Phthalates are chemicals used to improve the flexibility and durability of certain plastics, most used in PVC. Polyolefins such as PP and PE generally do not require any plasticisers like phthalates or any other comparable substances. However, there is potential residual traces of phthalates in polypropylenes, as part of catalyst residue. Some of them have been linked to certain cancers, metabolic disorders, and male infertility. As a result, the European Union strictly regulates the usage of phthalates in consumer products.
The role of Phthalates in the polymerisation process of propylene
Throughout their more than fifty years of history almost all types of polypropylene have been produced with the help of a Ziegler-Natta-catalyst (ZN-catalyst). The vast majority of the 4th generation polypropylene ZN catalysts are prepared starting from a Pre-catalyst mixture, containing, besides magnesium- and titanium (IV) chloride, an internal donor, which is very often a phthalate such as Dibutyl phthalate (DBP), Diisobutyl phthalate (DIBP) or Bis(2-ethylhexyl) phthalate (DEHP). The internal donor is essential for the control of the stereoregularity (isotacticity) of the final polymer and therefore has a major impact on the mechanical properties of the final material.
Before, or during, the polymerisation process the pre-catalyst is added to the reactor, where – together with an aluminium alkyl and an external donor, which is usually silane-based – the activated catalyst forms in situ. The activated catalyst polymerises propylene and its co-monomers into the various types of polypropylenes and thus is consumed or rapidly decomposed. The remaining trace degradation products are either removed in the process or end up as catalyst residues in the polypropylene. If completely surviving the polymerisation process, the used phthalates could theoretically be present in concentrations of about 1 mg/kg (or 1 ppm weight) in the final pellets. However, test results have shown phthalate values not exceeding 0.15 mg/kg PP and often even below the threshold of the analytical method of 0.01 mg/kg PP.
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 Figure 2. Propylene Polymerization |
Isotacticity of polypropylene (For whom is interested in)
| The presence of methyl group in PP backbone chain can provide various differing characteristics for PP, depending on the arrangement of methyl group in PP carbon atom, whether in isotactic, syndiotactic or atactic configuration (as shown in beside picture). Commercially available polypropylenes usually have an isotactic index between 85 and 95%. The tacticity effects the polymers physical properties. As the methyl group is in isotactic propylene consistently located at the same side, it forces the macromolecule in a helical shape, as also found in starch. An isotactic structure leads to a semi-crystalline polymer. The higher the isotacticity (the isotactic fraction), the greater the crystallinity, and thus also the softening point, rigidity, e-modulus and hardness. |
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Legal Framework on Phthalates
1.REACH – Registration, Evaluation, Authorisation and Restriction of Chemicals
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- Regulation (EC) 1907/2006 addresses the production and use of chemical substances and their potential impacts on both human health and the environment.
- COMMISSION REGULATION (EU) 2021/2045 of 23 November 2021 amending Annex XIV to Regulation (EC) No 1907/2006 of the European Parliament and of the Council concerning the REACH.
Dibutyl phthalate (DBP), Diisobutyl phthalate (DIBP), and Bis(2-ethylhexyl) phthalate (DEHP) are listed on REACH Annex XIV, which has recently been up-dated by Regulation (EU) 2021/2045 from 23 November 2021 adding the endocrine disrupting properties to the already existing entries of the three phthalates. That means that the concentration limit for those three substances requiring an authorization has been lowered from 0.3 wt% (3,000 mg/kg) to 0.1 wt% (1,000 mg/kg). The new sunset date applicable for mixtures that contain the phthalates between 0.1 and 0.3 wt% is 14 December 2024.
According to the European Chemicals Agency (ECHA), Substances of Very High Concern (SVHC) are substances that negatively and permanently impact human health and the environment. REACH regulates substances on the SVHC Candidate List, including phthalates.
Here are the phthalates that we could find on the SVHC Candidate List: BBP, DEHP, Bis(2-ethylhexyl) tetrabromophthalate, Bis(2-methoxyethyl) phthalate, DBP, DCHP, Dihexyl phthalate, Diisobutyl phthalate (DIBP), Diisopentyl phthalate, DPP, n-pentyl-isopentyl phthalate.
Importers and manufacturers of products containing SVHCs in concentrations exceeding 0.1% weight by weight (w/w) (or 1000 ppm weight) must notify:
- The ECHA regarding the substance’s presence in their products by registering the required information on the SCIP (Substances of Concern In articles as such or in complex objects (Products)) database; and
- Customers about the SVHC content in their products, when requested.
2. RoHS Directive 2011/65/EU
The RoHS directive restricts the use of certain hazardous substances in electrical and electronic equipment which can be substituted by safer alternatives. Annex II of the directive lists ten restricted substances, four of which are phthalates with a maximum permitted concentration value of 0.1%: phthalates: bis (2-ethylhexyl) phthalate (DEHP), butyl benzyl phthalate (BBP), dibutyl phthalate (DBP), and di-isobutyl phthalate (DIBP), where the restriction applies to medical devices, monitoring, and control instruments. These requirements “shall not apply to the applications listed in Annexes III and IV” (Article 4). Directive 2011/65/EU was published in 2011 by the EU, which is known as RoHS-Recast or RoHS 2. The latest amendment was published on July 11, 2023, and it is amending Annex IV, namely applications exempted from the restriction in Article 4(1) specific to medical devices and monitoring and control instruments.
3. Plastic Food Contact Materials Regulation (EU) 10/2011
COMMISSION REGULATION (EU) 2023/1442 of 11 July 2023 amending Annex I to Regulation (EU) No 10/2011 on plastic materials and articles intended to come into contact with food, as regards changes to substance authorisations and addition of new substances. This regulation sets substance restrictions for plastic materials and articles intended to come into contact with food (FCM). Note that general requirements for FCM (e.g. labelling) are covered by the EU FCM Framework Regulation. The regulation applies to:
- Plastic multi-layer FCM held together by adhesives or other means.
- FCM made in plastic (also when printed or coated).
- Plastic layers or plastic coatings meant to be in contact with food.
From the summarized table above, you would question what is specific migration limit (SML) à The specific migration limit (SML) is the maximum permitted quantity of a specific substance that can migrate from a food packaging material or food container into food. It is a safety limit derived from toxicological studies.
The next question would be do we need to measure SML for all PP/PE resin or food contact material according to this regulation? à Look at the below detail for DBP in regulation (EU) 2023/1442, the SML is 0,12 (mg/kg), however this specification is only used as condition (a) or (b). This implies that if your resin or product does not intentionally contain added phthalate as a plasticizer or technical support agent, with a concentration up to 0.05% (w/w), they are not subject to this requirement.
SIBUR’s test result on phthalates
Example grade: PP H030GP/3
Manufacturer: Zapsibneftekhim LLC
