European Union
In the member states of the EU, use of materials in food-contact plastic applications is controlled by Directives 2007/19, 2005/79, 2002/72, 90/128, 92/39, 82/711 and 85/572 (implemented in the UK by the Plastic Materials and Articles in contact with Food Regulations 1992, as amended).
Lists of permitted monomers and other starting materials have been prepared, with limits on usage and maximum permitted extraction laid down where appropriate.
Stearic acid appears in the "Annex II" list of permitted monomers and other starting substances in Directive 2002/72 under reference number 24550. No restrictions are set on its use in terms of specific migration limits (SML), maximum permitted quantity in the finished material (QM), any specifications relating to the substance or to the polymer. This is not surprising as stearic acid is found in large quantities in the body.
The preamble to the "approved list" states that, in the case of acids, certain metallic salts including calcium, magnesium and zinc are also automatically authorised. The material must be of "good technical quality".
Please note that Directive 2005/79/EC added an extra section to the introduction to Annex I. Under this entry, salts, double salts and acid salts of authorised acids, phenols and alcohols are authorised. In the case of these salts, however, a group SML of 25 mg/kg (expressed as Zn) applies, whatever the source of the zinc. The commission has indicated that this limit is to be reduced to 5mg/kg Zn, based on an opinion from the European Food Safety Agency. However, the online database is still reporting the original limit.
USA
In the United States, materials to be used in food-contact applications are controlled by the FDA and the following approvals covering the use of stearates in plastics, coatings and rubber appear in Title 21 of the Code of Federal Regulations:
MAGNESIUM STEARATE (CAS Registry Number 557-01-0)
"Granted prior sanction as a stabilizer in the manufacture of food-packaging materials and listed in §181.29 (STABILIZERS)"
Listed in §175.300 covering "resinous and polymeric coatings". These are described as "Resinous and polymeric coatings may be safely used as the food-contact surface of atricles intended for use in producing, manufacturing, packing, processing, preparing, treating, packaging, transporting, or holding food", used in accordance with the conditions prescribed in the section.
CALCIUM STEARATE (CAS Registry Number 1529-23-0)
"Granted prior sanction as a stabilizer in the manufacture of food-packaging materials and listed in §181.29 (STABILIZERS)"
"Cleared as a plasticizer employed in the preparation of rubber articles under §177.2600 (RUBBER ARTICLES INTENDED FOR REPEATED USE). Total plasticizers not to exceed 30% by weight of the rubber product."
"Cleared as an antioxidant and/or stabilizer in polymers used in the manufacture of articles or components of articles intended for use in producing, manufacturing, packing, processing, preparing, treating, packaging, transporting, or holding food under §178.2010 (ANTIOXIDANTS AND/OR STABILIZERS FOR POLYMERS). The quantity used shall not exceed that reasonably required to accomplish the intended technical effect."
Listed in §175.300 covering "resinous and polymeric coatings" : see the entry above for further information.
ZINC STEARATE (CAS Registry Number 557-05-1)
"Cleared for use in paper and paperboard for dry food contact under §176.180 (COMPONENTS OF PAPER AND PAPERBOARD IN CONTACT WITH DRY FOOD)"
"ZINC SALTS OF FATTY ACIDS" are permitted for use as activators in §177.2600 (RUBBER ARTICLES INTENDED FOR REPEATED USE) . The total quantity of permitted activators must not exceed 5% by weight of the rubber product.
"Cleared as an antioxidant and/or stabilizer in polymers used in the manufacture of articles or components of articles intended for use in producing, manufacturing, packing, processing, preparing, treating, packaging, transporting, or holding food under §178.2010 (ANTIOXIDANTS AND/OR STABILIZERS FOR POLYMERS). The quantity used shall not exceed that reasonably required to accomplish the intended technical effect."
Listed in §175.300 covering "resinous and polymeric coatings" : see the magnesium stearate entry above for further information.
The entries covering use in the USA have been checked in the current* 2009 edition of the relevant CFR sections. As FDA requirements are updated from time to time, it is strongly suggested that the current versions of the above sections of the Code of Federal Regulations be checked before use is commenced. The CFR can be accessed online at the US National Archives and Records Administration information system by clicking here.
* Please note that chapter 21 of the Code of Federal Regulations is updated on 1st April every year, the online versions appearing later, usually in June. The information above is current as at July 2016.