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Strategies to improve the aging, barrier and mechanical properties of chitosan, whey and wheat gluten protein films
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
2005 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Chitosan, Whey Protein Isolate (WPI) and vital wheat gluten (WG) are three biomaterials that have quite promising properties for packaging purposes. They have good film forming properties and good gas barrier properties in dry conditions. Moreover, because they are produced from industrial waste of food processing, they offer an ecological advantage over polymers made from petroleum. However, their physicochemical characteristics still must be improved for them to be of commercial interest for the food packaging industry. The purpose of this work was to study different strategies aiming to improve the water resistance and aging properties of these polymers, which are some of the key disadvantages of these materials.

The produced solution cast chitosan and WPI films were characterised with scanning electron microscopy (SEM), density measurements and thermogravimetry. The water vapour transmission rate was determined at a relative humidity of 11%. In the first part, mechanical properties of solid films and seals were assessed by tensile testing. WG film’s tensile properties and oxygen and water vapour permeabilities were measured as a function of aging time. The changes in the protein structure were determined by infrared spectroscopy and size-exclusion high-performance liquid chromatography and the film structure was revealed by optical and scanning electron microscopy. Gluten-clay nanocomposites were characterised by tensile testing, X-ray diffraction and transmission electron microscopy.

The incorporation of a hydrophobic biodegradable polymer, poly ( ε-caprolactone), PCL, in both chitosan and whey protein, yielded a significant decrease in water vapour transmission rate. It was observed that a certain amount of the PCL particles were ellipsoidal in chitosan and fibrous in WPI. The obtained data also indicated that the particle shape had an important influence in the water vapour transmission rate.

In the second part, the aging properties of WG films, plasticized with glycerol and cast from water/ethanol solutions with pH=4 or pH=11 were investigated. WG films made from alkaline solutions were mechanically more time-stable than the acidic ones, the latter being initially very ductile but turning brittle towards the end of the aging period. The protein solubility measurements indicated that the protein structure of the acidic films was initially significantly less aggregated than the in basic films. During aging the acidic films lost more mass than the basic films through slow evaporation of volatiles (water/ethanol) and through migration of glycerol to the paper support. The oxygen permeability was also lower for the basic films.

In the last part, the properties of new and aged glycerol-plasticized WG films at acidic and basic conditions containing ≤4.5 wt% natural or quaternary-ammonium-salt-modified montmorillonite were studied. Films of WG with montmorillonite were possible to produce by solution casting. The aging rate of acidic and basic films was unaffected by the incorporation of clay. However, the large reduction in water vapour permeability for most systems suggested that the clay sheets were evenly distributed within the films. The film prepared from basic solution and containing natural clay was almost completely exfoliated as revealed by transmission electron microscopy and X-ray diffraction. The best water vapour barrier properties were obtained by using modified clay.

Place, publisher, year, edition, pages
Stockholm: KTH , 2005. , 68 p.
Series
Trita-FPT-Report, ISSN 1652-2443 ; 2005:14
Keyword [en]
Chemistry, biodegradable polymers, chitosan, whey protein, wheat gluten, poly(ε-caprolactone), montmorillonite, food packaging, permeability, mechanical properties, aging, pH, solubility, migration, solution casting.
Keyword [sv]
Kemi
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-208ISBN: 91-7178-049-1 (print)OAI: oai:DiVA.org:kth-208DiVA: diva2:7916
Public defence
2005-05-27, K2, Teknikringen 28, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20101013Available from: 2005-05-18 Created: 2005-05-18 Last updated: 2010-10-13Bibliographically approved
List of papers
1. Transport properties of chitosan and whey blended with poly(ε-caprolactone) assessed by standard permeability measurements and microcalorimetry
Open this publication in new window or tab >>Transport properties of chitosan and whey blended with poly(ε-caprolactone) assessed by standard permeability measurements and microcalorimetry
2001 (English)In: Polymer, ISSN 0032-3861, E-ISSN 1873-2291, Vol. 42, no 9, 4401-4408 p.Article in journal (Refereed) Published
Abstract [en]

Blends of poly(p-caprolactone) (PCL) with chitosan and a whey-protein-isolate (WPI) were prepared by solution mixing and film casting. The purpose was to increase the water vapour resistivity of chitosan and whey by blending them with a hydrophobic biodegradable polymer. The water vapour transmission rate was determined by a standard technique and by a new technique based on microcalorimetry. The blends were characterised by scanning electron microscopy (SEM), density measurements and thermogravimetry. Oxygen permeability was measured on the pure components and on some of the blends. The incorporation of PCL yielded a pronounced decrease in water vapour transmission rate of both chitosan and the WPI measured at a relative humidity gradient of 11 to 0%. A volume content of 17-18% of PCL lowered the water vapour transmission rate by 70-90%. It was found that the majority of the PCL particles were ellipsoidal in chitosan and fibrous in the WPI and the data indicated that the particle shape had an important influence on the water vapour transmission rate. The large decrease in water vapour transmission rate was also due to a reduction in water solubility because of limited swelling of the constrained chitosan or WPI matrix in the presence of PCL. SEM revealed that the miscibility/compatibility between PCL and the matrices was good. The water vapour transmission rate of the films decreased with increasing vacuum-drying time of the chitosan and WPI solutions. Microcalorimetry provided accurate estimates of water vapour transmission rate. Furthermore. this technique proved to be very flexible and the water vapour transmission rate could be determined over a broad range of relative humidities in a single experiment.

Keyword
chitosan, whey, transport properties
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-5127 (URN)10.1016/S0032-3861(00)00680-7 (DOI)000167050400049 ()
Note
QC 20101005Available from: 2005-05-18 Created: 2005-05-18 Last updated: 2017-12-04Bibliographically approved
2. Mechanical and physical properties of chitosan and whey blended with poly(ε- caprolactone)
Open this publication in new window or tab >>Mechanical and physical properties of chitosan and whey blended with poly(ε- caprolactone)
2002 (English)In: International Journal of Polymeric Materials, ISSN 0091-4037, E-ISSN 1563-535X, Vol. 51, no 3, 275-289 p.Article in journal (Refereed) Published
Abstract [en]

Properties important for packaging were studied on blends of 0-15 wt% poly( caprolactone) and chitosan and a whey-protein-isolate. The blends were obtained by solution mixing, and films were produced by solvent casting. Transparency was measured by UV/VIS spectroscopy and the printability was qualitatively estimted by using a red ethanol dye. Mechanical properties of solid films and seals were assessed by tensile tests. Stiffness and folding endurence were also measured. The blend morphology was characterized by scanning electron microscopy. It was found that all the blends were transparent. The whey-protein-isolate had the best printability properties and printability remained in the poly( -caprolactone)-blends. Film stiffness decreased and strain at break increased strongly when the pure chitosan and the pure whey-protein-isolate were wetted. The addition of poly( -caprolactone) to chitosan and whey-protein-isolate had only a moderate effect on the toughness properties but a strong effect on the modulus which could be predicted by the Halpin-Tsai model. The modulus of the whey-protein-isolate increased and the modulus of the chitosan decreased with the addiion of poly( -caprolactone). It was found that it was impossible to seal chitosan with a standard heat-pulse sealing technique. The whey-protein-isolate was sealable but the strength of the seals was lower than the intrinsic strength of the pure whey-protein-isolate. The folding endurance properties of chitosan and its blends were far better than those of the whey-protein-isolate and its blends.

Keyword
Poly(ε-caprolactone), Chitosan, Whey, Physical Properties, Optical Properties, Blends
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-5128 (URN)10.1080/00914030213038 (DOI)
Note
QC 20101013Available from: 2005-05-18 Created: 2005-05-18 Last updated: 2017-12-04Bibliographically approved
3. 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
Show others...
2006 (English)In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 7, no 5, 1657-1664 p.Article in journal (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 ()2-s2.0-33744517880 (Scopus ID)
Note
QC 20100708Available from: 2010-07-08 Created: 2010-07-08 Last updated: 2017-12-12Bibliographically approved
4. Properties of new and aged montmorillonite-wheat gluten composite films
Open this publication in new window or tab >>Properties of new and aged montmorillonite-wheat gluten composite films
Show others...
2006 (English)In: Journal of Agricultural and Food Chemistry, ISSN 0021-8561, E-ISSN 1520-5118, Vol. 54, no 4, 1283-1288 p.Article in journal (Refereed) Published
Abstract [en]

The properties of new and aged glycerol-plasticized vital wheat gluten films containing ≤4.5 wt % natural or quaternary ammonium salt modified montmorillonite clay were investigated. The films were cast from pH 4 or pH 11 ethanol/water solutions. The films, aged for ≤120 days, were characterized by tensile testing, X-ray diffraction, and transmission electron microscopy. In addition, water vapor permeability (11% relative humidity) and the content of volatile components were measured. The large reduction in the water vapor permeability with respect to the pristine polymer suggests that the clay platelets were evenly distributed within the films and oriented preferably with the platelet long axis parallel to the film surface. The film prepared from pH 11 solution containing natural clay was, as revealed by transmission electron microscopy and X-ray diffraction, almost completely exfoliated. This film was consequently also the strongest, the stiffest, and the most brittle and, together with the pH 11 film containing modified clay, it also showed the greatest decrease in water vapor permeability. The large blocking effect of the clay had no effect on the aging kinetics of the films. During aging, the pH 4 and pH 11 film strength and the pH 4 film stiffness increased and the pH 4 film ductility decreased at the same rate with or without clay. This suggests that the aging was not diffusion rate limited, that is, that the loss of volatile components or the migration of glycerol or glycerol/wheat gluten phase separation was not limited by diffusion kinetics. The aging rate seemed to be determined by slow structural changes, possibly involving protein denaturation and aggregation processes.

Keyword
Wheat gluten, aging, montmorillonite, cast films, tensile properties, water vapor permeability
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-5130 (URN)10.1021/jf0522614 (DOI)000235627800043 ()2-s2.0-33644905614 (Scopus ID)
Note
Uppdaterad från submitted till published: 20101013. QC 20101013Available from: 2005-05-18 Created: 2005-05-18 Last updated: 2017-12-04Bibliographically approved

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