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An overview of plasticizers and their effects on human health and environment

Over 500 plasticizers are available in the global, though only about 50-100 are used for commercial purposes. About 90% of all plasticizers are used in PVC, and the other end-uses for plasticizers include synthetic rubbers, cellulosics, and acrylics. 
Plasticizer performance is best when the molecules contain both polar and non-polar groups. The polar groups help the plasticizer be retained in the system, while the non-polar groups attenuate the attractive forces between the polymer chains to give flexibility. It should be noted that the plasticizer is an integral part of the final product so as to provide long-lived benefits. Smaller, polar materials are effective in increasing processability as well, although volitization of the plasticizer is an issue. Conversely, polymeric plasticizers are retained better and provide better performance at extremes in temperature, but provide little benefit in processability.

Many different materials are used as plasticizers in PVC.  The most commonly used materials are phthalate esters. These colourless, odourless liquids are produced by a simple chemical reaction between an alcohol and phthalic anhydride. Produced by the reaction of a suitable alcohol with phthalic anhydride or terephthalic acid, phthalate ester plasticizers are the most extensively used plasticizers in the world.  While methanol and up to C17 alcohols are utilized to manufacture phthalate ester plasticizers, C4-C10 alcohols are the ones typically used in plasticizers. Linear alcohols can also be used to produce plasticizers, although their use is increasingly out of favor due to the high cost of ethylene (a raw material for these products) as compared to the raw materials for the C9-C10 plasticizers.
Di-2-ethylhexyl phthalate (DEHP; also called di-octylphthalate or DOP) is the phthalate ester produced from the reaction of 2-ethyl hexanol alcohol (derived from propylene) and phthalic anhydride.  Even though its health effects have been questioned, it is still widely used as a plasticizer due to its plasticizing performance and low cost.
Increasingly, and especially in commodity all-purpose applications, the C9 (diisononylphthalate (DINP)) and C10 (diisodecylphthalate (DIDP)) iso-phthalate plasticizers are competing with DEHP.  It is generally accepted that the C9 and C10 phthalates provide modest cost/benefit performance advantages over DEHP.

Commodity phthalates are used in many applications such as flooring, wall coverings, vinyl skins, sheaths for electric cables, coated fabrics and shoes.  The linear phthalates have lower volatility when compared to the branched phthalates with the same molecular weight.  They impart better cold temperature flexibility and resistance to photo-degradation.  Consequently, they are used in PVC roofing, anti-fogging synthetic leather for car interiors, and certain automotive electrical cables. Many other specialty phthalates are produced, though volumes are much smaller than DEHP, DINP, or DIDP.  Specialty phthalates esters produced from low carbon number alcohols provide rapid fusion. Other specialty phthalates include benzylbutyl phthalate, diisoundecyl phthalate (which possess a low volatility), and semi-linear and linear phthalates (used in applications where plasticizers of low viscosity are needed).
Phthalates were first produced in the 1920s, though they found limited commercial use. However, since the 1950s, large quantities of phthalates have been consumed to plasticize PVC.  Plasticized PVC is used in applications such as medical tubing, blood bags, footwear, stationery goods, flooring and wall-coverings, electrical cable insulation, clothing and toys. In addition, phthalates are used in other non-PVC applications such as rubber products, paints, printing inks, adhesives, lubricant and some cosmetic products.  The most commonly used phthalates are di-2-ethyl hexyl phthalate (DEHP also called dioctyl phthalate (DOP)), diisodecyl phthalate (DIDP, DEHP, diisononyl phthalate (DINP) and dibutyl phthalate (DBP).  Other phthalates such as benzyl butyl phthalate (BBP) are used in the manufacture of PVC foam used primary for flooring applications.  Of all the phthalates, DEHP is the most widely used, accounting for more that 50% of all phthalates used in PVC globally.

Since the early 1980s, there have been concerns regarding the use of phthalates and their effects on human health and the environment. The first indication that phthalates could cause an increased incidence of liver tumor in rats and mice was in 1980 after the NTP/NCI Bioassay Program in the U.S.  By the late 1980s, a controversy surrounded the use of plasticized PVC cling film in food packaging applications, with growing concerns that material from plasticized PVC could leach into food and cause harm. However, the plasticizers used in cling film were not phthalates, and cling film was proven safe to use. By the 1990s, several other issues regarding the use of phthalates were raised. There was concern about their effects on the environment, human reproductive system and function of hormones in the human body.  These concerns were based on research performed in the late 1990s on animals (rats), even though results obtained were not relevant to humans. Another major concern surrounding phthalates was their exposure to children via breast milk, toys and medical equipment. A study in Norway showed that bronchial obstruction in children was directly related to the amount of plasticizer-emitting material present in the house. In 1998, toy companies came under attack from activist groups such as Green Peace, who lobbied against PVC use in children products.  Consequently, Mattel and First Year stopped using phthalates in their toys by 1999.
As a result of these concerns, the European Commission in 1999 temporarily banned the use of six phthalates in toys which were used in oral applications designed for children under three years old (the concentration of six phthalates (DINP, DBP, DIDP, DNOP, DEHP and BBP) should not be more than 0.1% in products intended to be place in the mouth of children under three years old).  This temporary ban would subsequently be renewed 23-24 times until a permanent ban was adapted in 2005.  This was due to the concerns of over exposure of children to these additives at a critical stage of development.  This step was also consistent with previous actions taken by other European governments. The ongoing debate over phthalates use, especially in Europe , has led to a decrease in the demand for phthalates in the European market for the most common phthalate (DEHP).  Indeed, demand for DEHP started decreasing in 1999.  Following declining demand, BASF ceased production of DEHP in October of 2004.  Additionally in 2004, a Swedish Danish research group found strong links between allergies and DEHP and BBP. In the same year, a research group from Washington University found no adverse effects in adolescents who were exposed to phthalates during development.  However, in early 2005, there was another study showing that phthalates mimicked female hormones, resulting in feminization of boys.

In July 2005, the EU permanently banned the use of DEHP, DBP and BBP in all children's articles. Additionally, the EU banned the use of DINP, DIDP, and DNOP in children's articles which can be put in the mouth.   This ban became effective on January 16, 2007 .  The restriction on the use of phthalates in Europe has pushed other regions to consider reducing the use of these plasticizers even though studies showed that phthalates pose little or no health risks to humans or the environment.  Currently, there is a ban on phthalates in San Francisco (USA) that is being contested by the American Chemistry Council (the ban was to take effect January 1, 2007 , but is delayed because of a law suit).  Taiwan took a similar approach and banned the use of two phthalate plasticizers shortly after the ban in Europe . Canada has also put phthalates on its high priority list of chemicals, which should be evaluated similarly to the European Union's Registration, Evaluation and Authorization of Chemicals (REACH) initiative.  Large cosmetic companies in the USA such as L'Oreal and Revlon, have taken the initiative of banning the use of DBP in their cosmetic products.

China is not only the largest DOP consuming region, it is also among the fastest growing, with growth projected at 2.1% for the 2006-2011 period. Environmental issues are projected to cause DOP demand to remain almost flat in North America, while decreasing DOP demand in Western Europe and Japan. South Korea, Japan and China constituted about 31% of the global DINP demand in 2006, and are anticipated to grow to 42% of global demand by 2011.

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