Nano Fibrils Research Articles

Synthesis and Characterization of Bacterial Cellulose/Nano‐Graphite Nanocomposite Membranes

AbstractA bacterial cellulose (BC)/nano‐graphite nanocomposite membrane has been synthesized by impregnating nano‐graphite into the BC membrane. Microscopic measurements show that nano‐graphite flakes are evenly distributed in the BC matrix, and the thickness size of a nano‐graphite is around 28 nm. In addition, X‐ray measurements showed that the best average size of nano‐graphite crystallites in the BC matrix is 33.4 nm. Nano‐graphite flakes entered the membrane pores and are trapped between the nano fibrils of cellulose. This process is assisted by an ultrasonic process (contact time). For each concentration of nano‐graphite or graphite solution, mass of the nanocomposite membrane containing nano‐graphite is greater than that containing graphite. The mass is increased with increasing contact time between nano‐graphite solutions and BC membranes. The increasing mass indicated the increase in the carbon content which is shown by energy dispersive spectroscopy data. Conductivity of the nanocomposite membrane, in consequence, is significantly increased with the increasing concentration of nanographite solution. For contact time of 24 h, the conductivity is 1.74 S cm−1.

Positive streamers: inception and propagation along mineral-oil/solid interfaces

This paper presents an experimental characterization of the prebreakdown phenomena in liquid/solid interfaces. The characterization is devoted to the 2nd mode positive streamers initiated and propagated along interfaces of mineral-oil and solids with different chemical composition and physical properties. Polymers of low density polyethylene (LDPE), polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE) polyvinylidene fluoride (PVDF) and papers made of kraft paper and a kraft fibril paper (made from cellulosic micro and nano fibrils), lignin-free paper and paper with high lignin content (referred to as k107 kraft paper) are used as the solid to study their influence on the streamer inception and propagation. The streamers are initiated at the interface by applying steps of voltage to a point-plane electrode arrangement with a solid (dielectric barrier) into the gap. The solid is placed diagonal to the oil gap and near to the point electrode. Shadowgraphs, charge and light intensity recordings are obtained during the inception and propagation of the streamers. Thus, estimations of the streamer length, velocity, current and average charge, are also presented. A time delay has been observed before the initiation of the streamer. This delay is probably correlated to the initiation process and formation of the gaseous phase of the streamer near to the interface. The threshold propagation voltage of the 2nd mode streamers at mineral-oil/solid interfaces is shown to be independent of the interface. However, the inception voltage is highly influenced by the interface. Additionally, the observed characteristics of streamers propagation (e.g. current, length, velocity, etc) along the tested interfaces cannot be fully explained by a capacitive coupling effect (permittivity mismatch). This open a discussion for the possibility that properties of the solid such as chemical composition, wettability and surface roughness can influence the streamer propagation.

Development of in situ nanofibrillar poly (lactic acid)/poly (butylene terephthalate) composites: Non-isothermal crystallization and crystal morphology

Tuned one-step melt spinning of poly (lactic acid) (PLA)/poly (butylene terephthalate) (PBT) blends containing 1–10 wt% of PBT, was carried out successfully to induce in situ nanofibrils of PBT with average diameter of 23–51.4 nm. Scanning electron microscopy (SEM) images showed the morphology of PBT nanofibrils (NFs) in the PLA matrix and it was found that the aspect ratio of PBT NFs was more than 400. The crystal morphology of the PLA melt spun fibers in the presence and absence of PBT NFs was analyzed using polarized optical microscopy. Dramatic changes in the crystal morphology of PLA were observed in the presence of PBT NFs. Scattered spherulites in the PLA fibers changed to very small crystals oriented in the PBT NFs direction in the PLA/PBT fibers. Non-isothermal crystallization studies of PLA in the in situ nanofibrillar composites (NFCs) prepared by compression molding demonstrated a significant improvement of crystallinity (27.5%) as well as crystallization rate. Enhanced crystallization rate provided comparative conditions to study the crystal forms of PLA and their relative populations nucleated during the cold and melt crystallizations. Moreover, the crystallization behavior of PLA/PBT blend with droplet-matrix morphology was compared with that of the NFC sample at the same PBT content to emphasize the tremendous effect of the morphological tailoring of blends.

Self-assembled cell sheets composed of mesenchymal stem cells and gelatin nanofibers for the treatment of full-thickness wounds.

Cell sheet engineering has attracted great attention because thin layers of tissue can be easily transplanted to defect sites. Wound-dressing materials are required to support fast re-epithelization, both with keratinocytes and fibroblasts, to enhance the prognosis and therapeutic outcomes. We prepared self-assembled cell sheets composed of adipocyte-derived stem cells (ADSCs) and surface-engineered nanofibrils (NFs). NFs were surface-engineered with multilayers of gelatin so that the cell sheets could spontaneously assemble within 3 days in cell culture plates. Dorsal wounds transplanted with the cell sheets exhibited higher wound-healing rates when a high concentration of gelatin was immobilized on the surfaces of the NFs. Histochemical staining revealed that those with gelatin-immobilized NFs showed a higher expression of cytokeratin and collagen in the re-epithelized epidermis. Keratinocytic differentiation of the epidermis was molecularly evidenced by the higher expression of keratinocyte-specific genes.

Effect of Flow Channel Configuration on Nano Fibril Alignment by Elongational Flow

Effect of Flow Channel Configuration on Nano Fibril Alignment by Elongational Flow

Structure and properties of high quality natural cellulose nano fibrils from a novel material Ficus natalensis barkcloth

We report for the first time the extraction of cellulose nano fibrils from Ficus natalensis barkcloth fibers by means of chemical treatments and catalytic oxidation of cellulose fibers by using 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO). After every stage of treatments, the structural properties of barkcloth fibers powder (BC-PW), cellulose fibers (BC-NB) and cellulose nano fibrils (BC-CNF) were carefully characterized by means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) for morphological analysis, Fourier-transform infrared spectroscopy (FTIR) and X-ray diffraction techniques for chemical analysis, and thermal properties were done by thermo-gravimetric analysis. FTIR results revealed the progressive removal of non-cellulosic contents and X-ray diffraction (XRD) analysis showed that the crystallinity increased with the successive alkali and bleaching treatments. Finally, by evaluating the TEM images, the average diameter of the nano-cellulose fibrils from Ficus natalensis barkcloth was also confirmed as 28 ± 0.6 nm and the length in hundred nano meters was recorded. The resultant cellulose nano fibrils maintaining the cellulose I structure had dimensional properties in nano-scale, higher crystallinity (68.5), and better thermal stability (305.62°C). The barkcloth cellulose nano fibrils can be used in nano technology like food packing material, nano composites and medical textiles.

Plasmon Based Cellulose Nano Fibril–PVA Film for Effective Ultra Violet Radiation Blocking

Recent years have witnessed significant interest in biodegradable and transparent ultraviolet (UV) protecting films from renewable resources. In the present paper, preparation, characterization and evaluation of UV radiation blocking capability of transparent and flexible cellulose nano fibril (CNF)–poly vinyl alcohol (PVA) films are described. Synthesized films exhibited good transparency in the visible region and UV blocking ability. Addition of plasmonic silver (~ 22 nm) to the films lead to complete blocking of UV radiations. Synthesized films were highly stable for a long exposure to intense sunlight. The defined methods show a straightforward procedure for the fabrication of environment friendly UV-radiation blocking films for industrial/commercial/textile applications.

Michael-Type Addition of Gelatin on Electrospun Nanofibrils for Self-Assembly of Cell Sheets Composed of Human Dermal Fibroblasts.

To facilitate cell sheet formation of human dermal fibroblasts, gelatin moieties were chemically decorated onto the surface of electrospun nanofibrils (NFs). Poly(caprolactone) [PCL] was electrospun onto fibrous meshes and then fragmented into nanofibrils by optimized milling and hydrolysis. After aminolysis of the NFs, methacrylated gelatin (GelMA) was reacted via Michael-type addition with the surface-exposed amines of the aminolyzed NFs (ahPCL NFs). GelMA was immobilized on the ahPCL NFs. Analysis of ahPCL NFs and native NFs conducted using X-ray photoelectron spectroscopy confirmed that gelatin was chemically conjugated onto the NFs. Human dermal fibroblasts (HDF) and the decorated NFs were self-assembled into cell sheets, and cells in the matrix showed highly spreading morphology by confocal microscopy. Our results indicate that the degree of cell spreading and cellular viability was much higher in the presence of GelMA immobilized in ahPCL NFs.

Electrospun nanohybrid hydrogels for enhanced differentiation of myoblasts

Enhancement of myogenic differentiation was accomplished with nanohybrid hydrogels composed of fragmented electrospun nanofibrils (NFs) and gelatin/alginate hydrogels. Electrospun nanofibrous meshes were fragmented and hydrolyzed to short fragments of NFs and subsequently embedded in gelatin/alginate hydrogels and further crosslinked with C2C12 cells. Cell-incorporated NF-embedded hydrogels exhibited a lower swelling ratio and higher mechanical properties as compared to hydrogels without NF due to the rigidity of NF and increased matrix-to-cell interaction. Viability of C2C12 cells in the hydrogels gradually increased in proportion to the amount of NF in the hydrogels. Both confocal microscopy and myogenic gene expression analysis indicated that the formation and maturation of myotubes and the expression of muscle motor proteins were significantly accelerated when NF-embedded hydrogels were employed. Contraction behavior of matured myotubes under electrical stimulation revealed that myotubes in NF-embedded hydrogels exhibited a longer contraction length than that of myotubes in hydrogels without NF. Thus, the nanohybrid matrix demonstrates the potential of nanofiber-embedded hydrogels for engineering myotube formation with topographical cues.

Electrospun cellulose Nano fibril reinforced PLA/PBS composite scaffold for vascular tissue engineering

Today, tissue engineered scaffolds made by electrospinning are becoming a central focus of vascular prostheses research due to their ability to assist native tissue recovery. Compared to a single material, multifunctional composite scaffold could provide more suitable microenvironment for the tissue regeneration. In this study, electrospun composite scaffolds are developed by reinforcing a matrix of poly (lactic acid) (PLA) and poly (butylene succinate) (PBS) by cellulose nano-fibrils (CNFs). Initially, PLA/PBS fibrous scaffolds with different ratio were prepared. The best properties and bioactivity of the scaffolds were obtained at equal ratio of PLA and PBS. Overall performance of electrospun scaffolds improved greatly by introduction of CNF into the PLA/PBS scaffolds. The developed composite scaffolds were found to meet some of the essential requirements for vascular tissue regeneration. They showed a uniform fibrous structure with desirable size dimension, cell-friendly surface characteristics, sustainable biodegradation behaviour and sustainable mechanical property compared to native tissue. In addition, the CNF composite scaffolds supported attachment and proliferation of human fibroblast cells more than PLA, PBS or their blends alone. Overall the developed composite scaffolds demonstrated their potency for vascular tissue engineering application.

A Study on the Effect of Fibre Dimensions on the Thermal Conductivity of Pineapple Leaf Fibre Reinforced Polypropylene Composites

This research was carried out to study the thermal conductivity (TC) properties of pineapple leaf fibre (PALF) reinforced polypropylene (PP) composites. The pineapple leaf fibre dimensions were altered specifically at the macro, micro and nano dimensional states. It was considered that the thermal conductivity (TC) behavior of pineapple leaf fibre/polypropylene (PALF/PP) composites would be significantly higher when the pineapple leaf fibre which is the reinforcement agent undergoes dimensional changes. The study also considered the effect the fibre surface modification agents would have on the thermal behavior of the reinforced pineapple leaf fibre /polypropylene composites. The fibre surface modification agents used in this study are sodium hydroxide, zinc chloride, acetic anhydride and nitric acid. The guided plate steady state approach for determining thermal conductivity was used in this research. Results showed that the micro and nano fibrils of the reinforcing agent contributed to the enhanced thermal conductivity behavior of the reinforced pineapple leaf fibre/polypropylene composites. The results obtained also showed that the reinforced microfibrils pineapple leaf fibre /polypropylene composites and reinforced nanofibrils pineapple leaf fibre/polypropylene composites modified with nitric acid exhibits higher thermal conductivity than reinforced pineapple leaf fibre/polypropylene (PALF/PP) composites modified with acetic anhydride, zinc chloride, sodium hydroxide and the unmodified pineapple leaf fibre in descending order respectively.

Optimization of a green process for the extraction of nanofibril from windmill palm fiber using response surface methodology (RSM)

The aim of this work is to improve the yield of nanofibril (NF) from windmill palm cellulose. NF was extracted via ammonium persulfate oxidation (APSO). Four factors (time, solution, temperature, cellulose weight) were used to analyze the influence on NF yield. On the basis of single factor analysis, the Central Composite Design (CCD) of response surface methodology (RSM) was used to design four factors and five levels experiment, and the NF yield was taken as the response value, finally the yield prediction model of regression equation was established via CCD. NF morphology was characterized by AFM. The results proved that the model could well predict yield, and there was interaction among factors, moreover, the influence of single factor was more remarkable than that of interaction among factors. At the same time, the results showed length and diameter of NF were uniform. APSO method accorded with green chemistry and was expected to be one of the efficient methods to extract NF.

Coaxial Hydro-Nanofibrils for Self-Assembly of Cell Sheets Producing Skin Bilayers.

Bilayered cell sheets were fabricated with coaxial hydro-nanofibrils for three-dimensional (3D) cultivation in a biomimetic environment. Polycaprolactone (PCL) was electrospun and hydrolyzed to release fragmented nanofibrils (NF) in an alkaline condition. Methacrylated gelatin (GelMA) was adsorbed and phototethered on the surface of the fibrils to prepare coaxial NF composed of hydrophilic shells and hydrophobic cores. GelMA layers on the NF were characterized by X-ray photoemission spectroscopy, Fourier-transform infrared spectroscopy, and thermogravimetric analysis. The GelMA showed higher decoration level on NF compared to that on native gelatin. GelMA-decorated NF significantly enhanced cell proliferation rate and phenotypic expression of human dermal fibroblasts when spontaneous formation of cell sheets was observed for 7 days. HaCaT cells were layered on top of the fibroblast sheets and further cultivated in air-water interfaces to prepare bilayered skin sheets. After 21 days of incubation, the top layers of the bilayered sheets showed higher expression of pan-keratin, and the dermal cells showed higher proliferation in the GelMA-decorated NF.

Fabrication of a glycation induced amyloid nanofibril and polyalizarin yellow R nanobiocomposite: Application for electrocatalytic determination of hydrogen peroxide

Amyloid fibrils were produced in a solution of bovine serum albumin (BSA) in buffer solution in the presence of fructose. The solution was incubated for 20 weeks in the dark. We used glycation induced bovine serum albumin in which fibrilogenesis (nano fibrils) followed by using fluorescence (Thioflavin T), Dynamic Light Scattering (DLS) and Transmission Electron Microscopy (TEM) to achieve the size and morphology of fibrils. A novel electrochemical biosensor for the detection of hydrogen peroxide was developed based on immobilizing poly (alizarin yellow R) and amyloid nano-fibrils on glassy carbon electrode (PAYR/AMLNFibs/GCE). The electrocatalytic response of the biosensor was proportional to the hydrogen peroxide concentration in the range of 1 μM to 2.2 mM with a limit of detection and sensitivity of 290 nM and 0.024 μA/μM, respectively. The modified electrode demonstrated many advantages such as high sensitivity, low detection of limit and excellent catalytic activity.

Control of Cellulose Nano Fibril Alignment by Electric Field in Elongational Flow for High Strength Single Fiber Fabrication.

Control of Cellulose Nano Fibril Alignment by Electric Field in Elongational Flow for High Strength Single Fiber Fabrication.

Efficient removal of anionic dye (Congo red) by dialdehyde microfibrillated cellulose/chitosan composite film with significantly improved stability in dye solution

A novel composite film with efficient removal of anionic dye (Congo red) was developed using chitosan and dialdehyde microfibrillated cellulose nano fibrils. Microfibrillated cellulose with three dimensional network structure was prepared from microcrystalline cellulose by high-pressure homogenization. Then it was surface modified by periodate to prepare dialdehyde microfibrillated cellulose (DAMFC). DAMFC/chitosan composite films were prepared by solvent-casting. During the compounding of DAMFC with chitosan, a Schiff base was formed through the reaction between the aldehyde groups of DAMFC and amino groups of chitosan. A giant network structure was therefore formed. The addition of DAMFC resulted in remarkably increased adsorption capacity of the chitosan material as well as drastically improved stability in dye solution. The adsorption performance was investigated with respect to pH, temperature, contact time, and the initial dye concentration. The possible adsorption mechanism was proposed. Various isotherm models have been used to fit the data, and kinetic parameters were evaluated.

Degradability and sustainability of nanocomposites based on polylactic acid and chitin nano fibrils

Plastic food packaging materials currently in use are hardly recyclable and very often post consume plastic packaging is directed to incineration or landfill. Use of bio-recyclable plastic will have positive effect on environment, and is gaining importance in particular for the production of active packaging, where a longer shelf-life of the packed food, coupled with improved sustainability can justify the higher cost of biodegradable polymers versus current petro based polymers used in packaging. Among other biodegradable polymers polylactic acid (PLA) has attracted researcher and industries attention for the production of plastic food packaging. In the present contribute we report a study to evaluate the degradability in compost of some representative examples of materials prepared with PLA and chitin nano-fibrils (NC). Since blending a biodegradable polymer with an active compound might hinder the compost ability of the materials produced, it is important to perform test of degradability on innovative materials even if based on biobased and biodegradable components. As well the production of bio-based, biodegradable materials when based on innovative processes, may present several steps that may have a negative effect on sustainability being not optimised in yield, energy consumption and proper valorization of each stream generated in the process. A life cycle assessment study is very important to spot the critical steps in the process and propose corrective actions in the production cycle in order to make the final material more sustainable. The materials based on PLA and NC passed the test of disintegration in compost, evidencing no toxicity on germination of cress seeds. The process of production of NC fibrils, was mostly affected by the high consume of water, and use of chemicals thus plans for recovery and re-use of the water based buffer will improve the sustainability of the process. The bio-nanocomposites based on PLA and NC have a positive environmental effect due to being based on natural resources and having compost ability as possible end of life scenario.

Non-terminal behavior as a finger print to follow droplet deformation

It is well-established that rheology can trace structural dynamics and conjectures the forming/formed morphology. The objective of this work is to trace the droplet deformation via conducting fiber spinning process. In this regard, two types of polymer blends Polypropylene (PP)/Polyamide6 (PA6) and Polypropylene/Polytrimethylene terephthalate (PTT) with various ratios (99/1, 94/6, 90/10, and 80/20) were melt-blended on co-rotating twin screw extruder and thereafter, were spun. Scanning electron microscopy (SEM) images represent a droplet and fibrillar morphologies for as-extruded samples and spun blend fibers respectively. Unlike PA6 as dispersed phase, PTT droplets in PP/PTT blend system shows improved spinnability. Linear melt viscoelastic data were gathered by performing rheological approaches in linear region. Conducting frequency sweep at 240°C is revealed a terminal behavior for Gʹ and a Newtonian plateau for η* at low frequencies. However, at 195°C dynamic rheological data pertinent to fibers represent a non-terminal trend for Gʹ and viscosity upturn at low frequencies respectively. These distinguishable characteristics can be considered as spinnability of droplets which reflect fibrillation mechanism, and fibrillar growth can be followed by scanning the viscoelastic responses at low frequency region which enhanced upon fibril growth. According to SEM and rheological test results, PTT, as an engineering plastics, manifests higher capability of forming nano fibrils.

First mode negative streamers along mineral oil-solid interfaces

This document presents an experimental study on the propagation of first mode negative streamers along mineral oil-solid interfaces. Samples made of an oil impregnated kraft paper and a low-porosity paper made from cellulosic micro and nano fibrils, as well as different polymeric films (low density polyethylene (LDPE), polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF)) are used as the solid. A comparison of the length, charge and velocity of streamers for all different mineral oil-solid interfaces is reported. It is shown that streamers propagate longer and faster along mineral oil-solid interfaces with low surface roughness, low porosity and higher electrical permittivity than mineral oil. Those streamers show a quasi-continuous injection of charge in the early stage of their propagation. This quasi-continuous charge injection consists of a sequence of small charge steps separated by few tens of nanoseconds in between. In comparison, the streamers that propagate along surfaces with similar permittivity to the mineral oil have lower injection of charge and higher stopping voltage conditions than streamers propagating free in the liquid without any solid barrier.

Characterization of Amylose Nanogels and Microgels Containing Ionic Polysaccharides.

We prepared and characterized amylose nanogels containing ionic polysaccharides which we used were 4-O-methyl-D-glucurono-D-xylan (GX), alginate, xanthan, and chitosan. Gelation under a shear force followed by a wet pulverization leads to the formation of hybrid nanogels. The resultant nanogels were characterized by particle size analysis, zeta-potential measurement and atomic force microscopy (AFM). Wet pulverization under a pressure of 200 MPa reduced the particle size of the gels from 20−26 μm to 240−670 nm. Zeta potential measurement showed that the ionic polysaccharides increased surface charges of the amylose gels. AFM observations showed the network consisting of submicron size amylose-polysaccharide nano fibrils. The fibrils containing GX were dispersed uniformly, while those containing only amylose were partly aggregated.