纤维素纳米晶体制备工艺优化的研究

以微晶纤维素(MCC)为原料经硫酸水解制备纤维素纳米晶体(CNC)。采用单因素法结合正交试验系统地研究了硫酸质量分数、反应温度和反应时间对纤维素纳米晶体得率以及平均粒径的影响,并通过扫描电镜(SEM)、原子力显微镜(AFM)、X射线衍射仪(XRD)、纳米激光粒度仪对CNC的性能进行了表征,揭示了酸水解制备CNC的机理。结果表明：CNC制备的最佳工艺参数为硫酸质量分数64%、反应温度45 ℃、反应时间90 min,在此条件下CNC的得率为24.6%,粒径为204.8 nm。CNC水悬浮液呈一种稳定的淡蓝色胶体状态,其微观形貌比较规整,呈短棒状,直径约10~20 nm,长度在150~300 nm之间;XRD结果显示CNC的晶型为纤维素Ⅰ型,结晶度为80.2%。     

Biological Assemblies Provide Novel Templates for the Synthesis of Biocomposites and Facilitate Cell Adhesion

Mechanical mismatch and the lack of interactions between implants and the natural tissue environment are major drawbacks in bone tissue engineering. Biomaterials mimicking the self‐assembly process and the composition of the bone matrix should provide new routes for fabricating biomaterials possessing novel osteoconductive and osteoinductive properties for bone repair. In the present study, bioinspired strategies are employed to design de novo self‐assembled chimeric protein hydrogels comprising leucine zipper motifs flanking a dentin matrix protein 1 domain, which is characterized as a mineralization nucleator. Results show that this chimeric protein could function as a hydroxyapatite nucleator in pseudo‐physiological buffer with the formation of highly oriented apatites similar to biogenic bone mineral. It could also function as an inductive substrate for osteoblast adhesion, promote cell surface integrin presentation and clustering, and modulate the formation of focal contacts. Such biomimetic “bottom‐up” construction with dual osteoconductive and osteoinductive properties should open new avenues for bone tissue engineering.     

Toughening polylactide by direct blending of cellulose nanocrystals and epoxidized soybean oil

Polylactide (PLA) is a bio-based polymeric material which is earth abundant in nature. It also possesses abundant strength and stiffness making it a promising material for industrial applications. However, its brittle behavior is currently limiting research work on them. As such, an eco-friendly blending approach is developed in this study in order to fabricate a ductile and toughen PLA composites using renewable bio-based materials as a precursor. Specifically, PLA, epoxidized soybean oil (ESO), and frangible powder form of cellulose nanocrystals (CNCs) are melt blended to prepare the ternary composite system (PLA/CNC/ESO). During the composite routing, it is found out that the ESO successfully attached to the surface of CNC which in turn results in CNC/ESO mixtures in the PLA matrix. This intrinsic combination induces cavitation which consumes the energy produced under the stretching and impacting, resulting in the turning of the PLA's brittle phenomenon. In fact, a reasonable increase in the ductility is observed. The elongation and notched impact strength of the ternary nanocomposite are found to be ∼32% and ∼4.8 kJ m⁻², respectively, which are comparatively higher than that of neat PLA or PLA/CNC composites. Differential scanning calorimetry analyses show that the ESO layer on CNC affects the thermal characteristics of PLA in the ternary composite while thermogravimetric analysis shows that there is an increase in the char yield of the composite. Furthermore, scanning electron microscopy analysis shows that the synthesis approach adopted here enables a mechanistically turning of the PLA's brittle phenomenon to ductile. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48221.     

Modified cellulose nanocrystals enhancement to mechanical properties and water resistance of vegetable oil-based waterborne polyurethane

Environmentally friendly and lightweight silylated cellulose nanocrystal (SCNCs)/waterborne polyurethane (WPU) composite films that exhibit excellent mechanical properties and water resistance were prepared. The cellulose nanocrystals (CNCs) of the filamentous structure were surface-modified by γ-aminopropyltriethoxysilane (APTES) and then introduced into a castor oil-based aqueous polyurethane (WPU) matrix by in situ polymerization. The morphology and silylation degree of CNCs were characterized by scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and Fourier infrared transform spectroscopy at different APTES concentrations. The results showed that the surface of the nanocellulose crystal has the best silylation morphology and thermal stability with incorporation of 6 wt % APTES. The thermal stability, mechanical properties, surface morphology, and water resistance of the nanocomposites were investigated by TGA, tensile test, SEM and optical contact angle, water absorption test, and mechanical property test after immersed in water. It was found that the effective introduction of modified CNCs resulted in a significant increase in tensile strength at high levels, and the thermal stability and hydrophobicity of the material were improved simultaneously, reaching the percolation threshold at a 0.50 wt % SCNCs as determined theoretically. This study provided an approach to the design and development of surface-modified CNCs/vegetable oil-based polymer composites by using an appropriate concentration of silane coupling agent to modify CNCs and improve the compatibility between nanocellulose and vegetable oil-based polymer matrices. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48228.     

纤维素纳米晶改性光固化水性聚氨酯丙烯酸酯及其性能研究

以纤维素纳米晶（ CNC）作为添加物,对紫外光固化水性聚氨酯丙烯酸酯（ UV-WPUA）进行共混改性。通过实时红外、转矩流变仪、紫外 -可见光分光光度计、扫描电子显微镜（ SEM）、电子万能试验机等表征手段探究了 CNC的添加量对复合树脂及其光固化涂层的性能影响。结果表明：当 CNC的添加量为 2%时, CNC颗粒在复合树脂中分散性良好,复合涂层的可见光透过率大于 85%,铅笔硬度 3H,附着力 0级,拉伸强度 9. 8 MPa,复合涂层的综合性能最好。     

Annealing temperature dependence of Er photoluminescence in alternately Er-doped Si-rich Al2O3 multilayer film

Alternately Er-doped Si-rich Al₂O₃ multilayer film, which consists of 20 layers of alternate Er-Si-codoped Al₂O₃ and Si-doped Al₂O₃ layers, has been synthesized by magnetron cosputtering. The structural and optical properties of the multilayer film as a function of annealing temperature in the range of 700-1100 °C were studied by Raman, X-ray diffraction, high-resolution transmission electron microscopy and photoluminescence (PL). The results show that Si atoms in the multilayer film cluster and have been crystallized gradually into Si nanocrystals with increasing annealing temperature to 950 °C. Upon annealing above 950 °C, however, the Er₂O₃ and Er₄Al₂O₉ phases have been formed, resulting in a rapid decrease of PL intensity. It is necessary to control the size and spatial distributions of Si-NCs and optically activate Er³⁺ ions in order to improve PL response.     

Hybrid organic-inorganic ZnS-loaded nanocomposite films for stable optical coatings

Nanocomposite films consisting of a sol-gel hybrid organic-inorganic matrix incorporating ZnS nanocrystals (NCs) have been developed. The nanocomposites films have high visible transparency, enhanced refractive index and photochemical stability. Usage of the diphenyldimethoxysilane and of the ZnS NCs at different concentrations allowed tuning the optical characteristics. Hybrid matrix, NCs and nanocomposite films were characterized by X-Ray Diffraction, High Resolution Transmission Microscopy, spectroscopic ellipsometry, UV-visible and Fourier Transform Infrared Spectroscopy. Applications of nanocomposite films are being investigated as a stable coating for optical purposes.     

Silicon Nanocrystals: Photosensitizers for Oxygen Molecules

Molecular oxygen plays an important role in many of the chemical reactions involved in the synthesis of biological life. In this review, we explore the interaction between O₂ and silicon nanocrystals, which can be employed in the photosynthesis of singlet oxygen. We demonstrate that nanoscale Si has entirely new properties owing to morphological and quantum size effects, i.e., large accessible surface areas and excitons of variable energies and with well‐defined spin structures. These features result in new emerging functionality for nanoscale silicon: it is a very efficient spin‐flip activator of O₂, and therefore, a chemically and biologically active material. This whole effect is based on energy transfer from long‐lived electronic excitations confined in Si nanocrystals to surrounding O₂ via the exchange of single electrons of opposite spin, thus enabling the spin‐flip activation of O₂. Further, we discuss the implications of these findings for physics, chemistry, biology, and medicine.     

Blue luminescence from poly(methyl methacrylate) modified ZnO and anatase TiO2 nanocrystals prepared using γ radiation

The surface of ZnO and anatase TiO₂ nanocrystals was modified by PMMA through γ radiation. The modified nanocrystals were investigated with photoluminescence (PL) and Fourier transform infrared (FTIR) spectra. A stable blue luminescence peak (420 nm) can be observed for the modified ZnO and anatase TiO₂ nanocrystals. The intensities of luminescence of the modified ZnO and anatase TiO₂ in aqueous solution are very stable, even unchanged after storage time of one month.