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Processing and Development of Wheat Gluten Plastics
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials.
2008 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

 Renewable packaging materials are of interest for a more sustainable environment. Wheat gluten is one of the most interesting candidates to replace petroleum-based oxygen-barrier polymers for packaging applications. The high amount of hydrogen bonds makes wheat gluten interesting as oxygen barrier films with sufficient elastomeric mechanical properties. Wheat gluten based materials are homogeneous, mechanically strong and relatively water insoluble compared with other biological materials. Several studies of wheat gluten films have been performed on solution cast films and a few studies have been executed on compression molding. Extrusion, without solvents, is the most common and fastest processing method for the production of packaging films. In order to develop wheat gluten films to commercially competitive material it is crucial to make the material extrudable.The temperature window for extrusion of glycerol-plasticized wheat gluten was increased by the use of salicylic acid, a known scorch retarder and radical scavenger. Small effects of shear-induced heating during extrusion at the higher temperatures suggested that the acid acted as a lubricant and viscosity reducer. The latter was suggested to originate primarily from the salicylic-acid-induced reduction in the degree of protein aggregation/crosslinking, as indicated by size-exclusion high-performance liquid chromatography and chemiluminescence. Electron paramagnetic resonance spectroscopy on extruded films indicated that the beneficial effect of salicylic acid was due to its radical scavenging effect. The complex shear modulus increased more slowly with increasing salicylic acid content above 110-120°C, indicating that the aggregation/crosslinking rate was slower with salicylic acid, i.e. that it did have a scorch-retarding effect, besides yielding a lower final degree/complexity of aggregation.Sodium hydroxide was used as an additive to be able to extrude gluten at alkaline conditions. The oxygen barrier, at dry conditions, was improved significantly with the addition of sodium hydroxide. Oxygen transmission rate measurements, tensile tests, protein solubility, glycerol migration, infrared spectroscopy and electrophoresis were used to assess the properties of the extrudate. It was observed that the extrudate with 3 wt.% sodium hydroxide had the most suitable combination of properties, low oxygen permeability, large strain at break and relatively small aging-induced changes in mechanical properties, the reason probably due to high protein aggregation and low plasticizer migration.As an alternative method to get alkaline conditions ammonium hydroxide was added. It resulted in a three times stronger film compared to the pure gluten glycerol material and had an oxygen barrier that can favorably be compared with these of oriented polyethylene terephtalat or Nylon 66.Several plasticizers were examined in a screening test where the extrusion properties were predicted in a plasticorder. The temperature and melt viscosity were recorded during the kneading. The most promising plasticizers were chosen to further studies with tensile tests. Glycerol was shown to be the most efficient plasticizer for thermoformed gluten films.In order to use wheat gluten as a packaging material, it is important to be able to seal it. Wheat gluten films, molded at 100–130°C, were sealed by impulse sealing at 120– 175°C. The lap-shear and peel strength of the sealed films were evaluated. The lapshear strength was greater than or similar to that of polyethylene film, although the peel strength was poorer.

Place, publisher, year, edition, pages
Stockholm: KTH , 2008. , 47 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2008:65
Keyword [en]
Wheat Gluten, Extrusion, Processing
National Category
Other Basic Medicine
Identifiers
URN: urn:nbn:se:kth:diva-9177ISBN: 978-91-7415-129-9 (print)OAI: oai:DiVA.org:kth-9176DiVA: diva2:25585
Public defence
2008-10-10, F3, Lindstedtsväg 26, KTH, Stockholm, 14:00 (English)
Opponent
Supervisors
Note
QC 20100915Available from: 2008-10-03 Created: 2008-09-30 Last updated: 2018-01-13Bibliographically approved
List of papers
1. Enlarged processing window of plasticized wheat gluten using salicylic acid
Open this publication in new window or tab >>Enlarged processing window of plasticized wheat gluten using salicylic acid
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2006 (English)In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 7, no 3, 771-776 p.Article in journal (Refereed) Published
Abstract [en]

The temperature window for the extrusion of glycerol-plasticized wheat gluten was increased by the use of salicylic acid, a known scorch retarder and radical scavenger. It was possible to extrude 30 wt % glycerol-wheat gluten films with a die-head temperature as high as 135 °C, rather than 95 °C, by incorporating only 1 wt % salicylic acid. Small effects of shear-induced heating during extrusion at the higher temperatures suggested that the acid acted as a lubricant and viscosity reducer. The latter was suggested to originate primarily from the salicylic-acid-induced reduction in the degree of protein aggregation/cross-linking, as indicated by size-exclusion high-performance liquid chromatography and chemiluminescence. Electron paramagnetic resonance spectroscopy on extruded films indicated that the beneficial effect of salicylic acid was due to its radical scavenging effect. Tensile tests on extrudates revealed that the materials produced at the substantially higher processing temperature were still ductile. The complex shear modulus increased more slowly with increasing salicylic acid content above 110-120 °C, indicating that the aggregation/cross-linking rate was slower with salicylic acid, th t is, that it did have a scorch-retarding effect, besides yielding a lower final degree/complexity of aggregation.

Keyword
FLOUR PROTEINS, EXTRUSION CHEMISTRY, FILMS, AGGREGATION, TEMPERATURE, MECHANISM, KINETICS
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-9199 (URN)10.1021/bm050822u (DOI)000236136400020 ()2-s2.0-33645521779 (Scopus ID)
Note
QC 20100913Available from: 2008-10-03 Created: 2008-10-03 Last updated: 2017-12-12Bibliographically approved
2. Properties of Extruded Vital Wheat Gluten Sheets with Sodium Hydroxide and Salicylic Acid
Open this publication in new window or tab >>Properties of Extruded Vital Wheat Gluten Sheets with Sodium Hydroxide and Salicylic Acid
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2009 (English)In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 10, no 3, 479-488 p.Article in journal (Refereed) Published
Abstract [en]

This paper presents a novel approach to improve the barrier and mechanical properties of extruded glycerol-plasticized vital wheat gluten sheets. The sheets were extruded with a single screw extruder at alkaline conditions using 3-5 wt % NaOH. Salicylic acid (SA), known to improve the extrudability of wheat gluten, was also added alone or in combination with NaOH. Oxygen transmission rate and volatile mass measurements, tensile tests, protein solubility, glycerol migration, infrared spectroscopy, and electrophoresis were used to assess the properties of the extrudate. Electrophoresis showed that the gluten/glycerol sheet and the sheet with 3 wt % NaOH and I wt % SA contained the same building blocks in terms of proteins and protein subunits, although the protein solubility in these samples was different. The oxygen barrier, at dry conditions, was improved significantly with the addition of NaOH, On the other hand, the addition of salicylic acid yielded poorer barrier properties. The extrudate was placed on a blotting paper and its aging properties were investigated during the first 120 days. It was observed that the extrudate with 3 wt % NaOH had the most suitable combination of properties (low oxygen permeability, large strain at break, and relatively small aging-induced changes in mechanical properties); the reason is probably due to low plasticizer migration and an optimal protein aggregation/polymerization.

Keyword
RHEOLOGICAL PROPERTIES, PROTEIN-COMPOSITION, BARRIER PROPERTIES, WATER-VAPOR, FILMS, TEMPERATURE, FLOUR, PERMEABILITY, CONFORMATION, AGGREGATION
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-14026 (URN)10.1021/bm800691h (DOI)000264059400003 ()2-s2.0-65249159003 (Scopus ID)
Note
QC 20100708. Tidigare titel: Properties of plasticized vital wheat gluten sheets with sodiumAvailable from: 2010-07-08 Created: 2010-07-08 Last updated: 2017-12-12Bibliographically approved
3. Extrusion of wheat gluten with ammonium hydroxide
Open this publication in new window or tab >>Extrusion of wheat gluten with ammonium hydroxide
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(English)Manuscript (Other academic)
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-9201 (URN)
Note
QC 20100915Available from: 2008-10-03 Created: 2008-10-03 Last updated: 2010-09-15Bibliographically approved
4. Plasticizers for thermoformed wheat gluten films
Open this publication in new window or tab >>Plasticizers for thermoformed wheat gluten films
(English)Manuscript (Other academic)
Keyword
Wheat gluten, compression molding, mixing, plasticisers
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-9202 (URN)
Note
QC 20100915Available from: 2008-10-03 Created: 2008-10-03 Last updated: 2010-09-15Bibliographically approved
5. 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, 56-63 p.Article in journal (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 ()
Note
QC 20100708Available from: 2007-09-19 Created: 2007-09-19 Last updated: 2010-09-15Bibliographically approved

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