GLYMO-free high-performance adhesive solutions

GLYMO-free adhesive solutions - Ensuring food safety for demanding flexible packaging applications

Henkel is at the forefront of developing GLYMO- and GLYEO-free adhesive alternatives that still have the same adhesive performance you have come to expect from our products. Learn about the different types of applications below:

What is GLYMO?

GLYMO is an epoxy silane. Its precise name is [3‐(2,3‐Epoxypropoxy)propyl]trimethoxy silane, CAS No 2530-83-8, Food Contact Material (FCM) substance number 1068. It is an adhesion promoter used in food packaging, i.e. for laminated pouches that must be resistant to sterilization and hot filling. In some cases, it is also used for microwaveable packaging.

Why GLYMO is used today?

This adhesion promoter has very favorable attributes, which is why it can be found in a variety of applications. It increases, for example, the adhesion between aluminum and polyolefin foils and maintains the strength of the bonding even at elevated temperatures. GLYMO is the best-known representative of the epoxy silanes, a group of substances which contain an epoxy three ring as the predominant structure element. Another substance of this group is GLYEO ([3-(2,3-Epoxypropoxy)propyl]triethoxy silane, CAS No 2602-34-8), which is also used as an adhesion promoter.

What are the principles of epoxy silanes as adhesion promoter?

The silane group of GLYMO forms a covalent bond to the aluminum surface while the epoxy group reacts with the polyurethane adhesives. This reaction leads to a stable and heat resistant bond.

What is the chemical structure of adhesion promoter GLYMO and GLYEO?

Why is the European Union paying attention to GLYMO now?

Due to the fact that GLYMO is used in a wide variety of food contact applications, the European Union in 2017 had a closer look at existing evaluations of its properties. For this instance, a potential to alter genes or gene expression was detected, leading to a categorization as “potentially genotoxic”. Hence, the European Union is now working on a legislative framework for 2020 to regulate the use of epoxy silanes according to their potential. The deadline is foreseen for September 2020. For this reason, FEICA, the Association of the European Adhesive & Sealant Industry, recommends replacing the adhesion promoter all together as soon as possible. This will have far-reaching implications for the entire industry and is expected to significantly raise demand for suitable alternatives.

What is the legal framework for GLYMO today in Europe?

In September 2019, the European Commission revisited a discussion of GLYMO on the topic of currently being potentially genotoxic and insufficiently regulated. The need for taking specific measures with regard to this substance was confirmed. A draft is currently being prepared. It must be expected that all epoxy silanes will be regulated with this legislation, not just GLYMO. The upcoming legislation will establish special conditions of use that would be applicable to the manufacturing of a wide range of food contact materials. Such products are, for example, food contact coatings, adhesives, printing inks, silicones, paper and board, rubber, combinations thereof, and combinations with plastics and/or inorganic substances. This draft will potentially also include an exemption allowing GLYMO to remain on the market, relying on a clear and well justified argument that the use is safe. However, this procedure will be tied to extensive testing to prove application safety.

What is the legal background for GLYMO?

The precise current legal framework is constituted as followed: GLYMO was added to the list of authorized monomers, other starting materials, additives, and polymer production aids by the 11th amendment to the Plastics Regulation (Regulation (EU) 2018/831) of June 5, 2018. This amendment permits the use of GLYMO as a component of sizing agents to treat glass fibers imbedded in low-diffusivity plastics, such as in polyethylene terephthalate (PET), polycarbonate (PC), polybutylene terephthalate (PBTP), thermoset polyesters, and epoxy bisphenol vinyl ester. The Union list is a positive list of substances that may expressively be used in the manufacturing of plastics in contact with foods. Their application must be conforming with the restrictions named in this list.

Regulation (EU) 2018/831 granted a transitional period until June 26, 2019 for materials and articles that comply with the old measures until stock is used up. The 12th amendment of the Plastics Regulation (Regulation (EU) 2019/37) of January 10, 2019 corrected the use of this specific epoxy silane. Since then, the substance has been evaluated as a reactive monomer and not as an additive, as was originally the case in Regulation (EU) 2018/831. The restrictions for this substance, however, have not been changed. The transition period for materials that comply with the old measures ended on January 31, 2020 for the 12th amendment. In Regulation (EU) 2018/831, the authority justifies the severe restrictions for the newly listed substance with the genotoxic potential of the epoxy silane.

How has GLYMO been tested from toxicological point of view?

GLYMO as well as very close structural analogues have been tested in vitro and in vivo for potential genotoxic effects. This data indicates that GLYMO has an intrinsic potential to induce gene mutations. Tests show conflicting results with respect to chromosome damage caused by GLYMO. GLYMO manufacturers have proposed an additional in vivo genotoxicity study to clarify its genotoxic properties, especially considering the oral exposure route. However, it is not yet clear when the results of this study will be available.

How does the toxicological situation for GLYMO look like?

Therefore, for the time being, GLYMO must be considered to have a genotoxic potential. Incidentally, this opinion has recently been confirmed by the European Food Safety Authority (EFSA) in a respective scientific opinion. For Food Contact Materials applying GLYMO containing raw materials, the corresponding risk can only be managed by strictly controlling and limiting consumer exposure, e.g. by following the principles of the Threshold of Toxicological Concern (TTC) concept. According to this concept, the genotoxicity/cancer-risk can only be considered tolerable for an end consumer if the exposure does not exceed 0.15 µg/person/day. As a similar toxicological profile must also be expected for structurally similar chemicals such as GLYEO or for degradation or reaction products of GLYMO or GLYEO still containing the epoxy group, the TTC threshold should be applied to these substances as well.

How is the analytical assessment of GLYMO performed?

For a thorough risk assessment of GLYMO, the transfer of this substance onto the packed foodstuff needs to be evaluated. This transfer is simulated in migration tests. The packaging material is brought into contact with food simulants and stored for a certain period of time at an elevated temperature. Afterwards, the amount of GLYMO in the food simulant is measured, which can be done by means of gas chromatography coupled to a mass spectrometric detector (GC-MS). To achieve very low limits of detection (0.15 ppb is needed for the assessment of GLYMO), modern instruments such as GC coupled to a triple quadrupole detector (GC-MS/MS) are needed.

Contact with fatty foodstuff is simulated with the food simulant vegetable oil or the substitute simulants 95% ethanol and isooctane, respectively. Using these simulants, GLYMO can be determined as described before. Simulating contact with aqueous or acidic foodstuff, however, is carried out with 10% ethanol or 3% acetic acid as food simulants, respectively. Using these simulants, GLYMO can no longer be detected. This is due to GLYMO’s instability in aqueous food simulants. GLYMO readily reacts with the food simulants, forming a variety of degradation products which cannot easily be assessed via GC-MS methods.

How are GLYMO degradation products formed?

GLYMO is first hydrolyzed to [3-(oxiran-2-ylmethoxy)propyl]silanetriol (1) and then further hydrolyzed to [3-(trihydroxysilyl)propoxy]propane-1,2-diol (2). Both hydrolysis products form dimers (3, 4). In addition, higher oligomers (e.g. trimer, cyclic tetramer) were detectable. The epoxy group is marked in red. It is present in GLYMO and in several degradation products of GLYMO.

Since some of the GLYMO reaction products still contain an epoxy moiety, a genotoxic potential cannot be excluded. Therefore, determination of GLYMO and its reaction products at very low levels (i.e. 0.15 ppb) is needed. For this purpose, Henkel Corporate Analytics proposed structures of relevant GLYMO degradation products and developed a test method for reliable quantification. Degradation of GLYMO in aqueous simulants can be monitored via nuclear magnetic resonance spectroscopy (NMR), a technique yielding detailed structural information. In addition, measurements via liquid chromatography coupled to a mass spectrometric detector (LC-MS) were performed to confirm molecular structures and to postulate structures of further degradation products.

How are GLYMO and GLYEO degradation products defined?

Quantification of GLYMO degradation products in aqueous simulants was performed via liquid chromatography tandem mass spectrometry (LC-MS/MS). Specific reference material is needed for LC-MS/MS analysis. Since GLYMO degradation products are not commercially available as reference material, the reference standards were synthesized in-house and characterized via NMR.

The same principle applies to GLYEO. While intact, GLYEO can be measured in fatty food simulants via GC-MS/MS at very low concentrations; it is not stable in aqueous and acidic food simulants. Hence, assessment of GLYEO degradation products needs sophisticated methods such as the combination of NMR and LC-MS/MS.

What implications does the legislative change of GLYMO have?

The upcoming legislation on GLYMO will pose many challenges for the whole value chain, particularly for packaging converters. The application of GLYMO as an adhesion promoter will still be permitted, if it can be demonstrated that it does not endanger human health, as mentioned in Article 3 of the framework regulation. Therefore, the silane and its derivates need to be below the analytical detection limit of 0.15 ppb in the foodstuff and must be tested prior to using the packaging for pharmaceutical or food contact applications. The current situation is that products containing epoxy silane are not permitted to be used for fatty filling goods and must not be detectable for aqueous filling goods.

The critical part, however, will be that converters and packaging manufacturers need to provide proof for absence of GLYMO and its derivates. This implies two factors: having the right adhesive and the right testing method to prove it. Henkel Corporate Analytics developed a unique approach for GLYMO derivates, which is leading within the market. The testing, however, will create additional workload and administrational paperwork for the converter’s quality control departments.

What is the Triple Safety Evaluation?

As a global leader in adhesive and coating technologies, Henkel possesses ample know-how within the field of analysis of adhesives and the assessment of raw materials. Henkel uses this expertise to help its customers to deepen their understanding on food safe packaging. With this in mind, Henkel developed a procedure of a “Triple safety evaluation” to help make the production processes of food contact packaging and the products themselves as safe as possible.

The first part of the system consists of a supplier information assessment relating to a strict raw material selection process for Good Manufacturing Practice (GMP) compliance: the supplier information assessment asking for specifications according to food contact criteria and a commitment towards maximum concentration levels of substances of concern and absolute product information transparency.

With the second part of the evaluation, Henkel builds on its more than 100 years of experience in analysis of adhesives. Within its state-of-the-art analytical center test laboratories, in accordance with DIN EN ISO/IEC 17025:2018, GMP and GLP standards, Henkel is able to cover most relevant analytical requests from all business sectors and related external markets with a guarantee of independence of the evaluation.

And as a third and concluding assessment, Henkel has a toxicological strategy in place where regular analytics are not sufficient for defining whether all food safety risks have been eliminated. Here, the unique toxicological department at Henkel steps in to ensure safety is provided for food applications.

How does Henkel approach the topic of GLYMO?

Based on this procedure, Henkel prepared its own toxicological risk assessment for the GLYMO compound back in 2013. Henkel has developed a particular test method that enables reliable and precise results. Nevertheless, it is far more efficient to avoid this time-consuming and costly procedure altogether by using alternative laminating adhesives that are free from GLYMO – and structurally similar chemicals such as GLYEO. Food safety continues to be a key pillar of the flexible packaging industry – with the expected regulation of GLYMO as further proof of this.

Henkel has anticipated this development and started many years ago to develop new adhesive systems that are free of any epoxy silanes such as GLYMO and GLYEO. Since then, this information has proactively been passed on along the value chain in the corresponding food contact statements (see chapter “Remark on silane adhesion promoters”). These proactive statements are part of Henkel’s commitment to share knowledge on potentially hazardous substances with all partners within the industry. GLYMO and GLYEO containing adhesives are generally applied in high-performance laminate structures that typically undergo long approval processes before their final introduction to the market.

What is Henkel’s recommendation regarding GLYMO and GLYEO?

With the deadline coming soon and technical solutions being available, the industry has to shift to GLYMO- and GLYEO-free systems as soon as possible. Henkel continues to develop new laminating adhesive systems for high-performance applications without the use of epoxy silanes to constantly expand their modular LOCTITE LIOFOL range. Pouches made with the new adhesives work exceptionally well for a range of pet food, medical supply, and convenience food applications.