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resin content of different wood types and cell wall locations at various conditions and impregnation regimes; larch ¼ Larix decidua Mill., pine ¼ Pinus sylvestris L., spruce ¼ Picea abies [L.] Karst
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Melamine-formaldehyde (MF) resin impregnation has shown considerable potential to improve a number of wood properties, such as surface hardness and weathering resistance. In this study, selected factors influencing the uptake of MF resin into the cell wall of softwood were studied. Using UV-microspectroscopy, it could be shown that water soluble MF...
Contexts in source publication
Context 1
... higher MF concentrations distinct peaks appeared around 240 nm. Table 1 lists MF contents (v/v) determined in late- wood secondary walls (S2) from sapwood and heart- wood of three species. Measurements were done at different impregnation durations, wood types, cell wall locations and impregnation regimes. ...Context 2
... (1964) gives a calculated maximum volumetric swelling in organic liq- uids of the cell wall of about 38%. This number is in the range of the observed 24% (v/v) MF resin in spruce sapwood after 20 h of penetration (Table 1). ...Context 3
... consistently lower MF concentration was found in heartwood compared to sapwood (Table 1), with the difference being more pronounced in larch than in pine. This is in agreement with Bailey and Preston (1969) who reported for Douglas fir a markedly lower concentration of silver grains in heartwood cell walls compared to sapwood. ...Context 4
... water in cell wall capillaries through increasingly less polar liquids with low surface tension, the collapse of these pores may be partially prevented, with a certain level of porosity preserved dry (Stamm, 1964;Bower and Wellons, 1974). Results obtained in this study show that the MF uptake was increased due to solvent exchange drying (factor of 2.5), however, the increase was not dramatic (Table 1). Since similar impregnation results were achieved with fully water saturated cell walls, the feasibility of solvent exchange drying as a possible pre- treatment to increase resin uptake can be questioned. ...Context 5
... measurements show that more MF resin had penetrated fully water saturated spruce cell walls after 1 h, than dried cell walls after 20 h. The initial difference progressively disappeared with increased duration of impregnation (Table 1, Fig. 3). The initial difference in resin uptake might be explained by the fact that MF resin per se cannot penetrate into dry cell walls. ...Context 6
... are showing that drying of the cell wall from its native, fully water satu- rated state leads to an unrecoverable loss of porosity (Tynj€ a al€ a a and K€ a arenlampi, 2001). In our study this phenomenon had no or only a minor effect on the im- pregnation of cell walls using MF resin (Table 1). ...Context 7
... final aspect investigated in this study was the effect of resin concentration on the penetration of MF resin into dry cell walls. Presence of water enhanced impregnation and more than twice the resin content was found in the cell walls after treatment with 25% resin, compared to impregnation with 55-60% resin (Table 1). With this, it has to be taken into account that increased viscosity at higher resin concentrations may have con- tributed to the slower resin uptake. ...Similar publications
Tuning the supramolecular morphology of an equimolar complex of riboflavin and melamine by the in situ formation of different size silver nanoparticles, affecting the photoluminescence property.
Citations
... Other treatment with chemical components and different types of resin impregnation (DMDHEU, melamine, phenol, furfuryl) were investigated by e.g. [19,13,21,14,11,17] and many more. Beside of the published study from [4] using alkaline, densification and partial extraction of wood polymers will attract attention. ...
... Thermosetting resins used for wood modification purposes are characterized by their molecular weight (size) and polarity, which allows to enter the macropores (cell lumen) but also the nanopores of the water-swollen wood cell wall [255,262,[273][274][275][276][277]. Similar to other impregnation modification techniques, treatments with thermosetting resins create a bulking effect (CWB), as the cell wall is set in a permanent swollen state when resin molecules polymerize within the cell wall ( Figure 8). ...
Wood modifications are becoming popular as a way to enhance the performance of wood, either to make it more durable, improve the performance of wood, or give it new functionality as a multifunctional or smart material. While wood modifications have been examined since the early 1900s, the topic has become a dominant area of study in wood science over the past decade. This review summarizes recent advances and provides future perspective on a selection of wood modifications, i.e., the methods that are currently commercialized (acetylation, furfurylation, and thermal modification), a rediscovered ancient practice (charring), a family of polymerization modifications that have so far made it to the pilot scale, and examples of novel wood-based functional materials explored at laboratory scale.
... Resin modification is a promising technology for enhancing the durability and mechanical performance of timber. Most studies consider synthetic resins, such as melamine urea formaldehyde and phenol formaldehyde (Gindl et al. 2003, Stefanowski et al. 2018) however there is interest in bio-based alternative resins for wood treatment. A bio-based resin derived from cashew nut shell liquid (CNSL) was used in this study (Fitchett et al. 2003, Khan et al. 2000a. ...
Resin modification using a bio-based resin derived from cashew nut shell liquid (CNSL) was undertaken on the sapwood of three species of tropical hardwood timber: Obeche (Triplochiton scleroxylon), Gmelina (Gmelina arborea) and Alstonia (Alstonia scholaris). The species had been selected on the basis of low density to enable uptake of resin, however level of uptake varied, in relation to presence of tyloses within the vessels. Dynamic mechanical analysis (DMA) was used to observe the secondary relaxations of the timbers and the glass transition (Tg) of the resin. A thermal scan from-150 to +150°C was used in three point bending, with multiple frequencies (0.1 Hz, 1.0 Hz and 10 Hz). The glass transition temperature of cured CNSL resin was observed between 60 and 75°C, with the value increasing with frequency used for testing. Each species was impregnated with three concentrations of CNSL resin solution, giving three different weight percent gain (WPG) levels. Within each species, the Tg of resin was seen to increase as the WPG of resin increased. However, between species this relationship did not hold. Alstonia scholaris, which had the highest WPG values (17.4, 31.4 and 42.5%) recorded only intermediate values of Tg, whereas Gmelina, which had lowest WPG values (4.6, 4.8 and 10.8%), showed the highest range of Tg values. It is proposed that differences in wood anatomy and cell structure influence the distribution of resin, and size of droplets, plugs or layers of resin formed within the modified wood. In samples with higher WPG (Alstonia and Obeche), the activation energy of the resin Tg event was 738 and 767 kJ/mol respectively.
... MF is a thermosetting resin which is available in high concentrations (65-75%) and requires dilution due to its high viscosity; the dilution process requires the MF resin to be produced in an etherified form to increase water tolerance and enables the MF resin to penetrate the timber cellular structure [75]. With MF being one of the hardest and stiffest isotropic polymeric materials, substituting PF resins with MF resins in the impregnation of timber has shown potential in improving several properties of timber, such as MOE, hardness, weathering resistance, and dimensional stability [75,76]. Almost complete fixation of the timber after thermal compression is seen with specimen soaking and boiling under water [75], performing better than THM treatments in soaking cycles and efficiency in production due to the elimination of drying and cooling stages [77,78]. ...
Timber densification is a process that has been around since the early 1900s and is predominantly used to enhance the structural properties of timber. The process of densification provides the timber with a greater mechanical strength, hardness, abrasion resistance, and dimensional stability in comparison to its virgin counterparts. It alters the cellular structure of the timber through compression, chemical impregnation, or the combination of the two. This in turn closes the voids of the timber or fills the porosity of the cell wall structure,
increasing the density of the timber and, therefore, changing its properties. Several processes are reported in literature which produce densified timber, considering the effect of various parameters, such as the compression ratio, and the temperature on the mechanical
properties of the densified timber. This paper presents an overview of the current processes of timber densification and its corresponding effects. The material properties of densified timber, applications, and possible future directions are also explored, as the potential of this innovative material is still not fully realised.
... Melamine-formaldehyde formulations are often referred as aminoplastic resins, and is one of the most essential aminoplastic resins useful in decorative laminates, coating materials and the production of panels. The advantages of MF resins include unique surface properties, excellent resistance against temperature, scratch, fire retardancy, moisture and mechanical stress [88,89]. ...
Nanomaterials are receiving global attention due to outstanding high effectiveness and thermal stability, fire retardancy, excellent physical-mechanical properties, good technological properties, and biocompatibility. In this review, a survey of the literature on extending the performance of melamine-formaldehyde resin (MFR) based on nanomaterials is presented. The properties-performance relationships for different nanomaterials modified MFR are closely examined. MFR adhesives are commonly used because they have superior adhesive properties and water resistance. Nano-technology has a massive potential to enhance polymer composites with improved performance. Nanomaterial-improved polymers for adhesives have been progressed to enhance the properties of wood composites. MFR is one of the most common thermoset resins for coating applications. Based on nanotechnology, it is possible to design advanced MFR-based polymers for industrial uses such as coatings. In this critical review, for the first time, it is emphasized the importance of the recent progress on the impact of nanomaterials to improve the performance of MFR adhesives such as mechanical properties, thermal stability, fire retardancy and free formaldehyde emission, and various aspects of such engineered polymers are discussed and accentuated. Using nanoparticles in liquid MFR adhesives has the potential to significantly lower environmental and health hazards. Eventually, based on the above discussion, the challenges and perspectives about future enhancements emphasizes the necessity of a new vision into the high-level analysis of what happens at the MFR and nanomaterial studies that are not actually clear in the research on the coating industry. To synthesize MFR nanocomposites for industrial use, the processing of these nanocomposites must be developed from lab-scale to industrially appropriate approaches.
... Methylation of the methylol melamine with methanol improves its miscibility with water, limits self-condensation during storage and allows the use of aqueous solutions of low molecular weight for polymerisation inside the wood. The molecules are small enough to enter not only the wood lumens but also the nanopores in the water-swollen cell wall (Gindl et al. 2003;Rapp et al. 2005). Heat curing at elevated temperatures removes the water and induces self-condensation of the MF resin via methylene bridges or ether bonds (Pizzi 2003). ...
The wood-water interactions of modified beech wood ( Fagus sylvatica L.) were studied. Specimens were thermally modified at 180 (TM 1 ), 200 (TM 2 ) and 220 °C (TM 3 ), acetylated (Acet), and melamine formaldehyde (MF) resin (Mel) modified. Afterwards, the water vapour characteristics, i.e. water vapour sorption isotherms, equilibrium moisture content (EMC), dimensional stability of specimens conditioned at 30, 65 and 90% RH and liquid water characteristics, i.e. water absorption, maximum moisture content (MC), leachability and swelling kinetics, were determined and the results compared with reference (Ref) specimens. From the results, it is evident that the scale of wood-water interactions was highly dependent on the thermal modification temperature and type of chemical modification. The water vapour isotherms of thermally modified wood decreased, whereas more severe treatment exhibited more distinct reduction. The EMC values of the Mel and TM 1 specimens decreased only at high RH, whereas the most significant decrease, within the whole range of observation, was found in the Acet group. The maximum MC reduction was achieved by acetylation. As a consequence of swelling reduction, dimensional stability expressed as anti-swelling efficiency (ASE) was considerably improved. A relatively high initial linear-phase swelling rate was found for the Ref specimens, whereas modified wood exhibited comparatively slow and gradual swelling.
... [27][28][29] The MF resin solution not only fills the empty lumen space of wood cells but can also penetrate into the wood cell wall during soaking treatment. [30,31] In addition, MF is optically transparent with RI (≈1.50, Table S1) similar to the wood substrate (≈1.54). [32] An interesting possibility for reduced environmental stress is that MF resins can be biobased. ...
... This finding confirms that MF successfully impregnated the wood cell wall in the present process, forming a nanocomposite in cell wall domains, as observed for some other processing methods. [30] The difference in N signal contrast between lumen and cell wall is because of lower MF content in the cell wall. The dark lines in Fig. 3a and b are from debond gaps. ...
Transparent wood (TW) biocomposites combine high optical transmittance and good mechanical properties and can contribute to sustainable development. The safety against fire is important for building applications. Here, a “green” bleached wood reinforcement is impregnated by water soluble and flame-retardant melamine formaldehyde (MF) in a scalable process, for a wood content of 25 vol%. FE-SEM is used for characterization of optical defects and EDX to examine MF distribution at nanoscale cell wall pore space. Curing (FTIR-ATR), mechanical properties, optical transmittance (74% at 1.2 mm thickness) and flame-retardant properties are also characterized (self-extinguishing behavior and cone calorimetry), and scattering mechanisms are discussed. The fire growth rate of transparent wood was less than half the values for neat wood. Transparent wood/MF biocomposites show interesting wood-MF synergies and are of practical interest in building applications. Critical aspects of processing are analyzed for minimization of optical defects.
... They have been commercially used available for over sixty years. They have been used for exterior and semi exterior wood panels where they have provided advantages such as water and heat resistance, hardening, low flammability and shorter hardening times in comparison to urea formaldehyde adhesives [10,11]. The higher resistance of melamine formaldehyde to water absorption is due to the considerably less dissolution of melamine in water. ...
Antimony trioxide (AT) was added to melamine formaldehyde (MF) adhesive at concentrations of 4% and 8% to produce fiberboard panels. The microcrystalline cellulose (MCC) loading for the panels was 5 and 10% based on dry adhesive amount. It was determined that the antimony trioxide usage resulted in a positive effect on the physical properties of fiberboard panels. The modulus of rupture, modulus of elasticity, and internal bonding values of the fiberboard samples increased with increment antimony trioxide amount. The limiting oxygen index (LOI) levels of the antimony trioxide added samples were higher compared to those of control, MCC and MCC/AT samples. The addition of 8% of antimony trioxide resulted in the highest LOI value. The results revealed that antimony trioxide plays a significant role as a flame retardant. Thermal gravimetric analysis (TGA) curves of microcrystalline cellulose and antimony trioxide added samples showed similar thermal behavior.
... The impregnation of wood with various monomers and resins, and then their conversion into a polymer in situ, is one of the approaches to improve wood properties (Hill 2006). Some materials that have been used in commercial systems for wood impregnation include vinyl monomers (Li 2011), furfuryl alcohol (Buchelt et al. 2012), amino and phenolic resins (Gindl et al. 2003), and silicone compounds (Mai and Militz 2004). In-situ polymerization of monomer or resin in wood by one of the common methods, such as curing, adding a hardener, or with radiation, leads to a new product called a wood polymer. ...
Furfural (F) cannot be easily polymerized like furfuryl alcohol, but it is an aldehyde that can react with urea (U) to make a polymeric network. The possibility of preparing F/U polymer along with an acidic catalyzer (maleic anhydride; M) was evaluated as a means to improve some selected properties of birch (Betula pendula) wood. The F+U/M resin was introduced into the wood with a double treatment technology. The first step involved dilution of F in water and methanol, and the second step was immersion in a U/M aqueous solution. The color of treated wood was darkened after resin curing from brown to a spectrum of black depending on the amount of loaded resin. The 60 to 80% of materials were converted to a non-leachable polymer based on the different formulations. The water absorption and volumetric swelling of the treated samples decreased with an increase in weight percent gain (WPG). The analysis of mechanical strength showed that treatment with F + U/M reduced to some extent the hardness and the impact bending of wood, while modulus of rupture, modulus of elasticity, and compression parallel to the grain with WPG were increased. The exposure of the samples to the accelerated weathering showed noticeable changes in color and roughness.
... Nevertheless, the viscosity of the 8-30MF formulation was still considered low and not a problem for achieving suitable impregnation of the wood boards. 31,32 Simultaneously, the upper pH of 8-30MF is also limited due to the lower water solubility of BA at higher pH. BA converts into borax under alkali conditions, and borax has a lower water solubility than BA. ...
... The penetration of MF resin is also favored as its relatively low molecular weights make it easier to diffuse into the cell wall as previously reported. 32 Weight percentage gain (WPG) data showed the amount of loaded chemicals within the wood structure after the treatments (Figure 1b). WPG depends on various parameters such as the solid content and viscosity of the formulation, impregnation procedures, wood species and tissues, etc. ...
... This further suggests that diffusion of the MF prepolymer into the cell walls followed by in situ polymerization may result in cell wall reinforcement. 32 Previous reported studies show that the diffusion of the prepolymer after curing may permanently bulk the cell walls and thus increase the dimensional stability of treated wood. 39 The MF fragmented coatings were also observed in the bordered pits ( Figure S2b), which resulted in completely filled-in pits/voids. ...
The objective of the work was to improve the leaching resistance of fire-retardant (FR) modified wood by the incorporation of a thermoset resin. Here, Scots pine (Pinus sylvestris L.) sapwood was impregnated with melamine form-aldehyde (MF) resin and hydrophilic FRs guanyl-urea phosphate/ boric acid by a vacuum-pressure treatment. Resistance to leaching of FR-modified wood was evaluated, after conducting an accelerated aging test according to European standard EN 84. Inductively coupled plasma analysis showed that the incorporation of MF resin significantly reduced the leachability of FRs. Scanning electron microscopy/energy-dispersive X-ray spectrometry revealed that the mechanism of water resistance was by doping the FRs into MF resin microspheres. Fourier transform infrared spectra showed the chemical functionality changes of FR-modified wood such as the formation of methylene bridges by drying the modified wood specimens. An increase in the thermal stability of FR-modified wood was confirmed by thermal gravimetric analysis. Excellent fire performance of FR-modified wood after leaching was affirmed by the limiting oxygen index and cone calorimeter tests.
