Preparation and performance of lignin–phenol–formaldehyde adhesives

Steam explosion lignin phenol formaldehyde (SEL–PF) adhesives were prepared by ternary gradual copolymerization. The parameters for the phenolate of steam explosion lignin (SEL) and preparation of SEL–PF adhesives were optimized. Under the optimum phenolate conditions, the phenolic hydroxyl content of lignin increased by 130%, whilst the methoxyl content was reduced by 68%. The SEL–PF adhesives were used to prepare plywoods by hot-pressing. The pH value, viscosity, solid content, free phenol content and free formaldehyde content of SEL–PF adhesives were investigated. The bonding strengths of the plywoods glued with SEL–PF adhesives were determined. The maximum SEL replacement percentage of phenol reached 70 wt%, and the properties of adhesives and plywoods met the Chinese National Standard (GB/T 14732-2006) for first grade plywood.     

Influence of nanoclay on urea–glyoxalated lignin–formaldehyde resins for wood adhesive

In this research, the influence of nanoclay on urea–glyoxalated lignin–formaldehyde (GLUF) resin properties has been investigated. To prepare the GLUF resin, glyoxalated soda baggase lignin (15 wt%) was added as an alternative for the second urea during the UF resin synthesis. The prepared GLUF resin was mixed with the 0.5%, 1%, and 1.5% nanoclay by mechanically stirring for 5 min at room temperature. The physicochemical properties of the prepared resins were measured according to standard methods. Then the resins were used in particleboard production and the physical and mechanical properties of the manufactured panels were determined. Finally, from the results obtained, the best prepared resin was selected and its properties were analyzed by differential scanning calorimetry (DSC), Fourier transform infrared spectrometry (FTIR), and X-ray diffractometry (XRD). Generally the results indicated that the addition of sodium-montmorillonite (NaMMT) up to 1.5% appears to improve the performance of GLUF resins in particleboards. The results also showed that nanoclays improved mechanical strength (modulus of elasticity (MOE), Modulus of Rupture (MOR), and internal bond (IB) strength) of the panels bonded with GLUF resins. The panels containing GLUF resin and nanoclay yielded lower formaldehyde emission as well as water absorption content than those made from the neat GLUF resins. XRD characterization indicated that NaMMT only intercalated when mixed with GLUF resin. Based on DSC results, the addition of NaMMT could accelerate the curing of GLUF resins. The enthalpy of the cure reaction (ΔH) of GLUF resin containing NaMMT was increased compared with neat GLUF resin. Also the results of FTIR analysis indicated that addition of NaMMT change the GLUF resins structures.     

The effect of soda bagasse lignin modified by ionic liquids on properties of the urea–formaldehyde resin as a wood adhesive

The aim of this research was to investigate the influence of lignin modified by ionic liquids on physical and mechanical properties of plywood panels bonded with the urea–formaldehyde (UF) resin. For this purpose, soda bagasse lignin was modified by the 1-ethyl-3-methylimidazolium acetate ([Emim][OAc]) ionic liquid and then the various contents of unmodified and modified lignins (10, 15, and 20%) were added at pH=7 instead of second urea during the UF resin synthesis. The physicochemical properties of the prepared resins as well as the water absorption, shear strength, and formaldehyde emission of the plywood panels made with these adhesives were measured according to standard methods. According to Fourier Transform Infrared (FTIR) Spectrometry, by treatment of lignin, the C=O, C–C, and C–H bonds decrease while the content of the C–N bond dramatically increases. Based on the finding of this research, the performance of soda bagasse lignin in UF resins dramatically improves by modification by ILs; as the resins with modified lignin yielded lower formaldehyde emission and water absorption when compared to those made from unmodified lignin and commercial UF adhesives, respectively. The shear strength as well as wood failure percentages are lower for the panels produced with modified lignin than for the panels produced with UF resins alone.     

Properties of plywood panels bonded with ionic liquid-modified lignin–phenol–formaldehyde resin

The aim of this research was to investigate the physical and mechanical properties of plywood panels bonded with ionic liquid-modified lignin–phenol–formaldehyde (LPF) resin. For this purpose, soda bagasse lignin was modified by 1-ethyl-3-methylimidazolium acetate ([Emim][OAc]) ionic liquid, and then, various contents of modified lignins (10, 15, and 20 wt%) were added as a substitute of phenol in phenol–formaldehyde (PF) resin synthesis. The properties of the synthesized resin were compared with those of a control PF resin. The changes in curing behavior of the resins prepared were analyzed by differential scanning calorimetry (DSC). The physical properties of the resins prepared, as well as the water absorption, thickness swelling, shear strength, and formaldehyde emission of the plywood panels bonded with these adhesives, were measured according to standard methods. DSC analysis indicated that in comparison with PF resins, curing of the LPF resin occurred at lower temperatures. The physical properties of the synthesized resins indicated that viscosity and solid content increased, while gel time and density decreased by addition of treated lignin to the PF resin. Although the panels containing resins with modified lignin yielded low formaldehyde emission, their dimensional stability was worse than those bonded with a commercial PF adhesive. The plywood prepared using IL-treated lignin PF resins has shear strength, which satisfy the requirements of the relevant standards specifications and significantly better than that of panels prepared with the control PF resin. The mechanical properties of the panels could be significantly enhanced with increased percentage of treated lignin content from 0 to 20 wt%.     

Synthesis and characterization of fluorine-containing poly-styrene-acrylate latex with core–shell structure using a reactive surfactant

Fluorine-containing poly-styrene-acrylate (PSA) latex with core–shell structure was successfully synthesized by seeded semicontinuous emulsion polymerization using fluorine monomer Actyflon-G₀₄ and reactive emulsifier DNS-86. The chemical composition, morphology of latex, and surface composition of the latex film were characterized by Fourier transform infrared spectra, transmission electron microscopy, and X-ray photoelectron spectroscopy, respectively. The stability properties of latex were tested by Ca²⁺, centrifugal and mechanical stability tests, and the latex film was studied by water contact angle, water absorption ratio, and thermo-gravimetric analysis. The results show that fluorine-containing PSA latex particles with crosslinked core and crosslinked shell structure have excellent stability properties, and the film of latex has excellent water repellency, thermal stability, and chemical resistance properties when the amount of fluorine monomer was only 8.0 wt%.     

Investigation of formaldehyde-free wood adhesives from kraft lignin and a polyaminoamide–epichlorohydrin resin

A formaldehyde-free wood adhesive system consisting of kraft lignin and a polyaminoamide-epichlorohydrin (PAE) resin (a paper wet strength agent) has been investigated in detail. The lignin-PAE adhesives were prepared by mixing an alkaline kraft lignin solution and a PAE solution. Mixing times longer than 20 min had little impact on the shear strength of the wood composites bonded with the lignin-PAE adhesives. The shear strength of the wood composites bonded with the lignin-PAE adhesives increased and then flattened out when the press time and the press temperature increased. The shear strength and water resistance of the wood composites bonded with the lignin-PAE adhesives depended strongly on the lignin/PAE weight ratio. Of the weight ratios studied, the 3:1 lignin/PAE weight ratio resulted in the highest shear strength and the highest water resistance of the resulting wood composites. The wood composites bonded with the lignin-PAE adhesives did not delaminate and retained very high strengths even after they underwent a boiling-water test. The lignin-PAE adhesives could be stored at room temperature for two days without losing their adhesion ability. PAE was the crosslinking agent in this lignin-PAE adhesive. Possible reactions between lignin and PAE are discussed in detail.     

Synthesis and structural characterization of urea–isobutyraldehyde–formaldehyde resins

Urea–isobutyraldehyde–formaldehyde (UIF) resins were synthesized using urea, isobutyraldehyde, and formaldehyde; sulfuric acid was used as a catalyst. The effects of molar ratio of urea/isobutyraldehyde/formaldehyde (U/I/F) on the properties of resins were investigated, and the structures of the resins were characterized by FTIR, ¹H-NMR, and ¹³C-NMR. When U/I/F was 1.0/3.6/2.4, the yield of the resin was 76.5%. The softening point and hydroxyl value were 90°C and 32 mg KOH/g, respectively. The FTIR, ¹H-NMR, and ¹³C-NMR results showed that an α-ureidoalkylation reaction occurred between urea and isobutyraldehyde to form a lactam. The UIF resins also contained hydroxyl groups and aldehyde groups; the content of aldehyde groups in the resin increased as the amount of isobutyraldehyde increased.     

Acid–base characterization of wood and selected thermoplastics

The objective of this work was to study the acid–base properties of wood, poly(vinyl chloride) (PVC), nylon 6 and 6,6 by wetting and inverse gas chromatography (IGC) analyses. Information about the acid–base characteristics of these materials should be useful to improve the intermolecular bonding properties in wood-plastic composites. The acid–base properties of pine wood veneers, PVC and nylon 6,6 were determined by contact angle analysis using the work of adhesion (or Fowkes), van Oss–Chaudhury–Good (vOCG) and Chang–Qin–Chen (CQC) approaches. The IGC analysis was performed on maple wood, PVC and nylon 6 particles, and was carried out at infinite dilution using a series of both non-polar and polar acid–base probe gases. The contact angle analysis of the wood veneers using both the work of adhesion and the vOCG approaches showed that the presence of wood extractives was the dominant factor influencing the acid–base properties of the veneers. Particularly, it was shown that aging of non-extracted veneers increased and decreased their acidic and basic properties, respectively. This is presumably due to reorientation of functional groups and oxidation at the wood extractives–air interface. In the vOCG model, considerably higher base/acid ratios were obtained when using probe liquid parameters according to van Oss compared to those obtained by using liquid parameters according to Della Volpe and Siboni. Based on both the vOCG and the CQC models it was shown that nylon 6,6 had greater acid and base parameters than PVC. Additionally, the CQC model seems to be a promising tool to determine the acid–base characteristics of materials. The IGC analysis showed that nylon 6 had greater acid and base parameters than both wood and PVC which implies a strong ability to enter into acid–base interactions. The results also suggested that an increase in the basic character of wood could have the potential to improve its bonding with both PVC and nylon 6.     

Preparation of highly phenol substituted bio-oil–phenol–formaldehyde adhesives with enhanced bonding performance using furfural as crosslinking agent

Highly phenol substituted bio-oil–phenol–formaldehyde (BPF) adhesives were prepared via the phenolization-copolymerization method, in which furfural was used as a novel crosslinking agent to improve the bonding performance. The effects of bio-oil percentage, furfural content, curing temperature, and pressure on the performance of BPF adhesives have been studied in detail. A BPF adhesive with 75% bio-oil percentage and 15% furfural loading (named 75BPF_15) was synthesized, which was cured at 180 °C and 4 MPa. Compared to the conventional phenol–formaldehyde adhesive, the wet tensile strength of 75BPF_15 adhesive reached 2.84 MPa, which was significantly higher than the 1.54 MPa of PF. A possible mechanism of BPF adhesives crosslinked with furfural is proposed. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 46995.     

Synthesis and characterization of thermosensitive core–shell polymeric nanoparticles

Thermosensitive core–shell nanoparticles were synthesized by semicontinuous heterophase polymerization of styrene, followed by a seeded polymerization for forming a shell of poly(N-isopropyl acrylamide) (PNIPAM). Nanoparticles characterization by scanning transmission electronic microscopy showed core–shell morphology with average particle diameters around 40 nm. An inverse dependence of the particle size with temperature in the range 20–55 °C was identified by quasielastic light scattering measurements. As was expected for core–shell particles with PNIPAM as the shell, a volume phase transition near 32 °C was detected. In spite of thermosensitive properties of core–shell nanoparticles synthesized here, the volume percentage loss values were not so high, probably due to their relatively low content of PNIPAM.     

Selective partition of caffeine from coffee bean and guaraná seed extracts using alcohol–salt aqueous two-phase systems

This work proposes the application of flexible alcoholic aqueous two-phase systems to manipulate the partition of caffeine. An optimization study was performed the caffeine partitioning towards top phase (60.0 wt% 2-propanol + 20.0 wt% K₃PO₄ at 303 K – K_caf = 3.4 and R_T = 89.1%) and bottom phase (60.0 wt% methanol + 17.5 wt% K₂HPO₄/KH₂PO₄ at 278 K – K_caf = 0.06 and R_B = 81.1%). These processes were evaluated by applying them to real biomass as guaraná seeds (purification factor (PF) = 6.59-fold) and coffee beans (PF = 3.24-fold) for the 2-propanol and K₂HPO₄/KH₂PO₄ system.     

Synthesis of porous silicon nitride using silica/carbon composite derived from phenol–resorcinol–formaldehyde gel

Mesoporous silicon nitride (Si₃N₄), which is one of the most promising structural materials for applications in high-temperature filtration, was synthesized from the carbothermal reduction and nitridation of a pyrolyzed silica-containing phenol-resorcinol-formaldehyde (PRF) gel. The PRF gel was synthesized by combining sol–gel and polymerization of phenol, resorcinol and formaldehyde using sodium carbonate as a catalyst. Silica was incorporated into the gel by addition of 3-aminopropyl trimethoxysilane (APTMS) as a silica precursor. After aging and being freeze-dried, the silica/PRF composite was pyrolyzed under nitrogen gas to convert it into porous silica/carbon composite. The combination of phenol-formaldehyde (PF) and resorcinol-formaldehyde (RF) gels into PRF gel, allows further enhancement in porosity of the silica/carbon composite via pre-calcination in the range of 400–500 °C, since carbon derived from PF gel and that from RF gel have different thermal stability. The final product obtained after final calcination to remove residual carbon has a surface area as high as 194 m²/g, which is significantly much higher than the conventional Si₃N₄ granules. Specific surface area of the product is affected by molar ratio of phenol-to-resorcinol, molar ratio of silica-to-carbon, and the pre-calcination temperature.     

Effect of alkalinity on the structure of phenol–formaldehyde resol resins

Two phenol–formaldehyde resol resin series with different methylation- and condensation-stage alkalinities were studied. The first series was impregnation resins having a methylation alkalinity between 0.5 and 1.5 wt % and a condensation alkalinity of 1.5 wt %. The second series was adhesive resins with a methylation alkalinity between 0.5 and 3.5 wt % and a condensation alkalinity of 6.0 wt %. The chemical structure was analyzed by ¹³C-NMR spectroscopy, and reactivity, by differential scanning calorimetry (DSC). The methylation alkalinity was found to affect the distribution of the structural groups of both phenol–formaldehyde impregnation and adhesive resins, but not to the same extent as did the total condensation alkalinity. Also, the results of the DSC analysis illustrate best the reactivity differences due to the condensation alkalinity. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 258–262, 2001     

Synthesis and properties of microencapsulated phase change material with a urea–formaldehyde resin shell and paraffin wax core

During this study, paraffin wax with low melting point was encapsulated in a urea–formaldehyde resin to prepare a novel microencapsulated phase change material (Micro-P6) for temperature regulation and thermal energy storage. The structure and properties of Micro-P6 were characterized by using Fourier transform infrared spectroscopy, differential scanning calorimeter, laser particle size analyzer, thermogravimetric analysis, contact angle analysis, and scanning electron microscope. The results indicated that the chemical structure of Micro-P6 meets the designed core–shell structure; and the paraffin wax with low melting point was successfully encapsulated by using urea–formaldehyde resin; and the Micro-P6 shows a spherical structure and rough surface, and the average size is 8.0–10.0 μm. Then, the performances of Micro-P6, such as core content, mechanical property, thermal conductivity and durability, were tested. Based on above characterization and performance test, it was indicated that the synthesized Micro-P6 could be used in the field of cementing and construction for temperature regulation and thermal energy storage. The applications of Micro-P6 in the field of cementing and construction will be completed in our next study. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48578.     

Fabrication,performances, and reaction mechanism of urea–formaldehyde resin adhesive with isocyanate

In order to improve the performances of urea–formaldehyde (UF) resin adhesive and reduce formaldehyde emission, the isocyanate was applied to modify the UF resin adhesive. The effects of the composition ratio of the isocyanate/UF resin on the thermal stability and molecular structure of the composite adhesive were investigated by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and thermogravimetric analyzer. The results showed that the appropriate addition of the isocyanate into the UF resin is favorable to improve the performances of the composite adhesive due to the chemical cross-linking reaction of the isocyanate with UF. Furthermore, the reaction mechanism of the UF resin adhesive with isocyanate was analyzed in detail. These research results can be applied to aid materials engineering design for the development of new adhesive, quality assurance, and characterization assessment of durability.     

Synthesis and characterization of highly durable and reusable superabsorbent core–shell particles

Superabsorbent core–shell particles were synthesized via a two-step process. A silica core was prepared by co-condensation of tetraethyl orthosilicate and vinyl triethoxysilane. The vinyl-functionalized silica particles were then polymerized with acrylamide monomer via free-radical polymerization to yield silica-polyacrylamide (PAM) hybrid particles. The crosslinking density and porosity of PAM on the hybrid particles were controlled by adjusting the concentration of the crosslinker, n,n′-methylenebisacrylamide (MBA). The structure of core–shell particles was confirmed by scanning and transmission electron microscopy techniques. The hybrid particles with 3.0%MBA could absorb water up to 70 g/g. These hybrid particles also removed 80% of methylene blue from solution within 24 h and this efficacy was maintained for seven cycles. The weight remaining of the hybrid particles after nine cycles was higher than that of pure PAM after three cycles indicating the high durability and reusability of the core–shell particles. POLYM. ENG. SCI., 60: 306–313, 2019. © 2019 Society of Plastics Engineers     

Effect of both grafting and blending modifications on the performance of lignosulphonate-modified sulphanilic acid–phenol–formaldehyde condensates

Modifying sulphanilic acid–phenol–formaldehyde condensates (SPF) with sodium lignosulphonate (LS) allows for both the grafting (GSPF) and blending (BSPF) of a series of products from SPF and LS with different LS content. The grafted macromolecule SPF-g-LS was confirmed to exist in GSPF by low-angle laser light scattering (LALLS) and Fourier-Transform infrared (FTIR) spectroscopy. GSPF formed different adsorption configurations on cement particles than BSPF, which ultimately affected their dispersive properties, because of the high charge density and large steric hindrance of the SPF-g-LS macromolecule. Both the absolute value of the ζ potential and the paste fluidity of the cement particles were greater for GSPF than BSPF at identical LS contents. GSPF and BSPF both significantly inhibited cement bleeding relative to SPF; however, this inhibition was greater for GSPF than BSPF at identical LS contents.     

Synthesis and characterization of local clay–titanium dioxide core–shell extender pigments

A simple chemical technique has been used to prepare core–shell extender pigments based on Nigerian indigenous clays as core and titanium dioxide as shell. The prepared core–shell extender pigments were characterized using X-ray fluorescence and scanning electron microscopy. The physico-chemical properties of these extender pigments were also evaluated according to ASTM measurements. The study showed that the prepared core–shell pigments were nontoxic and environmentally friendly. They are of low cost and can be incorporated in semi-gloss paints, paper, rubber, and plastic composites without much effect on the volume. The characteristics of these pigments showed that they combine the properties of both their precursors, and have the potential to overcome their disadvantages, e.g., low hiding power of clays and photochemical activity of titanium dioxide.