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A NEW RECYCLING PROCESS FOR WASTE PANELS

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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.
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A NEW RECYCLING PROCESS FOR WASTE PANELS
George Mantanis1, Eleftheria Athanassiadou2, João Manuel Aires Coutinho3 and
Panagiotis Nakos2
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
Abstract
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.
Introduction
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
particleboard industry.
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
[12] - 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
a bulldozer.
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
washed.
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
conditions.
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.
Run Density
kg/m3 IB
N/mm2 MOR
N/mm2 24h swelling
% Perforator
class
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
Conclusions
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).
Acknowledgements
The authors would like to thank Mrs. Alexandra Gouveia, production manager of VALBOPAN,
whose technical assistance was valuable and is highly appreciated.
References
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fuer die Anwendung im Moebel- oder Innenausbau, in der Verpackungsmittelherstellung, in der
Holzwarenherstellung oder im Hochbau mit einer Wanddicke zwischen 2mm und 1000mm und
Verfahren zu seiner Herstellung, German Patent no. DE 4201201.
2. 1992. Verfahren zum Recycling von Holzwerkstoffen, German Patent no. DE 4224629.
3. Roffael, E., Dix, B., 1994. Waste liquor derived from chemical thermal pulping of particleboards
and fibreboards containing bonding agents, U.S. Patent no. 5,705,542.
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thermohydrolytischen Spaltung – Die kontinuierliche Prozesstechnologie, Proceedings of the 2nd
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Proceedings of the 6th European Panel Products Symposium, Llandudno, Wales, United
Kingdom, BioComposites Centre, ISBN 1 84220 040 2, pp. 159-166.
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relative forming machine employing the device, International patent application, WO 98/40173.
11. Olofsson, T., 1999. Refining Technology for Low Grade Materials including Urban Wood
Waste, Proceedings of the 3rd European Panel Products Symposium, Llandudno, Wales, United
Kingdom, BioComposites Centre, pp. 155-163.
12. Nakos, P., Athanassiadou, E., Aires Coutinho, J.M., 2000. Production of High Added Value
Products from Wastes, International patent application, WO 01/39946.
... Most of the methods studied in latest researches on recycling of wood panels are based on hydrothermal treatment. Usually, recycled fibers lose their quality as a result of these methods (Dix et al. 2001a, b;Michanickl and Boehme 2003;Mantanis et al. 2004;Lykidis and Grigoriou 2008;Roffael et al. 2009;Nicewicz and Danecki 2010). When recycling MDF wastes by hydrothermal methods, first fibers are heated using steam treatment (hydrothermal) and then they are separated by utilization of refiner (Mantanis et al. 2004). ...
... Usually, recycled fibers lose their quality as a result of these methods (Dix et al. 2001a, b;Michanickl and Boehme 2003;Mantanis et al. 2004;Lykidis and Grigoriou 2008;Roffael et al. 2009;Nicewicz and Danecki 2010). When recycling MDF wastes by hydrothermal methods, first fibers are heated using steam treatment (hydrothermal) and then they are separated by utilization of refiner (Mantanis et al. 2004). Continuous heating at high temperatures and mechanical defibrillation cause fiber degeneration and destruction of lignocellulosic mass as well as degradation of wood polymers and decreased efficiency. ...
... The decrease in formaldehyde emission from recycled MDF panels may be due to the existence of UF resin residues (mostly urea, due to the volatility of formaldehyde) on the surface of the recycled fibers which act as scavenger (Athanassiadou et al. 2005;Roffael et al. 2009). Similar results were reported in previous studies (Mantanis et al. 2004;Lykidis and Grigoriou 2008;Dix et al. 2001b;Athanasiadou et al. 2005). Additionally, the presence of UF resin on the surface of recycled fibers can be confirmed by the results of total composition percentage previously shown in Table 4. ...
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In this study, the performance of the electrical method in MDF wastes recycling was determined. For investigating the practical aspect of the electrical method, the hydrothermal method as a known recycling method was studied too. The recycling process by electrical method conducted for two different time durations (2 and 4 min) at a temperature of 100 °C and recycling using the hydrothermal method was done at a temperature of 105 °C for 150 min under 4 bar pressure with subsequent refining step. Recycled fibers were analyzed by determination of the chemical composition of fibers and fiber classification. After that, laboratory MDF boards with dimensions of 35 × 35 × 12 mm³ and density of 0.7 g/cm³ were manufactured. Practical properties of MDF boards including thickness swelling, modulus of rupture, modulus of elasticity and internal bonding were studied according to EN standard. Formaldehyde emission of boards was measured using the desiccator method. The results showed that some changes in the chemical composition of recycled fibers had occurred as compared to the original fibers, especially for the hydrothermal method where lignin content was significantly reduced. Fiber classification test showed significant reduction in the length of the fibers recycled by hydrothermal method as compared to other fibers. Investigations of the quality of manufactured MDF boards showed that the electrical method performed better in comparison with the hydrothermal method. The results of this study confirmed the positive effect of recycled fibers on reducing the formaldehyde emission from MDF boards which can be considered as an excellent benefit for the recycling process due to the importance of environmental and human health issues.
... Fibres contained in the waste particles can be recycled using microwave technology (Harrison, 2012). In addition, end-use wood panels can also be reused in the manufacture of MDF (Mantanis et al., 2004). In a study in an industrial zone comprising SMEs, 27% of all wastes, including glass, metal, and wood, were shown to be re-used in manufacturing industries. ...
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Despite the continuous introduction of new materials and technologies in the production of wood-based composites, hardboards (HB), remain in the range of wood products, due to their good consumer and exploitation properties. The production of these products is characterized by the intensive consumption of raw materials. In the wet production process, much of the raw material used is taken up by water involved in the formation of the wood-fibre mat. It forms a significant share in the value of the finished product, resulting in a smaller added value. At present, the utilization of wastewater from the production of the HB is unsatisfactory. Its high fibre content creates sludges that can be recycled or thermally utilized. The present study is aimed at reviewing the possible methods of utilizing the wastewater and fibre sludge in it. This will provide the Bulgarian producers with a means of enhancing production efficiency and applying the circular economy principles.
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The enhanced technological possibilities to utilise wood waste and residues in the production of wood-based panels can help towards the transition to a circular, low-carbon bioeconomy. The cascading use of wood resources, defined as “the efficient utilisation of resources by using residues and recycled materials for material use to extend total biomass availability within a given system” is one of the leading principles for achieving this goal. The wood-based panel industry is characterised by significant amounts of waste and residues that present a great volume potential for cascading. The aim of the present study is to define the basic guidelines for cascading use of wood waste from the production of wood-based panels and analyse the economic impact in terms of economic efficiency in line with the circular and bioeconomy principles. Time series analysis of wood waste and raw material flows in the Republic of Bulgaria, economic assessment of the current utilisation of wood waste in the wood-based panel industry along with comparative analysis of the potential utilization methods have been presented. The existing technical and market barriers to the cascading use of wood have also been discussed.
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Annually, a large volume of medium density fiber board (MDF) wastes are generated which consists of used furniture and other constructed items, the parts obtained from trimming and edge cutting of boards in MDF producer factories and cutting of boards during conversion processes. In this study, changes in the chemical properties of wood fibers after hydrothermal recycling of MDF wastes as an important aspect of recycling process which may be effective on quality of recycled MDF boards was investigated. Hydrothermal recycling was done at 3 different temperature (105, 125 and 150 °C) in which subsequently defibrillation step was performed. Recycled fibers were analyzed by determination of chemical composition of fibers, pH value and possible existence of UF resin residues on the surface of recycled fibers. Gel time of UF resin in the mixture of fibers was measured. Additionally, laboratory MDF boards with dimension of 35 × 35 × 12 mm and density of 0.7 g/cm³ were manufactured. Practical properties of MDF boards were studied according to EN standard. Significant quality fall off was observed in recycled MDF boards as compared to original ones. Also, the results showed that some chemical changes were occurred in fibers after recycling process which may be effective on properties of new (recycled) MDF boards. FT-IR results confirmed the presence of UF resin residues on the surface of recycled fibers which considered as reason for deterioration in properties of recycled MDF boards. Also, the results obtained from gel time measurements confirmed the negative effect of recycled fibers on the curing of UF resin.
Stoffliche Verwertung von Holzwerkstoffen
  • E Roffael
Roffael, E., 1997. Stoffliche Verwertung von Holzwerkstoffen, Adhäsion 41, pp. 24-27.
Wood Panel Recycling: An Introduction to the Fibresolve Process
  • S Riddiough
Riddiough, S., 2002. Wood Panel Recycling: An Introduction to the Fibresolve Process, Proceedings of the 6th European Panel Products Symposium, Llandudno, Wales, United Kingdom, BioComposites Centre, ISBN 1 84220 040 2, pp. 159-166.
Erfahrungen der Industrie mit dem WKI-Verfahren zum Recycling von Holzwerkstoffen
  • C Boehme
  • B Wittke
Boehme, C., Wittke, B., 2002. Erfahrungen der Industrie mit dem WKI-Verfahren zum Recycling von Holzwerkstoffen, Proceedings of the 2nd Conference on Environmental Protection in the Wood Industry (Umweltschutz in der Holzwerkstoffindustrie), 21-22 March 2002, Goettingen, Germany, University of Goettingen, pp. 44-49.
Roller device to separate chips and particles of different gradings, and the relative forming machine employing the device, International patent application, WO 98/40173. r11 Refining Technology for Low Grade Materials including Urban Wood Waste Production of High Added Value Products from Wastes
  • R Paladin
  • T Olofsson
Paladin, R., 1998. Roller device to separate chips and particles of different gradings, and the relative forming machine employing the device, International patent application, WO 98/40173. r11. Olofsson, T., 1999. Refining Technology for Low Grade Materials including Urban Wood Waste, Proceedings of the 3rd European Panel Products Symposium, Llandudno, Wales, United Kingdom, BioComposites Centre, pp. 155-163. 12. Nakos, P., Athanassiadou, E., Aires Coutinho, J.M., 2000. Production of High Added Value Products from Wastes, International patent application, WO 01/39946.
Recycling von Holzwerkstoffen durch das Verfahren der thermohydrolytischen Spaltung – Die kontinuierliche Prozesstechnologie
  • R Kirchner
  • A Kharazipour
Kirchner, R., Kharazipour, A. 2002. Recycling von Holzwerkstoffen durch das Verfahren der thermohydrolytischen Spaltung – Die kontinuierliche Prozesstechnologie, Proceedings of the 2nd Conference on Environmental Protection in the Wood Industry (Umweltschutz in der Holzwerkstoffindustrie), 21-22 March 2002, Goettingen, Germany, University of Goettingen, pp. 72-81.
Ebenes oder gekruemmtes Halbzeug oder Fertigprodukt aus Holzwerkstoff fuer die Anwendung im Moebel-oder Innenausbau, in der Verpackungsmittelherstellung
  • A Moeller
Moeller, A., 1992. Ebenes oder gekruemmtes Halbzeug oder Fertigprodukt aus Holzwerkstoff fuer die Anwendung im Moebel-oder Innenausbau, in der Verpackungsmittelherstellung, in der Holzwarenherstellung oder im Hochbau mit einer Wanddicke zwischen 2mm und 1000mm und Verfahren zu seiner Herstellung, German Patent no. DE 4201201.
Roller device to separate chips and particles of different gradings, and the relative forming machine employing the device, International patent application
  • R Paladin
Paladin, R., 1998. Roller device to separate chips and particles of different gradings, and the relative forming machine employing the device, International patent application, WO 98/40173.
Waste liquor derived from chemical thermal pulping of particleboards and fibreboards containing bonding agents
  • E Roffael
  • B Dix
Roffael, E., Dix, B., 1994. Waste liquor derived from chemical thermal pulping of particleboards and fibreboards containing bonding agents, U.S. Patent no. 5,705,542.
Production of High Added Value Products from Wastes, International patent application
  • P Nakos
  • E Athanassiadou
  • J M Aires Coutinho
Nakos, P., Athanassiadou, E., Aires Coutinho, J.M., 2000. Production of High Added Value Products from Wastes, International patent application, WO 01/39946.