| 1. |
- 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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| 2. |
- 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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| 3. |
- 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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| 4. |
- Flodberg, G., et al.
(author)
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Migration of monomers from liquid crystalline poly(p-hydroxybenzoic acid-co-2-hydroxy-6-naphthoic acid)
- 2002
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In: Food Additives and Contaminants. - : Informa UK Limited. - 0265-203X .- 1464-5122. ; 19:5, s. 492-501
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Journal article (peer-reviewed)abstract
- Liquid-crystalline co-polyesters (e.g. a random co-polyester based on p-hydroxybenzoic acid (HBA) and 2-hydroxy-6-naphthoic acid (HNA) known as Vectra A950) offer good barrier properties, but for food-contact use require overall and specific migration testing. For Vectra A950 films, the highest overall migration level obtained was 2.3 mg kg(-1) in olive oil (10 days at 40degrees C) well below the EC limit of 60 mg kg(-1). The highest specific migration for p-hydroxybenzoic acid was 15.2 mug dm(-2) in olive oil (2 h at 175degreesC). For 2-hydroxy-6-naphthoic acid, the highest value obtained was 4.3 mug dm(-2) in 10% ethanol (4 h at 100degrees C), although it was not on the EC positive and cannot yet be used for food-contact materials. At conditions considered as severe, the estimated daily intake for p-hydroxybenzoic acid was calculated as 11.9 mug/person day(-1) and for 2-hydroxy-6-naphthoic acid it was 5.3 mug/person day(-1). The results exceed the threshold of regulation of 1.5 mug/person day(-1).
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