Unsaturated Polyester UP

Unsaturated Polyester UP 
Unsaturated polyesters Polyester resins are thermoset materials that first became available over 60 years ago. The principal advantage of polyester resins is the ease in which they may be fabricated, a consequence of polymerisation via a free radical reaction. Such reactions are rapid and easily controllable, thus production cost is relatively low.
Unsaturated polyester resins are very versatile materials. At room temperature, the liquid resins are stable for months even years but can be triggered to cure by a peroxide catalyst.
Styrene is by far the most commonly used diluent: it links the polyester chains to form strong three-dimensional polymer network. The curing reaction is exothermic, often providing adequate heat for a satisfactory cure.
UP Resins are most commonly used as composite materials. These polymers are made up of at least two separate components; reinforced fibre and embedding matrix. Other additives may be used to improve properties or characteristics. Carbon, aramide or most commonly glass fibres may be used yielding FRP (Fibre Reinforced Plastic) or specifically GRP (Glass Reinforced Plastics) in the case of glass. Materials basically bridge the gap between conventional, commodity plastics and specialist engineering plastics. Production takes place by introducing reinforcement while the resin is in an uncured, liquid state. 
UP Resins can be made very flame retardant and chemically resistant they also give excellent weatherability. Dimensional stability and rigidity is very good. Plus, of course, they can be easily reinforced with fibres of various types as part of the moulding stage rather than having to use pre-blended reinforcing agents.
These materials lend themselves to low volume applications with simple tooling, by use of hand lay-up methods of fabrication, or for mass production using injection moulding.
Typically UP Resins is processed by mixing a liquid UP resin with a curing system. Reinforcement can be applied at this stage. FRP Resins can be processed by a variety of processes as indicated below. 

Processing Methods:
Contact Moulding 
Compression Moulding
Injection Moulding
Continuous Lamination
Transfer Moulding
Filament Winding

A new polyester resin material called SMC (Sheet Moulding Compound) was formulated in the 1960s and following this BMC (Bulk Moulding Compounds) or DMC (Dough Moulding Compounds). These products may be generically referred to as PMCs (polyester moulding compounds). Compounds of this type contain chopped glass fibres and resin, they offer the advantage that, during formation, fibres and resins are able to flow under the action of heat and pressure in a hot press (or compression) moulding system. Systems of this nature facilitate the moulding of complex details from simple material packs. Cycle times tend to be between two and ten minutes. High pressures and tooling costs associated with such processes mean those forming quantities of less than 10,000 tend not to be economic.

Tensile Strength n/a N/mm? 
Notched Impact Strength n/a Kj/m? 
Thermal Coefficient of expansion n/a x 10-6 
Max Cont Use Temp n/a oC 
Density n/a g/cm3 

The nature of the Unsaturated Polyester means that physical properties are dependant on the additional materials used, and the conditions of curing, for a specific application. 

Dilute Acid *** 
Dilute Alkalis *** 
Oils and Greases ** 
Aliphatic Hydrocarbons * 
Aromatic Hydrocarbons * 
Halogenated Hydrocarbons * 
Alcohols *** 

* poor ** moderate *** good **** very good 

UP Resins are widely used in a host of applications where advantage may be taken of their good range of mechanical properties, corrosion resistance and low weight.
Un-reinforced versions are most commonly used for clear casting resins, coatings, buttons, body fillers, work-surfaces (such as polyester marble), polyester concrete (for applications such as road drainage) and in the manufacture of Gel Coats (applied to composite materials to improve the surface finish). 

The largest market for reinforced polyester resin (composite materials) is the building and sanitary ware market; here the material finds usage as structural parts (e.g. replacement of concrete clad steel), cladding panels, sheeting (e.g. for pre-fabricated buildings), roofing tiles, pipes and also for applications such as bathroom furniture (e.g. baths and shower trays). 

The Transport market makes significant usage of UP Resins. Since the materials tend to lend themselves to lower volume applications it is most commonly used in aeroplanes, trucks, buses and coaches. Established markets include parts such as bumper beams, body panels, sunroof frames, catalytic converter heat shields, dashboard carriers, seat structures, battery supports and spring systems. In addition to weight reduction, polyester parts have the opportunity to reduce painting costs (should composite parts require painting, however, a conductive primer coat or in-mould coating, with lower paint transfer efficiency and lower rates of work means that part price overtakes costs associated with electro-galvanised steel). Polyester parts also provide good corrosion resistance properties.

Rail cars, rolling stock and shipping containers are also manufactured using UP resin composites. The marine market is also heavily reliant on UP Resins, principally for the manufacture of luxury boat hulls. 

Other markets for UP Resins include the caravan panel market and the material is widely used in storage vessels (where the chemical resistance of the material is highly valued).


The actual preparation of the first polyester resin is accredited to both Berzelius in 1847 and Gay-Lussac and Pelouze in 1883. The unsaturated polyester resins used in today’s re-inforced plastics (RP) are combinations of reactive monomers. Carleton Ellis introduced the idea for the combination in the 1930’s. Ellis discovered that unsaturated polyester resins made by reacting glycols with maleric anhydride could be cured to insoluble solids simply by adding a peroxide catalyst. He applied for a patent on this idea in 1936. 
Ellis later discovered that a more useful product could be made by combining the unsaturated polyester alkyd with such reactive monomers as vinyl acetate or styrene, which makes it easier to add the catalyst and apply the resin.

The first use of glass fibre reinforced polyester composites was in aircraft ducting, with the first non-military application in boat hulls. The invention of the pultrusion line allowed development of unsaturated polyester based materials into new application areas such as oil wells, fishing rods and electrical insulation devices. The filament winding process further expanded the potential market for unsaturated polyester resins. This technique was initially developed for making military rocket cases and nozzle’s, however, potential for use in the making of pipes and storage vessels was soon recognised.