天然木质微/纳纤丝增强纳米复合材料的研究现状

纤维素是世界上最丰富、可再生且能生物分解的天然高分子聚合物,其强度主要来源于镶嵌于木素和半纤维素形成的基质结构中的微/纳纤丝或针状晶体——一种完美的高强度的纳米晶体结构。近二十多年来,如何从纤维素中分离微/纳纤丝和用其来增强高分子聚合物受到许多学者的关注。本文简要叙述了木质微/纳纤丝的分离和性能评价方法以及其增强的纳米复合材料的制备和特性检测手段。     

Emerging Biomedical Applications of Nano-Chitins and Nano-Chitosans Obtained via Advanced Eco-Friendly Technologies from Marine Resources

The present review article is intended to direct attention to the technological advances made in the 2010–2014 quinquennium for the isolation and manufacture of nanofibrillar chitin and chitosan. Otherwise called nanocrystals or whiskers, n-chitin and n-chitosan are obtained either by mechanical chitin disassembly and fibrillation optionally assisted by sonication, or by e-spinning of solutions of polysaccharides often accompanied by poly(ethylene oxide) or poly(caprolactone). The biomedical areas where n-chitin may find applications include hemostasis and wound healing, regeneration of tissues such as joints and bones, cell culture, antimicrobial agents, and dermal protection. The biomedical applications of n-chitosan include epithelial tissue regeneration, bone and dental tissue regeneration, as well as protection against bacteria, fungi and viruses. It has been found that the nano size enhances the performances of chitins and chitosans in all cases considered, with no exceptions. Biotechnological approaches will boost the applications of the said safe, eco-friendly and benign nanomaterials not only in these fields, but also for biosensors and in targeted drug delivery areas.     

Biomedical exploitation of chitin and chitosan via mechano-chemical disassembly, electrospinning, dissolution in imidazolium ionic liquids, and supercritical drying

Recently developed technology permits to optimize simultaneously surface area, porosity, density, rigidity and surface morphology of chitin-derived materials of biomedical interest. Safe and ecofriendly disassembly of chitin has superseded the dangerous acid hydrolysis and provides higher yields and scaling-up possibilities: the chitosan nanofibrils are finding applications in reinforced bone scaffolds and composite dressings for dermal wounds. Electrospun chitosan nanofibers, in the form of biocompatible thin mats and non-wovens, are being actively studied: composites of gelatin + chitosan + polyurethane have been proposed for cardiac valves and for nerve conduits; fibers are also manufactured from electrospun particles that self-assemble during subsequent freeze-drying. Ionic liquids (salts of alkylated imidazolium) are suitable as non-aqueous solvents that permit desirable reactions to occur for drug delivery purposes. Gel drying with supercritical CO(2) leads to structures most similar to the extracellular matrix, even when the chitosan is crosslinked, or in combination with metal oxides of interest in orthopedics.     

Protective Effect of Chitin Urocanate Nanofibers against Ultraviolet Radiation

Urocanic acid is a major ultraviolet (UV)-absorbing chromophore. Chitins are highly crystalline structures that are found predominantly in crustacean shells. Alpha-chitin consists of microfibers that contain nanofibrils embedded in a protein matrix. Acid hydrolysis is a common method used to prepare chitin nanofibrils (NFs). We typically obtain NFs by hydrolyzing chitin with acetic acid. However, in the present study, we used urocanic acid to prepare urocanic acid chitin NFs (UNFs) and examined its protective effect against UVB radiation. Hos: HR-1 mice coated with UNFs were UVB irradiated (302 nm, 150 mJ/cm²), and these mice showed markedly lower UVB radiation-induced cutaneous erythema than the control. Additionally, sunburn cells were rarely detected in the epidermis of UNFs-coated mice after UVB irradiation. Although the difference was not as significant as UNFs, the number of sunburn cells in mice treated with acetic acid chitin nanofibrils (ANFs) tended to be lower than in control mice. These results demonstrate that ANFs have a protective effect against UVB and suggest that the anti-inflammatory and antioxidant effects of NFs influence the protective effect of ANFs against UVB radiation. The combination of NFs with other substances that possess UV-protective effects, such as urocanic acid, may provide an enhanced protective effect against UVB radiation.     

纳米纤维素的形貌及快速表征方法的比较

以商品南方松溶解浆、漂白桉木浆为原料,采用硫酸水解法、纤维素酶预处理法、2,2,6,6-四甲基哌啶氧自由基(TEMPO)氧化法以及机械法分别制备了纳米纤维素,利用透射电镜(TEM)、原子力显微镜(AFM)详细表征了不同方法制备的纳米微晶纤维素(CNC)和纳米纤丝纤维素(CNF)。采用了多种商品粒度仪快速定性表征了纳米纤维素的大小,CNC为棒状纳米晶须结构,直径约为20 nm,长度为10~200 nm;CNF一般为网状结构,尺寸较大且分布较宽,单根CNF直径从几纳米到几百纳米不等。依据离心分离以及布朗运动制备的2种仪器非常适合半定量快速表征非网状结构的纳米微晶纤维素,实验重复性也很好。     

纤维素酶协同机械法制备微/纳纤丝

以杨木纸浆纤维为原料,采用纤维素酶水解法协同机械处理法制备出微/纳纤丝（Micro/Nanofibrils）.酶处理制备微/纳纤丝的影响因素按大小依次为：时间、加酶量、料液比.最佳工艺条件：处理时间为36 h,加酶量30 FPU,料液比为1∶40.酶解后纤维的结晶度为84.2％,纤维素含量为95.26％,再经过纤丝进行超声和高压均质间歇式处理来制备微/纳纤丝.从SEM图可以看出,纤丝表面起毛、分丝帚化,次生壁中层S2上微纤丝暴露,分离出了细小纤维.纤维的直径分布在25～55 nm,宽度方向已经达到纳米级纤丝要求.     

NaClO添加量对TEMPO氧化纳米微纤丝结构与性能的影响

以毛竹粉为原料,采用TEMPO催化氧化联合超声处理制备纳米微纤丝,通过改变Na Cl O与纤维素的质量比,研究了Na Cl O添加量对纳米纤维素的长径比、纤维形态以及羧基含量等特性的影响。结果表明:随着Na Cl O添加量的增加,纳米纤维素羧基含量逐渐提高,长径比增大;当Na Cl O添加量为15 mmol/g时,纳米纤维素羧基含量可高达1.646 mmol/g,横截面直径可达6～10 nm,长径比为273～455;随着纳米纤维素羧基含量的增加,纳米纤维素悬浮液的透光率和剪切黏度不断增大。虽然TEMPO催化氧化程度不断加深,但纳米纤维素的晶型并未遭到破坏,仍然呈现出典型的纤维素I晶体结构,而随着羧基含量的增加,纳米纤维素的结晶度和热稳定性有一定程度的下降。     

纤维素酶协同超声波处理制备杨木微/纳纤丝

杨木纤维经纤维素酶预处理后,用超声波法制备杨木微/纳纤丝,利用扫描电子显微镜、X射线衍射仪和红外光谱仪对制备的杨木微/纳纤丝进行表征分析.结果表明:纤维素酶可降解纤维素的部分无定形区并能润胀纤维,再用超声波处理能制备出微/纳纤丝,所制备的杨木微/纳纤丝宽度在50 nm-1μM之间;杨木微/纳纤丝保持了天然纤维的晶型,结...