1,721,031 research outputs found
Multi applicable stereocomplex PLA particles decorated with cyclodextrins
No full textIn this work, an innovative approach to covalently anchor cyclodextrins (CDs) on the surface of submicrometric particles, prepared from an equimolar mixture of poly(L-lactide) (PLLA) and poly(D-lactide) (PDLA), was developed. The idea of the applied method lays in the potential reactivity of amino CDs towards the polymer functionalities to produce an aminolysis reaction, which should lead to the direct grafting of cyclodextrin molecules on the polymer surface. A preliminary investigation demonstrated the significant capacity of the modified particles to adsorb a model pollutant (alizarin red) and a hydrophobic drug (ketoprofen)
On an effective approach to improve the properties and the drug release of chitosan-based microparticles
No full textThe work investigated the possibility to develop an easy scalable treatment capable of modifying only the surface of chitosan-based materials, limiting the degradation of the bulk and the burst release of a drug, without compromising the properties of the polymeric matrix. To this aim, microparticles of CHI were superficially coated with poly-(styrene-co-maleic anhydride) (PSMA), taking advantage of the potential reactivity of chitosan amino groups and maleic functionalities of PSMA. The specific reactions/interactions occurring between the two polymers were studied by IR measurements, while FE-SEM analysis evidenced the modification of the morphology of the particles contacted with PSMA. Contact angle measurements demonstrated the change of wettability in the modified systems and TGA analysis allowed to estimate the amount of the deposited PSMA. The above treatment turned out to improve the particle stability both in an acidic environment and in an enzymatic system. The release properties of the treated and of the untreated particles, over a period of 10 h, were tested using, as model drug, the protein Bovine Serum Albumin (BSA). Finally, the cytocompatibility of the developed composite microparticles was assessed on MCF-7 human breast cancer cells, which measurements demonstrated the non-toxicity of the treatment
Preparation Of Polymer/Clay Nanocomposites Via Dispersion Of Silylated Montmorillonite Into A UV Curable Epoxy Matrix
No full textSurface modification of clay minerals plays an important role for their application as fillers for polymeric materials. Among the many modification reactions, the silanization reaction uses alkoxysilanes and exploits the OH reactive sites of the montmorillonite structure. We found that using an excess of silane it is possible to functionalize the clay mineral and, at the same time, to intercalate some monomers or oligomers into the clay mineral galleries, greatly enhancing the interlayer distance. The montmorillonite modified in this way has been then used in the preparation of nanocomposite coatings by mixing it with a photocurable epoxy matrix. After UV irradiation the coatings obtained were submitted to morphological, thermal and mechanical analysis. The photopolymerization kinetics was also investigated. The introduction of the modified montmorillonite allowed to obtain transparent nanocomposite coatings characterized by a mixed intercalated/exfoliated structure and better thermal and scratch resistance performances in comparison with the montmorillonite free coating
Polyhedral oligomeric silsesquioxane (POSS) surface grafting: A novel method to enhance polylactide hydrolysis resistance
Full text linkThis work considers the development of an easy and scalable approach to change the features of poly(L-lactide) (PLLA) films, which is based on the application of a surface treatment with an amino-functionalized polyhedral oligomeric silsesquioxane (POSS). Indeed, the developed approach is based on the potential reactivity of POSS amino group towards the polymer functionalities to produce an aminolysis reaction, which should promote the direct grafting of the silsesquioxane molecules on the polymer surface. Neat and treated films were studied by infrared spectroscopy and X-ray photoelectron spectroscopy, which proved the effectiveness of POSS grafting. Moreover, scanning electron microscopy measurements demonstrated the homogeneous distribution of Si on the film surface treated with the silsesquioxane. The influence of the film treatment on the surface wettability was evidenced by contact angle measurements. These findings demonstrated a relevant enhancement of the surface hydrophobicity, which increase turned out to depend on the conditions applied, as it increased by increasing the reaction temperature and the contact time. Finally, in order to evaluate the stability of neat and of the treated PLLA films the surface morphology of the samples treated with pH 7.4 buffer at 50 °C was studied
On the development of an effective method to produce conductive pcl film
Full text linkThe aim of this work was to develop an effective approach to improve the graphite dispersion and, consequently, the electrical conductivity of nanocomposites based on polycaprolactone (PCL) and graphite nanoplates (GNP). With this aim, a polymeric additive was designed to be compatible with the polymer matrix and capable of interacting with the graphite layers. Indeed, the compound consists of a low molecular mass PCL ending with a pyrene group (Pyr‐PCL). The exploitation of such a molecule is expected to promote from one side specific interactions of the pyrene terminal group with the surface of graphite layers and from the other to guarantee the compatibility with PCL, having a chain with the same nature as the matrix. The features of the nanocomposites prepared by directly blending PCL with GNP were compared with those of the same systems also containing the additive. Moreover, a neat mixture, based on PCL and PCL‐Pyr, was prepared and characterized. The specific interactions between the ad hoc synthesized compound and graphite were verified by UV measurements, while SEM characterization demonstrated a finer dispersion of GNP in the samples containing Pyr‐PCL. GNP nucleating effect, proved by the increase in the crystallization temperature, was observed in all the samples containing the nanofiller. Moreover, a significant improvement of the electrical conductivity was found in the systems based on the pyrenyl terminated PCL. This peculiar and interesting phenomenon was related to the optimized nanofiller dispersion and to the ameliorated compatibility with the polymer matrix
Star-shaped furoate-PCL: An effective compound for the development of graphite nanoplatelets-based films
No full textThe aim of this study was to improve the dispersibility of graphite nanoplatelets (GNP) in films based on poly(ε-caprolactone) (PCL). To this end, a star-shaped PCL with furoate-like end groups (PCL-Fur), potentially capable of interacting/reacting with the surface of the graphene layers through Diels-Alder reactions, was synthesized by enzymatic catalysis. PCL-Fur was applied for film development by blending it with a commercial high molecular weight PCL (PCL-L) and GNP. The reactivity of GNP with respect to furoate groups was demonstrated by studying the thermal behavior of the GNP/methyl 2-furoate system, while the dispersibility of graphite in the solution containing PCL-Fur was studied by UV–Vis measurements. GNP proved to be well dispersed and adhered to the polymer matrix in the PCL-L/PCL-Fur/GNP composite films prepared by casting, in contrast to the films based on the neat PCL-L. This fine GNP dispersion resulted in films characterized by high electrical conductivity
Preparation, Characterization, and Properties of Novel PSMA−POSS Systems by Reactive Blending
No full textNovel hybrid systems based on styrene−maleic anhydride copolymers (PSMA) and a polyhedral oligomeric silsesquioxane characterized by an amino group as reactive side (POSS-NH2) have been synthesized by one-step reactive blending. The features of the above materials were compared with those of systems based on polystyrene (PS) or an unreactive POSS in order to highlight the effect of both the reactivity of the silsesquioxane and the polymer matrix functionality on the material final characteristics. FTIR measurements evidenced the occurrence of imidization reaction between the MA group of PSMA and the amino group of POSS molecule, with the consequent formation of a cyclic imide linkage binding POSS to the polymer backbone. This reaction turned out to promote POSS distribution in the polymer matrix, as only the systems characterized by the aforementioned functionalities allowed to obtain a silsesquioxane dispersion at nanometric level. By following the evolution of the system features, in terms of glass transition temperature (Tg), morphology, yield, and crystallinity, with the mixing time, it has been verified that using a Tmix lower than POSS melting temperature, a surface reaction at the POSS crystal/polymer boundary occurs, leading to the formation of a very peculiar two-phase structure evolving with time. The two phases have been found to contain different POSS concentrations. Biphasic systems, studied by means of differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA), have showed two Tg, depending on the presence of unbound POSS acting as a plasticizer. Films prepared from the systems PSMA−POSS containing low amounts of silsesquioxane (up to 10 wt %) have been found to be completely transparent, while the transparency of those based on higher POSS content has been achieved only after removing the unbound POSS. Indeed, the role of silsesquioxane on surface properties has been assessed by evaluating film wettability
Thermoreversible Cross-Linked Rubber Prepared via Melt Blending and Its Nanocomposites
No full textA covalent adaptable network based on the thermoreversible cross-linking of an ethylene-propylene rubber through Diels-Alder (DA) reaction was prepared for the first time through melt blending as an environmental-friendly alternative to traditional synthesis in organic solvents. Functionalization of the rubber with furan groups was performed in a melt blender and subsequently mixed with different amounts of bismaleimide in a microextruder. Cross-linking was confirmed by FT-IR spectroscopy and insolubility at room temperature, while its thermoreversible character was confirmed by a solubility test at 110 °C and by remolding via hot-pressing. Mechanical and thermomechanical properties of the obtained rubbers showed potential to compete with conventionally cross-linked elastomers, with stiffness in the range 1-1.7 MPa and strain at break in the range 200-500%, while allowing recycling via a simple melt processing step. Nanocomposites based on the thermoreversible rubber were prepared with reduced graphene oxide (rGO), showing significantly increasing stiffness up to ca. 8 MPa, ∼2-fold increased strength, and thermal conductivity up to ∼0.5 W/(m K). Results in this paper may open for industrially viable and sustainable applications of thermoreversible elastomers
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