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.     

High bonding strength and boiling water resistance of soy protein‐based adhesives via organosilicon–acrylate microemulsion and epoxy synergistic interfacial enhancement

Boiling water resistance, an important indicator of wood adhesives, represents the capability of adhesives for exterior woodwork applications. However, soy‐based adhesives show poor behaviors in this respect, which limit their applications in outdoor environments. In this article, we report a synergistic modification method of integrating a cocrosslinking system of epoxied polyamideamine‐epichlorohydrin (PAE) and organosilicon–acrylate copolymer latexes (OACLs) to improve soybean meal (SM)‐based adhesive properties. Tailored PAE and OACL SM‐based adhesives demonstrated robust crosslinking structures via multi‐interfacial interactions, where PAE and OACL served as building blocks of an interpenetrating network, which was characterized by Fourier transform infrared spectroscopy, X‐ray diffraction, thermogravimetric analysis, and scanning electron microscopy. The dry‐shear strength, wet‐shear strength, and boiling water strength of the resulting SM‐based adhesives were 1.41 ± 0.13, 1.32 ± 0.17, and 1.20 ± 0.11 MPa, respectively, with 15 wt % OACL loading; these were 41, 45, and 90% increases, respectively, over the SM–PAE adhesive with which we compared them. Most importantly, the excellent boiling water resistance of the adhesives make them practical for exterior plywood. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46061.     

Adhesion properties of soy protein crosslinked with organic calcium silicate hydrate hybrids

The objective of this work was to investigate if inorganic calcium silicate hydrate (CSH) hybrids would improve soy protein wet adhesion properties. 3‐aminopropyltriethoxysilane (APTES) was used as a crosslinking agent to make covalent linkage between organic soy protein and inorganic CSH phases. Soy protein–calcium silicate hydrate (MSP‐CSH) composites with different mole ratio of APTES were prepared and the effect of crosslinking reaction on physicochemical properties such as thermal, rheological, FTIR spectroscopic, and morphological and adhesion properties were studied with physical aging effect. Covalent linkage was observed between CSH and soy protein using the FTIR technique. With aging effect, the denaturation temperature (T_d) and enthalpies (ΔH_d) of each fraction of soy protein increased in DSC thermograms, representing higher thermal stability, and the viscoelasticity of the composites also increased. The roughly coated surface of the MSP‐CSH composite was observed in SEM images. All these changes further confirmed the interaction between CSH and soy protein molecules. Dry and wet adhesion strength of the MSP‐CSH composites was higher than the control MSP alone. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40693.     

Accelerated weathering behavior of castor oil bio-based thermosets

Bio-based thermosets based on vegetable oils are promissory materials due to their good performance, renewability and biodegradability. In this work, accelerated weathering tests were performed over bio-based thermosets obtained from castor oil to evaluate the long-term performance under environmental conditions. The thermosets were obtained through homopolymerization or copolymerization with styrene of maleated castor oil methacrylate. The changes in chemical and physical properties were monitored by Fourier-transform infrared spectroscopy (FTIR), color measurements, scanning electron microscopy (SEM) and proton nuclear magnetic resonance (¹HNMR). Both materials showed evidences of chemical changes, such as formation of double bonds and hydroxyl groups, as well as the decomposition of carbonyl ester groups. The observed physical changes were discoloration as well as the formation of cracks and blistering. However, the degradation phenomena were less severe in the copolymer due to the high stability of styrene moieties.     

Microparticles and latexes prepared via suspension polymerization of a biobased vegetable oil and renewable carboxylic acid

Novel bio-based microparticles and latexes are synthesized using green chemistry principles through the reaction of aconitic acid (a sugarcane byproduct) and epoxidized linseed oil (ELO). No volatile solvents have been used, and no initiators are present in this polymerization. Using different agitation techniques, we investigate the particles and latexes formed via suspension polymerization in contrast to bulk dispersion polymerization. With the addition of water and a small amount of surfactant to the ELO and aconitic system, a thermally stable material up to 250°C is created that exhibits adhesive and hydrophobic properties. These microparticle latexes are anticipated for applications in hydrophobic coating and personal care products.     

Development and evaluation of pressure sensitive adhesives from a fatty ester

Novel pressure sensitive adhesives (PSAs) were developed from renewable methyl oleate (MO) and fully evaluated for their peel strength, tack force and shear resistance. MO was epoxidized and selectively hydrolyzed on the ester group to form epoxidized oleic acid (EOA) that is a bifunctional monomer containing both a carboxylic acid group and an epoxy group. EOA was step‐growth polymerized to form a hydroxyl‐containing polyester, which was then cured in the presence of a small amount of a polyfunctional epoxide [epoxidized soybean oil or trimethylolpropane triglycidyl ether (TMPTGE)] to afford PSAs. The PSAs from the polyester cured with TMPTGE exhibited high peel strength (2.4 N/10 mm), high tack force (5.8 N), and sufficient shear resistance (9.0 min). The PSAs can be fully based on renewable natural materials, and their preparations are environmentally friendly. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41143.     

Tung oil‐based thermosetting polymers for self‐healing applications

Several bio‐renewable thermosetting polymers were successfully prepared from tung oil through cationic polymerization for the use as the healing agent in self‐healing microencapsulated applications. The tung oil triglyceride was blended with its methyl ester, which was produced by saponification followed by esterification. The changes in storage modulus, loss modulus, and glass transition temperature as functions of the methyl ester content were measured using dynamic mechanical analysis. In addition, the fraction of cross‐linked material in the polymer was calculated by Soxhlet extraction, while proton nuclear magnetic resonance, Fourier transform infrared spectroscopy and TEM were used to investigate the structure of the copolymer networks. The thermal stability of the thermosets as a function of their methyl ester blend contents was determined by thermogravimetric analysis. Finally, the adhesive properties of the thermosets were studied using compressive lap shear and the fracture surfaces were analyzed using SEM. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40406.     

Recent synthetic approaches and emerging bio‐inspired strategies for the development of sustainable pressure‐sensitive adhesives derived from renewable building blocks

In this review, we provide a bird's eye view of recent developments in the field of pressure‐sensitive adhesives (PSAs) derived from renewable monomeric building blocks. This emerging research field has been driven by increasing sustainability requirements in the adhesive industry and bridges the gap existing between highly optimized petroleum‐based synthetic PSA systems, which display superior performance but lack biobased content, and historical PSAs derived from naturally occurring biopolymers (e.g., starch and natural rubber), which provide more environmentally friendly bonding solutions but have inherent technical limitations that prevent their more widespread implementation in today's technically demanding applications. We critically reviewed a representative (and exhaustive) survey of recent synthetic approaches to the development of biobased PSAs from the academic (articles) and industrial (patents) literature categorized in two families: chain‐growth and step‐growth polymerization routes. Finally, we draw a parallel between renewable synthetic PSAs and nature's self‐adhesive glues, highlighting how the synergy between green chemistry and biomimetic concepts could inspire the emergence of a new generation of smart, synthetic, biobased PSAs with differentiated properties that approach the ones that are found in the natural world and with a wide spectrum of potential applications in the industrial and medical sectors. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40669.     

High-performance thermosets with tailored properties derived from multi-arm stared vanillin and carbon fiber composites

Vanillin, a rigid compound can be separated from lignin, is a promising sustainable candidate for industrial and high performance polymers, while synthesis of hexa-epoxies is challenging. Meanwhile, carbon fiber reinforced bio-based polymers combining high performance are more difficult to be achieved because of the contradictions of liquidity and high rigidity in the polymer structure and performance. In this paper, a novel hexa-epoxy functionalized bio-based epoxy resin (HPVIGEP) with a multi-arm star structure, which simultaneously reduced the viscosity and improved thermo-mechanical properties. The rheological behavior analysis results of HPVIGEP indicated that the viscosity was 3406.9 mPa·s at 25°C, which dramatically decreased by 75.8% compared to DGEBA (14,096 mPa·s), leading to excellent processability and adaptability. At the same time, the study on mechanical properties revealed that the cured HPVIGEP manifested 30.6%, 33.7% and 49.0% in higher tensile strength, tensile modulus and storage modulus (30°C) than of cured commercial epoxy, respectively. The tensile strength and flexural strength of carbon fiber composites which were applied HPVIGEP were increased by 9.3% and 10.9%, respectively. In a word, this work provides the promise for the application of environmentally friendly bio-based composite materials.     

Heat‐sealing properties of soy protein isolate/polyvinyl alcohol film made compatible by glycerol

Heat‐sealing properties are necessary for packaging materials. Soy protein isolate/polyvinyl alcohol (SPI/PVA) blend film is a biodegradable potential packaging material. We analyzed the effects of PVA content (0–20%), glycerol content (1–3%), and sealing temperature (180–230°C) on the heat‐sealing properties of SPI/PVA blend film. Results showed that SPI/PVA film obtained the desired sealing properties when the PVA content exceeded 15%. The sealing strength increased with the PVA content, reaching a maximum upon blending with 20% PVA and 1% glycerol at 220°C. The temperature at sealing strength was approximately twice that at 180°C. However, glycerol migrated to the surface and hindered the entanglement of macromolecular chains in the sealing interface, thereby resulting in reduction of seal strength. Glycerol vaporization at 204°C led to aesthetically unacceptable blistering in the sealing area. Therefore, the optimum sealing temperature of the blended film was ～200°C. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40308.     

Comparison of thermoset soy protein resin toughening by natural rubber and epoxidized natural rubber

Fully bio‐based soy protein isolate (SPI) resins were toughened using natural rubber (NR) and epoxidized natural rubber (ENR). Resin compositions containing up to 30 wt % NR or ENR were prepared and characterized for their physical, chemical and mechanical properties. Crosslinking between SPI and ENR was confirmed using ¹H‐NMR and ATR‐FTIR. All SPI/NR resins exhibited two distinctive drops in their modulus at glass transition temperature (T_g ) and degradation temperature (T_d ) at around ?50 and 215 °C, corresponding to major segmental motions of NR and SPI, respectively. SPI/ENR resins showed similar T_g and T_d transitions at slightly higher temperatures. For SPI/ENR specimens the increase in ENR content from 0 to 30 wt % showed major increase in T_g from ?23 to 13 °C as a result of crosslinking between SPI and ENR. The increase in ENR content from 0 to 30 wt % increased the fracture toughness from 0.13 to 1.02 MPa with minimum loss of tensile properties. The results indicated that ENR was not only more effective in toughening SPI than NR but the tensile properties of SPI/ENR were also significantly higher than the corresponding compositions of SPI/NR. SPI/ENR green resin with higher toughness could be used as fully biodegradable thermoset resin in many applications including green composites. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44665.     

Analyzing the interactions and miscibility of silk fibroin/mucin blends

Mucin, a glycoprotein with viscoelastic properties, and silk fibroin, a protein excreted from silkworms with properties of thermal and mechanical resistance, have been probed as building blocks in the design of biomaterials. Aiming to evaluate the interaction and miscibility between mucin and fibroin, we synthesized silk fibroin and mucin (SF/MU) blends for biomedical applications. The morphological analysis of the SF/MU blends showed the presence of two phases, suggesting a partial miscibility between the polymers. The degradation temperature of the SF/MU blends increased with an increase in the silk fibroin content, indicating that silk fibroin contributed to the thermal stability of the blends. The glass transition temperature of the SF/MU blends lay between the values of the pure polymers. The Fourier-transform infrared spectroscopy results pointed out that the interaction between fibroin and mucin occurred between the amine group of silk fibroin and mucin carboxyl and hydroxyl groups. The outcomes of this work provided essential information on the miscibility of the SF/MU blends. These findings will be critical for further studies with fibroin and mucin-based biomaterials, especially in mucoadhesive systems and wound healing applications.     

Lignin–phenol–formaldehyde resin adhesives prepared with biorefinery technical lignins

In this study, four biorefinery technical lignins were used to synthesize lignin–phenol–formaldehyde (LPF) resin adhesives with a proposed formulation that was designed based on accurate analysis of the active sites in lignin with ³¹P nuclear magnetic resonance (NMR). The properties of the LPF resin adhesives and the plywoods prepared with them were tested. The structural features and curing behavior of the LPF resin adhesives were thoroughly investigated by solution‐ and solid‐state ¹³C NMR. Results indicated that the proposed formulation exhibited favorable adaptability for all four of these technical lignins for synthesis of LPF resin adhesives. High‐performance plywood with low emissions of formaldehyde could be successfully prepared with the synthesized LPF resin adhesives. All the LPF resin adhesives exhibited similar structure and curing behavior with the commercial phenol–formaldehyde (CPF) resin adhesive. However, the LPF resin adhesives showed relatively higher curing temperatures as compared with the CPF resin adhesive. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42493.     

Rheological behaviors exhibited by soy protein systems under dynamic aqueous environments

In this study, rheological behaviors of soy protein and soy flour as powders, pastes, and dispersions are characterized over a range of water contents and temperature to understand their processing in adhesives or paints. At ambient temperature, soy protein samples were characterized by low critical strain values (<0.1%), whereas soy flour samples exhibit linear viscoelastic regions >1% strain with 30–90% water content. On heating, the aqueous soy protein and soy flour compositions have complex rheological behaviors due to plasticization by water and the thermal denaturing and crosslinking of protein and carbohydrate with increasing temperature. Below 100 °C, soy protein rheological behaviors were attributable to the glass transition of the 7S and 11S soy globulin fractions, polymer flow, and plasticization by residual moisture. Above 100 °C, the onset of protein crosslinking was observed with this shifting to higher temperatures for samples still dehydrating. With soy flour samples, the residual moisture present above 100 °C similarly increase protein crosslinking to higher temperatures (125–148 °C) for samples with initial water contents of 30–90%. These results provide a basis for understanding why soy systems undergoing heat processing and rapid dehydration will require higher temperature and longer processing time to attain a cured, crosslinked state. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45513.     

Production of silk fibroin nanoparticles using ionic liquids and high‐power ultrasounds

Biopolymeric nanoparticles have attracted great research interest in the last few years due to their multiple applications. This article describes how high‐power ultrasounds are capable of enhancing the dissolution process of silk proteins in ionic liquids (ILs) and how silk fibroin nanoparticles (SFNs) can be obtained directly from the silk/ionic liquid solution (SIL) by rapid desolvation in polar organic solvents. The silk fibroin integrity is highly preserved during the dissolution process, as confirmed by sodium dodecyl sulfate‐polyacrylamide gel electrophoresis (SDS‐PAGE) of the SIL. These regenerated SFNs are insoluble in water and other common organic solvents and are indistinguishable from the classical SFNs with respect to their diameter (180 ± 5 nm), Zeta potential (?25 ± 3 mV), high degree of β‐sheet and low cytotoxicity. Large amounts of silk can be turned into biomaterials directly from the SIL solution for use in a wide range of applications, while the ILs can be recovered from the coagulant solution under reduced pressure and reused without loss of their solvent properties. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41702.     

The properties and suitability of commercial bio-based epoxies for use in fiber-reinforced composites

Environmental concerns about fiber composites are leading manufacturers to consider bio-based alternatives to petroleum-derived epoxies. Such a substitution is hindered by a lack of information, so commercially available bio-based epoxy systems have been compared, their mechanical properties measured, and fiber composites produced by vacuum infusion. Most high bio-based content resins for infusion use conventional curing agents. Bio-based content is generally added using Epicerol, but also other bio-based precursors. A diglycidyl ether of bisphenol A system produced using Epicerol achieves 20 % bio-based content, but achieves higher contents when Epicerol is used in diluents. Fully bio-based monomers can be deleterious to the mechanical properties and glass transition temperature (T_g), so are used sparingly. The most-promising systems (28 % to 43 % bio-based) compare well to conventional epoxies, possessing good strength, stiffness, toughness, and a reasonable T_g. These partially bio-based epoxies offer an immediate lower-carbon alternative for vacuum-infused composites in marine, sports equipment, and wind energy.     

Improvement of water resistance of wheat flour-based adhesives by thermal–chemical treatment and chemical crosslinking

A water-resistant adhesive for plywood panels for engineered wood floors was developed using thermal–chemically treated wheat flour (WF), polyvinyl alcohol (PVA), and polymeric diphenylmethane diisocyanate (p-MDI) as the cross-linker. The thermal–chemical treatment was performed at 100°C in the presence of sulfuric acid or sodium dodecyl sulfate (SDS). Fourier transform infrared spectroscopy, X-ray diffraction spectroscopy, and scanning electron microscopy were used to investigate the chemical structure, crystalline degree, and morphology change, respectively, of the thermal–chemically treated WF. The boiling water-insoluble content and acetaldehyde values of the thermal–chemically treated WF were also evaluated and compared with those of the controls—native WF and thermally treated WF alone. The bond property evaluation showed that the water resistance of the thermal-SDS-treated WF (T-SDS-WF)-based adhesive was significantly improved, which is mainly attributed to the formation of a three-dimensional crosslinking network resulting from self-crosslinking of the wheat protein, the Maillard reaction between the wheat starch and wheat protein, and the increased crosslinking between T-SDS-WF and p-MDI. Overall, the developed WF-based adhesive is a promising bio-based candidate in the production of plywood for engineered wood floors.     

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.     

Surface and degradation properties of thermoplastic blends from albumin and zein‐based plastics

The use of traditional petroleum‐based thermoplastics in food packaging applications pose an environmental hazard, as their lack of biodegradability creates waste that environmental systems are unable to cope with. To address this issue, the investigation of surface, biodegradation, and water solubility properties of the albumin and zein thermoplastic blends plasticized with glycerol and mixed with varying amounts of low‐density polyethylene (LDPE) is conducted. When subjected to soil burial, albumin as a bioplastic completely biodegrades within two months, while a zein‐based bioplastic is more resilient to attacks from microbes within the soil (4.34% of intial mass remains). If albumin and zein proteins are used in the production of thermoplastics in tandem with LDPE, it could be possible to produce a plastic that will naturally biodegrade over time, decreasing the environmental impact of the use of thermoplastics in medical and food packaging applications. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44646.     

Water-repellent films from corn protein and tomato cutin

Flexible and hydrophobic biobased films were obtained using zein esterified with methanol and para-toluene (p-toluene) sulfonic acid, cutin from tomato peels and ethanol. Esterification was confirmed by proton nuclear magnetic resonance and attenuated total reflectance–Fourier transform infrared spectroscopy (ATR-FTIR). Non-modified zein films were brittle and hydrophilic. ATR-FTIR demonstrated that zein esterification increased zein hydrophobicity. Without cutin, esterified zein films were hydrophobic but brittle. Addition of cutin yielded films that were flexible and hydrophobic, as demonstrated by contact angle measurements. Principal component analysis (PCA) of ATR-FTIR data showed that intensities at 3195 cm⁻¹ and 3490 cm⁻¹ were correlated to the relative hydrophobicity of zein films. PCA also showed that films of esterified zein and cutin were more hydrophobic than their counterparts (non-modified zein without cutin). Optical and scanning electron microscopy demonstrated that esterified zein was compatible with cutin and yielded cohesive films, which did not fracture upon bending.