Gennaro Gentile

Eco-Challenges of Bio-Based Polymer Composites

In recent years bio-based polymer composites have been the subject of many scientific and research projects, as well as many commercial programs. Growing global environmental and social concern, the high rate of depletion of petroleum resources and new environmental regulations have forced the search for new composites and green materials, compatible with the environment. The aim of this article is to present a brief review of the most suitable and commonly used biodegradable polymer matrices and NF reinforcements in eco-composites and nanocomposites, with special focus on PLA based materials.

Polyacrylates for conservation: chemico-physical properties and durability of different commercial products

With the aim of identifying the most suitable commercial water dispersed polyacrylates to be used in the conservation and restoration field, the properties of four commercial polymers were compared with those shown by Primal AC33, a product made and commercialized by Rohm and Haas, widely used as a consolidating and adhesive agent for art works, and nowadays out of production. Chemical, molecular, thermal, mechanical and optical investigation techniques were applied on films obtained from the polymer water dispersions cast at room temperature. Selected polymers were characterized before and after artificial aging under a xenon-arc lamp in order to determine their photooxidative stability. It was found that Acrilem IC15, among the selected products, was the material with improved physico-chemical properties and photooxidative stability with respect to that shown by the discontinued Primal AC33.

Water-dispersed polymers for the conservation and restoration of Cultural Heritage: a molecular, thermal, structural and mechanical characterisation

A molecular, thermal, structural and mechanical characterisation of two different commercial water-dispersed polymers, i.e. an unreactive aliphatic polyetherurethane (trade name Akeogard AT40) and a VDF/HFP/TFE terpolymer (trade name Fluorobase T300) has been performed by means of differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and dynamic mechanical thermal analysis (DMTA), Fourier transform infrared spectroscopy (FTIR) and Fourier transform nuclear magnetic resonance (FT NMR), wide and small angle X-ray scattering (WAXS and SAXS) techniques and an Instron machine. Such polymers were selected from among the available products used for conservation and restoration by Cultural Heritage, with the view of using water-based polyurethanes and fluorinated copolymers as coatings for artefacts belonging to Cultural Heritage, consisting of natural fibrous polymers, mainly textiles. The results obtained so far suggest that a comparatively higher potential for the conservation and restoration of textiles with a cultural value is shown by AT40 polyurethane. Notwithstanding this, the structural properties assessed in water-cast films for both the polymers indicate that desired properties could be conferred by suitably selecting the chemical and molecular structure of the starting monomeric units.

Biodegradable PVOH-based foams for packaging applications

Biodegradable poly(vinyl alcohol) (PVOH) based foams were prepared through an ecofriendly methodology. Different amount of recycled multilayer cartons (MC), composed of cellulose and low-density polyethylene (80/20 wt/wt), were added as a direct cellulose source to PVOH. Foams were realized through a modified overrun process without using chemical agents or promoting chemical reactions. In particular, the air entrapped during the high-speed mixing of the PVOH/MC water dispersion was able to create a porous morphology. The effects of the addition of MC on microstructure, swelling behavior, and mechanical and thermal properties of foams were investigated. Materials were characterized by a dual-pore structure. Improvements of the swelling behavior, mechanical properties, and thermal stability were recorded as a function of MC content. These findings can be considered as a result of a good interaction between filler and polymer.

Polyvinyl alcohol biodegradable foams containing cellulose fibres

The preparation of polyvinyl alcohol (PVOH) based foams containing pulp cellulose fibres and microfibrillated cellulose (MFC) fibre is reported, aiming at the realization of sustainable “green-composites.” Foams were obtained through an eco-friendly preparation method able to generate a pore structure by entrapping air into the polymer/filler aqueous dispersion during a high-speed mixing. The effect of pulp cellulose fibres (Bc1000) and MFC on foam microstructure, water vapor absorption behavior, and mechanical properties was studied. The addition of small amount of MFC (1–5 wt%) induced a progressive decrease of the average cell diameter and an increase of the cell density; whereas Bc1000 cellulose fibres affected the cell shape and regularity of PVOH based foams. A reduction of the water vapor absorption in PVOH/MFC and PVOH/Bc1000 was recorded with respect to neat PVOH foam, in particular for foams containing pulp cellulose fibres. Finally, both MFC and Bc1000 increased the Young modulus and the compression deflection of PVOH based foams.

Amorphized cellulose as filler in biocomposites based on poly(ɛ-caprolactone)

Amorphous cellulose particles, obtained through a solvent-free mechano-chemical process, have been tested for the first time as a potential filler for biodegradable composites based on poly(ɛ-caprolactone) (PCL). Commercial cellulose fibers have been also tested for comparison. An effective interfacial strategy based on a compatibilizing agent, a modified PCL, has been used to improve the polymer/filler interfacial adhesion. Composites have been tested through physico-mechanical characterizations and soil burial degradation tests, in order to evaluate the influence of cellulose structure and morphology and polymer/filler interfacial adhesion on the final properties of the realized materials. The use of the amorphous cellulose particles combined with the presence of a suitable interfacial agent has allowed to modulate relevant technological properties of the realized composites, such as tensile and thermal properties, water absorption, water vapor transmission rate and biodegradation kinetic.

Silicon-Filled Rectangular Waveguides and Frequency Scanning Antennas for mm-Wave Integrated Systems

We present a technology for the manufacturing of silicon-filled integrated waveguides enabling the realization of low-loss high-performance millimeter-wave passive components and high gain array antennas, thus facilitating the realization of highly integrated millimeter-wave systems. The proposed technology employs deep reactive-ion-etching (DRIE) techniques with aluminum metallization steps to integrate rectangular waveguides with high geometrical accuracy and continuous metallic side walls. Measurement results of integrated rectangular waveguides are reported exhibiting losses of 0.15 dB/ λg at 105 GHz. Moreover, ultra-wideband coplanar to waveguide transitions with 0.6 dB insertion loss at 105 GHz and return loss better than 15 dB from 80 to 110 GHz are described and characterized. The design, integration and measured performance of a frequency scanning slotted-waveguide array antenna is reported, achieving a measured beam steering capability of 82 ° within a band of 23 GHz and a half-power beam-width (HPBW) of 8.5 ° at 96 GHz. Finally, to showcase the capability of this technology to facilitate low-cost mm-wave system level integration, a frequency modulated continuous wave (FMCW) transmit-receive IC for imaging radar applications is flip-chip mounted directly on the integrated array and experimentally characterized.

Artificial Biomelanin: Highly Light-Absorbing Nano-Sized Eumelanin by Biomimetic Synthesis in Chicken Egg White

The spontaneous oxidative polymerization of 0.01-1% w/w 5,6-dihydroxyindole (DHI) in chicken egg white (CEW) in the absence of added solvents leads to a black, water-soluble, and processable artificial biomelanin (ABM) with robust and 1 order of magnitude stronger broadband light absorption compared to natural and synthetic eumelanin suspensions. Small angle neutron scattering (SANS) and transmission electron microscopy (TEM) analysis indicated the presence in the ABM matrix of isolated eumelanin nanoparticles (≤100 nm) differing in shape from pure DHI melanin nanoparticles (SANS evidence). Electron paramagnetic resonance (EPR) spectra showed a slightly asymmetric signal (g ∼ 2.0035) similar to that of solid DHI melanin but with a smaller amplitude (ΔB), suggesting hindered spin delocalization in biomatrix. Enhanced light absorption, altered nanoparticle morphology and decreased free radical delocalization in ABM would reflect CEW-induced inhibition of eumelanin aggregation during polymerization accompanied in part by covalent binding of growing polymer to the proteins (SDS-PAGE evidence). The technological potential of eumelanin nanosizing by biomimetic synthesis within a CEW biomatrix is demonstrated by the preparation of an ABM-based black flexible film with characteristics comparable to those of commercially available polymers typically used in electronics and biomedical applications.

Hybrid ferroelectric–polymer microfluidic device for dielectrophoretic self-assembling of nanoparticles

Carbon nanoparticles are becoming ubiquitous in many fields of science and technology. However, a grand challenge remains in assembling, patterning, and positioning or even simple manipulation of CNTs for complex functional assemblies. CNTs have in fact enormous perspectives for application in biotechnologies as bactericide agents or as prominent tools for investigating cell mechanisms, or more in general as functionalized nanoparticle-vectors, but their exploitation requires viable technology at the lab-on-a-chip scale. Many approaches have been attempted in developing technologies for manipulating CNTs. One elective approach is based on electric fields driven mechanisms such as DEP forces. A variety of chips have been designed and realized with this aim. Here we report on a novel hybrid microfluidic chip made by assembling a polar-dielectric crystal with polymeric microfluidic channels. One challenging feature of such a hybrid device approach, based on an electrode-free dielectrophoretic (DEP) approach, is that it makes use of surface charge templates for self-assembling and manipulation of CNTs in liquid media directly into a microfluidic channel. Here various examples of self-assembly in microfluidic channels as well as separation and collection of two classes of nano/microparticles are reported. The method can open the way to novel fabrication protocols for the realisation of future flexible devices with new and more complex functionalities, highly desirable in electronics as well as in biotechnology at the lab-on-a-chip scale.

Chitosan hydrogels embedding hyper-crosslinked polymer particles as reusable broad-spectrum adsorbents for dye removal

The removal of dye and toxic ionic pollutants from water is an extremely important issue that requires systematic and efficient adsorbent preparation strategies. To address this challenge, we developed composite chitosan (CS)-based hydrogels containing hyper-crosslinked polymer (HCP) particles to be used as broad-spectrum adsorbents. The goal is to efficiently combine the dye adsorption ability of chitosan and the capacity of the porous particles of trapping pollutant molecules. The HCP particles are well distributed and firmly embedded into the chitosan matrix and the composite hydrogels exhibit improved mechanical properties. Adsorption experiments reveal a synergistic effect between CS and HCP particles, and the samples are able to remove both anionic and cationic dyes (indigo carmine, rhodamine 6G and sunset yellow) from water. The maximum dye uptake is higher than that of comparable biosorbents. Moreover, the mechanical properties of the composite hydrogels are enhanced respect to pure CS, and the samples can be regenerated and reused keeping their adsorption ability unaltered over successive cycles of adsorption, desorption, and washing.