| 1. |
- Hedenqvist, Mikael S., et al.
(author)
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Barrier properties of SiOx-coated polymers : multi-layer modelling and effects of mechanical folding
- 2003
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In: Surface & Coatings Technology. - : Elsevier BV. - 0257-8972 .- 1879-3347. ; 172:1, s. 7-12
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Journal article (peer-reviewed)abstract
- The oxygen permeability properties of poly(ethylene terephthalate), low- and high-density polyethylenes and polypropylene coated with SiOx using cold plasma were studied. A previously developed computer model for the calculation of transport properties in laminates containing very different layer thickness was fitted to experimental permeability data to obtain the oxygen transport properties of the SiOx coating. For the first time, to the best of our knowledge, it was possible to obtain the oxygen diffusivity and solubility of a SiOx coating on a polymer substrate. The effects of folding the laminates through 90degrees on the permeability properties of the SiOx coating were also investigated. The surface roughness of the substrates was obtained by atomic force microscopy and the morphology of the laminate surfaces was analysed by scanning electron microscopy. The oxygen diffusivity and solubility of a 45-nm-thick SiOx coating deposited on a 4000-fold thicker polypropylene substrate were 5 x 10(-12) cm(2) s(-1) and 0.72 cm(2) (STP) cm(-3) atm(-1), respectively. The diffusivity was approximately four orders of magnitude lower than that of the polymer substrate and, surprisingly, the solubility was higher than that of the polypropylene film. A hypothesis to explain these results is that the coating contained voids and, according to the permeability time lag, these were not continuous through the coating. The oxygen permeability of the coating increased with increasing substrate surface roughness, and was consequently lowest for poly(ethylene terephthalate). The folding operation initiated cracks in the coating, and the resulting increase in oxygen permeability was greater in the rougher substrates.
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| 2. |
- Jansson, S. E. A., et al.
(author)
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Packaging materials for fermented milk : Effects of material crystallinity and polarity on food quality
- 2001
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In: Packaging technology & science. - : Wiley. - 0894-3214 .- 1099-1522. ; 14:3, s. 119-127
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Journal article (peer-reviewed)abstract
- The ability of a packaging material to protect the food product and extend its shelf-life depends on several material properties. In this work the effects of material crystallinity and polarity on the quality of fermented milk were studied. The fermented milk is a high-quality Swedish product, similar to yoghurt. The quality of the food product was determined as a function of storage time by containing the liquid in pouches of different materials. The material crystallinity was varied by using very low-density polyethylene, high-density polyethylene and aluminium laminate as packaging materials. Aluminium was used on account of its '100%' gas-tightness. The polarity was varied by comparing an aliphatic polyketone with polyethylene of similar crystallinity. The carbon dioxide (CO2) and oxygen (O-2) contents in the headspace of the pouches were determined. The food quality was determined by measuring whey syneresis, viscosity and the content of desired Bifidobacteria, as well as of undesired yeast and mould. A trained taste panel determined the degree of acidity and of the sparkling taste. It was found that the content of CO2 increased and that of O-2 decreased in the pouches with increasing degree of crystallinity and increasing polarity. The sparkling taste of fermented milk was a clear function of the headspace CO2 content. The data presented here could thus be used to 'design' a package for a desired sparkling taste of the fermented milk by selecting a certain material crystallinity. Whey syneresis, viscosity and content of Bifidobacteria were found to be independent of pouch material. While the degree of whey syneresis and the viscosity increased with increasing storage time, the content of Bifidobacteria slowly decreased. The content of yeast and mould in the liquid was below the existing limit values for foodstuffs. The degrees of acidity and sparkling taste were highest for the liquids contained in aluminium and polyketone pouches, although the differences in acidulous taste between the various pouch materials were small.
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| 3. |
- Jansson, S. E. A., et al.
(author)
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Packaging materials for fermented milk Part 2 : Solute-induced changes and effects of material polarity and thickness on food quality
- 2002
-
In: Packaging technology & science. - : Wiley. - 0894-3214 .- 1099-1522. ; 15:6, s. 287-300
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Journal article (peer-reviewed)abstract
- This work is a continuation of the application of a developed methodology for the selection of packaging material for a specific food product, in this case the 'demanding' food product. fermented milk. The effects of different packaging material parameters on the quality of fermented milk were studied. Food quality after storage was determined as a function of material polarity and pouch thickness by storing the liquid in pouches of different materials. The material polarity was varied by using laminates with polyethylene, poly(ethylene-co-vinyl alcohol) with two different ethylene contents and an aliphatic polyketone. The effects of pouch thickness were studied using high-density polyethylene films of different thicknesses between 25 mum and 200 mum. The interactions between the milk product and the pouch material were analysed by oxygen and water permeability, gas chromatography-mass spectrometry and tensile testing. The CO2 and O-2 contents in the headspace of the pouches were determined. The food quality was determined by measuring whey syneresis and the contents of Bifidobacteria, Enterobacteriaceae, yeast and mould. A trained taste panel determined the sensory properties. The content of CO2, and consequently the sparkling taste, increased with increasing polarity and/or pouch thickness. The CO2 content was affected more easily by changes in material polarity than by changes in pouch thickness. The increase in whey syneresis and the decrease in Bifidobacteria content with time were independent Of material polarity and pouch thickness. The contents Of Enterobacteriaceae, yeast and mould in the liquid were always below existing limits for foodstuffs. A newly developed method was used by which the CO2 and 02 permeabilities of the pouch/packaging could be estimated, using the kinetics of the gas composition in the pouch headspace. Permeability values, as estimated by the method, revealed that the CO2 production and the O-2 consumption rates of the fermented milk were dependent on the CO2 and O-2 headspace concentrations. An increase in permeability, determined by conventional methods, suggested that both the non-polar and the polar polymers were plasticized by fermented milk. The plasticization was, however, modest and undetectable when the polyethylene tensile test data were analysed.
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| 4. |
- Karlsson, G. E., et al.
(author)
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Determining limonene diffusion in molten polyethylene from within 0.1 mu s molecular dynamics trajectories
- 2002
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In: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 35:19, s. 7453-7459
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Journal article (peer-reviewed)abstract
- Molecular dynamics simulations of the diffusion of limonene into molten polyethylene were performed in order to explore the possibility of using atomistic simulations to predict the diffusion of larger solute molecules in polymers. The system contained 6000 anisotropic united atom methylene units with a molar mass of 84 000 g mol(-1). A united atom limonene molecule (C10H16) was introduced into the polyethylene matrix. Limonene trajectories were generated for 2-100. ns at 77-227 degreesC. The simulated diffusivities were compared with experimental zero-concentration diffusivities of limonene in natural rubber and ultrahigh molar mass polyethylene, obtained from desorption measurements in the same temperature range. The simulated diffusivities and activation energy were within 30%. and 16% of the experimental thermodynamic diffusivities and activation energies, respectively. The simulated average diffusivities, obtained from 10 trajectories, changed by only 33% when the simulation time was shortened from 100 ns to 500 ps. The limonene molecule vibrated in a cagelike fashion on a 1-2 ps scale, whereas on a larger time scale the jumping was liquidlike. The limonene molecule showed tumbling during its motion through the polyethylene matrix.
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| 5. |
- Karlsson, G. E., et al.
(author)
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Physical properties of dense amorphous poly(vinyl alcohol) as revealed by molecular dynamics simulation
- 2002
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In: Journal of Macromolecular Science, Part B. - 0022-2348 .- 1525-609X. ; B41:2, s. 185-206
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Journal article (peer-reviewed)abstract
- Dense amorphous poly(vinyl alcohol) (PVAL) built from a chain with 145 repeating units was studied by constant number of particles, pressure, and temperature-molecular dynamics simulations at temperatures between 400 and 527K. The results of the simulations were compared with pressure-volume-temperature data, solubility parameter, x-ray scattering pattern, and data for the characteristic ratio. The fractional free-volume distribution was computed and the diffusion characteristics of water in the polymer were studied. Experimental water desorption data were obtained and they were compared with the results obtained from the simulations. The AMBER-force field was initially adopted to generate the dynamics, but this force field yielded structures with too high specific volumes. The size of the oxygen atoms was then decreased until the maximum difference between experimental and simulated specific volumes was within 2.2%. This modification of the force field resulted in satisfactory agreement between experimental and simulated data for the volume expansion coefficient and the compressibility in the temperature range from 402 to 502K. The essential features in the local packing of the atoms as revealed by wide-angle x-ray scattering were also present in the simulated structures. Simulated values for the characteristic ratio were in agreement with earlier reported experimental values. The solubility parameter showed only minor deviations from reported experimental values. Water-molecule trajectories yielded diffusivity in accordance with the experimental zero-concentration diffusivity. The water molecule makes well-resolved jumps (cage-like penetrant motion) even at the highest temperature of simulation, 510K. The water molecule rotates much faster than it makes jumps in the PVAL matrix. The lifetimes of the hydrogen bonds between polymer chain segments were longer than for those of the hydrogen bonds formed between water and polymer chain segments. This finding suggests that the primary rate-controlling factor for water diffusion in this polymer is the constraining effect of hydrogen bonds formed between polymer chain segments.
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| 6. |
- Backman, Anna, et al.
(author)
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Transport properties of uniaxially oriented aliphatic polyketone
- 2004
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In: Journal of Polymer Science Part B. - : Wiley. - 0887-6266 .- 1099-0488. ; 42:6, s. 947-955
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Journal article (peer-reviewed)abstract
- The oxygen, carbon dioxide, and water-transport properties of a uniaxially oriented aliphatic polyketone were determined. The polyketone was drawn to 5-10 times its original length. The transport properties were related to changes in crystallinity estimated by differential scanning calorimetry and density measurements and by changes in the molecular and crystal orientation assessed by, respectively, infrared and X-ray spectroscopy. The film structures were characterized by confocal scanning laser microscopy and scanning electron microscopy. Stress-strain tests on the drawn specimens enabled the impacts of orientation on the transport and mechanical properties to be compared. A draw-induced increase in crystallinity and molecular orientation yielded permeabilities at a draw ratio of 10 that were 30-40% of the original value, and the percentage decrease was basically independent of the type of gas/vapor molecule. Also, the diffusivities of oxygen and carbon dioxide decreased by an order of magnitude. The fact that the amorphous permeability was peaking at a draw ratio of about 5 was a consequence of a peak in amorphous solubility, which was very high for oxygen and absent for water. It was suggested that the peak in solubility was mainly caused by the destruction of the polymer hydrogen-bond network during drawing and crystal reorientation. The impact of structural reorganization within the polymer and presence of surface valleys seemed to have less impact on the mechanical properties than on the transport properties. This suggested that transport data are more sensitive than mechanical data in probing material defects and changes in molecular packing and morphology.
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| 7. |
- Camacho, W., et al.
(author)
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Near infrared (NIR) spectroscopy compared with thermogravimetric analysis as a tool for on-line prediction of water diffusion in polyamide 6,6
- 2002
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In: Polymer international. - : Wiley. - 0959-8103 .- 1097-0126. ; 51:12, s. 1366-1370
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Journal article (peer-reviewed)abstract
- NIR spectroscopy in the transmission mode and thermogravimetric analysis were used to predict diffusion of water into polyamide 6,6 samples immersed in water at 40, 60, 75 and 90degreesC for different periods of time. The sorption curves between 40 and 75 were sigmoidal indicating that the surface concentration was time dependent. The sorption curves were readily fitted by the use of a time-dependent surface concentration and a water-concentration-dependent diffusivity. The zero-concentration water diffusivity decreased non-linearly and the activation energy of diffusion increased from 24 to 58 kJ mol(-1), with decreasing temperature. The surface concentration relaxation time decreased rapidly. The sorption of water in thick polyamide samples was readily characterized by FT-NIR spectroscopy. The accuracy and feasibility of this method was similar to conventional thermogravimetric methods. The greatest advantage of FT-NIR, however, is the possibility of detecting and monitoring the moisture concentration on-line and in a non-destructive way.
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| 8. |
- Flodberg, G., et al.
(author)
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Barrier properties of blends based on liquid crystalline polymers and polyethylene
- 2000
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In: Polymer Engineering and Science. - : Wiley. - 0032-3888 .- 1548-2634. ; 40:9, s. 1969-1978
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Journal article (peer-reviewed)abstract
- Blends of an extrusion-grade polyethylene and two different liquid crystalline polymers of Vectra type were prepared by melt mixing using poly(ethylene-co-methacrylic acid) as compatibilizer. Oxygen and water vapor permeability, transparency and welding strength of compression molded and film blown specimens were studied. The compression molded blends showed gas permeabilities conforming to the Maxwell equation assuming low permeability liquid crystalline polymer spheres in a high permeability polyethylene matrix One of the liquid crystalline polymers with suitable rheological properties formed a more continuous phase in the film blown blends and a substantial decrease in oxygen and water vapor permeability was observed in these blends. The compression molded blends with 50% liquid crystalline polymer and some of blow molded blends showed very high gas permeabilities. It is believed that voids forming continuous paths through the structure were present in these samples. The blends showed significantly higher opacity than pure polyethylene.
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| 9. |
- Flodberg, G., et al.
(author)
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Barrier properties of injection molded blends of liquid crystalline polyesters (Vectra) and high-density polyethylene
- 2003
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In: Polymer Engineering and Science. - : Wiley. - 0032-3888 .- 1548-2634. ; 43:5, s. 1044-1057
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Journal article (peer-reviewed)abstract
- Blends of an extrusion-grade high-density polyethylene and two liquid crystalline copolyesters (LCP; Vectra A950 and Vectra RD501) were prepared by melt mixing and injection molding, and the. morphologies and oxygen permeabilities of the blends were assessed. Scanning electron microscopy revealed that the LCP was present in the blends as mixed oriented bands and small spheres at low LCP contents (4-9 vol%), Whereas blends with more than 18 vol% LCP showed LCP lamellae of macroscopic lateral size (mm). Scanning electron microscopy revealed a two-dimensional continuity of the LCP domains in the disc plane due to radial shear deformation and circumferential stretching of the melt leaving the central gate of the disc-shaped cavity. The oxygen permeability, diffusivity and solubility decreased with increasing LCP content of the blends. The decrease in permeability with respect to polyethylene was significant (46%-55%) already at 9 vol% LCP. At 27 vol% LCP, the decrease with respect to polyethylene, was 92% for the Vectra A950 blend and 98% for the Vectra RD501 blend. These blends showed a greater decrease in diffusivity (86%-92%) than in solubility (39%-76%) with respect to polyethylene, which showed the very pronounced effect of the LCP lamellae on the geometrical impedance factor. Microvoids were present in all the blends despite the use of a very high injection pressure (180 MPa) but their impact on the oxygen permeability was negligible for the Vectra. RD501 blends and relatively small for the Vectra A950 blends.
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| 10. |
- Flodberg, G., et al.
(author)
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Liquid Crystalline Polymer Pouches for Local Anaesthetic Emulsion
- 2001
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In: Packaging technology & science. - : Wiley. - 0894-3214 .- 1099-1522. ; 14:4, s. 159-170
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Journal article (peer-reviewed)abstract
- In order to enhance the long-term properties of a high-pH local anaesthetic drug, emulsion tests were conducted where the emulsion was stored in pouches made of a compression moulded high-barrier liquid-crystalline polymer, Vectra A950. The oxygen permeability of the pouch materia I was too low to be detected at 23 degreesC and 0% relative humidity with the instrument used. The water vapour transmission rate was 0.135 (g.mm/m(2).day) at 38 degreesC and 100% relative humidity. The emulsion, containing prilocain and lidocain as active substances, was stored in pouches which were sealed by the thermal impulse technique at 260 degreesC for 1.08 s. It was possible to obtain good quality films and good quality seals by optimization of the compression moulding and sealing operations. The concentrations of prilocain and lidocain in the emulsion were studied for 14 weeks at two different temperatures, 40 degreesC and 60 degreesC, and at 100% relative humidity. The decrease in concentration was higher for prilocain (5.4-8.3%) than for lidocain (3.4-3.6%). The loss of the substances from the emulsion was due mainly to adsorption onto the polar surface of the liquid crystalline polymer.
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