Adhesives in the Food Sector

Mineral Oil Hydrocarbons in Adhesives Used in the Food Sector: A FEICA Perspective Adhesives are among the most important components used in food packaging and contain various substances such as mineral oils, waxes, resins and oligomers. Particularly in recent years, concerns about potential health problems that packaging may cause have come to the fore, and since a significant portion of adhesives may contain mineral oil hydrocarbons harmful to human health, many international organizations are making efforts to regulate this matter.

Mineral oil hydrocarbons (MOH)

Mineral oil hydrocarbons (MOH) are a large group of organic chemicals found in every environment. MOH are complex chemical mixtures and are mostly obtained from crude oil. There are different sources of food contamination from MOH: MOH are used as additives in many different materials that come into contact with food (FCM), such as plastics, adhesives, rubber products, jute and sisal fibres, waxed paper and cardboard, and printing inks. MOH are also applied as lubricants and defoamers, as well as cleaning agents and non-stick substances during the production of food and FCM. Environmental pollution and unintentional packaging contamination are other sources of MOH in food. Food packaging made from recycled paper and cardboard in particular contains high levels of MOH originating from newspaper ink, which are mineral oil-based and not food-grade. MOH consist essentially of mineral oil saturated hydrocarbons (MOSH) and mineral oil aromatic hydrocarbons (MOAH). Straight-chain, often branched hydrocarbons known as paraffins and cyclic, saturated hydrocarbons make up MOSH (commonly referred to as naphthenes). MOAH includes mono- or polycyclic aromatic hydrocarbons. In general, naphthenes and MOAH are highly alkaline. MOAH represents the most toxic fraction due to its mutagenic and carcinogenic properties, strongly affects the composition of a MOH mixture, and thus determines its toxicity. MOSH is less toxic but accumulates in human tissues forming microgranulomas. MOAH is also considered a potential endocrine disruptor. In many patients, an autoimmune response has been observed as a result of exposure to MOH arising from non-nutritional sources.

Migration

Food packaging can interact with food depending on many factors such as the packaging material, the properties of the food, storage temperature, exposure to UV light and product storage period. This interaction causes contamination known as migration, which occurs from packaging materials in contact with food towards food. All packaging materials in contact with food interact with food in a unidirectional or bidirectional manner. The chemicals that can pass from packaging to food are very diverse and depend on the type of packaging material. In inert materials (stainless steel, ceramics, glass), only chemicals from the inner surface in direct contact with the food substance can pass. This passage occurs through surface change from the inner surface to food. Chemical diffusion from within or outside the packaging material (printing inks, adhesives) is not possible. This stems from the chemical structure of inert material, which has small pore sizes that prevent the passage of molecules and individual atoms. However, oily foods in glass packaging can be contaminated by the transfer of plasticizers (such as epoxidized soya bean oil (ESBO) and phthalates) from the cap. Migration can be reduced by careful production or the use of specially developed low-migration caps. Non-inert materials such as paper, cardboard and plastic can be a direct source of migration. Chemicals can also pass through the packaging from outside. Printing inks that have been shown to pass from cardboard to dry foods are an example of this. The large pore size of paper-based materials allows smaller molecules to pass from outside to food inside. The use of barrier materials can significantly reduce food contamination. Cardboard containing food items with an aluminium foil layer and an inner bag made of plastic with barrier properties is among such materials. A special case of migration is offset migration. In such transfers, the printed outer layer of food packaging can transfer chemicals to the inner layer in direct contact with food when both layers are in direct contact with each other. Offset migration occurs when beverage cartons are stored in rolls or paper cups are nested inside each other.

Mineral Oil Hydrocarbons (MOH) Analysis

To determine the extent of chemical transfer from packaging to food, measurements are made not on actual food items but on food analogues, also known as food simulants. Food analogues are used instead of food because they facilitate chemical analysis: chemical detection and quantification require analytical methods specially developed for each relevant chemical and food analogue type. Food analogues differ in their chemical properties, so each represents several different food types: hydrophilic (water-based), lipophilic (oily foods) or amphiphilic (foods with both aqueous and oily properties). For example, transfer to oily food is measured with the food analogue vegetable oil. Food analogues Simulant A (10% ethanol) or Simulant B (3% acetic acid) are used in water-based food and beverages. Dry foods are simulated with a synthetic polymer with a specific pore size. Amphiphilic butter and other foods are simulated with 50% ethanol solution. The frequent detection of high MOH levels in packaging materials made from recycled paper and cardboard has sparked a discussion on how to reduce such contamination. Recycled papers and cardboards usually do not consist of FCM-grade materials. Recycled newspapers, magazines and other paper types contain mineral oil-based printing inks, adhesives, coatings, additives and contaminant substances from previous uses. The replacement of mineral oil-based printing inks will be the first step in the long term to reduce the burden of MOH in recycled paper and cardboard. Inner bags and barrier layers are already widely applied to reduce the migration of MOH from recycled paper and cardboard to food.

Preventing Migration in Adhesives

In this context, it is important for adhesive manufacturers to assess, and if necessary reduce or eliminate, mineral oil hydrocarbon contact with food items. First, a risk assessment should be carried out regarding the intended use of the adhesives. At this point, it is vital to prevent the migration risk, defined as the passage of chemical contaminants from materials in contact with food to food. Although adhesives usually constitute less than 5% of the packaging and are not intended for direct food contact, unintended contact can occur at edges and joints or when volatile substances pass through the packaging. Therefore, as stated in the guidance issued by the European Adhesives and Sealants Industry Association (FEICA) on 27 May 2016, overall migration is merely a measure of inertness and has no toxicological significance; the analysis of migration of specific compounds is much more important. However, apart from screening purposes, testing of materials in contact with food (FCM) that come into contact with finished food under real conditions of use is preferred rather than testing adhesives as separate compounds. Tests performed on pure adhesive without a substrate or structural material may result in overestimation of transfer to food as a result of ignoring many factors. According to the guidance issued by FEICA, these factors include curing times and conditions, the interaction of the adhesive with other FCM layers, the barrier properties of other FCM layers and the distribution of components within the FCM. Due to their complex chemical structure and the scope of potential FCM applications, migration test conditions should be adapted separately for each adhesive group. The adhesive groups included in the guidance include reactive polyurethane (PU) adhesives, natural polymer-based adhesives, dispersions, emulsions (adhesives based on vinyl acetate polymers (PVAc) or ethylene vinyl acetate (EVA) copolymers and acrylic-based adhesives) styrene acrylate terpolymers and reactive systems including polymers and copolymers, cold seals, hot seals and hot melt adhesives. Adhesive manufacturers must check whether mineral oil hydrocarbons used in formulations and posing a migration risk are listed in Regulation (EU) No. 10/2011 (FCM No. 93, 94, 95). In such a case, the restrictions provided by the Plastics Regulation apply. If this is not the case, the adhesive manufacturer must follow appropriate procedures to ensure that the adhesives are suitable for their intended use. Different applications are recommended depending on the adhesive type. For some special applications, water-based adhesives may contain MOH from defoaming agents (usually maximum concentrations do not exceed 0.5%). Although unlikely, if the intended application of the water-based adhesive poses a migration risk to food, it should be checked whether the mineral oil-based defoaming agent complies with the relevant food contact legislation, or composition information and toxicological data (carbon number distribution, PAH content, Ames test results, etc.) should be requested from the supplier of the defoaming agent used in the adhesive to carry out a risk assessment. If mineral oil hydrocarbon components cannot be sufficiently assessed and the risk of migration to food cannot be minimized, the adhesive manufacturer should reduce the mineral oil defoaming agent content as much as possible. Adhesive manufacturers should list mineral oil defoaming agents as a restricted substance with a specific migration limit (SML) table with the expected maximum concentration (10ppb) and provide the necessary information to enable risk assessment by the downstream user. Hot melt adhesives such as ethylene vinyl acetate and polyolefins contain mineral oil hydrocarbons used for box and cardboard sealing purposes. Sometimes paraffinic waxes or hydrocarbon resins found in MOH fractions may be used in the formulation, which can lead to misinterpretation of results. Therefore, if hydrocarbon resins are used, it should be ensured that they are evaluated by FCM 97 or other supporting documentation from the supplier (toxicological data, compliance information). If mineral oil hydrocarbon components are not compliant with the Plastics Regulation (EU) No. 10/2011, they should be replaced with components compliant with FCM No. 93, 94, or composition information and toxicological data including carbon number distribution, PAH content and Ames test results should be requested from the mineral oil supplier and a risk assessment should be carried out for the adhesive in the intended application. If necessary, the content of mineral oil hydrocarbon components should be reduced. If the migration risk of mineral oil hydrocarbons to food cannot be ignored, a functional barrier is recommended. Most hot melt pressure-sensitive adhesives contain mineral oils. For PSA hotmelts, oil substitution is difficult but it is possible to use more refined oil with fewer naphthenic/aromatic components. Prepared by: Murat Soygür Sources https://www.foodpackagingforum.org/news/migrationtesting-of-adhesives https://www.feica.eu/application/files/6915/4142/8246/feica_guidance_fc_status_adhesives_mineral_oil.pdf