Armin Thumm

Near infrared hyperspectral imaging applied to mapping chemical composition in wood samples

This paper describes a method for the two-dimensional mapping of chemical composition on the transverse face of cross-sectional discs from trees. The method uses an imaging spectrograph coupled to a near infrared (NIR) camera (900–1700 nm) to obtain NIR hyperspectral data sets which are processed using partial least squares regression to visualise the distribution and variation of lignin, galactose and glucose in Pinus radiata discs with R2/standard error of performance values of 0.84/1.48 (lignin), 0.87/0.68 (galactose) and 0.87/0.95 (glucose). The hardware design and software control are described along with a method for calibration based on one dimension spatially resolved predictions of chemical composition from conventional NIR spectroscopy. The NIR imaging system was designed as a rapid and cost-effective means of mapping chemical composition over the entire disc at a spatial resolution of ∼4mm2/pixel. The resulting maps of chemical composition clearly indicate, at high spatial resolution, the extent of heterogeneity that occurs in logs.

X-ray photoelectron spectroscopy determination of urea formaldehyde resin coverage on MDF fibre

Quantification of fibre resin coverage is essential for the understanding of panel integrity in medium density fibreboard (MDF) and similar panel products. X-ray photo-electron spectroscopy (XPS) was used to determine the proportion of fibre surface covered by nitrogen containing UF resin in blowline resinated and dry-blended MDF. Coverage values were dependent on processing variables such as resin content, wax content, resin spray droplet size and for blowline resination, the position of the resin injection nozzle along the blowline. Comparison of XPS coverage values with those obtained using confocal laser scanning microscopy (CLSM) revealed substantially differing absolute resin coverage of fibre between the two techniques. For dry-blended panels there was a correlation between the two techniques. However, grouping resin coverage values having more than one processing variation did not establish any relationship between XPS and CLSM coverage values, whether for dry-blended or blowline resinated MDF. Wax movement as well as deposition of other materials on the fibre surface during hot pressing were observed to contribute to lower surface %N content, which may limit the usefulness of the XPS technique.ZusammenfassungDie quantitative Bestimmung der Leimbedeckung von Fasern ist notwendig, um den Zusammenhalt von mitteldichten Faserplatten (MDF) und ähnlichen Plattenprodukten zu verstehen. Röntgenphotoelektronen-Spektroskopie wurde benutzt, um zu bestimmen, welcher Anteil der Faseroberfläche mit stickstoffhaltigem Harnstoff-Formaldehyd-Harz bedeckt ist, wenn die Fasern im „blowline“ Verfahren beleimt wurden, und wenn sie trocken mit Leim durchmischt wurden. Die Leimbeschichtung war abhängig von Verfahrensgrößen wie Leimzugabe, Wachszugabe und Leimtropfengröße. Bei der „blowline“ Beleimung hatte zudem die Position der Leimdüse entlang der „blowline“ einen Einfluss. Ein Vergleich der Bedeckungswerte wie sie mit XPS bestimmt wurden, mit denen die durch die Benutzung eines konfokalen Laser Scanning Mikroskop (CLSM) erzielt wurden, zeigte einen deutlichen Unterschied in den gemessen Werten für die absolute Leimbedeckung der Fasern. Für die Platten die im Trockenmischverfahren hergestellt wurden, zeigte sich eine Korrelation zwischen den beiden Methoden. Wenn jedoch Bedeckungswerte gruppiert wurden, die mehr als eine unterschiedliche Prozessgröße hatten, konnte kein Zusammenhang zwischen XPS und CLSM Bedeckungswerten hergestellt werden, und zwar weder für trocken beleimte Fasern noch für „blowline“ beleimte Fasern. Es wurde beobachtet, dass während der Heißpressung eine Migration des Wachses als auch eine Deposition anderer Stoffe zu einer Reduzierung des prozentualen Stickstoffgehalts der Oberfläche beitragen. Dies könnte die Tauglichkeit der XPS Methode beeinträchtigten.

Resin and wax distribution and mobility during medium density fibreboard manufacture

Fluorescently labelled UF resin and paraffin wax have been used at a medium density fibreboard (MDF) production facility to characterise resin and wax distribution and mobility on MDF fibre and panels. The major findings from these comprehensive mill-scale trials have been the mobility of UF resin on fibre throughout the MDF process, while wax mobility occurs only on panel pressing. Complex interactions exist between resin distribution and wood fibre wall penetration which collectively provide evidence for three-dimensional resin movement on fibre through the production process. Fibre exiting the blowline had relatively high rates of resin coverage with resin droplet sizes dominated by the process of resin smearing through fibre-fibre contacts. On passing through the dryer resin coverage of fibre reduces, before increasing again on panel pressing. Wax distribution on unpressed fibre was dependent on the mode of application with emulsion and slack wax addition at the refiner being relatively similar, but differing to emulsified wax added via the blowline. On pressing, wax distribution in panels was distinguished by wax type, and was independent of the addition points.ZusammenfassungUnter Verwendung von fluoreszenzmarkiertem Harnstoffharz und Paraffin wurden in einem MDF-Werk die Verteilung und Ausbreitung von Klebstoff und Wachs auf Fasern und MDF-Platten untersucht. Die Ergebnisse dieser umfangreichen Untersuchung im Industriemaßstab zeigten, dass sich Harnstoffharz während der gesamten Plattenherstellung auf den Fasern ausbreitet, während sich Wachs nur während des Pressvorgangs der Platten ausbreitet. Zwischen der Harzverteilung und der Eindringung in die Holzzellwände bestehen komplexe Wechselbeziehungen, die die dreidimensionale Ausbreitung auf der Faseroberfläche bei der Herstellung belegen. Nach der Blowline-Beleimung wiesen die Fasern eine relativ hohe Harzbedeckung auf, wobei die Größe der Harztröpfchen durch die Verschmierungen infolge des Aneinanderreibens der Fasern bestimmt wurde. Während der Trocknung nimmt die Harzbedeckung der Fasern ab und beim Pressen der Platten wieder zu. Die Wachsverteilung ungepresster Fasern hing von der Art des Auftrags ab, wobei die Verteilung bei der Zugabe von Emulsion und Rohparaffin im Refiner ähnlich war, jedoch bei der Zugabe von emulgiertem Wachs in der Blowline deutlich unterschiedlich. Beim Pressen unterschied sich die Wachsverteilung in den Platten je nach Wachsart, war jedoch unabhängig davon, wo das Wachs zugegeben wurde.

The interactions between wax and UF resin in medium density fibreboard

Through the use of fluorescently labelled paraffin wax and UF resin, fluorescence microscopy has been used to simultaneously visualise wax and resin components on medium density fibreboard (MDF) fibre. To simulate differing application methods, the wax and resin were applied to fibre either separately or as a mixture. Visualisation on unpressed fibre and in panels suggests the application order can lead to differing wax-resin behaviours and how each interact with fibre. Both qualitative and quantitative analyses of wax and resin distribution on fibre established that the main differences in behaviours were due to wax and occur on pressing. Applying wax first to fibre led to wax droplet agglomeration in panels whereas applying wax after resin or as a mixture appeared to allow wax to be retained as relatively smaller droplets within the resin matrix. This also manifested itself in differences in wax overlap with resin in panels, where a relatively low overlap was observed when applying wax first, despite a substantially higher overlap in unpressed fibre. Application of wax after resin or as a mixture resulted in the wax generally staying with the resin. The observed differences in wax distribution were also correlated with panel cold water soak properties.ZusammenfassungMit fluoreszenzmarkiertem Paraffin und UF-Harz wurden Wachs- und Harzkomponenten auf MDF-Fasern mit dem Fluoreszenzmikroskop simultan visualisiert. Um verschiedene Auftragsmethoden zu simulieren, wurden Wachs und Harz entweder einzeln oder als Mischung auf die Fasern aufgetragen. Die Visualisierung auf ungepressten Fasern und in den Platten ergab, dass die Art des Auftrags das Verhalten zwischen Wachs und Harz und deren Verteilung auf der Faser beeinflusst. Sowohl die qualitative als auch die quantitative Untersuchung der Wachs- und Harzverteilung auf der Faser zeigten, dass die Hauptunterschiede auf das Wachs zurückzuführen sind und beim Pressen auftreten. Wird Wachs zuerst auf die Faser aufgetragen, führte dies zu einer Tröpfchenagglomeration in den Platten. Umgekehrt, wenn Wachs nach dem Harz oder als Mischung aufgetragen wird, schien sich das Wachs in relativ kleineren Tröpfchen in der Harzmatrix zu verteilen. Dies zeigte sich auch in der unterschiedlichen Vermischung von Wachs und Harz in den Platten, wobei eine relativ geringe Vermischung zu sehen war, wenn das Wachs zuerst aufgetragen wurde, trotz einer wesentlich höheren Vermischung auf den ungepressten Fasern. Wird Wachs nach dem Harz oder als Mischung aufgetragen, blieb das Wachs generell mit dem Harz verbunden. Die beobachteten Unterschiede in der Wachsverteilung korrelierten auch mit dem Verhalten der Platten nach Kaltwasserlagerung.

Mapping within-stem variation of chemical composition by near infrared hyperspectral imaging

A near infrared (NIR) imaging spectrograph was used to generate maps of chemical composition distribution on the surface of transverse wood discs taken from tree stems. The measured chemical components were lignin, galactose, glucose and mannose as well as cellulose and hemicelluloses, which were calculated from monomeric sugars. These components were determined using NIR-based chemistry models, which had been developed specifically for the imaging spectrograph. Explained test-set variation for key constituents ranged between 60% (galactan) and 78% (lignin). Day-to-day variability was 1–2% (standard deviation/range) depending on the chemical property. Various operational parameters such as room temperature, sample temperature, sample surface preparation and sample thickness were found to have a non-negligible, but manageable, influence on predicted results. The influence of room and sample temperatures could be reduced by incorporating temperature changes into the chemistry model. Extractives, transported to, and concentrated at, the disc surface during drying, needed to be physically removed from the surface to avoid an unpredictable influence on chemical results. Wood fibre angles at the disc surface needed to be aligned in a consistent manner to the camera. NIR information was found to derive from a sample depth of up to 10 mm. This distance was consequently chosen as the minimal sample thickness.

Natural Durability of the Heartwood of Coast Redwood [Sequoia Sempervirens (D.Don) Endl.] and its Prediction Using near Infrared Spectroscopy:

The heartwood of plantation-grown coast redwood trees from three forests in the North Island, New Zealand, was evaluated using in vitro decay tests with fungal cultures to determine variation in natural durability and its prediction using near infrared (NIR) spectroscopy. The NIR spectra were acquired from the solid wood surface, prior to decay testing, using a fibre-optic probe attached to a Bruker MPA FT-NIR spectrometer and an imaging spectrograph coupled to a NIR line camera. The partial least squares (PLS) regression models of mass loss with fungal decay testing, based on spectra collected with the FT-NIR spectrometer, had better predictive performance than the NIR line camera, as evidenced by fewer latent variables and slightly better R2. The ratios of prediction to deviation (RPD) were 1.3 to 1.4 for both the spectrometer and camera system, which suggests the PLS regression models could be used to segregate the heartwood of coast redwood for high- and low values of natural durability.

Improving Hygrothermal Performance in Epoxy-Biofibre Composites

Confocal microscopy and water diffusivity measurements were used to characterise the development of defects in biofibre-reinforced composite materials. Biofibres swelled more than the matrix when the specimen was immersed in water, but the associated distortion of the matrix rarely caused defects. The biofibres shrank faster than the matrix when the specimen was dried in air, causing debonding at the fibre-matrix interfaces and microcracks within the fibres. We started with coarse technical fibres from the leaves of harakeke (Phormium tenax), treated a portion with 1% NaOH, and pulped a portion at 170 °C. Water diffusivities for the corresponding composites increased over the first 3 wet-dry cycles, particularly for the composite made with untreated fibre, but were too small to be of concern for the composite made from pulped fibre.

Labile Extractable Urea-Formaldehyde Resin Components from Medium-Density Fiberboard*

Abstract Urea-formaldehyde (UF) resin is the predominant adhesive used in the manufacture of medium-density fiberboard (MDF). While it is well known that this resin is susceptible to moisture and h...

Fundamentals of MDF Panel Dimensional Stability: Analysis of MDF High-Density Layers

Abstract The inherent resin and fiber chemistry of medium density fiberboard (MDF) panels has been compared with panel cold water soak properties. In hot-pressed panels it was observed that resin type and hydrophobicity significantly impact panel swell behavior. Resin affects both fiber hydrophobicity and equilibrium moisture content (EMC), but does not prevent water uptake. It is the influence of resin type on high-density layer thickness swell which suggests resin efficacy is important to retaining bonding in the fiber network and resisting fiber spring-back and panel swell. Fiber contact angles were found to be of less importance, only manifesting when comparing E0 and E1 urea formaldehyde (UF) resins. The E0 panel was considerably more hydrophilic, impacting its wetting behavior, and contributing to greater panel layer thickness swells. For cold-pressed panels, the absence of a high-density layer and relative fiber hydrophobicity were important. Cold-pressed polymeric methylene diisocyanate (pMDI) panels had greater hydrophobicity than E1 UF resin panels which, together with the greater bonding of pMDI, led to improved panel water soak properties. In the case of the cold-pressed E1 UF resin, the relatively hydrophilic fiber and relatively even density profile contributed to an extremely poor water soak performance. Overall, results show that the interactions of contributing factors to panel swell are complex and all may significantly affect panel water soak behaviors.