Profile Polyesters

The addition of SMC and BMC to reinforced polyesters has changed the basic mechanical property picture very little. The same is true for low profile polyesters. The mechanical performance is at the same general level that is attained with the older wet systems, such as preform and mat, and premix molding. 

The development of low profile polyester resin adds an additional dimension to SMC and BMC. The post-molding finishing steps with FRP have been a strong deterrent in high appearance requirement applications. The low profile resins utilize thermoplastic additives to obtain... 

In 2010 Cook Medical launched a new three-piece modular device with an 18 Fr hydrophilic braided sheath and a lower-profile polyester woven graft fabric. While it has received its CE mark in Europe, it is still going through clinical trials in the United States. The TX2 is Cook s thoracic stent-graft. It also comes in a low-profile (LP) iteration. 

E A Davies. Non Shrink or low Profile Polyester Moulding Compounds for the Automotive Industry. 7th International Reinforced Plastics Conference, Brighton, UK 1970. 

The tendency of thick sections of DMC structural parts to crack has been overcome by using low-profile polyester resins (or low-shrink resins). These are prepared by making a blend of a thermoplastic (e.g., acrylic) polymer-styrene system with a polyester-styrene system. Moldings of this blend cured at elevated temperatures exhibit negligible shrinkage and minimal warpage and have very smooth surface, to which paint may be applied with very little pretreatment. 

Figure 7. Pressure profiles in function of die length for differential pulling velocities. Polyester-glass fiber system, low profile polyester. Experimental points of Sumerak (Ref 11) and model results (Ref 23). Note Volumetric fibercontent Vz=0.508, 1.016, and 1.524x10" m/s.

Dicylopentadiene Resins. Dicyclopentadiene (DCPD) can be used as a reactive component in polyester resins in two distinct reactions with maleic anhydride (7). The addition reaction of maleic anhydride in the presence of an equivalent of water produces a dicyclopentadiene acid maleate that can condense with ethylene or diethylene glycol to form low molecular weight, highly reactive resins. These resins, introduced commercially in 1980, have largely displaced OfXv o-phthahc resins in marine apphcations because of beneficial shrinkage properties that reduce surface profile. The inherent low viscosity of these polymers also allows for the use of high levels of fillers, such as alumina tfihydrate, to extend the resin-enhancing, fiame-retardant properties for apphcation in bathtub products (Table 4). 

A variety of thermosetting resins are used in SMC. Polyesters represent the most volume and are available in systems that provide low shrinkage and low surface profile by means of special additives. Class A automotive surface requirements have resulted in the development of sophisticated systems that commercially produce auto body panels that can be taken direcdy from the mold and processed through standard automotive painting systems, without additional surface finishing. Vinyl ester and epoxy resins (qv) are also used in SMC for more stmcturaHy demanding appHcations. 

The primary UPR end markets are construction, automotive, and marine industries widi applications such as house paneling, tub and shower applications, chemical-resistant storage tanks, pultruded profiles, and fiberglass composite boat hulls. The UPR industry is mature, with a world production close to 1.7 million tons (Table 2.2), but must face two important issues increasingly strict regulations for styrene emissions and poor recycling potential for polyester thermosets.48 49... 

Recently, Brich and coworkers (40) reported the synthesis of lactide/glycolide polymers branched with different polyols. Polyvinyl-alcohol and dextran acetate were used to afford polymers exhibiting degradation profiles significantly different from that of linear poly-lactides. The biphasic release profile often observed with the linear polyesters was smoothened somewhat to a monophasic profile. Further, the overall degradation rate is accelerated. It was speculated that these polymers can potentially afford more uniform drug release kinetics. This potential has not yet been fully demonstrated. 

Typical additive packages for engineering thermoplastics have been described by Titzschkau [9], such as processing aids for PA, PP, or PET/PBT, three-component additive packages for polyamides and polyesters (nucleating agent, lubricant and process heat stabiliser) and coated copper stabilisers for polyamides. Additive packages or combinations of up to five or more additives are quite common. A typical white window PVC profile formulation comprises an acrylic impact modifier, TiC>2, CaCC>3, calcium stearate, a... 

Baudoin etal. [168,169] first presented qualitative depth profiles of lacquer and polymer coatings by means of r.f. GD-OES. Quantitative depth profiles were successively obtained by Payling et al. [170] on prepainted metal coated steel. Samples comprised a (rutile) pigmented silicone-modified polyester topcoat over a polymer primer, on top of an aluminium-zinc-silicon alloy coated steel substrate. With GD-OES in r.f. mode, it was possible to determine the depth profile through the polymer topcoat, polymer primer coat, metal alloy coating, and alloy layer binding to the steel substrate with a total depth of 50 im, all in about 60 min on the one sample. GD-OES depth profiles of unexposed and weathered silicone-modified polyesters were also reported [171]. Radiofrequency GD-OES has further been used to... 

Many industrial semi-crystalline polymer materials like polypropylene, polyamides, or polyesters contain nucleating agents or clarifiers which form needle-shaped aggregates already in the polymer melt. "For this purpose the pattern is desmeared using the measured primary beam. For a less involved treatment it may be sufficient to know the integral width of the primary beam profile in fiber direction. 

Baking the polyester film at 200 C improved the planarity of the film profiles over the 20, 50 and 100 [Mi wide holes. These profiles were leveled better than those for the baked positive photoresist film. During baking, the polyester film shrinks less than the positive photoresist film and may also have either a lower viscosity and/or a longer, low viscosity flow period. 

Figure 5.11 Calculated degree of polycondensation related to the axis of PET chips, shown as axial profiles for a cylindrical particle T, 220 °C hydraulic diameter (dh). 2.9 mm [12b]. From Weger, F., Solid-state postcondensation of polyesters and polyamides, presentation given at the Frankl and Thomas Polymer Seminar, 16 June, 1994, Greenville, SC, USA, and reproduced with permission of EMS Inventa-Fischer, GmbH Co. KG...

Low-profile additives, which control shrinkage, have emerged as a distinct science and class of additive. Unsaturated polyester resins, as do all thermosetting polymers, shrink when cured. Low-profile additives are a major class of additives used to control shrinkage, which vastly improves surface quality. This science is credited with the opening of automotive markets where surface quality is of prime importance. In exterior automotive body panels, Class A surfaces are required for market acceptance. 

Low-profile additives are generally materials such as poly (vinyl acetate), polystyrene, polyethylene or polycarbonate. During the unsaturated polyester cure cycle, the low-profile additives separate into a second phase, which expand to counteract the shrinkage of the curing unsaturated polyester resin. Material development and the science of low-profile additives have helped create substantial markets for unsaturated polyesters. Their use in automotive markets, where Class A show room quality surfaces is a requirement, is an example of this. 

Sheet molding compounds (SMCs) and bulk molding compounds (BMCs) are the dominant materials used in automotive applications. These composites of unsaturated polyester resin, fillers and fiberglass have advantages of high stiffness, heat resistance and low coefficient of expansion. Coupled with low creep resistance, which is a distinct advantage over thermoplastic competition, and low-profile additives, which can yield Class A surfaces, these materials are well suited for applications from exterior body panels to under the hood components. 

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