QLK5-1999-01221 High added-value composite panels through recycling of waste lignocellulosic materials

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Biocomposites/Boards : Paper/Pulp : Quality of Life - 5.3.2 The Forestry-Wood Chain

Contract No:	QLK5-1999-01221
Source:	Final Report

Final Report - Summary
March 2003

Nowadays, as much as 90 % (or more) of all furniture made in Europe is based on wood-based panels, especially on particleboards and medium density fibreboards (MDF). According to environmental regulations in some European countries disposal of used furniture in landfills will be (or is already) forbidden by the beginning of 2005. Leached binders from wood-based panels may contaminate underground water, biological degradation leads to the formation of methane which contributes to the "Green-House-Effect" about 30 times more than carbon dioxide.

Due to environmental aspects, increasing attention has been given to the issue of recycling in the particleboard and fibreboard industry. Many methods have been developed for recycling of particleboards. In Germany, the thermo-hydrolytic pulping of mechanically disintegrated chipboards has attracted industrial interest. Industrial scale trials have proved the suitability of the thermo-hydrolytic degradation methods as a raw material for particleboard manufacture. However, no experience in the industrial scale has been gained on the use of recycled fibres as a raw material for the production of MDF. Not only particle- and fibreboards can be recycled to wood-based panels, but also waste paper can be used as a raw material for making medium density fibreboards (MDF). Thermo-mechanical fibres can be substituted partially by waste paper for the production of MDF.

The aim of the project was the development of a new recycling technology for the processing of waste composite panels (particleboard, medium density fibreboards) and waste low-grade paper, either alone or in mixture, to obtain fibres suitable for the production of MDF. The technology is based on application of the twin-screw extruder technology and also targeted at reactivating the aminoplastic resin used for the bonding of waste panels, so as to enable reduction of the resin level needed to rebond the fibres obtained through recycling.

The material to be extruded during the extruder process is subjected to thermohydroiysis under the action of high shear. Due to such shear action the material is defibrated and the morphological structure of the lignocellulosics is disrupted.

In the first part of the work, samples of industrially produced waste uncoated UF-bonded particleboards (PB) and UF-bonded medium density fibreboards (MDF), pine wood and different kinds of waste low-grade paper (mixed waste paper, mixed news print, corrugated waste paper) were collected from the trade market. The samples (PB, MDF, pine wood, waste low-grade papers) were each defibrated in the twin-screw extruder, in addition mixtures of the samples were also treated in the same way. Different twin-screw extruder profiles (added devices, added chemicals, speed of the screws, temperature profiles) were tested in order to find optimal extruding conditions and to obtain the best quality of extruded fibres.

Besides the extruder technology fibres from waste PB, waste MDF and pine wood were produced using the conventional refiner technology (IMP-Process). In another set of experiments mixtures of waste PB, waste MDF, waste low-grade paper and pine wood were also pulped using the TMP-Process.

The extruded and refined fibres were characterised chemically. Extruded fibres obtained from waste PB and waste MDF only showed a negligible decrease in the nitrogen content compared to the original raw material. The nitrogen content of the refined fibres produced from waste MDF decreased in comparison to the original waste MDF, indicating a degradation of resin when using the refiner technique. Compared to the extruder technique it seems that the refiner technique is a relatively harsh treatment leading to more degradation in the resin. Moreover, refined fibres from waste PB and waste MDF showed mostly lower formaldehyde emission than extruded fibres. Furthermore, the extruded fibres from waste low-grade paper were analysed and evaluated for their mechanical properties. From the results it becomes obvious that mixed news print and mixed waste paper need to be pre-treated prior to extrusion to remove impurities like fillers and dirt, whereas corrugated waste paper can be extruded directly without any pre-treatment. Generally, extrusion of waste low-grade paper leads to a shortening in the fibre length.

Representative samples of extruded and refined fibres were used for the production of MDF in laboratory-scale. The results reveal that MDF produced at lab-scale from extruded pine wood fibres showed better performance than those from refined pine wood fibres. No significant differences could be observed in the mechanical properties of MDF produced with extruded fibres from different waste composites (PB, MDF). Selective previous trials with extruded fibres were repeated to double-check the quality of the extruded fibres. The board testing results were also good. Moreover, the results reveal that there were more or less no differences in the physical-mechanical properties of the following products:

• MDF, made from blow line resinated fresh pine fibres,
• MDF made from mixtures of blow line resinated fresh fibres and waste MDF vfibres,
• MDF made from blow line resinated refined fresh fibres and unglued refined waste MDF fibres.

Production of extruded fibres from waste MDF in pilot-scale was done in order to produce large amount of recycled fibres that could be used for partial substitution of virgin fibres in the manufacturing of MDF in industrial scale. Two types of waste MDF were tested for production of extruded fibres in pilot-scale: MDF with low (8%) and high resin content (18%). During work to optimise the extruding process it was found that waste MDF with high resin content are more difficult to handle and extrude in comparison to boards containing low resin content. Waste MDF with high resin content had to be hammer-milled before extrusion, after hammer-milling the material looked like flakes and showed a great proportion of fibre clusters under the microscope. The majority of the fibres were still agglomerated due to the presence of the resin. Waste MDF with low resin content can be extruded without any previous hammer-milling. After extrusion the granulometric distribution of fibres obtained from not hammer-milled waste MDF (low resin content) and hammer-milled waste MDF (high resin content) was more or less equal. Thus, for the production of extruded fibres in pilot-scale waste MDF with low resin content were used (1550 kg).

Production of MDF in industrial-scale with extruded fibres was done in a MDFplant. As there was a limited amount of extruded fibres a substitution level of 15 % 85 was chosen to work with. Moreover, it was agreed to keep the binder level, the level of adding hardener and paraffin constant as they are usually used in the MDF-plant. Also the pressing parameters were kept unchanged. Before starting the trial MDF with 100 % glued virgin fibres as a reference were produced. During the trial the unglued extruded fibres were mixed thoroughly with the glued virgin fibres. The mixing ratio was 85% glued virgin fibres and 15% unglued extruded fibres.

After the industrial trial the industrially produced MDF were tested regarding their mechanical-technical properties, surface properties and formaldehyde emission. The board properties were in full conformity with the properties obtained from MDF in laboratory-scale trials. Deterioration in the thickness swelling properties of the MDF not occurred due to the use of extruded fibres. MDF made by partial using of recycled fibres from waste MDF showed similar mechanical-technological properties to MDF made from virgin fibres only. Deterioration of surface quality could not be observed. The formaldehyde emission behaviour of MDF with extruded fibres was even better than boards with virgin fibres.

Conclusions

In summary, it can be concluded that adding recycled fibres in the amounts mentioned in the report has no negative impact on the properties of the boards, as evaluated by the common techniques used in the wood-based panels industry. Thus, extruded fibres from waste MDF can be taken as a raw material for partial substituvon of virgin fibres in making new MDF. The results of the industrial trials were more promising than expected as they also showed that using recycled fibres may lead to less consumption of resin due to the activation of inherent resin in the boards. This means positive effects on the economy of the process through saving resin. Factories using this technique can be confident, that using the recycling fibres as a partial substitute of virgin fibres would lead to any change in the technology.

In conclusion - the complete objective of the research work has been achieved