In the recent weeks we have seen some very interesting developments in packaging material based on wood fibres. Packaging material made from wood fibres belongs to the oldest packaging materials known to mankind.
From the whole range of wood-fibre based packaging material, cellulose film is the oldest transparent packaging product. It was first marketed in the USA in the 1920’s as cellophane. It was the most popular packaging film used until the 1960’s when polyolefin based products began to dominate the packaging market.
In the more environmentally-conscious marketplace of today, cellulose film is returning to popularity because it is on average 94% from renewable raw materials. Unlike the man-made polymers in plastics, which are largely derived from petroleum, cellulose films are manufactured from a natural polymer, cellulose, which is a component of plants and trees. The raw material for cellulose film that is used today is a renewable virgin wood-pulp, often sourced from plantations following sustainable forestry principles.
That’s all nothing new and even an old story, except that the keyword here is “virgin”. The recent developments I want to highlight today are all three not related to virgin wood fibres, but to the waste of the paper mills and forestry industry. In other words sourced from by-products such as wood fibres and tree oils and even cellulose sludge. All transformed into packaging material.
Wood-Based Clear Packaging Film
Aalto University and VTT Technical Research Centre, both from Finland, developed a wood-based material with properties like plastic, suitable to be used as packaging material. These include food packaging, where the material – nano-fibrillated cellulose film (NFC) – can help increase the shelf life of a product.
Nano-fibrillated cellulose typically binds high amounts of water and forms gels with only a few per cent dry matter content. This characteristic has been a bottleneck for manufacturing on an industrial-scale. In most cases, fibril cellulose films are manufactured through pressurised filtering but the gel-like nature of the material makes this route difficult. In addition, the wires and membranes used for filtering may leave a so-called “mark” on the film which has a negative impact on the evenness of the surface.
According to the method developed by VTT and Aalto University nano-fibrillated cellulose films are manufactured by evenly coating fibril cellulose on plastic films so that the spreading and adhesion on the surface of the plastic can be controlled. The films are dried in a controlled manner by using a range of existing techniques. Thanks to the management of spreading, adhesion and drying, the films do not shrink and are completely even.
The more fibrillated cellulose material is used, the more transparent a film can be manufactured.
To date, the researchers have piloted this technique using a scaled-down production model, which has generated a 2-3 metre NFC roll.
According to the press release the technique wouldn’t require packaging companies to install completely new technologies.
Wood fibre bioplastic packaging
It is generally estimated that 30-50% of all (petroleum based) plastics in Europe are used for packaging. As a result there is increasing pressure on the packaging industry to develop environmentally sustainable materials.
The use of by-products from the forest and paper-industry in food packaging is low-cost and can act as an alternative to petroleum resources.
Biodegradable plastic food packaging, made using up to 25% wood fibres, could soon be available, as a result of the EU-funded Bio-Based Composite Development project. The FORBIOPLAST project was set up to develop biodegradable food packaging using by-products from the forestry and paper-industry such as wood fibres and tree oils.
However, there is more development needed in relation to food packaging technology as there are still limitations with high pressure processing (HPP) and long storage. But in time the researchers believe this technology can replace the traditional retortable tray.
One product being tested is made using biodegradable polyactic acid (PLA) and 25% wood fibres. Tests are on-going to assess the migration qualities and safety of the material for use with food.
Tests have also been conducted with higher levels of wood fibres, but researchers found that “the result became too brittle”.
The project is also looking to develop an eco-friendly fish crate using polyurethane made with wood fibres and tall oil – tree oil obtained as a by-product of paper production.
Once research and development has been completed, the technology will be passed on to Hungarian and Romanian packaging companies.
Nano-fibres made of cellulose sludge
Researchers from Luleå University of Technology in Sweden have succeeded in recycling cellulose sludge for production of cellulose nano-fibres, and have now proven it to be an economic and environmental success.
A few years ago, cellulose industries in Sweden, disposed some of their waste as sludge into the ocean. It is now prohibited, and the sludge is stored in large tanks on land. This particular cellulose sludge makes it possible, to produce, so far, the most profitable production of cellulose nano-fibres from bio-residue products. The yield of the manufacture of cellulose nano-fibres from the sludge is 95%, compared with cellulose nano-fibre production from wood chips 48%, lignin residues 48%, carrot residues 20%, barley 14% and grass 13%.
For example, at one single cellulose manufacturer, Domsjö Fabrikerna in Sweden, a producer of special cellulose, which is used to in the manufacturing of viscose fibres, causes one thousand tons of sludge as a residue each year. In the current situation the sludge is not re-used.
Professor Kristiina Oksman explains: “The separation of cellulose nano-fibres from bio-residues is energy demanding but when we separate the waste from Domsjö, the energy consumption is lower. The special cellulose from Domsjö has a very small size and it also has high cellulose content and therefore the fibres do not need to be chemically pre-treated before the production of cellulose nano-fibres”.
Mehdi Joonobi, postdoc and Professor Kristiina Oksman at the Department of Engineering Sciences and Mathematics at LTU, who carried out the research, which is part of the Bio4Energy project, conclude that the outcome of the re-use of this sludge, can be, for example, create cheaper and more environmentally-friendly milk cartons and other paper and packaging products.
Cellulose nano-fibres, manufactured from this sludge, are probably shorter than the cellulose nano-fibres made from pulp but are finer and can form dense films with excellent barrier properties.
There are some more developments in wood-fibre based packaging material, but in other sectors than flexible film. I keep them for a next article.