Volatility of plasticizers

Plasticizer diffusion, deposition, and accumulation on a material surface are controlled by the degree of the compatibihty between the plasticizer and the matrix, the surface energy of the liquid/solid interface, and the volatility of plasticizer. Volatihty and migration are controlled by different properties of the plasticizers therefore they are not related (Figure 7.8). Plasticizers have high boiling points so evaporation is typically slow. The rate can be calculated from the Hertz equation ... 

Thermogravimetrical analysis provides information on loss of mass which may be a result of degradation with volatilization of plasticizer component, plasticizer evaporation, or degradation and volatilization of any other component of the tested mixture (most likely polymer and stabilizer because test formulations are usually kept simple). Beeause of these different reasons for mass loss the results are difficult to interpret. In some studies reported here, evaporation loss of plasticizer was distinguished from loss of degradation products by ranning two separate tests one for the pure plasticizer and the other for the entire composition. This may help to better understand reasons for mass loss but it... 

Volatility of pure plasticizers and the volatility of plasticizers in plasticized PVC differ (Figure 11.60). Temperatiue of loss of a pure plasticizer is consistently lower than the temperature of plasticizer loss from plastisol. This is due to interaction between plasticizer and PVC chain. In order to remove the plasticizer from plastisol, additional energy is required to overcome the energy of hydrogen bonding. Compatibility between the plasticizer and the polymer also plays a role since small differences are recorded for higher molecular weight (less compatible) plasticizers. ... 

The actual rate of volatilization of plasticizers from water apparently has not been experimentally measured. The rates of volatilization, however, estimated using the Sonth-worth Method to estimate gas-phase and liqnid-phase mass transfer coefficients, were reported in HSDB, and summarized in Table 18.10. VolatiUzation was estimated nnder two scenarios (Figure 18.1) a shallow (1-m deep) river moving at a rate of 1 m/sec below an air mass moving at 3 m/sec. The second scenario was a shallow (1-m deep) lake moving at 0.05 m/sec below a breeze of 0.5 m/sec. The estimated volatilization half-lives of the plasticizers followed the trend established by their Heniy Law constants. Consequently, the predicted half-lives of ditridecyl phthalate, di-(2-ethylhexyl) adipate, di-(2-ethylhexyl) azelate, diundecyl, diisooctyl, dihexyl, dinonyl phthalate were less than 6 days. The same plasticizers would likely be more persistent in the lake scenario. The volatilization rates of the other plasticizers appeared to be much slower, and volatilization from water may not be a significant environmental pathway. Furthermore, the Southworth estimation technique does not take into acconnt sorption of dissolved chemicals by suspended particles. Sorption would increase the residence time of dissolved plasticizers. The predicted volatilization rates, however, were based on Hemy s Law constants which are themselves only estimates. 

All of the 23 plasticizers in Table 18.1 occur as viscous or oily liquids that range from colorless to an amber color. If these liquids were spilled on soil or sediments, a portion of the liquid could volatilize into the air, depending on the specific compound, but most of the 23 plasticizers have vapor pressures that are less than 10 mm Hg at 25°C (Table 18.13). The vapor pressures of nine of the compounds have not been measured. For these plasticizers, vapor pressures were estimated using the Fragment Constant Method. As noted earlier, most of these chemicals will also be adsorbed by soil and sediments which would reduce the extent of volatiUzation. The rate of volatilization of plasticizers from soil has not been measured. For the purpose of illustration, the Dow Method was applied to estimate the half-life of each plasticizer if it was spilled on the surface of a dry soil. The Dow Method is a simple relationship that was derived for the evaporation of pesticides from bare soil ... 

Finally, many polymers tend to be hard and brittle. When these properties are undesirable, plasticizers are added to increase softness and pliability. Most such polymers are phthalates, and with the advent of mass-produced plastics, they have become ubiquitous. "New-car smell" results from the volatilization of plasticizers from synthetic upholstery and simileir materials when enough of the plasticizer is gone, the material becomes brittle and can crack. Plasticizers have recently been identified for further study as a possible health concern for children, who tend to put soft plastic toys in U eir mouth. 

The other major area of use is in lead-stabilized wire coverings that require only modest loss of elongation after accelerated heat aging tests. Elongation is lost because of two factors volatilization of plasticizer and oxidative degradation (of resin and plasticizer). No antioxidant can compensate for a completely inappropriate choice of plasticizer. Nevertheless, use of 0.25-0.5 parts per 100 of resin (phr) of BPA can enable a broader plasticizer choice—often more than offsetting the cost of the antioxidant. When a lead stabilizer is replaced with barium/zinc or calcium/zinc, BPA should be retained only in black. In other colors, use should be made of antioxidants with low zinc sensitivity. 

Fig. 2. Volatile loss of plasticizers from flexible PVC (BSS 35) where M represents Cg [...

Ammonium acetate has limited commercial uses. It serves as an analytical reagent, and in the production of foam mbber and vinyl plastics it is also used as a diaphoretic and diuretic in pharmaceutical appHcations. The salt has some importance as a mordant in textile dyeing. In a hot dye bath, gradual volatilization of ammonia from the ammonium acetate causes the dye solution to become progressively more acidic. This increase in acidity enhances the color and permanence of the dyeing process. 

Internal antistats are considered permanent antistats. This permanence is based on the concept that most plastic products are disposable, so that the antistat is not required to last long. The antistatic effectiveness of an internal antistat can decrease over time. One study showed large increases in surface resistivity on antistatic bags stored at 71 °C for six months. Antistatic bags stored at room temperature showed only a small increase in surface resistivity (137). Loss of antistatic effectiveness is attributed to the volatility of the antistatic agent. The antistat does not easily wear off the plastic, but it can be removed with solvents and/or repeated wear. 

Plasticizers. Plasticizers are materials that soften and flexibilize inherently rigid, and even britde polymers. Organic esters are widely used as plasticizers in polymers (97,98). These esters include the benzoats, phthalates, terephthalates, and trimeUitates, and aUphatic dibasic acid esters. Eor example, triethylene glycol bis(2-ethylbutyrate) [95-08-9] is a plasticizer for poly(vinyl butyral) [63148-65-2] which is used in laminated safety glass (see Vinyl POLYMERS, poly(vinyl acetals)). Di(2-ethyUiexyl)phthalate [117-81-7] (DOP) is a preeminent plasticizer. Variation of acid and/or alcohol component(s) modifies the efficacy of the resultant ester as a plasticizer. In phthalate plasticizers, molecular sizes of the alcohol moiety can be varied from methyl to tridecyl to control permanence, compatibiUty, and efficiency branched (eg, 2-ethylhexyl, isodecyl) for rapid absorption and fusion linear (C6—Cll) for low temperature flexibiUty and low volatility and aromatic (benzyl) for solvating. Terephthalates are recognized for their migration resistance, and trimeUitates for their low volatility in plasticizer appHcations. 

Plasticizers can be classified according to their chemical nature. The most important classes of plasticizers used in rubber adhesives are phthalates, polymeric plasticizers, and esters. The group phthalate plasticizers constitutes the biggest and most widely used plasticizers. The linear alkyl phthalates impart improved low-temperature performance and have reduced volatility. Most of the polymeric plasticizers are saturated polyesters obtained by reaction of a diol with a dicarboxylic acid. The most common diols are propanediol, 1,3- and 1,4-butanediol, and 1,6-hexanediol. Adipic, phthalic and sebacic acids are common carboxylic acids used in the manufacture of polymeric plasticizers. Some poly-hydroxybutyrates are used in rubber adhesive formulations. Both the molecular weight and the chemical nature determine the performance of the polymeric plasticizers. Increasing the molecular weight reduces the volatility of the plasticizer but reduces the plasticizing efficiency and low-temperature properties. Typical esters used as plasticizers are n-butyl acetate and cellulose acetobutyrate. 

It is desirable that the plasticizer compounded with a polymer be permanently retained. Loss of plasticizer changes the properties of a given formulation, and can be produced by volatilization, extraction or migration. The volatility of a plasticizer in a formulation can be related to the surface area, thickness of the polymeric material, and viscosity (e.g. molecular weight) of the plasticizer itself. 

There are, however, certain materials used as ingredients in the manufacture of plastics, which almost invariably give a corrosive product. Included in this category are wood, which is frequently used as a filler or as part of a composite drying oils, used in paints, adhesives, jointing compounds and linoleum and esters of volatile acids frequently retained in certain cold setting formulations, especially some paints. ... 

Preservative availability may be appreciably reduced by interaction with packaging materials. Examples include the permeation of phenolic preservatives into the rubber wads and teats of multi-dose injection or eye-drop containers and by their interaction with flexible nylon tubes for creams. Quaternary ammonium preservative levels in formulations have been significantly reduced by adsorption onto the surfaces of plastic and glass containers. Volatile preservatives such as chloroform are so readily lost by the routine opening and closing of containers that their usefulness is somewhat restricted to preservation of medicines in sealed, impervious containers during storage, with quite short use lives once opened. 

Direct desorption MS has been used to identify the nature and amount of volatiles produced during processing, i.e. drying, extruding, moulding, etc. of plastic compositions. Programming of the heating in the mass... 

Di-ft-octylphthalate may be released to the atmosphere through volatilization of the compound from plastics, as a result of manufacturing processes, and through incineration (Vista Chemical 1992). 

Most all of the organic compounds which have been reported from studies of cotton plant parts and cotton trash have been included in this review. Only those which seem most unlikely to be cotton-derived natural products have been excluded. For example, the phthallates reported as "air space volatiles of the cotton plant" are likely artifacts derived from cjommon plastics (.9) some hydrocarbons found to be in cotton lint and waste probably came from a source obtained from petrolexim W and aflatoxln is presumably a mold metabolite (36). A few other compounds have been excluded for similar reasons. 

Plastic explosives contain one or more of the explosives listed above, moulded in an inert, flexible binder. Because powders do not readily hold a shape and TNT is the only common melt-castable explosive, most of the explosive powders (RDX, HMX, PETN, 1,3,5-triamino-2,4,6-trinitrobenzene (TATB)) are plasticized to make a mouldable material, for example, C-4, Semtex H, PE4, sheet explosive. A variety of plasticizers are added, but the maximum level is usually 10-15% because most plasticizers are inert and would degrade explosive output. Plastic explosives were originally developed for convenient use in military demolitions but have since been widely used in terrorist bombs. For detection techniques that rely on vapour signatures, such as canine olfaction, it is worth considering that the plasticizer is much more volatile than the explosive component. 

Over 30 commercial formulations have been surveyed in depth. Compressive strength measurements permit the exclusion of materials obviously prone to fail under pressure. FTIR (MX-1, Nicolet Instrument Corp.) analysis has identified formulations with volatile diluents capable of chemically modifying the composite membrane. Through the use of FTIR it was possible with an otherwise successful formulation to identify the presence of butyl glycidyl ether (BGE) as a diluent. Subsequently experimentation showed that vapor of BGE is capable of plasticizing porous polysulfone with a drop in both flux and rejection of the membrane. Collaboration with the supplier resulted in substitution of a nonvolatile glycidyl ether diluent to avoid the problem. 

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