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- Johansson, Kenth S., et al.
(author)
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Surface modification of wheat gluten films for improved water resistance
- 2010
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In: Abstracts of Papers of the American Chemical Society. - : American Chemical Society (ACS). - 0065-7727. ; 240
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Journal article (other academic/artistic)abstract
- Renewable packaging materials are of interest for a more sustainable environment, and wheat gluten (WG) is one of the most interesting candidates to replace petroleum-based oxygen-barrier polymers for packaging applications. This is due to its attractive combination of flexibility and strength, high gas (especially O2) barrier properties under low humidity conditions and renewability. The main drawback of WG, as with most biopolymers, is its water and moisture sensitivity. The aim of this study was therefore to improve the hydrophobicity of WG films by means of surface modification while maintaining the excellent O2 barrier properties. The surface modification work included a combination of electrospinning of WG fibers and different plasma surface modifications. The latter involved He plasma treatment for crosslinking the WG film prior to the deposition of electrospun WG fibers, O2/Ar plasma etching of the WG films with and without electrospun WG fibers for increasing the surface roughness, and plasma polymerization of hexamethyldisiloxane (HMDSO) and other hydrophobic precursors for hydrophobicity. The plasma polymerization trials were performed both at reduced and atmospheric pressure conditions. The aim of the combined work was to maximize the hydrophobicity by combining a suitable nano-microstructure of the WG fibers with the hydrophobicity of the plasma-deposited coatings. The surface modification work was mainly evaluated by means of water contact angle measurements (hydrophobicity), Scanning Electron Microscopy (surface structures), Water Vapor Transmission Rate (WVTR) (moisture barrier) and Oxygen Transmission Rate (OTR) measurements (oxygen barrier). The surface modification work resulted in significantly improved hydrophobic properties of the WG films. The initial water contact angle increased from 65 to 110-130 degrees, depending on the combinations of electrospinning and plasma modification conditions. The plasma coatings prepared at ambient conditions resulted in slightly lower contact angles compared the plasma coating prepared at reduced pressure. The WVTR and OTR measurements are still in progress and will be reported at the meeting.
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| 2. |
- Dalhus, Bjørn, et al.
(author)
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Structural basis for thermophilic protein stability : structures of thermophilic and mesophilic malate dehydrogenases.
- 2002
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In: J Mol Biol. - 0022-2836. ; 318:3, s. 707-21
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Journal article (peer-reviewed)abstract
- The three-dimensional structure of four malate dehydrogenases (MDH) from thermophilic and mesophilic phototropic bacteria have been determined by X-ray crystallography and the corresponding structures compared. In contrast to the dimeric quaternary structure of most MDHs, these MDHs are tetramers and are structurally related to tetrameric malate dehydrogenases from Archaea and to lactate dehydrogenases. The tetramers are dimers of dimers, where the structures of each subunit and the dimers are similar to the dimeric malate dehydrogenases. The difference in optimal growth temperature of the corresponding organisms is relatively small, ranging from 32 to 55 degrees C. Nevertheless, on the basis of the four crystal structures, a number of factors that are likely to contribute to the relative thermostability in the present series have been identified. It appears from the results obtained, that the difference in thermostability between MDH from the mesophilic Chlorobium vibrioforme on one hand and from the moderate thermophile Chlorobium tepidum on the other hand is mainly due to the presence of polar residues that form additional hydrogen bonds within each subunit. Furthermore, for the even more thermostable Chloroflexus aurantiacus MDH, the use of charged residues to form additional ionic interactions across the dimer-dimer interface is favored. This enzyme has a favorable intercalation of His-Trp as well as additional aromatic contacts at the monomer-monomer interface in each dimer. A structural alignment of tetrameric and dimeric prokaryotic MDHs reveal that structural elements that differ among dimeric and tetrameric MDHs are located in a few loop regions. (c) 2002 Elsevier Science Ltd.
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| 3. |
- Johansson, Kenth S.
(author)
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20 - Surface Modification of Plastics
- 2017
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In: Applied Plastics Engineering Handbook (Second Edition). - : Elsevier. - 9780323390408 ; , s. 443-487
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Book chapter (other academic/artistic)abstract
- Abstract This chapter gives an overview of different methods for improving surface properties of plastics. Plastics are inherently hydrophobic, low surface energy materials and thus do not adhere well to other materials. Adhesion improvement is the most common application but other surface characteristics, such as wettability, water- and chemical resistance, nonfouling, tribological behavior, oxygen, and moisture transmission are also addressed. It has been estimated that 70% of the total production of plastic materials must be surface treated prior to processing. The methods range from vacuum to atmospheric pressure, wet to dry, simple to sophisticated, and inexpensive to very costly to obtain the required functional characteristics of plastics. Most methods used today are dry and environmentally sound. The methods presented are roughly divided in surface activation (e.g., plasma, corona, flame, and UV laser) and surface coating (e.g., plasma polymerization, chemical vapor deposition, Parylene, physical vapor deposition) techniques.
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| 4. |
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| 5. |
- Johansson, Kenth S.
(author)
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Gas barrier properties of plasma-deposited coatings : Substrate effects
- 2000
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In: Polymer Surface Modification. - : VSP International Science Publishers. ; , s. 575-603
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Book chapter (peer-reviewed)abstract
- Plasma deposition of ultra-thin, glasslike SiOx high gas barrier coatings on conventional packaging materials such as polyethylene terphthalate (PET), oriented polypropylene (OPP) and low density polyethylene (LDPE) films has been investigated. In particular, the influence of the polymer film substrate on the gas barrier properties has been examined. It is obvious that the surface roughness in combination with the gas permeability of the polymer film substrate, is the most important parameter and determines the level of oxygen transmission rates (OTR). The roughness of the films increases in the following order: PET
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