report
2.5.3 Food packaging based on nanoclay composites: multilayer PET

Short application description

The polymer composites incorporating clay nanoparticles are among the first nanocomposites to emerge on the market as improved materials for food packaging. Nanoclays are nanoparticles of layered mineral silicates with a specialized structure, characterized by platelet morphology. The platelets have submicron dimensions, excepting their thickness, which is only about one nanometer. These platelets force gases to follow a tortuous path through the polymer greatly slowing their transmission. Nano-layer structure of clays thus increases the path of diffusion that penetrating molecules of gases or other substances must take and significantly improves the polymer's barrier properties.

Depending on chemical composition and nanoparticle morphology, nanoclays are organized into several classes such as montmorillonite, bentonite, kaolinite, hectorite, and halloysite. Organically-modified nanoclays (organoclays) are an attractive class of hybrid organic-inorganic nanomaterials with potential uses in polymer nanocomposites, as rheological modifiers, gas absorbents and drug delivery carriers. Based on report from Pira International Conference held in 2005, there are eight nanocomposite barrier products available. Seven are based on polyamide 6 and one is a specialized polyamide known as MXD6 (see Table 3).

* LANXESS was spun-off from Bayer in early 2005

Table 3 - Polyamide nanocomposite products and producers

Source: Maul, P.: Barrier Enhancement Using Additives. Nanocor Inc., Pira International Conference, Brussels, December 2005.

Functional requirements

The fundamental functional requirement on the nanoclay multilayer PET bottle is the low penetration rate of gases (particularly carbon dioxide and oxygen), water, alcohol and other substances which can significantly extend the shelf life of stored beverages. A typical example is the plastic bottle to ship beer. Plastic beer bottles of volume 500 ml or less require significant barrier protection against oxygen ingress. In addition they require considerable barrier to CO2 loss. In this respect beer packaging is perhaps the most demanding for barrier enhancement. European producers wished to package lager beer in a 330 ml bottle and achieve five month's shelf life. During this period total oxygen ingress was limited to 2 ppm and CO2 loss could be just 10 %.

Boundary conditions

The further development in this area is strongly dependent on the perception of nanotechnologies in food contact materials by the public. Food companies are still hesitant to incorporate nanomaterials for uncertainty of future regulations and standards and for fear of negative consumer reactions. Experts consider also higher price as another possible barrier to further development of market applicable products in this area. Another hampering aspect is the absence of reliable data relevant to consumer health and lack or regulations for use of nanomaterials, especially for food contact materials.

Product examples

Commercial products fall into two general categories: regular and high load. Regular products have nanoclay loading in the 2-4% range and high load 5-8%. Regular load products bring 2 times barrier improvement for oxygen and water vapour transmission. High load products are 4-5x better than neat polymer and about 2x better for CO2.

Nanoclay composites for food application (multilayer PET) include:

•  Imperm® (Nanocor)
•  Aegis® (Honeywell)
•  Durethan® KU2-2601 (Bayer AG)

a) Imperm®

Imperm® from Nanocor® Inc. is is fully approved for use as a non-contact barrier layer in multilayer structures. It is used in multi-layer PET bottles to minimise the loss of CO2 from the drink and the ingress of O2 into the bottle, thus keeping beverages fresher and extending shelf-life. Imperm's impact on CO2 retention makes it attractive for the rapidly advancing plastic beer bottle sector, as well as smaller portion carbonated soft drink (CSD) bottles. Small portion monolayer CSD bottles have short (8 weeks) shelf life. But the addition of 3 % Imperm nearly triples it, providing ample shelf life for problem-free distribution.

b) Aegis® OX, Aegis® HFX, Aegis® CSDE

Aegis® OX barrier nylon resin is an oxygen-scavenging nylon formulated for the high-oxygen barrier demands of plastic beer and flavoured alcoholic beverage (FAB) bottles. Multilayer polyethylene terephthalate (PET) bottles made with Aegis® OX barrier nylon resin demonstrate near zero oxygen transmission rates for extended periods of time, depending on barrier loading. Typical loading is between five and eight weight percent or 25 to 75 micron barrier layer thickness. Oxygen barrier is comparable to the performance of glass bottles. In addition, Aegis® OX barrier nylon resin provides excellent barrier to carbon dioxide while delivering glass-like clarity and recyclability. Multilayer bottles containing Aegis® OX barrier nylon resins demonstrate superior resistance to delaminating. Aegis® HFX barrier nylon resin is an oxygen-scavenging nylon formulated for the high oxygen barrier demands of juice, tea, and condiment bottles. Typically these applications are non-carbonated but call for excellent oxygen protection in conjunction with superior delamination performance. Hot-filled and/or hot-stored bottles place stringent demands on the integrity of the multilayer interface. Bottles made with Aegis® HFX barrier nylon resin display very low levels of delamination in all phases of the bottle supply chain.  Aegis® CSDE barrier nylon resin is a passive (non-scavenging) nylon formulated for the high carbon dioxide retention demands of carbonated soft drink and carbonated water applications. Typically these applications require excellent delamination performance due to high carbonation levels and complex bottle geometry.

c) Durethan® KU2-2601

Durethan® KU2-2601 from Bayer AG is a new hybrid plastic, which comprises polyamide (PA) and layered silicate barriers. The plastic incorporates Nanocor's clay to produce a film with increased barrier properties, enhanced gloss and stiffness. It is intended for use in applications where conventional PA is too permeable and EVOH coatings too expensive, e.g. paperboard juice containers. Durethan KU2-2601 packaging film is lighter, stronger and more heat resistant than those currently on the market.

Economical information for present products

Nanocomposites are the fastest growing segment in the forty billion dollar polymer composite market. This segment is estimated to more than double in size in the next four years. Analysts predict that nanoclays will be the largest component of the nanocomposite market in 2010.

Figure 6 - Nanocomposite market

Source: http://www.naturalnano.com

Currently, clay particles at the nanoscale are the most common commercial application of nanoparticles in food packaging and account for nearly 70% of the market volume (the market for food packaging containing nanomaterials has been predicted to reach $360m in 2008 and $20bn by 2020)[1]. They are less expensive to produce than some other nanomaterials because full-scale production facilities already exist and the basic materials come from available natural sources.

The plastic bottle is slowly emerging as alternative packaging format for beer. Carlton & United Breweries first introduced PET beer bottles in 1996 and during the period from the late 1990s to the early 2000s, around 20 beer brands were introduced in plastic bottles, including Heineken which used creative packaging to differentiate its Cruzcampo brand.

The economical information about the plastic bottles containing nanoclays is not publicly available, however, the market seems to be very promising. Outstanding barrier properties of theses layers resulting in low permeability for gases and other substances, extended shelf life of beverages, light weight and resistance to shock are significant prerequisites for further replacement of glass bottles and metal cans by nanoclay multilayer PET bottles.

[1] Packaging-Gateway.Com (http://www.packaging-gateway.com )