Cellulose-Based Nanofibers Processing Techniques and Methods Based on Bottom-Up Approach-A Review

In the past decades, cellulose (one of the most important natural polymers), in the form of nanofibers, has received special attention. The nanofibrous morphology may provide exceptional properties to materials due to the high aspect ratio and dimensions in the nanometer range of the nanofibers. The first feature may lead to important consequences in mechanical behavior if there exists a particular orientation of fibers. On the other hand, nano-sizes provide a high surface-tovolume ratio, which can have important consequences on many properties, such as the wettability. There are two basic approaches for cellulose nanofibers preparation. The top-down approach implies the isolation/extraction of cellulose nanofibrils (CNFs) and nanocrystals (CNCs) from a variety of natural resources, whereby dimensions of isolates are limited by the source of cellulose and extraction procedures. The bottom-up approach can be considered in this context as the production of nanofibers using various spinning techniques, resulting in nonwoven mats or filaments. During the spinning, depending on the method and processing conditions, good control of the resulting nanofibers dimensions and, consequently, the properties of the produced materials, is possible. Pulp, cotton, and already isolated CNFs/CNCs may be used as precursors for spinning, alongside cellulose derivatives, namely esters and ethers. This review focuses on various spinning techniques to produce submicrometric fibers comprised of cellulose and cellulose derivatives. The spinning of cellulose requires the preparation of spinning solutions; therefore, an overview of various solvents is presented showing their influence on spinnability and resulting properties of nanofibers. In addition, it is shown how bottom-up spinning techniques can be used for recycling cellulose waste into new materials with added value. The application of produced cellulose fibers in various fields is also highlighted, ranging from drug delivery systems, high-strength nonwovens and filaments, filtration membranes, to biomedical scaffolds.This research was funded by CONEX-Plus program of Universidad Carlos III de Madrid and the European Commission through the Marie-Sklodowska Curie COFUND Action (Grant Agreement No 801538). The authors also appreciate the financial support received from AEI (Ministerio de Ciencia e Innovación of Spain, PID2020-112713RB-C22]; the Universidad Carlos III de Madrid due to Fondos de Investigación of Fco. Javier González Benito [2012/00130/004] and the strategic Action in Multifunctional Nanocomposite Materials [Code: 2011/00287/003]

Preparation of cellulose acetate film with dual hydrophobic-hydrophilic properties using solution blow spinning

Solution blow spinning (SBS), a processing method alternative to electrospinning, where pressured air is used instead of an electric field, was used in this work for the preparation of cellulose acetate (CA) materials. The sequential use of SBS to produce a double-layered film is also investigated. Mixtures of acetone with acetic acid or N,N-dimethylformamide (DMF) were studied as systems for polymer solution preparation. The type of produced material (flat film or multi-structured membranes constituted from submicrometric fibers with beads), its thermal properties, crystallinity, and morphology are more dependent on the solvent system than other SBS processing parameters. Roughness and porosity of differently produced materials influence wettability measured by the contact angle, which ranges in this work from approx. 69.8 degrees ± 3 degrees for a flat film to 104 degrees ± 5 degrees for fibrous material. Finally, a double-layered film, prepared by sequential SBS of individual layers different in terms of wettability, renders a standalone film of dual wettability, with one side hydrophobic and the other hydrophilic.This work was financially supported by CONEX-Plus program of Universidad Carlos III de Madrid (UC3M) and the European Commission through the Marie-Sklodowska Curie COFUND Action (Grant Agreement No 801538). Authors also appreciate the financial support received from AEI, The Ministry of Science and Innovation of Spain [PID2020-112713RB-C22 and –C21], Universidad Carlos III de Madrid, Funds for Investigation of Fco. Javier González Benito [2012/00130/004] and the strategic Action in Multifunctional Nanocomposite Materials [ 2011/00287/003]

Polymeric materials with antibacterial activity: A review

Infections caused by bacteria are one of the main causes of mortality in hospitals all over the world. Bacteria can grow on many different surfaces and when this occurs, and bacteria colonize a surface, biofilms are formed. In this context, one of the main concerns is biofilm formation on medical devices such as urinary catheters, cardiac valves, pacemakers or prothesis. The development of bacteria also occurs on materials used for food packaging, wearable electronics or the textile industry. In all these applications polymeric materials are usually present. Research and development of polymer-based antibacterial materials is crucial to avoid the proliferation of bacteria. In this paper, we present a review about polymeric materials with antibacterial materials. The main strategies to produce materials with antibacterial properties are presented, for instance, the incorporation of inorganic particles, micro or nanostructuration of the surfaces and antifouling strategies are considered. The antibacterial mechanism exerted in each case is discussed. Methods of materials preparation are examined, presenting the main advantages or disadvantages of each one based on their potential uses. Finally, a review of the main characterization techniques and methods used to study polymer based antibacterial materials is carried out, including the use of single force cell spectroscopy, contact angle measurements and surface roughness to evaluate the role of the physicochemical properties and the micro or nanostructure in antibacterial behavior of the materials

PVDF/BaTiO3/carbon nanotubes ternary nanocomposites: Effect of nanofillers and processing

Ternary thermoplastic systems based on poly(vinylidene fluoride), PVDF, filled with barium titanate, BaTiO3, submicrometric particles and carbon nanotubes, CNT, were prepared. Their structure and morphology were studied as a function of composition and finally correlated with thermal and mechanical properties. High energy ball milling, HEBM, under cryogenic conditions and subsequent hot pressing were used to obtain films with quite uniform dispersion of the nanofillers. The presence of BaTiO3 particles and CNT did not modify the thermodegradation mechanism of the PVDF. However, enough amount of BaTiO3 seemed to inhibit the volatility of the products of pyrolysis, hindering the decomposition of PVDF. The presence of CNT favored the PVDF thermodegradation probably due to improved heat transmission by an increase in the thermal conductivity. Variations in PVDF thermal transitions were more dependent of processing conditions. Improvements in the mechanical properties of PVDF were ascribed to a reinforcing effect of the fillers. This effect only happened below the fraction of percolation of CNT, pointing out that CNT reinforce through an optimum load transfer from the PVDF matrix to the nanofillers

Preparation, Properties and Water Dissolution Behavior of Polyethylene Oxide Mats Prepared by Solution Blow Spinning

The relationship between processing conditions, structure and morphology are key issues to understanding the final properties of materials. For instance, in the case of polymers to be used as scaffolds in tissue engineering, wound dressings and membranes, morphology tuning is essential to control mechanical and wettability behaviors. In this work, the relationship between the processing conditions of the solution blow spinning process (SBS) used to prepare nonwoven mats of polyethylene oxide (PEO), and the structure and morphology of the resulting materials are studied systematically, to account for the thermal and mechanical behaviors and dissolution in water. After finding the optimal SBS processing conditions (air pressure, feed rate, working distance and polymer concentration), the effect of the solvent composition has been considered. The structure and morphology of the blow spun fibers are studied as well as their thermal, mechanical behaviors and dissolution in water. We demonstrate that the morphology of the fibers (size and porosity) changes with the solvent composition, which is reflected in different thermal and mechanical responses and in the dissolution rates of the materials in water.This work was financially supported by AEI (Ministerio de Ciencia e Innovación of Spain, PID2020-112713RB-C22 and -C21]; the Universidad Carlos III de Madrid, Fondos de Investigación of Fco. Javier González Benito [2012/00130/004] and the strategic Action in Multifunctional Nanocomposite Materials [Code: 2011/00287/003]

Wettability behavior of solution blow spun polysulfone by controlling morphology

Solution blow spinning (SBS) is used to prepare polysulfone materials (PSf) with different morphologies changing the processing conditions. Morphological study is done by scanning electron microscopy. Materials mainly constituted by beads and fibers are obtained. An optimization strategy based on desirability function approach together with Box–Behnken design is employed to find the best processing conditions to produce PSf materials with tailored morphology. Feed rate and air pressure are the variables of SBS processing conditions with the highest influence on the relative amount of fibers produced while air pressure and a particular balance between work distance and feed rate have the highest impact on the size of fibers. Contact angle measurements are used to understand SBS PSf wettability as a function of morphology. It is demonstrated the possibility of designing PSf materials with particular wettability behavior induced by tailored morphologies obtained from a particular election of SBS processing conditions.Fondos de Investigación de Fco. Javier González Benito,política de reinversión de costes generales, Universidad Carlos III de Madrid (2012/00130/004) and Acción Estratégica en Materiales Compuestos Poliméricos e Interfases, Universidad Carlos III de Madrid (2011/00287/002). Ministerio de Asuntos económicos y Transformación Digital (Ref. UC3M: 2013/00540/001). Besides,authors greatly appreciate the Consejo Nacional de Ciencia y Tecnología (CONACyT-México) for financial support associated to a the scholarship number 625396

Airbrushed Polysulfone (PSF)/Hydroxyapatite (HA) Nanocomposites: Effect of the Presence of Nanoparticles on Mechanical Behavior

Nanocomposite films of polysulfone (PSF)—hydroxyapatite (HA) were prepared with a commercial airbrush. Structural, thermal, and mechanical characterization allows obtaining new information to understand the role of the nanofiller–polymer matrix interphase in the final performance of these materials in relation to its possible applications in the restoration of bones. Fourier-transform infrared spectroscopy shows that there are hardly any structural changes in the polymer when adding HA particles. From thermal analysis (differential scanning calorimetry and thermogravimetry), it can be highlighted that the presence of HA does not significantly affect the glass transition temperature of the PSF but decelerates its thermal degradation. All this information points out that any change in the PSF performance because of the addition of HA particles cannot be due to specific interactions between the filler and the polymer. Results obtained from uniaxial tensile tests indicate that the addition of small amounts of HA particles (1% wt) leads to elastic moduli higher than the upper bound predicted by the rule of mixtures suggesting there must be a high contribution of the interphase. A simple model of the nanocomposite is proposed for which three contributions must be considered, particles, interphase and matrix, in such a way that interphases arising from different particles can interact by combining with each other thus leading to a decrease in its global contribution when the amount of particles is high enough. The mechanical behavior can be explained considering a balance between the contribution of the interphase and the number of particles. Finally, a particular mechanism is proposed to explain why in certain nanocomposites relatively high concentrations of nanoparticles may substantially increase the strain to failure.The authors wish to acknowledge financial support from Fondos de Investigación de Fco., Javier González Benito, política de reinversión de costes generales, Universidad Carlos III de Madrid (2012/00130/004), Acción Estratégica en Materiales Compuestos Poliméricos e Interfases, Universidad Carlos III de Madrid (2011/00287/002) and Adquisición de un microscopio electrónico de barrido de emisión de campo y ambiental (FEDER) (2013/00540/001), and project number 2020/00355/001 from CAM (Comunidad Autónoma de Madrid). This work has been supported by Comunidad de Madrid (Spain) multiannual agreement with UC3M (“Excelencia para el Profesorado Universitario”- EPUC3M04) fifth regional research plan 2016–2020

Monitoring of curing process by fluorescence technique. Fluorescence probe and label based on 5-dimethylaminonaphthalene-1-sulfonamide derivatives (DNS)

The curing reaction of glycidyl ether bisphenol A (DGEBA) with n-butyl amine and/or N-methylethylenediamine was monitored by fluorescence spectroscopy. 5-Dimethylaminonaphthalene-1-sulfonamide (DNS) fluorophore was used as a probe and/or label. Fourier transform infrared (FTIR) analysis revealed that the rate constant for the addition reaction of the primary amino group hydrogen of n-butylamine to the epoxide ring is more than four times larger than that arising from a secondary amine. Significant differences have been observed between the fluorescence behavior of the DNS as a probe and label, especially in the system DGEBA-N-butyl amine. Integrated fluorescence intensity for the DNS label, in contrast to the DNS probe, indicates the most important changes in chemical transformations of this reaction mixture (the onset of tertiary amino groups and maximum concentration of secondary amino groups). Similarly, the dependence of the half-bandwidth on the epoxy groups conversion for the DNS label shows these stages of the curing reaction as well. In the system DGEBA-N-methylethylenediamine, the reactivity of the secondary amino group hydrogen is higher than that of the primary amino group. A change in slope of the dependence of integrated fluorescence intensity on epoxy group conversion clearly indicates the gel point and entry of the system into the glassy state. The DNS probe does not sense any of these changes. From the emission spectra of the DNS probe and/or label, the average value = SigmaIF(nu)nu/SigmaIF(nu) of the emission band position has been correlated with the epoxy group conversion determined by FTIR. Smooth dependencies were obtained in all cases. This enables one to monitor on line and in real time the epoxy group conversion.We would like to thank the European Commission for funding through the BRITE-EuRam Project (BE97-4472) and to CAM (07N/0002/98)

Consolidation of fir wood by poly(vinyl butyral-covinyl alcohol-co-vinyl acetate) treatment: Study of surface and mechanical characteristics

The authors gratefully acknowledge funding from 2012/00130/004 (Fondos de Investigación de Fco.Javier González Benito, política de reinversión de costes generales, Universidad Carlos III de Madrid) and2011/00287/002 (Acción Estratégica en Materiales Compuestos Poliméricos e Interfases, Universidad Carlos III de Madrid)

Curing of linear and crosslinked epoxy systems: A fluorescence study with dansyl derivatives

The curing of diglycidyl ether of bisphenol A (DGEBA) with N,N′-dimethylethylenediamine (N,N′-DMEDA) or ethylenediamine (EDA) was monitored by fluorescence spectroscopy and Fourier transform infrared (in the near-infrared region). 5-Dimethylamino-naphthalene-1-sulfonamide (DNS) derivatives were used as probes (fluorophores added to the reaction mixture) and labels (fluorophores attached by covalent bonds to diglycidyl reactants). The term containing the ratio of the reaction rate constants for the addition of the secondary and primary amine hydrogens to the epoxide was included in the reduced reaction rate term for the autocatalyzed and catalyzed epoxide curing reactions. The changes in the integrated fluorescence intensities of the labels during the epoxy group conversion indicated, in some cases, the most important changes in the chemical transformations of the reaction mixture: the epoxy group conversion, during which a rapid increase in the tertiary amino group concentration was first observed; the gel point (for EDA); and the entry of the system into the glassy state (for N,N′-DMEDA and EDA). The fluorescence probes monitored neither the gel point nor the threshold of the glassy state. For the DGEBA–N,N′-DMEDA system, a wavy dependence of the integrated fluorescence intensities of the DNS labels on the epoxy group conversion might reflect the molar concentrations of polymer homologues (referred to the initial number of moles in the system) in the reaction mixtures of the diepoxide and secondary diamine.The authors thank the anonymous reviewers for their constructive comments and the European Commission for funding through the BRITE-EuRam project (BE97-4472) and Comunidad Autónoma de Madrid (CAM) (07N/0002/98)