Nearly 7 million tons of coated paper, paperboard, and cardboard, are manufactured worldwide annually. The dominant coating material is petroleum based polyethylene (PE). Currently, alternative coating materials that don’t cause environmental harm throughout their life cycle are being sought because of consumer, political, and legislative pressure to reduce fossil fuel based plastics use.
PE Coating vs. Aqueous Coating
FDA direct food compliant water-based (aqueous) coatings, like those supplied by Cork, have provided an alternative to PE coated paper and board. Aqueous coatings are formulated across a broad spectrum of desired properties that are often packaged product specific. For example, aqueous coatings are commonly used for fast food carry out packaging (i.e. such products as French fries, onion rings, burgers, various sandwiches, fried chicken, and Chinese food). Other food products such as bakery, pastries, frozen foods, microwavable and ovenable foods, and roasted chicken, are also routinely packaged.
Differing food products might require water, and/or grease/oil resistance, a low Moisture Vapor Transmission Rate (MVTR), odor and taste protection, temperature or chemical resistance, anti-wicking, product release, with good scuff resistance, and appropriate coefficient of friction (COF) properties. Aqueous coatings that offer these properties, plus gluability, and heat seal ability are replacing PE coatings. Other aqueous coated paper board products are formed into paper plates, trays, and cartons. Foremost, aqueous coated paper and paper board is, sustainable, biodegradable, compostable, recyclable, and repulpable (without hydro-pulping).
Furthermore, aqueous coatings can be applied off-line or in-line, giving control to the printer to create a substrate designed to satisfy an individual customers requirements.
Coated paper and paper board, containing about 20 mass percent of PE, is one of the most widely used materials for food and beverage packaging ranging from milk cartons and soup packets to fast food boxes and cups. Much of this ends up in landfills with the paper component degrading rapidly while the petrochemical based PE coatings take decades to break down. An American Forest & Paper Assoc. survey shows that 87% of the U.S. population and 73% of U.S. communities have access to paperboard recycling. A stipulation is that the container must be clean in and out. Poly board sees a “hydro-pulping” process separating paper fiber from PE after which the pulp is recycled.
PE’s dominance as a food packaging plastic is due to its relatively low cost, its range of versatile properties, and the ease with which it can be processed.
Poly board is a substrate consisting of rigid paper board that is extrusion coated with a layer of PE to provide a substrate with improved barrier properties.
Paper board, coated on both surfaces with PE, is extensively used for containers to package liquid products, high-moisture and fatty food products. Single surface PE coated paperboard is widely used as external cartons for many foods with a short shelf life, and over a wide temperature range (frozen to ambient). PE is easily heat sealed for closure.
Poly Board Benefits
- Good water resistance
- Moderate MVTR permeability
- Good grease/oil resistance
- Good heat seal ability
- Relative chemical inertness
- FDA direct food contact compliance
Poly Board Negatives
- Highly permeable to oxygen-gases
- Poor odor barrier
- Recycling requires hydro-pulping
- PE is not readily biodegradable
- Poor composting performance
- Relative high cost vs. aqueous coatings
Polyethylene (PE), a polyolefin, is a thermoplastic, organic polymer, consisting of long hydrocarbon chains. The light versatile synthetic resin is produced by the polymerization of ethylene. Ethylene, a gaseous hydrocarbon, is commonly produced by the cracking of ethane, which is a component of natural gas, or it can be distilled from petroleum. Most grades have excellent chemical resistance, and are resistant to gentle oxidizing and reducing agents.
Viable alternatives to poly board (replacements) are coming from research to provide barrier and functional coatings which will overcome the shortcomings of PE. Various technologies are being explored worldwide that have the potential to offer a required range of properties, while exhibiting desired Green tendencies.
Environmentally Friendly Coatings
In Europe, EU-funded research is aimed at developing an environmentally friendly alternative to petrochemical based coatings for liquid and dry foods. The BIO-BOARD project seeks to use food processing by-products, whey from cheese production, and potato juice from starch production, to produce protein-based coatings to replace PE coated board. While making important strides toward commercialization, coat weight reduction and the development of production processes remain to be resolved.
Yet another European effort to go Green and improve recyclability has seen the successful commercialization of replacing petro-chemical sourced PE with Green bio-based sourced material, however the result is still poly board.
Another technology modifies the chemistry of PE extrusion coatings so that polyolefin blends are created wherein 40% of the LDPE is replaced by calcium carbonate. The result is a lower cost PE material with high printable surface energy, better MVTR barrier, and heat seal performance, combined with better recyclability.
Targeting a sustainable paper cup, bio-plastic technology is being exploited, resulting in growing production of ecologically friendly cups made from virgin paper extrusion coated with a PLA corn starch based coating. Replacing traditional petroleum-based PE coated paper cups that have been difficult to recycle, PLA coated cups are bio-degradable, compostable, recyclable, and carbon neutral. PLA exhibits good fat, oil and flavor barrier properties, is printable, has intermediate vapor permeability, some O2 and CO2 gas barrier properties, and is heat sealable.
Cork, from its inception, has developed and offered a wide range of aqueous coatings. A grouping of FDA compliant barrier coatings suitable for coating paper and paper board substrates for liquid and dry food conveyance are among these.