Weathering of chemically modified wood

The weathering characteristics and microscopic structure of unfinished acetylated and untreated radiata pine are reported. Samples were exposed outdoors over 28 weeks in Rotorua, New Zealand. Acetylated veneer had improved checking resistance when compared with untreated veneer, confirming results of a previous study on accelerated weathering of untreated and acetylated veneer. Colour changes of naturally weathered untreated and acetylated veneer were very different to that of artificially weathered veneer. Acetylated veneer was only slightly less grey than untreated veneer after 28 weeks' natural weathering.     

Weathering of chemically modified wood

Acctylation of radiata pine vencer was shown to improve the colour stability and weathering resistance of material exposed to accelerated weathering conditions. Two exterior finishes, an opaque acrylic stain and a semi-transparent alkyd stain, as well as unfinished veneer, were studied. Significantly less checking was observed for unfinished, acetylated samples or acetylated vencers finished with the alkyd stain when compared with untreated controls. Examination of unifinished samples by scanning electron microscopy (SEM) showed that, although checking was not completely prevented by acetylation of the vencer, it gave significant protection from the effects of weathering.     

Utilisation of chemically modified lampante oil for wood protection

Within the Slovenian region of Istria, the olive growing and oil production industry is strong. This industry has a long history and the olives grown here have high levels of biologically active compounds including a variety of phenolic compounds. Using residual materials generated by this industry in potential wood protection systems would not only valorise low-value materials and stimulate rural economies but would also provide an alternative to currently used oil-based protection systems. The objective of this study was to produce an oil treatment for wood protection and assess its efficacy in reducing leaching, weathering effects, and fungal decay. Two maleinisation techniques were used to chemically modify low-value lampante oil in an attempt to limit leaching when impregnated in wood. Pinus sylvestris (Scots pine) and Fagus sylvatica (European beech) were treated with the modified oils and underwent leaching, accelerated weathering, and decay tests. Leaching of the treatment oils was relatively low compared with other experiments and beech wood specimens treated with a direct maleinisation treatment showed improvement in performance compared to control specimens. In addition, it was found that the modified oils were not completely removed from the wood after solvent extraction indicating that they could potentially be used as an immobilisation agent in combination with other treatments thereby reducing the amount of active component of the protective agent.     

Bonding of densified beech wood using adhesives based on thermally modified soy proteins

The bondability/glueability of aged and sanded thermo-hydro-mechanically (THM) densified beech wood (Fagus sylvatica L.) was tested and compared with undensified sanded beech wood as a control. THM and control specimens were bonded with five different soy protein isolate (SPI) based adhesives. Commercial SPI powder was thermally modified in the vacuum chamber at 50 or 100?°C and pH adjusted (to pH 10.0) dispersions in water prepared at 24, 50 or 90?°C. Wettability was determined with measuring the sessile drop contact angles of water. Effective penetrations (EPs) and tensile shear strengths of THM and control specimens were determined. THM and control wood had similar wettability. Although THM wood had lower moisture content than control wood, it absorbed the water more slowly than control wood. THM specimens showed lower EPs than control specimens when comparing individual adhesives due to increased density of THM wood. Adhesives prepared with SPI thermally modified at 50?°C showed statistically significantly lower tensile shear strength of bonded THM specimens than that of bonded control specimens. THM densification had no significant effect on the bonding strengths of adhesives prepared with non-modified SPI and SPI thermally modified at 100?°C.     

Analysis of the swelling behaviour of chemically modified softwood: A novel approach

Volume changes due to modification with acetic and hexanoic anhydride are due to the volume occupied by the reagent and an associated void volume. The void volume is larger in hexanoic anhydride modified wood. Less weight of water per gm of unmodified wood was accommodated by acetic anhydride modified wood than by hexanoic modified wood, at equivalent WPG. A non-linear relationship was found between weight of water per gm of unmodified Corsican pine wood and bulking, whereas a linear relationship would be predicted. However, this takes no account of void volume. When the value of void volume is deducted from the bulking a linear relationship was indeed obtained with acetic anhydride, but not with hexanoic anhydride modified Corsican pine. It seems therefore that the free volume model offers a reasonable explanation of the differences in swelling recorded for Corsican pine sapwood modifying to varying wpg’s with acetic anhydride.     

三聚氰胺改性脲醛树脂胶在MDF生产中的应用

本文叙述了用三聚氰胺改性脲醛树脂胶的方法,并对改性胶进行了理化分析,提出了改性脲醛胶在中密度纤维板生产中的应用方法。     

Characterisation of thermally modified wood: molecular reasons for wood performance improvement

Relatively mild thermal treatments of wood according to a two step process which leads to improved dimensional stability and improved timber performance were investigated by solid phase CP-MAS 13C-NMR to understand at molecular level the reasons for the improvements reported. All the occurrences described appear to be the consequence of reactions which are known in wood chemistry. These are the formation of acetic acid liberated from the hemicelluloses, which further catalyses carbohydrates cleavage, causing a reduction of degree of polymerisation of the carbohydrates. Acid catalysed degradation results in the formation of formaldehyde, furfural and other aldehydes as well as some lignin cleavage at Cα and O4 and believed to cause some aldehyde production from lignin units Cγ, all occurring in the first reaction step. Lignin autocondensation through the cleaved, positively charged benzylic Cα to form some methylene bridges presumably starts already to occur in this first phase. The increase in the number of free reactive sites on the aromatic ring of some lignin units already occurs in this phase but continues into the next. In the second treatment step completion of the autocondensation of lignin is believed to occur through the formation of methylene bridges connecting aromatic rings. The aromatic nuclei sites are released by demethoxylation and through the cleaved, positively charged benzylic Cα. Reactions of some of the aldehyde groups formed in the first step phase occur with lignin aromatic nuclei sites to connect aromatic rings through methylene bridges. The extent of these reactions is mild, but nonetheless they lead to an increase in cross-linking with consequent improvement in dimensional stability and decreased hygroscopicity of wood.     

Determination of surface area and pore volume of holocellulose and chemically modified wood flour using the nitrogen adsorption technique

Very low surface area (ca. 0.5 m²/g) and a low pore volume (ca. 0.002 cm³/g) have been obtained for oven dried wood, using the nitrogen adsorption technique. The microporous structure of wood flour was partially preserved by the solvent exchange drying (SED) employed in this study, in particular when toluene was used as a final solvent. However, the resulted surface area (ca. 6 m²/g) and a pore volume values (ca. 0.015 cm³/g) indicated that such a structure is in no way representative of a fully swollen cell wall. By using solvent exchange drying (SED), it is possible to preserve the swollen pore structure of holocellulose samples. However, with samples which contain significant amounts of lignin, such as native wood, it is not possible to prevent re-collapse of the pores. This problem arises because as micropore swelling occurs, the surrounding lignin network of the cell wall is stretched. When the molecules occupying the micropores are removed, the lignin returns to its original configuration, re-collapsing the micropores in the process. Chemical modification resulted in significant reduction in surface area and pore volume, possibly a result of pore blocking by the large acyl group.

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Bestimmen der inneren Oberfläche und des Porenvolumens von Holocellulose und chemisch modifiziertem Holzmehl mit Hilfe der Sickstoffadsorptions-Methode

Zusammenfassung Sehr geringe Oberflächenanteile (ca. 0,5 m²/g) und Porenvolumina (ca. 0,002 cm³/g) wurden in ofengetrocknetem Holz mit Hilfe der Stickstoffadsorptios-Methode gefunden. Die Mikroporenstruktur in Holzmehl blieb nach Trocknen durch Lösemittelaustausch (SED) teilweise erhalten, insbesondere, wenn Toluol als letztes Lösemittel verwendet wurde. Allerdings zeigen die gemessenen Oberflächen (ca. 6 m²/g) und Volumina (ca. 0,015 cm³/g), daß solche Strukturen keineswegs den Verhältnissen in der gequollenen Holzzellwand entsprechen. Bei Holocellulosen kann die Porenstruktur des gequollenen Zustands nach Lösemittelaustausch erhalten werden. In Proben, die beträchtliche Mengen an Lignin enthalten, wie ursprüngliches Holz, ist es jedoch nicht möglich, den Kollaps der Poren zu verhindern. Das Problem ergibt sich dadurch, daß aufgrund des Quellens der Mikroporen das umgebende Lignin-Netzwerk der Zellwand gestreckt wird. Wenn die Lösemittel-Moleküle in den Mikroporen durch Trocknen entfernt werden, kehrt das Lignin in die ursprüngliche Konfiguraton zurück und verschließt so die Mikroporen wieder. Chemische Modifizierung hatte eine beträchtliche Verringerung der Flächen und Volumina zur Folge, womöglich durch Blockieren der Poren durch die großen Acetylgruppen.

     

Bonding performance of heat treated wood with structural adhesives

Bonding of untreated, intermediate (hydro-thermolysed) and heat treated wood with melamine-urea-formaldehyde (MUF), phenol-resorcinol-formaldehyde (PRF) and polyurethane (PUR) adhesives was studied. An industrial heat treatment process (Plato ^®) was used, which included two separate heat treatment stages and a drying stage in-between. Laminated beams having four lamellas were prepared from untreated and treated timber for mechanical testing of the bond lines. The results of the tests showed that heat treatment affected the shear strength and the delamination of the laminated wood depending on the adhesive system used for bonding. The PUR and MUF adhesives performed in a rather similar way, and better than the PRF adhesive. The shear strength of laminated wood bonded with the waterborne MUF and PRF adhesives decreased for the specimens made of hydro-thermolysed timber and decreased further for the specimens made of fully heat treated timber. The difference in adhesive bond shear strength between untreated, intermediate and fully treated wood was less obvious in the case of the PUR adhesive. Delamination of the PRF bond line decreased drastically for all the specimens made of heat treated timber.     

木材工业用酚醛树脂的改性研究现状

从降低成本、提高性能的角度阐述了近几年来木材工业用酚醛树脂胶粘剂改性研究及应用的现状。     

Functional properties and retrogradation behaviour of native and chemically modified starch of mucuna bean (Mucuna pruriens)

Mucuna bean (Mucuna pruriens) starch was isolated and subjected to chemical modification by oxidation and acetylation. The proximate analysis of the non‐starch components of the native starch on a dry weight basis was 92 g kg^?1 moisture, 5 g kg^?1 ash, 2 g kg^?1 fat, 7 g kg^?1 crude fibre and 19 g kg^?1 protein. Chemical modification reduced the values for all the non‐starch components except the moisture level. For all the samples, swelling power and solubility increased as the temperature increased in the range 50–90 °C. The swelling power of mucuna native starch (MNS) and mucuna acetylated starch (MAS) increased with increasing acidity and alkalinity, while that of mucuna oxidised starch (MOS) only increased with increasing pH in the acidic range. The maximal solubility of all the starches was observed at pH 12. All the starch samples absorbed more oil than water. The lowest gelation concentration followed the trend MAS < MNS < MOS. Chemical modification reduced the gelatinisation temperature (Tp), while peak viscosity (Pv), hot paste viscosity (Hv) and cold paste viscosity (Cv) decreased after oxidation but increased following acetylation. The setback tendency of the native starch was reduced significantly after chemical modification. However, the breakdown value of MNS, 65 BU (Brabender units), was lower than that of MOS (78 BU) but higher than that of MAS (40 BU). Differential scanning calorimetry studies of gelatinisation and retrogradation revealed that chemical modification reduced the onset temperature (T_o), peak temperature (T_p) and conclusion temperature (T_c). Oxidation and acetylation reduced the gelatinisation and retrogradation enthalpies of the native starch. The enthalpy of retrogradation of the starches increased as the length of storage increased. Copyright © 2003 Society of Chemical Industry     

Swelling kinetics of thermally modified wood

European Journal of Wood and Wood Products - The swelling kinetics of native and thermally modified wood was studied. Norway spruce, Scots pine, European beech, and English oak specimens of...     

On the formaldehyde release of wood particles

The emission of formaldehyde from softwood particles, as measured by the flask method (EN 717-3), depends highly on the particle size. Therefore, no definite value for the formaldehyde release from wood can be given.     

Proteolytic activity and immunoreactivity of chemically modified papain

The effect of different chemical modifications of papain on the proteolytic activity and immunoreactivity has been studied. Modification with Dextran T 2000 caused increasing decline in proteolytic activity both with increasing degree of dextran oxidation and amount of bound dextran, whilst the immunoreactivity determined by nephelometry remained unchanged. Modification of papain with glutaraldehyde and formaldehyde causes rapid drops in both activities, even at very low concentrations of agents. Acetylation of papain showed expressive maxima of both proteolytic and immunochemical activities at the same degree of enzyme acetylation. Modification with diazobenzenesulfonic acid caused a high increase in immunoreactivity and a small increase in proteolytic activity.     

Pressure-assisted gelation of chemically modified poultry meat batters

Changes were induced in the characteristics of poultry meat protein using specific chemical modifiers to investigate the effect of pressurization, prior to heating, on gelation, texture and thermal behaviour of meat batters. Values of hardness and chewiness were higher in cooked meat batters treated with urea than in a salt-only sample, but cohesiveness was similar. The β-mercaptoethanol treatment produced a heat-induced gel with very similar properties to the salt-only gel. The rheological behaviours of salt-only and β-mercaptoethanol samples were very similar, but storage modulus values were higher in samples with urea, which accelerated gelation. The pressure-induced reduction of differences in the textural properties of meat batters suggests that hydrophobic interactions play an important role in heat-induced gelation. Differential scanning calorimetry showed that urea clearly destabilized chicken meat batters, while β-mercaptoethanol had very little influence on their thermal behaviour. Pressurization tended to equalize batters and final cooking definitively equalized them.     

Proteolytic activity and immunoreactivity of chemically modified Papain

Summary The effect of different chemical modifications of papain on the proteolytic activity and immunoreactivity has been studied. Modification with Dextran T 2000 caused increasing decline in proteolytic activity both with increasing degree of dextran oxidation and amount of bound dextran, whilst the immunoreactivity determined by nephelometry remained unchanged. Modification of papain with glutaraldehyde and formaldehyde causes rapid drops in both activities, even at very low concentrations of agents. Acetylation of papain showed expressive maxima of both proteolytic and immunochemical activities at the same degree of enzyme acetylation. Modification with diazobenzensulphonic acid caused a high increase in immunoreactivity and a small increase in proteolytic activity.

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Proteolytische Aktivität und Immunreaktivität von chemisch modifiziertem Papain

Zusammenfassung Es wurde der Einfluß verschiedener chemischer Modifizierung des Papains auf dessen proteolytische Aktivität und Immunreaktivität untersucht. Die Modifikation des Papains mit Dextran T 2000 1äßt die proteolytische Aktivität bei steigender Dextran-oxidation und mit der Menge des gebundenen Dextrans abnehmen, wobei die Immunreaktivität, nephelometrisch bestimmt, unverändert bleibt. Bei der Modifizierung von Papain mit Glutaraldehyd und Formaldehyd werden beide Aktivitäten, auch bei sehr niedrigen Konzentrationen der Reagentien, stark erniedrigt. Das acetylierte Papain zeigt ein scharfes Maximum der proteolytischen und der immunchemischen Aktivität bei demselben Grad der Enzymacetylierung. Die Modifizierung von Papain mit der Diazobenzosulfonsäure verursacht einen hohen Anstieg der Immunreaktivität und einen nur geringen der proteolytischen Aktivität.

     

Mechano-sorptive behaviour of wood and its use for moisture content determination

The enhanced ability of small wooden beams to deform under decreasing moisture content conditions when subjected to constant bending and torsional stresses, has been studied. Initially green samples of Eucalyptus grandis and Pinus sylvestris were used. The purpose of the study was to determine whether the increased deformation during desorption or drying conditions, as reported by other workers, could be used as an indicator of the instantaneous average moisture content. For both species, relative torsional and bending deformation (RTD and RBD) increased with decreasing moisture content and the deformation also increased with increasing temperature. In the case of E. grandis both RTD and RBD could be used to determine moisture content under drying conditions while for P. sylvestris the relationship between RBD and moisture content was more pronounced than that between RTD and moisture content.