Why do plastics behave so differently? Which properties are crucial for flexible packaging films? And what role do recycling, specifications and additives play?
These questions were the focus of the web seminar Plastics for packaging films – Basics for flexible packaging films, part A. Dr. Heiko Schenck provided participants with a practical introduction to polymers and connected fundamental polymer science with the everyday challenges of film production, quality assurance and recycling.
Flexible packaging in a changing market
At the beginning of the web seminar, Heiko Schenck placed flexible plastic packaging within the wider European packaging market. He highlighted several developments influencing packaging demand, including smaller households and pack sizes, home delivery, centralised production and the ongoing trend towards downgauging, which reduces the amount of material required for a packaging application.
For plastic packaging, the most important polymers discussed were polyethylene (PE), polypropylene (PP) and polyester (PET). One of the major strengths of polymers is not only their comparatively low weight, but also the wide range of possibilities for tailoring their properties to specific applications resulting in a better performance and/or less weight/waste.
Polymer structure determines performance
One of the key topics was the relationship between a polymer’s molecular structure and its resulting properties.
Two factors were particularly important:
- the length of the polymer chains
- the degree of crystallinity
According to the presentation, these parameters have a significant influence on how a polymer behaves. Increasing crystallinity can, for example, increase tensile strength, stiffness, chemical resistance and barrier performance. The effect on transparency and other properties depends on the polymer concerned.
Another important aspect is the molecular weight distribution. Polymer production is a statistical process, so not every molecule has exactly the same chain length. The web seminar demonstrated how modern production technologies can achieve narrower distributions, reducing very short and very long polymer chains and thereby improving product quality for certain applications.
Understanding how polymers are produced
The web seminar also introduced three major polymer production processes: polymerisation, polycondensation and polyaddition. Understanding their differences is particularly relevant when considering future recycling options.
Polyester and polyamide received special attention. For these materials, the production process can be reversed chemically to recover monomers. These monomers can then be used again to manufacture new polymers, providing an important route for chemical recycling.
This illustrates an important principle: the chemistry of a polymer not only determines its processing and performance characteristics, but can also influence the recycling technologies available for the material.
Circular economy requires more than one solution
A central message from the web seminar was that there is no single route towards a circular plastics economy.
Instead, different approaches will have to work alongside each other. Heiko Schenck discussed mechanical recycling, chemical recycling and continued virgin feedstock use, while also addressing opportunities for bio-based raw materials.
Mechanical recycling is already established for applications such as transport packaging. Chemical recycling offers additional possibilities, particularly when mechanical recycling reaches its limits. The web seminar also addressed the potential use of plant-based feedstocks, including agricultural residues, for polymer production.
Food packaging presents particular challenges. Even comparatively simple polymer structures can be contaminated by food, fats or other substances after use, making direct recycling back into food-contact applications more difficult.
A technical data sheet is not a specification
One of the most practical sections of the web web seminar focused on quality control and specifications.
Technical data sheets provide useful information about a polymer, such as density, melt flow rate and mechanical properties. However, the values stated are typically representative values rather than guaranteed values for every individual production lot.
Polymers naturally have production tolerances. For converters, it is therefore important to understand which parameters are critical for their particular production process and which variations can be tolerated.
Heiko Schenck recommended defining relevant specifications together with the supplier where necessary. This provides both sides with clearly defined operational ranges, which can help to prevent problems during production.
A particularly practical recommendation from the web seminar was:
Always keep retention samples of incoming raw materials.
In case of a quality issue or complaint, these samples can provide valuable evidence when identifying whether the cause originated in the supplied material or at another stage of the process.
Among the analytical methods discussed were melt flow measurements and thermal analysis using DSC. These can provide valuable information about viscosity, melting behaviour, glass transition and possible polymer contamination.
Why additives and masterbatches matter
Another important message was that a polymer on its own is often not sufficient to provide all the properties required by a packaging application.
Additives can be used to influence a wide range of characteristics, including:
- anti-block behaviour
- slip properties
- anti-fog performance
- ageing resistance
- UV stability and UV barrier
- antistatic properties
- colouring
- certain barrier properties.
Masterbatches make it possible to introduce active substances at manageable dosing rates and to achieve better distribution within the polymer. The web seminar also explained the difference between polymer blends and masterbatches: while blends combine polymers to modify material properties, masterbatches act as concentrates for pigments or other active substances.
The key takeaway: Know your polymer
The web seminar made it clear that polymer chemistry, film properties, processing, quality assurance and recyclability are closely interconnected.
Four practical messages stand out:
- Polymer properties vary within certain ranges. Understanding these variations is important for reliable processing.
- Chain length and crystallinity are key factors determining many polymer properties.
- Technical data sheets provide guidance, while specifications provide greater certainty for parameters critical to an individual production process.
- Circularity requires a combination of approaches, including material reduction, mechanical recycling and chemical recycling.
For anyone developing, producing, converting or using flexible packaging films, a solid understanding of the polymers involved therefore provides an essential foundation.
Plastics for packaging films – Basics for flexible packaging films, part A offered exactly this foundation and demonstrated how basic polymer knowledge can help professionals better understand material selection, processing behaviour, quality issues and future recycling options.
