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![Crystal structure and hydrogen-bonding system in Cellulose I (exactly cellulose Iβ). The blue and red broken lines show both intra-chain and inter-chain hydrogen bonds [185], Copyright (2019), with permission from Elsevier.](profile/Mohammad-Farajollah-Pour/publication/364200919/figure/fig12/AS:11431281088646727@1665220630898/Crystal-structure-and-hydrogen-bonding-system-in-Cellulose-I-exactly-cellulose-Ib-The.png)
Crystal structure and hydrogen-bonding system in Cellulose I (exactly cellulose Iβ). The blue and red broken lines show both intra-chain and inter-chain hydrogen bonds [185], Copyright (2019), with permission from Elsevier.
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![Fig. 3. The ubiquitous occurrence of cellulose in nature [107],...](profile/Mohammad-Farajollah-Pour/publication/364200919/figure/fig3/AS:11431281088657520@1665220630293/The-ubiquitous-occurrence-of-cellulose-in-nature-107-Copyright-2010-with-permission_Q320.jpg)
In recent years, growing consideration of the concepts of ecological sustainability, environmentally friendly, recyclability, non-toxicity and biodegradability towards a green environment, have led scientists to focus on the utilization of natural fibers as green reinforcing agents for improving thermal, physical, and mechanical characteristics of...
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... Formaldehyde can also polymerize on its own, and this reaction occurs by condensation of formaldehyde molecules to each other. However, this chemical reaction occurs mostly in an acidic environment [24,25]. ...
In this research, it has been determined that the ratio of phenol to formaldehyde is an important factor in determining the properties of the resulting resin. In experimental studies, a molar ratio (1/1.5) of phenol/formaldehyde is used. With higher phenol ratios, resins with better thermal stability and chemical resistance are obtained. However, considering production costs, optimization studies have been carried out according to the final product's desired characteristics and the application's special requirements. It appears that the amounts of phenol and formaldehyde used in the production process depend on the phenol/formaldehyde ratio selected according to the desired properties. In the reaction between phenol and formaldehyde to form phenol formaldehyde resin (PFR), high temperature, and pressure can be preferred to facilitate the reaction and achieve higher yield. In this study, physical interactions and chemical reactions are monitored at atmospheric pressure at temperatures of 70 °C, 80 °C, 90 °C, and 100 °C. According to the results obtained the bulk density of PFR decreases as the production temperature increases. Additionally, increasing the production temperature increases Shore D hardness of PFR. At low production temperatures, the thermal conductivity of PFR is also low. Sulfuric acid is used to catalyze the chemical reaction between phenol and formaldehyde. The manufacturing process of PFR is often optimized through experimental trials to maximize resin yield, quality, and cost-effectiveness. The production of PFR depends on the ratio of phenol to formaldehyde, amounts of reactants, reaction conditions, catalyst selection, and optimization parameters. According to these factors, efficient and cost-effective resin production is envisaged in industrial applications.
... It holds substantial practical significance in advancing their application in high-temperature engineering environments. 6 The mechanistic study of resin oxidative degradation by infrared spectroscopy and other methods has attracted early attention. Conley et al. analyzed the chemical structural changes of the phenol-formaldehyde resin during air oxidation degradation at 373−473 K by infrared spectroscopy. ...
... Moreover, as mentioned by Kristak et al. (2023), it is difficult to compare the outcomes of individual studies because they are obtained with different testing methods and the experiments are performed at different testing conditions. However, according to what is known so far, Réh et al. (2021) listed the following approaches to minimize the harmful emissions from wood-based materials: synthesis of ultra-low-emitting formaldehyde UF adhesive types with low or very low formaldehyde content, i.e. having low formaldehyde to urea molar ratios (Lubis et al. 2022, Frihart et al. 2023, the use of various inorganic, organic, and mineral compounds as formaldehyde scavengers in the adhesive systems (Barbu et al. 2020, Camlibel 2020, Taghiyari et al. 2020a, 2020b, Kord et al. 2022, modification of pressing parameters applied (pressing temperature and pressing time) (Puttasukkha et al. 2015), post-treatments or surface treatments of final products (Roffael 2011, Costa et al. 2013, and development of eco-friendly, formaldehyde-free, biobased wood adhesives (Hemmilä et al. 2017, Arias et al. 2021, Dorieh et al. 2022, Hussin et al. 2022. Although many of these methods have been widely studied for years, according to Demir (2023) modification of conventional adhesives with formaldehyde scavengers is still the most preferred one. ...
Research on reducing the formaldehyde emission from wood-based materials bonded with urea-formaldehyde (UF) resin has attracted the attention of scientists for years. Many studies investigated the possibility of using amines for this purpose; however, the outcomes of the vast majority of them have shown that the limiting factor is reduced resin reactivity and consequently, deterioration of the strength of the resultant materials as well. Therefore, the aim of this research work was to investigate and evaluate the effect of the pressing protocol applied (pressing temperature and time), and hardener content (20% ammonium nitrate solution) on the properties of plywood bonded with UF adhesive system modified with 1% of propylamine. Manufactured plywood was tested in terms of shear strength (in dry and wet conditions) and formaldehyde emission (measured initially and after 4 weeks). Based on the results, it was found that it is possible to produce plywood with equally good characteristics as the reference, non-modified variant by increasing hardener content from 3% to 7%, increasing pressing temperature from 120°C to 150°C, and extending the pressing time from 240 to 300 s. Markedly, the implementation of these adjustments also contributed to a further decrease in formaldehyde emission.
... 95% of all adhesives applied in the wood-based materials industry [5,6]. Therefore, considering their dominant market share and the growing requirements in terms of the performance of wood-based materials, studies on the possibility of their enhancement are still the subject of numerous scientific works conducted worldwide [7][8][9]. ...
Due to the fact that impregnation with fire retardant usually reduces the strength of the produced particleboards, this research was carried out to investigate whether it is possible to use phenol-formaldehyde (PF) resin modified using various amounts (0%, 5%, 10%, 15%, and 20%) of polymeric 4,4-methylene diphenyl diisocyanate (pMDI) for this purpose. The need to optimize the addition of pMDI is particularly important due to health and environmental aspects and high price. Furthermore, the curing process of hybrid resins is still not fully explained, especially in the case of small loadings. Manufactured particleboards differed in the share of impregnated particles (50% and 100%). The mixture of potassium carbonate and urea was used as the impregnating solution. Based on the outcomes of hybrid resins properties, it was found that the addition of pMDI leads to the increase in solid content, pH, and viscosity of the mixtures, to the improvement in resin reactivity determined using differential scanning calorimetry and to the decrease in thermal stability in the cured state evaluated using thermogravimetric analysis. Moreover, particleboard property results have shown that using impregnated particles (both 50% and 100%) decreased the strength of manufactured boards bonded using neat PF resin. However, the introduction of pMDI allowed us to compensate for the negative impact of fire-retardant-treated wood and it was found that the optimal loading of pMDI for the board containing 50% of impregnated particles is 5% and for board made entirely of treated wood it is 10%.
... Wood composites are manufactured from different wood and non-wood lignocellulosic raw materials, bonded together with synthetic or bio-based adhesives and used for particular value-added applications and service requirements [1-9]. Conventional woodbased composites are manufactured with synthetic, formaldehyde-based resins, commonly produced from petroleum-based components, such as urea, phenol and melamine [10][11][12][13]. The use of these thermoset adhesives has several drawbacks related to the release of harmful volatile organic compounds, such as formaldehyde emissions from the created wood-based composites. ...
... Wood composites are manufactured from different wood and non-wood lignocellulosic raw materials, bonded together with synthetic or bio-based adhesives and used for particular value-added applications and service requirements [1][2][3][4][5][6][7][8][9]. Conventional woodbased composites are manufactured with synthetic, formaldehyde-based resins, commonly produced from petroleum-based components, such as urea, phenol and melamine [10][11][12][13]. The use of these thermoset adhesives has several drawbacks related to the release of harmful volatile organic compounds, such as formaldehyde emissions from the created wood-based composites. ...
The ongoing twin transition of the wood-based panel industry towards a green, digital, and more resilient bioeconomy is essential for a successful transformation, with the aim of decarbonising the sector and implementing a circular development model, transforming linear industrial value chains to minimize pollution and waste generation, and providing more sustainable growth and jobs. This green transition represents an opportunity to place the wood-based panel industry on a new path of more sustainable and inclusive growth, tackling climate change and reducing our dependence on fossil-derived raw materials, thus improving the industry's resource efficiency and security. A crucial circular economy principle is exploiting natural resources more effectively to produce various value-added wood-based products, as the demand for wood and wood-based components is anticipated to triple between 2010 and 2050. In efforts to promote effective recycling and reuse, the upcycling of wood and wood-based materials and the search for substitute raw materials, recent legislative regulations and increased awareness of social environments have posed new challenges to both industry and academia. These regulations and laws are related to enhancing the "cascading use" of wood or prioritising the value-added, non-fuel applications of wood and other lignocellulosic resources.
... One key topic to be investigated is the curing process and characteristics of resin under vacuum conditions since the curing behavior of resin directly affects both the hot-pressing procedure and the quality of the plywood products. The cure of PF resins is complex due to the interaction between the chemical kinetics and changes in their physical properties [7][8][9][10][11][12]. One method to investigate the cure of PF resins is to determine their gel times and temperatures. ...
... Wood composites are engineered wood-based materials that are fabricated from a wide variety of wood and other non-wood lignocellulosic materials, bonded with synthetic or natural bio-based adhesive systems, and designed for specific value-added applications and performance requirements [1-6]. Traditional wood-based composites are fabricated using synthetic formaldehyde-based adhesives that are commonly formed from fossil-derived constituents, such as urea, phenol, and melamine [7][8][9]. Along with their undisputable advantages, these adhesives are characterized by certain problems related to the emission of hazardous volatile organic compounds (VOCs), including free formaldehyde emissions from the finished wood composites, which is carcinogenic to humans and harmful to the environment [10-12]. The growing environmental concerns connected with the adoption of circular economy principles and the new, stricter legislative requirements for the emission of harmful VOCs, such as free formaldehyde, from wood composites pose new challenges for researchers and industrial practice. ...
... Wood composites are engineered wood-based materials that are fabricated from a wide variety of wood and other non-wood lignocellulosic materials, bonded with synthetic or natural bio-based adhesive systems, and designed for specific value-added applications and performance requirements [1][2][3][4][5][6]. Traditional wood-based composites are fabricated using synthetic formaldehyde-based adhesives that are commonly formed from fossil-derived constituents, such as urea, phenol, and melamine [7][8][9]. Along with their undisputable advantages, these adhesives are characterized by certain problems related to the emission of hazardous volatile organic compounds (VOCs), including free formaldehyde emissions from the finished wood composites, which is carcinogenic to humans and harmful to the environment [10][11][12]. The growing environmental concerns connected with the adoption of circular economy principles and the new, stricter legislative requirements for the emission of harmful VOCs, such as free formaldehyde, from wood composites pose new challenges for researchers and industrial practice. ...
The wood of forest trees is a renewable, sustainable and easily workable material and has been widely used in construction, paper making, and furniture and as a feedstock for biofuels. Wood composites are engineered wood-based materials that are fabricated from a wide variety of wood and other non-wood lignocellulosic materials, bonded with synthetic or natural bio-based adhesive systems, and designed for specific value-added applications and performance requirements [1,2,3,4,5,6]. Traditional wood-based composites are fabricated using synthetic formaldehyde-based adhesives that are commonly formed from fossil-derived constituents, such as urea, phenol, and melamine [7,8,9]. Along with their undisputable advantages, these adhesives are characterized by certain problems related to the emission of hazardous volatile organic compounds (VOCs), including free formaldehyde emissions from the finished wood composites, which is carcinogenic to humans and harmful to the environment [10,11,12]. The growing environmental concerns connected with the adoption of circular economy principles and the new, stricter legislative requirements for the emission of harmful VOCs, such as free formaldehyde, from wood composites pose new challenges for researchers and industrial practice. These challenges are related to the development of sustainable, eco-friendly wood composites [13,14,15], the optimization of the available lignocellulosic raw materials [16,17,18], and the use of alternative resources [19,20,21,22,23]. The harmful release of formaldehyde from wood composites can be reduced by applying formaldehyde scavengers to conventional adhesive systems [24,25,26,27], by the surface treatment of the finished wood composites, or by the application of novel bio-based wood adhesives as environmentally friendly alternatives to traditional synthetic resins [28,29,30]. Another alternative to the use of synthetic formaldehyde-based adhesives is the manufacturing of binderless wood composites, since wood is a natural polymer material that is rich in lignocellulosic compounds such as cellulose, hemicellulose, and lignin.
The article examines the effect of the complex effect of technological factors on the properties of a composite material in the production of aspen veneer plywood used for the production of LVL blocks used in construction. To obtain composite plywood, it is proposed to use an aspen veneer compacted by rolling and a complex binder including phenol-formaldehyde resin of the SFG-3014 brand and nanocrystalline cellulose treated in an ultrasonic field, in the presence of electromagnetic action on the finished plywood by a pulsed magnetic field. Introduction to binder 2 wt. The use of nanocrystalline cellulose made it possible to obtain plywood with increased physical and mechanical properties: tensile strength during static bending (at 155 %), when chipping along the adhesive seam (at 330 %), impact strength during bending (at 144 %). The hydrophobization of the veneer with cardanol ensured a decrease in moisture absorption of plywood (at 300 %) and swelling in the direction of pressing (at 125 %). The study was carried out according to the Hartley plan with varying factors: the content of nanocrystalline cellulose in the binder (from 2 to 6 wt.%), pressing pressure (from 3 to 9 MPa), exposure time to a pulsed magnetic field (from 1 to 9 min).
