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Heat-sealing properties of compression-molded wheat gluten films
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials.
STFI Packforsk AB.
STFI Packforsk AB.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
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.

Place, publisher, year, edition, pages
2007. Vol. 1, no 1, 56-63 p.
Keyword [en]
wheat gluten; compression molding; mechanical properties; sealing properties; lap-shear strength; peel strength
National Category
Chemical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-7475DOI: 10.1166/jbmb.2007.006ISI: 000253201400007OAI: oai:DiVA.org:kth-7475DiVA: diva2:12511
Note
QC 20100708Available from: 2007-09-19 Created: 2007-09-19 Last updated: 2010-09-15Bibliographically approved
In thesis
1. Aging and heat-sealing properties of films based on wheat gluten
Open this publication in new window or tab >>Aging and heat-sealing properties of films based on wheat gluten
2007 (English)Licentiate thesis, comprehensive summary (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, edition, pages
Stockholm: KTH, 2007. 59 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2007:58
Keyword
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)
Presentation
2007-09-21, Sal K2, KTH, Teknikringen 28, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20101103Available from: 2007-09-19 Created: 2007-09-19 Last updated: 2010-11-03Bibliographically approved
2. Processing and Development of Wheat Gluten Plastics
Open this publication in new window or tab >>Processing and Development of Wheat Gluten Plastics
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
Wheat Gluten, Extrusion, Processing
National Category
Other Basic Medicine
Identifiers
urn:nbn:se:kth:diva-9177 (URN)978-91-7415-129-9 (ISBN)
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: 2010-09-15Bibliographically approved
3. Protein-based Packaging Films, Sheets and Composites: Process Development and Functional Properties
Open this publication in new window or tab >>Protein-based Packaging Films, Sheets and Composites: Process Development and Functional Properties
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The depletion of the petroleum resources and a number of environmental concerns led to considerable research efforts in the field of biodegradable materials over the last few decades. Of the diverse range of biopolymers, wheat gluten (WG) stands out as an alternative to synthetic plastics in packaging applications due to its attractive combination of flexibility and strength, high gas barrier properties under low humidity conditions and renewability. The availability of raw materials has also been largely increased with an increase in the production of WG as a low-cost surplus material due to increasing demand for ethanol as fuel. In this study, WG was processed into films, sheets and composites using some of the most widely used techniques including solution casting, compression molding, extrusion and injection molding, accompanying process optimizations and characterization of their functional properties. This thesis consists mainly of six parts based on the purpose of the study. The first part addresses the aging and optical properties of the cast film in order to understand the mechanisms and reasons for the time-dependant physical and chemical changes. The films plasticized with glycerol were cast from acidic (pH 4) and basic (pH11) solutions. 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 became 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. 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. In addition the greater plasticizer loss of the pH 4 film was presumably due to its initial lower degree of protein aggregation/polymerization. Glycerol content did not significantly change the opacity and pH 4 films showed good contact clarity because of less Maillard reaction. In the second part, the heat-sealability of WG films was investigated, using an impulse-heat sealer, as the sealability is one of the most important properties in the use of flexible packaging materials. It was observed that the WG films were readily sealable while preserving their mechanical 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. The third part describes the possibility of using industrial hemp fibers to reinforce wheat gluten sheets based on evaluation of the fiber contents, fiber distribution and bonding between the fibers and matrix. It was found that the hemp fibers enhanced the mechanical properties, in which the fiber contents played a significant role in the strength. The fiber bonding was improved by addition of diamine as a cross-linker, while the fiber distribution needed to be improved. The fourth part presents a novel approach to improve the barrier and mechanical properties of extruded WG sheets with a single screw extruder at alkaline conditions using 3-5wt.% NaOH with or without 1 wt.% salicylic acid. The oxygen barrier, at dry conditions, was improved significantly with the addition of NaOH, while the addition of salicylic acid yielded poorer barrier properties. It was also observed that the WG sheets with 3 wt.% NaOH had the most suitable combination of low oxygen permeability and relatively small time-dependant changes in mechanical properties, probably due to low plasticizer migration and an optimal protein aggregation/polymerization. In the fifth part WG/PLA laminates were characterized for the purpose of improving the water barrier properties. The lamination was performed at 110°C and scanning electron microscopy showed that the laminated films were uniform in thickness. The laminates significantly suppressed the mass loss and showed promising water vapor barrier properties in humid conditions indicating possible applications in packaging. The final part addresses the development of injection molding processes for WG. Injection-molded nanocomposites of WG/MMT were also characterized. WG sheets were successively processed using injection molding and the process temperatures were found to preferably be in a range of 170-200°C, which was varied depending on the sample compositions. The clay was found to enhance the processability, being well dispersed in the matrix. The natural clay increased the tensile stiffness, whereas the modified clay increased the surface hydrophobicity. Both clays decreased the Tg and increased the thermal stability of the nanocomposites. The overall conclusion was that injection molding is a promising method for producing WG items of simple shapes. Further studies will reveal if gluten can also be used for making more complex shapes.

Place, publisher, year, edition, pages
Stockholm: KTH, 2009. 81 p.
Keyword
wheat gluten, solution casting, compression molding, extrusion, injection molding, aging, migration, opacity, heat sealability, hemp fiber, laminate, polylactic acid, clay, nanocomposites.
National Category
Other Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-10567 (URN)978-91-7415-358-3 (ISBN)
Public defence
2009-06-12, H1, Teknikringen 33, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20100708Available from: 2009-06-04 Created: 2009-05-26 Last updated: 2011-03-23Bibliographically approved

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