Zhenhua Gao

FTIR and XPS study of the reaction of phenyl isocyanate and cellulose with different moisture contents

Purpose – To evaluate the competing reaction of isocyanate with cellulose and water which can provide direction for further studies on bonding and curing reactions of isocyanate with wood.Design/methodology/approach – Two modern analytical techniques, Fourier transform infra‐red (FTIR) and X‐ray photoelectron spectroscopy (XPS), were used. The FTIR was used to identify the products of the reaction of phenyl isocyanate (PI) with alcohol, water, and cellulose; while the XPS was used to evaluate the proportions of isocyanate that reacted with water or cellulose when PI reacted with cellulose at different moisture contents (MCs), respectively.Findings – Methods for the IR identifications of reaction results of PI with n‐propanol, water, and cellulose, in which the reactions of PI with water and PI with cellulose resulted in N,N′‐diphenylurea and carbamate, respectively, were developed. It was discovered that the extent of reaction of isocyanate and cellulose decreased with increasing cellulose MC, and 92.98 p...

Phenolated larch‐bark formaldehyde adhesive with multiple additions of sodium hydroxide

Purpose – 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.Design/methodology/approach – 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.Findings – 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 cen...

Reaction kinetics of toluene diisocynate and propanol by in situ FTIR

Purpose – 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.Design/methodology/approach – 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.Findings – 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 associat...

Synthesis and characterisation of one‐part ambient temperature curing polyurethane adhesives for wood bonding

The effects of polyol types, polyol molecular weights, NCO/OH molar ratio, solvent types, and resin solid contents of the one‐part ambient temperature curing adhesives were studied. The results showed that the one‐part ambient temperature curing polyurethane prepared had fast rate of setting and good bonding, meeting the requirements of a typical structural adhesive.

DSC characterisation of urea‐formaldehyde (UF) resin curing

Purpose – 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.Design/methodology/approach – 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.Findings – A model equation, Tp=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 kinet...

Effects of thermal treatment on the properties of defatted soya bean flour and its adhesion to plywood

With an attempt to economically and efficiently improve the water resistance of defatted soya bean flour (DSF)-based wood adhesives, DSF was subjected to thermal treatment at various temperatures (65°C, 80°C, 95°C, 110°C and 125°C) for 30 min. The effects of thermal treatment temperature onto the chemical structure, crystalline degree, water-insoluble content and acetaldehyde value of the thermally treated DSF (T-DSF) were investigated. The thermal stabilities and bonding properties of soya bean adhesives prepared from T-DSF and cross-linker epichlorohydrin-modified polyamide (EMPA) were also investigated. Test results indicated that both the water-insoluble content and the acetaldehyde value of T-DSF increased after thermal treatment, reaching the highest values of 27.28% and 26.81 mg g−1, respectively. All plywood bonded with the T-DSF-based adhesive withstood a 28 h boiling–dry–boiling accelerated ageing treatment, while plywood bonded with the DSF-based adhesive delaminated after 4 h of water boiling, demonstrating the significantly improved water resistance of the T-DSF-based adhesives. Related analyses also confirmed that this improvement was due to: (i) the formation of insoluble cross-linked structures of T-DSF resulting from protein–protein self-cross-linking reactions and the protein–carbohydrate Maillard reaction and (ii) increased cross-linking efficiency between T-DSF and cross-linker EMPA owing to more T-DSF-reactive groups being released after thermal treatment.

Bio-based reactive diluents as sustainable replacements for styrene in MAESO resin

Four different biorenewable methacrylated/acrylated monomers, namely, methacrylated fatty acid (MFA), methacrylated eugenol (ME), isobornyl methacrylate (IM), and isobornyl acrylate (IA) were employed as reactive diluents (RDs) to replace styrene (St) in a maleinated acrylated epoxidized soybean oil (MAESO) resin to produce bio-based thermosetting resins using free radical polymerization. The curing kinetics, gelation times, double bond conversions, thermal–mechanical properties, and thermal stabilities of MAESO-RD resin systems were characterized using DSC, rheometer, FT-IR, DMA, and TGA. The results indicate that all four RD monomers possess high bio-based carbon content (BBC) ranging from 63.2 to 76.9% and low volatilities (less than 7 wt% loss after being held isothermally at 30 °C for 5 h). Moreover, the viscosity of the MAESO-RD systems can be tailored to acceptable levels to fit the requirements for liquid molding techniques. Because of the introduction of RDs to the MAESO resin, the reaction mixtures showed an improved reactivity and an accelerated reaction rate. FT-IR results showed that almost all the CC double bonds within MAESO-RD systems were converted. The glass transition temperatures (Tg) of the MAESO-RDs ranged from 44.8 to 100.8 °C, thus extending the range of application. More importantly, the Tg of MAESO-ME resin (98.1 °C) was comparable to that of MAESO-St resin (100.8 °C). Overall, this work provided four potential RDs candidates to completely replace styrene in the MAESO resin, with the ME monomer being the most promising one.

Liquefaction of soybean protein and its effects on the properties of soybean protein adhesive

Purpose 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. Design/methodology/approach 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. Findings 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. Research limitations/implications 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. Practical implications 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. Social implications 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. Originality/value 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 Effect of Thermo-Chemical Treatment on the Water Resistance of Defatted Soybean Flour-Based Wood Adhesive

The aim of this study was to effectively improve the water resistance of a defatted soybean flour (DSF)-based adhesive by subjecting DSF to thermo-chemical treatment in the presence of sodium dodecyl sulfate (SDS), and then the crosslinking with epichlorohydrin-modified polyamide (EMPA). The effect of thermo-chemical treatment on the structures and properties of the DSF and DSF-based adhesive were investigated by plywood evaluation, boiling-water-insoluble content, and acetaldehyde value measurements, as well as FTIR, X-ray photoelectron spectroscopic (XPS), X-ray diffraction spectroscopy (XRD), thermogravimetric analysis (TGA), and rheology analyses. The test results revealed that the water resistance of the DSF-based adhesive was significantly improved, attributed to the formation of a solid three-dimensional crosslinked network structure resulted from the repolymerization of DSF, the Maillard reaction between the protein and carbohydrate, and chemical crosslinking between the crosslinker and DSF. Moreover, SDS destroyed the hydrophobic interactions within protein and inhibited macromolecular aggregations during the thermal treatment. Therefore, more reactive groups buried within the globular structure of the soybean protein component of DSF could be released, which supported the repolymerization, Maillard reaction, and chemical crosslinking of DSF, thereby leading to an improved crosslinking density of the cured DSF-based adhesive. In addition, the adhesive composed of thermo-chemically treated DSF and EMPA exhibited preferable viscosity and viscosity stability suitable for the production of wood composites.