Warren J. Grigsby

Thermal Degradation of Condensed Tannins from Radiata Pine Bark

Abstract In order to understand the influence of the inherent chemistry on the relative thermal stability of condensed tannins, the thermal degradation behaviors of various radiata pine bark extracts have been investigated using thermogravimetric analysis (TGA). Generally, results suggest pine bark extract fractions may be readily processed at temperatures below 200°C if co-extracted polysaccharides contents are minimized. Those extracts possessing greater carbohydrate content and lower tannin purity tend to have decreased thermal stability. The initial onset temperature for degradation of relatively crude extracts with high proportions of carbohydrate contents were relatively low (ca. 150°C), whereas extract purification to < 5% carbohydrate content gave increases in thermal stability of at least 50°C. The complicity of the carbohydrate content in the degradation of the tannin samples was also supported by calculated Ozawa activation energies and modulated TGA experiments. While no increase in the thermal stability was gained by acetylating the pendant hydroxyl groups of the pine bark tannin extract, chemical variations such as sulfonation have a large effect on thermal degradation, promoting lower degradation temperatures.

Synchrotron-based X-ray Fluorescence Microscopy in Conjunction with Nanoindentation to Study Molecular-Scale Interactions of Phenol–Formaldehyde in Wood Cell Walls

Understanding and controlling molecular-scale interactions between adhesives and wood polymers are critical to accelerate the development of improved adhesives for advanced wood-based materials. The submicrometer resolution of synchrotron-based X-ray fluorescence microscopy (XFM) was found capable of mapping and quantifying infiltration of Br-labeled phenol-formaldehyde (BrPF) into wood cell walls. Cell wall infiltration of five BrPF adhesives with different average molecular weights (MWs) was mapped. Nanoindentation on the same cell walls was performed to assess the effects of BrPF infiltration on cell wall hygromechanical properties. For the same amount of weight uptake, lower MW BrPF adhesives were found to be more effective at decreasing moisture-induced mechanical softening. This greater effectiveness of lower MW phenolic adhesives likely resulted from their ability to more intimately associate with water sorption sites in the wood polymers. Evidence also suggests that a BrPF interpenetrating polymer network (IPN) formed within the wood polymers, which might also decrease moisture sorption by mechanically restraining wood polymers during swelling.

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.

Vegetable oil thermosets reinforced by tannin–lipid formulations

Totally bio-based thermosetting polymers which are comparable to synthetic polyester thermosets have been prepared from copolymerization of condensed tannin-fatty acid esters with vegetable oils. Oxidative copolymerization of tannin linoleate/acetate mixed esters with linseed oil and tung oil produced polymer films ranging from soft rubbers to rigid thermosets. Tannin incorporation into the formulations was essential for the final product to achieve necessary mechanical strength. Films had ambient modulus values between 0.12 and 1.6 GPa, with glass transition temperatures ranging from 32 to 72 °C and calculated crosslink densities of 1020-57,700 mol m⁻³. Film stiffness, T(g) and crosslink density increase with greater tannin linoeate/acetate content due mainly to this tannin component providing rigidity through polyphenolic aromatic rings and unsaturated chains as crosslinking sites.

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.

Two-Dimensional FTIR as a Tool to Study the Chemical Interactions within Cellulose-Ionic Liquid Solutions

In this study two-dimensional FTIR analysis was applied to understand the temperature effects on processing cellulose solutions in imidazolium-based ionic liquids. Analysis of the imidazolium ion νC2–H peak revealed hydrogen bonding within cellulose solutions to be dynamic on heating and cooling. The extent of hydrogen bonding was stronger on heating, consistent with greater ion mobility at higher temperature when the ionic liquid network structure is broken. At ambient temperatures a blue shifted νC2–H peak was indicative of greater cation-anion interactions, consistent with the ionic liquid network structure. Both cellulose and water further impact the extent of hydrogen bonding in these solutions. The FTIR spectral changes appeared gradual with temperature and contrast shear induced rheology changes which were observed on heating above 70°C and cooling below 40°C. The influence of cellulose on solution viscosity was not distinguished on initial heating as the ionic liquid network structure dominates rheology behaviour. On cooling, the quantity of cellulose has a greater influence on solution rheology. Outcomes suggest processing cellulose in ionic liquids above 40°C and to reduce the impacts of cation-anion effects and enhance solubilisation, processing should be done at 70°C.

Production, composition and toxicology studies of Enzogenol® Pinus radiata bark extract

Enzogenol® pine bark extract is a dietary supplement and food ingredient produced by water extraction of Pinus radiata. We present production method, composition, and safety data from rat and dog toxicological and human clinical studies. The dry powder contains proanthocyanidins (>80%), taxifolin (1-2%), other flavonoids and phenolic acids (up to 8%), and carbohydrates (5-10%). Reverse mutation assays showed lack of mutagenic activity. Single and 14-day repeat dosing in rats and dogs had no influence on body weight, feed consumption, blood chemistry, and haematology at any dose level. There were no treatment related findings on gross and detailed necroscopy, organ weights, organ weight ratios and histology. The only adverse events were emesis and diarrhoea in dogs occurring mainly in un-fed condition and at the highest dose level in a total of 18% of applications. The MTD and NOAEL in the present rat and dog studies were 2500 and 750 mg/kg/day, respectively. Consumption of 480 mg/day for 6 months and 960 mg/day for 5 weeks in two human studies showed Enzogenol® had no adverse influence on liver and kidney function, haematology, and did not cause any adverse events. Our studies indicate lack of toxicity of Enzogenol® and support safe use as a food ingredient.

NMR Estimation of Extractables from Bark: Analysis Method for Quantifying Tannin Extraction from Bark

Abstract Extraction and recovery of radiata pine bark tannin for use in adhesives should endeavour to be optimal to ensure process viability. A NMR method has been developed to directly gauge the extent of tannin extraction from bark by analyzing processed residues. 13C Solid-state NMR spectra were obtained for a series of bark and residue samples. The respective peak areas and heights of extractable polyphenolic tannins were compared with residual lignocellulosic materials. From the ratio of NMR peak intensities, diminishing polyphenolic content was apparent with increasing degree of extraction. The percentage polyphenolic tannins removed by extraction could be estimated by a simple equation comparing integrated areas of a sample with those of pure bark. A comparison of percentage extraction values determined gravimetrically with NMR peak ratios gave a good relationship from which the extractables removed from a bark residue could be estimated, potentially providing a measurement of extraction efficiency of a bark processing operation.

Applying the Protective Role of Condensed Tannins to Acrylic-based Surface Coatings Exposed to Accelerated Weathering

Condensed tannins, extractable from tree bark have been assessed as functional additives to provide a protective role to acrylic-based coating resins. In addition to retaining high antioxidant capacity, the UV absorption properties of native and chemically modified tannins were found to be variously impacted by pH and degree of esterification or etherification. When added to acrylic-based coatings, these tannins were found to contribute colour to a white-base, but only small perceptive differences were found for clear coated wood using typical additive loadings of 0.1–0.4%. Integration of tannins in native or modified form to do not inhibit the cure of acrylic coatings or found to leach from cured coating films. Accelerated weathering was used to evaluate the photo-stability of tannin-modified acrylic and styrene-acrylic coatings. Native and modified tannins with maleate or methylcarboxylate groups retaining high antioxidant activity were associated with significantly greater coating longevity and performance than use of a synthetic photostabiliser. Moreover, esterified condensed tannins with a high degree of substitution also outperformed synthetic additives indicating the inherent UV absorption potential of these materials also contributed this efficacy within the acrylic and styrene-acrylic coating systems.