Packaging: materials and innovative technologies for paper and cardboard design

University research in Italy is trying to support new ways of thinking aimed at promoting increasingly sustainable and performing packaging, specifically from a technological viewpoint in this case.

Sustainability is an all-embracing concept, which can refer to many different aspects. In the sector of cellulose packaging, the term sustainability can be applied at various levels. It is definitely very important in terms of prevention, as sustainably designed packaging implies attention also during recycling and disposal. Universities are on the forefront when it comes to research on sustainable materials. Thanks to their work they help bring about increasingly sustainable and performing solutions. «Universities enable us to use a new language for the term sustainability and enterprises need to optimize their packaging and make them more sustainable». These are the words by Eliana Farotto, who is in charge of the Research & Development department of Comieco (the National Consortium for the Recovery and Recycling of Cellulose-based Packaging).

This article presents just some of the latest research studies carried out at Italian universities, specifically those with interesting applications in the food sector.

The first study has been carried out by the Design Department of the Milan Polytechnic (Politecnico di Milano), which conducted a research activity leading to the creation of new oil-repellent coatings based on natural substances for cellulose packaging in contact with fatty food. The second research study was conducted by the Group for the diffusion of polymers of Bologna University, Department for Civil, Environmental and Materials Engineering (Dipartimento di Ingegneria Civile, Chimica, Ambientale e dei Materiali, Dicam) which developed a protocol for the coupling of two biomaterials, i.e. polylactic acid and nanocellulose, and obtained a biodegradable film with good barrier properties against gases and water steam, which is as such particularly interesting for food packaging applications. In the first research activity, new coatings were studied that could act as a barrier to protect cellulose packaging; in the second case, the properties of a biodegradable film from the coupling of PLA and nanocellulose were investigated, highlighting the extremely good barrier properties of the film against gases like oxygen, nitrogen and CO2.

Barriers to fats for cellulose packaging

Agnese Piselli, PhD student – Milan Polytechnic (Politecnico di Milano, Italy), Design Department.

Agnese Piselli, PhD student – Milan Polytechnic (Politecnico di Milano, Italy), Design Department.

It is commonly known that the Italian legislation in the field of food packaging is very strict: virgin fibres offer the best guarantee in terms of food contact hygiene and safety, recycled fibres can be used at direct contact with dry food (e.g. rice, pasta, or salt, i.e. non extractive materials), while a «barrier» is needed for extractive food like humid and fatty food. And this sector is exactly where several research studies are currently focussing on: the development of innovative films and coatings. Agnese Piselli from the Milan Polytechnic Politecnico di Milanotalks about these latest developments. She completed a degree thesis in the field of Design & Engineering, i.e. a specialization targeted to the study of production materials and technologies for the manufacturing of industrial products. Her research work aimed at identifying new coatings obtained from natural substances and applied on cellulose packaging in contact with fatty food and was developed with the support of the Department for chemistry, materials and chemical engineering «Giulio Natta» at the Milan Polytechnic (Politecnico di Milano) and the Cipack (Interdepartmental Centre for Packaging in Parma) with the aim of improving quality, safety and sustainability of food cellulose packaging with oil-repellent properties. This research activity is undoubtedly in line also with the topic of the forthcoming Expo 2015 www.expo2015.organd has led to assume possible applications of these treatments, especially in the field of conservation, cooking and fresh gastronomy, including containers for fast food stores or frozen products.

Oil-repellency: why?

Research started from coating with an anti-fat barrier. The market surely offers several solutions that create barriers against fats: mechanical productions, combined materials, multilayer materials, like polythenate paper, mass additivation of certain substances or surface treatments, like polymeric solutions containing waxes for the production of waxed papers. However, there are also treatments based on natural substances, which are less developed but nonetheless equally interesting. These treatments can favour compatibility between barrier substances (coating) and the cellulose substrate.

The steps of research

Research focussed on the analysis of some natural substances, specifically polysaccharides, and thanks to support from Cipack researchers in Parma a new testing phase has been inaugurated. First, a preliminary market research activity has made it possible to identify the most widely used packaging in contact with fatty food; the selected cardboard samples correspond to the type of packaging normally used in fast food stores (e.g. chips packaging): in particular, both untreated anti-fat substrates and traditional anti-fat coatings in virgin and recycled fibres have been selected.

Finally, some chemical formulas with good anti-fat barrier have been chosen and several coating application techniques have been compared to identify the most promising coatings. The comparison between two techniques for the laying of the cellulose substrate, i.e. a manual coat spreading technique and spray coating, has shown that the latter definitely provides for the most promising results, as it enables both to spread the coating uniformly on the entire surface and to treat uneven surfaces.

Test phase: the Kit Test

Experimental tests have been carried out in three stages: kit test, «oil drop test», «drop bend test».

The kit test (or T 559 cm-12 test, i.e. a standard method to assess the resistance of a cellulose support to the absorption of fatty substances) consisted in the measurement of real fat resistance and was carried out with some reagents , i.e. toluene, heptane and castor oil, which have been carefully mixed in 12 solutions classified from the least to the most aggressive: starting from an intermediate solution, a drop is deposited and then removed after 15 seconds, and its absorption by the material is then checked. No oil absorption was observed in the case of selected natural coatings. The same result was even more striking when using supports in recycled fibres.

Second step: the «oil drop test» and the «drop bend test»

A second test (i.e. the «oil drop test») was developed ad hoc to measure absorption of the fatty substance at higher temperatures compared to the room temperature (i.e. a temperature comparable to the oven temperature): samples were tested for 120 minutes at 120 degrees. The complete absorption of the oil drop was observed for both untreated anti-fat virgin fibre and recycled fibre cardboard, and in samples treated with the oil-repellent coatings currently available on the market. In the case of anti-fat treated cardboard with natural coating spreading the test showed that the drop stays on the surface in spherical form, hence no absorption was observed or absorption occurred only on certain spots and in a few cases. The tests therefore proved that coating can serve as a good barrier against the absorption of fatty substances.

Finally, a third test (i.e. the «drop bend test») was also developed ad hoc to test resistance from fatty substances at the bending points, which are known to be critical for the coating resistance of packaging. This test did not provide promising results like the oil drop test; however, there is considerable room for improvement in this case, too.

Coatings’ good properties against the absorption of fatty substances

The tested coatings have featured good anti-fat barrier properties. Although they dot not yet represent a real alternative to traditional treatments, they are a good starting point to improve the compatibility of the cellulose support with its treatment, as well as to enhance the compostability of the food packaging. In view of the Expo 2015 international exhibition, this research activity helped assume some interesting application scenarios, especially in the fields of conservation, cooking and fresh gastronomy, fast food catering or containers for frozen products.

Barrier packaging with a multilayer approach

Marco Giacinti Baschetti, Alma Mater Studiorum – University of Bologna (Italy), Department of Civil, Chemical, Environmental, and Materials Engineering (Dicam).

Marco Giacinti Baschetti, Alma Mater Studiorum – University of Bologna (Italy), Department of Civil, Chemical, Environmental, and Materials Engineering (Dicam).

The second research activity described was conducted by the Group for the diffusion of polymers of Bologna University, Department for Civil, Environmental and Materials Engineering (Dipartimento di Ingegneria Civile, Chimica, Ambientale e dei Materiali, Dicam): we learn more about the study from Marco Giacinti Baschetti from the Alma Mater Studiorum, University of Bologna, Department of Civil, Chemical, Environmental, and Materials Engineering (Dicam http://www.eng.dicam.unibo.it).

Mr Baschetti states that «barrier materials enable to extend the lifecycle of products and reduce waste, however each product has specific properties that serve as barriers to the different gases and the choice of materials is therefore related to the properties of the final product». However, biomaterials today often feature values that are beyond the range of values of interest: for instance, the development of packaging from nanocellulose 1 or other biomaterials is not an easy objective to achieve. In the field of packaging, materials must comply with very different specifications depending on the type of product to preserve». In the case of dry biscuits, it is necessary to avoid water steam to enter the package and make them less fragrant, while in the case of perishable food (fresh cheese or fresh pasta) oxygen should be left outside. With fizzy drinks, instead, carbon dioxide should never permeate through the bottle. Today, a lot of the materials mentioned above and other potentially interesting materials do not unfortunately have all the requested properties to serve as ideal replacements of the packaging currently available on the market, whereby the latter can themselves be very complex. In particular, PLA has very good water resistance properties, but it is too permeable to gases and as such it is not used for packaging, while nanocellulose films block oxygen very well but they are very sensitive to water».

To solve these problems, the various materials are often combined in order to obtain a product that combines the best properties of both: «The easiest way is to overlap films of different materials so as to form a single multilayer material, where each layer has specific characteristics and serves a specific function: gas barrier, water barrier, but also mechanical support or simply printable surface for the outside of the product».

Multilayer approach: biopolymers (PLA) and MCF

The research activity focussed on the combination between PLA and nanocellulose with the aim of combining the water resistance properties of the former with the barrier properties of the latter without adding glues or additives that might reduce the biodegradability or renewability levels of the product. In this case the objective was reached with a plasma technique to combine the two materials PLA and MFC, which would otherwise be incompatible. Although preliminary, the results obtained are extremely interesting.

On the one hand, the combined films have helped develop outstanding oxygen barrier properties as well as mechanical properties, which are much better than the ones obtained with pure nanocellulose. Also water steam permeability appears to have improved, although three-layer films will have to be produced (to protect MFCs on both sides) instead of the two-layer films tested so far.

A protocol for the coupling of two biomaterials

The work carried out over the last two years by the Bologna research group has made it possible to develop a protocol for the coupling of two biomaterials, i.e. polylactic acid and nanocellulose, and obtain a biodegradable film with good barrier properties against gases and water steam, which is as such particularly interesting for food packaging applications. «Although the study is still in its preliminary stage, this material appears to be suitable for the packaging of fresh food, like cheese, pasta, meat. For these types of food non biodegradable plastic materials have been used so far, which have to be disposed of as unsorted waste because of the putrescible residues contaminating them and are therefore often bound for incineration».

The times for the industrial development of these systems are yet still uncertain, not only and not so much due to the lack of economies of scale, which is definitely the case, but above all due to high costs that do not make these solutions appealing on the market. While PLA is already mature as a product from an industrial and commercial viewpoint, nanocellulose has been a commercial product only for a few years and its prices are still not comparable to the prices of the other materials currently used for packaging.

Nanocellulose (MCF): history, characteristics, properties and applications

Nanocellulose in the form of nanocrystals or nanofibrils (microfibrillated cellulose MFC) has experienced a remarkable growth and development over the last few years thanks to its peculiar mechanical and barrier properties. The material, which has been known for some time now, was developed in the 1960s but was of limited interest due to its very high production costs. It was then rediscovered in the 1990s following the boom of nanomaterials and especially thanks to new productions methods, which helped reduce its costs by over 90%.

Cellulose nanofibres have thus contributed to open up a whole new area of research and can be potentially used in a large field of applications ranging from reinforcement in composite materials to additives in cosmetic creams regulating their consistency, up to biomedical applications, e.g. in controlled release systems, and packaging as barrier films. Nanocellulose films have been shown to serve as an ideal barrier against gases like oxygen, nitrogen and CO2, thereby proving to be very good in food packaging applications. Pure cellulose films are unfortunately too frail for industrial applications. Furthermore, this is a highly hydrophilic material, which loses a lot of its properties in the presence of humidity.

The nanucellulose used, available in two main types: MCF G1 (1 wt.%) and MCF G2 (0.67 wt.%). The producer is Inventia http://www.innventia.com.

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