Paola Fabbri

Flame retarding poly(methyl methacrylate) with nanostructured organic–inorganic hybrids coatings

Abstract Organic–inorganic hybrid materials were prepared starting from tetraethoxysilane and α- or α,ω-triethoxysilane terminated poly(e-caprolactone) (PCL–Si) using the sol–gel process. In all cases the formation of nanocomposites with a high level of interpenetration between organic and inorganic phases was noted. Poly(methyl methacrylate) slabs were dip-coated with PCL–Si/silica hybrids and a very strong increase of the flame resistance (also after UV irradiation) was noted for all coating compositions without marked differences with respect to hybrid compositions. This behavior was attributed to a preferential segregation of silica onto the outer surface, as evidenced by XPS analysis.

Solvent and Substrate Contributions to the Formation of Breath Figure Patterns in Polystyrene Films

The generation of ordered porous polymer structures by the breath figures (BFs) method has long been described as a complex phenomenon, in which several parameters combine in a fairly unknown way. The type of polymer and solvent, degree of humidity, and additives are just a few examples of the several parameters that have been described as playing a role in the generation of BFs. This work reports a detailed investigation over the role played by the solvent in the process of BFs generation from polystyrene (PS) solutions spread over different substrates, and discusses the geometrical aspects of the pores via a quantitative point of view by using a purposely developed software for image analysis. Results show that thermodynamic affinity between polymer and solvent is the key parameter for BFs formation, along with other solvent characteristics such as water miscibility, boiling point, and enthalpy. According to our findings, the role played by the substrate is strictly related to the type of solvent used in the generation of BFs.

Porous scaffolds of polycaprolactone reinforced with in situ generated hydroxyapatite for bone tissue engineering.

Polycaprolactone/hydroxyapatite (PCL/HA) composites were prepared by in situ generation of HA in the polymer solution starting from the precursors calcium nitrate tetrahydrate and ammonium dihydrogen phosphate via sol–gel process. Highly interconnected porosity was achieved by means of the salt-leaching technique using a mixture of sodium chloride and sodium bicarbonate as porogens. Structure and morphology of the PCL/HA composites were investigated by scanning electron microscopy, and mechanical properties were determined by means of tensile and compression tests. The possibility to employ the developed composites as scaffolds for bone tissue regeneration was assessed by cytotoxicity test of the PCL/HA composites extracts and cell adhesion and proliferation in vitro studies.

Transparent and conductive graphene oxide/poly(ethylene glycol) diacrylate coatings obtained by photopolymerization

Water-dispersed graphene oxide sheets were used to prepare graphene/poly(ethylene glycol) diacrylate resin composites by photopolymerization. It was found that graphene sheets undergo excellent morphological distribution within the resin system, giving rise to transparent composites with unaltered thermal properties with respect to the neat resin, that are electrically conductive at loading ratios as low as 0.02 wt.-% of graphene oxide. The proposed strategy based on photopolymerization provides an easy, energy-saving and environmental friendly technique that can find a wide application in coating technology, mainly for electromagnetic shielding and antistatic coatings.

Disposable fluorescence optical pH sensor for near neutral solutions.

The design, development and performance evaluation of a fluorescence-based pH sensor for on-line measurements is presented. The pKa of the sensing element has been calculated to be 7.9, thus the sensor is suitable for measurement of near neutral solutions. The sensor consists of a low-cost disposable polymer sensing probe, in contact with the solution under test, interrogated by an optoelectronic transduction system. The pH sensitive dye is based on fluorescein O-methacrylate, which has been covalently linked to a hydrogel matrix, realized through the use of HEMA (2-hydroxyethyl methacrylate), HDDA (1,6-hexanediol diacrylate) and PEGDA (polyethylene glycol diacrylate). The optical interrogation setup, together with the electronics, has been developed to acquire and process the fluorescence signal. The sensor works over a pH range between 6.5 and 9.0. In the range between 7.0 and 8.0, the sensor shows a linear behavior with a maximum linearity error of 5%. Thanks to the good performance of the sensing element and transduction system, the short term drift of the reading (measured over 40 min) is lower than 0.15%. The measuring system also exhibits good performance in terms of response time and reproducibility.

45S5 Bioglass®-derived scaffolds coated with organic–inorganic hybrids containing graphene

Highly porous 45S5 Bioglass®-based scaffolds fabricated by a foam replication technique were coated with electrically conductive organic-inorganic hybrid layers containing graphene by a solution method. α,ω-Triethoxysilane terminated poly (ethylene glycol) and tetraethoxysilane were used as the precursors of the organic-inorganic hybrid coatings, that contained 1.5 wt.% of homogeneously dispersed graphene nanoplatelets. The resulting coated scaffolds retained their original high porosity and interconnected pore structure after coating. The presence of graphene did not impair the bioactivity of the scaffolds in simulated body fluid. Initial tests carried out using MG-63 cells demonstrated that both uncoated scaffolds and scaffolds coated with organic/inorganic hybrids containing graphene offered the cultured cells an adequate surface for cell attachment, spreading and expression of extracellular matrix. The results showed that scaffolds coated with graphene are biocompatible and they can support cellular activity. The electrical conductivity introduced by the coating might have the potential to increase tissue growth when cell culture is carried out under an applied electric field.

Poly(caprolactone)/silica organic-inorganic hybrids as protective coatings for poly(methyl methacrylate) substrates

SummariesOrganic-inorganic hybrid materials (also known as ceramers or phase-interconnected nanocomposites) were prepared starting with tetraethyoxysilane and α,θ-triethoxysilane-terminated poly(ε-caprolactone) (PCL-Si) using the sol-gel process. In all cases the formation of nanocomposites with a high level of interpenetration between PCL and SiO2 phases was noted. Poly(methyl methacrylate) (PMMA) slabs were dip-coated with PCL-Si/silica hybrids and a preferential segregation of silica on to the outer surface was found, together with a PCL-rich coating PMMA interface. In all cases, a marked reduction in both the average roughness and the apparent friction coefficient was noted with respect to the uncoated PMMA. All the PCL-Si/SiO2-coated samples showed a significant increase in flame resistance before and after UV irradiation, while improvements in the anti-scratch properties were noted only in the case of the PMMA coated with silica-rich ceramers.RésuméDes matériaux hybrides organiques-inorganiques (connus également sous le nom de “ceramers et de “phase interconnected nanocomposites”) étaient préparés à partir du poly (ε- caprolactone) à fins de chaînes tétraéthoxysilane et α,ω-triéthoxysilane (PCL-Si) au moyen du procédé sol-gel. Dans tous les cas on a noté la formation de nanocomposites et un niveau élevé d’interpénétration entre les phases PCL et SiO2. Des plaques de poly(méthacrylate de méthyle) étaient revêtues, par immersion, d’hybrides PCL-Si/silice et on a trouvé une ségrégation préférentielle de silice sur la surface extérieur, aussi un revêtement riche en PCL au niveau de l’interface du PMMA. Dans tous les cas on a noté une diminution et de la rugosité moyenne et du coefficient de friction apparent par rapport au PMMA non revêtu. Tous les échantillons revêtus de PCL-Si/SiO2 ont manifesté une importante augmentation de résistance au feu avant et après irradiation UV, tandis que des améliorations de propriétés anti-eraflures étaient notées seulement dans le cas du PMMA qui était revêtu de ceramers riches en silice.ZusammenfassungOrganisch/anorganische Hybridmaterialien (auch bekannt als Keramere oder Phasenverbundene Nanokomposite) wurden durch einen Sol-Gel Prozess aus Tetraethoxysilan und α,ω-triethoxysilanterminierten Poly(ε-caprolacton) (PCL-Si) hergestellt. In allen Fällen ging die Bildung der Nanokomposite einher mit einem hohen Grad von gegenseitiger Penetration zwischen der PCL-Phase und der SiO2-Phase. Poly(methyl methacrylate) (PMMA)-Platten wurden in PCL-Si/Silikathybriden tauchbeschichtet. Wir stellten fest, dass sich das Silikat bevorzugt and der Außenoberfläche absetzte, während das Interface mit den PMMA-Platten reich an PCL war. In allen Fällen stellten wir eine deutliche Reduktion in der durchschnittlichen Rauheit der Platten und einen geringeren Reibungskoeffizienten, verglichen mit unbehandeltem PMMA, fest. Alle PCL-Si/SiO2-beschichteten Proben zeigten deutlich größere Feuerwiderstandsfähigkeit sowohl vor als auch nach UV-Härtung, während nur die Behandlung mit stark Silikat-haltigen Kerameren die Kratzfestigkeit nachhaltig verbesserte.

Poly(ε-caprolactone)-poly(fluoroalkylene oxide)-poly(ε-caprolactone) block copolymers as surface modifiers of poly(vinyl chloride)

SummariesBlends of poly(ε-caprolactone)-poly(fluoroalkylene oxide)-poly(ε-caprolactone) (PCL-PFPE-PCL) triblock copolymers (with different length of PFPE and PCL segments) and poly(vinyl chloride) (PVC) were prepared by casting from tetrahydrofuran solution. DSC analysis revealed a complex morphology deriving from miscibility between PCL and PVC segments. XPS analysis showed strong surface enrichment of PFPE segments for all films prepared. Treatment with a PFPE selective solvent showed that the fraction of PCL-PFPE-PCL removed from surface decreased with increasing length of PCL blocks, indicating an anchorage effect by PCL segments with respect to PVC matrix.RésuméDes mélanges de tribloc polymères, poly(caprolactone-b-perfluoropolyéther-b-caprolactone) (PCL-PFPE-PCL) (les segments PFPE ayant une longeur différente de celle des segments PCL) et de poly(chlorure de vinyle) (PVC) ont été préparées par moulage [“casting”] à partir d’une solution de tetrahydrofuran. Une analyse par DSC a révélé une morphologie complexe provenant de la miscibilité entre les segments PCL et PVC. Une analyse XPS a révélé un fort enrichissement de la surface par des segments PFPE dans le cas de tous les feuils préparés. Le traitement par solvant sélectif (PFPE) a démontré que la quantité de PCL-PFPE-PCL enlevé de la surface diminuait au fur et à mesure que la longeur des blocs PCL augmentait, ce qui indiquait qu’il y avait un effet d’ancrage par les segments PCL vis à vis de la matrice PVC.ZusammenfassungMischungen von Poly (Caprolacton-b-Perfluoropolyether-b-Caprolacton) (PCL-PFPE-PCL) Dreiblockcopolymere mit unterschiedlichen Längen der PFPE und PCL Segmente und PVC wurden mittlels einer Tetrahydrofuran-Lösung hergestellt.Eine DSC Analyse zeigte eine komplexe Morphologie, die sich aus der Mischbarkeit der PCL und PFPE-Segmente ergibt. Eine XPS-Analyse wies darüberhinaus auf, daß sich die Oberfläche aller hergestellten Filme stark mit PFPE angereichert hatte. Die Behandlung mit einem PFPE-spezifischen Lösungsmittel zeigte, daß der Anteil der PCL-PFPE-PCL-Moleküle, der von der Oberfläche entternt wurde, mit zunehmender Länger der PCL-Segmente abnahm. Dies weist darauf hin, das die PCL-Segmente bezüglich der PVC-Matrix einen Ankereffekt haben.

Poly(vinyl alcohol)-Based Film Potentially Suitable for Antimicrobial Packaging Applications

This work aimed at developing a thin and water-resistant food-grade poly(vinyl alcohol) (PVOH)-based matrix able to swell when in contact with high moisture content food products without rupturing to release antimicrobial agents onto the food surface. This film was prepared by blending PVOH and 7.20% (wt/wt of PVOH) of poly(ethylene glycol) (PEG) with citric acid as crosslinking agent. The film-forming solution was then casted onto a flat surface and the obtained film was 60 μm in thickness and showed a good transparency (close to T = 100%) in the visible region (400 to 700 nm). After immersion in water for 72 h at room temperature, the crosslinked matrix loses only 19.2% of its original weight (the percentage includes the amount of unreacted crosslinking agent, antimicrobial in itself). Water content, degree of swelling, and crosslinking density of the film prove that the presence of PEG diminishes the hydrophilic behavior of the material. Also the mechanical properties of the wet and dry film were assessed. Alongside this, 2.5% (wt/wt of dry film) of grapefruit seed extract (GSE), an antimicrobial agent, was added to the film-forming solution just before casting and the ability of the plastic matrix to release the additive was then evaluated in vitro against 2 GSE-susceptible microorganisms, Salmonella enteritidis and Listeria innocua. The results indicate that the developed matrix may be a promising food-grade material for the incorporation of active substances.

Construction and evaluation of a disposable pH sensor based on a large core plastic optical fiber

The fabrication and characterization of a disposable optical fiber sensor for the detection of pH in the range 5-8 are described. The sensing element is a drop of sol-gel hybrid material containing phenol red and deposited onto the tip of a large core plastic optical fiber. This fiber is also exploited for the optical interrogation. This probe can be used as a disposable part of a measuring system. The dynamic range and temporal response of the sensor are here investigated.