Chemo-thermo-mechanical Pulps Research Articles

Influence of thermo-mechanical and chemo-thermo-mechanical pulping on the properties of oak fibres

Thermo-mechanical pulps (TMP) and chemo-thermo-mechanical pulps (CTMP) were prepared from chips of oak wood with more than 70% heartwood. The fibres retrieved by both processes were separated by sieve analysis into different fibre fractions [≤ 0.1 mm (fine fraction) and > 1 mm (coarse fraction)]. Both fibre fractions were analysed for their extract content. The pH-value and buffering capacity of cold and hot water extracts, the formaldehyde release as well as the emission of volatile organic acids (formic and acetic acid) were also determined for the different fibre fractions. Further, the monosaccharides in the extractives before and after hydrolysis using trifluoroacetic acid (TFA) were assessed. The results make abundantly clear that the fine fraction (≤ 0.1 mm) contains a higher amount of water-soluble extracts than the coarse fraction (> 1 mm). After hydrolysis with TFA the amount of monosaccharides in the extractives, in particular the xylose content, increased tremendously, indicating that after pulping a part of the liberated carbohydrates is still in the oligomeric state. With increasing fineness of the fibres, the formaldehyde release, as determined by the flask method (EN 717-3), soars to higher values. The formaldehyde release of CTMP fibres was much lower than that of the TMP fibres. In contrast, the emission of acetic and formic acid from the CTMP was much higher than that from TMP. This may be due to the saponification of acetyl groups in the hemicelluloses of oak wood under the alkaline environment of the CTMP-process. The results explain in-depth why removing the water-soluble carbohydrates through washing the fibres negatively impacts their bondability by UF-resins, as established in previous publications.

Influence of pulping technology on the release of formaldehyde and volatile organic acids from oak fibres and medium density fibreboards (MDF) prepared therefrom

Chemo-thermomechanical pulps (CTMP) from oak wood release more formic and acetic acid than thermomechanical pulps (TMP) made from the same wood. In contrast, the emission of formaldehyde from CTMP is lower than that from TMP. Medium density fibreboards (MDF) made from TMP and CTMP emit less formic and acetic acid compared to the fibres, from which they are made. The formaldehyde release from MUF-bonded MDF made by using TMP and CTMP is higher than from the fibres (TMP and CTMP) used to make the boards.

Influence of washing chemo-thermo-mechanical pulps (CTMP) on the emission of volatile organic acids of medium density fibreboards (MDF) prepared therefrom

Washing of CTMP-pulps ahead of board making decreases the amount of extractable acetate and formate ions from the boards. The decrease in the amount of releasable acetic acid due to washing is enormous, whereas washing seems to have no detectable effect on the releasable amount of formic acid. This is likely due to the fact that formic acid is a much stronger acid than acetic acid.

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.

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.

Benetzung von TMP und CTMP aus Holz sowie gebrauchten mitteldichten Faserplatten (MDF)

TMP (thermo-mechanical pulps) and CTMP (chemo-thermo-mechanical pulps) were made from pine wood and recycling MDF, which has been prepared from pine wood too. The fibres were tested for their wettability using the method developed by Roffael et al (2002). The results reveal that TMP are much less wettable in comparison to CTMP from the same wood. Moreover, fibres made from UF-bonded MDF by the TMP- and CTMP-process are of much higher wettability compared to TMP and CTMP prepared directly from wood. No significant difference in the wettability between TMP and CTMP from UF-bonded MDF was detected. This behaviour has been attributed to the fact that the UF-resin in MDF degrades during thermohydrolytic pulping leading to the formation of ammonia and free urea. Therefore, pulping of UF-bonded boards takes place under chemo-thermo-mechanical conditions (CTMP).

Radicalization of Lignocellulosic Fibers, Related Structural and Morphological Changes

The radicalization of unbleached lignocellulosic fibers obtained from thermomechanical (TMP) and chemothermomechanical (CTMP) pulps was performed in heterogeneous phase by reaction with dioxygen in the presence of N,N'-ethylenebis(salicylideneiminato)cobalt(II), [Co(salen)], as catalyst. Phenoxy cobalt radicals immobilized in fibers were observed by electron paramagnetic resonance (EPR) spectroscopy; their amount depends on the fiber swelling induced by reaction medium. The absolute concentration of such radicals in fibers, about 10(16) spin/g, reaches values 10 times higher than that of phenoxy radicals formed in similar oxidative reactions catalyzed by laccase. The generation of phenoxy cobalt radicals in fibers was related to structural changes of lignin units, detected by mono- and bidimensional nuclear magnetic resonance ((13)C NMR and 2D-HSQC) investigations, and to morphological modifications in fibers observed by scanning electron microscopy (SEM).

Einsatz von Faserstoffen aus chemo-thermo-mechanisch (CTMP) aufgeschlossenen, gebrauchten Span- und Faserplatten zur Herstellung von mitteldichten Faserplatten (MDF)

Chemo-thermo-mechanical pulps (CTMP) were made from waste particle- and fibreboards. Medium density fiberboards (MDF) were made from industrial refiner fibers in combination with the CTMP using urea-formaldehyde resin as a binder. The physical properties and the formaldehyde content of the MDF were determined. The results reveal that MDF made from CTMP of waste particle- and fibreboards meet the standards according to EN 622-5, type MDF. The bending strength and internal bond of MDF made from industrial TMP is higher compared with MDF from chemo-thermo-mechanical pulps from waste panels. However, the thickness swelling of MDF made from pulps derived from waste panels is clearly lower compared with that of MDF made from industrial TMP. Furthermore, MDF made from pulps derived from waste panels show a lower formaldehyde content than MDF from virgin fibers. It seems that residues of chemicals from the pulping process (CTMP) act as a formaldehyde scavanger.

Einfluß der Trocknung von thermo-mechanischem (TMP) und chemo-thermo-mechanischem Holzstoff (CTMP) der Fichte auf die physikalisch-technologischen Eigenschaften von daraus hergestellten mitteldichten Faserplatten (MDF)

Thermo-mechanical pulps (TMP) and chemo-thermo-mechanical pulps (CTMP) were made from spruce under different pulping conditions. The fibres were dried at 150°C and 170°C, respectively. Medium density fibreboards (MDF) were produced in pilot plant scale from the pulps using urea-formaldehyde resin as binder. The results of testing the physical properties reveal that the drying temperature of the fibres has a significant influence on the thickness swelling and water absorption of the boards. MDF from fibres dried at higher temperature, generally show lower thickness swelling and water absorption than MDF made from fibres dried at lower temperature.

Thermomechanical (TMP) and Chemo-Thermomechanical Pulps (CTMP) for Medium Density Fibreboards (MDF)

Summary Thermomechanical (TMP) and chemo-thermomechanical pulps (CTMP) were prepared from spruce under different pulping conditions. The fibres were dried at 70 °C and medium density fibreboards (MDF) were made therefrom in pilot plant scale using urea-formaldehyde resins as a binder. The results of testing the physical-mechanical properties reveal that the pulping temperature has a significant influence on the thickness swelling and water absorption of the boards. MDF prepared from fibres produced at high pulping temperature (180 °C) generally show lower thickness swelling and water absorption than MDF made from fibres produced at low pulping temperature (140°C and 160 °C). However, high pulping temperature may have a negative effect on the internal bond strength of the boards. In general, CTMP leads to MDF with higher internal bonding strength compared to those derived from TMP. In addition, the influence of different drying conditions (150 °C and 170 °C) of TMP and CTMP on the physical-mechanical properties of MDF was assessed. MDF made from CTMP showed lower thickness swelling when dried under high temperature.

Einfluß von Holzaufschlußverfahren (TMP-, CTMP-Verfahren) und Aufschlußbedingungen auf die physikalisch-technologischen Eigenschaften von mitteldichten Faserplatten (MDF)

Thermo-mechanical pulps (TMP) and chemo-thermomechanical pulps (CTMP) were made from spruce under different pulping conditions. The fibres were dried at 70°C. Medium density fibreboards (MDF) were made in pilot plant scale from the pulps using urea-formaldehyde resin as a binder. The results of testing the physical properties reveal, that the pulping temperature has a significant influence on the thickness swelling and water absorption of the boards. MDF from fibres produced at high pulping temperature (180°C) generally show lower thickness swelling and water absorption than MDF made from fibres produced at lower pulping temperature (140°C and 160°C).

The effect of additives on the mechanical properties of dry-formed fibre networks

The effects of thermal bonding and friction-changing additives on the mechanical properties of dry-formed cellulosic networks have been evaluated. Calcium carbonate particles and a cationic surface active agent were used to change the coefficient of friction of cellulose (Chemothermo mechanical pulps; (CTMP) and rayon fibres. The parameters used to describe the networks were the storage modulus G′0 (measured at low strain amplitudes) and the critical strain γc (at which the network yields) obtained from the dynamic–mechanical measurements and the maximum force Fmax measured with a shear tester. The mechanical properties of the networks were improved as a result of the thermal bonding, which promotes stress transfer through the network structure. The friction-changing additives changed the ability of the fibres in the network to disentangle before the network ruptures. This change was, in the first place, reflected in corresponding changes in the critical strain γc and the maximum strength Fmax of thd dry-formed networks. © 1998 Chapman & Hall

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 physical-mechanical 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 (...)

ESCA (XPS) study on light-induced yellowing of thermomechanical and chemothermomechanical pulps

Thermomechanical and chemothermomechanical pulp samples have been derived from Norway spruce ( Picea abies) and characterized by brightness measurements and ESCA before and after exposure to artificial light irradiation. The surface O/C atomic ratios of the non-irradiated pulps were found to be between 0.3 and 0.37, which was interpreted as being due to their high surface lignin contents. The brightness reversion was accompanied by a considerable increase in the surface O/C ratio, by a decrease in the relative intensity of the C1 component of the C1s peak ( BE = 285.0 eV), and by increases in those of the C2 ( BE = 286.6 eV) and C3 ( BE = 288.2 eV) parts. It had no effect on the shapes of the O 1s peaks. The results were related to the photo-oxidation and photoyellowing of high-yield pulps.