Dialkyl phthalates, plasticizers

Phthalic anhydride Phthalic anhydride, unexpectedly obtained during a chromatographic separation, was found to be a decomposition product of the dialkyl phthalate plasticizer in tubing attached to the chromatographic column. (See 1724 cm" band.)... 

Phthalates The dialkyl phthalate plasticizer in flexible tubing made from polyvinyl chloride is leached readily from the tubing by organic solvents and appears occasionally as a contaminant in samples. (See 1754cm" band.)... 

Recently, market forces have combined to reduce the supply and increase the cost of linear sidechain dialkyl phthalate plasticizers. Diisodecyl phthalate (DIDP) is, in many ways, an attractive alternative to these linear plasticizers but questions remain about its effects on weathering properties of flexible PVC. This paper looks at the effects of using DIDP or blends of DIDP with linear phthalate in flexible PVC exposed to outdoor weathering. Degradation mechanisms and additive packages to limit weathering damage are also discussed. 

For decades, linear dialkyl phthalate plasticizers with sidechains between seven and eleven carbons in length, averaging 9 carbons (71 IP and more recently L9P), have been widely used in many North American made flexible PVC products for outdoor applications. Linear dialkyl phthalates are defined as those derived from commercial alcohols with very little side chain branching. These alcohols range from 100% normal products made by ethylene growth in the Ziegler process to 65% normal, 35% 2-methyl branched products made from oxonation of normal alpha olefins.[l] (91 IP and 1 IP have also been available, but at a premium price.) The relatively less branched alkyl sidechains in a linear, as opposed to a branched, dialkyl phthalate afford measurably improved... 

Neither branched nor linear plasticizers are particularly susceptible to biodegradation. Both have high resistance to biological attack. However, branched phthalates are somewhat more resistant than linear phthalates.[8] When reformulating flexible PVC for good weatherability, a switch from linear sidechain to branched sidechain dialkyl phthalate plasticizers will not increase susceptibility to biodegradation. 

Reformulating flexible PVC from linear to branched dialkyl phthalate plasticizers while maintaining constant durometer hardness will not significantly increase the modulus or decrease the elongation at break for the reformulated product. (See Table 5.) Stress cracking due to original flexible PVC product flexibility should not be a problem with DIDP-plasticized PVC. 

In contrast, for many products which do not have significant UV exposure, or, are highly filled or effectively pigmented, branched plasticizers like DIDP can be very satisfactory substitutes for linear plasticizers such as L9P or 71 IP. In fact there are end uses (such as geomembranes and pipe liners) in which branched plasticizers such as DIDP are preferred over their linear counterparts because of relatively lower plasticizer biodegradability and mobility. However, in virtually all other end uses for which outdoor weatherability is a consideration, those flexible PVC formulas which have effective UV blockers, UV absorbers and/or antioxidants can still perform well when made with branched dialkyl phthalate plasticizers. 

The chemical industry uses esters for a variety of purposes. Ethyl acetate, for instance, is a commonly used solvent, and dialkyl phthalates are used as plasticizers to keep polymers from becoming brittle. You may be aware that there is current concern about possible toxicity of phthalates at high concentrations, although a recent assessment by the U.S. Food and Drug Administration found the risk to be minimal for most people, with the possible exception of male infants. 

The major bulk processed thermoplastic using calendering is PVC sheets and films including blends and copolymers. A sample recipe to produce PVC sheet might include a plasticizer such as a dialkyl phthalate, pigment, filler, lubricant, and stabilizer. 

Since cellulose nitrate is intractable, in 1870 John W. Hyatt added camphor as a plasticizer to flexibilize this plastic. Some 60 years later, Waldo Semon used tricresyl phosphate as a plasticizer for PVC. Dialkyl phthalates, such as dioctyl phthalate (DOP) and other alkyl phthalates which replaced the more toxic tricresyl phosphate, are now used as plasticizers primarily for PVC at an annual rate of 1 million tons. 

Dibutyltartrate is a solv plasticizer for NC, DuPont (Ref 2) obtd a patent for the use of Dibutyltartrate as a constituent of pro-plnts which produce no flash from the gun barrel. An example of such a compn is NC, DNT ester of an org acid, such as dialkyl phthalate, dibutyltartrate or ethyl palmitate Refs 1) Beil 3, 518, (178), [332] 1021 ... 

The swelling method has been used successfully in a classic study by Doty and Zable (7) to evaluate the interaction of various plasticizers with poly(vinyl chloride). Figure 8 shows the n values of a series of dialkyl phthalates as a function of their molecular weight. It can be seen that dibutyl, dihexyl, and dioctyl phthalate have low n values-i.e., high solvent power for poly (vinyl chloride), (PVC), whereas the higher and lower esters have high n values, and therefore low solvent power. 

Figure 15. Plasticizer efficiency of a homologous series of dialkyl phthalates with PVC...

Poly(vinyl chloride) (PVC) is used for rigid structures like window frames and gutters with only small amounts of additives such as pigments. If PVC is used for flexible things like plastic bags, about 20-30% of dialkyl phthalates such as the compound below are incorporated during polymerization. Why is this ... 

The chemical industry uses esters for a variety of purposes. Ethyl acetate, for example, is a common solvent found in nail-polish remover, and dialkyl phthalates are used as so-called plasticizers to keep polymers from becoming brittle. 

Plasticizers—small organic molecules that act as lubricants between chains—are usually added to thermoplastics to keep them from becoming brittle at room temperature. A good example is polyCvinyl chloride), which is brittle when pure but becomes supple and pliable when a plasticizer is added. In fact, the drip bags used in hospitals to deliver intravenous solutions are made of poly vinyl chloride). Dialkyl phthalates such as di(2-ethyl-hexyl) phthalate are commonly used for this purpose, although questions about their safety have recently been raised. 

The variety of substances used as additives in polymers is considerable. For example, the fillers may include china clay, various forms of calcium carbonate, talc, silicas (diatomaceous silica), silicates, carbon black, etc. The impact modifiers typically include other polymers. Plasticizers include certain polymers with low (oligomers), dialkyl phthalates, dialkyl sebacates, chlorinated paraffin waxes, liquid paraffinic fractions, oil extracts, etc. Heat stabilizers include heavy metals salts such as basic lead carbonate, basic lead sulfate, dibasic lead phosphite (also acting as a light stabilizer), dibasic lead phthalate, stearates, ricinoleates, palmitates and octanoates of cadmium and barium, epoxide resins and oils, amines, diphenylurea, 2-phenylindole, aminocrotonates. The antioxidants include tris-nonyl phenyl phosphite, 2,6-di-ferf-butyl-p-cresol (BHT), octadecyl-3,5-di-terf-butyl-4-hydroxyhydrocinnamate, etc. The UV stabilizers include modified benzophenones and benzotriazoles. Processing lubricants include calcium stearate, stearic acid, lead stearate, various wax derivatives, glyceryl esters and long-chain acids. Fire retardants include antimony oxide, some pyrophosphates, etc. 

A frequent use of solubility parameters is the prediction of compatibility of blends of polymers with additives such as plasticizers used to modify the polymer properties. Plasticizers are generally involatile organic molecules such as dialkyl phthalates. Thus it was of interest to determine the usefulness of ICC method for estimating the solubility parameters of these compounds. 

Plasticizers. The major role of plasticizers is to reduce the polymer modulus by lowering its glass transition temperature (Tg). Plasticizers are usually low molecular weight organic compounds having a Tg of about — 50 °C. Common plasticizers used for PVC include dialkyl phthalate, aliphatic diesters and trialkyl phosphate. 

Taking DOP as the reference standard of performance for low-temperature flex efficiency, other commercial plasticizers that are significantly better performers include linear dialkyl phthalates and alkyl esters of sebacic, azelaic, adipic, phosphoric, and epoxidized oleic acids. Significantly poorer performers are tricresyl phosphate, diphenyl phthalate, butyl benzyl phthalate, and branched dialkyl phthalates. 

Plastic apparatus is also to be avoided when organic solvents are involved as plasticizers are easily leached out of such materials by the solvent and, after concentration of the sample, yield spectra that frequently mask that from the analyte. Dialkyl phthalates are the plasticizers most commonly encountered and can be recognized by their production... 

Dialkyl phthalates produced by the reaction of phthalic anhydride [85-44-9] with alcohols varying in chain length from C4 to Cn with 2-ethyl-l-hexanol [104-76-7] and 1-octanol [111-87-5] typically used, are the most commonly used plasticizers. While somewhat interchangeable, performance properties such as low temperature flexibility, volatility, processability, and extractability are governed... 

The main applications are with PVC. The plasticizers which can be blended in can be either low MW organic compounds, e.g. dialkyl phthalates, phosphates (tricresyl phosphate which has flame-retardant characteristics) or low-MW polymers, e.g. polycaprolactone, PMMA, or copolymers of ethylene and vinylacetate (EVA). These are called external plasticizers. Internal plasticization can be achieved by copolymerizing VC with a comonomer which has a low Tg, e.g. vinyl acetate. 

Many thermoplastics become britde at room temperature, which severely limits their utility. This is true of PVC. Pure PVC is highly susceptible to cracking at room temperature and is therefore useless for most appUcadons. To avoid this problem, the polymer can be prepared in the presence of small molecules called plasticizers. These molecules become trapped between the polymer chains where they function as lubricants. Common plasticizers are dialkyl phthalates, such as di-2-ethylhexyl phthalate used in vinyl upholstery, raincoats, shower curtains, inflatable boats, and garden hoses. Some plasticizers evaporate slowly with time, and the polymer ultimately returns to a britde state in which it can be easily cracked. Intravenous (IV) drip bags used in hospitals are typically made from PVC with plasticizers. 

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