures, taking up the shape of the mould and bonding to the fibres. Many composites are based on epoxies, though there is now a trend to using the cheaper polyesters. 

Saturated complex polyesters, particularly, poly (butylene terephthalate) (PBT) are used as engineering thermoplastics possesing good thermo - and wearstability, excellent moulding. These properties also allow to use them as matrix material for polymer composites [1], One of the perspective ways of search of effective catalysts for such systems is kinetic study of the reesterification model reaction, performed in the presence of various catalysts and comparison it with the results of the similar reaction without catalyst. Clarification on the example of model system of the most effective catalysts list allows to use them for obtaining both filled and nonfilled PBT and compare catalytic activity of various catalysts. The purpose of the... 

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