Vera A. Alvarez

Mechanical properties and water absorption behavior of composites made from a biodegradable matrix and alkaline-treated sisal fibers

Biocomposites were produced using a biodegradable material as matrix, and sisal fibers as reinforcement. The biodegradable material is a commercial product called MaterBi-Y, which is based on a cellulose derivatives and starch system. The characterization of these biocomposites was not done before and it is necessary in order to select a material instead of nonbiodegradable matrices. An alkaline treatment was performed in order to improve the mechanical properties of the fiber. The effect of the treatment on fiber properties and on impact, flexural, and tensile properties of composites were determined. Fiber content enhances the tensile properties of the biodegradable matrix. Water sorption studies were performed. The experimentally observed tensile properties (modulus and tensile strength) of short sisal fiber-reinforced cellulose derivatives/starch composites with different fiber loading are compared with the calculated values obtained from the existing theories of reinforcement.

Poly(vinyl alcohol)/cellulose nanowhiskers nanocomposite hydrogels for potential wound dressings.

Polyvinyl alcohol (PVA)/cellulose nanowhisker (CNW) nanocomposite hydrogels to be used for wound dressing were obtained by freezing-thawing technique and characterized by means of morphological, physical, thermal, mechanical, barrier and antimicrobial properties. First, cellulose nanowhiskers were obtained by the acid hydrolysis of commercial crystalline microcellulose (MCC) and characterized by its size, shape, morphological, structural and thermal properties. Then, PVA/CNW nanocomposites with several CNW contents (0, 1, 3, 5 and 7wt.%) were obtained. Morphological, thermal, chemical and physical characterization of the PVA/CNW nanocomposite hydrogels was carried out. It was found that the addition of CNW to the hydrogel allows controlling the pore morphology of the samples. On the other hand, the transparency of the samples was maintained, the thermal stability was increased, the mechanical properties were improved and the water vapor transmission rate was in the range of wound dressing applications after CNW incorporation inside the PVA hydrogel matrix. The evaluation of microbial penetration showed that the prepared hydrogels can be considered as a good barrier against different microorganisms. All obtained results indicate that the PVA/CNW materials are promising to be used as wound dressing.

Mechanical properties of polyvinylalcohol/hydroxyapatite cryogel as potential artificial cartilage

The technological advances in material science are not enough to overcome the challenge of construct a material be able to replace the cartilage. The designed material has to meet the mechanical properties of cartilage and has to be also capable to be integrated with the articulation. Articular cartilage damage is a persistent and increasing problem which affects millions of people worldwide. Poly vinyl alcohol (PVA) hydrogels are promising implants, due to their similar properties as soft tissue; however their low mechanical resistance and durability together with its lack to integrate with the surrounding tissue restrict their application in this area. The poor adhesion can be solved by the development a composite hydrogel with bioactive and biocompatible filler, as hydroxyapatite (HA). The aim of this work was to obtain and characterize (physically, chemically and mechanically) PVA/HA composite hydrogels for potential application as articular replacement. Hence, composite hydrogels were prepared by adding of different amounts of HA in an aqueous solution of PVA and subsequent freezing-thawing cycles. It was observed that the addition of HA modified the physical and chemical features of the hydrogel and promoted the material crosslinking and stability. Moreover, it was found that the mechanical properties (compression, tension and nanoindentation) of the hydrogels were improved by the addition of HA. All these result indicate that these materials could be used as a potential cartilage replacement. However, further in vitro and in vivo studies are mandatory for future possible clinical applications and are actually being carried out.

Effect of Water Sorption on the Flexural Properties of a Fully Biodegradable Composite

The water absorption process of the short-time process of a fully biodegradable composite is important in order to know the effect of water uptake on the mechanical properties before the polymer is hydrolysed. The matrix of the studied composites is a commercial blend based on starch and cellulose derivatives, named MaterBi-Y. The effect of the fibre content was also taken into account, because short sisal fibres’ content was changed from 5 to 15 wt%. Diffusion coefficients, the equilibrium water uptake and the flexural properties were determined during sorption experiments at different bath temperatures: 5, 25 and 60 C. Equations obtained from microscopic mass balances for diffusion in solids were used to model the water absorption of these composites as a function of immersion time.

Cellulosic materials as natural fillers in starch-containing matrix-based films: a review

In this work, the different cellulosic materials, namely cellulose and lignin are analyzed. In addition, the starch-containing matrices (isolated starch and flour) reinforced with cellulosic materials to be used in packaging applications are described. Many efforts have been exerted to develop biopackaging based on renewable polymers, since these could reduce the environmental impact caused by petrochemical resources. Special attention has had the starch as macromolecule for forming biodegradable packaging. For these reasons, shall also be subject of this review the effect of each type of cellulosic material on the starch-containing matrix-based thermoplastic materials. In this manner, this review contains a description of films based on starch-containing matrices and biocomposites, and then has a review of cellulosic material-based fillers. In the same way, this review contains an analysis of the works carried out on starch-containing matrices reinforced with cellulose and lignin. Finally, the manufacturing processes of starch/cellulose composites are provided as well as the conclusions and the outlook for future works.

Processing and characterization of thermoplastic starch/polycaprolactone/compatibilizer ternary blends for packaging applications

Thermoplastic starch (TPS)/polycaprolactone (PCL) blends were obtained by melt mixing. First, the best formulation of thermoplastic starch (starch, plasticizer and additives) was studied. The obtained films were characterized by means of differential scanning calorimetry, DSC (melting temperature and crystallinity degree); thermogravimetric analysis, TGA (real composition of the blend and thermal stability); tensile tests (mechanical properties); infrared spectroscopy, FTIR (interactions between components); scanning electron microscopy, SEM (morphology); and water absorption tests. The effect of PCL/TPS ratio on the previously mentioned characteristics and properties were studied. In addition, the effect of using PCL modified with maleic anhydride as compatibilizer was also analyzed. An optimal compatibilizer content was found improving the mechanical properties and slowing down the degradation rate in soil of the blends. On the other hand, a slight increase in the water absorption of the blends was found in comparison with the non-compatibilized ones.

Property tuning of poly(lactic acid)/cellulose bio-composites through blending with modified ethylene-vinyl acetate copolymer.

The effect of addition of an ethylene-vinyl acetate copolymer modified with glycidyl methacrylate (EVA-GMA) on the structure and properties of poly(lactic acid) (PLA) composites with cellulose micro fibres (CF) was investigated. Binary (PLA/CF) and ternary (PLA/EVA-GMA/CF) composites obtained by melt mixing in Brabender mixer were analysed by SEM, POM, WAXS, DSC, TGA and tensile tests. The miscibility and morphology of PLA/EVA-GMA blends were first examined as a function of composition: a large rise of PLA spherulite growth rate in the blends was discovered with increasing the EVA-GMA content (0-30 wt%) in the isothermal crystallization both from the melt and the solid state. PLA/EVA-GMA/CF ternary composites displayed improved adhesion and dispersion of fibres into the matrix as compared to PLA/CF system. Marked changes of thermodynamic and tensile parameters, as elastic modulus, strength and elongation at break were observed for the composites, depending on blend composition, polymer miscibility and fibre-matrix chemical interactions at the interface.

Films Made by Blending Poly(ε-Caprolactone) with Starch and Flour from Sagu Rhizome Grown at the Venezuelan Amazons

Starch-based composite films have been proposed as food packaging. In this context, the study of non-conventional starch sources (sagu, Canna edulis Kerr) has worldwide special attention, because these materials can impart different properties as carbohydrate polymers. A thorough study of the matrices used (sagu starch and flour) was carried out. In the same way, thermoplastic starch (TPS)/PCL blend and thermoplastic flour (TFS)/PCL blend were obtained by melt mixing followed by compression moulding containing glycerol as plasticizer. In this study, chemical composition of the matrices and their properties were related with the properties of the developed films. Moisture content, water solubility, X-ray diffraction, thermogravimetric analysis and mechanical and microstructural properties were evaluated in the films. Taking into account the results, the sagu flour has great potential as starchy source for food packaging applications. However, concretely the flour had lower compatibility with the PCL compared to the starch/PCL blend.

Eco-friendly films prepared from plantain flour/PCL blends under reactive extrusion conditions using zirconium octanoate as a catalyst

Plantain flour (Musa ssp., group AAB, sub-group clone Harton)/poly(ε-caprolactone) (PCL) blends, containing glycerol as a plasticizer, were prepared by reactive extrusion (REx) in a twin-screw extruder using zirconium octanoate (Zr(Oct)4) as a catalyst, followed by thermo-compression molding for film development. The films were then characterized in terms of their: infrared (FTIR) spectra, water solubility, thermogravimetric (TGA) curves, differential scanning calorimetry (DSC) thermograms, and X-ray diffraction (XDR) diffractograms, as well as their microstructural, mechanical and antimicrobial properties in order to (1) compare the effects of PCLs with two different molecular weights (Mw) on the characteristics of the plantain flour/PCL blends, and (2) determine whether using Zr(Oct)4 in the production of active composite polymer materials improves their properties. The plantain flour/PCL blends were all developed successfully. The higher Mw PCL gave more hydrophobic and thermally stable films with improved mechanical properties. The addition of the Zr(Oct)4 catalyst to the plantain flour/PCL blends also resulted in films with similar characteristics to those described above, due to the cross-linking of the polymers. In addition, the films containing the catalyst showed antimicrobial activity against Escherichia coli O157:H7 and Staphylococcus aureus indicating a dual effect of Zr(Oct)4, and making it an attractive alternative for the development of active films.

Effect of the addition of nanoclays on the water absorption and mechanical properties of glass fiber/up resin composites

Mechanical performance of composite materials must remain satisfactory during their life in service. However, composite structures such as wind blades are usually exposed to humid and severe environments, and the absorbed water can degrade the fiber–matrix interface decreasing the composite overall performance. Dual scale (nano-micro) composites can be obtained by adding nanoparticles to the polyester resin and reinforcing that nanomaterial with a glass fiber mat. These materials have good potential in the production of composite parts such as wind blades because nanoparticles dispersed in the polymer matrix could lower the water absorption of the composites and improve their performance in humid environments. However, nanosized reinforcing particles have high internal surface and therefore they tend to agglomerate and are difficult to disperse homogeneously in the polymeric matrix. Moreover, the final properties of the nanocomposites are strongly influenced by clay particles’ morphology and dispersion. In this work, the effect of the addition of pristine and organomodified nanoclays on the water absorption and mechanical properties of glass fiber/unsaturated polyester resin composites was studied. Results showed that the chemical treatments were effective in improving clay dispersion, reducing water absorption, and increasing the composites’ performance in humid environments. In addition, this work presents a procedure to use water absorption tests as means of accelerated humidity absorption tests.