Formulation of a novel soybean protein‐based wood adhesive with desired water resistance and technological applicability

A novel soybean protein‐based wood adhesive with good bond strength, excellent water resistance, and the desired technological applicability was formulated by combining thermal alkali degradation, thermal acid treatment, and crosslinking. The characterization results indicated that thermal alkali degradation could effectively improve the technological applicability, thermal acid treatment could positively improve the water resistance, and appropriate crosslinking modification could significantly enhance the bond strength and water resistance of the soybean protein adhesive. The crosslinker species, crosslinker level, and ratio of thermal alkali‐degraded soybean protein (DSP) to thermal acid‐treated soybean protein (TSP) had important effects on the primary properties of the soybean protein adhesives. The modified polyamide aqueous solution was the most preferable crosslinker because of its low viscosity, good crosslinking efficiency, and excellent miscibility with soybean protein solution. The optimal soybean protein adhesive that was formulated from 20 wt % modified polyamide as the crosslinker and a DSP/TSP ratio of 1:3 had a solid content of more than 35 wt %, suitable viscosity (～2180 mPa s), a long work life (>16 h), good dry bond strength (2.94 MPa), and 28 h of boiling–dry–boiling cycled wet strength (1.29 MPa) that met the required values for structural use according to JIS K6806‐2003 commercial standards. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43586.     

Copolymerization in UF/pMDI adhesives networks

Kinetic evidence in thermomechanical analysis experiments and carbon‐13 nuclear magnetic resonance spectroscopy (¹³C NMR) evidence indicates that the strength of a joint bonded with UF (urea–formaldehyde)/polymeric 4,4'‐diphenylmethane diisocyanate (pMDI) glue mixes is improved by coreaction of the methylol groups of UF resins with pMDI to form a certain number of methylene cross‐links. The formation of these methylene cross‐links is predominant, rather than formation of urethane bridges which still appear to form but which are in great minority. This reaction occurs in presence of water and under the predominantly acid hardening conditions, which is characteristic of aminoplastic resins (thus, in presence of a hardener). Coreaction occurs to a much lesser extent under alkaline conditions (hence, without UF resins hardeners). The predominant reaction is then different in UF/pMDI adhesive systems than that observed in phenol‐formaldehyde (PF)/pMDI adhesive systems. The same reaction observed for UF/pMDI system at higher temperatures has also been observed in PF/pMDI systems, but only at lower temperatures. The water introduced in the UF/pMDI mix by addition of the UF resin solution has been shown not to react with pMDI to an extent such as to contribute much, if at all, to the increase in strength of the hardened adhesive. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3681–3688, 2002     

Investigation of epoxy-based wood adhesives

Cold-set epoxy-based wood adhesives were investigated for production of exterior plywood. Effective adhesives were composed of bisphenol A diglycidyl ether (BPADGE), polyamidoamine (PAA), and polyethylenimine (PEI). Three-ply plywood panels were prepared with BPADGE–PAA–PEI adhesives and evaluated for their strengths and water resistance in accordance with a standard for exterior plywood. The effect of BPADGE/(PAA + PEI) weight ratio, PAA/PEI weight ratio, the mixing time for preparing the adhesive, and the pressing time for making plywood panels on the water resistance and the shear strengths of the plywood panels was investigated. The pot life of the adhesive was also measured. Plywood panels made with the BPADGE–PAA–PEI adhesives met the industrial requirements for exterior applications. Adhesion mechanisms are discussed in detail. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47741.     

Effect of montmorillonite clay addition on the morphological and physical properties of Jatropha curcas L. and Glycine max L. protein concentrate films

Protein concentrates from jatropha (JPC) and soy seeds (SPC) were obtained by solubilization and acid precipitation of proteins. JPC and SPC films were prepared by the casting method, using two different montmorillonite (MMT) clay concentrations and plasticized with glycerol. Film properties were evaluated by scanning electron microscopy, transmission electron microscopy, X‐ray diffraction (XRD), Fourier transform infrared spectroscopy, thermogravimetric analysis, tensile properties, water retention, and water vapor transmission rate (WVRT). Typical tactoid microcomposite structures were found to be heterogeneously dispersed in the films containing MMT. A small XRD peak was found in films with MMT. Slight improvements in thermal stability and tensile strength were observed in the films with MMT. Reductions in water retention and WVRT were obtained when MMT was added into the films. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44459.     

Functional properties of thermoformed wheat gluten/montmorillonite materials with respect to formulation and processing conditions

Wheat gluten (WG)/montmorillonite (MMT) films were prepared by a thermomechanical process consisting of first mixing the components in a two‐blade, counter‐rotating device and second thermoforming the obtained dough. A significant loss in protein solubility due to the formation and rearrangement of disulfide bonds was observed upon mixing and thermoforming. In the range of studied glycerol contents (25–42.8 wt %), it was shown that glycerol had no significant effect on the mechanical properties or water sensitivity of WG‐based films. Increasing the thermoforming temperature from 60 to 120°C led to considerable improvements of the mechanical properties (increases in both the stress and strain at break) and a significant reduction of the water sensitivity. The introduction of MMT (up to 5 wt %) allowed the achievement of mechanical properties that were not possible by just the variation of the glycerol content and the processing temperature. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effects of hydrolysis degree of soy protein isolate on the structure and performance of hydrolyzed soy protein isolate/urea/formaldehyde copolymer resin

The hydrolyzed soy protein isolate (HSPI) with different hydrolysis degree was applied to modify urea‐formaldehyde resins (UF) via copolymerization process. The properties of HSPI were characterized by attenuated total reflection Fourier transform infrared spectroscopy (ATR‐FTIR) and TGA. The results show that HSPI with different hydrolysis degree is obtained. ¹H NMR and ATR‐FTIR spectra indicate that HSPI with different hydrolysis degree can incorporate into the structure of cured and uncured UF. The UF modified with higher hydrolysis degree of HSPI possess more stable units and contribute to the lower exothermic peak temperature in DSC curves. The bonding strength of HSPI modified UF increases as the hydrolysis degree of HSPI increases at the hot‐press temperature of 120°C and decreases at the hot‐press temperature of 150°C. The best bonding strength is 1.53 MPa at the hot‐press temperature of 135°C and improved 56.12% compared with UF. In addition, the formaldehyde emission is dramatically reduced. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41469.     

Self-healing efficiency of cinnamaldehyde-crosslinked soy protein resins with elongated soy protein microcapsules

Self-healing green thermoset soy protein isolate (SPI) based resins, crosslinked with cinnamaldehyde (CA), were developed. Self-healing was achieved using elongated microcapsules (MCs) as against spherical MCs that have been used in most earlier studies. MCs containing SPI solution as healant within poly(d,l-lactide-co-glycolide) shells were prepared using Water-in-oil-in-water (w/o/w) emulsion solvent evaporation (ESE) technique. Process parameters such as sodium tripolyphosphate (STP) and poly(vinyl alcohol) (PVA) concentrations and stirring speed were optimized to obtain elongated MCs. The average aspect ratio of MCs was over four. SPI resins crosslinked with 10% CA (10%CA-SPI) increased Young's modulus and fracture stress by 54% and 87%, respectively, compared with their noncrosslinked counterpart. The resins containing 15% elongated MCs (15%MC-10%CA-SPI) showed self-healing efficiencies of over 42% in fracture stress and about 35% in toughness recovery, after 24 h of healing. Improvement in self-healing can be attributed to the high aspect ratio of the MCs that increases the probability of MCs being in the path of the microcracks and releasing the healant. Elongated MCs also contain higher amount of healant than spherical ones of same diameter. Self-healing resins and composites can not only help prevent their premature failure but also improve their performance as well as service life and safety.     

Effects of highly exfoliated montmorillonite layers on the properties of clay reinforced terpolymer nanocomposite plugging microspheres

In this study, exfoliated montmorillonite (MMT) nanolayers were successfully encapsulated in acrylamide/acrylic acid/2‐acrylamido‐2‐methylpropanesulfonic acid (AM/AA/AMPS) terpolymer microspheres by in situ inverse suspension polymerization with the aid of the organic intercalation modification and the lateral groups of terpolymer chains. The introduction of well‐dispersed MMT nanolayers reveals a significant enhancement of the comprehensive properties of these nanocomposite microspheres, such as the viscoelasticity, thermal stability, and plugging ability. Compared with the pure terpolymer, the elastic modulus (G′) of terpolymer/2.0 wt % O‐MMT nanocomposites is 4.30 times higher and the decomposition temperature of these nanocomposites increases by 40 °C. The plugging rate reaches as high as 86.6%. Besides, surface morphology, swelling degree, and wetting behavior can be effectively tuned by varying the content of exfoliated MMT. The wetting angle increases to 82.0 ° which is suitable for modifying the formation channels. These selected nanocomposite microspheres can effectively enter and plug the high permeable microchannels. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44894.     

Influence of the clay modification and compatibilizer on the structure and mechanical properties of ethylene–propylene–diene rubber/montmorillonite composites

Ethylene–propylene–diene rubber (EPDM)/montmorillonite (MMT) composites were prepared through a melt process, and three kinds of surfactants with different ammonium cations were used to modify MMT and affect the morphology of the composites. The morphology of the composites depended on the alkyl ammonium salt length, that is, the hydrophobicity of the organic surfactants. Organophilic montmorillonite (OMMT), modified by octadecyltrimethyl ammonium salt and distearyldimethyl ammonium salt, was intercalated and partially exfoliated in the EPDM matrix, whereas OMMT modified by hexadecyltrimethyl ammonium chloride exhibited a morphology in which OMMT existed as a common filler. Ethylene–propylene–diene rubber grafted with maleic anhydride (MAH‐g‐EPDM) was used as a compatibilizer and greatly affected the dispersion of OMMT. When OMMTs were modified by octadecyltrimethyl ammonium chloride and distearydimethyl ammonium chloride, the EPDM/OMMT/MAH‐g‐EPDM composites (100/15/5) had an exfoliated structure, and they showed good mechanical properties and high dynamic moduli. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 638–646, 2004     

Improvement of mechanical properties of polylactic acid adhesion joints with bio‐based adhesives by using air atmospheric plasma treatment

The packaging industry generates a high volume of wastes; so that, there is a high demand of biodegradable materials, which do not damage the environment. Nowadays, there is an interesting consumption of polylactic acid (PLA) due to its biodegradable features. This work focuses on the improvement of mechanical properties of PLA adhesion joints for uses in the packaging industry. In order to achieve that purpose, atmospheric plasma treatment is used to selectively modify PLA surface properties. The obtained experimental results show that the atmospheric plasma treatment is suitable to increase the mechanical performance of PLA–PLA adhesive joints. Optimum conditions for the atmospheric plasma treatment were obtained with a nozzle–substrate distance of 10 mm and an advance rate in the 100–300 mm s^?1 range; for these particular conditions, the effectiveness of the surface modification is the highest. The main plasma‐acting mechanisms are microetching together with the insertion of polar groups which lead to an interesting synergy that causes a remarkable increase in mechanical properties of adhesion joints. In particular, the shear strength of untreated PLA–PLA adhesion joints is close to 50 N cm^?2 and this value is increased up to values of about 168.7 N cm^?2 with optimum plasma treatment conditions. This indicates that atmospheric plasma treatment is both a technical and an environmental friendly technique to improve mechanical performance of PLA adhesive joints. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42391.     

The effects of clay dispersion on the mechanical,physical, and flame‐retarding properties of wood fiber/polyethylene/clay nanocomposites

In this study, nanosized clay particles were introduced into wood fiber/plastic composites (WPCs) to improve their mechanical properties and flame retardancy, which are especially important in various automotive and construction applications. A high degree of exfoliation for nanoclay in the wood fiber/high density polyethylene (HDPE) composites was successfully achieved with the aid of maleated HDPE (PE‐g‐MAn), through a melt blending masterbatch process. The structures and morphologies of the composites were determined using X‐ray diffraction (XRD) and transmission electron microscopy (TEM), respectively. This article presents the effects of clay content and degree of clay dispersion on the mechanical and physical properties and flame retardancy of wood fiber/HDPE composites that contained a small amount of clay, in the range of 3–5 wt %. We concluded that achieving a higher degree of dispersion for the nanosized clay particles is critical to enhance the mechanical properties and the flame retardancy of WPCs when small amounts of clay are used. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Asphaltenes as a tackifier for hot-melt adhesives based on the styrene-isoprene-styrene block copolymer

The use of heavy crude oil asphaltenes and resins (termed asphaltenes) as the components of hot-melt adhesives based on the styrene-isoprene triblock copolymer was considered. The rheological, thermophysical, strength, and adhesive characteristics of the mixtures containing from 10 to 40 wt% of asphaltenes were studied. The addition of 10 to 20 wt% of asphaltenes enhanced the strength and adhesive properties of the mixtures and only slightly changed their rheology. The higher concentrations of asphaltenes reduced the viscosity of the mixtures but did not lead to improved characteristics of the adhesives. The ambiguous effect of asphaltenes is probably due to their uneven distribution between the microphases of the block copolymer as well as their ability to act both plasticizers and reinforcing particles depending on temperature. A comparison of asphaltenes and conventional tackifiers based on hydrocarbon resins revealed their comparable effect on the properties of the block copolymer.     

Chemical phosphorylation improves the moisture resistance of soy flour‐based wood adhesive

A green‐chemistry approach to improve the moisture resistance of soy flour (SF)‐based wood adhesive is described. Chemical phosphorylation of SF (PSF), using POCl₃ as the phosphorylating agent, dramatically increased its wet bond strength. The optimum POCl₃:SF ratio that produced maximum wet bond strength was about 0.15 (g g^?1). The increase in wet bond strength of PSF (PSF0.15) was mostly due to the phosphate groups incorporated into the proteins and carbohydrates, and to a lesser degree to phosphorylation‐induced protein denaturation. The attached phosphate groups acted as cross‐linking agents, either via covalent esterification with hydroxyl groups on wood chips or via ionic and hydrogen‐bonding interactions with functional groups in wood chips. At hot‐press temperatures above 160°C the wet bond strength of PSF0.15 was >2.6 MPa, a level that might be acceptable for interior‐used hardwood plywood and particleboard. POCl₃ is a low cost, general‐purpose reagent and therefore PSF‐based adhesive is expected to be environmentally friendly. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40451.     

Mussel-inspired bio-based water-resistant soy adhesives with low-cost dopamine analogue-modified silkworm silk Fiber

Mussel-inspired dopamine chemistry is popular among engineers for surface modification on various substrates due to its high efficiency, handy operation process, and strong reactivity. However, the high cost of dopamine does not allow for mass production. In the present study, low-cost dopamine analogues (alkali lignin and tannic acid) were used to fabricate high-reactivity silkworm silk fiber (SF) via a simple dip-coating approach, and were then applied to a soy-based adhesive to enhance its performance. The SF tightly combines with soy protein mainly via a Schiff base reaction between polydopamine or dopamine analogue and the amine or thiol groups of soy protein; this forms a multiple crosslinked system and “reinforced concrete”-like structure, as confirmed by Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetry, and scanning electron microscopy analyses. As expected, the toughness of the soy-based adhesive obviously improved and the highest wet shear strength of the adhesive samples attained 1.50 MPa, which is far greater than relevant interior use requirements. Though dopamine-coated SF could significantly enhance the wet shear strength of the soy-based adhesive by 387.1% compared to the pristine SM adhesive, lignin-coated and tannic acid-coated SFs are more suitable for practical application due to the lower cost of raw materials. The results of this study may represent an effective and low-cost approach to mussel-inspired surface modification chemistry for the mass production of high-performance soy-based adhesives. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48785.     

Development of a new synthetic method based on in situ strategies for polyethylene/clay composites

Methods to make polymer composites comprise melt and solution blending, but in the particular case of polyolefins they are not appropriate due to the weak interfacial adhesion. In the present work, in situ blended (ISB) together with in situ polymerization (ISP) processes have been employed and compared using MAO/(nBuCp)₂ZrCl₂ as catalytic system and sepiolite clay as additive in ethylene polymerization. A new method as a combination of the previous ones (ISB + ISP) has been developed and applied to the synthesis of linear low‐density polyethylene (LLDPE). When ISB + ISP method is employed high catalytic activities are observed and this combination allows to increase the storage modulus at 25°C up to 26% with 2.8 wt % of clay in LLDPE when silica is employed as catalyst carrier; in that way, copolymer particles with good morphology with higher storage modulus are obtained, useful properties for their use in specific applications. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Characteristics of soy protein isolate‐montmorillonite composite films

Soy protein isolate/montmorillonite (SPI/MMT) nanocomposite films were prepared in which MMT was used as a nanofiller at 0, 3, 6, 9, 12, and 15 wt % relative to SPI dry weight. Effects of MMT on film properties including tensile strength, elongation at break, total soluble matter, water vapor permeability, and oxygen permeability were assessed. X‐ray diffraction patterns were determined, and morphologies of SPI and the SPI‐MMT composite films were visualized by scanning electron microscopy. Mechanical and barrier properties were improved by evidenced increases in tensile strength and modulus, and decreases in permeability to water vapor and oxygen. MMT concentrations of 3%–12% were optimal for improving functional properties of the composite films. X‐ray diffraction and scanning electron microscopy examinations revealed the formation of an intercalated and exfoliated structure on the addition of MMT into the SPI matrix. We conclude that intercalated and exfoliated MMT silicates enhance mechanical and barrier properties of SPI films. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Wheat gluten fractions as wood adhesives—glutenins versus gliadins

Plant proteins, such as wheat gluten, constitute attractive raw materials for sustainable wood adhesives. In this study, alkaline water dispersions of the protein classes of wheat gluten, glutenin, and gliadin were used as adhesives to bond together wood substrates of beech. The aim of the study is to measure the tensile shear strength of the wood substrates to compare the adhesive performance of glutenin and gliadin and to investigate the influence of application method and penetration of the dispersions into the wood material. A sodium hydroxide solution (0.1M) was used as dispersing and denaturing agent. Dispersions with different protein concentrations and viscosities were used, employing wheat gluten dispersions as references. Two different application methods, a press temperature of 110°C and a press time of 15 min, were employed. The tensile shear strength and water resistance of the wood substrates were compared, using a slightly modified version of the European Standard EN 204. The bond lines of the substrates were examined by optical microscopy to study the penetration and bond‐line thickness. The results reveal that the adhesive properties of gliadin are inferior to that of both glutenin and wheat gluten, especially in terms of water resistance. However, the tensile shear strength and the water resistance of gliadin are significantly improved when over‐penetration of the protein into the wood material is avoided, rendering the adhesive performance of gliadin equal to that of glutenin and wheat gluten. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Effects of interactions between soy protein isolate and pectin on properties of soy protein-based films

Composite films in coacervation condition offer an alternative to change properties of protein-based films, and they present potential applications such as inclusion, stabilization, and release of bioactive compounds in foods. Maximum interactions between soy protein isolate (SPI) (5%) and high methoxyl pectin (PEC) (0.5, 1, 1.5, and 2%), by zeta potential analysis, are found at a pH of 3. The transparency of the SPI films is lost at this pH. When PEC is added to SPI films, the elasticity, solubility, and permeability to water vapor are not significantly altered, but the tensile strength increases. Permeabilities to oxygen are higher for low PEC contents, but as PEC is added, their values are typical of SPI films produced at a pH of 11. A homogeneous structure is found at the higher PEC concentrations. The interactions of PEC–SPI can be useful to tailor films and coatings for applications such as to carry and protect substances of interest. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48732.     

Dynamic mechanical,thermal, and morphological properties of silane‐treated montmorillonite reinforced polycarbonate nanocomposites

Three different loading of 3‐aminopropyltriethoxysilane (APS) was used to modify the Na‐montmorillonite via cation exchange technique. The Na‐MMT and silane‐treated montmorillonite (STMMT) were melt‐compounded with polycarbonate (PC) by using Haake Minilab machine. The PC nanocomposite samples were prepared by using Haake Minijet injection molding technique. The intercalation and exfoliation of the PC/MMT nanocomposites were characterized by using X‐ray diffraction (XRD) and transmission electron microscopy (TEM). The thermal properties of the PC nanocomposites were investigated by using dynamic mechanical analyzer and thermogravimetry analyzer. XRD and TEM results revealed partial intercalation and exfoliation of STMMT in PC matrix. Increase of APS concentration significantly enhanced the storage modulus (E′) and improved the thermal stability of PC nanocomposites. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Improving performance of polyvinyl acetate (PVA) as a binder for wood by combination with melamine based adhesives

In this study blending PVA with MUF and MF was evaluated as an approach to enhance the performance of PVA towards water and elevated temperatures. MF and MUF were added to PVA at different proportions: 15%, 30%, 50%, 70% and 100%. Blends of PVA with MF and MUF were used as adhesives to bond wood joints. The shear strength of wood joints was measured at dry and wet states, and elevated temperatures. Thermogravimetric analysis was used to study thermal stability of PVA and its blends with MF and MUF. The structural changes caused by the inclusions were characterized by Fourier transforms infrared spectroscopy (FT-IR). The results showed that shear strength of wood joints were improved by the addition of MF and MUF to PVA in all conditions. Adding small amounts of MUF or MF (as low as 15%) enhanced the performance of wood joints towards water and elevated temperatures. The extent of improvement was sometimes so high that the strength of glue line surpassed strength of wood in wet conditions leading to wood failure rather than glue failure. MF had more effectiveness in improving shear strength of wood joints than MUF in all conditions. Thermal stability of PVA was increased by MF but the effect of MUF on thermal stability of PVA was dependent on MUF proportions and temperatures. FT-IR analyses showed that there are some chemical bonds between PVA and MF. Considering costs, effectiveness and formaldehyde emission, adding 15% MF to PVA seems the optimal proportion of MF in the PVA blends.