Polyester resins plasticisers

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.)... 

Low molecular weight liquid polyester resins are useful as plasticisers, particularly for PVC, where they are less volatile and have greater resistance to extraction by water than monomeric plasticisers. Examples of such plasticisers are polyfpropylene adipate) and poly(propylene sebacate). In some cases monobasic acids such as lauric acid are used to control the molecular weight. 

Chemicals polyester resins and plasticisers, PVC, formaldehyde resins, aldehydes, alcohols and acids for the coatings industry. 

Phthalic anhydride (PA, CgH403), the anhydride of phthalic acid, is widely used in the chemical industry as an important organic intermediate for the production of plasticisers ( 60%), unsaturated polyester resins (19%), and alkyd resins (14%), and also for fine chemicals ( 7%) such as dyes, insecticides, and pharmaceuticals. The values given in brackets are the mean values of Japan, USA, and Western Europe use in 1997 (Weissermel and Arpe, 2003). The current worldwide PA production is 4.5 million toimes (2005). 

The most common plasticiser for PVA is DBP (di-butyl phthalate) as higher molecular weight phthalates are not compatible. Superior non-migratory properties are conferred by certain polyester plasticisers, such as Reoplex -400, which is particularly useful for PVA-based glass fibre size used to maintain coherence of the glass fibre mat before reinforcing with polyester resin, as well as in adhesive applications. 

Flame retardance in polymeric materials may be achieved by two different mechanisms. The first is by using an inherently flame retardant material as a substantial component of the polymeric material or compound. This approach is exemplified by the use of chlorendic acid as a reactive component of flame retardant polyester resins, or the use of substantial quantities of phosphate plasticisers in non-flame PVC compounds, eg for automotive leather-cloth. 

A traditional additive which has been used for many years to confer flame retardant properties on a variety of materials including plasticised PVC, polyolefins and glass-reinforced polyester resins, is antimony trioxide. This is added at levels of 2-15 phr depending on the degree of flame retardance required. Its activity is much enhanced by the presence of chlorine, so that it is common practice to add approximately equal quantities of 70% chlorinated paraffin wax... 

Reaction of polyhydroxy compounds with polybasic acids gives rise to condensation polymers containing ester (—COO—) groups. Because of the presence of these groups such polycondensates are known as polyesters and find use in such diverse applications as fibres, surface coatings, plasticisers, rubbers and laminating resins. These materials are discussed in detail in Chapter 25. 

Compared with the phenolics and polyesters the resins have better heat resistance, better chemical resistance, particularly to alkalis, greater hardness and better water resistance. In these respects they are similar to, and often slightly superior to, the epoxide resins. Unlike the epoxides they have a poor adhesion to wood and metal, this being somewhat improved by incorporating plasticisers such as poly(vinyl acetate) and poly(vinyl formal) but with a consequent reduction in chemical resistance. The cured resins are black in colour. 

The minimum service temperature is determined primarily by the Tg of the soft phase component. Thus the SBS materials ctm be used down towards the Tg of the polybutadiene phase, approaching -100°C. Where polyethers have been used as the soft phase in polyurethane, polyamide or polyester, the soft phase Tg is about -60°C, whilst the polyester polyurethanes will typically be limited to a minimum temperature of about 0°C. The thermoplastic polyolefin rubbers, using ethylene-propylene materials for the soft phase, have similar minimum temperatures to the polyether-based polymers. Such minimum temperatures can also be affected by the presence of plasticisers, including mineral oils, and by resins if these become incorporated into the soft phase. It should, perhaps, be added that if the polymer component of the soft phase was crystallisable, then the higher would also affect the minimum service temperature, this depending on the level of crystallinity. 

Aromatic amines formed from the reduction of azo colorants in toy products were analysed by means of HPLC-PDA [703], Drews et al. [704] have applied HPLC/ELSD and UV/VIS detection for quantifying SFE and ASE extracts of butyl stearate finish on various commercial yarns. From the calibrated ELSD response the total extract (finish and polyester trimer) is obtained and from the UV/VIS response the trimer only. Representative SFE-ELSD/UV finish analysis data compare satisfactorily to their corresponding SFE gravimetric weight recovery results. GC, HPLC and SEC are also used for characterisation of low-MW compounds (e.g. curing agents, plasticisers, by-products of curing reactions) in epoxy resin adhesives. 

Four different polyester plasticisers for PVC, having moderate acid numbers (11.5 to 20.5 mg KOH/g resin), were synthesised. These polyesters were modified by converting the terminal COOH group to Ba(II) and Cd(II) carboxylate salts in order to introduce the capability of heat stabilisation for PVC. The modified polyesters were applied as dual function polyesters, i.e. as plasticisers and stabilisers at the same time. The thermal stabilisation efficiency of the plasticised PVC films formed was tested photometrically and the data obtained were compared with that afforded by Irgastab BZ 556. The efficiencies of these modified polyesters as heat stabilisers for PVC were found to be comparable with those of Irgastab BZ 556. 38 refs. CIBA-GEIGY CO. 

Examples of the oils used in the non-oxidising type of polyesters are coconut, castor oil, hydrogenated castor oil and Mesua ferrea L. seed oil, all mainly non-drying oils with a low degree of unsaturation, hence polymerisation does not occur in the presence of air under ambient conditions. These polyesters are used with amino resins such as urea and melamine-formaldehyde (ME) resin for stoving finishes. They are also used as plasticisers in other industrial lacquers. 

Several additives are susceptible to microorganisms, notably certain PVC plasticisers, especially the epoxy oils and esters, polyesters and sebacates. Most aryl plasticisers are more resistant than their alkyl equivalents. Natural fillers such as starch and wood flour are also attacked, although if the particles are fully encapsulated by resin they will have considerable protection. This is important for wood-plastics composites, currently being promoted as potential substitutes for wood, MDF and even UPVC. It is possible for microorganisms to attack certain lubricants such as polyethylene waxes and pigments. 

Affolter [230] has discussed methods of characterisation and identification of polyester plasticisers. Polymeric and monomeric plasticisers were distinguished on the basis of molecular weight determination, TG, and TLC, and chemically identified by IR spectroscopy, and by the determination of monomeric units by saponification. These methods use sample sizes of about 1 g. Marcilla et al. [231] have studied the thermal degradation behaviour of ten commercial PVC resins by TG. TG was also used to study eight commercial phthalate and adipate plasticisers. Different kinetic models were suggested for the correlation of weight loss data at four heating rates for two resins and three plasticisers. 

Another well-known biodegradable aliphatic polyester is poly(s-caprolactone) (PCL). These polymers can be divided into two groups based on MW. Material with a MW of up to several thousand is a waxy solid or viscous liquid. These PCL are used as PU intermediates, reactive diluents for high solids coatings, and plasticisers for vinyl resins. The other type of PCL has a MW greater than 20,000 and is resinous with good mechanical strength. The primary worldwide PCL producers are Dow Chemical (formerly Union Carbide) in the United States, Solvay in Europe, and Daicel Chemical Industries in Japan. 

A primary plasticiser for PVC is regarded as one which is fully compatible with the resin up to at least 100 parts per hundred parts resin (phr) and can be satisfactorily used for many applications as the sole plasticiser. Phthalate and phosphate esters and certain polyesters come into this category. A secondary plasticiser has limited compatibility with PVC, but is normally incorporated in a PVC compound as a partial replacement for a primary plasticiser to impart a specific desirable physical property. Low temperature plasticisers such as sebacates and adipates are typical of this category. Plasticiser extenders are plasticisers of limited efficiency and compatibility such as chlorinated paraffins and certain hydrocarbon oils, which are included in the composition to reduce costs. 

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