Chemische Eigenschaften von TMP und CTMP, hergestellt aus Kiefernholz und UF-Harz-gebundenen mitteldichten Faserplatten (MDF)

Thermo-mechanical (TMP) and chemo-thermo-mechanical pulps (CTMP) were prepared from pine wood and from UF-bonded MDF made from pine wood. For preparing TMP pine chips as well as UF-bonded MDF were digested under pressure at 170 °C. Thereafter, the digested chips and MDF were defibrated at 170 °C using a single disc refiner. CTMP was prepared from pine wood with 0.25% NaOH (based on dry wood) under the conditions set forth above. CTMP was also made from MDF under two conditions using 0.15% sodium hydroxide (% based on dry MDF) and a mixture of sodium sulphite (1%) and sodium hydroxide (0.25%). The pulps show distinct differences in their properties: TMP from UF-bonded MDF shows lower extractive content in cold and hot water, lower pH-value and higher buffering capacity towards alkali of the cold water extractives than the CTMP counterpart. Moreover, CTMP prepared by using sodium hydroxide alone as a pulping agent increases the content of formate and acetate ions in the cold water extractives. The use of a mixture of sodium sulfite and sodium hydroxide as a pulping agent decreases, however, significantly the content of formate and acetate ions in the cold water extractives. This may be due to the buffering action of sodium sulfite. In general, CTMP decreases the formaldehyde release of the fibres, as measured by the flask method. In presence of sodium sulfite as a pulping agent for recycled MDF, the formaldehyde release is slashed to almost 30% of its original value. The formaldehyde release of CTMP from UF-bonded boards seems to be in the same range as that of TMP from virgin wood.      

Über die Eignung von thermo-mechanischem (TMP) und chemo-thermomechanischem (CTMP) Holzstoff aus Buchen- und Kiefernholz für die Herstellung von mitteldichten Faserplatten (MDF)

Medium density fibreboards (MDF) were made from thermomechanical (TMP) and chemo-thermo-mechanical pulps (CTMP) derived from pine wood. As a binder a melamine reinforced urea formaldehyde resin (UF-resin) and diisocyanate polymers (PMDI) were applied. The mechanical-technical properties of the boards as well as some of their chemical properties were evaluated. The results of the investigation led to the following conclusions: MDF from CTMP showed in general higher mechanical properties (bending strength) compared to MDF from TMP. Moreover, the formaldehyde release of the CTMP-boards was lower. This may be due to the formaldehyde scavenging properties of the used pulping chemicals during the process of CTMP. MDF from CTMP showed much higher release of acetic acid compared to MDF from TMP. This is likely to higher deacetylation of the wood substance during CTMP process compared to the TMP technique.     

Zum Einfluss des Holzes sowie des Holzaufschlussverfahrens auf das Benetzungsverhalten von Kiefern- und Fichten-Faserstoffen

The main objective of this research work was to study the wettability of thermomechanical pulps (TMP) prepared from heart- and sapwood of Scots pine (Pinus sylvestris [L.]). The TMP were prepared at different pulping temperatures (150 °C, 180 °C). Furthermore, thermomechanical (TMP) and chemo-thermomechanical pulps (CTMP) from Norway spruce (Picea abies [Karst.]) were also investigated. In this case both TMP and CTMP were prepared at 140 °C and 180 °C. Sheets of all pulps were prepared according to a method developed by Roffael et al. (2002). Sheets of TMP pulps from pine sapwood showed much better wettability compared with their counterparts from heartwoods. Pulps from heartwood experienced a dramatic decrease in their wettability when increasing the pulping temperature from 150 °C to 180 °C. In contrast increasing the temperature from 150° to 180 °C seems to have no deleterious effect on the wettability of pulps prepared from sapwood. This phenomenon has been explained by the higher extractive content in pine wood. Comparing TMP and CTMP pulps from Norway spruce leads to the result that in general CTMP pulps are of higher wettability. This can be attributed to the high hydrophobic extractive content in TMP pulps on the one hand and to the higher alkalinity of CTMP pulps on the other hand.     

Über die Eignung von thermo-mechanischem und chemo-thermo-mechanischem Holzstoff (TMP und CTMP) aus Buchen- und Kiefernholz für die Herstellung von mitteldichten Faserplatten (MDF)

Medium density fibreboards (MDF) were made from beech in laboratory and pilot plant scale from thermo-mechanical (TMP) and chemo-thermo-mechanical pulps (CTMP) using both melamine reinforced urea-formaldehyde resin (UF-resin) and diphenylmethane diisocyanate polymers (PMDI). The physicalmechanical and chemical properties of the boards were evaluated. From the results the following conclusions can be drawn:

1. Both TMP and CTMP led, on using UF-resin, to MDF with very high mechanical properties exceeding the required values in European standards.
2. Pulping temperature seems to have an influence on the mechanical properties of the boards, prepared from TMP and CTMP. Increasing the pulping temperature from 150°C to 170°C negatively affects the mechanical board properties, whereas the properties of MDF from CTMP (sulfonic group content between 0.2% and 0.3%) increases by elevating the maximum pulping temperature from 150°C to 170°C.
3. The pulping chemicals in the CTMP-process (Na₂SO₃ and/or NaOH) decrease the formaldehyde release from the boards, as they act as scavengers for formaldehyde.
4. Due to higher deacetylation degree during CTMP process, MDF made from CTMP release more than 4 times acetic acid than MDF from TMP. The release of formic acid is quite different, it is in MDF, made from TMP higher than in MDF from CTMP.
5. MDF with very high mechanical properties can also be made from beech pulps (TMP) using PMDI. PMDI in combination with a formaldehyde scavenger in the middle layer and UF-resin in the surface layer leads to boards with very low formaldehyde release.

     

Abbau von UF-Harzen beim TMP- und CTMP-Aufschluss von mitteldichten Faserplatten (MDF)

Thermo-mechanical (TMP) and chemo-thermo-mechanical pulping (CTMP) of UF-bonded MDF induce considerable degradation of the UF-resin in the board and lead to a conspicuous increase in the content of water extractives of the fibres. Moreover, the water extractives of the fibres have a higher pH-value and a lower buffering capacity as well as higher acetate and formate ions content than the extractives of the original board. However, the lignin content seems rather to increase than to decrease. This is possibly due to reaction between lignin and formaldehyde from the resin.     

Use of UF-bonded recycling particle- and fibreboards in MDF-production

The work is related to the use of thermomechanical pulps (TMP) prepared from recycling UF-bonded particle- and fibreboards as a partial substitute for TMP made directly from wood in MDF. The results reveal that TMP from recycling boards show striking differences in their morphological characteristics and chemical properties compared to TMP prepared directly from wood. TMP from recycling boards are of shorter fibre length and higher content of fine fraction. Moreover, their cold water extractives are of higher pH-value and contain appreciably higher amounts of acetate and formate ions. TMP from recycling boards releases also more formaldehyde compared to TMP made directly from wood. Moreover, the results clearly show that TMP from recycling boards can be used up to 30% as a partial substitute for TMP from wood in making UF-bonded MDF without any noteworthy deterioration of the physical-mechanical board properties. Also, the formaldehyde release of the boards made using TMP from recycling boards experiences no negative change. Only small differences were found in the content of formate and acetate ions as well as in the release of volatile acids from MDF made from recycling fibre- and particleboards on the one side and boards directly made from wood on the other side. All the results indicate that chemical interaction seems to take place between the chemically degraded resin in UF-bonded recycling boards and the new binder used in making MDF.     

Einfluß der Lagerung von Industrierestholz der Klefer und Fichte auf seine Eignung für die Herstellung von Spanplatten und mitteldichten Faserplatten (MDF)

Particle- and medium density fibreboards (MDF) were prepared from chips of spruce and pine, a byproduct of sawing wood in a saw mill with a profiling unti. The wood residues were stored in piles of 40 m³ volume for different time periods. The physical-technological properties of the particle- and fibrebroads prepared therefrom were evalutated and the formaldehyde release of the boards was assessed. The results reveal: In general, there is a positive influence of storage on the thickness swelling and internal bond strength of UF-bonded particleboards; the bending strength of UF-bonded particleboards showed no pronounced response to storage. The prositive influence of storage onthe thickness swelling and internal bond strength was much higher in case of boards made from pine chips than in case of spruce boards. On using PMDI as a binder for particleboards no significant influence of storage on the thickness swelling, internal bond strength and bending strength was detected. The influence of storage on the thickness swelling of UF-bonded MDF from pine fibres was much less pregnant than on that of UF-bonded particleboards. On UF-bonded MDF from spruce the influence of storage, if any, was negligible. On using PMDI as a binder for MDF there was no detectable change in the thickness swelling due to storage. The internal bond strength of UF-bonded MDF experiences only subtle positive change due to storage of pine wood chips. However, no notable change was detected in case of MDF from spruce. Storage has almost no influence on the chemical properties of boards.     

Zur Hydrophobierung von mitteldichten Faserplatten (MDF) mit Paraffinen Teil 3: Methoden zur Erfassung der Hydrophobierung von Faserstoffen durch Paraffine

The first part of this publication deals with the influence of chain length and amount of n-paraffins as well as the chemical composition of technical paraffins (chain length and amount of n- and iso-alkanes) on the thickness swelling, water absorption and internal bond strength of MDF (Roffael et al. 2005a). The second part reports on the effect of resination process (blender- and blowline-technique) as well as different methods of adding paraffin dispersion in both resination processes on paraffin sizing of MDF (Roffael et al. 2005b). This paper describes two different methods for evaluation of paraffin sizing on thermo-mechanical pulps (TMP). In one method the sizing degree was measured by determining the wettability of handsheets made from paraffin sized TMP as previously described by Roffael et al. (2002). In the other method paraffin sizing of fibres was determined by using the well known Cobb test which quantifies the water absorption of handsheets. Industrial produced TMP of Scots pine was resinated in the blender by using an MUF-resin together with n-paraffin dispersions of different chain length (C₂₀, C₂₈, C₃₆). The MUF-resin was not cured. Handsheets were manufactured from the MUF-resinated TMP and kraft pulp (ratio 1:1). On using 0.25% n-paraffin (based on dried fibres) wettability of handsheets decreased with increasing chain length of n-paraffins (C₂₀ to C₃₆). Also the results of the Cobb test (Cobb₃₀) showed that water absorption of handsheets decreased by using n-paraffins with higher chain length. Further investigations were carried out on handsheets, manufactured from kraft pulp and TMP resinated in the bowline (ratio 1:1). Within the blowline-process three technical paraffins with different chemical composition were applied in two different ways. In one case the paraffin dispersion was added to the chips before thermo-mechanical pulping. In the other case the paraffin dispersion was added to the fibres together with the resin in the blowline. Results of wettability and of water absorption of handsheets (Cobb test) showed that adding paraffin dispersion to the chips prior to thermo-mechanical pulping leads to more effective paraffin sizing than applying the paraffin dispersion to the fibres together with the resin in the blowline. Moreover, the influence of type of softwood (Scots pine and Norway spruce) on the paraffin sizing of TMP was investigated. Irrespective of the chemical composition of the used technical paraffins it was found, that handsheets manufactured from TMP of Norway spruce showed better wettability and higher water absorption than handsheets manufactured from TMP of Scots pine. The lower water absorption of handsheets manufactured from TMP of Scots pine may be due to the higher content of hydrophobic extractives in pine.     

Über die Abgabe von Ameisen- und Essigsäure aus Deck- und Mittelschichten von aus CTMP hergestellten mitteldichten Faserplatten (MDF)

Volatile acids (formic and acetic acid) from the surface and core layers of medium density fibre-boards (MDF) made from chemo-thermo-mechanical pulps (CTMP) were measured following the flask method technique. The results indicate explicitly that the emission of acids from the core layer is much higher than from the surface layer. The results are indicative of the influx of the steam distillable volatile acids from the surface layers to the core layer during pressing operation.     

Influence of resin content and pulping temperature on the formaldehyde release from medium density fibreboards (MDF)

Increasing the binder content from 12?% to 20?% in medium density fibreboards (MDF) using a slightly melamine modified (3?% melamine) UF-resin of a molar ratio F:U of 1:1 causes a decrease in the formaldehyde release from the boards prepared under the same conditions. The formaldehyde emanation was measured using the perforator (EN120) and the flask method (EN 717-3) after a reaction period of 3?h and 24?h. The results apply for boards made from thermo-mechanical pulps (TMP) prepared by pulping wood at 140?°C and 175?°C. The pulping temperature of wood also impacts the formaldehyde release from MDF prepared therefrom. Ascending the pulping temperature from 140?°C to 175?°C has a positive, but less significant influence on the formaldehyde release compared to that of increasing the binder content from 12?% to 20?%. Insofar, it becomes evident from the results that the conclusions drawn in the literature pertaining to the influence of resin content in case of high molar ratio resins do not necessarily apply to low molar ratio resins.     

Zur Wirkung der wasserlöslichen Holzbestandteile auf die Faser-zu-Faser-Bindung in mitteldichten Faserplatten (MDF)

Zusammenfassung  Hackschnitzel aus Buchenholz wurden thermomechanisch zu Fasern aufgeschlossen. Ein Teil der hergestellten Fasern wurde mit Wasser bei Raumtemperatur gewaschen. Beide Fasertypen wurden anschließend bei 70°C auf eine Feuchte von etwa 5% getrocknet. Aus den Fasern wurden mit säurehärtendem Harnstoff- (UF-Harz) und alkalisch härtendem Tanninformaldehydharz (TF-Harz) MDF hergestellt. An den ungewaschenen und gewaschenen Fasern sowie an den aus ungewaschenen und gewaschenen Fasern mit UF- und TF-Harz unter jeweils gleichen Bedingungen hergestellten 16 mm dicken mitteldichten Faserplatten (MDF) wurden die Ausgleichsfeuchten bei 20°C und relativen Luftfeuchten von 35%, 65% und 85% ermittelt. Zum Vergleich wurden die Ausgleichsfeuchten von Buchenholzspänen mitbestimmt. Ferner wurde an den Platten die Querzugfestigkeit ermittelt und der pH-Wert der kaltwässrigen Plattenextrakte bestimmt. Die Ausgleichsfeuchten der Fasern nehmen durch den Faseraufschluss deutlich ab. Durch das Waschen der Fasern sinkt die Ausgleichsfeuchte weiter ab. Die Ausgleichsfeuchten der mit säurehärtendem UF-Harz gebundenen MDF liegen nach Klimatisierung bei 20°C und 65% und 85% relativer Luftfeuchte niedriger als die der Fasern. Bei den TF-Harz-gebundenen MDF sind die Verhältnisse umgekehrt. Die mit UF-Harz gebundenen MDF haben geringere Ausgleichsfeuchten als die mit TF-Harz hergestellten MDF. Die Ausgleichsfeuchten der MDF aus gewaschenen Fasern liegen höher als die der MDF aus ungewaschenen Fasern. Des Weiteren wurde der pH-Wert der bei 20°C und 65% relativer Luftfeuchte klimatisierten MDF ermittelt. Er steigt, wie zu erwarten ist, durch das Waschen der Fasern an. Die Querzugfestigkeit der UF-Harz-gebundenen MDF sinkt durch das Waschen der Fasern deutlich ab, die der TF-Harz-gebundenen MDF steigt um fast 10%.

---

On the impact of water soluble wood components on the fibre-to-fibre bonds in MDF

Thermomechanical pulps from beech were in part washed by water at room temperature to remove water soluble components. MDF bonded with acid curing UF-resin and alkaline curing TF-resin were prepared from unwashed and washed fibres under exactly the same conditions on using the same binder. The equilibrium moisture contents (EMC) of pulps and from MDF were measured. The EMC of pulps was lower than that of the chips used for pulping. Washing of pulps leads to further decrease in the EMC. The EMC of the MDF bonded by alkaline curing TF-resin was higher than that of the fibres. In contrast, UF-bonded MDF had lower EMC than wood fibres. In general, the EMC of MDF produced from washed fibres were higher than that of the MDF produced from unwashed fibres. The UF-MDF has lower EMC than that of TF-MDF. The pH-value of the MDF made from washed fibres was higher than that of the MDF produced from unwashed fibres. The pH-value of UF-MDF is lower than the pH-value of the TF-MDF. The transverse tensile strength of UF-MDF produced from washed fibres were lower than that of the MDF made from unwashed fibres. In contrast, the transverse tensile strength of TF-MDF prepared from washed fibres was higher than from unwashed fibres. The difference in behaviour of unwashed and washed fibres is probably, at least partially, due to the influence of washing on the pH-value of fibres and the different interaction between the fibres and the used resin systems.

---

---

Förderung: Die Förderung des Forschungsprojektes erfolgte teilweise durch das Land Rheinland-Pfalz.

---

Einfluß der Lagerung von Industrierestholz der Kiefer und Fichte auf seine Eignung für die Herstellung von Spanplatten und mitteldichten Faserplatten (MDF)

Particles and fibres were prepared from saw mill wastes (chips) after different storage periods. The particles and fibres were chemically analysed regarding the change in their pH-value, buffering capacity, extractive content, release of volatile acids and formaldehyde release. Furthermore, the physical-mechanical properties of UF- and PMDI-bonded particleboards and fibreboards prepared therefrom were assessed. The results reveal:

1. Storage leads to an improvement in the properties of UF-bonded particleboards prepared from pine chips as the internal bond strength increases and the thickness swelling decreases.
2. Particleboards made from spruce prior to storage show in general better mechanical properties and lower thickness swelling compared to those prepared from pine wood. However the differences dwindle upon storage.
3. Storage seems to have almost no influence on bending properties of particles bonded with PMDI, as no significant change in the properties of the boards due to storage was detected.
4. Storage of chips from wood felled in spring has less impact on the properties of the boards than that of chips from winterfelled wood (Schäfer und Roffael, 1997).
5. The properties of MDF made from spruce using UF-resin as a binder show higher mechanical strength properties and less thickness swelling compared to those prepared from pine wood. However, after storage only subtle differences between boards made from spruce and pine were detected.
6. On using PMDI as a binder no significant changes in the properties of the MDF due to storage under the boundary conditions indicated in the work were detected.

     

Über die Eignung von thermo-mechanischem und chemo-thermo-mechanischem Holzstoff (TMP und CTMP) aus Buchen- und Kiefernholz für die Herstellung von mitteldichten Faserplatten (MDF)

A condensed review on the state of the art of the producton of medium density fibreboards is given. Thereafter, results of investigations on pulping beech and pine wood under differnet conditions according to the TMP- and CTMP-process are presented. The pulps derived from both wood species were analysed for some of their physical and chemical properties. The results reveal: Within the TMP- and CTMP-process, both the chemical and biological oxygen demand increase with increasing pulping temperature. In general, however, waste water from the CTMP-process has higher chemical and biological oxygen demand. The CTMP-process seems to be milder than the TMP-process as it leads to pulps with higher fibre length, especially in case of beech. The content of acetyle groups is much lower in CTMP-pulps than in TMP-pulps, CTMP-pulps emit also more acetic acid than TMP-pulps. With increasing pulping temperature the pH-value decreases and the buffering capacity towards alkali increases. MDF were prepared from TMP- and CTMP-pulps and their properties were evaluated. The results are included in the next parts of the publication.     

Veränderungen der chemischen Eigenschaften von Fasern und MDF durch Waschen der aufgeschlossenen Fasern

Thermomechanical pulps from beech were in parts washed by water at room temperature to remove water soluble components. MDF were prepared from unwashed and washed fibres under exactly the same conditions. The chemical properties of the fibres as well as of the boards from unwashed and washed fibres were assessed using conventional methods. The results reveal that washing of the thermomechanical pulps (TMP) increased the pH-value and decreased the alkaline buffering capacity of their water extractives. Moreover, the emission of formaldehyde and furfural from the fibres and from the medium density fibreboard (MDF) prepared therefrom declined significantly. Also, the emission of volatile acids from fibres and boards dropped enormously. Moreover, the amount of extractable urea from the boards increased significantly.     

On the release of volatile acids from wood-based panels – chemical aspects –

Wood-based panels release different amounts of volatile organic acids, which depend, among other factors, on the binder used. The volatile acids released from the boards can be measured using the flask method following the principle of measuring the formaldehyde release according to EN 717-3. Particleboards bonded with alkaline curing phenol-formaldehyde resins (PF-boards) release higher amounts of acetic and lower amounts of formic acid compared to those boards bonded by acid curing urea-formaldehyde reins (UF-resins) or binders based on polymeric diphenylemethandiisocyanates (PMDI). This has been explained by the equilibrium reaction between sodium hydroxide in PF-resins and volatile acids, which leaves less free formic acid than free acetic acid to emanate from the boards. Increasing the binder content in the boards also leads to an increase in the over all amount of sodium hydroxide in the boards. Accordingly, less free acids are left, which could be released from the boards. Fibres made by the chemo-thermo-mechanical process (CTMP) using sodium hydroxide and sodium sulphite as pulping agents release less formic acid than those made by the thermo-mechanical pulping (TMP). This behaviour was also attributed to the equilibrium reaction between the alkali in CTMP-boards and the volatile acids.     

Influence of pulping process on the emission of formaldehyde and volatile organic acids from pulps and medium density fibreboards (MDF)

Cold water extracts from pulps produced by the chemo-thermomechanical technique (CTMP process) contain higher amounts of formate and acetate ions compared to cold water extracts from pulps produced by the thermo-mechanical process (TMP process). The CTMP shows a higher emission of acetic acid than the corresponding TMP. However, the release of formic acid is lower than that from TMP due to the higher pH-value of CTMP. Furthermore, the release of formaldehyde from CTMP is lower than that from TMP due to Cannizzaro reaction catalysed by alkali. Moreover, binderless fibreboards from CTMP are significantly lower in the formaldehyde release compared to binderless boards from TMP. The use of MUF-resin increases the formaldehyde release of the boards from TMP and CTMP. Furthermore, MUF-bonded boards from TMP and CTMP are of higher pH-value and lower emission of formic and acetic acid.     

Halbzellstoffe nach dem NSSC-Verfahren aus Pappelholz

Semi-chemical pulps from poplar wood of different clones, sites and ages were prepared according to the NSSC-method. The results reveal: Poplar semi-chemical pulps show higher strength properties than industrial as well as laboratory made NSSC-pulps from beech wood. However, the pulping conditions have to be optimized for every clone. Under used pulping conditions semi-chemical pulps from the clone “Scott Pauley” were of lower strength properties compared to those of other clones. The results show clearly that for the buildup of the strength properties the site is by far more important than the age of the trees used for pulping. Semi-chemical pulps obtained from different height levels show wide differences in their mechanical properties. Bark content up to 15% has no significant influence on the mechanical properties of NSSC-pulps from poplar wood but on their yield.     

Einfluss der Aufschlusstemperatur auf die morphologischen Eigenschaften von TMP aus Kiefernholz

Chips from pine wood were subjected to thermo-mechanical pulping (TMP) at 140 and 180?^oC for 5 minutes, whereas the cooked chips were defibrated using a single disk pressurized refiner at the same temperatures (140 and 180?^oC). The fibres were tested for some of their morphological properties including fibre length, fibre width, cellwall thickness. Moreover, the fine fibre fraction (zero fibres) and the content of splinters were also estimated. The results reveal, that increasing the temperature during thermo-mechanical pulping decreases the fibre length, the cell width and the fibre wall thickness. It also increases the amount of fine fibres and increases the curl factor.     

马尾松SGP TMP和CTMP用作新闻纸浆料的比较

对以马尾松为原料生产TMP和CTMP用作新闻纸浆料进行了实验并与SGP的生产实际质量进行了比较,得出马尾松CTMP在强度指标方面优于马尾松TMP和SGP,用50％TMP和50％CTMP为原料可生产出比用80％SGP和20％化浆为原料强度高的新闻纸的结论。     

速生杨木CTMP制浆及其应用

杨木用于制浆的前景广阔。本文研究了杨木ＣＴＭＰ制浆的试验条件，如化学品用量、磨浆、漂白和污染负荷，以及对纸浆和纸张质量的影响等。用杨木ＣＴＭＰ浆与其它化学浆配抄可以制得良好的新闻纸和胶印书刊纸。