Citrate esters

Citric acid is used as a chelating agent in catalyst systems for making resins, and citrate esters are used as plasticizers (qv) in PVC film, especially in food packaging (207). 

Citric acid esters are used as plasticizers ia plastics such as poly(viayl chloride), poly(vinhdene chloride), poly(viQyl acetate), poly(viQyl butyral), polypropylene, chlorinated rubber, ethylceUulose, and cellulose nitrate. Most citrate esters are nontoxic and are acceptable by the FDA for use in food-contact packaging and for flavor in certain foods. As a plasticizer, citrate esters provide good heat and light stabiUty and excellent flexibiUty at low temperatures. Triethyl citrate, tri- -butyl citrate, isopropyl citrate, and stearyl citrate are considered GRAS for use as food ingredients (224—228). 

Labrecque, L.V., Kumar, R.A., Dave, V., Gross, R.A. and McCarthy, S.P. 1997. Citrate esters as plasticizers for polyjlactic acid). Journal of Applied Polymer Science 66 1507-13. 

Plasticisers Monomeric and polymeric phthalate esters, adipate and citrate esters... 

Codeine phosphate in a paracetamol-codeine effervescent tablet was found to react at room temperature with the citric acid constituents to form citrate esters of codeine. The esterification was confirmed in a solid-state reaction at an elevated temperature. Tartaric acid also yielded an ester with codeine phosphate in a similar non-solvolytic reaction. 

Monoisopropyl citrate, stearyl citrate, triethyl citrate (TEC), butyl and octyl maleates, and fumarates are other important plasticizers for the preparation of stable PC pastes and of low-temperature-resistant PVC products. Triethyl citrate and triethyl acetyldtrate are among the few plasticizers to have good solvency for cellulose acetate. In comparison with diethyl phthalate, with which they are in competition in this application, there are slight but not serious differences in volatility and water sensitivity. The interest in citrate esters is due to a favorable assessment of their physiological properties. They are intended for plastic components used for packaging of food products. 

Following suspicions that DEHP can act as an EDC, the maximum permitted content in the EU was set at 0.1%, which meant that in practice their use was forbidden. They have been replaced mainly by adipate and citrate esters, in the belief that they present less hazards [36]. 

Citrate esters Triethyl citrate, tributyl citrate, acetyl triethyl citrate, acetyl tributyl citrate... 

Some of these polymers have a narrow ratios or have such high viscosities that require the addition of plasticizers such as phthalate or citrate esters, low molecular weight polyethylene glycol (PEG), and/or propylene glycol to process robustly or improve flow during extrusion. 

Table 11.9 Thermal and mechanical properties of PLA plasticized with different citrate esters...

A lot of plasticizers typically with two ester groups have been described in the literature [39] including aliphatic diesters of phthalic acid, like diethyl phthalate, and diesters of aliphatic dicarboxylic acids like dibutyl adipate or azelate [22] as well as glycerol triacetate (triacetin), citrate esters, and phosphates [39]. Although these kind of plasticizers work well for decades in various applications, the accelerated retention test shows [39] that exudation and volatilization must be taken into account and can cause changes in the material performance. Thus, attempts have been made to synthesize long-chain esters of cellulose (LCCEs) with acid chain lengths of up to 20 carbon atoms (see [21] and references cited therein), which could be processed without external plasticizers. Positive results are reported for cellulose acetate hexanoate and cellulose acetate nonanoate [21] but these esters did not go into production. 

Diethyl phthalate used as a plasticizer in cellulose acetate films was found to be completely degraded in 4 weeks of composting degradatioa Citrate esters used as a plasticizer in cellulose acetate improved properties and processing characteristics but also dramatically increased its biodegradability. These two examples show that plasticizers can also be effectively used in biodegradable materials. 

Other plasticizers employed in the technology of PVC formulation include citrate esters (56), terephthalate and isobutyrate esters (57), chlorinated paraffins (58), and benzoic acid esters (59). These materials would be used where such characteristics as veiy low toxicity or flame retardancy could not be achieved by the more commonly employed materials described above. 

E.H. Hull, "Citrate Ester Plastieizers" in Plastics Additives and Modifiers Handbook, J. Edenbaum, ed., VanNostrand Reinhold, New York, 1992, pp. 420-430. 

Harte, L, Birkinshaw, C., Jones, E., Kennedy, J., and DeBarra, E. (2013) The effect of citrate ester plasticizers on the thermal and mechanical properties of poly(DL-lactide). /. Appl. Polym. Sci.,... 

Labrecque LV, Kumar RA, Dave V et al (1997) Citrate esters as plasticizers for poly(lactic acid). J Appl Polym Sci 66 1507-1513... 

Citrate esters have gained some importance as an alternate to DEHP in medical, toy, and food applications. The citrate esters are more volatile, less compatible, more water sensitive, more difficult to fuse, and more costly than DEHP. 

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