| 1. |
- Castro-Mayorga, J. L., et al.
(author)
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The impact of zinc oxide particle morphology as an antimicrobial and when incorporated in poly(3-hydroxybutyrate-co-3-hydroxyvalerate) films for food packaging and food contact surfaces applications
- 2017
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In: Food and Bioproducts Processing. - : Institution of Chemical Engineers. - 0960-3085 .- 1744-3571. ; 101, s. 32-44
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Journal article (peer-reviewed)abstract
- In this work, zinc oxide (ZnO) micron and nano sized-particles with different morphologies were synthesized by aqueous precipitation and evaluated as antimicrobial agents against foodborne pathogens. The most effective bactericide system was selected to prepare active poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) films by three different methods (i) direct melt-mixing, (ii) melt-mixing of preincorporated ZnO into PHBV18 (18 mol% valerate content) fiber mats made by electrospinning, and, (iii) as a coating of the annealed electrospun PHBV18/ZnO fiber mats over compression molded PHBV. Results showed that ZnO successfully improved the thermal stability of the PHBV18, being the preincorporation method the most efficient in mitigating the negative impact that the PHBV18 had on the thermal stability, barrier and optical properties of the PHBV films. Similar behavior was found for the coating structure although this film showed effective and prolonged antibacterial activity against Listeria monocytogenes. This study highlights the suitability of the PHBV/ZnO nanostructures for active food packaging and food contact surface applications.
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| 2. |
- González-Ausejo, J., et al.
(author)
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Assessing the thermoformability of poly(3-hydroxybutyrate-co-3-hydroxyvalerate)/poly(acid lactic) blends compatibilized with diisocyanates
- 2017
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In: Polymer testing. - : Elsevier. - 0142-9418 .- 1873-2348. ; 62, s. 235-245
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Journal article (peer-reviewed)abstract
- 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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| 3. |
- Fernández, A., et al.
(author)
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Effects of ionizing radiation in ethylene-vinyl alcohol copolymers and in composites containing microfibrillated cellulose
- 2008
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In: Journal of Applied Polymer Science. - : Wiley. - 0021-8995 .- 1097-4628. ; 109:1, s. 126-134
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Journal article (peer-reviewed)abstract
- This study reports on the effect of gamma radiation on morphological, thermal, and water barrier properties of pure ethylene vinyl alcohol copolymers (EVOH29 and EVOH44) and its biocomposites with the nanofiller microfibrillated cellulose (2 wt%). Added microfibrillated cellulose (MFC) preserved the transparency of EVOH films but led to a decrease in water barrier properties. Gamma irradiation at low (30 kGy) and high doses (60 kGy) caused some irreversible changes in the phase morphology of EVOH29 and EVOH44 copolymers that could be associated to crosslinking and other chemical alterations. Additionally, the EVOH copolymers and the EVOH composites reduced the number of hygroscopic hydroxyl functionalities during the irradiation processing and novel carbonyl based chemistry was, in turn, detected. As a result of the above alterations, the water barrier properties of both neat materials and composites irradiated at low doses were notably enhanced, counteracting the detrimental effect on water barrier of adding MFC to the EVOH matrix. © 2008 Wiley Periodicals, Inc.
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| 4. |
- Lôpez-Rubio, A., et al.
(author)
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Enhanced film forming and film properties of amylopectin using micro-fibrillated cellulose
- 2007
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In: Carbohydrate Polymers. - : Elsevier BV. - 0144-8617 .- 1879-1344. ; 68:4, s. 718-727
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Journal article (peer-reviewed)abstract
- This work describes a novel approach to produce amylopectin films with enhanced properties by the addition of micro fibrillated cellulose (MFC). Aqueous dispersions of gelatinized amylopectin, glycerol (0-38 wt%) and MFC (0-10 wt%) were cast at ambient temperature and 50% relative humidity and, after 10 days of storage, the tensile properties were investigated. The structure of the composite films was revealed by optical, atomic force and transmission electron microscopy. The moisture content was determined by thermogravimetry and the temperature-dependent film rigidity was measured by thermal mechanical analysis. Synchrotron simultaneous small- and wide-angle X-ray measurements revealed that the solutions had to be heated to above 85 degrees C in order to achieve complete gelatinization. Optical microscopy and atomic force microscopy revealed uniformly distributed MFC aggregates in the films, with a length of 10-90 mu m and a width spanning from a few hundred nanometers to several microns. Transmission electron microscopy showed that, in addition to aggregates, single MFC microfibrils were also embedded in the amylopectin matrix. It was impossible to cast antylopectin films of sufficient quality with less than 38 wt% glycerol. However, when MFC was added it was possible to produce high quality films even without glycerol. The film without glycerol was stiff and strong but not brittle. It was suggested that this remarkable effect was due to its comparatively high moisture content. Consequently MFC acted both as a "conventional" reinforcement because of its fibrous structure and also indirectly as a plasticiser because its presence led to an increase in film moisture content.
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| 5. |
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| 6. |
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| 7. |
- Sanchez-Garcia, M. D., et al.
(author)
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Incorporating Amylopectin in Poly(lactic acid) by Melt Blending Using Poly(ethylene-co-vinyl alcohol) as a Thermoplastic Carrier. II. Physical Properties
- 2011
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In: Journal of Applied Polymer Science. - : Wiley. - 0021-8995 .- 1097-4628. ; 119:6, s. 3708-3716
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Journal article (peer-reviewed)abstract
- This study adds to a previous morphological work (paper I) with further characterization of the developed poly(lactic acid) (PLA) blends containing amylopectin, which made use of an ethylene-vinyl alcohol copolymer (EVOH) as a melt-compoundable carrier for the polysaccharide in the biopolyester. The effect of using glycerol as compatibilizer was also characterized. Water and oxygen transport parameters, mechanical properties, and comparative biodegradability tests were evaluated for the blends. From the results, the barrier properties to oxygen were only seen to improve at 0% RH and mostly for the PLA-EVOH blends, which furthermore showed a positive deviation from the rule of mixtures. At high relative humidity, the blends showed somewhat poorer barrier performance due to the comparatively higher improvement in barrier of the neat PLA at 80% RH. Interestingly, room temperature biodegradability testing suggested that low additions of the blending elements seemed to facilitate the biodegradability of the biopolyester. Despite the fact that properties were not so dramatically improved, incorporating renewable resources within PLA seems as a potentially viable route to reduce PLA supply dependency, retain good optical properties and to overcome some drawbacks associated to the use of this biopolyester. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 119: 3708-3716, 2011
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| 8. |
- Johansson, Kristin, 1983-
(author)
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Oxygen-reducing enzymes in coatings and films for active packaging
- 2013
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Doctoral thesis (other academic/artistic)abstract
- Oxygen scavengers are used in active packages to protect the food against deteriorative oxidation processes. The aim of this work was to investigate the possibilities to produce oxygen-scavenging packaging materials based on oxygen-reducing enzymes. The enzymes were incorporated into a dispersion coating formulation applied onto a food-packaging board using conventional laboratory coating techniques.Various enzymes were used: a glucose oxidase, an oxalate oxidase and three laccases originating from different organisms. All of the enzymes were successfully incorporated into a coating layer and could be reactivated after drying. For at least two of the enzymes, re-activation was possible not only by using liquid water but also by using water vapour. Re-activation of the glucose oxidase and a laccase required relative humidities of greater than 75% and greater than 92%, respectively.Catalytic reduction of oxygen gas by glucose oxidase was promoted by creating an open structure through addition of clay to the coating at a level above the critical pigment volume concentration. Migration of the enzyme and the substrate was reduced by adding an extrusion-coated liner of polypropylene on top of the coating.For the laccase-catalysed reduction of oxygen it was possible to use lignin derivatives as substrates for the enzymatic reaction. The laccase-catalysed reaction created a polymeric network by cross-linking of lignin-based entities, which resulted in increased stiffness and increased water-resistance of biopolymer films. The laccases were also investigated with regard to their potential to function as oxygen scavengers at low temperatures. At 7°C all three laccases retained more than 20% of the activity they had at room temperature (25°C), which suggests that the system is also useful for packaging of refrigerated food.
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| 9. |
- Pourrahimi, Amir Masoud, et al.
(author)
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Water-based synthesis and cleaning methods for high purity ZnO nanoparticles - comparing acetate, chloride, sulphate and nitrate zinc salt precursors
- 2014
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In: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 4:67, s. 35568-35577
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Journal article (peer-reviewed)abstract
- A low temperature (60 degrees C) aqueous synthesis method of high purity ZnO nanoparticles intended as fillers for ultra-low electrical conductivity insulations is described. Particles were prepared under identical conditions from different zinc salts based on nitrate, chloride, sulphate or acetate to compare their abilities to form high yields of sub-50 nm particles with narrow size distribution. The acetate salt gave uniform 25 nm ZnO particles with a conical prism shape. The chloride and sulphate derived particles showed mixed morphologies of nanoprisms and submicron petals, whereas the nitrate salt yielded prisms assembled into well-defined flower shapes with spiky edges. The micron-sized flower shapes were confirmed by Xray diffraction to consist of the smaller prism units. Photoluminescence spectroscopy showed emission in the blue-violet region with little variation depending on precursor salt, suggesting that the spectra were dependent on the primary nanoprism formation and rather independent of the final particle morphology. Microscopy revealed that the salt residuals after the reaction showed different affinity to the particle surfaces depending on the type of salt used, with the acetate creating ca. 20 nm thick hydrated shells; and in falling order of affinity: chloride, sulphate and nitrate. An acetate ion shielding effect during the synthesis was therefore assumed, preventing nanoparticle fusion during growth. Varying the concentrations of the counter-ions confirmed the shielding and only the acetate anions showed an ability to stabilize solitary nanoprisms formation in reaction yields from 2 to 10 g L-1. Ultrasonic particle surface cleaning was significantly more efficient than water replacement, resulting in a stable aqueous dispersion with a high zeta potential of 38.9 mV at pH 8.
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