The shift towards paper-based packaging solutions is more than just a design trend. It marks the beginning of a profound change along the entire value chain – from pulp production to the final packaging. It is becoming clear that the technological basis for these modern packaging solutions is closely linked to the pulp processes used. In particular, mechanical and thermomechanical processes are gaining in importance when it comes to the resource-efficient production of packaging pulp.
Pulp packaging is convincing on various levels: it is often based on recycled paper, is light, dimensionally stable and can be easily recycled in existing recycling loops. Modern processes such as thermoforming now make it possible to produce pulp packaging with precise contours and smooth surfaces – it is hardly distinguishable from plastic in terms of look and feel. Products such as meal trays made from bagasse (a fibrous residue produced when processing sugar cane), to-go boxes or technical packaging material for electronic devices prove how sustainability and functionality can go hand in hand.
Companies such as PAPACKS and NextGenPaper are driving the development of these solutions with innovative materials and new manufacturing processes. The market is responding accordingly – even big brands like Procter & Gamble are now turning to fibre-based packaging in combination with alternative raw materials such as cup plant fibres, which are obtained from a perennial, sunflower-like plant native to North America.
The technological basis: pulp from mechanical processing
However, this packaging involves a sophisticated manufacturing process. The selection and processing of the pulp plays a key role in this. For moulded pulp packaging, mechanically produced pulps are often used – in particular, wood pulp or TMP (thermomechanical pulp). These pulps contain all the lignin of the wood and thus provide a high fibre yield. Mechanical processes offer clear advantages, especially for packaging, where the ageing resistance of the material is less important than its formability and stability.
Another advantage is that mechanical processes require significantly fewer chemical additives, making the overall process more sustainable. They are also particularly suitable for processing recycled materials, which further reduces the carbon footprint.
Chemical or mechanical processes provide the pulp
In the production of pulp, wood is basically broken down into its component parts to expose the fibres for later paper production. Three methods are available for this: chemical, mechanical and semi-chemical processing. In the predominant sulphate process, the wood is digested with an alkaline cooking liquor. In a large digester, the wood is cooked at high temperatures and pressures with a liquor made from sodium sulfide and caustic soda. The chemical reaction causes the lignin to be released from the wood, while the cellulose fibres remain intact. The resulting black liquor is then burned, thereby recovering valuable energy – an important aspect for the energy efficiency of the process. The advantage of the sulphate process, also known as the ‘Kraft process’, lies in the high strength of the pulp and the broad raw material base – even resistant wood types can be processed with it.
In mechanical pulp production, the wood is defibrated purely mechanically in a refiner with the addition of water and heat. Although processes such as wood pulp or thermomechanical processing (TMP) require more energy, they deliver a higher fibre yield: mechanical pulps contain all the lignin, which reduces the resistance of the paper to ageing but makes them ideal for applications such as newsprint or cardboard. The disadvantage of mechanical processes is their extremely high energy consumption.
Precise measurement and control technology in the pulping plants, fibre material towers and pump systems ensure an energy-efficient process flow and optimal utilisation of the plants. It is particularly important to use technology that works reliably even with fluctuating material densities and abrasive media – a typical situation when processing waste paper or secondary raw materials.
