In the European Union alone, the baby diaper market was valued at around €4.45 billion in 2006, up from just under €3.7 billion in 1997, and the market is still growing. Producers have responded in recent years to demands from environmental groups and customers for a reduction in the weight in diapers and change in composition to make them more eco-friendly. The average diaper weighed 64.2 grams in 1987 compared with 40.4 grams in 2005. Fluff pulp content has fallen from 52.8 grams to 14.1 grams of the total, while superabsorbers have risen to more than 13 grams from 0.7 grams in the 1980s. Polypropylene nonwovens now represent seven grams of the total compared with 4.2 grams in 1987.

    While these developments have been welcomed in terms of performance, cost effectiveness and weight reduction, they mean that a major part of the production of a diaper is now based on fossil oil derivatives. However, as talk of climate change and landfill usage has entered the public domain, and as oil prices have fluctuated rapidly, there are now good reasons for wanting to reverse the balance. With this aim in mind, Swedish market pulp producer, Södra Cell and SCA Hygiene Products AB have joined forces with Chalmers University of Technology and Vinnova (the Swedish government agency for Innovation Systems).

    The result is a unique four-year project, WooDi, which will aim to find a way of reducing the amount of oil-based materials in the absorbent porous structure of a diaper by at least 50%, replacing it with wood-based ma­terials. If replacing the core of the product (the part that absorbs and retains liquid) proves successful, in the longer term, the team has a vision of a totally wood-based diaper.

    Heading up the project is SCA Hygiene Products’ Torgny Falk who explains that there can be no compromise when it comes to the performance of a wood-based alternative to the diaper’s superabsorbent materials. “It would be pointless to produce a diaper that has to be changed more frequently or weighs more. That would mean using more materials rather than less, higher transportation costs and so on. Our aim is to increase sustainability while retaining the same performance we have today.”

    Work began in April 2008 and the project is divided into six parts with four PhD students from Chalmers dedicated to the research. Backup and expertise are coming from both SCA and Södra Cell. Three of these subprojects are focused on fiber modification and fiber bonding technology development. One is dedicated to creating and evaluating fiber network structures, while another subproject will focus on environmental and sustainability aspects.

    In addition, another subproject within WooDi deals with production aspects.

    Caroline Löfgren, Södra Cell’s coordinator for the project, said the aim is to ensure that any ideas that come to fruition could be replicated on a commercial scale and not just in the lab. To this end, in a new way of working, Södra Cell, SCA and Chalmers will organize a production forum and workshops twice a year to bring together their researchers, process engineers and other specialists to discuss and work with production aspects. Ms. Löfgren is based at Södra’s R&D center in Värö, some 60 km south of Gothenberg, within easy reach of Falk who is located in the city.

    “SCA has an in-depth knowledge of the product itself, while Södra Cell has great expertise in fiber and cellulose,” Mr. Falk said. “We also have people who can contribute to this and Chalmers has a dedicated forestry department. So while we have different skills and different areas of specialization, this is one project with a common goal and Södra and SCA are both involved in the whole project. We want to cooperate with and learn from each other as much as we can, to go beyond what we have done before.”

    The project is partly financed by the Swedish government agency Vin­nova, which has contributed €2 million in industry research money.

    SCA and Södra Cell are contributing the re­maining amount of about €1.5 million.

    Nine months into the project, Falk explains the major challenges are increasing the absorption capacity of wood fibers and their absorption retention, while retaining cost effectiveness. “Improving the retention pro­perties of wood fibers so they can lock urine in more effectively will certainly be a challenge,” he says. “Superabsorbent materials have much better retention than wood fibers, which means they can be saturated without releasing fluid when put under pressure, for example. If you exert any pressure on wet pulp, it caves in. Absorption per cubic centimeter is currently much better in superabsorbent particles so we will be working with Södra Cell and Chal­mers to see how we can make pulp structures better in this respect.”

    Ms. Löfgren added, “We want to see if we can control the stiffness of the fibers and select the right kind of fibers, so we could tailor- make a fiber network for the absorption core.”

    “For now,” Falk said, “we are only focusing on the absorbent core and excluding components such as the shell, elastic binding and fastening system. If we get this stage right, those could be next.”