Celina Bernal

Biodegradability and plasticizing effect of yerba mate extract on cassava starch edible films.

Biodegradable and edible cassava starch-glycerol based films with different concentrations of yerba mate extract (0, 5 and 20wt.%) were prepared by casting. The plasticizing effect of yerba mate extract when it was incorporated into the matrix as an antioxidant was investigated. Thermal degradation and biodegradability of the obtained biofilms were also studied. Thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), attenuated total reflectance Fourier transform infrared spectroscopy (ATR/FTIR), X-ray diffraction analysis (XRD), water absorbance, stability in different solutions and biodegradability studies were performed. The clear correlation among the results obtained from the different analysis confirmed the plasticizing effect of yerba mate extract on the starch-glycerol matrix. Also, the extract led to a decrease in the degradation time of the films in soil ensuring their complete biodegradability before two weeks and to films stability in acidic and alkaline media. The plasticizing effect of yerba mate extract makes it an attractive additive for starch films which will be used as packaging or coating; and its contribution to an earlier biodegradability will contribute to waste reduction.

Fracture behavior of a commercial starch/polycaprolactone blend reinforced with different layered silicates

In the present work, composites based on a commercial starch/PCL blend (MaterBi-Z) reinforced with three different nanoclays: natural montmorillonite (Cloisite Na(+) (MMT)) and two modified montmorillonites (Cloisite 30B (C30B) and Cloisite 10A (C10A)) were prepared in an intensive mixer. The aim of this investigation was to determine the effect of the different nanoclays on the quasi-static fracture behavior of MaterBi-Z nanocomposites. An improvement in the fracture behavior for the composite with low contents of C30B was obtained, probably due to the easy debonding of clay achieved from a relatively weak filler-matrix interaction. On the other hand, a strong interaction had a detrimental effect on the material fracture toughness for the MaterBi-Z/C10A composites as a result of the higher compatibility of this organo-modified clay with the hydrophobic matrix. Intermediate values of fracture toughness, determined using the J-integral approach (Jc), were found for the composites with MMT due to its intermediate interaction with the matrix. The different filler-matrix interactions observed were also confirmed from the application of Pukánszky and Maurer model. In addition, multifractal analysis was applied to describe the topography of fracture surfaces. Thus, the complex fracture process could be successfully described by both experimental and theoretical tools. The obtained results suggest that it is possible to tailor the mechanical properties of the studied composites taking into account their further application.

Active and smart biodegradable packaging based on starch and natural extracts

Active and smart biodegradable films from cassava starch and glycerol with 5wt.% of different natural extracts such as green tea and basil were obtained by casting. Their functional capacity as antioxidants and their physicochemical properties achieved from the incorporation of these types of extracts were evaluated. The content of phenolic compounds in the extracts led to films with significant antioxidant activity, being greater in the case of the system containing green tea extract. Color changes in both materials after immersion in different media (acid and basic) due to the presence of chlorophyll and carotenoids in the extracts were observed, but the film with basil extract reacted most notably to the different pH. These films degraded in soil under two weeks and were thermal stable up to 240°C. Finally, the incorporation of extracts of green tea and basil led to thermoplastic starch films with lower water vapor permeability retaining their flexibility.

Mechanical Behavior of Starch–Carbon Nanotubes Composites

This chapter is focused on the mechanical behavior of plasticized starch-based nanocomposites reinforced with carbon nanotubes. It starts with a general introduction about the most important materials that involve those nanocomposites, such as starch and multiwalled carbon nanotubes. Then, a presentation of the most relevant published results on the mechanical properties of starch matrix and starch–carbon nanotubes composites is reported. Factors affecting these properties such as crystallinity, water content and plasticizers are discussed. The mechanical behavior of these composites is discussed in separate sections regarding tensile properties, impact behavior, and viscoelastic behavior as well as the most important influencing factors on these properties. Finally, concluding remarks and future trends on the improvement of the mechanical response of starch–carbon nanotubes composites are presented.

Recent innovative results on natural fibre composites

A novel fibre treatment recently proposed in the literature was optimised in the case of woven jute fabric/vinylester laminates to obtain the best tensile properties. It consists on an alkali treatment superimposed to biaxial tensile stress. Optimisation was performed by changing the treatment time. The novel fibre treatment was compared with traditional chemical methods. Tensile properties exhibited a maximum with the treatment time at 4 h due to the less efficient period of time and to the excessive fibre damage for times shorter and longer than 4 h, respectively. All composites with fibres treated with alkali under stress exhibited improved tensile strength in comparison with the composites with untreated fibres or with fibres treated with traditional methods due to the better interfacial properties and the structural changes of the fibres promoted by the novel treatment. Stiffness values were only higher for the composite with fibres treated with alkali under stress for 4 h, probably in correspondence with a maximum in the stiffness of the individual fibres.

Fracture Behavior of Recyclable All-Polypropylene Composites Composed of α- and β-Modifications

The fracture behavior of all-PP composites was studied under quasi-static loading conditions. Fracture toughness was evaluated by means of different fracture mechanics approaches depending on materials’ behavior. Composites consolidated at low temperature exhibited pop-in features and the failure occurs typically by delamination and tape stretching and fracture. With increasing consolidation quality – i.e., with increasing processing temperature – the delamination became less pronounced, and so the tape stretching occurred, before the specimens break. In composites consolidated at the highest temperature investigated (190°C), the laminate-like structure typical of self-reinforced composites produced according to film-stacking method was lost. Accordingly, composites behave as if they were only α-PP and β-PP matrices: α-rPP exhibited typical brittle fracture of α-PP, while β-rPP exhibited the stable behavior with fully yielded ligament before crack propagation commonly observed for β-PP. In general, stress–strain behavior changed from stable to unstable and fracture toughness strongly decreased as consolidation quality increased. Based on these results and previous findings, it can be concluded that the properties of self-reinforced PP composites can be tailored for a given application through the quality of consolidation.