Rapid Solvent-Free Microcrystalline Cellulose Melt Functionalization with L-Lactide for the Fabrication of Green Poly-Lactic Acid Biocomposites

A green approach is proposed to achieve a rapid surface functionalization of microcrystalline cellulose (MCC) in 30 min by a solvent-free grafting by the reaction of L-lactide through compression molding without the need for an inert atmosphere. A sufficient hydrophobization of the MCC surface is achieved with an amount of grafted poly(L-lactic acid) (PLLA) oligomers of 7 wt % with respect to MCC. The obtained PLLA-g-MCC is subsequently melt-compounded with poly(lactic acid) (PLA) through extrusion and injection molding. As a result of higher compatibility and interfacial adhesion of the functionalized filler with PLA, PLA/ MCC-g-PLLA biocomposites with a cellulose content ranging from 4 to 20 wt % exhibit an enhancement in important physicochemical properties (i.e., water vapor barrier, crystallinity, stiffness) compared to both pure PLA and formulations containing an equal or higher amount of nonfunctionalized MCC. At the same time, the materials retain the mechanical strength and resistance to thermal degradation of PLA. The physicochemical characteristics, excellent biocompatibility, and biodegradability of PLA and cellulose and the simplicity, rapidity, and cost-effectiveness of the grafting process render these biocomposites suitable for several applications within the plastics domain including packaging, agriculture, automotive, consumer goods, and household appliances

Photochromic Polymer Gratings

In this Full Paper, the possibility of reversibly changing the diffraction efficiency of gratings, fabricated by soft molding lithography on polymer films, containing photochromic molecules, is demonstrated. In particular, alternating UV and visible laser irradiation of the gratings causes the doped photochromic molecules to undergo transformations, which induce reversible dimensional changes to the samples. As a result, reversible changes are monitored in the intensity of the beams of a diode laser, transmitted and diffracted from the gratings. These changes affect the diffraction efficiency, which is increased upon irradiation with UV and decreased after irradiation with visible laser light. Such gratings are promising candidates for the fabrication of modern optical components such as optical switching devices

Directional enhancement of refractive index and tunable wettability of polymeric coatings due to preferential dispersion of colloidal TiO2 nanorods towards their surface

Abstract We demonstrate the fabrication of nanocomposite coatings, of organic-capped colloidal TiO 2 nanorods dispersed into a poly(methyl methacrylate) matrix, with rising value of refractive index from the bottom to the top layers, and UV-induced surface wettability alteration, in a reversible manner. This behaviour is attributable to preferential dispersion of the TiO 2 nanoparticles towards the superficial layers of the coatings. Above a critical TiO 2 loading, the nanorods at the surface form aggregates deteriorating the optical and the surface properties of the nanocomposites. The optimal conditions for nanocomposite films preparation in terms of optimized nanorods dispersion, optical clarity, and surface smoothness are determined

Photocatalytic Activity of Cellulose Acetate Nanoceria/Pt Hybrid Mats Driven by Visible Light Irradiation

A photocatalytic system for the degradation of aqueous organic pollutants under visible light irradiation is obtained by an innovative approach based on ceria/platinum (Pt) hybrid nanoclusters on cellulose acetate fibrous membranes. The catalytic materials are fabricated by supersonic beam deposition of Pt nanoclusters directly on the surface of electrospun cellulose acetate fibrous mats, pre-loaded with a cerium salt precursor that is transformed into ceria nanoparticles directly in the solid mats by a simple thermal treatment. The presence of Pt enhances the oxygen vacancies on the surface of the formed ceria nanoparticles and reduces their band gap, resulting in a significant improvement of the photocatalytic performance of the composite mats under visible light irradiation. Upon the appropriate pretreatment and visible light irradiation, we prove that the most efficient mats, with both ceria nanoparticles and Pt nanoclusters, present a degradation efficiency of methylene blue of 70% and a photodegradation rate improved by about five times compared to the ceria loaded samples, without Pt. The present results bring a significant improvement of the photocatalytic performance of polymeric nanocomposite fibrous systems under visible light irradiation, for efficient wastewater treatment applications

Investigation of the electro-spinnability of alginate solutions containing gold precursor HAuCl4

Alginate nanofibers with an average diameter of 75 nm have been prepared by the electrospinning process. In addition, the spinnability of the solutions in the presence of the gold precursor HAuCl4 was investigated. At low concentrations of HAuCl4 well-formed nanofibers were produced, whereas as its concentration increases the nanofibrous mats present an increased number of bead-like defects. Herein, the in situ preparation of gold nanoparticles (Au NPs) is discussed since sodium alginate (SA) acts as the reducing agent and a mechanism is proposed in order to explain the bead-effect as well as the surface morphology of the alginate fibers decorated with Au NPs

Maltodextrin-amino acids electrospun scaffolds cross-linked with Maillard-type reaction for skin tissue engineering

The goal of this work is the design and the development of scaffolds based on maltodextrin (MD) to recover chronic lesions. MD was mixed with arginine/lysine/polylysine and the electrospinning was successfully used to prepare scaffolds with uniform and continuous nanofibers having regular shape and smooth surface. A thermal treatment was applied to obtain insoluble scaffolds in aqueous environment, taking the advantage of amino acids-polysaccharide conjugates formed via Maillard-type reaction. The morphological analysis showed that the scaffolds had nanofibrous structures, and that the cross-linking by heating did not significantly change the nanofibers' dimensions and did not alter the system stability. Moreover, the heating process caused a reduction of free amino group and proportionally increased scaffold cross-linking degree. The scaffolds were elastic and resistant to break, and possessed negative zeta potential in physiological fluids. These were characterized by direct antioxidant properties and Fe chelation capability (indirect antioxidant properties). Moreover, the scaffolds were cytocompatible towards fibroblasts and monocytes-derived macrophages, and did not show any significant pro-inflammatory activity. Finally, those proved to accelerate the recovery of the burn/excisional wounds. Considering all the features, MD-poly/amino acids scaffolds could be considered as promising medical devices for the treatment of chronic wounds.Authors thank Horizon 2020 Research and Innovation Programme under Grant Agreement No. 814607, for funding the research project

Single-Shot Laser Additive Manufacturing of High Fill-Factor Microlens Arrays

High fill-factor microlens arrays (MLA) are key for improving photon collection efficiency in light-sensitive devices. Although several techniques are now capable of producing high-quality MLA, they can be limited in fill-factor, precision, the range of suitable substrates, or the possibility to generate arbitrary arrays. Here, a novel additive direct-write method for rapid and customized fabrication of high fill-factor MLA over a variety of substrates is demonstrated. This approach uses a single laser pulse to delaminate and catapult a polymeric microdisc from a film onto a substrate of interest. Following a thermal reflow process, the printed disc can be converted into a planoconvex microlens offering excellent sphericity and high smoothness (RRMS< 40 \uc3\u85). Importantly, the transfer of solid microdiscs enables fill-factors close to 100%, not achievable with standard direct-write methods such as inkjet printing or microdispensing. Arbitrary generation of MLA over flexible and curved surfaces, with microlenses presenting a curvature ranging from 20 to 240 \uc2\ub5m and diffraction-limited performance, is demonstrated. The ease of implementation and versatility of the approach, combined with its potential parallelization, paves the way for the high-throughput fabrication of tailored MLA directly on top of functional devices

Stone sustainable protection and preservation using a zein-based hydrophobic coating

In the present work, the efficiency of an ecofriendly 5% (w/v) solution of zein in DMSO was evaluated as protective material for stone. The solution was sprayed on 5 × 5 × 1 cm slabs of Serena stone, a sandstone widely used in Florentine architecture, in order to create a hydrophobic coating. The obtained coating turned out to be hydrophobic, showing WCA of around 120°, while a reduction of 8.4% in water uptake was observed during 15 days. SEM and profilometer analyses stated that the zein coating application resulted in the formation of a compact film on the stone's surface with a continuous structure characterized by micro-scale roughness. XPS analysis confirmed the presence of the thin conformal layer over the stone. A mechanism of hydrophobic surface formation, in which both the roughness and the solvent's evaporation style are believed to play a significant role, was finally proposed. Accelerated aging tests indicated a good resistance to aging in terms of hydrophobicity and color variations, where the overall color parameter of ΔE &lt; 2.0 was maintained, indicating invisible color changes to the naked eye. This sustainable approach can be easily scaled and may represent a valuable alternative to the most common synthetic treatments used nowadays in stone protection.In the present work, the efficiency of an ecofriendly 5% (w/v) solution of zein in DMSO was evaluated as protective material for stone. The solution was sprayed on 5 x 5 x 1 cm slabs of Serena stone, a sandstone widely used in Florentine architecture, in order to create a hydrophobic coating. The obtained coating turned out to be hydrophobic, showing WCA of around 120 degrees, while a reduction of 8.4% in water uptake was observed during 15 days. SEM and profilometer analyses stated that the zein coating application resulted in the formation of a compact film on the stone's surface with a continuous structure characterized by micro-scale roughness. XPS analysis confirmed the presence of the thin conformal layer over the stone. A mechanism of hydrophobic surface formation, in which both the roughness and the solvent's evaporation style are believed to play a significant role, was finally proposed. Accelerated aging tests indicated a good resistance to aging in terms of hydrophobicity and color variations, where the overall color parameter of Delta E < 2.0 was maintained, indicating invisible color changes to the naked eye. This sustainable approach can be easily scaled and may represent a valuable alternative to the most common synthetic treatments used nowadays in stone protection

Paper sensors based on fluorescence changes of carbon nanodots for optical detection of nanomaterials

This article belongs to the Special Issue Sustainable Development of Nanotechnologies: Risks and Opportunities for Occupational Safety and Health.A paper sensor was designed in order to detect the presence of nanomaterials, such as ZnO and silica nanoparticles, as well as graphene nanoplatelets (GnP), based on fluorescence changes of carbon nanodots. Paper strips were functionalized with carbon nanodots using polyvinyl alcohol (PVA) as binder. The carbon nanodots were highly fluorescent and, hence, rendered the (cellulosic) paper stripes emissive. In the presence of silica and ZnO nanoparticles, the fluorescence emission of the carbon nanodots was quenched and the emission decay was shortened, whereas in the presence of GnP only emission quenching occurred. These different photoluminescence (PL) quenching mechanisms, which are evident from lifetime measurements, convey selectivity to the sensor. The change in fluorescence of the carbon dot-functionalized paper is also evident to the naked eye under illumination with a UV lamp, which enables easy detection of the nanomaterials. The sensor was able to detect the nanomaterials upon direct contact, either by dipping it in their aqueous dispersions, or by sweeping it over their powders. The use of the proposed optical sensor permits the detection of nanomaterials in a straightforward manner, opening new ways for the development of optical sensors for practical applications.This research was part of the Project “Nano and Key enabling technologies within the innovation processes: risk and opportunities in occupational settings by prevention through design (NanoKey__EPTR0003))”, funded by the Italian Workers’ Compensation Authority (INAIL) and coordinated in cooperation between the INAIL Department of Occupational and Environmental Medicine Epidemiology and Hygiene, and the Italian Institute of Technology (IIT).Peer reviewe