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- Bohlin, Erik, 1968-
(författare)
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Optics of coated paperboard : Aspects of surface treatment on porous structures
- 2010
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Calendering of coated and uncoated paper is widely used to enhance optical properties such as gloss and print quality. The aim of this thesis is to characterize coatings and prints, and to validate models using experimental results from optical measurements of physical samples. Calendering of coated paper often leads to a brightness decrease. The mechanism for this is not altogether clear. One common explanation is that the porosity of the coating layer decreases and hence the scattering decreases. By comparing simulated and measured results it was shown that modifications of the surface properties account for the brightness decrease of ground calcium carbonate coated substrates with calendering. Monte Carlo light scattering simulations, taking into account the measured decrease of surface microroughness and increased effective refractive index, showed that surface modifications accounted for most of the observed brightness decrease of the ground calcium carbonate coated substrate, whereas the bulk scattering and absorption coefficients were not affected by calendering. It was also shown that the scattering coefficient is significantly dependent on the coat weight whereas the physical absorption coefficient is not. The penetration of ink in the z-direction of a substrate influences the quality of the print. The ink penetration affects print density, mottling and dot gain, common print effects that influence the preference of consumers. The pressure in the printing nip and the porosity of the substrate both affect the amount of ink that is pressed into the porous structure of a coating layer during printing. By printing pilot coated paperboard with different coating porosity and measuring the resulting optical properties of the prints, a basis for simulations of the different layers, that is to say the coating, the print and the mixed layer in between, was created. Results show that ink distribution is strongly affected by the roughness of the substrate. Fibres and fibre flocks underneath the two coating layers created an unevenly distributed coating thickness that affected the print quality. Differences in pore size and pore size distribution also affected the behaviour of the ink. A coating layer of broad pigment particle size distribution resulted in a relatively low print density, in comparison to coatings of narrowly distributed particle sizes. Comparison of dot gain showed that the coating layer of a narrow particle size distribution had a relatively low dot gain compared to others. In this work, these results are explained by the differences in ink distributions on and in the coating layers.
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| 3. |
- Johansson, Kristin, et al.
(författare)
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Extruded polymer films for optimal enzyme-catalyzed oxygen scavenging
- 2014
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Ingår i: Chemical Engineering Science. - Amsterdam : Elsevier. - 0009-2509 .- 1873-4405. ; 108, s. 1-8
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Tidskriftsartikel (refereegranskat)abstract
- The use of enzymes as oxygen scavengers has a great potential in the food packaging industry. Enzymes can be incorporated into a coating layer that can be applied directly onto the packaging material. For the system to be fully functional, there is however a need for the packaging to have some barrier properties, to be sealable through heat, and to ensure low or no migration of the active coating to the food. Various combinations of the polypropylene (PP), poly(lactic acid) (PLA) and low density polyethylene (LDPE) were extruded onto board coated with the oxygen-scavenging enzyme. Properties such as oxygen-transmission rate, water-vapor transmission rate, heat-sealability, migration and oxygen scavenging capacity were evaluated. All combinations of extruded material resulted in a packaging material able to scavenge the oxygen at both 84% and 100% relative humidity. The greatest decrease in oxygen concentration of the head space of air-tight chambers was achieved with the material extruded with PLA on at least one side. It was found that the extruded plastic is necessary in order to meet the EU directives on migration from food packaging materials of not more than a total of 10 mg/dm2 material. All plastics were heat sealable against themselves but not against any of the other plastics and only LDPE adhered strongly to the enzyme-containing coating
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| 4. |
- Johansson, Kristin, 1983-
(författare)
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Oxygen-reducing enzymes in coatings and films for active packaging
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)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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| 5. |
- Johansson, Kristin, 1983-, et al.
(författare)
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Oxygen-scavenging coatings and films based on lignosulfonates and laccase
- 2012
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Ingår i: Journal of Biotechnology. - Amsterdam : Elsevier. - 0168-1656 .- 1873-4863. ; 161:1, s. 14-18
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Tidskriftsartikel (refereegranskat)abstract
- Laccase and lignosulfonates were included in coating colors and embedded in latex-based or starch-based films and coatings on foil or board. After 6 days at 23C and 100% relative humidity, the oxygen content in airtight chambers decreased from 1.0% (synthetic gas consisting of 99% N2 and 1% O2) to 0.3% in the presence of board coated with lignosulfonate and laccase, while the oxygen content remained unchanged in control experiments without enzyme. The water stability of lignosulfonate-containing latex-based coatings and starch-based films was improved after laccase-catalyzed oxidation of lignosulfonates, which indicates polymerization to products with lower solubility in water. Furthermore, the E' modulus of starch-based films increased with 30%, which indicates laccase-catalyzed polymerization of lignosulfonates resulting in increased stiffness of the film. The results suggest that laccases and lignosulfonates can be used as an oxygen-scavenging system in active packaging and that enzyme-catalyzed polymerization of lignosulfonates contributes to improved water stability and mechanical properties. 2012 Elsevier B.V.
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| 6. |
- Johansson, Kristin, et al.
(författare)
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The effects of coating structure and water-holding capacity on the oxygen-scavenging ability of enzymes embedded in the coating layer
- 2013
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Ingår i: TAPPI Journal. - : TAPPI Press. - 0734-1415. ; 12:6, s. 43-52
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Tidskriftsartikel (refereegranskat)abstract
- Enzymes catalyzing oxygen scavenging were embedded in latex-based coatings with and without barrier kaolin clay to produce material for active packages. The clay was used to create a porous structure, and the closed-structure matrix consisted of a biopolymer comprising either starch or gelatin to increase the water uptake of the coating. The effects of the porous open structure and of the water uptake of the coated layer on the oxygen-scavenging ability of the embedded enzymes were examined at both 75% and 100% relative humidity. The results showed that the porous clay structure led to higher oxygen-scavenging capacity than that of a closed structure at both test conditions by enabling a high diffusion rate for oxygen and glucose to the active sites of the enzymes. The addition of a water-holding biopolymer did not always significantly affect the oxygen-scavenging capacity. However for a less-porous layer at 100% relative humidity, an increase in the amount of biopolymer resulted in an increase in oxygen-scavenging capacity. The results were treated statistically using multiple-factor analysis where the most important factor for the oxygen-scavenging ability was found to be the addition of clay. The coatings were also characterized with respect to water vapor uptake, overall migration, porosity, and scanning electron microscopy images.
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