Inmaculada Martínez

Wheat gluten-based materials plasticised with glycerol and water by thermoplastic mixing and thermomoulding

BACKGROUND Gluten has been investigated as a source for biodegradable polymeric materials because it is a renewable, available and low-cost raw material. The aim of this study was to evaluate the influence of some variables involved in the two stages of protein/plasticiser thermo-mechanical processing, where a mixture of glycerol and water was used as the plasticiser. RESULTS Gluten/glycerol/water blends mixed under different thermal conditions (adiabatic starting at 25 °C and isothermal at 60 and 90 °C) exhibited shear thinning capillary flow behaviour, where a marked increase in flow properties was obtained at the highest temperature. Two thermal events, glass transitions related to the plasticiser blend and gluten, were detected by Modulated Differential Scanning Calorimetry (MDSC) and Dynamic Mechanical Analysis (DMA) tests. Moderate moulding temperature led to less resistant materials showing higher ductility, whereas higher mixing and moulding temperatures led to bioplastics with higher mechanical properties. CONCLUSION A moulding temperature of 130 °C (close to the denaturation temperature) was found to be suitable for the thermomoulding process. In addition, the use of moderate mixing temperature seems to be convenient for those applications that required materials exhibiting high water absorption behaviour and suitable mechanical properties. Protein extractability results reflect the benefits of combining high shear and high temperature during processing to improve cross-linking reactions.

Modelling of pyrolysis and combustion of gluten–glycerol-based bioplastics

Non-isothermal thermogravimetric analysis, under nitrogen and air atmospheres, has been applied to study the thermal degradation of wheat gluten and gluten-glycerol-based bioplastics. In order to explain experimental data, thermal degradation has been simulated using the so-called pseudo-components, which are related to protein fraction (mainly gliadin and glutenin), residual starch and plasticiser. Thus, the proposed models have been used to shed some light on the thermal decomposition of these materials, which have been found affected by their compositions and microstructures. Modelling confirms the experimental bioplastic and gluten isolate compositions, e.g. bioplastic moisture content, starch concentration and the expected gliadin/glutenin ratio. According to the simulation, the glycerol volatilisation is affected by bioplastic moisture content and hindered by the protein matrix. A fact pointing out that glycerol/water blend plays relevant plasticizing roles in the protein matrix through diverse physicochemical interactions.

Development of antimicrobial active packaging materials based on gluten proteins

BACKGROUND The incorporation of natural biocide agents into protein-based bioplastics, a source of biodegradable polymeric materials, manufactured by a thermo-mechanical method is a way to contribute to a sustainable food packaging industry. This study assesses the antimicrobial activity of 10 different biocides incorporated into wheat gluten-based bioplastics. The effect that formulation, processing, and further thermal treatments exert on the thermo-mechanical properties, water absorption characteristics and rheological behaviour of these materials is also studied. RESULTS Bioplastics containing six of the 10 examined bioactive agents have demonstrated suitable antimicrobial activity at 37 °C after their incorporation into the bioplastic. Moreover, the essential oils are able to create an antimicrobial atmosphere within a Petri dish. CONCLUSION Depending on the selected biocide, its addition may alter the bioplastics protein network in a different extent, which leads to materials exhibiting less water uptake and different rheological and thermo-mechanical behaviours.

Influence of tragacanth gum in egg white based bioplastics: Thermomechanical and water uptake properties

This study aims to extend the range of applications of tragacanth gum by studying its incorporation into bioplastics formulation, exploring the influence that different gum contents (0-20wt.%) exert over the thermomechanical and water uptake properties of bioplastics based on egg white albumen protein (EW). The effect of plasticizer nature was also evaluated through the modification of the water/glycerol ratio within the plasticizer fraction (fixed at 40wt.%). The addition of tragacanth gum generally yielded an enhancement of the water uptake capacity, being doubled at the highest content. Conversely, presence of tragacanth gum resulted in a considerable decrease in the bioplastic mechanical properties: both tensile strength and maximum elongation were reduced up to 75% approximately when compared to the gum-free system. Ageing of selected samples was also studied, revealing an important effect of storage time when tragacanth gum is present, possibly due to its hydrophilic character.

Development of Biocomposite Superabsorbent Nanomaterials: Effect of Processing Technique

Nanoclay particles have been usually introduced into protein-based bioplastics to obtain composite materials, showing enhanced mechanical properties. However, the addition of partially exfoliated nanoclay particles in these protein matrices may also involve an increase of others properties such as water absorption capacity, which may lead to the obtention of super absorbent biodegradable materials. Processing technologies exerted a remarkable influence on the techno-functional properties of the soy-based bioplastics studied in this research. On the one hand, extrusion technique led to bioplastics which showed enhanced mechanical properties. On the other hand, injection moulding technique yielded to non-exfoliated nanoclay particles within the protein matrix, which involved improvements of water absorption capacity. The development of superabsorbent protein-based biodegradable materials implied a deep knowledge of physicochemical properties of proteins and processing conditions of bioplastics. Extrusion or injection moulding techniques could be selected to obtain tailored protein-based bioplastics with enhanced properties.

New Bitumens Obtained from Physical Distillation of a Conventional Bitumen Mixed with EVA Copolymer

Bitumen phases separated from 5% and 12% EVA/bitumen blends are investigated. Basic characterization is carried out using a peculiar thin layer chromatographer, the Iatroscan. The rheological and technical analysis lead us to conclude that these macromolecular materials, obtained from physical distillation of the blends, constitute new bitumens of unique properties.