A NEW RECYCLING PROCESS FOR WASTE PANELS
George Mantanis1, Eleftheria Athanassiadou2, João Manuel Aires Coutinho3 and
1 Dept. of Wood & Furniture Technology and Design, TEI Larissas, Greece
2 CHIMAR HELLAS S.A., Thessaloniki, Greece
3 AIRES COUTINHO R&D Ltd., Caldas da Rainha, Portugal
At the end of their service life, wood-based panels become eventually waste wood.
Deploying in landfills is no longer considered as an acceptable solution for their handling
due to the high organic load included. The recycling of this waste to be employed as raw
material for the wood panel industry, which traditionally makes use of wood processing
residues, has hence gained more importance and been examined from earlier times.
Technical problems and the lack of enforcing legislative regulations have delayed, however,
the industrial implementation of the new technologies proposed. Recent research efforts
enabled the development of a new process for the recycling of end-use wood panels into new
marketable fibreboards. This patent pending process is based on the refiner technique and
allows the use of mixtures of fresh wood and waste panel chips as a raw material for dry-
process fibreboard production. The process is applicable in existing fibreboard plants with
only minor operation modifications and therefore, there is no need of major capital
investment in additional equipment to effect the recycling. At the refining stage, chemical
agents are employed and the process enables the use of significant amounts of waste
material replacing over 20% of the wood feed and providing significant savings. The aim of
the present work was to validate the industrial applicability of the new process in the
recycling of waste medium-density fibreboards. The new fibreboards obtained during the
industrial scale tests were of acceptable quality, and the testing results revealed that under
conventional gluing and pressing conditions, the process effectively recycles the waste
boards into new ones at least at 25% wood substitution level. Further validation and
optimisation work is underway in the direction of using other waste panel types and also
increasing the level of waste in the feed material.
The composite wood panels industry is mainly a worldwide creation of the past century. The pace of
development has been rapid and a continued high development is also expected for this century.
Technological breakthroughs with new processing machines, quality control devices, higher quality
1 To whom correspondence should be addressed.
adhesives and use of other lignocellulosic materials than wood as a raw material will possibly play an
important role in the future of this industry.
In Europe, particleboards and medium density fibreboards (MDF) became the backbone of furniture
and displaced to a very high extent solid wood from this area. Therefore, it was logical that the
development of the furniture industry has been dramatically influenced by that of the fibre- and
Pieces of furniture have a life span of 30 to 40 years in Europe. According to environmental
regulations in certain European countries (e.g. Germany), deploying of used furniture on landfills will
be forbidden by the beginning of 2005, as the interaction between organic materials and the
environment is of a very complex nature. Leached chemicals may influence the groundwater, and
moreover, biological degradation leads to the formation of methane, which contributes to the Green-
House-Effect about 80 times more than carbon dioxide. Figure 1 summarises the reasons against
dumping of organic waste materials.
Due to the above-mentioned reasons, increasing attention has been given to the issue of recycling in
the fibre- and particleboard industry. Many methods have been developed for the recycling of
composite wood panels and wood derived products [1-9]. They are based on the mechanical or
hydrothermal treatment of the wastes or their combination to recover wood elements mostly suitable
for the production of particleboards. They also require special equipment for the treatment of the
waste, which in most cases is of high cost and unconventional to standard board manufacturing
processes. Also processes have been developed for the recycling of wood wastes and are presently
used with satisfactory results [10-11].
However, in the medium-density-fibreboard (MDF) industry today, it appears that technically only
limited amounts of waste fibreboard can be re-used in the production (2-3%), without a drop in the
press speed. In the market it is apparent the need for a new process that could recycle efficiently
waste wood materials at high levels to produce MDF. This, eventually, would allow significant
savings in raw materials for an MDF mill, apart from the environmental benefits.
1. Conventionally increasing costs of landfilling due to reduced landfill capacity
2. Legislative measures prohibiting the dumping of organic matter
3. Generation of methane and carbon dioxide in dumps, which can be considered as anaerobic
reactors. Methane contributes to the green house effect eighty times more than carbon
dioxide (1t CH4 equivalent to 88t CO2 in global warming of the atmosphere)
4. Polluted leaching water from dumps may penetrate in the earth crust and contaminate
surface and underground water
5. In the dumps energy content of wood and wood-based panels is wasted and no utilization is
made of the organic biomass
Figure 1 Reasons against deploying organic materials on landfills.
Purpose of Work
The purpose of this work was therefore to scale-up an innovative process - which is patent protected
 - that would enable substitution of fresh wood feed with waste wood materials at high levels
(>20%) without a reduction in MDF plant productivity. This paper presents the preliminary results
obtained from the industrial trials performed using this new process. The industrial trials were carried
out at the facilities of the MDF mill VALBOPAN Fibras de Madeira SA, in Portugal.
Materials and Methods
Pine wood free of bark was used in the trials. Waste boards consisted of fibreboard production
residues of four different grades: (a) standard MDF, (b) moisture resistant MDF, (c) colour
impregnated MDF and d) hardboard. A brief description of the trials is given below:
Hammermilling/Mixing: The waste MDF boards were first hammermilled in a conventional way. In
the wood yard, chips of fresh wood and waste MDF were mixed at a ratio 3:1 (on a volume basis) by
Screening/Washing: Metal items were removed using a metal detector (magnet). All materials were
passed through a screener, where part of the dust was removed, and were then soaked in water and
Digesting/Refining/Gluing: The overall digestion time was kept constant at ca. 3½ min. The refining
conditions were the same as the typical ones used in MDF mills. The pressure used was 8.2 bar.
Average fibre throughput was ca. 5.0 t/h. A urea-formaldehyde (UF) resin of E2 type was applied in
the blowline. The resin hardener was ammonium sulphate (0.85% w/w on dry resin), while the resin
addition level was kept constant at 10% w/w (on dry fibre). A crosslinking agent (additive A) was
added in the glue mix (at levels 0%, 5% and 10% w/w). A wax emulsion was added at 1% w/w level
based on dry fibre. Another key chemical agent (additive B) was added in the system allowing the
efficient processing of both fresh wood and waste board materials. The dosing of this agent was
constant at the level of 1% w/w on wood fibre (on a dry/dry basis).
Drying/Pressing: Drying was done conventionally with a tube dryer; the dryer temperatures at both
the dryer entrance and exit were rather low. The fibre exited the dryer having a moisture content of
8.0-8.5%. The press time in the two single-opening presses was 16sec/mm thickness. Boards of
16mm thickness were produced. Random samples of MDF boards produced during the trials were
evaluated for density, mechanical properties (IB, MOR) and 24-hour swelling. Board testing was
done at the lab facilities of CHIMAR HELLAS S.A. (former Adhesives Research Institute (ARI)
Ltd.) in order to evaluate the efficiency of the new technology and board performance under different
The experimental plan of the trials is shown in Table 1.
Table 1 Experimental plan of the industrial trials performed.
Run Raw materials
(wood : waste) Additive A
(%) Additive B
0 100:0 0 0
1 75:25 0 1
2 75:25 5 1
3 75:25 10 1
Results and Discussion
Table 2 presents the results from the testing of the properties of the MDF boards produced in the
industrial trials. The internal bond (IB) strength of the control boards was high at 1.02 N/mm². With
the use of 25% waste boards, the IB dropped significantly down to 0.60 N/mm² (run 1). However, at
the subsequent runs (runs 2 & 3) when the additive A was introduced into the system, the IB
improved dramatically. When additive A was used at 10% level, this property was almost completely
recovered. Quite similar behaviour was observed with the modulus of elasticity (MOR) values of the
boards. Surprisingly, the swell properties, apparently, improved also when waste boards were used as
feedstock; finally, the boards from the runs 2 and 3 gave significantly better swelling values.
In overall, it can be observed that even at the 25% substitution level of wood - and without a change
in the press cycle and productivity – the new process can result in ‘recycled’ MDF boards with
properties which far fulfil the European standards. It should also be mentioned that the formaldehyde
emission of the MDF decreased with the addition of the waste (the boards fit in the E2 formaldehyde
emission class (perforator class) since a UF resin of the E2 type was applied).
Table 2 Properties of industrial MDF produced by recycling.
N/mm2 24h swelling
0 755 1.02 36.5 8.0 E2
1 747 0.60 32.4 8.2 E2
2 752 0.72 36.0 7.2 E2
3 745 0.98 37.8 7.0 E2
The results obtained from these trials are very promising in the sense that it was possible, for the first
time, to recycle in an efficient way high amounts of waste MDF originating from the plant’s own
production (or from end users) without a deterioration in physical properties and without any loss in
the plant productivity.
In conclusion, the new process appears to be well operational in MDF mills employing single-
opening presses for E2 class MDF products without any technical risk.
Nonetheless, it should be stressed that the above-mentioned results have come out at the completion
of the optimisation phase of the new process. Presently, the emphasis is being shifted towards the
implementation and adaptation of the process in modern MDF plants employing E1 resin systems and
continuous press technology. Preliminary results have been very encouraging in that respect.
Notably, another main target is to use as starting materials, not only waste raw MDF, but also
laminated and/or veneered MDF or particleboard (already tested with satisfactory results).
The authors would like to thank Mrs. Alexandra Gouveia, production manager of VALBOPAN,
whose technical assistance was valuable and is highly appreciated.
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