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Multi-material multilayer plastic packaging (MMPP) is widely applied in fast moving consumer goods (FMCG) combining functionalities of distinct materials. These packaging structures can enhance properties, such as resource-use efficiency and barrier performance leading to consequential benefits like a prolonged shelf-life. Nevertheless, they represent a challenge for existing recycling systems, confronting circular economy principles. This study aim was to foresight the future of recycling technologies for MMPP in the next five to ten years. Future scenarios were identified, including (1) high-performance material recycling, (2) recycling into hydrocarbons, (3) business as usual, and (4) downcycling. In-depth interviews and a feedback survey were methods used to validate the scenario matrix while defining experts' expectations towards the future. The analysis showed that distinct technologies will develop unevenly in different parts of the world. A mix of all scenarios is probable in the upcoming years, depending, essentially, on regulations and technology availability. Advanced high-performance material recycling encounters systemic bottlenecks, such as insufficient sorting technology for post-consumer waste. In contrast, chemical recycling (feedstock) is concentrating investments as a solution, requiring low input-characterization. Additionally, design for recycling trends might reduce multilayers’ complexity. A gap between recycling targets and recycling technologies was identified, representing short-term opportunities for more sustainable materials, such as bio-based.

This article describes nanocomposite films with separately grown protein nanofibrils (PNFs) in a nonfibrillar protein matrix from the same protein starting material (whey). Tensile tests on the glycerol-plasticized films indicate an increased elastic modulus and a decreased extensibility with increasing content of PNFs, although the films are still ductile at the maximum PNF content (15 wt %). Infrared spectroscopy confirms that the strongly hydrogen-bonded β-sheets in the PNFs are retained in the composites. The films appear with a PNF-induced undulated upper surface. It is shown that micrometer-scale spatial variations in the glycerol distribution are not the cause of these undulations. Instead, the undulations seem to be a feature of the PNF material itself. It was also shown that, apart from plasticizing the protein film, the presence of glycerol seemed to favor to some extent exfoliation of stacked β-sheets in the proteins, as revealed by X-ray diffraction.

To understand if and how extraction conditions influence properties of molded protein films, Crambe abyssinica protein concentrates were produced from deoiled seed meal under various extraction con ...

In this study, we combined two wheat proteins, gliadin (Gli)/glutenin (GT), and modified potato starch (MPS) into composites using extrusion. In the Gli/GT–MPS composites, we studied the structural dynamics of proteins and starch, protein–starch interactions, protein properties, and composite morphology in relation to mechanical and barrier properties. Materials with different ratios of Gli/GT and MPS were extruded using either glycerol or glycerol–water at 110 and 130 °C. For the first time, a hierarchical hexagonal structure of Gli proteins was observed in Gli–MPS composite at both extrusion temperatures. The higher temperature (130 °C) induced a higher degree of protein cross-links, an increase in the polymer size, and formation of β-sheets compared to 110 °C. The combination of plasticizers (glycerol and water) favored a micro-structural morphology with improved gelatinization of starch, processability, as well as strength, stiffness, and extensibility of GT–MPS composites. The highest amount of the o...

Gliadin and glutenin proteins with 10, 20, 30 and 40% of glycerol were compression molded into films (130 °C) and evaluated for protein polymerization, β-sheet structure and nano-structural morphology. Here, for the first time we show how different amounts of glycerol impact the nano-structure and functional properties of the gliadin and glutenin films. Most polymerized protein was found in the gliadin films with 20 and 30% glycerol, and in all the glutenin films (except 10%), by RP-HPLC. A β-sheet-rich protein structure was found to be high in the 10 and 20% glycerol gliadin films, and in the 20 and 30% glycerol glutenin films by FT-IR. Glycerol content of 20, 30 and 40% impacted the nano-structural morphology of the gliadin glycerol films observed by SAXS, and to a limited extent for 10 and 20% glycerol gliadin films revealed by WAXS. No ordered nano-structure was found for the glutenin glycerol films. The 20%, 30% and 40% glycerol films were the most tunable for specific mechanical properties. For the ...

The aim of the present study was to develop an understanding of how wheat plants can be used as a “green factory” by the modulation of genotype (G) and environmental (E) interactions to fine-tune the structure and increase the strength of gluten based materials.

Despite the increasing production of wheat gluten (WG) for industrial use, minor attention has been given to the impact of the separation procedure on the gluten quality. The purpose of the present ...

Protein macromolecules adopted for biological and bio-based material functions are known to develop a structured protein network upon chemical modification. In this study, we aimed to evaluate the ...

In the present study, we were able to produce composites of wheat gluten (WG) protein and a novel genetically modified potato starch (MPS) with attractive mechanical and gas barrier properties using extrusion. Characterization of the MPS revealed an altered chain length distribution of the amylopectin fraction and slightly increased amylose content compared to wild type potato starch. WG and MPS of different ratios plasticized with either glycerol or glycerol and water were extruded at 110 and 130 degrees C. The nanomorphology of the composites showed the MPS having semicrystalline structure of a characteristic lamellar arrangement with an approximately 100 A period observed by small-angle X-ray scattering and a B-type crystal Structure observed by wide-angle X-ray scattering analysis. WG has a structure resembling the hexagonal macromolecular arrangement as reported previously in WG films. A larger amount of beta-sheets was observed in the samples 70/30 and 30/70 WG-MPS processed at 130 degrees C with 45% glycerol. Highly polymerized WG protein was found in the samples processed at 130 degrees C versus 110 degrees C. Also, greater amounts of WG protein in the blend resulted in greater extensibility (110 degrees C) and a decrease in both E-modulus and maximum stress at 110 and 130 degrees C, respectively. Under ambient conditions the WG-MPS composite (70/30) with 45% glycerol showed excellent gas barrier properties to be further explored in multilayer film packaging applications.

Commercial potato protein concentrate (PPC) was investigated as a source of thermoformed bio-based plastic film. Pressing temperatures of 100 to 190 °C with 15 to 25% glycerol were used to form PPC films. The shape of the tensile stress–strain curve in thermoformed PPC was controlled by glycerol level and was independent of processing temperature. Tensile testing revealed that elongation at break increased with processing temperature while Young's modulus was unaffected by processing temperature, both in contrast to previous results in protein based systems. Also in contrast to previous studies, Young's modulus was found to be only sensitive to glycerol level. Maximum tensile stress increased with increasing processing temperature for PPC films. Maximum stress and strain at break correlated with the extractable high molecular weight protein content of the processed films measured with size exclusion chromatography. Infrared absorption indicated that the content of β-sheet structure increased from the commercial protein concentrate to that pressed at 100 °C, but did not further develop with increasing press temperature. Changes in structural arrangements were observed by small angle X-ray scattering indicating the development of different correlation distances with processing temperature but with no clear long range order at the supramolecular level. The novel Young's modulus behaviour appears to be due to constant secondary structure or the effect of aggregated protein structure formed during protein production. Unique strain at break behaviour with processing temperature was demonstrated, likely due to new connections formed between those aggregates.

Wheat gluten and chitosan are renewable materials that suffer from some poor properties that limit their use as a potential replacement of petroleum-based polymers. However, polymer blends based on ...

Crambe abyssinica is a plant with potential for use in industrial (non-food) plant oil production. The side stream from this oil production is a high-protein crambe meal that has limited value, as it is not fit for food or feed use. However, it contains proteins that could potentially make it a suitable raw material for higher-value products. The purpose of this study was to find methods of making this side stream into extruded films, showing that products with a higher value can be produced. The study mainly considered the development of material compositions and methods of preparing and extruding the material. Wheat gluten was added as a supportive protein matrix material, together with glycerol as a plasticizer and urea as a denaturant. The extrudate was evaluated with respect to mechanical (tensile testing) and oxygen barrier properties, and the extrudate structure was revealed visually and by scanning electron microscopy. A denser, more homogeneous material had a lower oxygen transmission rate, higher strength, and higher extensibility. The most homogeneous films were made at an extruder die temperature of 125-130 °C. It is shown here that a film can be extruded with promising mechanical and oxygen barrier properties, the latter especially after a final compression molding step.

Wheat starch carbamates of different degrees of substitution were produced in laboratory experiments and for the first time their film forming performance were investigated. The carbamation reaction between urea and starch was investigated using a factorial design. Long reaction time, 2 h, and high urea content, 10 and 25%, resulted in a high degree of substitution, 0.07 and 0.15, respectively. These starch carbamates were assumed to be cross-linked and showed best film forming properties resulting in continuous and firm films. Furthermore, a high degree of carbamate substitution favored a decrease in glass transition temperature (T-g) in cast films. The addition of acid as a catalyst for carbamation of starch produced inconsistent results and mainly lead to degradation of starch molecules that caused brittle films. FTIR and C-13 NMR analyses confirmed the covalent bonding between urea and starch in starch carbamates. In a final step, production of starch carbamates was successfully scaled up. A potential industrial use of these starches is as oxygen barrier in multilayer food packaging.

Ten chemical additives were selected from the literature for their proposed modifying activity in protein-protein interactions. These consisted of acids, bases, reducing agents, and denaturants and were added to residual deoiled meals of Crambe abyssinica (crambe) and Brassica carinata (carinata) to modify the properties of plastics produced through hot compression molding at 130 °C. The films produced were examined for tensile properties, protein solubility, molecular weight distribution, and water absorption. Of the additives tested, NaOH had the greatest positive effect on tensile properties, with increases of 105% in maximum stress and 200% in strain at maximum stress for crambe and a 70% increase in strain at maximum stress for carinata. Stiffness was not increased by any of the applied additives. Changes in tensile strength and elongation for crambe and elongation for carinata were related to changes in protein solubility. Increased pH was the most successful in improving the protein aggregation and mechanical properties within the complex chemistry of residual oilseed meals.

Here, we investigated the structure of natural montmorillonite (MMT) and modified Cloisite C15A (MMT pre-intercalated with a dimethyl-dehydrogenated tallow quaternary ammonium surfactant) nanoclays in the wheat gluten-urea matrix in order to obtain a nanocomposite with improved barrier and mechanical properties. Small-angle X-ray scattering indicated that the characteristic hexagonal closed packed structure of the wheat gluten-urea matrix was not found in the CISA system and existed only in the 3 and 5 wt % MMT composites. SAXS/WAXS, TGA, and water vapor/oxygen barrier properties indicated that the dispersion of the C15A clay was somewhat better than the natural MMT clay. Confocal laser scanning microscopy showed MMT clay clusters and C15A clay particles dispersed in the protein matrix, and these were preferentially oriented in the extrusion direction only at 5 wt % of the CIS clay. The water vapor/oxygen barrier properties were improved with the presence of clay. Independent of the clay content used, the stiffness decreased and the extensibility increased in the presence of C15A due to the surfactant induced changes on the protein. The opposite "more expected" clay effect (increasing stiffness and decreasing extensibility) was observed for the MMT composites.

For economic reasons and to save time there is a need to shorten the drying operation associated with the production of chitosan materials. Hence it is of interest to extrude chitosan at as high a ...

Wheat gluten (WG) and its components, gliadin and glutenin proteins, form the largest polymers in nature, which complicates the structural architecture of these proteins. Wheat gluten, gliadin and glutenin proteins in unmodified form showed few secondary structural features. Structural modification of these proteins using heat, pressure and the chemical chaperone glycerol resulted in a shift to organized structure. In modified gliadin, nano-structural molecular arrangements in the form of hexagonal closed packed (HCP) assemblies with lattice parameter of (58 A) were obvious together with development of intermolecular disulphide bonds. Modification of glutenin resulted in highly polymerized structure with proteins linked not only by disulphide bonds, but also with other covalent and irreversible bonds, as well as the highest proportion of β-sheets. From a combination of experimental evidence and protein algorithms, we have proposed tertiary structure models of unmodified and modified gliadin and glutenin proteins. An increased understanding of gliadin and glutenin proteins structure and behavior are of utmost importance to understand the applicability of these proteins for various applications including plastic materials, foams, adhesives, films and coatings.

This study presents the oxygen-barrier properties of paperboards with a wheat gluten (WG)/montmorillonite clay (MMT) multilayer coating, in which MMT was sandwiched between two layers of WG. Urea was added to the WG to facilitate the coating procedure and the clay was applied as an aqueous dispersion. With a coating thickness of similar to 20 mu m, oxygen transmission rates were 8-10 cm(3/)(m(2) day atm) at 50% RH, which meant that the oxygen barrier was ca. 25 times better than that given by a single-layer WG-coated paperboard (uncoated paperboard showed infinite values). The water vapor transmission rate (WVTR) was 28-39 g/(m(2) day) using a 50-0% RH gradient, which was 6-to 8-fold lower than the value for uncoated paperboard. Tensile tests revealed small, if any, mechanical effects when the paperboard was coated. A protein solubility analysis indicated that urea-containing WG films were slightly more intermolecularly cross-linked than urea-free WG films. X-ray diffraction revealed that the MMT layer consisted of unswollen tactoids similar to those observed in the MMT powder. The Cobb(60) data showed that both WG and clay increased the water absorbency. (C) 2013 Elsevier B.V. All rights reserved.

For a number of applications, gluten protein polymer structures are of the highest importance in determining end-use properties. The present article focuses on gluten protein structures in the wheat grain, genotype- and environment-related changes, protein structures in various applications, and their impact on quality. Protein structures in mature wheat grain or flour are strongly related to end-use properties, although influenced by genetic and environment interactions. Nitrogen availability during wheat development and genetically determined plant development rhythm are the most important parameters determining the gluten protein polymer structure, although temperature during plant development interacts with the impact of the mentioned parameters. Glutenin subunits are the main proteins incorporated in the gluten protein polymer in extracted wheat flour. During dough mixing, gliadins are also incorporated through disulfide-sulfhydryl exchange reactions. Gluten protein polymer size and complexi...

With the increased use of plant oils as sustainable feedstocks, industrial oilseed meal from Crambe abyssinica (crambe) and Brassica carinata (carinata) can become a potential source for oilseed meal based plastics. In this study, crambe and carinata oilseed meal plastics were produced with 10–30 % glycerol and compression molding at 100–180 °C. Size exclusion HPLC was used to relate tensile properties to changes in protein solubility and molecular weight distribution. By combining glycerol and thermal processing, increased flexibility has been observed compared to previous work on unplasticized oilseed meal. Tensile results varied from a brittle crambe based material (10 % glycerol, 130 °C), Young’s modulus 240 MPa, strain at maximum stress of 2 %, to a soft and flexible carinata based material (30 % glycerol, 100 °C), Young’s modulus 6.5 MPa, strain at maximum stress of 13 %. Strength and stiffness development with increasing molding temperature is in agreement with the protein profiles obtained. Thus, the highest mechanical parameters were obtained at the protein solubility minimum at 140 °C. Higher temperatures caused protein degradation, increasing the level of low molecular weight extractable proteins. In carinata based materials the strain at maximum stress decreased as the protein aggregation developed. Results presented indicate that both crambe and carinata oilseed meal based materials can have their properties modulated through thermal treatment and the addition of plasticizers.

This is, to our knowledge, the first study of wheat-gluten-based nanocomposite films prepared by a solvent-free extrusion process. Wheat gluten/montmorillonite nanocomposite films were obtained in a single screw-extruder using urea as a combined denaturant and plasticizer. The oxygen permeability and water vapor transmission rate of the films decreased by respectively factors of 1.9 and 1.3 when 5 wt.% clay was added. At the same time, the stiffness increased by a factor of 1.5, without any critical loss of extensibility. Field emission scanning electron microscopy (FE-SEM) and Energy-dispersive X-ray analysis indicated that the clay particles were layered mainly in the plane of the extruded film. It was possible to identify individual platelets/tactoids with FE-SEM and, together with findings from transmission electron microscopy, atomic force microscopy and X-ray diffraction, it was concluded that the clay existed as individual clay platelets, intercalated tactoids and agglomerates. Thermogravimetric analysis showed that the thermal stability of the extrudates was improved by the addition of clay.

A full biouse of crops for multiple end-uses would contribute to a more economically attractive and thereby more sustainable use of the crop. The purpose of this paper was to evaluate options to develop materials from residuals of rapeseed, originating from the biodiesel (RME) production. Compression molding of rapeseed flour and rapeseed cake residuals was evaluated together with additions of different amount of plasticizer (glycerol), as well as use of various pressing temperatures and times. The results were promising and led to a compact and hard, although somewhat brittle material. The potential to produce materials from the rapeseed residuals from RME production is thus high. Glycerol content was the most important factor increasing tensile strength in the material followed by pressing time. No clear protein polymerization was detected in the produced materials. Thus, despite the promising results, methods to obtain increased protein polymerization should be searched for. Therefore, binding agents, additives, or pretreatment of the rapeseed residuals are needed, or the proteins have to be purified, in order to generate a better polymerization of the proteins.

In this study, we report that the addition of ammonium hydroxide (NH4OH) significantly enhance the properties of extruded WG-based materials. The grainy structure disappeared and the extrudate became more uniform and glossy. The barrier properties improved and the oxygen permeability at dry conditions was as low as that for a number of petroleum-based plastics (poly(ethylene terephthalate and polyamide 66). The protein structure in this material was extensively aggregated, which improved the strength and stiffness; there was a ca 4-fold increase in maximum stress compared to that of the NH4OH-free samples. The protein solubility decreased to almost zero. Even a severe sonication treatment in sodium dodecyl sulphate (SDS) did not increase the solubility. The only type of protein that it was possible to extract was the 'thermo-resistant' ω-gliadins lacking disulfide-bonds. Our result provides new opportunities to develop a WG-based film extrudate for potential use as e.g. a renewable barrier layer in food and non-food laminate packagings.

A Russian Doll encapsulation architecture utilizing pairs of free-standing barrier films and epoxy seals separated by nitrogen spacers is presented, enabling the use of low-cost epoxy to attach two or more free-standing barrier films to a substrate with improved barrier performance. The performance of various Russian Doll encapsulations was evaluated with the calcium thin film optical transmission test, showing improved performance of the Russian doll configuration relative to a non-nested barrier/spacer architecture, and demonstrating that water vapor transmission rates (WVTR) of 0.00021 g/(m2, day) or below can be achieved with low-cost materials in this architecture. This WVTR correlates to a predicted lifetime of more than 10 years for bulk heterojunction solar cell modules fabricated and tested by Konarka Technologies (Lowell, MA, USA).

Laminates of compression-molded glycerol-plasticized wheat gluten (WG) films surrounded and supported by poly(lactic acid) (PLA) films have been produced and characterized. The objective was to obtain a fully renewable high gas barrier film with sufficient mechanical integrity to function in, for example, extrusion-coating paper/board applications. It was shown that the lamination made it possible to make films with a broad range of glycerol contents (0-30 wt %) with greater strength than single unsupported WG films. The low plasticizer contents yielded laminates with very good oxygen barrier properties. In addition, whereas the unsupported WG films had an immeasurably high water vapor transmission rate (WVTR), the laminate showed values that were finite and surprisingly, in several cases, also lower than that of PLA. Besides being a mechanical support (as evidenced by bending and tensile data) and a shield between the WG and surrounding moisture, the PLA layer also prevented the loss of the glycerol plasticizer from the WG layer. This was observed after the laminate had been aged on an "absorbing" blotting paper for up to 17 weeks. The interlayer adhesion (peel strength) decreased with decreasing glycerol content and increasing WG film molding temperature (130 degrees C instead of 110 degrees C). The latter effect was probably due to a higher protein aggregation, as revealed by infrared spectroscopy. The lamination temperature (110-140 degrees C) did not, however, have a major effect on the final peel strength.

The preparation of carboxymethylated microfibrillated cellulose (MFC) films by dispersion-casting from aqueous dispersions and by surface coating on base papers is described. The oxygen permeability of MFC films were studied at different relative humidity (RH). At low RH (0%), the MFC films showed very low oxygen permeability as compared with films prepared from plasticized starch, whey protein and arabinoxylan and values in the same range as that of conventional synthetic films, e.g., ethylene vinyl alcohol. At higher RH’s, the oxygen permeability increased exponentially, presumably due to the plasticizing and swelling of the carboxymethylated nanofibers by water molecules. The effect of moisture on the barrier and mechanical properties of the films was further studied using water vapor sorption isotherms and by humidity scans in dynamic mechanical analysis. The influences of the degree of nanofibrillation/dispersion on the microstructure and optical properties of the films were evaluated by field-emission scanning electron microscopy (FE-SEM) and light transmittance measurements, respectively. FE-SEM micrographs showed that the MFC films consisted of randomly assembled nanofibers with a thickness of 5–10 nm, although some larger aggregates were also formed. The use of MFC as surface coating on various base papers considerably reduced the air permeability. Environmental scanning electron microscopy (E-SEM) micrographs indicated that the MFC layer reduced sheet porosity, i.e., the dense structure formed by the nanofibers resulted in superior oil barrier properties.

The impulse heat-sealing properties of wheat gluten films were investigated. Films containing 30 wt% glycerol were compression molded at 100–130 °C and then sealed in a lap-shear or peel-test geometry at 120–175 °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 °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 °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.

The purpose of this work was to add economic value to crambe meal, the protein-rich byproduct from the industrial extraction of Crambe abyssinica seed oil, by using it as a potential feedstock for ...

The purpose of this study was to study the transport of monocarboxylic acids in chitosan films, since this is important for understanding and predicting the drying kinetics of chitosan from aqueous solutions. Despite the wealth of data on chitosan films prepared from aqueous monocarboxylic acid solutions, this transport has not been reported. Chitosan films were exposed to formic, acetic, propionic and butyric acid vapours, it was found that the rate of uptake decreased with increasing molecular size. The equilibration time was unexpectedly long, especially for propionic and butyric acid, nine months. A clear two-stage uptake curve was observed for propionic acid. Evidently, the rate of uptake was determined by acid-induced changes in the material. X-ray diffraction and infrared spectroscopy indicated that the structure of the chitosan acetate and buffered chitosan films changed during exposure to acid and during the subsequent drying. The dried films previously exposed to the acid showed less crystalline features than the original material and a novel repeating structure possibly involving acid molecules. The molar mass of the chitosan decreased on exposure to acid but tensile tests revealed that the films were always ductile. The films exposed to acid vapour (propionic and butyric acid) for the longest period of time were insoluble in the size-exclusion chromatography eluent, and they were also the most ductile/extensible of all samples studied.

High-amylose potato starches were produced through genetic modification resulting in changed granule morphology and composition, with higher amylose content and increased chain length of amylopectin. The increased amylose content and structural changes in amylopectin enhanced film-forming behavior and improved barrier and tensile properties in starch films. The molecular structure in these starches was related to film-forming properties. Solution-cast films of high-amylose starch revealed a homogeneous structure with increasing surface roughness at higher amylose content, possibly due to amylose aggregation. Films exhibited significantly higher stress and strain at break compared with films of wild-type starch, which could be attributable to the longer chains of amylopectin being involved in the interconnected network and more interaction between chains, as shown using transmission electron microscopy. The oxygen permeability of high-amylose starch films was significantly decreased compared with wildtype starch. The nature of the modified starches makes them an interesting candidate for replacement of non-renewable oxygen and grease barrier polymers used today. (C) 2015 Elsevier Ltd. All rights reserved.

The diffusion of methanol in solution-cast whey-protein-isolate/poly(vinylidene pyrrolidone)-coated montmorillonite composite films was studied. The filler content was 0-4.8 vol%. Desorption experi ...

Greaseproof paper has a dense structure and therefore provides a natural barrier against materials like fat and oils. The barrier is obtained by extensive refining of the pulp. This refining is however a costly operation, not only in terms of direct costs for the refining but also in terms of indirect costs because the energy consumption for the drying of the paper is affected by the refining. A full-scale trial was performed to investigate the role of the pulp with respect to the energy demand and the barrier properties of the final papers. Paper made of 100% sulphite pulp with a low degree of refining exhibited the lowest energy consumption at a given level of air permeance. In addition, the effect of refining on the air permeance was compared with that of calendering. The calendering affected the air permeance less than the refining. The papers produced in the full-scale trial were later used as substrates for coatings and for detailed studies of the paper structure. Coating with chitosan was examined on a bench-scale and on a pilot scale. The studies showed that greaseproof paper can be upgraded with an oxygen barrier, but also that suitable coating techniques are lacking for the application of the coating in a sufficient amount. The influence of the base paper on the barrier properties of chitosan-coated paper was investigated in another study, in which it was found that greaseproof paper possesses a unique coating hold-out which cannot be met by other types of paper with a more open structure. It was also found that the coated paper had a lower oxygen permeability than the chitosan coating itself, and this indicates that the dense surface layer of greaseproof paper contributed to the oxygen permeability of the coated paper. The pore volume fraction of the greaseproof paper was found to be approximately 40% and it is therefore surprising that its air permeance is so low. To bring understanding to this question, the structure of greaseproof paper was studied using several methods. It was found that the structure was dominated by very small pores with a median diameter of

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 degrees 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.

The properties of new and aged glycerol-plasticized vital wheat gluten films containingor =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 foror =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.

In order to investigate ways of incorporating an oxygen- or air-barrier component, in this case chitosan or chitosan-acetic acid salt (chitosan salt), at an early stage in the paper-making process, sheets of chitosan and pulp fiber were produced in a hand sheet mould or solution cast in petri dishes. Some sheets were buffered in an alkaline solution, in order to reduce the moisture sensitivity. The sheets were characterized with respect to air permeance, oxygen permeability, fracture stress and strain, young's modulus and moisture content. The addition of the chitosan solution to the pulp slurry led to a substantial loss of fiber and chitosan through the wire screen and consequently a low grammage and high sheet porosity and air permeance. Forming a wet pulp fiber sheet before introducing the chitosan solution increased the grammage and the amount of remaining chitosan, the latter revealed by infrared spectroscopy. In addition, pressing the sheets before drying reduced the porosity and the air permeance. Air mixing, included in conventional laboratory sheet making, yielded a more heterogeneous sheet and inferior mechanical and barrier properties. In general, the paper sheets prepared in the hand sheet mould became weaker, softer and less ductile with increasing content of chitosan. Only solution casting in petri dishes resulted in good barrier properties. Scanning electron microscopy showed that holes were absent in this case. In addition, optical microscopy and infrared spectroscopy revealed that the chitosan-salt formed a continuous phase and that it was uniformly distributed in the sheet. Interestingly, the problem of shrinkage when chitosan salt sheets are buffered for improved high-moisture gas-barrier properties, was reduced significantly by the restraining action of the pulp fibers.

Extrusion coating was used to obtain montmorillonite/polyethylene-coated paperboard. The coating was prepared from a master batch containing maleated polyethylene, low-density polyethylene and 32 w ...

A comparison was made of oxygen barrier properties and wall thickness distribution of different thermoformed trays. The thermoformed trays were manufactured with three drawing depths and two different thermoforming methods; with and without plug-assist. Four different polymer combinations were evaluated. The oxygen transmission rate (OTR) [cm3/(package/day)] was measured at three conditions (23°C/50% relative humidity (RH) with 0% RH inside, 6°C/80% RH with 0% RH inside, and 6°C/80% RH with 100% RH inside. Wall thickness was measured at five different positions in the trays. In general, temperature had more influence on the oxygen transmission rate (OTR) than the humidity. The OTR in the packages increased with increasing drawing depth, but the increase was not linear. Other effects besides thinning, such as orientation, may have influenced the OTR, since the relationship between OTR, given as cm3/(m2/day), and the drawing depth was not linear. Plug-assisted thermoforming only had an effect on the OTR in trays with 70 mm drawing depth made of 600 µm thick laminate of PP/PE, which was probably due to exceeding the maximum drawing depth of this material. There was no correlation between the OTR value in the packages and the wall thickness in either of the positions, but a quite high correlation between the drawing depth and the relative wall thickness in all measured positions was observed. Copyright © 2004 John Wiley & Sons, Ltd.

Packaging-related properties of coated films of chitosan-acetic acid salt and whey protein concentrate (WPC) were studied. Chitosan (84.7% degree of deacetylation) and WPC (65-67% protein) were sol ...

Films of whey protein and chitosan acetic acid salt have lower oxygen permeability than, for example, ethylene-co-vinylalcohol under dry conditions, but water and water vapor seriously impair the gas barrier properties. To reduce the oxygen permeability at 90% relative humidity and the water-vapor transmission rate at 100% relative humidity, the films were coated with an alkyd, a beeswax compound, or a nitrocellulose lacquer. Permeability and transmission rate measurements were performed in accordance with standard methods and showed that the beeswax compound and the nitrocellulose were appropriate as water-vapor barriers. Overall migration to water was measured after 10 days exposure time, with the coated surface exposed to the water, showing that the alkyd-coated and the nitrocellulose-coated films were both below the safety limit for food contact. Water absorbency tests, performed by the Cobb method, showed that the films coated with the beeswax compound or with nitrocellulose lacquer exhibit lower absorbency than the alkyd-coated films.

Protein macromolecules adopted for biological and bio-based material functions are known to develop a structured protein network upon chemical modification. In this study, we aimed to evaluate the impact of chemical additives such as, NaOH, NH4OH and salicylic acid (SA), on the secondary and nano-structural transitions of wheat proteins. Further, the effect of chemically induced modifications in protein macromolecular structure was anticipated in relation to functional properties. The gliadin-NH4OH-SA film showed a supramolecular protein organization into hexagonal structures with 65 Å lattice parameter, and other not previously observed structural entities having a characteristic distance of 50 Å. Proteins in gliadin-NH4OH-SA films were highly polymerized, with increased amount of disulfide crosslinks and β-sheets, causing improved strength and stiffness. Glutenin and WG proteins with NH4OH-SA showed extensive aggregation and an increase in β-sheet content together with irreversible crosslinks. Irreversible crosslinks hindered a high order structure formation in glutenins, and this resulted in films with only moderately improved stiffness. Thus, formation of nano-hierarchical structures based on β-sheets and disulfide crosslinks are the major reasons of high strength and stiffness in wheat protein based films.

The present study is aimed at evaluating the use of plant-based polymers and fibres for the production of sustainable biocomposites. For the first time, plasticiser/solvent-free hemp fibre-reinforced wheat gluten and hemp-gliadin and glutenin composites were obtained by compression moulding at different temperatures. The plasticiser/solvent-free sample preparation method developed in this study facilitated the use of a powdered protein matrix with a mat of randomly oriented hemp fibres. The tensile and protein cross-linking properties, as well as the biodegradability, were investigated. The addition of hemp fibre to the protein matrix increased the E-modulus by 20 to 60% at 130 °C. An increase in moulding temperature from 110 to 130 °C resulted in an increase in maximum stress due to the formation of intermolecular bonds between protein chains. The gliadin composites had higher E-modulus and maximum stress and showed a larger increase in protein polymerisation with increased temperature compared to the glutenin composites. A comparison of tensile properties revealed that the composites were stiffer and stronger compared to several similarly produced biobased composites. The composites were found to be fully biodegradable under a simulated soil environment after 180 days. Biocomposites produced in the present study were found to be environmentally friendly with fairly good mechanical properties.

Antimicrobial glycerol-plasticized wheat gluten (WG) films containing potassium sorbate (PS) were successfully produced by compression moulding; a thermoplastic process involving high temperature and high pressure. Antifungal properties of the films were tested against Aspergillus niger and Fusarium incarnatum by the agar diffusion assay. The results indicated that films containing more than 10 wt.% PS showed antimicrobial activity against A. niger while films containing 2.5 wt.% or more of PS showed antimicrobial activity against F. incarnatum. It was also found that when the film was exposed to an absorbing medium (the agar solution), most of the PS was released, an interesting feature for edible active packaging. Despite the loss, a very promising result was that, without seeding of spores, the films resisted microbial growth for at least one week when the films were left in the agar solution. X-ray diffraction and field emission scanning electron microscopy revealed that the PS crystals were dissolved in the wheat gluten material. In addition to the antimicrobial properties, dynamic mechanical, tensile, PS loss, water vapour transmission rate and oxygen permeability data also indicated that PS acted as a plasticiser in the wheat gluten film. (C) 2011 Elsevier Ltd. All rights reserved.

This paper presents a novel approach to reduce the water vapor transmission rate (WVTR) and water absorbance of wheat gluten/paperboard laminates by introducing a hydrophobic component (oleic acid (OA)) into the hydrophilic plasticizer (glycerol). Whereas the paperboard showed immeasurably high WVTR, the laminate with gluten/glycerol yielded finite values. More importantly, by incorporating 75 wt.% OA into the plasticizer, the WVTR and water absorbance were reduced by, respectively, a factor of three and 1.5–2. Of particular interest was that the mechanical properties were not changing dramatically between 0 and 50 wt.% OA. The results showed clear benefits of combining a gluten film with paperboard. Whereas the paperboard provided toughness, the WG layer contributed with improved moisture barrier properties. In addition, WVTR indicated that the paperboard reduced the swelling of the outer gluten/glycerol layer in moist conditions; a free standing gluten/glycerol film would yield infinite, rather than finite, WVTR values.

Evaluation of structure and morphology of extruded wheat gluten (WG) films showed WG protein assemblies elucidated on a range of length scales from nano (4.4 angstrom and 9 to 10 angstrom, up to 70 angstrom) to micro (10 mu m). The presence of NaOH in WG films induced a tetragonal structure with unit cell parameters, a = 51.85 angstrom and c = 40.65 angstrom, whereas NH(4)OH resulted in a bidimensional hexagonal close-packed (HCP) structure with a lattice parameter of 70 angstrom. In the WG films with NH(4)OH, a highly polymerized protein pattern with intimately mixed glutenins and gliadins bounded through SH/SS interchange reactions was found. A large content of beta-sheet structures was also found in these films, and the film structure was oriented in the extrusion direction. In conclusion, this study highlights complexities of the supramolecular structures and conformations of wheat gluten polymeric proteins in biofilms not previously reported for biobased materials.

This is, to our knowledge, the first study of the injection molding of materials where wheat gluten (WG) is the main component. In addition to a plasticizer (glycerol), 5 wt.% natural montmorillonite clay was added. X-ray indicated intercalated clay and transmission electron microscopy indicated locally good clay platelet dispersion. Prior to feeding into the injection molder, the material was first compression molded into plates and pelletized. The filling of the circular mold via the central gate was characterized by a divergent flow yielding, in general, a stronger and stiffer material in the circumferential direction. It was observed that 20-30 wt.% glycerol yielded the best combination of processability and mechanical properties. The clay yielded improved processability, plate homogeneity and tensile stiffness. IR spectroscopy and protein solubility indicated that the injection molding process yielded a highly aggregated structure. The overall conclusion was that injection molding is a very promising method for producing WG objects.

This is, to our knowledge, the first success on solvent-free extrusion of wheat gluten (WG) into high quality films without using NaOH/salicylic acid. It was possible by using urea (concentrations: 10, 15 and 20 wt%) in the single screw-extruder process. Tensile testing, oxygen permeability, water vapor transmission rate, infrared spectroscopy (IR), confocal laser scanning microscopy (CLSM) and protein solubility were used to assess the properties of the extrudates. As the urea concentration increased, the strength and stiffness decreased while the extensibility increased. The oxygen permeability was low and increased, as did the water vapor transmission rate, with increasing urea concentration. The protein solubility of urea-containing films was found to be significantly lower than that of the native gluten and glycerol-plasticized WG extrudate. CLSM, together with the protein solubility, indicated that the urea films were aggregated/polymerized and IR spectroscopy revealed that these films contained a sizeable amount of beta-sheets with a high degree of hydrogen bonds associated with protein aggregation. The aggregation did not change with increasing urea concentration, which suggests that the changes in the mechanical and permeability properties were due to urea-induced plasticisation.