Jorge R. Robledo-Ortíz

Bacterial immobilization by adhesion onto agave-fiber/polymer foamed composites

Adhesion of Pseudomonas putida F1 onto agave-fiber/recycled-polyethylene foamed composites was studied under different controlled conditions. The adhesion process was analyzed in batch experiments controlling factors such as pH, contact time, temperature, initial biomass concentration and ionic strength; and was verified by scanning electron microscopy (SEM). The number of adhered bacteria after the experimental time was determined by difference between concentration of suspended cells in NaCl solution contained in two different Erlenmeyer flasks, one of the flasks with composite pellets and the other one without them. The concentration of cells in each flask was obtained using the serial dilution technique. Experimental data analysis showed that adsorption follows first-order kinetics. And it was further corroborated to be an irreversible process. For the first time, an equation is proposed here to predict the correlation between adhered bacteria and aqueous pH. In addition to the obvious reuse of waste material, these results suggested that agave-fiber/polymer foamed composites could be used as support for bacterial immobilization to be applied, among others in environmental processes such as bioremediation and biofiltration of gases with almost limitless possibilities.

Effect of fiber content and surface treatment on the mechanical properties of natural fiber composites produced by rotomolding

Abstract In this study, natural fibers (agave, coir, and pine) were surface treated with maleated polyethylene (MAPE) with two main objectives: (1) to improve the mechanical properties of natural fiber composites produced by rotational molding and (2) to increase the fiber content in the composite. The rotomolded composites were produced at 0, 10, 20, 30, and 40% wt. of fiber contents (treated or untreated) and characterized in terms of morphology and mechanical properties (hardness, impact, tension, and flexion). The results showed that MAPE surface treatment was more successful for agave and coir than for pine fibers due to their respective chemical composition. In general, surface treatment led to better fiber distribution and a more uniform composite morphology allowing the possibility to use higher fiber contents in rotational molding. At low fiber contents (10 and 20% wt.), the mechanical properties were improved using treated fiber composites (TFC) compared to the neat polymer and untreated fiber composites (UFC). Although the mechanical properties of TFC decreased at high fiber contents (30 and 40% wt.), they were substantially higher (about 160, 400, and 100% for impact, tensile, and flexural properties, respectively) than for UFC.

Film processability, morphology, and properties of polyamide-6/low density polyethylene blends

The processing, morphology, and tensile properties of blown films prepared from polyamide-6 (PA6) and low density polyethylene (LDPE) blends with and without compatibilizer (Surlyn® 9020) are studied. The results indicate that the presence of PA6 and a compatibilizer has a great influence on blend rheology as well as mechanical and barrier properties of LDPE films where the morphology of the dispersed phase (PA6) plays an important role. In this study, film morphology is controlled mainly by variations in draw ratio and bubble pressure. It is shown that biaxial orientation of the films explains the anisotropic behavior of the mechanical properties and improved barrier properties due to the production of a lamellar structure.

Morphological and mechanical characterization of foamed polyethylene via biaxial rotational molding

Foamed linear medium density polyethylene parts were prepared by rotational molding in biaxial mode, using different amounts of chemical-blowing agent (azodicarbonamide). Morphological and mechanical properties are presented and discussed in terms of foam density, cell density, average cell diameter, and open cell content. Internal air temperature of the mold was measured as a function of time. Significant differences were observed between unfoamed and foamed parts. The use of an exothermic chemical-blowing agent increased the peak internal air temperature and part cooling was slower due to the presence of gas bubbles acting as insulating material. The most important changes were observed for foam density: adding 1 phr of azodicarbonamide the density decreased from 0.931 g/cm3 (0 phr azodicarbonamide) to 0.295 g/cm3. Finally, the mechanical properties were highly influenced by azodicarbonamide content. Tensile and impact properties were correlated with part density using a simple power–law equation.

Effect of Freeze-Line Position and Stretching Force on the Morphology of LDPE-PA6 Blown Films:

Blends of low density polyethylene (LDPE) and polyamide-6 (PA6) are produced via blown film extrusion to study the effect of freeze-line position and stretching force on blend morphology. An experimental setup is designed to measure the stretching force as a function of draw ratio (DR) and freeze-line position for 4, 6, and 10 wt% PA6 in LDPE. Numerical simulations of the non-isothermal and viscoelastic process are in good agreement with the experimental data of film dimensions. However, as reported many times in the literature, the calculated stretching force is underestimated and can be predicted more precisely by using a simple correction factor. The results also show that the dispersed phase deformation increases with DR and decreases with freeze-line height.

Polylactic acid functionalization with maleic anhydride and its use as coupling agent in natural fiber biocomposites: a review

Abstract Due to its renewability and biodegradability, biopolymers have developed interest in order to substitute oil-derived plastics. In particular, polylactic acid (PLA) is a promising biopolymer in terms of mechanical and biodegradable properties that is used for different applications. Nevertheless, PLA has some disadvantages like brittleness and processing instability. In order to overcome these drawbacks, it has been blended with natural fibers, leading to a fully biodegradable biocomposite material with enhanced properties. However, blending a hydrophobic biopolymer with hydrophilic fibers leads to poor interfacial adhesion producing interfacial voids, cavities and defects and consequently low performance properties. In this sense, this article reviews different strategies of biopolymer functionalization to improve compatibility in biocomposite materials. First, the effect of different parameters on biopolymers functionalization via melt and reactive extrusion processes is discussed. Finally, coupling efficiency of functionalized biopolymers is analyzed in terms of mechanical and thermal properties.

Self-hybridization and Coupling Agent Effect on the Properties of Natural Fiber/HDPE Composites

This work investigates the combination of different fiber sizes (self-hybridization) on the mechanical properties of composite materials. High density polyethylene composites based on agave and pine fibers were prepared using different ratios of long and short fibers. Furthermore, the effect of coupling agent (maleated polyethylene) versus self-hybridization was evaluated. Several studies in the past have shown that coupling agents can improve the mechanical properties of natural fiber composites. Nevertheless, this study shows that a combination of two particle sizes is also an interesting option to increase mechanical properties like impact strength, as well as tensile and flexural moduli. On the other hand, the presence of coupling agent enhanced the fiber-matrix interfacial adhesion and its effect was more evident on the tensile strength.