Thiol-assisted bioinspired deposition of polyurethane onto cellulose as robust elastomer for reinforcing soy protein-based composites

The development of natural fiber-reinforced composites is environmentally friendly and therefore presents great potential; however, these composites are characterized by poor water resistance and interfacial bonding, which therefore limits its practical applications. This study reported a facile and novel approach for the construction of a high-performance microfibrillated cellulose (MFC) elastomer using thiol-functionalized polyurethane (PU-SH) with the assistance of a bioinspired dopamine platform. This elastomer was then employed as a reactive reinforcer to improve soy protein isolated (SPI) adhesive. The surface modification of MFC included the formation of a polydopamine (PDA) layer and Michael addition reactions between PU-SH and PDA, which were characterized by the Fourier-transform infrared spectroscopy, thermogravimetric analysis, and X-ray photoelectron spectroscopy measurements. It was found that the high-functional MFC elastomer served as a reactive cross-linker that gave rise to multiple physical and chemical interactions with the SPI matrix. This resulted in the optimization of the crosslinking system, which ultimately contributed to the solution of the bottleneck issues for natural fiber-reinforced composites. Consequently, the modified SPI-based adhesives notably enhanced the shear strength to 1.38 MPa, displaying a 236.6% increment compared to the unmodified adhesive. This strategy may provide a new insight into the design and preparation of superior natural plant-reinforced composites.     

Techno-economic assessment of VOC-emission reduction strategies based on the ARGUS model

Volatile organic compounds (VOC) are subject to several international environmental regulations such as the UNECE Gothenburg Protocol (1999) and the corresponding European NEC-Directive (on national emission ceilings for SO₂, NO_x, VOC and NH₃; 2001/81/EC). The mass flow optimization model ARGUS is proposed as a bottom-up approach for the elaboration of cost-effective VOC emission reduction strategies on a national and regional level. Various scenarios reflecting different time delays and pathways for the implementation of the emission reduction targets can be considered. The application of ARGUS is demonstrated for the sector of metal degreasing in Austria.     

Effects of resin open time and melamine addition on cold pre-pressing performance of a urea–formaldehyde resin

The pre-pressing performance of urea formaldehyde resins has a significant impact on plywood production efficiency. This paper reports on the effects of the time elapsed after the addition of the hardener (“resin open time”) and of a melamine addition on the cold pre-pressing performance of UF resins. The changes in pH and viscosity, the thermal behaviour, and the structural composition as well as the performance during cold pre-pressing of veneers were investigated. Cold pre-pressing performance was measured by testing pre-pressed three-ply plywood stacks. The results showed that the cold pre-pressing performance is enhanced with longer time after preparation of the resin mix before application onto the veneers and also by longer pre-pressing times. All plywood stacks with at least 2 h pre-pressing time reached the so-called G1 grade (where the re-opened area of the cold pre-pressed plywood stack was 0), which meets the industrially accepted requirements for plywood fabrication. Further, the addition of melamine improved the cold pre-pressing behaviour compared to the investigated UF resin without melamine, showing an earlier start of the development of the pre-pressing shear strength and higher G grades at the various cold pressing times. There are two main reasons for the enhanced cold pre-pressing performance of the resin under the investigated conditions: (1) influence of the “resin open time”: a certain further condensation of the resin after preparing the glue mix (addition of hardener) leading to increased molar mass and viscosity ultimately transforming the resin from liquid-state to gel-state; (2) a higher methylol content in the resin after incorporation of melamine into the resin, which enhanced the formation of hydrogen bonds between the resin and the wood surface. These conclusions represent a feasible approach for the improvement of the cold pre-pressing properties and thus the practical applicability of UF resins with low molar ratios.     

Activating relaxation-controlled diffusion mechanisms for tailored moisture resistance of gelatin-based bioadhesives for engineered wood products

The feasibility of tailoring the moisture resistance of bioadhesives by activating relaxation-controlled diffusion mechanisms is demonstrated herein using gelatin, a hydrophilic biopolymer, as a model biobased resin for engineered wood products. The effect of gelatin-to-water concentration and tannin addition on the governing kinetics of water transport in gelatin-based bioadhesives was investigated in this work. Time-dependent flexural mechanical properties of laminated (a) gelatin and (b) gelatin–tannin wood veneer composites conditioned at both moderate and high humidity were characterized and compared to oriented strand board and plywood. Results indicate that increases in both gelatin and tannin content not only decrease rates of water uptake, volumetric swelling, and maximum moisture contents of gelatin-based resins, but also increasingly induce relaxation-controlled moisture diffusion behavior, which implies short-term moisture resistance and long-term moisture affinity. This behavior could be leveraged to address both in-service (i.e., strength, stiffness) and out-of-service (i.e., rapid biodegradation) requirements for engineered wood products.     

Design of artificial nacre-like hybrid films as shielding to mitigate electromagnetic pollution

Multifunctional designs of biomimetic layered materials are in great demand for broadening their applications. Artificial hybrid films are fabricated using a simple evaporation-induced assembly method, using nacre as the structural model, two-dimensional reduced graphene oxide (RGO) and magnetic graphene (MG) as inorganic building blocks and poly(vinyl alcohol) (PVA) as glue. The nacre-like films exhibit good mechanical performance, such as high stiffness, strength and toughness. The biomimetic materials possess the shielding properties of electromagnetic pollution. MG based nacre-like films present more significant electromagnetic interference (EMI) shielding performance than RGO film, because of a synergism between dielectric loss of graphene and magnetic loss of magnetic nanoparticles. Average EMI shielding effectiveness (SE) reaches ∼20.3 dB over the frequency range of 8.2–12.4 GHz (X band) for MG hybrid film only 0.36 mm thick. The lightweight, flexible and thin MG artificial hybrid films possess good potential for EMI shielding applications.     

Performances of larch (larix gmelini) tannin modified urea–formaldehyde (TUF) resin and plywood bonded by TUF resin

Tannin from larch (Larix gmelini) bark extracts, as a natural renewable resource, was used to prepare tannin–urea–formaldehyde (TUF) resin. The chemical structures of larch tannin and TUF resin were characterized by matrix‐assisted laser desorption/ionization‐time of flight mass spectrometry and ¹³C nuclear magnetic resonance. The thermal behaviors of TUF resin were evaluated by differential scanning calorimetry (DSC) and thermomechanical analysis (TMA). The performances of TUF resin were investigated by measuring the bond strength and formaldehyde emission of its bonded plywood. It was clearly shown that larch tannin is mainly composed of prodelphinidin repeating units. Phenolic groups were introduced into TUF resin mainly linked by methylene bond. Larch tannin has an adverse effect on the resin curing. However, it promoted the rigidity and flexibility of the glued system and upgraded the properties of plywood. Therefore, larch tannin could be applied in the modification of urea–formaldehyde resin. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41064.     

Development and mechanism characterization of high performance soy-based bio-adhesives

The techniques for denaturing defatted soy flour (DSF) for the production of high performance soy-based bio-adhesives (SBA) have been developed. The developed soy based products from various stages of process were characterized using FTIR and XPS to examine the denaturing mechanisms. The results from the orthogonal statistics [L₉(3⁴)] showed that the optimized ratio of DSF:H₂O was 2:8 by weight and the best combination of acid:salt:alkali was 2.38:0.002:7.98% total mass of DSF and H₂O. The FTIR and XPS spectra illustrated the change of chemical groups and conversion of the protonized products: the amide link hydrolysis and decarboxylation have taken place when DSF was denaturized by acid and salt with the active groups, –NH₂, –COOH and –OH, increased. The alkali modification caused some aminolysis with the active groups increased further. Curing SBA made amide links reestablished and hence caused amination, resulting in the improvement of cross-linkage of soy-protein and hence water-resistance.     

Fractal dimension analysis of interface and impact strength in core–shell structural bamboo plastic composites

To analyze quantitatively the interface of core–shell structural bamboo plastic composites (BPCs) surface, the relationship between the microstructure of composite surface and the macroscopic impact performance was investigated. The effect of shell layer on the interface and impact strength of the core–shell BPCs was studied by scanning electron microscope (SEM) images, computer image processing technique and fractal theory. The fractal dimensions of the core–shell BPCs were calculated and the relationship between the measured impact strength and the fractal dimensions of the core–shell BPCs fracture surface was discussed. The results showed that the fractal dimensions of the interface and fracture surface were within the range of about 2.1725 to 2.1970 and 2.2075 to 2.2204, respectively. All the correlative coefficients were higher than 0.99, therefore, the strong linear correlation indicated that the fractal characterization of the interface and impact fracture surface for the BPCs was possible, and also proved that the interface could be analyzed quantitatively depending on the feature parameters of the fractal dimension. The relationship between the fractal dimension and the measured impact strength was linear. The bigger the fractal dimension of surface, the bigger the impact strength and stronger the interfacial bond were. Thus, using the fractal dimensions the surface morphology of core–shell structural BPCs can be described and it may provide a new approach to investigate the inherent rules of fractal characteristics and Charpy impact strength of the BPCs with core–shell structure.