Finnish researchers have developed a new process which means recycled paper and cardboard could soon be used as a raw material for developing biodegradable nonwovens. David Stevenson finds out more.
A new process that enables recycled paper and cardboard to be used as a raw material for biodegradable nonwovens has been developed by the VTT Technical Research Centre of Finland.
Hygiene and home care products, such as nappies, sanitary towels and cleaning cloths, are among the many items that can be manufactured from the biodegradable nonwovens, according to the researchers.
In general, nonwovens are essentially consumer goods that once used will end up in a landfill site along with other community waste. In metropolitan areas alone, an estimated 10,000 tonnes of nappies and sanitary towels are disposed of each year. The principle raw material in nonwovens manufacture is biologically non-degradable polyester. Up to now, market entry for bio-based nonwovens derived from wood has been stalled because of prohibitive production costs.
However, the innovative process from Finland, which is a combination of three different technologies, could change this. Firstly it converts the recycled paper or cardboard into dissolving pulp, then manufactures textile fibres by means of cellulose carbamate, and finally produces nonwovens through foam forming.
“In order to initially produce the dissolving pulp several process steps need to take place,” said research team leader Marjo Määttänen.
She told WTiN that firstly the cardboard is shredded. It is then subjected to a mechanical fractionation stage, which removes fine and inorganic materials. After this it undergoes alkaline delignification treatments to remove lignin, hemicelluloses, and Xylan. The resulting pulp is then bleached to improve its brightness, and then acid washed to remove metals from it.
Following this step turning the pulp into a nonwoven material begins with the carbamate process.
The dissolving pulp, which is virtually pure cellulose, is treated with urea, hydrogen peroxide and sodium hydroxide to produce cellulose carbamate. This process breaks down the cellulose so it can be spun into fibres through spinnerets, and was developed by VTT to be less environmentally harmful than the traditional viscose process, as it uses chemicals which are not as dangerous.
After these steps senior scientist Karita Kinnunen used a foam-forming technique to produce the biodegradable nonwoven sheets. Traditionally, the cellulose fibres would be transferred to a wire mesh mould in water suspension. However, the technique used by VTT researchers instead uses a wet foam consisting of water, foaming agents and about 60–70% air. The cellulose carbamate is mixed with the foam, poured into the mould and then allowed to settle, before the liquid is removed using a specially-designed suction table, and after this the sheet is left overnight to fully dry.
Ali Harlin, research professor at VTT, said: “Now for the first time we can make use of recycled paper and cardboard as a nonwovens raw material.
“The new process means that bio-based nonwovens are now more competitive on price in comparison with plastic-based products. The manufacturing costs of cardboard-based nonwovens are around 20% lower than for nonwovens produced from wood raw materials. New business opportunities should open up fairly rapidly, since the technology required for manufacturing nonwovens from recycled materials is already in place.”
He added that the initial technology behind the process had already been industrialised for the fibreglass industry, but the researchers extended this to create the new method, which took around 18 months to develop and test.
According to VTT, every year Europe alone generates around 60 million tonnes of recycled paper, of which cardboard makes up around 40%. The demand exists for new applications and technology for exploiting recycled paper due to the EU’s objective of raising the proportion of recycled paper to 70%.
Around 1.9 million tonnes of various types of nonwovens were manufactured in Europe in 2011. Strong growth in the global market for nonwovens is forecast to continue for the foreseeable future. Apart from hygiene, health and cleaning products, the nonwovens have further applications in, among others, the construction industry.
The method developed by the Finnish researchers could extend the future possibilities for re-use, particularly in the case of cardboard, which is more cost-effective as a raw material than fine paper. Additionally, it is anticipated that the forest industry will be among those likely to benefit from new business opportunities opened up by nonwovens based on recycled paper and cardboard.
Professor Harlin added: “So far we have received a lot of connections and contacts from companies that are in the field of hygiene products, napkins, and wipes. We also believe that the process could be used to create certain filters, due to that the quality if the fibre.
“We will also look at developing composites, but we haven’t researched this area enough to reach the highest possible mechanical standards. However, we have reached exceptionally high quality levels for various products using the biodegradable nonwovens.”