What is MDO-PE and what do you need it for?

Admittedly, as packaging manufacturers, we live a bit in our own world sometimes…

There are many acronyms that initially seem cryptic to people from outside this world. To make sure it doesn’t stay that way, we’ve picked out an important word from this vocabulary today and will try to explain it in simple words. Feel free to let us know if we have succeeded!

Most of us are familiar with classic types of plastic such as polyethylene terephthalate (PET), polypropylene (PP) or polyethylene (PE). Each of these polymers has its own properties and is therefore well suited to different applications.

Since the focus in flexible packaging has shifted towards design for recycling, the properties of plastics have been re-evaluated and their manufacturing processes further developed. Certain materials are particularly suitable for designing Design for Recycling or oftentimes so-called “mono-material packaging”. MDO-PE or mono-orientated polyethylene is one of them.

To obtain MDO-PE, polyethylene is subjected to a special process: it is stretched in the machine’s running direction. This is necessary because PE itself can be a very stretchy (LDPE) or rather hazy (HDPE) plastic. Standard PE can be used very well for sealing processes, but makes life difficult when it comes to printing or stability of the final pack.

So why do we want to use polyethylene at all and not focus on other plastics such as the less soft PET?

One of the reasons lies in the current development of the recycling infrastructure: there are very good existing recycling loops for polyethylene in many European countries. Also, PE is more versatile than other polymers.
If you take PET, for example, it is difficult to seal or could therefore not be easily integrated into modern, fast production processes (we will be writing a blog about PET and its different variations soon ;)).

How do you produce MDO-PE?

After polyethylene has been extruded on a blown film line, the film is stretched. This can either take place “in-line” (how it should be…), i.e. in the same machine, or in a further process step. To do this, the film is heated to a certain temperature and passed over several increasingly fast-moving rollers, which stretches the film further and further. In order to retain the new shape of the film, the now orientated film must be “heat-set”. This is done by rapid cooling, which gives the film its final shape.

The stretching of the film “elongates” the polymer chains of the PE, which leads to greater crystallinity, higher strength and rigidity.

What is MDO-PE used for and what is its advantage?

The orientation has changed the physical properties of the PE film in such a way that it is comparable to common printing substrates, such as PET, in terms of printability and mechanical performance. As a result, PE can be processed using all common printing technologies – whether gravure, flexographic or digital printing. It can even be used on high-speed systems. We have already been present during print runs on 9-colour gravure printing systems that reach speeds of 600 m/min with our own MDO-PE (CrystalPE).

As impressive as this material is, you can’t pack products with MDO-PE alone

In order to achieve a high-performance, D4R-compliant packaging film, the MDO-PE is then classically laminated against a PE-based sealing film. The end result – if you did not add too much further ingredients such as barriers or printing inks – is a printed, D4R, mono-PE packaging solution.

We hope that we have given you an exciting brief insight into our world. If you have any questions about extrusion, we will be happy to put you in touch with our experts. A simple mail to contact@adapa-group.com is enough. It is always impressive how much they know about the production of plastic films!