纤维素纳米晶体提升柚皮素抗氧化活性的研究

柚皮素是一种黄酮类化合物,具有广泛的药理活性,具有抗炎、抗氧化、抗癌、降血脂等药理作用。然而,柚皮素在水中溶解性能差,生物利用度低,限制了其在临床中的应用。本研究以纤维素纳米晶体(Cellulose nanocrystals,CNCs)为载体,以柚皮素为疏水药物模型,利用反溶剂重结晶法成功制备了CNCs/柚皮素纳米复合物,并表征了所得纳米复合物的性能,分析了纳米复合物中柚皮素的溶出性能和抗氧化活性。结果表明,形成CNCs/柚皮素纳米复合物后,柚皮素得到充分的纳米化和稳定分散,从结晶态转变为无定型态。负载CNCs的柚皮素在水中的溶出性能得到显著提升,120min时累积溶出度达到93.4%;经CNCs负载后,当柚皮素浓度为50μg/mL时,羟基自由基清除率达44.3%,柚皮素的体外抗氧化活性显著提高。     

纳米微晶纤维素的表面基团及其改性

纳米微晶纤维素(Nanocrystalline Cellulose,NCC)是一种纤维素经酸水解后获得的棒状晶体,由于其原料丰富、可再生、生物兼容性好以及机械性能优良等特点,已成为纳米材料研究领域的热点。本文为探索其进一步改性应用,重点分析了NCC表面存在的基团种类,对其化学改性方法进行了概括,并对其进一步发展应用进行了展望。     

莲子淀粉纳米晶的制备及其结构特性研究

本文以莲子淀粉为原料,采用酸解法制备莲子淀粉纳米晶,通过扫描电子显微镜、激光粒度仪、凝胶渗透色谱、X-射线衍射、傅里叶红外光谱等对莲子淀粉纳米晶的结构进行表征。研究结果表明,莲子淀粉纳米晶的颗粒形态为方形片状和球型,结晶结构仍为C型,淀粉颗粒的晶型结构没有发生改变。当酸水解条件为：硫酸浓度4 mol/L,40℃条件下水解5天,莲子淀粉纳米晶的粒径最小、结晶度最高、分子质量最小。莲子淀粉纳米晶与其它种类淀粉纳米晶相关研究的文献进行对比发现：莲子淀粉纳米晶的颗粒形态同时包含了A型和B型结晶结构的淀粉纳米晶的颗粒形态,其颗粒大小略大于其他种类淀粉纳米晶。该研究为淀粉纳米晶的理化及功能特性研究提供一定理论依据。     

Growth of silver nanowires on carbon fiber to produce hybrid/waterborne polyurethane composites with improved electrical properties

One dimensional silver nanowires (AgNWs) were grown on carbon fiber (CF) by a facile polyol method. Fourier transform infrared spectrometer (FTIR), laser Raman spectrometer (Raman), field‐emission scanning electron microscopy (FESEM), X ray diffraction instrument (XRD), energy dispersive spectrometer (EDS), and X‐ray photoelectron spectrometer (XPS) were carried out to reveal the structure, morphology, and formation mechanism of the CF‐AgNWs. It was found that AgNO₃ concentration of 1.5 mM, reaction temperature of 160°C, and reaction time of 120 min were appropriate conditions for growth of AgNWs on CF. Moreover, a mechanism was suggested that the cysteamine on CF acted as nucleation centers for growth of silver nanoparticles and then small sized silver nanoparticles reduced from silver nitrate were grown on CF via the silver bonding to sulfur. Through an Ostwald ripening process, small sized silver nanoparticles were grown into larger particles. With the assistance of polyvinylpyrolidone (PVP), these larger particles were directed to grow in a definite direction to form nanowires. It was found that the resistance of CF‐AgNWs was decreased to 19.5 Ω, compared with that of CF (102.6 Ω) with the same quality. Thus, the CF‐AgNWs was added into waterborne polyurethane (WPU) to improve the electrical and dielectric properties of WPU. Results showed the WPU/CF‐AgNWs composite presented a lower percolation threshold than WPU/CF composite. When the content was 2.5 wt %, the volume resistivity of the WPU/CF‐AgNWs (1.90 × 10⁴ Ω cm^?1) was lower by approximately three orders of magnitude than that of WPU/CF (4.19 × 10⁷ Ω cm^?1). When the content was 2.5 wt %, the dielectric constant and dielectric loss of the WPU/CF‐AgNWs were improved to 15.24 and 0.21, which were 34.5 and 40.8% higher than that of WPU/CF. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43056.     

Oil sorbers based on renewable sources and coffee grounds

This work presents useful composites for oil spill cleanup processes. These systems are composed of a polyester matrix loaded with coffee ground powder and maghemite. They were prepared by in situ polymerization. The aliphatic monomers proportion—castor oil and glycerin—was studied with the aim of understanding the effect of feed ratio on the product properties. The materials were studied using several techniques, including Fourier Transform Infrared Spectroscopy, Ultraviolet‐visible Spectrophotometry, and Wide Angle X‐ray Scattering, with magnetic force tests used for the characterization of materials. Density tests showed the presence of coffee grounds causes an important reduction in the density values of composites, improving their flotation. The interaction between composites and petroleum is more than twice that between composites and water. Moreover, for all magnetizable composites, the removal capability was (25.1 ± 1.2) g/g (petroleum/composite), allowing us to state that this is a promising material for use in oil spill cleanup processes. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43127.     

Controlled co‐delivery of hydrophilic and hydrophobic drugs from thermosensitive and crystallizable copolymer nanoparticles

Functionalized amphiphilic block copolymers poly(N‐isopropyl acrylamide)‐b‐poly(stearyl methacrylate) (PNIPAM‐PSMA) are synthesized. Their self‐assembled core‐shell nanoparticles have the hydrophilic thermosensitive shell and hydrophobic crystallizable core. Nanoparticles exhibit volume phase transition at temperature of 38 °C and its poly(stearyl methacrylate) (PSMA) moiety could form nano size crystals to retain drugs, making them good carriers for drug co‐delivery system. Thermosensitivity and crystallinity of nanoparticles are characterized with dynamic light scattering (DLS), differential scanning calorimetry (DSC), small‐angle X‐ray scattering (SAXS), and atomic force microscopy (AFM). The interactions and relationship between chemical structures of copolymer nanoparticles and loading drugs are discussed. Different loading techniques and combined loading of hydrophobic/hydrophilic drugs are studied. Nanoparticles show a good and controllable drug loading capacity (DL) of hydrophilic/hydrophobic drugs. The drugs release kinetics is analyzed with Fick's law and Weibull model. A general method for analyzing drug release kinetics from nanoparticles is proposed. Weibull model is well fitted and the parameters with definite physical meaning are analyzed. PNIPAM‐PSMA nanoparticles show a quite different thermal response, temporal regulation, and sustained release effect of hydrophilic and hydrophobic drugs, suggesting a promising application in extended and controlled co‐delivery system of multi‐drug. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44132.     

Synthesis of poly(N‐isopropylacrylamide) by distillation precipitation polymerization and quantitative grafting on mesoporous silica

In this work, syntheses of thermoresponsive poly(N‐isopropylacrylamide) (PNIPAM) with different molecular weights were carried out in ethanol by distillation precipitation polymerization (DPP) technique. The synthesized polymers were fully characterized by attenuated total reflection Fourier‐transform infrared (ATR‐FTIR) spectroscopy, nuclear magnetic resonance spectroscopy, and size exclusion chromatography techniques. The lower critical solution temperatures of the polymers were determined with differential scanning calorimetry. A simple and versatile method for the in situ synthesis and grafting of PNIPAM on mesoporus silica nanoparticles (MSNs) with improved control over quantitative grafting is devised. The PNIPAM grafted MSNs were characterized with ATR‐FTIR, thermogravimetric analysis, transmission electron microscopy, and dynamic light scattering analyses. From the results obtained it is showed that quantitative grafting of PNIPAM on MSNs from 1 to 20% by weight can be tuned by manipulating the in situ DPP reaction conditions. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44181.     

Micromechanical analysis of long fiber‐reinforced composites with nanoparticle incorporation into the interphase region

The influence of the distribution type, Young's modulus, and volume fraction of the nanoparticles within the interphase region on the mechanical behavior of long fiber‐reinforced composites with epoxy resin matrix under transverse tensile loading is investigated in this article. An infinite material containing unidirectional long fiber and periodic distribution of elastic, spherical nanoparticles was modeled using a unit cell approach. A stiffness degradation technique has been used to simulate the damage and crack progress of the matrix subjected to mechanical loading. A series of computational experiments performed to study the influence of the nanoparticle indicate that the mechanical properties, nanoparticle‐fiber distance, and volume fraction of nanoparticle have a significant effect on both the stiffness and strength properties of these composite materials. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41573.     

Preparation of a hydrophobically enhanced antifouling isotactic polypropylene/silicone dioxide flat‐sheet membrane via thermally induced phase separation for vacuum membrane distillation

Isotactic polypropylene (iPP) hydrophobic flat‐sheet membranes were fabricated for use in vacuum membrane distillation (VMD) through a thermally induced phase‐separation process with dispersing hydrophobically modified SiO₂ nanoparticles in the casting solution to achieve a higher hydrophobicity and to sustain a stable flux in VMD. The contact angle (CA) measurements indicated that the incorporation of nano‐SiO₂ into a casting solution mixture containing 20 wt % iPP had a 20.9% higher CA relative to that of SiO₂‐free membranes. The addition of nano‐SiO₂ also induced morphological changes in the membrane structure, including changes in the pore size distribution, porosity, and suppression of macrovoids. The pore size distribution of the iPP–SiO₂ membranes became narrower compared with that of the SiO₂‐free membranes, and the porosity also improved from 35.45 to 59.75% with SiO₂ addition. The average pore size and maximum pore size of the iPP–SiO₂ membranes both decreased. The ability of the membranes to concentrate an astragalus aqueous solution (a type of traditional Chinese medicine) with VMD was investigated. The surface hydrophobicity and antifouling performance of the iPP–SiO₂ membranes improved with nano‐SiO₂ addition to the membrane casting solution. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42615.     

Fabrication of cellulose nanofiber‐based ultrafiltration membranes by spray coating approach

Ultrafiltration membranes containing a cellulose nanofiber barrier layer were fabricated by the spray coating method, where the thickness and uniformity of the barrier layer were systematically investigated as a function of air pressure, flow rate and concentration of the cellulose nanofiber suspension. In specific, the surface morphology of the barrier layer was studied by scanning electron microscopy and its uniformity was examined by the fluorescence dye imaging method. The ultrafiltration performance of the membranes fabricated by the spray coating method was also compared with that of the membranes made by the knife coating approach using dextran molecules as probe, where the former consistently exhibited significantly higher permeation flux while remaining the same rejection ratio. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44583.