scholarly journals Thermal Degradation of Bonding Strength of Aspen Plywood

2020 ◽  
Vol 71 (2) ◽  
pp. 185-192
Author(s):  
Pavlo Bekhta ◽  
Nataliya Bekhta
Keyword(s):  
Exposure Time ◽  
Bonding Strength ◽  
Elevated Temperatures ◽  
Phenol Formaldehyde ◽  
Mass Density ◽  
Urea Formaldehyde ◽  
Statistical Regression ◽  
Colour Difference ◽  
Initial Strength ◽  
Shear Strength Test

The objective of this research was to study the effect of exposure time on the bonding strength of aspen plywood at elevated temperatures. The plywood samples were manufactured under laboratory conditions using two types of adhesive: urea-formaldehyde (UF) and phenol-formaldehyde (PF). The plywood samples were tested after exposure to three different temperatures (150 °C, 200 °C and 250 °C) and three exposure time levels (1, 2 and 3 hours) at each temperature. Additionally, a set of control samples was tested at room temperature. The quality of bonding was assessed by shear strength test in compliance with the requirements of the standard EN 314-1. The mass and density losses as well as colour changes of the plywood samples were also determined. The findings of this study indicated that exposure of plywood panels to elevated temperature caused significant degradation of their bonding strength. PF plywood samples lost 63.2 % of their initial strength after 3 h of exposure at 250 °C, while UF samples lost 65.9 % of their initial strength already after 3 h of exposure at the temperature of 200 °C. Statistical regression-based models were also developed for predicting the loss of plywood bonding strength as functions of mass and density losses and total colour difference. As the mass/density losses or total colour difference of panels increased, the losses in bonding strength increased too.

scholarly journals Effect of Veneer-Drying Temperature on Selected Properties and Formaldehyde Emission of Birch Plywood

Polymers ◽  
2020 ◽  
Vol 12 (3) ◽  
pp. 593 ◽  
Author(s):  
Pavlo Bekhta ◽  
Ján Sedliačik ◽  
Nataliya Bekhta
Keyword(s):  
Modulus Of Elasticity ◽  
Bonding Strength ◽  
Elevated Temperatures ◽  
Bending Strength ◽  
Phenol Formaldehyde ◽  
Urea Formaldehyde ◽  
Physical And Mechanical Properties ◽  
Formaldehyde Emission ◽  
Bonding Quality ◽  
Mean Values

In this study, the effect of the veneer-drying process at elevated temperatures on selected properties and formaldehyde emission of plywood panels was determined. We assume that during the veneer drying at high temperatures, more formaldehyde is released from it, and therefore, a lower formaldehyde emission can be expected from the finished plywood. Prior to bonding, birch veneers were dried at 160 °C (control) and 185 °C in an industrial veneer steam dryer (SD) and at 180 °C, 240 °C and 280 °C in an industrial veneer gas dryer (GD). Two types of adhesives were used: urea–formaldehyde (UF) and phenol–formaldehyde (PF) resins. Bonding quality, bending strength and modulus of elasticity in bending, water absorption and thickness swelling of plywood samples were determined. The formaldehyde emission level of samples was also measured. It was concluded from the study that the effects of veneer-drying temperatures on the bonding strength and physical and mechanical properties of plywood panels were significant. Veneer-drying temperatures of 185 °C/SD, 180 °C/GD and 240 °C/GD negatively affected the bending strength and the modulus of elasticity along and across the fibres for both UF and PF plywood samples. Bonding strength mean values obtained from all test panels were above the required value (1.0 MPa) indicated in EN 314-2 standard. The lowest formaldehyde emissions for the UF and PF plywood samples were observed in the samples from veneer dried in a steam dryer at 185 °C/SD.

Thermal degradation of bending properties of structural wood and wood-based composites

Holzforschung ◽  
2011 ◽  
Vol 65 (2) ◽  
Author(s):  
Arijit Sinha ◽  
Rakesh Gupta ◽  
John A. Nairn
Keyword(s):  
Thermal Degradation ◽  
Exposure Time ◽  
Structural Integrity ◽  
Elevated Temperatures ◽  
Bending Strength ◽  
Oriented Strand Board ◽  
Thermal Exposure ◽  
Effect Of Temperature ◽  
Statistical Regression ◽  
Single Family

Abstract Wood and wood-based composites are being used extensi-vely in single-family residential dwellings. Therefore, it is important to categorize their response when exposed to elevated temperatures for a sustained period of time. In fire-resistant design for wood structures, the main goal is to ensure that enough structural integrity is maintained, during and after a fire, to prevent collapse and to maintain means of egress. Another goal is an ability to assess post-fire structural integrity and residual strength of an existing structure. The objectives of this study are: (a) to study the effect of temperature and exposure time on bending strength (MOR) and stiffness (MOE) of solid sawn lumber (SSL), laminated veneer lumber (LVL), oriented strand board (OSB) and plywood; and (b) to develop predictive relations between different temperatures and times of exposure and the thermal degradation of strength. A total of 1080 samples were tested in static bending under various heat treatments. The results indicated that exposure to elevated temperature caused significant degradation of bending strength and stiffness. A statistical regression-based model and a kinetics-based model were developed and evaluated for predicting the strength loss of wood and wood-based composites as a function of thermal exposure temperature and exposure time. The kinetics-based model fit the data better and predictions consistently matched the observed values, making the model preferred over the regression approach.

Preparation and Application of Modified Soybean Protein Adhesives

2010 ◽  
Vol 139-141 ◽  
pp. 706-709
Author(s):  
Zi Tao Sang ◽  
Shi Feng Zhang ◽  
Qiang Gao ◽  
Jian Zhang Li
Keyword(s):  
Sodium Hydroxide ◽  
Bonding Strength ◽  
Phenol Formaldehyde ◽  
Soybean Protein ◽  
Ftir Spectra ◽  
Absorption Peak ◽  
Type I ◽  
Curing Process ◽  
Protein Adhesives

In this study, a sodium hydroxide modified soybean protein adhesive (NSP adhesive) was prepared and mixed with phenol-formaldehyde (PF) resin in a ratio of 7:3 to form a compound adhesive (NSPF adhesive), and three-layer plywoods were prepared using the NSP adhesive and the NSPF adhesive. In order to understand the reactions between SP and PF resin during the curing process of NSPF adhesive, the SEM and FTIR spectra were employed to character the adhesives and the bonding strength of the plywoods was measured. The results showed that the bonding strength of the poplar plywood prepared with NSPF reached 1.00 MPa, and met type I plywood requirement in GB/T 17657-1999. There was new absorption peak appear at 1390 cm-1 in the FTIR spectra of NSPF adhesive, indicating that there were -NHCH2- structures generate in NSPF during the curing process in this research.

scholarly journals Lignosulphonates as an Alternative to Non-Renewable Binders in Wood-Based Materials

Polymers ◽  
2021 ◽  
Vol 13 (23) ◽  
pp. 4196
Author(s):  
Sofia Gonçalves ◽  
João Ferra ◽  
Nádia Paiva ◽  
Jorge Martins ◽  
Luísa H. Carvalho ◽  
...  
Keyword(s):  
Phenolic Compounds ◽  
Aromatic Ring ◽  
Phenol Formaldehyde ◽  
Urea Formaldehyde ◽  
Value Added ◽  
Wood Adhesives ◽  
Renewable Source ◽  
Pressing Time ◽  
Value Added Products ◽  
Total Market

Lignin is a widely abundant renewable source of phenolic compounds. Despite the growing interest on using it as a substitute for its petroleum-based counterparts, only 1 to 2% of the global lignin production is used for obtaining value-added products. Lignosulphonates (LS), derived from the sulphite pulping process, account for 90% of the total market of commercial lignin. The most successful industrial attempts to use lignin for wood adhesives are based on using this polymer as a partial substitute in phenol-formaldehyde or urea-formaldehyde resins. Alternatively, formaldehyde-free adhesives with lignin and lignosulphonates have also been developed with promising results. However, the low number of reactive sites available in lignin’s aromatic ring and high polydispersity have hindered its application in resin synthesis. Currently, finding suitable crosslinkers for LS and decreasing the long pressing time associated with lignin adhesives remains a challenge. Thus, several methods have been proposed to improve the reactivity of lignin molecules. In this paper, techniques to extract, characterize, as well as improve the reactivity of LS are addressed. The most recent advances in the application of LS in wood adhesives, with and without combination with formaldehyde, are also reviewed.

scholarly journals Phenol-formaldehyde resins with suitable bonding strength synthesized from “less-reactive” hardwood lignin fractions

Holzforschung ◽  
2020 ◽  
Vol 74 (2) ◽  
pp. 175-183 ◽  
Author(s):  
Tainise V. Lourençon ◽  
Sami Alakurtti ◽  
Tommi Virtanen ◽  
Anna-Stiina Jääskeläinen ◽  
Tiina Liitiä ◽  
...  
Keyword(s):  
Theoretical Calculation ◽  
Bonding Strength ◽  
Phenol Formaldehyde ◽  
Chemical Reactivity ◽  
Lignin Valorization ◽  
Similar Performance ◽  
Press Time ◽  
Practical Implications ◽  
Resin Bonding ◽  
End Uses

AbstractThe substitution of phenol by lignin in phenol-formaldehyde (PF) resins is one of the most promising end uses of lignin valorization. Lignin from grasses and softwood has been the focus of the studies in this field as they present a higher number of theoretical reactive sites for resin synthesis. Herein we examined the composition and chemical reactivity of “less-reactive” hardwood lignin fractions and their performance in PF resins, synthesized by substituting 50 wt% of the phenol with lignin. Before resin synthesis, the samples were hydroxymethylated and the maximum formaldehyde consumption was recorded. By doing so, we observed that hardwood fractions consumed formaldehyde close to the theoretical calculation, whereas the reference softwood lignin consumed only about ¼ of the theoretical value. In the resin synthesis, we added formaldehyde to the formulation according to the measured maximum formaldehyde consumption. Thus, low values of free formaldehyde in lignin-PF (LPF) resins were achieved (<0.23%). Moreover, the resin bonding strength displayed similar performance irrespective of whether the LPF resins were made with softwood or hardwood lignin (range of 3.4–4.8 N mm−2 at 150°C and 45–480 s of press time). Furthermore, we concluded that hardwood kraft lignins present no disadvantage compared to softwood lignins in PF resin applications, which have significant practical implications.

scholarly journals Environmentally-Friendly High-Density Polyethylene-Bonded Plywood Panels

Polymers ◽  
2019 ◽  
Vol 11 (7) ◽  
pp. 1166 ◽  
Author(s):  
Pavlo Bekhta ◽  
Ján Sedliačik
Keyword(s):  
Mechanical Properties ◽  
Hot Pressing ◽  
High Density Polyethylene ◽  
Phenol Formaldehyde ◽  
Urea Formaldehyde ◽  
Physical And Mechanical Properties ◽  
Core Layer ◽  
High Density ◽  
Pressing Pressure ◽  
Pressing Time

Thermoplastic films exhibit good potential to be used as adhesives for the production of veneer-based composites. This work presents the first effort to develop and evaluate composites based on alder veneers and high-density polyethylene (HDPE) film. The effects of hot-pressing temperature (140, 160, and 180 °C), hot-pressing pressure (0.8, 1.2, and 1.6 MPa), hot-pressing time (1, 2, 3, and 5 min), and type of adhesives on the physical and mechanical properties of alder plywood panels were investigated. The effects of these variables on the core-layer temperature during the hot pressing of multiplywood panels using various adhesives were also studied. Three types of adhesives were used: urea–formaldehyde (UF), phenol–formaldehyde (PF), and HDPE film. UF and PF adhesives were used for the comparison. The findings of this work indicate that formaldehyde-free HDPE film adhesive gave values of mechanical properties of alder plywood panels that are comparable to those obtained with traditional UF and PF adhesives, even though the adhesive dosage and pressing pressure were lower than when UF and PF adhesives were used. The obtained bonding strength values of HDPE-bonded alder plywood panels ranged from 0.74 to 2.38 MPa and met the European Standard EN 314-2 for Class 1 plywood. The optimum conditions for the bonding of HDPE plywood were 160 °C, 0.8 MPa, and 3 min.

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