Cast MDO or Blown Film MDO: How Film Manufacturers Choose the Right Technology
Which trends are currently shaping film production when it comes to sustainability?
Lettowsky: For me, sustainability in flexible plastic packaging has two dimensions. The first is the clear trend toward monomaterial solutions – packaging concepts that are easier to recycle because they aren’t a mix of different polymers. That applies to the film itself and to all downstream processes such as laminating or printing. In short, it’s about “design for recycling”: the product is designed from the outset so that it can ultimately be recycled as simply and efficiently as possible.
Laue: There are many ways to improve recyclability through packaging design. It’s not just about the film structure – keyword monomaterial – but the whole package. Take the bottles where the cap has to stay attached: that’s design for recycling too. The goal is for materials to either be easy to separate at the end, or compatible from the very start.
How can Machine Direction Orientation, or MDO for short, support the recyclability of films?
Laue: With it, monomaterials achieve properties that used to be reserved for multi-material laminates. MDO is therefore one of the processes that makes monomaterial solutions like PE and PP films possible in the first place. Compared with established multi-material film laminates that have been optimized for maximum efficiency over decades, it is currently at a price disadvantage. That will change once regulations such as the European Union’s Packaging and Packaging Waste Regulation, better known as PPWR, take effect from 2030: from then on, packaging must be demonstrably recyclable. Monomaterial solutions made of PE or PP will then be the safest way to meet this requirement.
Lettowsky: The MDO unit, which I use to stretch plastic webs in the machine direction, has been around for a very long time. After years as a niche technology, interest in it has grown considerably over the past decade. After all, it lets me replace PET in multi-material laminates with recyclable PE, simply by stretching the PE. MDO technology thus makes it possible to modify PE so that it comes functionally close to established PET film.
Advantages of MDO technology:
- Enables PE monomaterial solutions to replace non-recyclable PET/PE laminates.
- Improves the mechanical properties of PE (including stiffness and heat resistance) and brings it closer to BOPET.
- Reduces the barrier content (e.g. EVOH) through the stretching process to below 5% of total weight while maintaining or improving barrier performance.
- Expands film functionalities (chemical resistance, straight tear (MDO-PP), targeted control of shrink behavior, etc.).
So MDO is also a good alternative for use in food packaging.
Laue: Absolutely. MDO was originally used for technical films, such as breathable films in diapers or roofing underlays. But recyclability requirements for food packaging are now opening up a new market segment for MDO technology. Stretching is the key to changing PE and PP so that established film laminates like BOPET/PE or BOPET/PP can be replaced. So the technology itself isn’t new – the market segment is.
Lettowsky: That’s really the core motivation behind MDO. The classic PET/PE laminate isn’t recyclable. The solution is to modify PE through MDO so it approaches the properties of PET. Only then can we achieve a pure, monomaterial-based laminate. PET has fantastic properties: high mechanical strength, heat resistance, and excellent suitability for printing and laminating processes. MDO-PE can get close to that.
MDO films can be produced using both the blown film and cast processes. How do the lines differ in design and operation?
Lettowsky: Ultimately, MDO works on the same principle in both processes: the web arrives, is heated, stretched, passed through an annealing process, and then cooled. Temperature ranges, stretch ratios – all of that is comparable, because the raw material requirements for PE or PP don’t change. The difference lies in the primary film fed into the stretching unit: in the blown film process, it’s a flattened tube that is stretched in two layers. In the cast process, it’s a simple, flat-cast web. Both have specific properties that tip the balance depending on the application and the desired end product.
Laue: With blown film or cast film, the question customers usually ask is: what’s the most economical solution for me? From that angle it’s hard to give a clear answer, because the two technologies aren’t all that different. The more important decision criteria should be different ones: first, where does my product focus lie? Second, how familiar am I with the respective manufacturing process? Anyone who has so far only worked with blown film has to rethink their technology if they want to move into the world of cast film.
Lettowsky: One of our major customers runs both technologies in-house. We ran a comprehensive head-to-head comparison there: cast MDO versus blown film MDO. The result: in many respects, there’s no clear winner. Not in process complexity, energy consumption, costs, or product quality. That’s why our recommendation is to stick with the process the manufacturer already knows. Only once they have mastered both is it worth looking at the details.
What are those details?
Lettowsky: With cast, I see three concrete advantages. First, the higher throughput. Second, the ability to recycle the edge trim inline, which is an established, standard part of the cast process. Third – and this is a specialty unique to Reifenhäuser – the so-called internal encapsulation of barrier materials such as EVOH in the coextrusion adapter: thanks to the encapsulation, the edge trim no longer contains any EVOH or tie layer. That means it can be fed back into the process without any issues – something blown film lines can’t do.
Laue: Blown film, in turn, currently has one important practical advantage: flexibility. On a blown film line, I can also run a normal, non-stretched laminating film using very similar raw materials, keeping the line fully utilized. That means I’m not tied to the MDO market. That doesn’t work as easily on a cast line running PE – the raw materials used for non-stretched PE cast film differ considerably here. If we look at PP as the starting material for the films, it’s exactly the other way around. PP has traditionally been the raw material of the cast film world. There, we have a huge range of raw materials with substantial overlap between the technologies in places. So when it comes to formulations, we can act very flexibly here. So blown film faces similar challenges in the PP space as cast does in the PE space.
Key questions packaging film manufacturers should ask themselves before entering MDO technology:
- Which process am I already familiar with: cast film or blown film?
- Which polymer do I primarily process: PE or PP?
- Do I also want to run non-stretched films on the line?
- What share of films with an EVOH barrier do I need?
- What annual output am I aiming for?
Are there any developments on the horizon that could affect the choice of process?
Lettowsky: The more the market for stretched PE film as a PET replacement develops and standardizes, the more important cast becomes – simply because of its higher throughput. Blown film will then tend to remain a specialty solution for customers with individual requirements that a standard film can no longer meet. But that’s a forecast for 2030 and beyond.
How do both processes affect the recyclability of barrier films containing EVOH?
Laue: With EVOH as the barrier material, the rule is that its share must stay below 5% of the total packaging weight – only then does the laminate count as recyclable. Stretching the film in the MDO process makes that possible. In the cast process, Reifenhäuser offers – as mentioned – internal encapsulation in the coextrusion adapter: the EVOH is integrated into the laminate so securely that it doesn’t end up in the edge trim. The trim can then be recycled directly inline as regrind, without any elaborate, energy-intensive reprocessing. This concept can’t be transferred to blown film lines.
To sum up: what should a film manufacturer base their decision on when choosing between a cast MDO or blown film MDO line?
Laue: The following questions are decisive: first, which market segment am I in, and which polymer do I use? Anyone strongly rooted in PP, for retort packaging for example, is better served by cast MDO lines than blown film lines. Second, which process do I already know? If I have a lot of blown film experience, entering MDO there is the more natural step. Switching to a new technology and adding MDO on top of that is a double challenge.
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Decision Tree and Market Entry
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What else should manufacturers know?
Lettowsky: My message, especially to blown film manufacturers, is this: with today’s installed machine base, future demand for stretched PE film – as a PET replacement – is nowhere near covered yet. There’s enormous market potential there. For every one of our customers, that’s a genuine opportunity to tap into an additional market that has so far been served by biaxially oriented PET. Securing a piece of that pie is a growth opportunity – but one that requires an investment of time.
Laue: That’s exactly why we recommend building up enough experience now, so you have a solution ready for the market once demand arrives. And it will arrive!
Want to learn more about introducing MDO technology in a personal conversation? Then reach out to our experts. They’re happy to advise you:
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