EFSA evaluates rPET chain extender substances to increase molecular weight

By Jenny Eagle

- Last updated on GMT

Related tags Polyethylene terephthalate Polymer

EFSA evaluates rPET chain extender substances
The European Food Safety Authority (EFSA) has carried out a study on two chain extender substances in rPET following a request from the Ministry of Health, Welfare and Sport, in the Netherlands, on behalf of Plastics Technologies and Products (PTP), in the Czech Republic.

EFSA was asked to evaluate the safety of tetraethyl orthosilicate (TEOS, CAS 78-10-4) and hexamethyldisilazane (HMDS, CAS 999-97-3) for use in food contact materials (FCMs).

Molecular weight of polymers after recycling

The two substances are used as a chain extender in recycled polyethylene terephthalate (rPET) to increase molecular weight.

According to PTP, TEOS is intended to be used with HMDS in a ratio of 97:3. The reaction rate of TEOS depends on the presence of HMDS.

The mixture is intended to be used at up to 0.12% w/w as a chain extender for polyethylene terephthalate (PET) to increase the molecular weight of the polymer after recycling.

The molecular weight values of the recycled PET do not return to the level of virgin PET and this is why the mixture is added at a specific step of the recycling process.

The substances TEOS and HMDS have a molecular weight of 208 and 161 Da, respectively.

"Both the substances have a high chemical purity and the impurities identified were typical, considering the information on the production process supplied as confidential by the applicant​,” it said in a report.

TEOS hydrolyses slowly in water. HMDS is unstable in moist air or in aqueous media and is converted rapidly into HMDSO and trimethylsilanol​.

Recycled PET

Tests for the specific migration of TEOS and HMDS were not carried out. Instead, the residual content of the substances was determined in recycled PET manufactured with the intended use level of the modifier mixture​.

The substances were not detected at the detection levels up to 4 μg/6 dm2. These results support that the substances react completely with the polymer chains in the recycled PET​.

Once Tetraethyl orthosilicate and hexamethyldisilazane built into the polyester backbone, no decomposition is foreseen under the conditions applied to process PET into the finished material and articles​.”

According to the findings, the Scientific Panel on Food Contact Materials, Enzymes, Flavourings and Processing Aids (CEF Panel) concluded the mixture composed of 97:3 TEOS and HMDS does not raise a safety concern for the consumer if it is used at up to 0.12% (w/w) for the production of recycled PET.

Products made from rPET are intended for contact with all types of foodstuffs, with or without prior pasteurization, for long-term storage at room temperature.

Measurements of residual content in the rPET suggest that TEOS and HMDS react completely with the PET chains.

Its migration study showed detected migrating substances from rPET using TEOS and HMDS correspond to oligomers identical to those from the virgin PET, at an estimated detection level of 3 μg/kg.

Based on toxicological data, the CEF panel concluded there is no indication of genotoxic potential for TEOS and HMDS and considers the mixture of TEOS and HMDS in a ratio of 97:3 safe for use in the production of rPET at up to 0.12% weight by weight.

Source:​ CEF “Scientific Opinion on the safety assessment of the substances tetraethyl orthosilicate, CAS No. 78-10-4, and hexamethyldisilazane, CAS No. 999 97 3, for use in food contact materials.​”

Date:​ January 12, 2016.

Reference:​ EFSA-Q-2012-01011 and EFSA-Q-2013-00029.

The dossiers were submitted on behalf of the applicant, PTP.

Follow us