Polyester resins moulding compositions

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... 

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. 

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. 

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

Plastic composites such as glass- or carbon-fibre reinforced materials are often based on polar epoxy or polyester resins, and are therefore compatible with the common adhesives as well as being readily bondable. Surface treatment is required simply to remove contaminants such as oils, dirt, and especially fluorocarbon mould release agents. The two main techniques used to achieve this are ... 

MODAR Modified acrylic liquid resins have been available since the mid 80s and are used in closed mould and pultrusion technologies. When combined with ATH they offer low smoke low toxicity fire performance in composites. These resins are more accurately described as oligourethane-methacrylates dissolved in methyl methacrylate solvent monomer . Crosslinking, through the methacrylate functionality on the backbone and the solvent is initiated in the same way as for unsaturated polyester resin by decomposing an organic peroxide, either thermally or chemically with an accelerator. 

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. 

Krigbaum [12] has reported on the use of glass fibre reinforced composites, both from Cytec Industries, based on Cyglas 685 unsaturated polyester [bulk moulding compound (BMC)] and Cyglas 695 vinyl ester resin (BMC) in automotive valve covers and other engine cover applications. The recycling of these valve covers is also discussed. 

Lotus, producers of composite cars since 1957, took a big step forward in 1974 with its new Elite (see Fig. 5.2). This was manufactured by the new VARI process (Vacuum Assisted Resin Injection), in which the two halves of the body are moulded in matched tools, and subsequently bonded together (see Fig. 5.3). The only chassis is a backbone top-hat section in steel otherwise the stability of the body is ensured by integral foam beams (see Fig. 5.4). These foam beams are used to locate and support uni-directional glass rovings, before the polyester resin is injected. The result is an extremely strong body, of which the present Esprit is the latest example. The Lotus system is extremely effective, but no claims are made that it will ever meet the cost and production needs of the mass market. The De Lorean... 

Unsaturated polyester (Butanox M-60) mixed with 1.5% of Methyl Ethyl Ketone Peroxide (MEKP) as catalyst was selected as a resin for the current work. Treatedbetelnut fiber reinforced polyester (T-BFRP) composite was fabricated using hand lay-up technique. In composite preparation, a metal mould (100 x 100 x 12 mm) was fabricated. The inner walls of the mould were coated with a thin layer of wax as release agent. The first layer of the composite was built by pouring a thin layer of polyester. A prepared mat was placed carefully on the polyester layer. Steel roller was used to arrange the mat and eliminate trapped bubbles. This process was repeated until the composite block was built containing 13 layers of fiber mats and 14 layers of polyester. The prepared blocks were pressed at approximate pressure of 50 kPa in order to compress the fiber mats and to force out the air bubbles. The blocks were cured for 24 hr and then machined into specimens in the size of 10 x 10 x 20 mm. 

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 first two materials are based on an unspecified epoxy resin, though the resin and size will be compatible. The second two composites are made with Stratyl 108, a polyester resin. The S-2 glass composite is an epoxy prepreg system. Manufacture was achieved by contact or prepreg moulding. 

The marine industry provides good opportunities for the use of adhesives. Boats made of composite materials dominate the boating industry. Manufacturers of fibreglass boats use various raw materials such as glass roving, woven fabrics, mats, sheet moulding compounds, vinyl ester resins, polyester resins, epoxy, balsa core, teak, foam, honeycomb cores, and gel coats for the production of boat hulls, decks, bulk heads, cock-pit, hatches, lids, and interiors. 

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. 

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). 

Resin transfer moulding (RTM) is a low-pressure variation of transfer moulding where, instead of granules or preforms, a pre-mixed resin and catalyst (hardener) is injected into a closed mould containing dry glass, carbon or aramid fibre reinforcement. When the resin has cooled, the mould is opened and the composite part ejected. The resins used include polyester, vinylester, epoxies, phenolics and methyl methacrylate combined with pigments and fillers. Applications include small complex aircraft and automotive components as well as automotive body parts, baths and containers. 

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