Green packaging by SACMI: materials, technological challenges, new applications

?Cellulose-based materials and related technologies in the plastic industry? was the subject of the ‘technology day’ organized by AIM - Associazione Italiana di Scienza e Tecnologia delle Macromolecole , held on 22nd November in SACMI’s Auditorium 1919.

The meeting brought together respected speakers from both the academic and business worlds, offering an opportunity to explore the scientific-technical-application aspects of an area vital to the future sustainability of the industry.

The event provided me with an opportunity to illustrate some of the key lines of development being explored by the SACMI Rigid Packaging Business Unit.

Here, the argument is not just limited to cellulose as it also covers PET and composites: a broad range of materials and related technological recipes with which SACMI aims to lead sustainable growth within the sector.

As we’ll see, in several cases these lines of research have resulted in actual products - ready for industrialization and therefore the market - that SACMI recently presented at key international trade fairs.

New PET yogurt pots and probiotic bottles

?PET is the recyclable material par excellence. Absolutely so, given the state-of-the-art of the technology, and especially as regards food grade re-use. This is largely thanks to excellent levels of resin cleaning performance at the recovery and reprocessing stages, making it well suited to high-end uses (i.e. contact with food).

That's why the SACMI Rigid Packaging Laboratory has an entire line of research dedicated to extending the application range of PET as a replacement for - to cite just a few - traditional polystyrene (PS), high-density polyethylene (HDPE) or the polypropylene (PP) used to make classic yogurt pots and probiotic drink bottles.

The new PET pot, already prototyped by the Laboratory and tested in the field by leading customers, makes optimal use of SACMI's compression and stretch-blowing know-how.

Example of preform and pot below:

I’d like to highlight the finish type without support ring, which goes through a two-stage stretch-blow process. Thanks to patented SACMI technology, this lets manufacturers achieve significant weight savings compared to solutions with a support ring.

?Another project under development concerns the manufacture of small probiotic bottles.

For both products, the process is a two-stage one, similar, as far as the blow-molding is concerned, to that typically used to produce beverage containers. With a key difference: to produce the preforms, SACMI uses compression, a process in which it is world leader. This allows for thinner walls - opening diameters remaining equal - and therefore the manufacture of light products while drawing on all the advantages of compression molding.

Another interesting aspect is that it’s possible to have preforms and bottles that feature a finish with a support ring, which can be used on traditional filling systems. Alternatively, manufacturers can adopt a finish without a support ring, saving weight.

The innate characteristics of the compression process - lower material extrusion temperature vs injection process, no gate and hot runners in the mold - make the solution potentially advantageous and easier to apply. Reduced thickness, in fact, helps ensure that no post-cooling is needed in preform production. The developed process offers extremely short cycle times and a high-performance, light container, ensuring energy and raw material savings while facilitating an efficient, all-new approach to container eco-design.

Versatility is also unmatched: during the blow-molding stage, changing the forming mold generates infinite design opportunities, allowing for easier segmentation by brand/product and the development of unique, distinctive shapes. Both container and bottle can be made of transparent PET or, if necessary, in colored or sleeved PET. Moreover, stretch-blowing allows for the easy insertion of information on the stretch-blown container as it’s simple to copy the information inserted in the blowing mold.

Bottle-to-bottle opportunities

Additional opportunities with an application of this type include the creation of a complete, integrated bottle-to-bottle system; this spans from disposal of the container to melting of the resin, which can be fed directly to the preform production system and the subsequent stretch-blow container molding station.

In this case we’re looking at further advances compared to the current state of the art that involve regrinding and an increase in the intrinsic viscosity (I.V.) of the PET (upcycling). This aims to restore the properties of PET which, post-upcycling, regains characteristics similar to those of a virgin polymer for granule production. In practice, the mechanical recycling and melting system feeds the plant directly, as if it were an ‘extruder’, consequently providing energy savings and logistical advantages. In this case, careful assessment of any upcoming regulations and standards are necessary.

Currently limited to dairy, the proposed application has potential in other industries (cosmetics, pharma), and, of course, with other food-contact products (such as spice jars). The SACMI Laboratory is, of course, constantly researching and validating new products.

The PET outlook appears even brighter when one considers that changes in standards could later impose higher taxes on resins-plastics that not do not come from recycling (not to mention the fact that the cost of the resin accounts for at least 80% of container cost).

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And the cap?

Remaining on the topic of PET, the Laboratory is also exploring the possibility of making the entire package (i.e. both container and cap) out of a single material. From a circular economy and supply chain simplification perspective (one material, one supply chain), this is, in principle, a perfect solution.

Limits and opportunities? One of the main challenges is that PET, by its nature, has characteristics that make it hard to adapt to the required cap design specifications (e.g. sealing properties).

Another problem is the ‘chemical’ compatibility of cap and bottle neck. For example, when cap and neck are made of the same material there is more friction between them; since these materials are rigid, that friction can be considerable and this could make it harder to unscrew the cap.

Research into these elements currently focuses on our understanding of how the material behaves and its relationship with the applicable range of molding technologies. More specifically, molded products are currently undergoing thermo-mechanical analysis and more ‘extreme’ characterization testing. This is so we can understand how to better adapt the molding process while exploiting the characteristics of compression technology.

Feasibility testing of the process - already at an advanced stage - and the transfer of knowledge on polyolefins will then be followed by careful performance assessment together with end users and converters.

The revolution in cellulose-based materials that are exempt from plastic

Cellulose is nature’s most abundant polymer. Needless to say, it is fully recyclable within the classic paper recycling chain. Hence the keen interest in this line of research and development, which could set the stage for a rigid packaging revolution with regard to liquid (and non-liquid) containers.

However, the challenge is an ambitious one. It requires testing of a wide range of cellulose-based materials, which, prior to molding, are present in airlay form. Cellulose has numerous sources and fiber types (long, short) etc., all of which are being investigated to assess their applicability-adaptability to the product.

One tested alternative consists of feeding the system with cellulose which is then ‘pulped’ and converted into a moldable material, with additives then being used so it can be pressed and compacted.

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In the scientific field, some of the key work aimed at increasing our understanding of phenomena associated with the dry forming of cellulose comes from INPT-ENSIACET and INRA ([1]) ([2]). Several reviews are to be found in the relevant in literature ([3]) ([4]).

The goal is to use thermal compression to make it easier - compared to other cellulose process technologies - to give molded materials the required mechanical and water-resistance properties. There follows an initial summary of properties as a function of process parameters:

Full metal isostatic molding

The type of mold and its characteristics play a crucial role in the effectiveness and efficiency of the cellulose fiber material molding process. Compared to a traditional paper production process and the alternative technologies so far tested, SACMI has come up with a dry molding process as opposed to wet molding, which is typically combined with porous molds.

This makes it less energy-intensive. Moreover, the process consumes no water and, above all, can be made ‘isostatic’ to achieve, in practice, true ‘full metal isostatic molding’. Until now, the latter has only been applied with ‘flat’ objects, yet has now been developed so the mold can also exert its pressure on the side walls (as is typically necessary with a capsule, which has a body, bottom and a certain depth) to compact the material adequately.

Reels of pure cellulose, yet also films and sheets: the system has several possible ‘inputs’ that can potentially be adapted to this type of process. Research is currently focusing on capsules and caps but in future the SACMI laboratory will extend those efforts to containers, such as those for coffee.

Different production scenarios are possible, from on-site closed-loop recycling of waste to a set-up that involves returning waste to the raw material supplier.

In every case, the result is an element that’s always compatible with traditional recycling processes and which can be disposed of inside the paper recycling stream

[1]High pressure compression-molding of α-cellulose and effects of operating conditions. T Pintiaux, D Viet, V Vandenbossche, L Rigal, A Rouilly Materials 6 (6), 2240-2261

[2]Cellulose consolidation under high-pressure and high-temperature uniaxial compression. T Pintiaux, M Heuls, V Vandenbossche, T Murphy, R Wuhrer, Cellulose 26 (5), 2941-2954.

[3]Binderless materials obtained by thermo-compressive processing of lignocellulosic fibers: A comprehensive review. T Pintiaux, D Viet, V Vandenbossche, L Rigal, A Rouilly Bio Resources 10 (1), 1915-1963.

[4]Hubbe, M., Pizzi, A., Zhang, H., and Halis, R. (2018). "Critical links governing performance of self-binding and natural binders for hot-pressed reconstituted lignocellulosic board without added formaldehyde: A review." BioRes. 13(1), 2049-2115.

The ‘composites’ opportunity

?‘Full’ recycling for food-grade use is not the only area being explored by the SACMI Laboratory. Further opportunities await: these include the development of ‘composite’ materials that remain suitably compostable yet, at the same time, offer better functional characteristics on the basis of the specific product-process.

In this sense, the SACMI Laboratory has been looking into composite bioplastics, plastics of natural origin which can contain very high concentrations of natural fibers. After having developed, over the years, compression techniques for PLA and its derivatives, the research now turns to PHAs (polyhydroxyalkanoates) and materials that can, in any case, be composted at home.

?As with PET, the tested process is similar to compression molding, with all the relative advantages: the system can handle high quantities of ‘solids’; lower extrusion temperatures degrade neither the polymeric material nor the fiber; high-viscosity materials can be handled thanks to the absence of ‘hot runners’ (the narrow mold channels through which material must be injected in an injection molding process).

Objects produced with these materials, of high natural fiber content, have, in addition to compostability, another interesting feature: adding fibers to the polymer drastically reduces the consumption of bioplastics, which are scarce and therefore expensive. Packaging and objects produced with composite bioplastics are particularly appealing if used in sectors in which the packaged product is itself also compostable. This avoid post-consumption separation of packaging and exhausted product.

?From this standpoint, SACMI has already experimentally produced samples of blown bottles, caps and coffee capsules, with a view to exploring this opportunity for sustainable rigid packaging too.

The prospects offered by SACMI technologies in the latter sector are significant as the composites field, in fact, uses many bio-materials that are heat sensitive (and natural additives can be even more so). Thanks to SACMI's patented cool melt technology, these more sensitive materials can be extruded and molded without degrading them.

For further information on SACMI laboratory services:

https://sacmi.com/en-us/Closures-preforms-containers/SACMI-R-D-Center

#greenpackaging #pet #compressionmoulding #drymoulding #compositematerials #sacmi?