纳米纤维素/壳聚糖/明胶复合膜的制备及其性能研究

以明胶（Gel）、壳聚糖（CS）、纳米纤维素（NCC）为原料,采用溶液共混法制备了不同NCC和CS质量比的纳米纤维素/壳聚糖/明胶复合膜。采用紫外-可见分光光度计、扫描电镜（SEM）、红外光谱仪（FT-IR）、X射线衍射仪（XRD）、热分析仪（TGA）和质构仪对所制备复合膜的透光性能、显微结构、化学结构、晶体结构、热学性能和力学性能进行了分析。结果表明：纳米纤维素、壳聚糖、明胶之间形成相互作用较强的网络结构。复合膜表面光滑,分散均匀,具有良好的相容性。随着纳米纤维素含量的增加,复合膜透光率呈下降的趋势。与壳聚糖膜相比,复合膜的热稳定性显著提高。当纳米纤维素与壳聚糖质量比为7：1时,复合膜拉伸强度最高可达到33 MPa,断裂伸长率可达到14.9%,吸水率最大值可达到341%。     

Surface modification of nanocrystalline cellulose and its application in natural rubber composites

As a biopolymer with high mechanical strength, nanocellulose was generally considered as a green filler for reinforcing polymer. In this study, nanocrystalline cellulose (NCC) isolated from softwood pulp was successfully modified by cetyltrimethyl ammonium bromide (CTMAB), a cationic surfactant, and the modified nanocrystalline cellulose (m-NCC) was used to reinforce natural rubber (NR). In this composite architecture, it was found that when the filler content was 5 or 10 phr, the surface modification of NCC improved the dispersion state of NCC in NR matrix and the interfacial interaction between NR and NCC. Therefore, the NR/m-NCC composites exhibited outstanding mechanical properties, and its tensile strength, elongation at break and tear strength was increased by 132.8, 20, and 66.1%, respectively, compared to pristine NR composites. Besides, the modified NCC could accelerate the vulcanization and improve wet-skid resistance and aging resistance of NR composites. It is envisioned that the modified NCC has the potential to be generalized to manufacturing other polymer matrix composites strengthened with nanocellulose.     

Moisture induced plasticity of amorphous cellulose films from ionic liquid

Amorphous cellulose films were created by regeneration from 1-Ethyl-3-methylimidazolium acetate (EmimAc) solutions. Their mechanical properties were analyzed as a function of water content. Cellulose with different molecular weights, i.e. microcrystalline cellulose (Avicel), Spruce cellulose and bacterial nanocellulose (BNC), were used for film preparation. All the regenerated films were free from EmimAc residues as shown by Fourier transform infrared spectroscopy (FTIR), amorphous as shown by wide angle X-ray spectroscopy (WAXS) and optical transparent. The equilibrium water content (w/w) was measured at different relative humidities. The plasticizing effect of water on the films was evidenced by both tensile tests and dynamical mechanical analysis (DMA) with humidity scans. The mechanical properties were clearly related to the proportional water uptake of the films. The sample with the longest cellulose chains, i.e. BNC, showed significantly larger elongation to brake at high moisture content which was owed to chain entanglements.     

Composites made from a soybean oil biopolyurethane and cellulose nanocrystals

Cellulose nanocrystals (CNC) obtained by acidic hydrolysis from microcrystalline cellulose were dispersed in a biopolyurethane matrix to prepare composite films. The polyurethane was prepared from a hydroxylated soybean oil (SO‐OH) and a polymeric diphenyldiisocyanate (pMDI), using a organotin compound as the catalyst. The composite films contained different concentrations of nanocelullose, without any macroscopic aggregates in all cases. Thermal, tensile and dynamic mechanical properties of the films were determined for all the samples. In particular, it was observed that the glass transition temperature of the nanocomposites slightly increased with the concentration of the cellulose nanocrystals. The nanocomposite with 1 wt% of nanocellulose showed the highest tensile strength of the series. POLYM. ENG. SCI., 58:125–132, 2018. © 2017 Society of Plastics Engineers     

Structure and properties of composite films prepared from cellulose and nanocrystalline titanium dioxide particles

Composite films were successfully prepared from cellulose and two kinds of nanocrystalline TiO₂ particles in a NaOH/urea aqueous solution (7.5 : 11 in wt %) by coagulation with H₂SO₄ solution. The structure, morphology, and properties of the films were characterized by transmission electron microscopy, scanning electron microscopy, X‐ray diffraction, TGA, tensile testing, UV–vis spectroscopy, and antibacterial test. The results indicated that TiO₂ particles in a cellulose matrix maintained the original nanocrystalline structure and properties. TiO₂(I) (anatase) and TiO₂(II) (the mixture of anatase and rutile) particles exhibited a certain miscibility with cellulose. The tensile strength of two kinds of composite films was higher than 70 and 75 MPa, when the content of TiO₂(I) and TiO₂(II) was 4 and 11 wt %, respectively. The cellulose composite films containing nanocrystalline TiO₂ particles displayed distinct antibacterial abilities and excellent UV absorption. This work provides a potential way for preparing functional composite materials from cellulose and inorganic nanoparticles in a NaOH/urea aqueous solution, without a destruction of the structure and properties of the particles. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3600–3608, 2006     

Cassava starch‐based nanocomposites reinforced with cellulose nanofibers extracted from sisal

Cellulose nanofibers were extracted from sisal and incorporated at different concentrations (0–5%) into cassava starch to produce nanocomposites. Films' morphology, thickness, transparency, swelling degree in water, water vapor permeability (WVP) as well as thermal and mechanical properties were studied. Cellulose nanofiber addition affected neither thickness (56.637 ± 2.939 µm) nor transparency (2.97 ± 1.07 mm^?1). WVP was reduced until a cellulose nanofiber content of 3.44%. Tensile force was increased up to a nanocellulose concentration of 3.25%. Elongation was decreased linearly upon cellulose nanofiber addition. Among all films, the greatest Young's modulus was 2.2 GPa. Cellulose nanofibers were found to reduce the onset temperature of thermal degradation, although melting temperature and enthalpy were higher for the nanocomposites. Because cellulose nanofibers were able to improve key properties of the films, the results obtained here can pave the route for the development and large‐scale production of novel biodegradable packaging materials. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44637.     

Improving the mechanical resistance of waterborne wood coatings by adding cellulose nanofibres

In the present study, microfibrillated cellulose (MFC) and nanocrystalline cellulose (NCC) were applied as additives for a waterborne acrylate/polyurethane-based wood coating in order to improve the mechanical resistance of coated wood surfaces. Coating mixtures containing up to 5 wt% nanocellulose were prepared by high-shear mixing and applied to wood substrates. The optical, mechanical and chemical properties of cured coatings were characterized. Surface roughness, gloss, scratch resistance, abrasion resistance and resistance against chemicals were determined according to the relevant European standards. Additionally, nanoindentation (NI) was used to assess the micromechanical properties of modified and unmodified coatings. Owing to a higher surface roughness, cellulose-filled coatings showed significantly lower levels of gloss than the unmodified coating indicating that nanocellulose acts as a matting agent. NI experiments revealed a slightly positive effect of nanocellulose addition on the hardness and modulus of the coatings. While scratch resistance improved consistently with increasing nanocellulose addition, abrasion resistance was found to improve only sporadically. Tensile tests on free-standing coating films revealed a significantly higher tensile strength and modulus for cellulose-filled coatings. Overall, the results suggest that the addition of cellulose nanofibres primarily improves the internal cohesion of the coating layer whereby MFC was more effective than NCC.     

Preparation of gelatin-based films modified with nanocrystalline cellulose

Gelatin is a natural biological macromolecule derived from the collagen in the connective tissue of the skin, bone and other tissues. It has been widely used in medicine, food and industrial production and other fields for easy molding, excellent compatibility and biodegradability. However, physical and chemical disadvantages impede its further application, seriously. Therefore, modification of the gelatin films becomes more and more important. In this study, the gelatin/nanocrystalline cellulose (NCC) composite films were prepared by casting method with 4% glycerol as plasticizer. The effect of NCC on the properties of the composite films was investigated by the characterization of its morphology and mechanical, thermal, and optical properties and water adsorption. The results showed that mechanical, thermal stability and water absorption properties of the gelatin/NCC composite film were obviously improved. The composite films showed the highest tensile strength (13.56?±?0.25 MPa) when the mass concentration of NCC was 0.6%. Adding NCC to gelatin benefited the thermal stability of composite films. The gelatin/NCC composite film of 0.4% NCC had the highest melting transition temperature (138.9 °C). The composite films exhibited the lower water absorption (271.1%) when mass concentration of NCC was 1.0%. Thus, these results indicated that NCC could affect the properties of gelatin-based composite films, and showed it has potential for application in food packing.     

Synthesis and characterization of polypropylene reinforced with cellulose I and II fibers

Recently, cellulose fiber–thermoplastic composites have played an important role in some applications. Plastics reinforced with cellulose and natural fibers have been widely studied. However, composites with regenerated cellulose have rarely been investigated. In this study, the lyocell fiber of Lenzing AG (cellulose II) and its raw material a bleached hardwood pulp (cellulose I) were used as reinforcement materials. The mechanical and thermal properties of polypropylene (PP) reinforced with pulp and lyocell fibers were characterized and compared with regard to the content of the fiber and the addition of maleated polypropylene (MAPP). PPs with cellulose I or II as a reinforcement material had similar mechanical properties. However, when MAPP was used as coupling agent, the mechanical properties of the composites were different. The crystallinity of the composites were determined by differential scanning calorimetry. Cellulose I (pulp) promoted the crystallization of PP, whereas cellulose II did not. MAPP reduced this effect in cellulose I fibers, but it induced crystallization when cellulose II (lyocell) was used as a reinforcement material. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 364–369, 2006     

桉木浆纳米纤维素响应面法优化制备及表征

采用响应面法优化桉木浆纳米纤维素(NCC)制备工艺条件并利用傅里叶变换红外(FTIR)、X射线衍射(XRD)、激光粒度分析法和透射电子显微镜(TEM)观察法对NCC进行性能表征。结果表明NCC最优制备工艺条件为硫酸浓度55%,反应温度52℃,水解时间4 h,NCC得率为65.80%,与响应面法预测值66.23%相接近;模型的决定系数为94.63%,说明模型拟合有效;制备的NCC为纤维素Ⅰ型,平均粒径365.7 nm,呈棒状。     

Morphology,thermal, and crystallization properties of poly(butylene succinate)‐grafted Nanocrystalline Cellulose by polymerization in situ

The compounds 1,4‐butanediol, succinic anhydride, and nanocellulose (NCC) were used to synthesize poly(butylene succinate)‐grafted Nanocrystalline Cellulose (PBS‐g‐NCC) nanocomposites via polymerization in situ. The resulting structures were examined by transmission electron microscopic (TEM), scanning electron microscope (SEM), ¹H and ¹³C‐nuclear magnetic resonance spectroscopic (NMR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and X‐ray diffraction (XRD) analyses. TEM showed the cellulose to be nanoscale and SEM analysis indicated that 3 wt% NCC dispersed well in PBS matrix. ¹H and ¹³C‐NMR analyses indicated the product to possess peaks characteristic of PBS. DSC analysis clearly showed that the NCC increased the PBS crystallinity when 3 wt% NCC was introduced into PBS matrixes by polymerization in situ, compared to pure PBS. TGA illustrated that the thermal stability of PBS‐g‐NCC was better than that of pure PBS, when 3 wt% NCC was added. XRD analysis suggested that 3 wt% NCC improved PBS crystallinity, which was in good agreement with the present DSC results. POLYM. ENG. SCI., 59:928–934, 2019. © 2018 Society of Plastics Engineers     

Tensile and morphological properties of nanocrystalline cellulose and nanofibrillated cellulose reinforced PLA bionanocomposites: A review

In recent years, bionanocomposites have received growing attention in science and industry due to their renewability, biodegradability and superior mechanical properties. Nanocellulose is another promising material that use as a reinforcement filler for bionanocomposite materials due to its lightweight, high surface area, high mechanical strength, high aspect ratio and low density. Different nanocellulose loading, sources, surface modification/functionalization and properties of nanocellulose are important in the production of bionanocomposites. In general, nanocellulose reinforced PLA bionanocomposite offers enhancement in tensile strength and elastic modulus. However, only minimal nanocellulose loadings are required for optimal results due to the incompatibility between the hydrophilic nanocellulose and hydrophobic PLA. This paper reviews the sources of nanocellulose and the properties of nanocellulose with a focus on the tensile and morphological properties of PLA bionanocomposites. Applications of nanocellulose in various industries are discussed in this article. This review article provides some important information. First, this study reviewed the application of nanostructured cellulose in biodegradable polymers. There are two types of nanostructured cellulose: nanocrystalline cellulose (NCC) and nanofibrillated cellulose (NFC). Second, the status on articles published on nanocellulose and PLA/nanocellulose over the past 10 years is reported. Third, the authors of this paper implemented a holistic and critical review to provide a comprehensive understanding of the different properties between NCC and NFC, the application of nanocellulose in bionanocomposites, as well as the properties of PLA and PLA bionanocomposites. Moreover, the influence of NCC and NFC on the tensile and morphological properties of bionanocomposites is covered in this article.     

超声波辅助纤维素酶水解制备纳米纤维素

以人纤浆为原料,利用超声波辅助纤维素酶水解制备纳米纤维素（NCC）,在单因素试验基础上,采用正交试验优化NCC的制备条件,并通过透射电镜（TEM）、X射线衍射（XRD）、红外光谱（FT-IR）、热重（TG）和Zeta电位测定对NCC的结构和性能进行了分析与表征。研究结果表明：NCC的最佳制备条件为酶用量为人纤浆质量的7%、50℃条件下酶解反应10 h,此时纳米纤维素的得率可达62.3%。TEM表征显示制备的纳米纤维素呈短棒状,纳米纤维素之间相互交织形成网络结构;XRD分析表明纳米纤维素的晶体结构并未发生改变,仍为纤维素Ⅰ型,结晶度由人纤浆的54.2%增大到73%;FT-IR分析显示纳米纤维素仍保持天然纤维素的化学结构;热重分析表明纳米纤维素的热稳定性较纤维素原料显著提高;Zeta电位测试结果表明纳米纤维素在水介质中具有良好的分散稳定性。     

Flow birefringence and viscosity of cellulose solutions in semi-dilute regime

An attempt was made to study the flow birefringence and the viscosity of the systems of cellulose in aqueous sodium hydroxide and cadoxen solutions. For this purpose alkali-soluble cellulose samples with crystal form I (simply denoted as cellulose I sample), prepared from conifer wood pulp by the steam-explosion method, and alkali-soluble cellulose samples with crystal form of cellulose II (cellulose II sample), regenerated from cuprammonium cellulose solution under specific conditions, were used. The extinction angle χ of aqueous alkali solutions of the cellulose I sample is significantly less shear rate (γ) dependent as compared with that of the cellulose II sample. In the latter system the χ versus γ relations for a given cellulose sample shifted to the higher γ side with decrease in the average molecular weight. The viscosity of the cellulose II sample in aqueous sodium hydroxide solutions is approximately twice that of the cellulose I sample in the same solvent if compared at the same molecular weight, same concentration, and same temperature. The latter solution showed a non-Newtonian property at relatively smaller γ than the former solution did. Spin-lattice relaxation time T₁ (by ¹³C-NMR) of cellulose in cadoxen solution was smaller in cellulose I, suggesting the existence of intra- and intermolecular hydrogen bondings at the C₆ position of cellulose molecules in cellulose I solution. A dynamic light scattering study on cellulose in cadoxen showed that in a 5 wt % solution of cellulose I cellulose particles are dispersed with time into smaller particles and the larger particles could be excluded by ultracentrifuge and in cellulose II solutions the cellulose particles had almost the same size during storage. The above findings indicate that in 5 wt% cellulose I solutions in aqueous alkali or in cadoxen, cellulose I is not dissolved molecularly, but a supra-molecular structure of the solid is at least partly reserved in the above solutions.     

Dispersion of cellulose crystallites by nonionic surfactants in a hydrophobic polymer matrix

Cellulose nanoparticles obtained by acid hydrolysis of cellulose paper were used to reinforce polystyrene composite films. The nonionic surfactant sorbitan monostearate was utilized to improve the dispersion properties of the hydrophilic cellulose in hydrophobic matrix and to prevent the formation of aggregates. Turbidity tests were used to measure dispersion stability of the cellulose crystallites in the hydrophobic solvent used in the composite manufacture. A correlation was found between the dispersion stability in solvent and the formation of aggregates in the polymeric composites. Nanocomposite films were processed using a casting/evaporation technique. Thermal and mechanical properties of processed composites were studied by differential scanning calorimetry (DSC) and dynamical mechanical analyses (DMA), respectively. The results showed that the optimum addition of surfactant produced better dispersion of the cellulose particles in the polystyrene matrix and improved the mechanical properties of the resulting composite due to an enhanced compatibility. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Structure and thermomechanical properties of stretched cellulose films

Regenerated and stretched cellulose films were investigated for structure and thermomechanical properties as a potential packaging material. Cellulose films were cast from lithium chloride/N, N‐dimethylacetamide and were stretched up to 30% in a dynamic mechanical analyzer sample holder. Wide‐angle X‐ray diffraction analysis indicated that the orientation factor was significantly increased due to stretching. In addition, the stretched films have a higher resistance to the thermal decomposition from thermo gravimetric analysis. The increased orientation of cellulose crystalline structure by the stretching process also increased the storage modulus of cellulose films characterized by dynamic mechanical analysis, which suggest that mechanical properties of cellulose films could be tuned during the stretching process. The α₂ and α₁ relaxations were found at 240 and 300°C, respectively, which are attributed to the micro‐Brownian motion of segments in amorphous region, and activation energies for relaxations were determined with the stretching levels. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Preparation and characterization of transparent cellulose films using an improved cellulose dissolution process

Effective dissolution of cellulosic macromolecules is the first predominant step to prepare functional bio‐based materials with desirable properties. In this study, we developed an improved dissolution process using a freeze‐drying pretreatment to promote the dissolution of cellulose. Rheological measurements of cellulose solutions and physicochemical characterization of regenerated cellulose films (scanning electron microscopy, Fourier transform infrared spectroscopy, X‐ray diffraction, and thermogravimetric analysis) were performed. Cellulose solution prepared from 5% microcrystalline cellulose (w:v) in the solvent exhibits a Newtonian fluid character while cellulose solutions at higher concentrations show a pseudo‐plastic fluid behavior. Results from physicochemical characterization indicate that a freeze‐drying pretreatment step of cellulose leads to a complete dissolution at 5% concentration while only part of cellulose is dissolved at 10% and 15% concentrations. The results obtained indicated that the use of a freeze‐drying pretreatment step under mild conditions lead to a complete dissolution of cellulose at 5% concentration. The cellulose films prepared from 5% concentration exhibited desirable properties such as good optical transparency, crystallinity, and thermal stability. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44871.     

Study of nanoreinforced shape memory polymers processed by casting and extrusion

Multi‐walled carbon nanotubes (CNTs) and cellulose nanofibers (CNFs) reinforced shape memory polyurethane (PU) composite fibers and films have been fabricated via extrusion and casting methods. Cellulose nanofibers were obtained through acid hydrolysis of microcrystalline cellulose. This treatment aided in achieving stable suspensions of cellulose crystals in dimethylformamide (DMF), for subsequent incorporation into the shape memory matrix. CNTs were covalent functionalized with carboxyl groups (CNT‐COOH) and 4,4′‐methylenebis (phenylisocyanate) (MDI) (CNT‐MDI) to improve the dispersion efficiency between the CNT and the polyurethane. Significant improvement in tensile modulus and strength were achieved by incorporating both fillers up to 1 wt% without sacrificing the elongation at break. Electron microscopy was used to investigate the degree of dispersion and fracture surfaces of the composite fibers and films. The effects of the filler (type and concentration) on the degree of crystallinity and thermal properties of the hard and soft segments that form the PU sample were studied by calorimetry. Overall, results indicated that the homogeneous dispersion of nanotubes and cellulose throughout the PU matrix and the strong interfacial adhesion between nanotubes and/or cellulose and the matrix are responsible for the enhancement of mechanical and shape memory properties of the composites. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Characterization of nanocellulose‐ reinforced shape memory polyurethanes

BACKGROUND: Shape memory polymers are capable of fixing a transient shape and of recovering their original dimensions by the application of an external stimulus. Their major drawback is their low stiffness compared to smart materials based on metals and ceramics. To overcome this disadvantage, nanocellulose was utilized as reinforcement. RESULTS: Composites were prepared by casting stable nanocellulose/segmented polyurethane suspensions. The heat of melting of the polyurethane soft segment phase increased on cellulose addition. Composites showed higher tensile modulus and strength than unfilled films (53% modulus increase at 1 wt% nanocellulose), with higher elongation at break. Creep deformation decreased as cellulose concentration increased (36% decrease in 60‐minute creep by addition of 1 wt% nanocellulose). The nanocomposites displayed shape memory properties equivalent to those of the neat polyurethane, with recoveries of the order of 95% (referred to second and further cycles). CONCLUSIONS: It is possible to markedly improve the rigidity of shape memory polymers by adding small amounts of well‐dispersed nanocellulose. However, this improvement did not have substantial effects on the material shape fixity or recovery. Shape memory behavior seems to continue to be controlled by the polymer properties. Copyright © 2007 Society of Chemical Industry     

蔗渣浆制备纳米纤维素及其气凝胶的研究

以蔗渣浆为原料,通过2,2,6,6-四甲基哌啶(TEMPO)催化氧化后,超声波处理制备纳米纤维素(NCC),再经冷冻干燥制备了纤维素气凝胶。通过透射电子显微镜(TEM)、傅里叶红外光谱(FT-IR)、热重分析(TG)、X射线衍射仪(XRD)、扫描电子显微镜(SEM)对NCC及其气凝胶形态和结构等进行了研究。TEM显示超声波作用30 min得到的NCC长度为100~400 nm,直径为20 nm左右;XRD显示氧化后NCC晶型仍为纤维素Ⅰ型;TG显示NCC相对蔗渣原料热稳定性降低;SEM显示NCC水悬浊液中,NCC质量分数为0.1%时,冷冻干燥得到的纤维素气凝胶为三维网状结构,NCC质量分数大于0.1%时,纤维素气凝胶为"蜂窝状"多孔结构。