• DOP is traditionally used as a general-purpose plasticizer for PVC. However, due to toxicity problems, it is on way out in many countries and banned for PVC products in food and health application.
• Among non-phthalate plasticizers, citrate plasticizers that are esters of citric acid, are strong contenders to replace DOP.
• Bio-based plasticizers are polymer additives meant for improving flexibility, softness, workability, and volatility of the plasticized materials.
• These are based on renewable resources and produced from vegetable raw materials such as soybean, palm, castor oil, citrates, stearic acid, and starch.
• The Bio-based Plasticizers are widely used in PVC formulations.

• Citrate plasticizers are valued because they are “natural products", which may have high bio-based content (depending on how they are made) and they have low toxicity, though they cost more.
• Citrate plasticizers offer better biodegradability and less biochemical side effects.
• Blood bags and multiple blood bags made from such citrate plasticized PVC film materials have high O₂transmissibility, and withstand breakage at low temperatures.
• Citrate plasticizers are used in food packaging products, cling wrap, and medical applications.
• It can also be used to increase gelation speed in PVC plastisols.
• Citrates are used in toys produced by the plastisol process.
• Esters of citric acid are also used as foam inhibitors.
• Citrates are compatible with polymers like PVC, PVA, PVB, polypropylene.

• Citric acid is a naturally occurring tribasic acid and carries a hydroxyl group, that impairs its compatibility with PVC.However, it acts as a unique raw material for plasticizers.
• Citrate plasticizers are manufactured by reacting citric acid with alcohols (ROH), having different R (alkyl) groups. Thus:
• Partial citrate esters (with free OH group available) are useful as plasticizers
• However, citric acid’s lone hydroxyl group impairs PVC compatibility.
• This drawback is removed by acetylation of OH group.

• In acetylation reaction, the hydrogen atom of an alcohol group is replaced with an acetyl group (CH₃C=O), due to which ester is formed.
• The products formed during acetylation consist of an acetoxy functional group AcO or OAc, (CH₃C=O)-O- that differs from the acetyl group by the presence of additional oxygen atom.
• Acetylation of citrate plasticizer improves its efficiency, tensile strength and elongation at break.
• Also, it does not support fungal growth.

Citric acid + 3 n-Butanol ➔ tri -n- butyl citrate (TBC)+ 3H₂O

Tri-n-butyl citrate + Acetic anhydride ➔ Acetyl tri-n-butyl citrate. (ATBC)

• Low molecular weight Tri ethyl citrate is used in cosmetic and personal care products.
• Mohan S. Mahal et al (Bayer Corp.) reported that preferred plasticizers for PVC include tri-esters of citric acid or acylated citric acid and 4 – 10 carbon alcohols such as acetyl tri-butyl citrate, n-butyryl tri-n-hexyl citrate and acetyl tri-n-octyl or decyl citrate.
• Higher molecular weight citrates like acetyl tri-n-hexyl citrate (ATHC) and n-butyl tri-n-hexyl citrate are recommended for medical devices, such as blood bags, and tubing.
• Higher molecular weight citrates are more permanent but less efficient than DEHP.

• Not all the citrates are suitable for PVC.
• Volatility reduces with increasing carbon atoms.
• Acetylated Tri butyl citrate has found limited use in PVC because of inferior low temperature properties and resistance to aqueous extractions.
• Some of the products that are used in vinyl formulations are:

1. Acetyl tri-n-butyl citrate is recommended for children’s toys, food wraps, beverage tubing and helmet crown liners.
2. Acetyl tri-n-hexyl citrate is recommended for medical devices.
3. n-Butyl tri-n-hexyl citrate is also recommended for medical devices.

• Volatility is high,
• Citrates lack permanency and therefore, are not employed in resilient applications like cables, flooring or roofing.
• They induce more fogging in film applications.