Plasticisers and Flame Retardants

Certain triesters can be incorporated into plastics where they act as plasticisers by reducing the amount of cross-linking which would otherwise take place in the polymerisation process. Triaryl phosphates were first used to plasticise cellulose nitrate and cellulose acetate. Trioctyl phosphate and octyl diphenyl phosphate are particularly suitable for plasticising PVC [21], 

Some triesters increase flame resistance and dye-ability when incorporated into organic polymers (Section 12.15). Triphenyl phosphate and the toxic tricresyl phosphate can be used as flame-retardant plasticisers for various celluloses and vinyls. Tris 2-ethylhexyl phosphate increases the flame resistance of vinyl sheet and enables it to retain low-temperature flexibility. Cresyldiphenyl phosphate finds use both as a plasticiser and as a flame retardant. 

FIGURE 12.19 Molecular structures of uranyl phosphate esters (a) [U02(Bu0)2P02-Bu3P0(N03)]2 and (b) [U02 (Bu0)2P02 2] . Filled circles=P, large unfilled circles=U. 

Isopropyl diphenyl phosphate has now largely replaced tricresyl phosphate as a plasticiser. The componnd 2-ethylhexyl diphenyl phosphate is a non-toxic flame-retardant plasticiser which is used in vinyl sheet for food wrappings and for many other purposes. It has wide use because of its favourable combination of plasticising efficiency, low temperature properties, migration resistance and fire retardancy. 

Widely used in the fireproofing of polyalkenes, polyurethanes and polystyrenes is the toxic compound tris (2,3 dibromopropyl)phosphate, (BrCH2 CHBr CH20)3P0, which is insoluble in water and decomposes at 200°C. 

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Used as plasticiser and flame retardant In paints (used, e.g., in road marking and as primer for surfaces exposed to sea water), varnishes and coatings... 

Used as plasticiser and flame retardant in PVC plastic and further use in manufacture of plastic product... 

Akzo Nobel sold its modest-sized plasticiser and flame retardant business to the American finance company Ripplewood Holdings in April 2004 for 320 M emos. The deal involved a phosphorus chemical manufacturing imit in Bitterfield, Germany and a factory in West Virginia that made phosphorus based FRs for use in polymethane foams, as well as plasticisers and lubricants. 

Various product forms may occur during storage (typical for fatty acid derivatives) or production. DSC has been used for detection of polymorphism of butylated hydroxyanisole (BHA) [91]. Similarly, DSC has allowed to detect various product forms of the hindered phenolic antioxidant octade-cyl 3-(3, 5 -di-f-butyl-4 -hydroxyphenyl) propionate (Anox PP 18), which caused handling problems during production [92]. The DSC method for purity determination as used for curatives, such as 2,2 -benzothiazyldisulfide (MBTS) [93], and for sulfur and accelerators [79], is also applicable to other additives, such as antioxidants and antiozonants. DSC and TGA have been used to establish the oxidation and weight loss characteristics of commercially available triaryl, trialkyl and alkyl-aryl phosphate esters, which are widely used as plasticisers and flame retardants in the polymer industry [94]. 

More recently, the same author [41] has described polymer analysis (polymer microstructure, copolymer composition, molecular weight distribution, functional groups, fractionation) together with polymer/additive analysis (separation of polymer and additives, identification of additives, volatiles and catalyst residues) the monograph provides a single source of information on polymer/additive analysis techniques up to 1980. Crompton described practical analytical methods for the determination of classes of additives (by functionality antioxidants, stabilisers, antiozonants, plasticisers, pigments, flame retardants, accelerators, etc.). Mitchell... 

Various additives show considerable extraction resistance, such as impact modifiers (polyacrylates and polyblends PVC/EVA, PVC/ABS, etc.), highpolymeric processing aids (PMMA-based), elastomers as high-MW plasticisers, reactive flame retardants (e.g. tetrabromobisphenol-A, tetrabromophthalic anhydride, tetrabromophthalate diol, dibromostyrene). Direct measurement of additives by UV and IR spectroscopy of moulded films is particularly useful in analysing for additives that are difficult to extract, although in such cases the calibration of standards may present a problem and interferences from other additives are possible. 

Recent legislation issues in Europe have involved the end-of-life disposal of vehicles and electrical goods. Food contact legislation has been updated. Plasticisers, brominated flame retardants and biocides have also been the subject of EU legislation. The EU s proposals on the testing of chemicals are expected to create difficulties for the plastics and additives industries, although compensations may become apparent. 

A wide variety of polymers can be foamed, including the polymethanes, polyisocyanurates, PVC, polystyrene, ABS, polycarbonate, PET, PBT, polyamides, PPO, EVA and the polyolefins. Other additives required for the foaming process besides blowing agents may include foam nucleating agents, stabilisers, surfactants, plasticisers, colourants, flame retardants and particulate fillers. 

Plastics additives may be divided into two main categories —those which modify polymer properties by physical means, such as plasticisers, lubricants, impact modifiers, fillers, pigments, etc, and additives which achieve their effect by chemical reactions such as PVC heat stabilisers, antioxidants, ultraviolet absorbers and flame retardants. In selecting them, however, care must be taken to match the additives to the polymer they are intended to protect, taking into account such factors as compatibility, efficiency and possible synergism of two or more additives in the particular polymer under consideration. 

It has already been mentioned in Chapter 5 that plasticisers are often replaced in part by extenders, materials which in themselves are not plasticisers but which can be tolerated up to a given concentration in a polymer-plasticiser system. Refinery oils and chlorinated waxes are widely used in PVC for this purpose with the prime aim of reducing cost although the chlorinated waxes may also be of use as flame retardants (q.v.). 

Organophosphate flame retardants and plasticisers Perfluorinated compounds Pharmaceuticals and personal care products Polar pesticides and their degradation/transformation products Surfactants and their metabolites... 

Worldwide consumption of performance additives (excluding plasticisers) grew from just over 2.7 mt in 1996 to 3.6 mt in 2001. Flame retardants make up 31 % of the volume and stabilisers, impact modifiers and lubricants each account for around 16-17%. Flame retardant markets (construction, E E devices, automotive) are headed for unprecedented development and change, being threatened by environmental, health... 

Brandt [200] has extracted tri(nonylphenyl) phosphite (TNPP) from a styrene-butadiene polymer using iso-octane. Brown [211] has reported US extraction of acrylic acid monomer from polyacrylates. Ultrasonication was also shown to be a fast and efficient extraction method for organophosphate ester flame retardants and plasticisers [212]. Greenpeace [213] has recently reported the concentration of phthalate esters in 72 toys (mostly made in China) using shaking and sonication extraction methods. Extraction and analytical procedures were carefully quality controlled. QC procedures and acceptance criteria were based on USEPA method 606 for the analysis of phthalates in water samples [214]. Extraction efficiency was tested by spiking blank matrix and by standard addition to phthalate-containing samples. For removal of fatty acids from the surface of EVA pellets a lmin ultrasonic bath treatment in isopropanol is sufficient [215]. It has been noticed that the experimental ultrasonic extraction conditions are often ill defined and do not allow independent verification. 

Successful combination of a chromatographic procedure for separating and isolating additive components with an on-line method for obtaining the IR spectrum enables detailed compositional and structural information to be obtained in a relatively short time frame, as shown in the case of additives in PP [501], and of a plasticiser (DEHP) and an aromatic phenyl phosphate flame retardant in a PVC fabric [502], RPLC-TSP-FTIR with diffuse reflectance detection has been used for dye analysis [512], The HPLC-separated components were deposited as a series of concentrated spots on a moving tape. HPLC-TSP-FTIR has analysed polystyrene samples [513,514], The LC Transform has also been employed for the identification of a stain in carpet yarn [515] and a contaminant in a multiwire cable [516], HPLC-FTIR can be used to maintain consistency of raw materials or to characterise a performance difference. 

Applications The general applications of XRD comprise routine phase identification, quantitative analysis, compositional studies of crystalline solid compounds, texture and residual stress analysis, high-and low-temperature studies, low-angle analysis, films, etc. Single-crystal X-ray diffraction has been used for detailed structural analysis of many pure polymer additives (antioxidants, flame retardants, plasticisers, fillers, pigments and dyes, etc.) and for conformational analysis. A variety of analytical techniques are used to identify and classify different crystal polymorphs, notably XRD, microscopy, DSC, FTIR and NIRS. A comprehensive review of the analytical techniques employed for the analysis of polymorphs has been compiled [324]. The Rietveld method has been used to model a mineral-filled PPS compound [325]. 

Various types of additives are essential to give plastics new or enhanced properties. However, the safety of flame retardants, plasticisers and stabilisers, as regards potential health hazards, is attracting attention. Brome-based flame retardants have been the subject of safety disputes for several years and several substitutes have been developed. The shift to lead-free stabilisers is making further progress. 

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