1,721,023 research outputs found
Double percolation of multiwalled carbon nanotubes in polystyrene/polylactic acid blends
No full textSelective localization of multi-walled carbon nanotubes (MWCNT) in polylactic acid/polystyrene (PLA/PS) bicontinuous blends is presented in this work. A masterbatch of PS with a 2 wt% content of MWCNT is prepared and then melt mixed with different amounts of PLA. This two-step process results in a double percolated morphology where PS percolates the PLA phase, and MWCNTs percolate the PS phase. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) evidence, respectively, the bicontinuous morphology and the high selectivity of MWCNT localization in the system. Double percolation leads to a very low electrical percolation threshold of about 0.45 vol% MWCNT on total volume and an electrical conductivity of 10(-9) S/cm
Light-responsive polymer micro-and nano-capsules
No full textA significant amount of academic and industrial research efforts are devoted to the
encapsulation of active substances within micro- or nanocarriers. The ultimate goal of core–shell
systems is the protection of the encapsulated substance from the environment, and its controlled
and targeted release. This can be accomplished by employing “stimuli-responsive” materials as
constituents of the capsule shell. Among a wide range of factors that induce the release of the
core material, we focus herein on the light stimulus. In polymers, this feature can be achieved
introducing a photo-sensitive segment, whose activation leads to either rupture or modification
of the diffusive properties of the capsule shell, allowing the delivery of the encapsulated material.
Micro- and nano-encapsulation techniques are constantly spreading towards wider application fields,
and many different active molecules have been encapsulated, such as additives for food-packaging,
pesticides, dyes, pharmaceutics, fragrances and flavors or cosmetics. Herein, a review on the
latest and most challenging polymer-based micro- and nano-sized hollow carriers exhibiting a
light-responsive release behavior is presented. A special focus is put on systems activated by
wavelengths less harmful for living organisms (mainly in the ultraviolet, visible and infrared range),
as well as on different preparation techniques, namely liposomes, self-assembly, layer-by-layer, and
interfacial polymerizatio
Photo-triggered release in polyamide nanosized capsules
No full textIn this work, nanosized capsules based on a lightly cross-linked polyamide containing azobenzene moieties in the main chain were synthesized by miniemulsion interfacial polymerization. The obtained nanocapsules were loaded either with toluene or with the fluorescent probe coumarin-6 as a core. Diameters of the nanocapsules were in the 100-900 nm range, depending on the selected emulsion conditions. The morphology and shape of the samples were observed by TEM and SEM while the emulsion droplets and nanocapsules size was measured by DLS. Under continuous UV irradiation the polymer underwent E-Z photoisomerization allowing the release of the encapsulated material. Variation in diameter of the nanocapsules with the time of UV irradiation was detected through DLS analysis. 10-30% growth was observed, depending on the sample. The kinetics of release of coumarin-6 was followed by spectrofluorimetry in ethanol. In absence of irradiation, the fluorescence intensity appeared to be constant over time, while it increased when the sample was irradiated with 360 nm UV light
Pros and cons of melt annealing on the properties of MWCNT/polypropylene composites
No full textThe combined effect of melt annealing and surface modification of multiwalled carbon nanotubes (MWCNT) on polypropylene (PP) based nanocomposites is reported. Melt annealing markedly improved the filler dispersion in PP. The rheological and electrical percolative threshold was achieved at a content of 3 wt% MWCNT, due to the dynamic reconstruction of nanotube network in the polymer matrix. This behaviour was particularly evident in the case of surface-modified MWCNT. However, the heat treatment also induced an overall worsening of mechanical properties due to polymer heterogeneous oxidation at a microscopic scale, as detected by oxygen mapping through SEM/EDS. Crack initiation sites eventually leading to the failure of the polymer were formed due to peroxide-mediated spreading of oxidation, radiating from residual polymerisation catalyst particles. FTIR-ATR spectroscopy demonstrated that blooming of the phenol stabilizer due to thermal annealing was responsible for early oxidation of polypropylene. The reported results highlight the advantages and drawbacks of physical strategies designed to improve the dispersion stability of nanotubes in polymer nanocomposites
Improving the Process Ability of Poly(3-Hydroxybutyrate) By A Polyphenolic Natural Additive
Full text linkThe severe environmental issues generated by the non-biodegradability of most polymeric materials has
fostered the search for more eco-friendly solutions. Polyhydroxybutyrate (PHB), produced by bacterial
cells and easily hydrolyzed is one of appealing choice but its properties are still not competitive with
those of standard polymers. Among others, one reason is related to the fact that the high processing
temperature (due to the high crystallization point) is responsible for severe thermal degradation. In this
paper, the effect of Tannic Acid (TA) as a thermal stabilizing processing agent for HPB is investigated by
rheological as well as calorimetric techniques under conditions similar to those used in real processing
applications. The results show that TA is effective in improving the thermal stability and processability of
PHB, while keeping its biodegradable attitude. Compared to neat PHB, TA containing samples show a
lower and delayed thermal degradation. FTIR measurements support the hypothesis that stabilization is
determined by TA/PHB crosslinkin
Photo-responsive polymer nanocapsules
No full textThis work reports on the preparation of UV-light responsive nanocapsules based on cross-linked polyamide, obtained by miniemulsion interfacial polymerization. The photo-triggered E-Z transition of azobenzene moieties of the polymer backbone enabled controlled release of encapsulated molecules. Appropriate selection of emulsion conditions allowed tailoring size distribution of the resulting nanocapsules. The light responsiveness of the nanocapsule systems has been evaluated by monitoring size change and release of a fluorescent probe upon UV irradiation, and an unambiguous relationship between capsule size and release kinetics has been highlighted. In particular, the smaller the capsule size, the faster the achieved release. Therefore, the photoresponsiveness of the nanosized capsule systems can be modulated by a proper selection of emulsion and processing parameters. The significance of the reported results lies in the size control of the encapsulating particles, which in turn enables to tailor their swelling kinetics, and to precisely design light-controlled release systems
Efficient Binding of Heavy Metals by Black Sesame Pigment: Toward Innovative Dietary Strategies to Prevent Bioaccumulation
No full textBlack sesame pigment (BSP) was shown to bind lead, cadmium, and mercury at pH 7.0 and to a lower extent at pH 2.0. BSP at 0.05 mg/mL removed the metals at 15 μM to a significant extent (>65% for cadmium and >90% for mercury and lead), with no changes following simulated digestion. The maximum binding capacities at pH 7.0 were 626.0 mg/g (lead), 42.2 mg/g (cadmium), and 69.3 mg/g (mercury). In the presence of essential metals, such as iron, calcium, and zinc, BSP retained high selectivity toward heavy metals. Model pigments from caffeic acid, ferulic acid, and coniferyl alcohol showed lower or comparable binding ability, suggesting that the marked properties of BSP may result from cooperativity of different sites likely carboxy groups and o-diphenol and guaiacyl functionalities. Direct evidence for the presence of such units was obtained by structural analysis of BSP by solid-state Fourier transform infrared spectroscopy and 13C nuclear magnetic resonance spectroscopy
An Antioxidant Bioinspired Phenolic Polymer for Efficient Stabilization of Polyethylene
No full textThe synthesis, structural characterization and properties of a new bioinspired phenolic polymer (polyCAME) produced by oxidative polymerization of caffeic acid methyl ester (CAME) with horseradish peroxidase (HRP)-H2O2 is reported as a new sustainable stabilizer toward polyethylene (PE) thermal and photo-oxidative degradation. PolyCAME exhibits high stability toward decarboxylation and oxidative degradation during the thermal processes associated with PE film preparation. Characterization of PE films by thermal methods, photo-oxidative treatments combined with chemiluminescence, and FTIR spectroscopy and mechanical tests indicate a significant effect of polyCAME on PE durability. Data from antioxidant capacity tests suggest that the protective effects of polyCAME are due to the potent scavenging activity on aggressive OH radicals, the efficient H-atom donor properties inducing free radical quenching, and the ferric ion reducing ability. PolyCAME is thus proposed as a novel easily accessible, eco-friendly, and biocompatible biomaterial for a sustainable approach to the stabilization of PE films in packaging and other applications
Covalent attachment of chromophores to chlorinated copolymers for optical waveguides: Synthesis and optical characterization.
No full textPolymeric optical devices are attracting increasing interest in the field of photonics because of the very
appealing performances as structures for both propagating and modulating light signals according to the
properties of the employed organic materials. This paper reports the preparation and characterization of
low-loss polymer waveguides fabricated from chlorinated copolymers by photochemical crosslinking. A
novel monomer derived from reaction between glycidyl methacrylate (GMA) and the chromophore
Disperse Red 19 (DR19) was prepared and successfully copolymerized with GMA and chlorostyrene (CS)
to obtain the dye-modified copolymer. The latter was crosslinked by photoinitiated polymerization of the
pendant epoxy groups, to obtain stable polymeric waveguides. It was found that the major product of the
reaction between GMA and DR19 was formed through transesterification of the methacrylate with
elimination of glycidol, while traces of products deriving from the epoxy ring-opening reaction were
detected. The presence of the nitro substituent on DR19 favoured chain-transfer reactions during the
polymerization reaction, leading to a decrease in the polymerization degree. It was also observed that the
presence of grafted DR19 negatively affected the crosslinking reaction, as a lower epoxy group conversion
was observed for the modified copolymer. Thermal analysis showed increased thermal stability for the
copolymer containing DR19. m-line spectroscopy was used to measure the refractive index at 632.8 nm.
The experimental results confirm that the new class of chlorine-based polymeric materials represent
a very attractive proposal in the panorama of materials employed in the fabrication of electro-optical
devices for telecommunication applications
Dual role of epoxidized soybean oil (ESO) as plasticizer and chain extender for biodegradable polybutylene succinate (PBS) formulations
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