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Email: packlab@unimi.it
Via Celoria 2, 20133 Milano (Italy)

Coatings

Coating technology is continuously attracting the interest of both research institutions and companies due to an increased awareness on the opportunity for improving many properties of food packaging materials.

 Bio-sealing coating applied on a polypropylene film

Also at Packlab, a large part of the research activity is devoted to this topic. In particular, three main sub-themes are still being carried out

Sealing coatings

Approximately three years ago, some of us decided to dedicate part of their research activity to the development of a new class of thin layers intended for partial replacement of the commonly used thermoplastic polymers (such as polyethylene) as well as the well-known cold sealants. Distinctive tract of our targeted goal was the use of only macromolecules of natural origin as starting raw materials, in order to both make these new solutions totally safe in terms of contact with food and recover by-products from industries/farms activities.

Bio-sealing coating on a bioriented polypropylene and metalized polyester film. In this case, the coating is intended to replace the well-known cold sealants in applications such as ice creams and chocolate-covered bakery products.

Initially our research has been carried out in our lab, using both common and more sophisticated techniques/equipments. Later on, we decided to scale-up our findings through a fruitful industrial partnership, thanks to which we accomplished our goal. To date, different sealing coatings have been produced by our team, each one with specific and unique features. They cover a wide spectrum of sealing temperatures, starting from 50°C to 110°C, so originating both peel-seals and high-strength closures. The innovation involved accounts for the high versatility of such coatings, together with lower cost, absence of release, zero environmental impact, and higher sustainability than conventional sealing solutions.


Barrier coatings

Among different routes, food quality preservation may be also achieved by developing packaging materials with tailored barrier properties against gases and vapors. It is usually achieved by either laminating two or more synthetic films to form a ’heavy’ multi-structure or applying thin layers (coatings) on a specific web in order to improve its starting properties. However, current barrier coatings still exhibit some drawbacks, in terms of cost, performance, environmental impact. With the aim of providing answers to the ever-increasing demands for new barrier structures especially from companies, we get started investigating new routes for producing coatings with high barrier properties against gases. In particular, we decided to exploit the potential benefits arising from the combination of petrol-based, inorganic and natural molecules, to produce structures able to act as a high barrier also at the highest relative humidity values. To date, we developed different types of coatings that may be used for several applications in the food packaging sector. It means that we developed a unique method to obtain thin coatings with tailored barrier performance against oxygen, depending on the specific final application. It has been possible by setting many combinations among ‘ingredients’ pertaining to the classes of natural, organic, and inorganic molecules. For example, we produced a composite coating that provides an oxygen barrier <1 ml m-2 day-1 in terms of oxygen transmission rate (OTR) even at high relative humidity conditions. At the same time, it is possible to produce a totally ‘green’ coating of 0.3 µm with an OTR ?0.05 ml m-2 day-1 under dry conditions. So, although the way is still rough going, we truly believe that exploiting the advantages arising from hybrid structures can lead to new thin materials with excellent barrier properties, according to the concept of packaging optimization.

Farris S., Introzzi L., Piergiovanni L. Evaluation of a bio-coating as a solution to improve barrier, friction and optical properties of plastic films. Packaging Technology and Science, 2009; 22: 69-83. DOI: 10.1002/pts.826


Electron Beam-modified coatings

Electron beam is a well established technique in fields different than food packaging. Recently, some research dealt with the possibility of using such powerful tool for improving some performance of packaging films. Thanks to a recent collaboration with a foreign company of food packaging, we get started developing a rational approach to investigate the potential use of such high energy electron beam on coatings applied as very thin layers on plastic substrates. In particular, our attention has been turned towards biomacromolecules used for producing the coatings. Preliminary results showed that the electron beam greatly influenced properties such as permeability and swelling behavior. However, it seems unrealistic that electrons lead to a polymerization process on such biomolecules. Rather, it seems that physical changes are induced by the irradiation, corroborating our hypothesis that morphology and structure of biopolymers may be changed by a controlled process. However, care must be taken on the setting of the main process parameters, which strongly affect the final result. Indeed, degradation of the overall structure is encountered when the electron beam is generated at maximum dose and voltage. Further experiments will reveal whether such a kind of approach can be considered as a promising new tool for the development of new engineered materials.