Dimethylene Ether Bridges Research Articles

Preparation and investigation of an eco-friendly plywood adhesive composed of sucrose and ammonium polyphosphate

ABSTRACT In this study, sucrose and ammonium polyphosphate (APP) were utilized as the raw materials to prepare an environmentally-friendly plywood adhesive. The bonding performance results showed that the optimal synthesis conditions of the sucrose-ammonium polyphosphate (SAPP) adhesive were an 80/20 mass ratio (sucrose/APP) at 115 oC for 3 h, and the optimal manufacturing conditions were 170 oC for 7 min. In addition, the maximum wet shear strength of the obtained three-ply plywood was 0.81 MPa, which satisfied the China National Standard GB/T 9846–2015 (wet shear strength≥0.7 MPa). The insoluble mass proportion was positively associated with the heating temperature and time. The TG and DSC analysis showed that a rapid mass loss of the SAPP adhesive occurred at 143.4 oC, and endothermic peaks appeared at 136.2 and 156.4 oC. The 13C NMR spectra showed that the adhesive contained monosaccharides, oligosaccharides, ketones, HMF, Schiff bases, and various other unknown substances. This implies that hydrolysis, caramelization, and the Amadori rearrangement occurred during synthesis. Furthermore, the FT-IR and Py-GC/MS results indicated that the cured SAPP adhesive was a complex polymer containing furan and nitrogenous compounds, which were connected by dimethylene ether bridges.

Development and investigation of a two-component adhesive composed of soybean flour and sugar solution for plywood manufacturing

ABSTRACT In this study, soybean flour (SF) and various sugar solutions were utilized as raw materials to prepare eco-friendly plywood adhesives. First, the optimal preparation conditions were investigated by testing the bond performance. When SF was mixed with synthesized sucrose-ammonium dihydrogen phosphate (SADP) solution with 50% solid content in a 1: 4 mass proportion, the wet shear strength of the plywood achieved a maximum value of 0.83 MPa. This value exceeds the minimum limit of China National Standard GB/T 9846-2015. Second, the curing behavior of the SF/SADP adhesive was studied by measuring the insoluble mass proportion and thermal analysis. The results showed that the curing reaction of this adhesive occurred near 170 °C. In addition, the curing mechanism was studied by ATR FT-IR and Py-GC/MS analysis. Based on the results, it was concluded that the cured adhesive formed a network structure via a polycondensation reaction between small-molecule compounds derived from the SADP solution and the products of the caramelization and soy flour. Dimethylene ether bridges were the main linkages of the final polymer. SEM microstructure analysis showed that the cured SF/SADP adhesive exhibited a more compact crosslinked structure than cured SADP.

The synthesis and characterization of phenolic resin with a high content of dimethylene ether bridges

Phenolic resins were synthesized using sodium montmorillonite (MMT) as a catalyst at a concentration of 3%, 5%, and 10%, the reaction time was 24 and 48 h, respectively. The phenolic resin yield was up to 69%. The chemical structure of the resins was determined by NMR, the thermal properties were determined by DSC and TGA, and molar masses were determined by SEC. The resins could not be easily classified as resol or novolac because the most common type of bonding between the aromatic rings was dimethylene ether (DME) bridges. Due to near neutral pH (6.7–7.1), some methylol groups were also present in the structure. Increasing the MMT concentration increased the molar mass of the resin; however, no influence of reaction time was observed. Increased MMT concentration, as well as longer reaction time, decreased the glass transition temperatures, which were very low, in the range of 8–24 °C. Increased content of DME increased the thermal stability of the resins.

Release of Melamine and Formaldehyde from Melamine-Formaldehyde Plastic Kitchenware.

The release of melamine and formaldehyde from kitchenware made of melamine resins is still a matter of great concern. To investigate the migration and release behavior of the monomers from melamine-based food contact materials into food simulants and food stuffs, cooking spoons were tested under so-called hot plate conditions at 100 °C. Release conditions using the real hot plate conditions with 3% acetic acid were compared with conditions in a conventional migration oven and with a release to deionized water. Furthermore, the kinetics of the release were studied using Arrhenius plots giving an activation energy for the release of melamine of 120 kJ/mol. Finally, a correlation between quality of the resins, specifically the kind of bridges between the monomers, and the release of melamine, was confirmed by CP/MAS 13C-NMR measurements of the melamine kitchenware. Obviously, the ratio of methylene bridges and dimethylene ether bridges connecting the melamine monomers during the curing process can be directly correlated with the amount of the monomers released into food.

Utilization of enzymatic hydrolysate from corn stover as a precursor to synthesize an eco-friendly plywood adhesive

In this study, concentrated enzymatic hydrolysate (EH) from corn stover and ammonium dihydrogen phosphate (ADP) were exploited as feedstocks to prepare a novel environment-friendly plywood adhesive. Firstly, the optimal synthesis conditions of the enzymatic hydrolysate-ammonium dihydrogen phosphate (EHADP) adhesive were investigated, and the results manifested that optimizing mass proportion between EH (solids) and ADP, synthesis temperature and time were 90/10, 100 °C and 1 h, respectively. When using EHADP synthesized under optimal synthesis conditions, the wet bond strength of the plywood met the requirements of China National Standard GB/T 9846-2015 (wet shear strength≥0.7 MPa). The chemical transformations during synthesis treatment on the uncured EHADP adhesive were analyzed by HPLC and 13C NMR, which showed that the EHADP adhesive was a complex mixture of ketones, monosaccharides, 5-HMF, furfural, deoxyfructosazine, Schiff bases, and amides. In addition, ATR FT-IR and Py-GC/MS were employed to analyze the curing mechanism of EHADP adhesive. The results showed that cured EHADP was formed mainly due to the polymerization of furan compounds, and the network was linked by imine linkages and dimethylene ether bridges. TG and DSC analysis showed that the mass degradation and endothermic reaction occurred at around 135℃, indicating the EHADP adhesive which prepared under the optimal synthesis conditions could cured at lower temperature.

Influence of Acid on the Curing Process of Tannin-sucrose Adhesives

Tannin and sucrose (TS) can be used in a biomaterial-based wood adhesive that requires a higher hot pressing temperature and longer time than traditional resins. To solve these problems, hydrochloric acid and citric acid were utilized as a catalyst during the curing process to decrease energy costs (forming TSH and TSC adhesives, respectively). Thermal analysis revealed that the addition of hydrochloric acid and citric acid resulted in decreases to the thermal thresholds associated with degradation and curing. The resultant insoluble matter ratio verified that the polymerization reaction happened at a lower temperature than the adhesive without acidic conditions. The FT-IR and solid state 13C NMR spectra showed that the addition of acid compounds acted catalytically and increased the generation of 5-HMF in uncured adhesives. The dimethylene-ether bridges and methylene bridge were formed during the heat treatment. The water resistance of the particleboards manufactured by TSC and TSH adhesives were notably enhanced when the hot-pressing temperature was 180 °C. However, an increased hot pressing temperature did not improve the mechanical properties of the particleboard bonded by TSH, which was due to cellulose and hemicellulose decomposition under strong acidity conditions.

Effects of Sulfuric Acid on the Curing Behavior and Bonding Performance of Tannin⁻Sucrose Adhesive.

The development of biomaterials-based adhesives is one of the main research directions for the wood-based material industry. In previous research, tannin and sucrose were used as adhesive to manufacture particleboard. However, the reaction conditions need to be optimized. In this study, sulfuric acid was added to the tannin–sucrose adhesive as a catalyst to improve the curing process. Thermal analysis, insoluble mass proportion, FT-IR, and solid state 13C NMR were used to investigate the effects of sulfuric acid on the curing behavior of tannin and sucrose. Thermal analysis showed weight loss and endotherm temperature reduced from 205 and 215 to 136 and 138 °C, respectively, by adding sulfuric acid. In case of the adhesive with pH = 1.0, the insoluble mass proportion achieved 81% at 160 °C, which was higher than the reference at 220 °C. FT-IR analysis of the uncured adhesives showed that adding sulfuric acid leads to hydrolysis of sucrose; then, glucose and fructose converted to 5-hydroxymehthylfurfural (HMF) and levulinic acid. Dimethylene ether bridges were observed by FT-IR analysis of the cured adhesives. The results of solid state 13C NMR spectrum indicated that 5-HMF participated in the curing process and formed methylene bridges with the C8 position of the resorcinol A-rings of tannin, whereas dimethylene ether bridges were detected as a major chemical chain of the polymer. Lab particleboards were produced using 20 wt % resin content at 180 °C and 10 min press time; the tannin–sucrose adhesive modified with sulfuric acid to pH = 1.0 exhibited better performance than the unmodified tannin–sucrose adhesive; the properties of the boards fulfilled the requirement of Japanese Industrial Standard (JIS) A5908 type 15.

Effects of the Addition of Citric Acid on Tannin-Sucrose Adhesive and Physical Properties of the Particleboard

The effects of citric acid on the curing properties of tannin-sucrose adhesives and on the physical properties of particleboard utilizing the adhesives were investigated. The citric acid content of tannin-sucrose adhesive was adjusted to 0.4, 1.8, 4.6, 13.8, 20.0, and 33.3%, which corresponded to pH values of the adhesive 40 wt% solution at 3.8, 3.0, 2.5, 2.0, 1.8, and 1.5, respectively. Thermal analysis showed that with increasing of citric acid content, the temperature of significant weight loss and the endothermic reaction of the tannin-sucrose-citric acid adhesive was reduced. When the adhesives were heated at 200 °C, boiled for 4 h, and adjusted to 20.0 and 33.3% citric acid content, the insoluble matter was increased significantly, and an absorption band derived from ester linkages and another peak, possibly from dimethylene ether bridges, were observed by FT-IR. The particleboards bonded with 20.0 and 33.3% citric acid adhesives at 200 °C satisfied the physical requirements of the type 18 Japanese Industrial Standards A 5908 (2003). Consequently, the addition of citric acid promoted the reaction between tannin and sucrose at a lower temperature, and the optimal hot pressing temperature decreased from 220 to 200 °C. The mechanical properties and water resistance of the particleboards were also enhanced.

Investigation of a New Natural Particleboard Adhesive Composed of Tannin and Sucrose. 2. Effect of Pressing Temperature and Time on Board Properties, and Characterization of Adhesive

In a previous study by the authors, particleboard was manufactured using a new natural adhesive composed of tannin and sucrose. The optimal ratio between tannin and sucrose was 25/75, and the suitable resin content was 30 to 40 wt%. In this study, the effects of hot pressing temperature and hot pressing time on board properties were investigated. The optimal values for the hot pressing temperature and hot pressing time were found to be 220 °C and 10 min, respectively. When the particleboard was made under these optimum conditions, the physical properties of the particleboard bonded with tannin and sucrose met the requirement of the JIS A 5908 type 18 standard (2003). Thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), insoluble matter, and Fourier transform infrared spectroscopy (FT-IR) tests were carried out. The results of TGA and DSC measurements showed that the weight loss and endothermic reaction of the adhesive composed of tannin and sucrose at a ratio of 25/75 occurred at 204 and 215 °C, respectively. When the adhesive was heated at 220 °C for longer than 10 min, the level of insoluble matter was higher than 70 wt%. FT-IR analysis showed the existence of a furan ring, a carbonyl group, and dimethylene ether bridges in the cured adhesives before and after the boiling treatment. When the heating time was longer than 10 min, no further change of chemical structure was observed.

Investigation of a new natural particleboard adhesive composed of tannin and sucrose

In the face of dwindling fossil fuel resources and the environmental imperative to reduce emissions associated with petrochemistry, there is strong demand for a wood composite bonding procedure using natural alternatives. In this study, particleboards were manufactured with a new material adhesive composed of tannin and sucrose, and hot-pressed at 200 °C for 10 min, to a target density of 0.8 g/cm3. We found optimal values for the mat moisture content, the ratio of tannin to sucrose and the resin content of 3–6 wt%, 25/75 and 30–40 wt%, respectively. When the particleboards were manufactured under these optimum conditions, the modulus of rupture and the modulus of elasticity were in the range of 19.6–21.2 MPa and 4.6–5.0 GPa, respectively. The internal bond strength was in the range of 1.1–1.3 MPa. Based on these results, the mechanical properties of particleboard bonded with tannin and sucrose were higher than the requirements of the JIS A 5908 type 18 standard (2003). In the thickness swelling test (TS), the value was in the range of 20–23 %; as the ratio of sucrose and resin content increased, the TS value decreased. The reaction mechanism between tannin and sucrose was studied by fourier transform infrared spectroscopy, and the dimethylene ether bridges were observed. Consequently, it is possible that a tannin and sucrose mixture can be used as a natural adhesive for particleboard.

Polymerization of resole resins with several formaldehyde/phenol molar ratios: Amine catalysts against sodium hydroxide catalysts

AbstractTriethylamine and sodium hydroxide catalyzed phenol/formaldehyde resole resins were investigated in terms of their behavior during both addition and polymerization reactions. Amine‐catalyzed prepolymers were mainly ortho‐substituted structures, whereas the sodium hydroxide catalyst directed the addition reaction to para reactive sites. During polymerization, triethylamine led to dimethylene ether bridges as the principal linkages between aromatic structures, increasing their final concentration as the starting hydroxymethyl group concentration increased. In contrast, the use of sodium hydroxide reduced dramatically the dimethylene ether bridge concentration, favoring methylene bridge formation. The influence of hydroxyl ions on the stability of quinone methide intermediates could be the reason for those differences. Despite the formation of dimethylene ether bridges, at higher curing temperatures, more oxidized groups started to appear in cured resoles when the formaldehyde/phenol molar ratio was higher. The presence of infrared bands associated with quinones, aldehydes, and/or carbonyl groups, mainly in high‐formaldehyde‐content resins, could indicate a direct oxidation process from dimethylene ether bridges and/or residual hydroxymethyl groups, without the formation of methylene bridges. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2623–2631, 2006

Fully quantitative carbon-13 NMR characterization of resol phenol–formaldehyde prepolymer resins

Different resol phenol–formaldehyde prepolymer resins have been synthesized with different Formaldehyde/Phenol (F/P) ratios or different catalysts and characterized by 13C NMR spectroscopy in solution. A fast quantitative measuring protocol is proposed based on the use of chromium(III)acetylacetonate as a relaxation agent. APT (attached proton test) and DEPT (distortionless enhancement by polarisation transfer) spectra were acquired to enable proper resonance assignments, especially in the regions with severe signal overlap. Equations are presented in which the methylene bridges (MB), the methylol groups (MG) and the dimethylene ether bridges (DMEB) of resol resins are quantitatively taken into account. Important structural factors determined quantitatively for resol prepolymer resins are the F/P ratio after reaction, the degree of polymerization ( n), the number average molecular weight ( M n) and the content of free ortho and para positions.

The Chemistry of Phenol-Formaldehyde Resin Vulcanization of EPDM: Part I. Evidence for Methylene Crosslinks

Abstract The application of phenol-formaldehyde resins as crosslinking agents is increasing in importance due to the good high temperature properties of the corresponding vulcanizate and the use in thermoplastic vulcanizates. With respect to the chemistry of phenol-formaldehyde cure (reaction mechanism and structure of crosslink) there are still problems that have to be resolved. The reaction products of the phenol-formaldehyde resin curing of EPDM, contain 2-ethylidene norbornene (ENB) as the third monomer, have been studied. Since such an investigation is rather difficult to perform for the polymer system, a low molecular weight model for EPDM was used: 2-ethylidene norbornane (ENBH). Reaction of ENBH and a resole results in scission of the dimethylene ether bridges, i.e. in degradation of the resole into mono-, bis- and terisooctylphenol units. These are consequently converted into products, consisting of two ENBH molecules linked by mono-, bis- and terisooctylphenol units. The solid resole seems to be a technological solution for storing phenol in combination with formaldehyde. These results support the use of 2-hydroxymethylphenol (HMP) as a low molecular weight model for the resole. At low temperatures and/or short reaction times HMP oligomers (= resoles) and HMP oligomers linked to one ENBH molecule are formed, which are converted into ENBH/HMP (1:1) condensation products. The reaction products of ENBH with both the resole and HMP are shown to contain methylene linked structures, as demonstrated by the formation of monisooctylphenol crosslinks and the presence of residual unsaturation and hydroxyl groups, besides chroman linked structures. This is the first experimental evidence that during phenol-formaldehyde resin cure of rubber, formation of methylene bridges occurs.

The Initial Stage of the Reaction of Melamine with Formaldehyde

Abstract The concentration-time relationships of the individual active species in the oligocondensation stage of the reaction of melamine with formaldehyde have been investigated, mainly by electrochemical methods. Based on the reaction equations, a kinetic model of the overall reaction was established and the rate constants were calculated by numerical methods. The results suggest the hydroxy-methylamines are converted to methylene and dimethylene ether bridged compounds by acid- and base-catalyzed reactions, respectively. At pH 7-10 the formation of methylene bridges by base-catalyzed scission of dimethylene ether bridges may occur.

13C NMR study of modification of urea formaldehyde resins by furfuryl alcohol

A method has been devised for determining from the 13C NMR spectra the structure of the products of interaction of furfuryl alcohol with urea and formaldehyde. Hemiformals form in a neutral medium. Boiling at pH 5·5 leads to the formation of dimethylene ether bridges between the furane cycles and the nitrogen atoms of the urea residues so that the additive is chemically incorporated into the structure of the resin. At pH 3·5 methylene bridges form between the cycles and secondary nitrogen atoms; a considerable part of furfuryl alcohol reacts over the second α-carbon atom of the furane cycle. The crosslinked resin also has methylene bridges between the furane cycles and the tertiary nitrogen atoms of the urea residues.

Urea‐formaldehyde resins 4. Formation of condensation products during resin preparation

AbstractThe formation of diurea compounds containing methylene and dimethylene ether bridges, respectively, as well as the formation of more highly condensed compounds during the preparation of urea‐formaldehyde resins under different conditions have been investigated. The quantitative determination of each individual diurea compound was carried out by means of liquid chromatography. Identification of diurea compounds with a dimethylene ether bridge was made by 1H‐NMR spectroscopy.

The effect of thermal reactions of the products of condensation of dihydric phenols with formaldehyde on their optical and electrophysical properties

Thermal reactions of the products of condensation of dihydric phenols with formaldehyde have been studied. It was found that when the polymers are heated in the region of 120–160° condensation of methylol groups occurs, with formation of dimethylene ether bridges, which decompose in the temperature range of 160–220° with formation of free radicals. Recombination of the radicals results in formation of an infusible, insoluble polymer. At higher temperatures the electrical conductivity of the polymers rises sharply as a result of formation of three dimensional structures. It is shown that polymers with semiconducting properties can be obtained by heat treatment of oligomeric products of condition of dihydric phenols with formaldehyde.