This paper reports on a novel route to develop EVOH-kaolinite nanocomposites by a melt intercalation process and on some relevant nanocomposite properties as a function of composition. The kaolinite ...clay used is a very cheap raw material of the tile industry and as such needed to be refined and chemically modified prior to the melt intercalation step. The modification was carried out with dimethyl-sulfoxide, methanol and octadecylamine in order to increase the basal plane distance of the original clay by a factor of more than three. Melt blended nanocomposites were characterized by WAXS, TEM, DSC, TGA and oxygen transmission rate. From the early results, partial exfoliation and intercalation of the clay platelets was the dominant morphology attained. An increase in thermal resistance, glass transition temperature, crystallinity and barrier properties to oxygen were also observed for mass clay loadings below 8%.
This paper reports the development of biodegradable active packaging films of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) by the incorporation of alpha- and gamma-cyclodextrins (α-CD ...andγ-CDs) containing oregano essential oil (OEO). Herein, both the kneading method (KM) and freeze-drying method (FDM) were first explored for the preparation of α-CD:OEO andγ-CD:OEO inclusion complexes at host:guest ratios of 80:20 wt/wt and 85:15 wt/wt, respectively. The results showed that KM was the most efficient method for the encapsulation of OEO in the CDs cavity in terms of simplicity and rapidity, while it was also yielded the inclusion complexes with the highest antimicrobial and antioxidant performance. The α-CD:OEO andγ-CD:OEO inclusion complexes obtained by KM were thereafter incorporated at 10, 15, 20, 25, and 30 wt% into PHBV fibres by electrospinning and annealed at 160 °C to produce contact transparent films. It was observed that the optimal concentration of α-CD:OEO andγ-CD:OEO inclusion complexes for homogeneous and continuous film formation was attained at contents of 15 and 25 wt%, respectively. Higher antimicrobial and antioxidant activities were obtained for the γ-CD:OEO inclusion complexes due to the greater encapsulation efficiency of OEO in γ-CD, resulting in PHBV films with good performance for up to 15 days. This aspect, together with their improved thermal stability and mechanical strength, give interesting applications to these biopolymer films in the design of active-releasing packaging materials to maintain the physical, chemical, and microbiological characteristics of food products.
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•An effective strategy was designed to obtain active food packaging films of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV).•The kneading method was the most efficient for the encapsulation of oregano essential oil (OEO) in α- and γ-cyclodextrins.•The contents of α-CD:OEO andγ-CD:OEO inclusion complexes were optimal at 15 and 25 wt%, respectively.•Higher active properties were attained for the films incorporating γ-CD:OEO due to their greater encapsulation efficiency.•The newly developed electrospun γ-CD:OEO PHBV films showed high antimicrobial and antioxidant activities for up to 15 days.
Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) is a renewable alternative to conventional barrier packaging polymers due to its thermoplastic properties, biodegradability and gas barrier ...performance but its potential industrial applications are limited by its high price and difficult processability. A thorough study concerning the thermoforming ability of PHBV, and blends with poly(lactic acid) (PLA) incorporating three different diisocyanates as compatibilizers (hexamethylene diisocyanate, poly(hexamethylene) diisocyanate and 1,4-phenylene diisocyanate) is herein presented after component melt blending. A straightforward universal qualitative method is proposed to assess the thermoformability, based on a visual inspection of a thermoformed specimen and the ability to reproduce the mold shape, and the thermoforming window of the material. The results reveal a significant improvement in the thermoforming capacity and a widening of the thermoforming windows as the correct amounts of diisocyanates are incorporated. The barrier properties and the biodisintegrability of the blends was also studied, confirming a predictable slight decrease of the barrier performance when PLA is added, but without negatively affecting the disintegrability under composting conditions with respect to pristine PHBV.
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•Synthesis of sol–gel coatings with different chemical composition.•Correlation between network formation and physical properties.•Control coating weight in contact with water, to determine their ...ability to degrade by hydrolysis.•Formation of pores and water uptake during the degradation by electrochemical analysis.•Principal parameters that determine the kinetics of degradation.
The design and development of suitable multilayered functional coatings for delaying corrosion advance in metals and become controlled-release vehicles requires that the properties of the coatings are known. Coatings prepared by the sol–gel method provide a good approach as protective layers on metallic surfaces. This kind of coating can be prepared from pure chemical reagents at room temperature and atmospheric pressure, with compositions in a very wide range of environmentally non-aggressive precursors. Sol–gel coatings based on siloxane bonded units were prepared, starting with an organic–inorganic hybrid system. Synthesis procedures included acid-catalysed hydrolysis, sol preparation, and the subsequent gelation and drying. The alkoxide precursors used were methyl-triethoxysilane (MTMOS) and tetraethyl-orthosilicate (TEOS) in molar ratios of 10:0, 9:1, 8:2 and 7:3. After determination of the optimal synthesis parameters, the materials were characterised by solid 29Si nuclear magnetic resonance (29Si NMR), Fourier transform infrared spectroscopy (FTIR), contact angle measurement and electrochemical impedance spectroscopy (EIS) test. Finally, the materials were assayed by controlling their weight in contact with water, to determine their ability to degrade by hydrolysis. Electrochemical analysis reveals the formation of pores and water uptake during the degradation. The quantity of TEOS is one of the principal parameters that determine the kinetics of degradation. There is a correlation between the degradation process obtained for long periods and the electrochemical parameters obtained by EIS in short times. The study tries to incorporate knowledge that can be used for designing the degradation process of the functional coatings and to control their properties in short times.
Nanofluids based on water with halloysite (Hal) nanotubes were prepared and characterized in order to evaluate its suitability to be used as a heat transfer fluid. A characterization of the Hal ...powder nanoparticles was performed by means of SEM, TEM, WAXS, FTIR and TGA so that chemical composition, size and shape were determined. Stability of nanofluids was analyzed by means of zeta potential and light transmission measurements. Thermal conductivity, specific heat and viscosity of nanofluids prepared at different solid contents (0.5, 1, 3 and 5% volume fraction) and temperatures (40, 60 and 80°C) were obtained in order to optimize the Prandtl number. The nanofluids exhibited a good performance for its application as heat transfer fluids, with low Prandtl numbers compared to other commonly used nanofluids. High thermal conductivity enhancement with moderate viscosity and good stability results was obtained for the Hal nanofluid.
•SEM, TEM, WAXS, FTIR and TGA characterization of halloysite nanotubes.•Preparation of stable halloysite/water nanofluids.•Study of thermal conductivity, specific heat and viscosity of halloysite nanofluids.•Nanofluids suitable for heat transfer systems: high conductivity and low viscosity.
•Organo-modified silica particles (OSP) and anticorrosive pigments (ZMP) were added to powder coatings.•Two opposite effects of addition OSP to coatings containing ZMP were detected.•OSP ...incorporation needs to be in low percentages to achieve a synergistic effect between the two additives.•The optimal combined system was established for 1.0wt% of OSP.
The addition of organo-modified silica particles (OSP) to powder coating containing zinc molybdenum phosphate pigment (ZMP) has been investigated. The OSP were directly incorporated at different concentrations (1, 2.5, 3.5 and 4.5wt%) in a polyester powder monolayer coating with 10wt% ZMP. The adhesion and anticorrosion properties were evaluated by means of adhesion studies and different electrochemical techniques: electrochemical impedance spectroscopy (EIS) and an accelerated cyclic electrochemical technique (ACET). The optimum quantity of OSP that gave maximum anticorrosive performance of the coating system was determined (1.0%), however two opposite effects of addition on the coatings led to a reduction of anticorrosive properties for higher contents. Finally, the electrochemical behaviour of the optimized combined system was compared to the effects achieved when both additives were separately added to powder coatings by means of an additional electrochemical test.
The addition of organo-modified silica particles (OSP) to organic monolayer coatings has been investigated as an alternative to the use of primers or surface pretreatments in galvanised steel ...substrates. A commercial additive consisting of trifunctional organosilane (alkyl-triethoxysilane) grafted on silica particles was directly incorporated at different concentrations (1, 2.5, 3.5 and 4.5wt%) as an integral additive in a polyester powder coating. The OSP were characterised physicochemically by means of FTIR and TGA, and the coating formulated by DSC. The anticorrosive properties of the systems were evaluated by means of electrochemical impedance spectroscopy (EIS), showing improvements with all the formulations containing the OSP, especially in the coating with 2.5% OSP. In order to explain this behaviour, morphological (using SEM) and adhesion studies were done. The formation of agglomerates in the powder coatings was detected when the concentration was over 2.5%. There was an improvement in the adhesion of the coating to the substrate for all the samples containing the OSP but especially for that containing 2.5%. The impact resistance was increased too, especially in the formulations with 2.5% and 3.5%.
In this paper the porosity, phases, mechanical properties and abrasive wear resistance of ceramic layers of Al2O3/TiO2 deposited by flame spray process were evaluated. The percentage of titania has a ...strong influence on the coatings porosity, as shown by the fact that with increasing titania content porosity will be reduced. The crystalline phases of the deposited layers changed according to the characteristics of the powder and the thermal process employed. While hardness depends only on the percentage of titania content, in the studied range, toughness depends on several factors, such as hardness, porosity and intergranular precipitation. The resistance to abrasive wear depends almost exclusively on the hardness of the coating.
•Optimal incorporation of CFs into PHBV was achieved by melt compounding at 150 rpm.•Green composite sheets with enhanced physical performance were produced.•CFs were also impregnated with OEO to ...develop a novel antibacterial filler.•Sheets with OEO-containing CFs showed bacteriostatic effect against G+ S. aureus.•Relevant applications in the active food packaging field are foreseen.
New packaging materials based on green composite sheets consisting of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and coconut fibers (CFs) were obtained by twin-screw extrusion (TSE) followed by compression molding. The effect of varying the CF weight content, i.e. 1, 3, 5, and 10 wt.-%, and the screw speed during melt processing, i.e. 75, 150, and 225 rpm, on both the aspect ratio and dispersion of the fibers was analyzed and related to the properties of the compression-molded sheets. Finally, the CFs were impregnated with oregano essential oil (OEO) by an innovative spray coating methodology and then incorporated into PHBV at the optimal processing conditions. The functionalized green composite sheets presented bacteriostatic effect against Staphylococcus aureus from fiber contents as low as 3 wt.-%. Therefore, the here-prepared CFs can be successfully applied as natural vehicles to entrap extracts and develop green composites of high interest in active food packaging to provide protection and shelf life extension.
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