Polyesters, unsaturated, minerals

The second largest use at 21% is for unsaturated polyester resins, which are the products of polycondensation reactions between molar equivalents of certain dicarboxyhc acids or thek anhydrides and glycols. One component, usually the diacid or anhydride, must be unsaturated. A vinyl monomer, usually styrene, is a diluent which later serves to fully cross-link the unsaturated portion of the polycondensate when a catalyst, usually a peroxide, is added. The diacids or anhydrides are usually phthahc anhydride, isophthahc acid, and maleic anhydride. Maleic anhydride provides the unsaturated bonds. The exact composition is adjusted to obtain the requked performance. Resins based on phthahc anhydride are used in boat hulls, tubs and spas, constmction, and synthetic marble surfaces. In most cases, the resins contain mineral or glass fibers that provide the requked stmctural strength. The market for the resins tends to be cychcal because products made from them sell far better in good economic times (see Polyesters,unsaturated). 

These ready to use molding compounds combine resin, reinforcement, mineral fillers, and various additives as required, controlling cure, shrinkage and other properties. The main resin used is, predominantly, TS polyester (unsaturated polyester) resin, with others being used such as epoxies and vinyl esters. Similarly, the main reinforcement is, predominantly, glass fiber, but fibers offering higher performance are added where specific properties are needed. 

Alkyds are formulated from polyester resins, cross-linking monomers, and fillers of mineral or glass. The unsaturated polyester resins used for thermosetting alkyds are the reaction products of polyfunctional organic alcohols (glycols) and dibasic organic acids. 

This is also known as Bulk Moulding Compound (BMC). It is blended through a mix of unsaturated polyester resin, crosslinking monomer, catalyst, mineral fillers and short-length fibrous reinforcement materials such as chopped glass fibre, usually in lengths of 6-25 mm. They are all mixed in different proportions to obtain the required electromechanical properties. The mix is processed and cured for a specific time, under a prescribed pressure and temperature, to obtain the DMC. 

The hydrosilylation of unsaturated polymers (e. g., polybutadiene, polyiso-prene, polyesters, other polyenes, polycarbonates) with a silane having hydrolyzable substituents at Si atoms has been reviewed recently [26] it leads to polymeric systems with enhanced activity toward mineral fillers. Both >C=C< and carbonyl bonds are capable of hydrosilylation (eq. (2)). 

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. 

Rheological properties of mineral-filled and mineral/glass-fibre-filled unsaturated polyester DMCs have been presented by Gandhi and Bums (1976), who found that a simple power law was useful to characterize the chemorheology of both systems (note that limited cure effects during compressional flow are assumed). This work was extended by a series of... 

Talc - Talc is a filler made by dry or wet grinding of mineral magnesium silicate. Talc improves stiffness, dimensional stability, flexural modulus, creep resistance, flow, surface smoothness, moisture resistance, tensile strength, and wear resistance of plastics. It also increases heat deflection temperature and decreases vapor permeability. Can be used as a film antiblock agent. Used mainly in polypropylene but also in thermoplastic and unsaturated polyesters and epoxy resins at low levels. Surface-modified grades are available. 

Two types of commercially available orthophthalate-type unsaturated polyester resins (UP) were used as liquid resins, together with a 55% DMP(dimethyl phthalate) solution of methyl ethyl ketone peroxide (MEKPO) as a catalyst and a 8% mineral turpentine of cobalt octoate (CoOc) as an accelerator. UP-2 containing CoOc accelerator of 0.75phr (parts per hundred parts of resin). The properties of the unsaturated polyester resins are listed in Table I. 

Fillers may be used at concentrations of 10% to 50%, targeted at some desired physical or chemical properties, but also frequently useful as cheape-ners. Wherever their major utility is to stiffen and strengthen, they will be termed "reinforcement," and in most cases have a fibrous structure. Useful fillers include limestone, quartz, silica, talcum, alumina and other minerals. Particle size and distribution are of highest importance. Low-cost fillers for thermosets (eliminating brittleness) include sawdust, paper or jute. The use of ground limestone (or precipitated Ca CO3) is mainly found in PVC and unsaturated polyester in the fields of construction and flooring. Currently,... 

Unsaturated polyesters These thermoset materials have quite good radiation resistance, especially if they contain mineral fillers or glass fibers. They can be expected to withstand greater than 1000 Mrads. (General radiation resistance excellent.)... 

As a further advantage, composites make effective use of some materials that are otherwise unable to stand alone, such as mineral fibers or wood flour. When incorporated into polymers— in particular those such as unsaturated polyesters or phenolics—particles can reduce manufacturing shrinkage and yield a more usable product. In service, zero thermal expansion coefficients can be achieved by a suitable choice of starting materials. 

Kandola, B.K. Nazar6, S. Horrocks, A.R. Thermal degradation behaviour of flame retardant unsaturated polyester resins incorporating functionalised nanoclays, in M. Le Bras, C.A. Wilkie, S. Bourbigot, S. Duquesne, and C. Jama, Eds., Fire Retardancy of Polymers New Applications of Mineral Fillers. Royal Society of Chemistry, London, 2005, pp. 147-160. 

Thermosetting polymers are usually liquids at room temperature. They are eonverted to solids by combining with other liquid reactants in the presence of liquid or paste catalysts. Heat may be applied to hasten the setting reaction. Unsaturated polyesters constitute the largest volume, followed by polyurethanes and polyureas. Phenol-, urea- and melamine-formaldehyde resins are used in large volumes in laminates, but these contain little or no mineral filler. Epoxies are a relatively low volume market for fillers. 

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