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Aging and heat-sealing properties of films based on wheat gluten
2007 (English)Licentiatavhandling, sammanläggning (Other scientific)
Abstract [en]

Recently the research interest of the possibility of using wheat gluten (WG) as packaging material has greatly increased due to its combination of high gas barrier, attractive mechanical, film-forming and renewable properties. The source is also readily available and inexpensive on a worldwide basis. The glycerol-plasticized WG films cast from pH 4 and pH 11 solutions were investigated in order to understand the mechanisms behind the undesired aging. The film prepared from the pH 11 solution was mechanically more stable upon aging than the pH 4 film, which was initially very ductile but turning brittle with time. It was revealed that the protein structure of the pH 4 film was initially less polymerized/aggregated and the polymerization increased during storage but it did not reach the degree of aggregation of the pH 11 film, whereas deamidation was occurred and increased in the pH 11 film. During aging, the pH 4 film lost more mass than the pH 11 film mainly due to migration of glycerol but also due to some loss of volatile mass and the greater plasticizer loss of pH 4 film was presumably due to its initial lower degree of protein aggregation /polymerization. The glycerol migration of cast films exposed to a porous paper was further investigated with respect to pH of cast solution, glycerol content and film thickness since it was the main reason for deterioration of the properties. The opacity was also characterized. The glycerol migration was quantified using GC method in order to determine only glycerol content, but not other volatile substances. Glycerol content did not significantly change the opacity and pH 4 films showed good contact clarity because of less Maillard reaction. Glycerol was extensively migrating to the paper support and the migration seemed to be diffusion controlled. The heat sealability of WG films was investigated, using an impulse-hear sealer. It was observed that the WG films were readily sealable keeping up their integrity. The sealing temperature had a negligible effect on the lap-shear strength, but the peel strength increased with sealing temperature. The lap-shear strength increased with increasing mold temperature and the failure mode changed.

Place, publisher, year, pages
Stockholm: KTH, 2007. 59 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2007:58
Keyword [en]
wheat gluten, aging, migration, opacity, heat sealability, shear strength
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-4489 (URN)978-91-7178-748-4 (ISRN)978-91-7178-749-1 (ISBN)oai:DiVA.org:kth-4489 (OAI)
Presentation
2007-09-21, Sal K2, KTH, Teknikringen 28, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20101103Available from2007-09-19 Created:2007-09-19 Last updated:2010-11-03Bibliographically approved
List of papers
1. Aging properties of films of plasticized vital wheat gluten cast from acidic and basic solutions
Open this publication in new window or tab >>Aging properties of films of plasticized vital wheat gluten cast from acidic and basic solutions
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2006 (English)In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 7, no 5, 1657-1664Artikel i tidskrift (Refereed) Published
Abstract [en]

In order to understand the mechanisms behind the undesired aging of films based on vital wheat gluten plasticized with glycerol, films cast from water/ethanol solutions were investigated. The effect of pH was studied by casting from solutions at pH 4 and pH 11. The films were aged for 120 days at 50% relative humidity and 23 C, and the tensile properties and oxygen and water vapor permeabilities were measured as a function of aging time. The changes in the protein structure were determined by infrared spectroscopy and size-exclusion and reverse-phase high-performance liquid chromatography, and the film structure was revealed by optical and scanning electron microscopy. The pH 11 film was mechanically more stable with time than the pH 4 film, the latter being initially very ductile but turning brittle toward the end of the aging period. The protein solubility and infrared spectroscopy measurements indicated that the protein structure of the pH 4 film was initially significantly less polymerized/ aggregated than that of the pH 11 film. The polymerization of the pH 4 film increased during storage but it did not reach the degree of aggregation of the pH 11 film. Reverse-phase chromatography indicated that the pH 11 films were to some extent deamidated and that this increased with aging. At the same time a large fraction of the aged pH 11 film was unaffected by reducing agents, suggesting that a time-induced isopeptide cross-linking had occurred. This isopeptide formation did not, however, change the overall degree of aggregation and consequently the mechanical properties of the film. During aging, the pH 4 films lost more mass than the pH 11 films mainly due to migration of glycerol but also due to some loss of volatile mass. Scanning electron and optical microscopy showed that the pH 11 film was more uniform in thickness and that the film structure was more homogeneous than that of the pH 4 film. The oxygen permeability was also lower for the pH 11 film. The fact that the pH 4 film experienced a larger and more rapid change in its mechanical properties with time than the pH 11 film, as a consequence of a greater loss of plasticizer, was presumably due to its initial lower degree of protein aggregation/ polymerization. Consequently, the cross-link density achieved at pH 4 was too low to effectively retain volatiles and glycerol within the matrix.

Keyword
hydrogen-ion equilibria, barrier properties, mechanical-properties, secondary structure, chemical properties, protein-composition, dope solution, transport, time, increase
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-14024 (URN)10.1021/bm0600973 (DOI)000237593600036 (ISI)2-s2.0-33744517880 (ScopusID)
Note
QC 20100708Available from2010-07-08 Created:2010-07-08 Last updated:2010-11-03Bibliographically approved
2. Heat-sealing properties of compression-molded wheat gluten films
Open this publication in new window or tab >>Heat-sealing properties of compression-molded wheat gluten films
2007 (English)In: Journal of Biobased Materials and Bioenergy, ISSN 1556-6560, Vol. 1, no 1, 56-63Artikel i tidskrift (Refereed) Published
Abstract [en]

The impulse heat-sealing properties of wheat gluten films were investigated. Films containing 30 wt% glycerol were compression molded at 100-130 degrees C and then sealed in a lap-shear or peel-test geometry at 120-175 degrees C. The tensile properties of the pristine films and the lap-shear and peel strength of the sealed films were evaluated and the seals were examined by scanning electron microscopy. Glycerol was added to the film surfaces prior to sealing in an attempt to enhance the seal strength. It was observed that the wheat gluten films were readily sealable. At a 120 degrees C sealing temperature and without glycerol as adhesive, the lap-shear strength was greater than or similar to that of polyethylene film, although the peel strength was poorer. The sealing temperature had a negligible effect on the lap-shear strength, but the peel strength increased with sealing temperature. The lap-shear strength increased with increasing mold temperature and the failure mode changed, especially in the absence of glycerol adhesive, from a cohesive (material failure) to an adhesive type. From previous results, it is known that the high-temperature (130 degrees C) compression-molded film was highly cross-linked and aggregated, and this prevents molecular interdiffusion and entanglement and thus leads to incomplete seal fusion and, in general, adhesive failure. The presence of glycerol adhesive had a beneficial affect on the peel strength but no, or only a minor, effect on the lap-shear strength.

Keyword
wheat gluten; compression molding; mechanical properties; sealing properties; lap-shear strength; peel strength
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-7475 (URN)10.1166/jbmb.2007.006 (DOI)000253201400007 (ISI)
Note
QC 20100708Available from2007-09-19 Created:2007-09-19 Last updated:2010-09-15Bibliographically approved
3. Comparison of properties of wheat gluten films prepared at pH 4 and pH 11; effects of glycerol content and film thickness
Open this publication in new window or tab >>Comparison of properties of wheat gluten films prepared at pH 4 and pH 11; effects of glycerol content and film thickness
(English)Manuskript (Other academic)
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-7476 (URN)
Note
QC 20101103Available from2007-09-19 Created:2007-09-19 Last updated:2010-11-03Bibliographically approved

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