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In industrial applications, formaldehyde-based wood adhesives have been used extensively because of their low costs and high reactivity. However, their real-world applications are hindered by some main bottlenecks, especially the formaldehyde emission and usage of nonrenewable raw materials. The purpose of this study is the development of sustainable and formaldehyde-free wood adhesive formulation.

In this study, starch and tannin-based wood adhesive were synthesized. Chemical structures and thermal properties of the prepared bio-based resin formulations were elucidated by using Fourier transform infrared and differential scanning calorimetry analysis, respectively. Laboratory scale particleboard production was carried out to determine the performance of the developed resin formulations. Obtained results were evaluated in dry medium (P2) according to European norms EN 312 (2010). Furthermore, the board formaldehyde content was determined by using the perforator method according to the European Norm EN 12460-5.

The results show that the improved starch and tannin-based wood adhesives were successful in their adhesive capacity, and the formaldehyde content of the final product was obtained as low as 0.75 mg/100 g. This paper highlights that the presented adhesive formulations could be a potential eco-friendly and cost-effective alternative to the formaldehyde-based wood adhesives for interior particleboard production.

Starch-based resins in the liquid form needed to be continuously mixed throughout their shelf life to prevent the starch from settling because it was not possible to dissolve the precipitated starch again after a while. For this reason, starch was given to the chips in powder form while preparing the particleboard.

In conclusion, this study shows that the developed bio-based resin formulations have a high potential to be used for producing interior-grade particleboards instead of commercial formaldehyde-based wood adhesives because the obtained results generally satisfied the interior grade particleboard requirements according to European norms EN 312, P2 class (2010). In addition, it was determined that the produced boards had significantly low formaldehyde content. The low formaldehyde content of the final boards was not because of the resin but because of the natural structure of the wood raw material, press parameters and environmental factors.

The developed bio-based resin system made it possible to obtain boards with significantly low formaldehyde content compared to commercial resins.

The developed bio-based resin formulation made it possible to produce laboratory-scale board prototypes at lower press factors and board densities compared to their counterparts.

The purpose of this paper is to study the possibility of preparing high performance, agro‐based composites from rice straw, using eco‐polyalcohol polymers‐based adhesive system. The utilization of rice straw (undesirable biowastes) for the production of high quality biocomposite products, will add economic value, help to reduce the environmental impact of waste disposal and, most importantly, provide a potentially inexpensive alternative to the existing commercial artificial wood‐panels.

Simple synthesizing and optimizing the polyalcohol polymers‐based non‐toxic adhesive system were carried out, by blending corn starch, as natural polyalcohol polymer with polyvinyl alcohol, as synthetic polyalcohol polymers‐based adhesive (St/PV adhesive), at temperature ∼75°C. The percentages of adhesive components, type of starch, bonding temperature and time were optimized. Assessment of the synthesized adhesive was performed from its adhesion behavior (bond strength), in comparison with commercial thermosetting resin (urea‐formaldehyde), as well as the properties (mechanical and physical properties) of the composites produced. The effects of amount and type of water resistance co‐additives (paraffin wax and polyester), on mechanical properties of RS‐based composite were also optimized.

The promising adhesive system exhibits improved performance over a previously commercially HCHO‐based adhesive (UF), and results bonding strength 9.8 N/mm2, as well as MOR, IB and TS of RS‐based composites up to 31 N/mm2, 0.49 N/mm2 and 20%, respectively.

Through the studied eco‐adhesive with relatively high natural polyalcohol polymer (starch) in presence of water‐resistance additive (PE) provided a good bonding strength and comparative RS‐based composite properties, with that produced from commercial UF. For the mechanical properties (MOR and IB) are complied the standard values; while water resistance is still higher. Further study is needed to solve this problem.

The approach provided a HCHO‐free adhesive with good bonding strength, comparative board strength and water resistance, reasonable working life, and without formaldehyde emission. Starch‐based adhesive with low percentages of polyvinyl alcohol is considered a promising inexpensive alternate adhesive in wood industry based on rice straw wastes, which traditionally required expensive pMDI.

The paper provides a potential way to utilise undesirable rice by‐product (RS), corn starch as industrial raw material. This will benefit farmers significantly. Meanwhile, the modified starch adhesive with low percentage of PVA is promising to partly or completely replace urea formaldehyde resin and pMDI that are mainly used in wood industry, or pMDI in RS‐based artificial wood, avoiding formaldehyde emission or toxic gases during exposed to burning, and reducing the dependence on petroleum products.

The purpose of this paper is to examine the effects of denaturised rice bran (RB) and route of its incorporation during synthesis of urea-formaldehyde adhesive, on the performance of the resulting adhesive, especially viscosity, free-formaldehyde (HCHO) and quality of the produced bagasse-based composites, in comparison with those produced from commercial urea formaldehyde (UF) and RB-added UF.

The experiments were carried out using different denaturised RB at different percentages (1-5 per cent) and pH’s (9-11 per cent). These denaturised RB were incorporated at the last synthesis stage of UF synthesis process. The assessment was carried out on both the viscosity and environmental safety of the adhesive system, as well as the quality of the manufactured bagasse-based composites, of the particleboards (static bending, internal bond (IB) strength and water resistance properties), in comparison to commercial UF and RB added to UF. The performance of the adhesive system was evidenced by the thermogravimetric analysis and differential scanning calorimetry analyses.

The results showed that maximum static bending [modulus of rupture (MOR) and modulus of elasticity (MOE)], IB strength and water resistance properties of the resulted wood product accompanied the incorporating 5 per cent of the denaturised RB (pH = 9.0), at the last synthesised stage of UF synthesis process. Where, this synthesis process provided adhesive with viscosity nearly approaching to commercial UF adhesive, and reduced the free-HCHO of adhesive and board by approximately 56 and 49 per cent, respectively. For mechanical and water resistance properties, it provided board with 24.5 MPa MOR, 3,029 MPa MOE, 0.64 MPa IB, 11 per cent swelling (SW) and 20.5 per cent absorption. These properties fulfil the requirements of high grade particleboards American National Standard Institute (ANSI) A208.1, especially with respect to static bending values and water swelling property.

Incorporating 5 per cent of pre-denaturised RB, at pH 9.0, in wet form, and in the last stage of synthesis UF, provided adhesive system with convenient viscosity together with lower free-HCHO and acceptable board properties, compared with that produced from commercial UF, or adding denaturised RB to already synthesised UF. For the mechanical (MOR, MOE and IB) and water resistance properties (SW per cent and absorption per cent) of the produced composite are complied the standard values of H-3 grade of particleboard.

Promising adhesive system is resulted from incorporating 5 per cent of pre-denaturised RB at pH 9.0, in wet form, during last stage of UF synthesis process.

Incorporating the RB by-product of oil production to commercial UF or during synthesis of UF will be benefit for saving the healthy of wood co-workers, and motivating the wood mill to export its wood products.

The article provides a potential simple way to solve the drawback of increasing the viscosity of UF, as a result of adding RB, via incorporating the RB during synthesis process. The viscosity of the synthesised RB-modified UF approaches RB-free UF, and consequently the adhesive system easily penetrates through agro-fibres, and provides good bonding behaviour and high performance wood product (both quality and environmental by minimising formaldehyde emission or toxic gasses during board formation).

The purpose of this paper is to prepare high-performance agro-based composites from the non-toxic rice bran-urea-formaldehyde (RB-UF) adhesive system. Investigations have continued for production high performance agro-based composites using environmentally acceptable approaches. The utilisation of such system with the available used local agro-based wood products (sugar-cane bagasse, SCB) adds economic value and helps reducing the environmental impact of commercial urea-formaldehyde (UF) adhesive, and most importantly, provides a potentially inexpensive alternative to the existing commercial artificial wood-panel mills.

Optimising the process for incorporating the RB in UF, as wood adhesive for binding the bagasse fibres, was carried out, by partially replacing commercial UF by denaturalised RB in slurry (wet) and dry form or through synthesis of UF. The denaturalisation of RB was carried out at different pHs (10-11) and at temperature 60°C for two hours. While incorporating the RB during synthesis of UF, it was carried out according to the method reported elsewhere. The formulation of adhesive components, pH value of the denaturalisation stage and the process of incorporating the RB were optimised. Assessment of the role of RB adhesive was specified from its free-formaldehyde (HCHO) content, as well as the properties (mechanical and physical properties) of the produced composites of bagasse particle board type, in comparison with the environmental impact of commercial thermosetting resin (UF).

The promising adhesive system exhibits improvement in the environmental performance (as E1 type) over a commercially UF adhesive (as E2 type), besides providing boards fulfill the requirements of grade H-3 (according to ANSI A208.1 (NPA1993). This adhesive system was resulted from replacing 30 per cent of UF by denalturalised RB (at pH 10) in slurry form. Where, its reduction in free-HCHO reached 53 per cent, as well as modulus of rupture (MOR), modulus of elasticity (MOE), internal bond (IB) and TS of the produced boards were approximately 24.2 N/mm2, approximately 3753 N/mm2, approximately 0.84 N/mm2 and approximately 11.4 per cent, respectively.

The eco-adhesive with relatively high percentage of low-cost commercial UF (70 per cent) and 30 per cent RB, as oil production by-product, in slurry form provides good board strength and is environmentally friendly compared to SCB-based composite properties, with that produced from commercial UF. The mechanical (MOR, MOE and IB) and water-resistance properties of the produced composite comply with the standard values.

The approach provided low HCHO-free UF adhesive with good comparative board strength and water resistance and reasonable working life. Replacing 30 per cent of UF by RB in slurry form and denaturalised at pH 10 is considered a promising inexpensive alternate adhesive (as E1) in the wood industry based on SCB wastes.

Incorporating the RB by-product of oil production to commercial UF will be beneficial for saving the health of wood co-workers and motivating the wood mill to export its wood products.

It provided a potentially simple way to improve both the utilisation of commercial UF and SCB as industrial substrates for particle-board production. This will benefit farmers, local wood mills in Upper Egypt, significantly. Meanwhile, incorporating low percentage of RB, as oil-mill by-products, is promising to partly replace UF resin in the wood industry, minimising formaldehyde emission or toxic gasses during board formation.

Poly (vinyl acetate)‐based emulsion polymer/isocyanates (EPI) structural wood adhesives were prepared and their performance benchmark tested according to the specifications of the Japanese JAS‐111 standard. The changes of the glass transition temperature of the cured emulsions relative to unmodified poly(vinyl acetate) emulsion, measured using differential scanning calorimetry, indicated the chemical structure changes resulting from modification of poly(vinyl acetate) emulsion. The EPI adhesives showed excellent water resistance and near‐colourless gluelines in wood joints, ease of application and additional significant advantages over other types of wood adhesives. The performance test results are interpreted on the basis of the viscoelastic behaviour of free‐standing adhesive films. Other types of crosslinkers were used in the study to compare with the isocyanate hardeners.

To investigate the role of spent sulphite liquor (SSL) retained on neutral sulphite bagasse pulp in the binding action of phenolic resin, for the purpose of enhancing its performance to produce high quality agro‐based composite.

Pulps used in this work as agro‐based fibres were prepared from Asplund defibrator and neutral sulphite pulping processes. The performance of the resol resin in presence of SSL, were evaluated in terms of the effects of SSL constituents and using novolac as phenolic resin, in comparison with that prepared from pulps in absence of SSL and conventionally prepared resol – Asplund bagasse composites. Preparation of pulp free from sulphonyl groups and pre‐out‐precipitating the resol or lignosulphonic acid (LSA) on the strength and water resistance properties of the composite produced was also examined. The degraded hemicellulose and LSA in SSL were polynomial correlated with the changes in composites properties.

All neutral sulphite pulps investigated, in presence of SSL, were found to enhance the strength quality of agro‐based composite compared to commercially available resol‐agro‐based composite. The retained SSL on NS‐raw bagasse pulp could replace the Asplund bagasse pulp together with resol resin in production of agro‐composite. As well as, using neutral sulphite – Asplund bagasse pulp reduced the percent of added resol to half, to produce commercial resol agro‐based composite. The performance of the composite produced from novolac resin‐SSL‐neutral sulphite pulp and resol‐LSA‐neutral sulphite pulp exceeded 1.5 to 1.9 times the strength of commercially available composite.

Despite the SSL retained on pulp success in improving the strength property of the resol resin‐agro‐composites, but it has an undesirable effect on water resistance of the product. This problem was resolved by avoiding the undesirable effect of sulphonyl groups on pulp fibres as well as the degraded hemicellulose in SSL.

The approach developed provided a simple and practical solution to enhancing the performance of phenolic resin as well as agro‐fibres and SSL wastes in the production of high performance lignocellulosic composite.

The resol, together with SSL constituents retained on neutral sulphite pulp, are economic bonding agents for agro‐fibres and could be used in wood mills for production of medium density fibre‐board.

The purpose of this paper is to prepare a water-resistant adhesive (SA) from soy flour (SF) with less water-soluble components.

Defatted SF was suspended and stirred in water. Then, the pH of dispersion was adjusted to a predetermined value (i.e. 8, 9 or 10) by the addition of 2M sodium hydroxide (NaOH) solution. After stirring at a predetermined temperature (25°C, 35°C, 45°C) for different time (1 h, 2 h, 3 h), the 2M hydrochloric acid (HCl) solution was added in a dropwise manner into the dispersion until the pH value was adjusted to 4.5. Then, the dispersion was centrifuged at 6,000 rpm for 2 min. The obtained precipitate with less water-soluble components was used as an adhesive (SA) directly.

SA had a wet strength of 1.02 MPa when used for the fabrication of poplar plywood. Polyvinyl alcohol (PVA) solution was applied to improve the tack of SAs to wood surface and the viscosities of SAs were decreased from 10,200 cP to 4,100 cP at room temperature after the PVA addition. The soy proteins in SAs were not denatured to a large extent according to the differential scanning calorimetry and light microscopy. The remained multilevel structures of soy protein played a positive contribution to the water resistance of SAs, and the bond lines of cured SAs were much more stable than those of the cured SF and soy protein concentrate (SPC).

The fluidity and solid content of soy adhesives is much lower than formaldehyde adhesives. Further investigations are needed to improve the fluidity of soy adhesives with high solid contents.

Novel water-resistant soy adhesives were provided.

This paper aims to focus on the liquefaction of soybean protein to obtain a homogeneous protein solution with a high solid/protein content but low viscosity, which may improve the bond properties and technological applicability of soybean protein adhesive.

The liquefactions of soybean protein in the presence of various amounts of sodium sulphite, urea and sodium dodecyl sulphate (SDS) are investigated, and their effects on the main properties of liquefied soybean protein and soybean protein adhesives are characterized by Fourier transform infrared spectroscopy (FT-IR), gel permeation chromatography (GPC), viscosity tracing and plywood evaluation. Meanwhile, the applicability of soybean protein adhesive composed of liquefied protein for particleboard is also investigated.

Soybean protein can be effectively liquefied to form a homogeneous protein solution with a soybean protein content of 25 per cent and viscosity as low as 772 mPa.s; the addition of sodium sulphite, urea and SDS are beneficial for the liquefaction of soybean protein and have important effects on the technological applicability and water resistance of the obtained adhesive. The optimal liquefying technology of soybean protein is obtained in the presence of 1.5 Wt.% of sodium sulphite, 5 Wt.% of urea, 1.5 Wt.% of SDS and 3 Wt.% of sodium hydroxide. The optimal soybean protein adhesive has the desired water resistance in terms of the boiling-dry-boiling aged wet bond strength, which is up to 1.08 MPa higher than the required value (0.98 MPa) for structural use according to the commercial standard JIS K6806-2003. The optimal liquefied protein has the great potential to prepare particleboard.

The protein content of liquefied soybean protein is expected to further increase from 25 to 40 Wt.% or even higher to further reduce the hot-pressing cycle or energy consumption of wood composites bonded by soybean protein adhesives.

The soybean protein adhesive composed of optimal liquefied protein has potential use in the manufacturing of structural-use plywood and has comparable applicability as a commercial urea-formaldehyde resin for the manufacturing of common particleboard.

Soybean protein adhesive is an environmentally safe bio-adhesive that does not lead to the release of toxic formaldehyde, and the renewable and abundant soybean protein can be used with higher value added by the application as wood adhesive.

A novel liquefaction approach of soybean protein is proposed, and the soybean protein adhesive based on the liquefied protein is obtained with good technological applicability and desired bond properties that extend the applications of the soybean protein adhesive from interior plywood to particleboard and exterior or structural plywood.

3-ply cross-laminated timber (CLT) is used to investigate the thermo-mechanical performance of intermediate-size assemblies comprised of T-shaped welded slotted-in steel doweled connections and CLT beams at ambient temperature (AT), after and during non-standard fire exposure.

The first set of experiments was performed as a benchmark to find the load-carrying capacity of the assembly and investigate the failure modes at AT. The post-fire performance (PFP) test was performed to investigate the residual strength of the assembly after 30-min exposure to a non-standard fire. The fire-performance (FP) test was conducted to investigate the thermo-mechanical behavior of the loaded assembly during non-standard fire exposure. In this case, the assembly was loaded to 67% of AT load-carrying capacity and partially exposed to a non-standard fire for 75 min.

Embedment failure and plastic deformation of the dowels in the beam were the dominant failure modes at AT. The load-carrying capacity of the assembly was reduced to 45% of the ambient capacity after 30 min of fire exposure. Plastic bending of the dowels was the principal failure mode, with row shear in the mid-layer of the CLT beam and tear-out failure of the header sides also observed. During the FP test, ductile embedment failure of the timber in contact with the dowels was the major failure mode at elevated temperature.

This paper presents for the first time the thermo-mechanical performance of CLT beam-to-girder connections at three different thermal conditions. For this purpose, the outside layers of the CLT beams were aligned horizontally.

1. Load-carrying capacity and failure modes of CLT beam-to-girder assembly with T-shaped steel doweled connections at ambient temperature presented.

2. Residual strength and failure modes of the assembly after 30-min partially exposure to the non-standard fire provided throughout the post-fire performance test.

3. Fire resistance of the assembly partially exposed to the non-standard fire highlighted.

Load-carrying capacity and failure modes of CLT beam-to-girder assembly with T-shaped steel doweled connections at ambient temperature presented.

Residual strength and failure modes of the assembly after 30-min partially exposure to the non-standard fire provided throughout the post-fire performance test.

Fire resistance of the assembly partially exposed to the non-standard fire highlighted.

The purpose of this paper is to describe the development of an eco‐friendly tannin‐phenol formaldehyde resin (PFT) applicable in the wood composite industry.

The bark of oak (Quercus castaneifolia) contains a large amount of condensed tannin. Condensed tannin, with a large amount of Catechol groups was considered for reducing the formaldehyde emission level on the adhesive system. Physical characteristics of synthesized PFT resin were evaluated.

For optimal extraction, three solvents were used in the extraction process. The results showed that a mixture of water‐methanol (1:1 v/v) as extracting solvent is the best solvent and yields about 14 per cent tannin based on dry weight of bark. For producing tannin phenol formaldehyde adhesive, 10 per cent, 20 per cent and 30 per cent (based on PF dry weight) of PF, substituted with natural extracted tannin. For evaluating PFT performance effects of percentage amount of substitution tannin content on the gel time, viscosity, pH, and density of adhesives were evaluated. Based on emission test (JIS A 1460‐2001) formaldehyde emission of PFT 10 per cent, 20 per cent and 30 per cent were 1.13, 1.12 and 0.4 mg/100 g, which is very low compared with tannin‐free PF.

Tannin‐PF adhesive compared to PF adhesive had lower PH, higher viscosity and shorter gel time.

The method developed provides a simple and excellent renewable resource “tannin” which can be used or partially substituted in phenol formaldehyde adhesive.

Results showed that replacing PF for tannin reduces modulus of rupture (MOR) and modulus of elasticity (MOE) slightly but has significant effects on IB, water absorption and thickness swelling.