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- Nestorson, Anna, et al.
(författare)
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Enzyme immobilization in latex dispersion coatings for active food packaging
- 2008
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Ingår i: Packaging technology & science. - : Wiley. - 0894-3214 .- 1099-1522. ; 21:4, s. 193-205
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Tidskriftsartikel (refereegranskat)abstract
- Carboxylated styrene acrylate latex samples have been functionalized by the immobilization and entrapment of the enzyme glucose oxidase (GOx), which can be used as an oxygen scavenger in food packaging. GOx was covalently immobilized both on the surface of already formed films and on the latex particles in dispersion, as well as entrapped within the polymer matrix. In the latter two cases, polymer films were formed after the enzyme had been added to the latex dispersion. The storage stability of the enzyme and the influence of adding clay were also studied. For a given amount of enzyme, the enzyme immobilized on the film surface showed an enzyme activity about 10 times higher than that of the enzyme present within the polymer matrix. This is probably due to the diffusion limitations of the substrate in the polymer matrix. The films with the enzyme present within the polymer matrix, however, showed a higher total oxygen-removal capacity than films with the enzyme immobilized on the surface. Entrapped enzyme showed a slightly higher activity than enzyme immobilized in the dispersion due to the negative effect of the activating chemicals used during the immobilization and on conformational constraints upon covalent bonding. Low amounts of clay added to the dispersion decreased the enzyme activity, but with higher amounts of clay the enzyme activity increased, probably because of the increased porosity and thus higher substrate accessibility. The most suitable storage condition for all the enzyme-containing films was +8°C, which is just above the glass transition temperature of the polymer used.
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- De Magistris, F., et al.
(författare)
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Influence of paper compressibility on flexographic printing quality
- 2008
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Ingår i: Progress in paper physics seminar 2008, proceedings, Espoo, Finland, 2-5 June 2008. - 9789512293919 ; , s. 243-245
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Konferensbidrag (populärvet., debatt m.m.)abstract
- The compression ability of fibres and fibre networks were investigated. The surface and bulk compressions of paper influence calendering, coating, surface sizing ability and the penetration of ink in printing. Two kraft pulps (spruce) were produced in the laboratory to obtain pulps with different levels of xylan. Using those kraft pulps alone or mixed with 50% of a commercial TMP pulp, single-layer sheets were formed in a Formette Dynamique sheet former. The pulps and mixture levels were chosen to obtain papers with systematically altered property variation but with constant grammage. The papers were characterized according to both bulk and surface compressibility. The papers were printed in a flexo IGTF1 laboratory printing press and the transferred amount of ink, dot gain, and mottling were analyzed.
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| 10. |
- Jonhed, Anna, 1975-, et al.
(författare)
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Effects of film forming and hydrophobic properties of starches on surface sized packaging paper
- 2008
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Ingår i: Packaging Technology and Science. - : Wiley. - 0894-3214 .- 1099-1522. ; 21:3, s. 123-135
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Tidskriftsartikel (refereegranskat)abstract
- The effect on mechanical and barrier properties upon addition of glycerol to temperature-responsive hydrophobically modified (HM) potato starch was studied on free films. The addition of glycerol lowered the glass transition temperature, the storage modulus, and the water vapor permeability (WVP) for the HM starch films. The HM starch phase separates upon cooling below an upper critical temperature into a solid and a liquid phase. Adding glycerol to the warm starch solution had an inhibiting effect on the particulate precipitation. Substrates surface sized with HM starch with various amounts of glycerol were investigated with respect to barrier properties; WVP, contact angle and Cobb values. Hydroxypropylated starch was used as a reference. Cobb values and WVP results on surface-sized substrates indicated that the film formation properties of the starches were of great importance for the final surface properties. Good film formation properties were essential for the gas barrier and water resistance while they were less important for high contact angles. The WVP decreased as the glycerol content of the sizes increased, but no sufficient water vapor barrier could be obtained. The HM starches investigated in this work provided good oxygen barrier and the contact angles indicated a hydrophobic character of the surface. The role of the precipitate was investigated, and surface sizing with the precipitate gave low WVP and high contact angles despite its poor film-forming properties under the experimental conditions. Cobb60 values were slightly improved for HM starch with increasing glycerol content over glycerol-free sizing.
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