Unsaturated polyester thickening

This is a material produced from the impregnation of glass fibre-mat (fibreglass, which is in the form of dry sheet, is commonly known as chopped stranded mat (CSM)) or rovings, with a liquid and unsaturated polyester resin, which thickens chemically to a dry sheet form. The total mix is sandwiched between polyethylene films and then roller-pressed to impregnate and consolidate it. 

Special effects have also been established during the improvement of the free-flow properties of products in powder form. Unfortunately, it is not yet possible to predict under which conditions a hydrophobic synthetic amorphous silica will produce better results than a hydrophilic (i.e., untreated) one. A similar situation exists in the area involving the thickening of technically important resins [e.g., special unsaturated polyester or epoxy resins (63)]. 

Polytrope. [Rheoxj Modified montmo-rillonite clay rheological additive, thickener for unsaturated polyester laminating resins. 

Formulation of SMC/BMC compounds is a very sophisticated balance of many ingredients to enhance specific properties and/or act synergistically with other components. Most SMC/BMC formulations have three main elements binder, filler and fiber reinforcement, from a choice of ingredients such as unsaturated polyester resin, monomer, catalyst, inhibitor, fillers, TP anti-shrinkage additives, flame-retardant, thickener, release agent, and glass fiber reinforcement. 

The main sectors for magnesium hydroxide use are in elastomers and thermoplastics, since they cause excessive thickening in the main thermoset application of unsaturated polyester systems. It is also much more expensive than ATH with which it shares comparable properties and flame retardancy, and so ATH will be preferred by processors wherever possible. As a result the principle opportunities are in applications where the extra thermal stability is essential, mainly in PP and polyamides. 

The primary role of MgO in unsaturated polyesters is as a reactive filler/thickening agent in SMC/BMC manufacturing. Incorporation of up to 5% MgO in the formulation allows the production of a tack-free sheet within a few days at room temperature. The sheets can then be easily handled prior to the high-temperature molding step. The increased viscosity assists dispersion uniformity and improves the flow characteristics of the compound prior to the onset of the cross-linking reaction. 

Contact resin n. A liquid resin that thickens or cross-links on heating and, when used for bonding laminates, requires little or no pressure. Typical components are an unsaturated monomer such as an allyl ester, or a mixture of styrene or other vinyl monomer with an unsaturated polyester or alkyd. 

Conventional SMC is prepared from unsaturated polyester resin and styrene, together with magnesium or calcium oxides or hydroxides. The bases serve to thicken the styrene-polyester solution, probably through ionomer formation.Usually, SMC is used together with fillers such as calcium carbonate and glass fiber reinforcement for high modulus. 

A hybrid thermoplastic polyester resin formulated for use in SMC/BMC applications and containing 22% recycled content. The resin provides excellent low profile properties for both structural and zero shrink applications and is soluble in many types of unsaturated polyester resin. It may be thickened using standard alkaline oxides and/or alkaline hydroxides and offers superior hot strength, impact properties and excellent bond and paint adhesion. 

A thickenable vinyl ester with fast glass wettability for the manufacture of SMC/BMC materials. Stated to have better rheology than unsaturated polyester SMC/BMC s, hence allowing the use of lower moulding pressures. (No further details provided by the manufacturer.)... 

The chemical thickening reaction that takes place involves reaction of the carboxyl groups on the unsaturated polyester resin with alkaline earth oxides or hydroxides such as magnesium oxide, magnesium hydroxide, calcium hydroxide or calcium oxide as illustrated below. 

However, when low profile additives were applied to these new chemically thickened formulations rather than the BMC and preform unthickened systems, problems were observed. The reaction of the unsaturated polyesters carboxyl groups with the magnesium oxide changed the compatibility between the resin and low profile additive. This caused a separation of the components which resulted in an exudate on the surface of the SMC. Not only did this complicate the compound handling but caused molding defects such as scumming, sticking and porosity. 

Too high a level of carboxyl in the low profile additive in chemically thickened systems can result in too much compatibility through these bonds with the unsaturated polyester resin. This results in less two-phase formation and hence poorer shrinkage control. 

The properties of unsaturated polyesters are also modified by a host of additives, such as thixotropic agents, chemical thickeners, fillers or extenders, fire-retardant chemicals, glass-fiber, and other reinforcement. A discussion of these areas is beyond the scope of this book. Most of this technology is disclosed in the extensive polyester patent literature. However, many books and review articles on polyester, " as well as manufacturers product literature, give good coverage of the subject. 

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