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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.

The purpose of this paper is to evaluate the effect of different amounts of sodium hydroxide (NaOH) introduced during the resin synthesis on the properties of bark‐phenol‐formaldehyde (BPF) adhesives aims at achieving a balance between storage life and other properties of BPF adhesives.

Based on the best synthetic technologies for the production of BPF adhesives obtained in a previous study, a new synthetic technology is developed for the production of BPF adhesives that involve a three‐step addition of NaOH using different amounts of NaOH in the third charge. Gel permeation chromatography is used to evaluate properties of the phenol‐formaldehyde (PF) and BPF adhesives.

The amount of NaOH in the third charge has an important influence on many BPF adhesive properties. The paper determines that the synthetic technology involving three‐step NaOH additions with only water introduced in the third charge of NaOH produces a BPF adhesive with the longest storage life and best bonding strength.

BPF adhesives are very complex systems with many unknown variables.

The improved storage life of the BPF adhesive prepared with the new synthetic technology is comparable to that of a commercial PF adhesive, which indicates that this new technology shows greater potential for commercial applications.

A new synthetic technology is developed to produce a BPF adhesive that is more comparable to commercial PF adhesives than other BPF adhesives in terms of storage life and other resin properties.

The purpose of this paper is to investigate the effects of multi-hydroxymethylated phenol (MHMP) on the properties of moisture-curing polyurethane (PU) resin, especially on the heat resistance.

The MHMPs with various active sites from 2.52 to 3.91 were synthesised and used as a modifier. The bond test (according to the JIS K6806-2003 standard) and thermogravimetric analysis (TGA) were used, respectively, to characterise the bond durability and heat resistance of MHMP-modified PU resin.

The MHMP with various F/P mole ratios had great effects on the properties of resultant PU resins. The increase of active sites of MHMP can improve the water resistance of resin due to the more cross-linking densities, while the decrease of active sites of MHMP can improve heat resistance of resin because more stable benzene ring introduced into the PU backbone.

In cases where heat resistance of the PU resin is of primary concern, the use of MHMP with fewer active sites or a lower F/P ratio is recommended. In other cases where bond durability is focussed, the modifier MHMP shall be synthesised with higher F/P ratio.

MHMP as a modifier can be used to improve the heat resistance of PU resin.

The MHMPs with various hydroxymethyl groups were synthesised and used as modifier of moisture-curing PU resins to improve their heat resistance.

The purpose of this paper is to investigate the effects of the components of whey‐protein based aqueous polymer‐isocyanate (API) adhesives on the bond strength.

The bond test (according to the JIS K6806‐2003 standard), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) were used to characterise the whey‐protein based API adhesives with various formulations and processing technologies.

The good bond strength of the optimised whey‐protein based API adhesive was attributed to the formation of strong chemical bonds in the bondline and to the additions of polyisocyanate, polyvinyl alcohol (PVA) and nano‐CaCO₃ powder that improved adhesive cohesive strength by either chemical crosslinks or mechanical interlocking. The blending procedures of whey protein, PVA, polyvinyl acetate (PVAc) and p‐p‐MDI had great impacts on the performances of the whey‐protein based API adhesives.

SEM micrographs showed that the effects of blending processes on the bond strength, pot life and colour might be attributed to the particle size of hydrophobic p‐MDI droplet and p‐MDI distribution in the protein‐PVA matrix.

The study lays the foundations of the formulation design and the processing technology for preparing whey‐protein based API adhesives.

The effects of the components of whey‐protein based API adhesives and the effects of blending processes on the bond strength were investigated by means bond strength evaluation, FTIR and SEM analyses; whey protein is utilised successfully to prepare novel API adhesives for structural uses.

The purpose of this paper is to develop an environmentally safe aqueous polymer‐isocyanate (API) wood adhesive for structural uses with whey protein isolate (WPI) that is a by‐product of cheese making.

The API formulations with whey proteins denatured at different heating temperatures and times, WPI/polyvinyl alcohol (PVA) denaturing processes, PVA contents and nano‐CaCO₃ (as filler) contents were investigated and optimised according to the JIS K6806‐2003 standard.

A whey‐protein based API adhesive was developed which had 28 h boiling‐dry‐boiling wet compression shear strength 6.81 MPa and dry compression shear strength 13.38 MPa beyond the required values (5.88 and 9.81 MPa, respectively) for structural use of commercial standards. The study also indicated that the thermal denaturation of 40 per cent WPI solution at 60‐63°C could unfold the globular structure of whey protein to some extent and therefore improve the bond strength and bond durability of whey‐protein based API adhesive; the additions of PVA and nano‐CaCO₃ as filler had a significant effect on the bond strength and bond durability of whey‐protein based API adhesive.

The thermally denatured WPI solutions (40 wt%) incline towards being decayed by moulds if not properly formulated.

Owing to the good bond strength and durability and environmental safety, the optimised whey‐protein based API adhesives have greater potential for commercial applications, especially for the structural wood bonds.

A novel API wood adhesive for structural use was developed using whey proteins that are often regarded as a waste due to their relatively small molecules and compact globular structures.

To evaluate the effect of the concentrations of isocyanate group and hydroxyl group and hydroxyl group species on the rate constants of isocyanate‐propanol reaction, and to reveal the kinetics of isocyanate‐hydroxyl reaction.

The in situ FTIR technique was employed to measure the group concentration evolutions, by which the rate constants were determined. Besides, the FTIR was used to detect the OH absorbance shifts during reaction and the OH absorbance at different concentrations. The kinetic mechanism of isocyanate‐propanol reaction was discussed with the combination of rate constants and FTIR spectra.

A new reaction mechanism, alcohol association mechanism, was proposed that could explain many phenomena. It was revealed that the rate constant was independent of the isocyanate concentration, while the concentration and species of hydroxyl groups had apparent effects on the rate constants. It was possible to calculate the number averaged degree of association of propanol with alcohol association mechanism.

The associated n‐propanol molecules that reacted with isocyanate to form urethane were the associated dimer and trimer predominately, while the iso‐propanol was the dimer.

The kinetics of isocyanate‐hydroxyl reaction and the alcohol association mechanism will be helpful to understand the preparation and curing of polyurethane, and their controls.

A new reaction mechanism, alcohol association mechanism, was proposed that could explain many phenomena that might not be interpreted by other mechanisms. The mechanism could be employed to calculate the number averaged degree of association of alcohols.

This paper aims to evaluate the effect of multiple additions of sodium hydroxide (NaOH) on the properties of bark‐phenol‐formaldehyde (BPF) adhesives, and to lay the foundations for further studies on bark utilisation.

Synthetic technologies that used multiple additions of NaOH were developed for the production of BPF adhesives. Differential scanning calorimetry (DSC), gel permeation chromatography (GPC) and plywood bond were used to evaluate properties of the PF and BPF adhesives.

The number of NaOH additions had an important effect on many BPF adhesive properties, such as gel time, free formaldehyde content in adhesive, thermosetting peak temperature, molecular weight distribution, as well as the wet shear strength and free formaldehyde release of the bonded plywood panels. The study determined that a two‐step process for adding NaOH offers a prospective synthetic technology for BPF adhesive production. This technology made it possible to use 28.6 per cent bark by weight and resulted in plywood with properties comparable with those of plywood bonded with a commercial PF adhesive. However, BPF adhesives prepared with more than two NaOH additions were fast‐curing.

BPF adhesives are very complex systems with many unknown variables, such as the chemical structures of bark derivatives from phenolation and adhesive synthesis. To further improve the curing rate and adhesion of BPF, future investigations should be based on a two‐addition process or attempt to increase the amount of NaOH in the second addition.

The BPF adhesive prepared with two NaOH additions and 28.6 per cent bark was comparable with a commercial PF adhesive in terms of adhesive properties and plywood bond quality. These results indicate that this technology shows potential for commercial applications.

Synthetic technologies using multiple additions of NaOH were developed to produce BPF adhesives. The BPF with two additions of NaOH seemed to be comparable with a commercial PF adhesive.

The purpose of this paper is to investigate the effects of various catalyst contents, resin solid contents, catalyst species and wood extract on urea‐formaldehyde (UF) curing by differential scanning calorimetry (DSC) technique. The finding obtained would benefit the manufacturers of UF‐bonded composite panels.

The UF curing rate under each condition in terms of DSC peak temperature was measured by high‐pressure DSC at a heating rate of 15°C/min; the correlations of peak temperature with catalyst content, resin solid content, catalyst species and wood extract, respectively, were regressed via a model equation, which described the curing characteristics of the UF bonding system.

A model equation, T_p=A · EXP(−B · CC per cent)+D, was proposed to characterise the DSC peak temperatures or the rate of UF curing with regressing coefficients greater than 0.97 (commonly greater than 0.99). The constants A and B in the model equation were found to correspond to kinetic characteristics of UF resin curing reaction. The constant D in the model equation is believed to be associated with the utmost peak temperature, which implies that the DSC peak temperature will finally reach a maximum with catalyst content increasing. It was also found that the wood extracts having higher pH value and base buffer capacity had stronger catalyses on UF curing.

The catalysts commonly used in medium density fibreboard plants or particleboard plants are those having the utmost peak temperature of about 90‐95°C; the catalyses of wood extracts were much weaker than that of catalyst NH₄Cl.

The model equation could be used to predict the peak temperature or the curing rate of UF resin, and to quantify the effects of wood extracts on UF curing.

The study developed a model equation that can well characterise the UF curing, and quantified the effects of wood extracts on UF curing.

This paper aims to investigate the effect of aluminum addition on the microstructure and mechanical properties of Mg-8Gd-4Y-1Zn alloy.

Mg-8Gd-4Y-1Zn-xAl (x = 0, 0.5, 1.0, 1.5, 2.0 Wt.%) alloys were prepared by the conventional gravity casting technology, and then microstructures, phase composition and mechanical properties were investigated by material characterization method, systematically.

Results show that the as-cast microstructure of Mg-8Gd-4Y-1Zn alloy mainly consists of a-Mg matrix as well as Mg₁₂REZn (18 R LPSO structure), and island-like Mg₃(RE, Zn) phase is distributed at the grain boundary. The addition of a small amount of Al (0.5 Wt.%) can decrease the content of island-like Mg₃(RE, Zn) phase, but significantly increase the content of long-period stacking ordered (LPSO) structure, resulting in the improvement of both tensile strength and elongation of Mg-8Gd-4Y-1Zn alloy. However, the addition of excessive Al will consume Re element and decrease the amount of LPSO structure, leading to the decrease of tensile properties. When the content of Al is 0.5 Wt.%, the tensile strength and elongation are 225 MPa and 9.0% of Mg-8Gd-4Y-1Zn alloy, which are 14% and 29% higher than that of Mg-8Gd-4Y-1Zn alloy, respectively.

Adding aluminum to Mg-8Gd-4Y-1Zn alloy strengthens its mechanical properties. And the effect of Al content on the alloy strengthening. The formation mechanism of LPSO structure with different aluminum content was revealed.