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In this work, both the bio-polyol and cellulose nanocrystals (CNCs) used to produce high bio-content polyurethane (PU) foams were prepared from microwave liquefaction of rape straw. As high as 40% petro-based polyol was replaced by bio-polyol and the bio-foams containing 40% bio-polyol (PU40) were further reinforced by incorporating 1 to 6% CNCs. GC–MS, 1 H NMR and FTIR observations demonstrated that the bio-polyol is a hydroxyl-rich source consisting of C5, C6 sugars and aromatics. The maximum physico-mechanical performance of bio-foam without CNCs was observed from the bio-foam containing 20% bio-polyol. When further increasing bio-polyol content from 20 to 40%, these properties dramatically decreased. This result was possibly due to the complex polyurethane crosslinking reactions with C5, C6 sugars and aromatics. As compared with reference (PU40), the Young's modulus and compressive stress in the optimal 4% CNCs reinforced bio-foam increased by 590% and 150%, respectively. It was noteworthy that these values were highly superior to those of the petro-based foam. Solid state 13 C NMR and FTIR analysis of CNC reinforced bio-foam evidenced that the hydroxyl-rich structure in CNCs participated in the cross-linking reactions, resulting in an increase of the polyurethane crosslinking density, which contributes to the increased physico-mechanical performance of bio-foam. [ABSTRACT FROM AUTHOR]

Filament fused fabrication (FFF) is an extrusion-based 3D printing technology for manufacturing thermoplastic components. One major obstacle facing 3D printed thermoplastic material is the reduced crystallinity resulting from a fast quench when material exiting the 3D printer hot nozzle solidifies quickly at the low-temperature platform, leading to weak mechanical performance. Here, we report an accelerated annealing strategy with the assistance of microwave heating, aiming to enhance crystallinity and mechanical performance of FFF 3D printed polylactic acid (PLA) composite. We selected naturally abundant cellulose fibers as precursors for producing carbonized cellulose nanofibers (CCNFs), and compounded CCNFs with PLA to produce bi-component filament for 3D printing final composite. After being irradiated with microwave, the embedded CCNFs in composite selectively absorbed microwave energy and generated heat. Subsequently, the localized heat transferred to the adjacent PLA regions, triggering amorphous PLA chains to repack and convert to new crystallites. In this work, annealing conditions, including heating method (i.e., oven annealing vs. microwave annealing), time (0–120 min), and temperature (80 vs. 120 °C), were systematically studied to understand the relevant effects on the resulting parameters including composite crystallinity and tensile strength. Microwave annealing method was also compared with conventional oven annealing method and results shows that microwave annealing significantly reduced the required annealing time to reach the maximum crystallinity and tensile strength. Notably, microwave annealing performed below cold crystallization temperature was exceptionally suitable to develop an optimized crystallinity and tensile strength for 3D printed PLA composite. Image 1 [ABSTRACT FROM AUTHOR]

In this study, the prepolymers (TYF) were prepared by formaldehyde and l -tyrosine, different amounts of TYF were added to prepare TYF modified urea-formaldehyde adhesives (LUF), and the gel time of resin, formaldehyde emission and wet shear strength of the plywood were tested. This result indicated that the optimal addition amount was 3 wt%, and the formaldehyde emission of plywood decreased by 23% to 0.57 mg/L, and the wet shear strength increased by 47% to 1.47 MPa. The thermal degradation and curing characteristics of urea-formaldehyde (UF) and LUF resins were characterized by thermogravimetric (TG) and differential scanning calorimetry (DSC), and the kinetic parameters were analyzed. The results showed that TYF could reduce the formaldehyde emission and improve the wet shear strength significantly. Moreover, the thermal degradation activation energy (E α) of UF resin was increased, and the thermal stability was enhanced. Although the initial and peak curing temperatures of LUF were higher, but the LUF cured more easily than the UF once the curing temperature was reached. [Display omitted] [ABSTRACT FROM AUTHOR]

Applications of eco-friendly soy protein (SP) adhesives in the wood industry are restricted by their poor wet bonding strength and mold resistance. In this study, we noted that epoxy crosslinking agents not only have cross-linking properties, but also antifungal properties and can be used as cross-linkable antifungal agents to simultaneously improve the mold resistance and strength of SP adhesives. In order to develop sustainable and highly active epoxy cross-linkable antifungal agents, biomass-derived oxalic acid (OA) was converted into epoxy oxalic acid (EOA) with two electron-withdrawing ester groups, with 99.93% antifungal activity. The 1% ultra-low amount of EOA (when used as crosslinking agent) was uniformly dispersed in the uncured adhesive, prompting the anti-mold life of the adhesive to increase from 2 to 26 days. After curing, the tighter and more stable cross-linked network structure of the adhesive was constructed by the reaction of low reactive groups such as amide II bonds with ultra-low amounts of EOA, and the dry and wet shear strengths were increased by 49.0% and 139.7%, respectively, compared with pure adhesives. In addition, the anti-mold life of the cured adhesive increased from 4 to more than 30 days under the action of residual EOA. This work demonstrates the novel antifungal effect of epoxy crosslinkers, providing a controllable, green, and sustainable idea for the high-efficient improvement of mold resistance and strength of bio-based adhesives. • Epoxy crosslinkers generally have antifungal properties and can act as antifungal agents. • Epoxy oxalic acid (EOA) exhibited 99.93% antifungal activity, derived from inexpensive bio-based oxalic acid. • Soy protein functional groups cross-linked with EOA to construct a stable cross-linked network structure of the adhesive. • The bonding strength and mold resistance of the adhesive were efficiently enhanced by ultra-low levels of EOA. [ABSTRACT FROM AUTHOR]

Soy-based adhesives are considered to be a substitute for toxic petroleum-based adhesives in wood industry because of its environmentally-friendly property. However, their application range is limited by the lack of high wet bond strength and high toughness. While it is possible to impart these properties to soy-based adhesives by adding a variety of corresponding modifiers, it is difficult to do so by adding a single modifier. In this work, a multifunctional cross-linking agent dodecanedioic acid diglycidyl ester (DADE) with high reactivity, toughening, and hydrophobic effects was synthesized and incorporated into soy-based adhesive to ameliorate the bonding performance of the adhesives. The reaction process between DADE and protein was confirmed by instrumental analyses. Results revealed that the introduction of 4% DADE increased the wet bond strength of the soy protein adhesive by 140% to 1.57 MPa, whereas the wet bond strength (1.11 MPa) of soybean meal adhesive containing 4% DADE was comparable to that of MUF resin. The micrographs of the fracture surface and the force-distance curves of the shear strength test showed that the toughness of the adhesives was significantly improved by DADE. These improvements were attributed to the long hydrophobic aliphatic chains and highly reactive groups from DADE. This modification method avoided using large amounts of chemical additives. This work may provide an efficient and low-consumption method for producing bio-based adhesives with excellent bonding properties. [Display omitted] • The resulting soy-based adhesive was an environmentally-friendly wood adhesive. • A multifunctional crosslinker with toughening and hydrophobic effects was developed. • The use of DADE avoided the addition of additional hydrophobic and toughening agents. • The strength of the SPD adhesive was higher than that of formaldehyde-based resin. [ABSTRACT FROM AUTHOR]

Sand blasting was proposed as a surface modification approach on the small diameter and thin culm wall bamboo species of Neosinocalamus affinis for the fabrication of laminated bamboo composites. The results revealed that sand blasting modification could almost wipe off the wax and silicons deposited on the green and yellow surfaces by removing or damaging the suberized and siliceous cells, pith membrane, and compact arranged sclereid, resulting in the uncovering of the porous structure. Meanwhile, the surface roughness was also increased by the sand blasting modification, which provided appropriate surface characteristics for resin permeability. The weight loss after sand blasting modification was merely 4.3%, and the internal structure was mostly preserved. Average modulus of rupture, modulus of elasticity, and compressive strength of the laminated bamboo composites fabricated from Neosinocalamus affinis were comparable to previous reported similar products and were higher than those from Phyllostachys pubescens and Phyllostachys bissetii. The findings in this study revealed that sand blasting modification could be used as an efficient and environmentally friendly approach on the high yield production of laminated bamboo composites from small diameter and thin culm wall bamboo species. • Sand blasting was efficient in cleaning up non-lignocellulosic substances on bamboo surfaces. • Laminated bamboo composites with yield of 96% was successfully fabricated. • The composites showed comparable mechanical strength with previously reported products. • Sand blasting surface modification was suitable for small diameter bamboo utilization. [ABSTRACT FROM AUTHOR]

Soy protein-based adhesives are biodegradable and renewable and are widely used in wood based products. However, the application of soy protein (SP) adhesives is also limited by its poor mildew resistance, water resistance and bonding strength, so it is necessary to find ways to promote the comprehensive performance of SP adhesives. In this study, hydroxymethyl l -tyrosine (TYF) synthesized from l -tyrosine and formaldehyde was used to enhance the mildew resistance and bonding strength of the SP adhesive. The results showed that the cross-linking reactions of TYF and SP molecules and the condensation reactions between an appropriate amount of TYF molecules enhanced the force between SP molecules and made the cross-linked structure more stable and compact, resulting in a significant increase in the bonding strength of the SP adhesive modified by TYF. Compared with the plywood prepared by the SPI adhesive, the SP adhesive modified with 6 wt% TYF had the best bonding performance, and its dry and wet shear strength were increased by 49.3% and 110.1%, respectively. In addition, l -tyrosine Schiff base, which had antibacterial, bactericidal and antiviral effects, was produced by dehydration of TYF molecules, so the mildew resistance of SP adhesives modified by TYF was effectively enhanced. [ABSTRACT FROM AUTHOR]

Although soy protein (SP) adhesives have shown great potential in promoting the green and sustainable development of the wood industry, the practical application of SP adhesives is limited by poor performance (bonging strength, mold resistance and water resistance). Cross-linking modification is considered to be the most effective modification method for SP adhesives. In this work, non-antibacterial l -tyrosine (TYR) was treated with epichlorohydrin to graft multiple epoxy groups and transformed into tetraepoxy l -tyrosine (ETY). Interestingly, ETY exhibited obvious antifungal properties with a bacteriostatic rate as high as 98.3%. Adding a low amount (3 wt%) of ETY, the wet shear strength of the modified adhesive was 169.1% higher than that of the pristine SP adhesive, reaching 1.83 MPa. Moreover, in an environment of 28 °C and 80% humidity, both uncured and cured SP adhesives (with 3 wt% ETY) exhibited an anti-mold period of more than 30 days. Therefore, this work reveals that non-antibacterial bio-based materials may be endowed with antibacterial properties through epoxidation and transformed into multifunctional modifiers, and provides a new way for the development of high-strength antibacterial bio-based adhesives. • Non-antibacterial bio-based materials may be endowed with antibacterial properties through epoxidation. • The antibacterial rate of tetraepoxy l -tyrosine is as high as 98.3%. • High performance adhesive modified by low amount of ETY. • The wet shear strength of the adhesive (with 3 wt% ETY) increased by 169.1% to 1.83 MPa. • Modified adhesives (with 3 wt% ETY) showed an anti-mold period of more than 30 days. [ABSTRACT FROM AUTHOR]

[Display omitted] • The fracture toughness of bamboo increased with the water content. • One function of water in bamboo was to soften the cell wall, which increased the plastic deformation of bamboo and impeded the propagation of cracks. • The other function of water in bamboo was to make the fracture surface smooth, which indicates that cracks propagated easily. • These two functions of water also affected the fracture toughness of other materials. Most engineering materials are chosen based on their fracture toughness rather than their strength. However, water molecules in air would interact with these materials and affect their fracture toughness, especially for the biomass materials. Bamboo is an excellent engineering material, and the effect of water content on its fracture toughness was still unknown. Thus, in this study, the effect of water on bamboo's fracture toughness was investigated, and the mechanism behind it was discussed. The results showed that the growth fracture toughness increased by 7.6 J/m2 per 1 % increase of environmental relative humidity. The effect of the water includes both promoting and impeding crack growth. The hydrated amorphous layer in cell wall impeded the propagation of cracks, while the water layer on cell wall promoted the propagation of cracks. The former effect was the stronger one in bamboo, and thus the fracture toughness increased. This competition mechanism stemmed from water was also found useful to explain the fracture properties of other kinds of materials, such as wood, stone, and clay. Therefore, a reasonable hypothesis to explain the mechanism of water content on fracture toughness of bamboo and even other materials was concluded in this study. [ABSTRACT FROM AUTHOR]

This work prepared a double-cross-linked biohybrid aerogel (DCBA) bead biosorbent from waste bamboo paper and chitosan by sequential physical (hydrogen bonding and electrostatic interaction between -COO- and -NH 3 + groups) and chemical (polymerization reaction between -COOH and -NH 2 , dehydration condensation between Si-OH and -OH) cross-linkings. The resulting DCBA bead was applied to remove cationic (Methylene blue, MB) and anionic (Congo red, CR) dyes in both single and binary systems. The MB and CR adsorption capacities of DCBA bead increased with increasing adsorbent dosage, contact time, temperature and initial dye concentration. With increasing solution pH, the MB adsorption capacity increased, while that for CR increased first and then decreased. The maximal adsorption capacities for MB and CR were 653.3 and 559.6 mg/g, respectively, in the single system. The thermodynamic analysis results showed a spontaneous and endothermic adsorption process. DCBA bead had a good stability and reusability with the removal efficiencies of 49.4% and 60.6% for MB and CR, respectively, after five cycles of adsorption-desorption. In the binary system, the adsorption of MB was inhibited by CR, while the removal of CR was enhanced by MB. • DCBA biosorbent was prepared using double cross-linking method. • The DCBA bead exhibited excellent stability and recyclability. • The maximum adsorption capacities of MB was 653.3 mg/g. • The maximum adsorption capacities of CR was 559.6 mg/g. • The adsorption mechanisms in single and binary systems were investigated. [ABSTRACT FROM AUTHOR]