Recent development in food emulsion stabilized by plant-based cellulose nanoparticles

In this review, we discuss the application of cellulose nanoparticles as a sustainable and cost-effective source of green stabilizers for formulation of foodstuff. Fibrillar cellulose nanocrystal and nanofibril stabilize Pickering systems because of their ability to adsorb at the oil/water interfaces, forming protective layers. They also form associative structures in the continuous phase, increasing their viscoelastic properties and preventing flocculation. We describe the chemical and structural features of nanocelluloses and discuss the principles that support their utilization as stabilizers, especially in the context of recent prospects in food and health domains, given safety and regulatory advances. In addition, we describe the benefits of combining nanocelluloses with other food ingredients to extend their functional attributes. Particularly, nanocellulose-based Pickering emulsions are used to create edible soft materials with multiple functionalities. This article is expected to stimulate the use of nanocelluloses as functional ingredients to create food products with improved performance and novel properties.     

Development of biopolymer/cellulose/silica nanostructured hybrid materials and their characterization by NMR relaxometry

The objective of this study was to investigate the preparation and properties of hybrid materials composed of poly(lactic acid) (PLA) and poly(lactic acid)/poly(lactic-co-glycolic acid) (PLA/PLGA) blends employing cellulose nanocrystals (CNCs) and/or organophilic silica (R972) as nanoparticles. The CNCs were obtained by acid hydrolysis of commercially available microcrystalline cellulose (MCC). The materials were produced in film form by solution casting. Organophilic silica was incorporated at a ratio of 3 wt.%, and CNCs were added at ratios of 3 wt.% and 5 wt.% in relation to the weight of the polymer matrix. Two series of films were obtained. The first was prepared using only PLA as the matrix, and the second was obtained using blends of PLA and PLGA. The properties of the films were evaluated by X-ray diffractometry, nuclear magnetic resonance, Fourier-transform infrared spectroscopy and measurement of mechanical properties. The results revealed that each nanoparticle, whether added individually or combined with the other type of nanoparticle, induced different final material properties. Cellulose nanocrystals can act as nucleating agents for the crystallization of PLA. There was an improvement in the mechanical performance of films with the addition of CNCs. Further, the incorporation of silica combined with CNCs resulted in the generation of films with the strongest mechanical properties. The results of this study indicate that silica decreases the surface tension between PLA-cellulose and PLA/PLGA-cellulose.     

Mechanically reinforced chitosan/cellulose nanocrystals composites with good transparency and biocompatibility

Chitosan/cellulose nanocrystals(CS/CNCs) composites were prepared with different contents of CNCs. Due to the homogeneous dispersion of CNCs and the strong interfacial interactions resulting from hydrogen bonding between CS chains and CNCs, the transparency of CS is well retained and the overall mechanical properties of CS are significantly improved. Furthermore, because both CS and CNCs are biocompatible materials, cell proliferation test shows that the obtained composites are noncytotoxic and can potentially meet safety requirements of biomedical applications. These advantages pave the way of potential applications of CS in the field of commercial plastics and encourage the use of CS as environmentfriendly material and biomedical material.     

Nanocellulose-based soft actuators and their applications

Nanocellulose has aroused growing attention in the design and fabrication of multifarious soft actuators thanks to its abundant source, appropriate mechanical properties, and sustainability. In this mini-review, an up-to-date account of recent progresses in nanocellulose-based actuators with homogeneous and heterogeneous structures is provided. The fundamental design concepts and synthesis strategies for nanocellulose-based soft actuators with a wide array of micro-architecture are described. Moreover, their actuation mechanisms, structure–function relationships, and emerging applications in the fields of soft robotics, biomedical science and bioelectronics are highlighted. Finally, a brief conclusion, the current challenges, and future perspectives in the development of nanocellulose-based actuators is presented. This mini-review provides new insights into the fundamental research and the technological application of advanced nanocellulose-based soft actuators.     

Thermal and mechanical properties of particulate fillers filled epoxy composites for electronic packaging application

Epoxy composites containing particulate fillers‐fused silica, glass powder, and mineral silica were investigated to be used as substrate materials in electronic packaging application. The content of fillers were varied between 0 and 40 vol%. The effects of the fillers on the thermal properties—thermal stability, thermal expansion and dynamic mechanical properties of the epoxy composites were studied, and it was found that fused silica, glass powder, and mineral silica increase the thermal stability and dynamic thermal mechanical properties and reduce the coefficient of thermal expansion (CTE). The lowest CTE value was observed at a fused silica content of 40 vol% for the epoxy composites, which was traced to the effect of its nature of low intrinsic CTE value of the fillers. The mechanical properties of the epoxy composites were determined in both flexural and single‐edge notch (SEN‐T) fracture toughness properties. Highest flexural strength, stiffness, and toughness values were observed at fillers content of 40 vol% for all the filled epoxy composites. Scanning electron microscopy (SEM) micrograph showed poor filler–matrix interaction in glass powder filled epoxy composites at 40 vol%. Copyright © 2007 John Wiley & Sons, Ltd.     

Engineering hairy cellulose nanocrystals for chemotherapy drug capture

Cancer is one of the leading causes of death worldwide, affecting millions of people every year. Although chemotherapy remains one of the most common cancer treatments in the world, the severe side effects of chemotherapy drugs impose serious concerns to cancer patients. In many cases, the chemotherapy can be localized to maximize the drug effects; however, the drug systemic circulation induces undesirable side effects. Here, we have developed a highly efficient cellulose-based nanoadsorbent that can capture more than 6,000 milligrams of doxorubicin (DOX), one of the most widely used chemotherapy drugs, per gram of the adsorbent at physiological conditions. Such drug capture capacity is more than 3,200% higher than other nanoadsorbents, such as DNA-based platforms. We show how anionic hairy cellulose nanocrystals, also known as electrosterically stabilized nanocrystalline cellulose (ENCC), bind to positively charged drugs in human serum and capture DOX immediately without imposing any cytotoxicity and hemolytic effects. We elucidate how ENCC provides a remarkable platform for biodetoxification at varying pH, ionic strength, ion type, and protein concentration. The outcome of this research may pave the way for developing the next-generation in vitro and in vivo drug capture additives and devices.     

Rheology,crystallization behavior,and mechanical properties of poly(butylene succinate-co-terephthalate)/cellulose nanocrystal composites

A series of biodegradable poly (butylene succinate-co-terephthalate) (PBST) with different aromatic units content was synthesized and then melt blended by adding cellulose nanocrystals (CNCs) to manufacture the full organic composites. A network-like structure of CNCs in PBST matrix was evaluated by rheometer. The storage modulus and complex viscosity at low frequency region were significantly enhanced with increasing CNC content. Meanwhile, the decreasing $\tan \delta$ and flow index were attributed to the excellent interaction between PBST and CNCs. When PBST has a content of the aromatic unit exceeds 30 mol%, the crystallization temperatures increased with increasing CNC contents. On the other hand, when PBST has 30 mol% content of the aromatic unit, the cold crystallization temperatures decreased with increasing CNC contents. These above observation in crystallization properties suggested that the CNC make a role of heterogeneous nucleation in PBST matrix. The result of mechanical properties evaluated by dynamic mechanical analysis showed a good reinforcement effect of the addition of stiff CNC. The PBST/CNC composites were suitable for cell growth and might have a potential as biomedical materials, which is confirmed by MTT assay.     

Piezoelectric Nanogenerator Based on Electrospun Cellulose Acetate/Nanocellulose Crystal Composite Membranes for Energy Harvesting Application

Nanogenerators, as the typical conversion of mechanical energy to electrical energy devices, have great potential in the application of providing sustainable energy sources for powering miniature devices. In this work, cellulose acetate/cellulose nanocrystal(CA/CNC) composite nanofiber membranes were prepared by electrospinning method and then utilized to manufacture a flexible pressure-driven nanogenerator. The addition of CNC not only increased the content of piezoelectric cellulose I crystallization but also strengthened the mechanical deformation of the nanofiber membranes, which could greatly enhance the piezoelectric performance of CA/CNC composite membranes. The CA/CNC composite nanofiber membrane with 20%(mass fraction) of CNC(CA/CNC-20%) showed optimal piezoelectric conversion performance with the output voltage of 1.2 V under the force of 5 N(frequency of 2 Hz). Furthermore, the output voltage of the CA/CNC-20% nanogenerator device exhibited a linear relationship with applied impact force, indicating the great potential in pressure sensors.     

木质纤维素纳米纤丝制备及形态特征分析

以阔叶树材杨木木粉为原料,始终保持纤维处在水润涨的状态下,利用亚氯酸钠在酸性条件下脱除木质素,氢氧化钾脱除半纤维素,然后借助高强度超声波的空化作用,依次制备了综纤维素、纯化纤维素及木质纤维素纳米纤丝(WCNF).通过傅里叶变换红外吸收光谱(FTIR)、X射线衍射(XRD)、扫描电镜(SEM)对WCNF制备过程中的化学组分、晶型结构、结晶度及形态特征变化进行了表征,并进一步利用图像分析系统对WCNF的直径分布进行了测量统计.结果表明,WCNF的主要成分为纤维素,其晶型结构仍为纤维素Ⅰ型,结晶度为65.68%,较之原料木粉提高了12.33%.所得纤丝的直径集中分布在5～32nm之间,长度大于10μm,长径比高于300,纤丝间相互交织成网状缠结结构.WCNF的高结晶度、高长径比、纳米尺度、网状缠结结构,显示其为一种十分理想的增强增韧材料.     

Study of migration of active components of phosphorescent oxygen sensors for food packaging applications

A study of migration of the active components of oxygen sensors into food is presented. Six types of sensors, based on different oxygen sensitive dyes (two metalloporphyrins and one ruthenium dye), polymers (polystyrene and polysulfone) and support materials, were exposed to a number of standard ‘food simulants’ recommended by FDA/EU guidelines and then assayed for migration or sensor components and changes in oxygen calibration. Both metalloporphyrin sensor dyes leached only in olive oil and in 95% ethanol (used as a positive control), at maximum levels of 19.22 μg/dm² for PtOEPK and 113.96 μg/dm² for PtTFPP. The RuDPP dye showed maximum leaching in 95% ethanol (25.19 μg/dm²) while also migrating in an acidic aqueous simulant. Planar supports such as polyester tended to enhance the stability of the sensor. Migration of the styrene monomer from the polystyrene encapsulation medium was concluded to be low enough to be insignificant. Migration of sensor components was shown to correlate with the changes in sensor response to oxygen. Based on these results, sensor combinations were ranked on the basis of their resistance to leaching and their general stability, safety and suitability for use on a large scale in packaged foods and related food applications was proven.     

Extraction of cellulose and preparation of nanocellulose from sisal fibers

In this work a study on the feasibility of extracting cellulose from sisal fiber, by means of two different procedures was carried out. These processes included usual chemical procedures such as acid hydrolysis, chlorination, alkaline extraction, and bleaching. The final products were characterized by means of Thermogravimetric Analysis (TGA), Infrared Spectroscopy (FTIR), X-Ray Diffraction (XRD), Differential Scanning Calorimetry (DSC) and Scanning Electronic Microscopy (SEM). The extraction procedures that were used led to purified cellulose. Advantages and disadvantages of both procedures were also analyzed. Finally, nanocellulose was produced by the acid hydrolysis of obtained cellulose and characterized by Atomic Force Microscopy (AFM).     

Characterization of extruded ethylene-vinyl alcohol copolymer based barrier blends with interest in food packaging applications

Based on previous work a number of optimum extruded blends with high contents of a high barrier ethylene-vinyl alcohol copolymer were selected and characterized in terms of phase morphology, water sorption and barrier properties. Blend components were an ethylene vinyl-alcohol copolymer (EVOH with 32 mol% ethylene), an amorphous polyamide (aPA) and a nylon-containing ionomer. A fine two phase structure was found for these blends in all cases. However, Raman spectroscopy results indicated a poor interface interaction between the blend components in the case of the EVOH/aPA blends. Higher interface interaction had been previously found in the dry EVOH/ionomer blends. Equilibrium moisture solubility and diffusion were found to be higher than expected from simple additivity. However, the oxygen transmission rate was found to be clearly lower than expected from the rule of mixtures, particularly under dry conditions, fitting closely a simple Maxwell model.     

Transcrystallization of polypropylene at cellulose nanocrystal surfaces

There is a resurgence of interest in composite materials incorporating cellulose as fibrous reinforcement in semicrystalline melt-processed polymers. Potential natural cellulose sources range from flax and ramie fibres down to whiskers and nanocrystals isolated from bacteria. It has long been known that the crystallization of matrix polymers such as polypropylene may be preferentially nucleated by Cellulose I surfaces, leading to a “transcrystalline” layer around the fiber. In this note, a transcrystalline layer at the edge of films cast from cellulose nanocrystal suspensions is demonstrated, and preferential nucleation of polypropylene on nanocrystals deposited on a glass surface is also observed.     

New Metallo-Supramolecular Terpyridine-Modified Cellulose Functional Nanomaterials

New metallo-supramolecular nanocellulosic derivatives were prepared by surface modification of cellulose nanocrystals with 4-chloro-2,2′:6′,2″-terpyridine and subsequent coupling with other terpyridine-functionalized derivatives via Ru^III/Ru^II reduction. The terpyridine-modified cellulose nanocrystals (CTP) were characterized using transmission electron microscopy (TEM), magic angle spinning ¹³C nuclear magnetic resonance (MAS-¹³C NMR), elemental analysis, as well as Fourier transform infrared (FTIR) and UV-Visible spectroscopy. Metallo-CTP with different optical properties, and expected magnetic and catalytic properties, were easily obtained upon reaction of the prepared CTP with different di- and trivalent transition metal ions (Fe⁺², Mn⁺², Co⁺², and Ru⁺³). Metallo-supramolecular nanocellulosic derivatives with different properties were prepared by subsequent coupling of Ru^III-CTP complex with other terpyridine ligands bearing different functionalities.     

Fracture evaluation of plasticized polylactic acid / poly (3-HYDROXYBUTYRATE) blends for commodities replacement in packaging applications

Nowadays, scientific and technological efforts are being carried out to diminish serious ecological problems caused by indiscriminate use of non-biocompostable polymers in the packaging industry. In this sense, novel biodegradable blends of different composition based on poly(lactic acid) (PLA), poly(3-hydroxybutyrate) (PHB) and tributyrin (TB) are developed and here proposed as an eco-friendly alternative. Materials are characterized by fracture experiments under quasi-static and biaxial impact loading. Fracture behavior is analyzed together with thermal, tensile and water permeation properties to evaluate their potential in-service performance. TB_PLA/PHB blends with 15 wt% TB exhibit better permeation and fracture toughness than currently used bio-based polymers, being in the range of polyethylene properties. Results highlight the potential of these new blends broadening the current application field of PLA.     

Optimization of the isolation of nanocrystals from microcrystalline cellulose by acid hydrolysis

The objective of this work was to find a rapid, high-yield process to obtain an aqueous stable colloid suspension of cellulose nanocrystals/whiskers. Large quantities are required since these whiskers are designed to be extruded into polymers in the production of nano-biocomposites. Microcrystalline cellulose (MCC), derived from Norway spruce (Picea abies), was used as the starting material. The processing parameters have been optimized by using response surface methodology. The factors that varied during the process were the concentration of MCC and sulfuric acid, the hydrolysis time and temperature, and the ultrasonic treatment time. Responses measured were the median size of the cellulose particles/whiskers and yield. The surface charge as calculated from conductometric titration, microscopic examinations (optical and transmission electron microscopy), and observation of birefringence were also investigated in order to determine the outcome (efficiency) of the process. With a sulfuric acid concentration of 63.5% (w/w), it was possible to obtain cellulose nanocrystals/whiskers with a length between 200 and 400 nm and a width less than 10 nm in approximately 2 h with a yield of 30% (of initial weight).     

Physical and mechanical testing of essential oil-embedded cellulose ester films

Polymer films made from cellulose esters are useful for embedding plant essential oils, either for food packaging or air freshener applications. Studies and testing were done on the physical and mechanical properties of cellulose ester-based films incorporating essential oils (EO) from lemongrass (Cybopogon citratus), rosemary pepper (Lippia sidoides) and basil (Ocimum gratissimum) at concentrations of 10 and 20% (v/w). Results obtained showed that, in all films, the addition of the essential oil caused a decrease in the water vapor permeability due to the hydrophobic nature of the oil. The use of 20% of EO caused lower transparency of the films, although the change was not observed visually. Mechanical testing was done on cellulose acetate, cellulose acetate propionate and cellulose acetate butyrate. It was found that incorporation of lemongrass, basil and rosemary pepper EO significantly affected the Young's modulus, tensile strength and elongation at break of the cellulose ester films. The results suggested that the essential oils interacted with the polymers like plasticizers. The results were confirmed with thermal and microscopic studies.     

Materials chemistry and the futurist eco-friendly applications of nanocellulose: Status and prospect

Cellulose, a linear biopolymer, is present naturally in all plants. Apart from being the planet’s predominant natural polymer, it also offers a variety of features including excellent biocompatibility, lower density, substantial strength and the most beneficial mechanical characteristics, inexpensive in cost. Applying the mechanical or chemical techniques, cellulosic materials are transformed into cellulose nanofibres (CNFs) and even cellulose nanocrystals (CNCs). These CNFs and CNCs exhibit excellent capabilities in comparison with native cellulose fibre. Nowadays, nanocellulose is being used in a variety of practical applications such as product packaging, papers as well as paperboard, food sector, healthcare, hygiene products, paints, skin care products and sensors. The current review article summarizes the cellulose, processing methods for nanocellulose, techniques used for chemical modification of cellulose surface and consequently its application as reinforcement in polymeric materials. This article also provides a comprehensive discussion of the historical development in the area of nanocellulose.     

纳米载体固定化酶的最新研究进展

催化剂是化学工业的重要基础,其中酶是重要的高效天然催化剂。近年来,酶被越来越多地应用于工业领域,如精细化工、食品工业、制药工业、纺织业和制浆造纸。然而,由于游离酶存在价格昂贵及操作稳定性(特别是回收与重复使用性能)低等缺点,其在工业上的进一步应用受到一定限制。对酶进行固定化是解决上述问题的有效途径。一个理想的酶固定化技术需要载体具有良好的生物相容性和高比表面积,能够负载适量的酶并且具有很好的重复使用性能,固定化酶的过程简单温和,所得到的固定化酶制剂具有良好的催化性能、稳定性以及工业应用价值。尽管固定化酶技术经过了多年的发展,但仍需进一步研究。近几年,人们研究了基于纤维素纳米晶类、聚多巴胺类纳米载体以及生物相容性合成有机物纳米胶等新型载体对酶的固定化,取得了较好的成果。本文综述了这些新型纳米载体的制备以及酶的固定化过程,阐述了纳米载体固定化酶的结构和催化性能,并展望了发展前景。纤维素是全球产量最高、来源最广的生物聚合物。纤维素经过一定的酸(常用硫酸和盐酸)水解处理后,剩下的是具有高结晶度的纤维素纳米晶。它具有高比表面积、高机械强度和高长径比等优异性能。因此,研究者利用纤维素纳米晶作为载体进行酶固定化,获得了高负载量、高催化性能的固定化酶制剂。基于仿生矿化法制备的聚多巴胺类材料近年来获得研究者越来越多的关注。多巴胺具有良好的自聚合能力,可以对无机、有机等各种材料进行表面修饰。同时,聚多巴胺中含有的活性官能团可以与酶发生交联,从而达到固定化酶的效果。基于合成性聚合物纳米胶载体的固定化酶技术同样是一个新兴的、有意义的研究领域。相关的固定化过程可分为两大类：(1)在酶分子表面通过原位聚合生成纳米胶(growing-from过程);(2)将酶与预先合成的纳米胶进行交联(grafting-to过程)。其中, growing-from过程是先将酶分子丙烯酰化,再进行原位聚合。而原位聚合又可分为自由基聚合、原子转移自由基聚合(ATRP)和可逆加成-断裂链转移聚合(RAFT)。其中, ATRP和 RAFT主要用于制备环境响应型的酶-聚合物纳米凝胶。