Abstract:A new and eco-friendly mussel-inspired surface modification pathway for bamboo fiber (BF) is presented in this study. The self-assembly polydopamine (PDA) coating can firmly adhere on BF surface, which also serves as a bridge to graft octadecylamine (ODA) for hydrophobic surface preparation. The as-formed PDA/ODA hybrid layer could supply abundant hydrophobic long-chain alkyls groups and generated a marked increase in BF surface roughness and a marked decrease in surface free energy. These changes provided advantages to improve fiber-matrix interfacial adhesion and wettability. Consequently, high performance was achieved by incorporating the hybrid modified BF into the polybutylene succinate (PBS) matrix. The resultant composite exhibited excellent mechanical properties, particularly tensile strength, which markedly increased by 77.2%. Meanwhile, considerable high water resistance with an absorption rate as low as 5.63% was also achieved. The gratifying macro-performance was primarily attributed to the excellent interfacial adhesion attained by hydrogen bonding and physical intertwining between the PDA/ODA coating on the BF and the PBS matrix, which was further determined by fracture morphology observations and dynamic mechanical analysis. Owing to the superior adhesive capacity of PDA, this mussel-inspired surface modification method may result in wide-ranging applications in polymer composites and be adapted to all natural fibers.
Abstract:In this study, a novel and convenient bio-inspired modification strategy was used to create stable superhydrophobic structures on halloysite clay nanotubes (HNTs) surfaces. The polydopamine (PDA) nanoparticles can firmly adhere on HNTs surfaces in a mail environment of pH 8.5 via the oxidative self-polymerization of dopamine and synthesize a rough nano-layer assisted with vitamin M, which provides a catechol functional platform for the secondary reaction to graft hydrophobic long-chain alkylamine for preparation of hierarchical micro/nano structures with superhydrophobic properties. The micromorphology, crystal structure, and surface chemical composition of the resultant superhydrophobic HNTs were characterized by field emission scanning electron (FE-SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The as-formed surfaces exhibited outstanding superhydrophobicity with a water contact angle (CA) of 156.3 ± 2.3 • , while having little effect on the crystal structures of HNTs. Meanwhile, the resultant HNTs also showed robust stability that can conquer various harsh conditions including strong acidic/alkaline solutions, organic solvents, water boiling, ultrasonic cleaning, and outdoor solar radiation. In addition, the novel HNTs exhibited excellent packaged capabilities of phase change materials (PCMs) for practical application in thermal energy storage, which improved the mass fractions by 22.94% for stearic acid and showed good recyclability. These HNTs also exhibited good oil/water separation ability. Consequently, due to the superior merits of high efficiency, easy operation, and non-toxicity, this bionic surface modification approach may make HNTs have great potentials for extensive applications.
A fiber nonlinearity compensation scheme based on a complex-valued dimension-reduced neural network is proposed. The proposed scheme performs all calculations in complex values and employs a dimension-reduced triplet feature vector to reduce the size of the input layer. Simulation and experiment results show that the proposed neural network needed only 20% of computational complexity to reach the saturated performance gain of the real-valued triplet-input neural network, and had a similar saturated gain to the one-step-per-span digital backpropagation. In addition, the proposed scheme was 1.7 dB more robust to the noise from training data and required less bit precision for quantizing trained weights, compared with the real-valued triplet-input neural network.
A bio-inspired approach to coating polydopamine (PDA) onto bamboo fiber (BF) was developed to enhance the poor interfacial bonding of BF/polybutylene succinate (PBS) biocomposites. The macroscopic features, functional groups, nanoscale topography, and crystallinity of the PDA-coated BF (D-BF) were investigated with digital photography, Fourier transform infrared (FTIR) spectroscopy, atomic force microscopy (AFM), and X-ray diffraction (XRD), respectively. The effects of the PDA loading rate on the performance of the D-BF/PBS biocomposites were also evaluated through the mechanical properties tests, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), and scanning electron microscopy (SEM). Treating BF with an optimum concentration of dopamine (DOPA) decreased the polarity of the bamboo fiber, while maintaining the crystal structure of the cellulose. The thermal stability, mechanical properties, and storage modulus of the D-BF/PBS biocomposites were noticeably enhanced because of the good interfacial compatibility. Moreover, the glass transition temperature (Tg) and crystallinity of the biocomposites increased with higher DOPA loading rates. The best properties were observed with a DOPA concentration of 1.0 mg/mL. These findings exhibited the feasibility for the application of PDA in the biomass fiber-reinforced biodegradable polymer composites industry.
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