Leandro N. Ludueña

Extraction of cellulose nanowhiskers from natural fibers and agricultural byproducts

In this work the feasibility of extracting cellulose from cotton, sisal and flax fibers, corn stover and rice husk by means of usual chemical procedures such as acid hydrolysis, chlorination, alkaline extraction, and bleaching was analyzed. Cellulose nanowhiskers from these sources, and from commercial cellulose, were produced by the acid hydrolysis of the obtained celluloses. The final products were characterized by means of Thermogravimetric Analysis (TGA), Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), Scanning Electronic Microscopy (SEM) and Atomic Force Microscopy (AFM). The chemical procedure used to obtain cellulose nanowhiskers was effective in all cases but differences on the thermal stability, chemical composition, crystallinity and morphology were found due to the dissimilar nature of the different sources. Thus, this work demonstrates that the morphology and physical properties of cellulose nanowhiskers synthesized by the same conditions are strongly dependent on their source.

Viscoelastic behavior of polycaprolactone/clay nanocomposites

The creep behavior of polycaprolactone and polycaprolactone/clay nanocomposites prepared by melt intercalation was studied. Sodium montmorillonite and organo-modified montmorillonite were used as reinforcement in order to analyze the effect of clay dispersion degree. Both a viscoelastic creep model named Burgers (four parameters) and an empirical method called Findley power law were applied to fit the experimental data (elastic, primary creep stage, and secondary creep stages). An additional effort was conducted to relate the parameter analysis of the Burgers model with the experimental behavior at each creep stage. The variation of the theoretical parameters illustrated the influence of the nanofillers on the experimental creep performance of the bulk matrix. Time–temperature superposition principle was used to predict the long-term behavior based on the short-term experimental data. The Findley power law model was also employed to reproduce the master curves. Both experimental curves and models demonstrated that the incorporation of the clay produces a significant improvement on the creep resistance at short times. This effect was higher for the best-dispersed nanocomposite. The latter result was strictly related to the great enhancement of the elastic behavior since in that case the time-dependent deformations were higher than those of the neat matrix.

Preparation and characterization of polystyrene/starch blends for packaging applications

Polystyrene/thermoplastic starch blends from 90/10 to 50/50 (w/w) were prepared by melt blending. Blends were characterized by scanning electron microscopy (morphology); thermogravimetric analysis (thermal stability and weight content of each component); Fourier transform infrared spectroscopy (identification of functional groups); differential scanning calorimetry (thermal properties); tensile tests (strength, modulus, elongation at break and tenacity) and biodegradation in soil (biodegradability). The biodegradation process was also followed by thermogravimetric analysis calculating the loss of each component after removing the samples from soil at different time intervals. Scanning electron microscopy results showed good starch dispersion in the blend. The Fourier transform infrared spectroscopy analysis suggested that only physical interaction took place between the polystyrene and the thermoplastic starch. The tensile tests revealed a considerable decrease in the mechanical properties of the polystyrene-thermoplastic starch blends as a function of the thermoplastic starch content. The 50/50 blend showed decreases of 48% in the Young’s modulus, 62% in the tensile strength and increases of 62% in the elongation at break, in comparison to neat polystyrene. The biodegradability tests showed that the greater the thermoplastic starch concentration in the blend, the faster the mass loss, which was also confirmed by the thermogravimetric analysis and Fourier transform infrared spectroscopy analysis.

Dissimilar Tendencies of Innovative Green Clay Organo-Modifier on the Final Properties of Poly(ε-caprolactone) Based Nanocomposites

Composites based on poly(ε-caprolactone) (PCL) were prepared by melt blending the polymer with natural and modified bentonite. Soy lecithin (SL), a natural and nontoxic biosurfactant, was used as modifier agent. Three organoclays with different SL contents were employed as fillers and composites containing 1 and 2 wt% of each clay, were prepared. Thermal (by thermogravimetric analysis, and differential scanning calorimetry), morphological (by X-ray diffraction (XRD) and melt rheology), mechanical (by tensile tests) and barrier properties (by means of water vapor permeability tests) of matrix and composites were studied as a function of clay type and content. Morphological analysis by XRD showed nanocomposites with intercalated-exfoliated structures while melt rheology suggests thermal degradation of PCL matrix catalyzed by SL bentonite modifier. Thermal and mechanical properties were consistent with this assumption, due to the slight increment in crystallinity percentage and detriment in the Young’s modulus of the nanocomposites in comparison with the neat matrix. On the other hand, water vapor permeability of PCL significantly decreased in composites, as is expected for polymer/clay nanocomposites, favoring its potential application as food packaging. Thus, dissimilar tendencies were found in the final properties of the nanocomposites that were attributed to the matrix molecular weight degradation catalyzed by the novel green clay organo-modifier.

Biodegradable Polymer/Clay Nanocomposites

This chapter is a comprehensive source for biodegradable polymer/clay nanocomposite research. The work focuses on several strategies to obtain well-dispersed nanocomposites with improved mechanical properties. Different strategies for optimization of biodegradable polymer-clay nanocomposites were identified and treated herein. The two most important strategies are based on the chemical modification of the clay and on the processing conditions. The combination of these two factors greatly affects the resulting structure of the nano composite, being always the goal to obtain a good dispersion of the reinforcement within the polymeric matrix. Challenges in processing conditions have been analyzed and the prospective for future research has been addressed.

Isothermal crystallization of polycaprolactone/modified clay biodegradable nanocomposites

AbstractIn this paper, the isothermal crystallization of polycaprolactone (PCL)/modified clay nanocomposites, at several temperatures, was studied. The effects of clay type (organo-modified bentonite B-TBHP and organo-modified montmorillonite C20A) and also the clay content were analysed. Bulk crystallization was studied by differential scanning calorimetry and modelled by the Avrami equation. Special effort was made to correlate the crystallization parameters with the clay dispersion degree inside the polymer matrix. The lowest induction time and fastest overall crystallization rate were obtained with the B-TBHP nanocomposites, which showed the lowest clay dispersion degree. In contrast, C20A nanocomposites showed higher clay dispersion degree inside the PCL matrix and higher induction times and lower overall crystallization rate than B-TBHP ones, even retarding the formation of the equilibrium nucleus with critical dimensions in comparison with neat PCL.

Effect of extrusion conditions and post-extrusion techniques on the morphology and thermal/mechanical properties of polycaprolactone/clay nanocomposites

The effect of extrusion conditions on the performance of polycaprolactone /organo-modified clay nanocomposites was studied. It was demonstrated that the extrusion parameters have negligible effect on the molecular weight of polycaprolactone, on the morphology of the nanocomposites and on the final thermal/mechanical properties of the materials. This result was a consequence of the previous optimization of both polymer/clay compatibility and clay processing stability. Finally, the molten–polycaprolactone/clay mixtures were post-processed by different techniques submitting the mixtures to extensional flow. Clay platelets alignment was observed as a function of the extensional flow intensity which further improved the mechanical properties of the nanocomposites.

Fracture behavior of polycaprolactone/clay nanocomposites

The effect of clay-organo modifier on the thermal and mechanical properties and fracture behaviors of pure polycaprolactone (PCL) and 5 wt% PCL/clay nanocomposites were studied. The different materials were prepared by melt intercalation. It was demonstrated by X-ray diffractometry, differential scanning calorimetry, tensile, and fracture tests that the addition of modified nanoclays affected significantly the final properties of the materials. The optimal combination of properties was achieved with the PCL reinforced with 5 wt% of C30B obtaining improvements of 17% in the Young’s modulus and 1500% in the specific essential fracture work.

Revalorization of rice husk waste as a source of cellulose and silica

Cellulose and silica were obtained from rice husk by a multi-step procedure. Three different strategies including different alkaline and bleaching steps were evaluated by Fourier transform infrared spectroscopy (FTIR) in order to choose the sequence that combines the better conditions to obtain both subproducts simultaneously. The effects of the different steps on the structure and morphology of original material treated by the selected procedure were analyzed by X-ray diffraction (XRD), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). The results suggest that it is possible to obtain both by-products with a simple procedure, giving an added value to this waste.

Non-isothermal crystallization of PCL/CLAY nanocomposites

Fil: Lanfranconi, Matias R.. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnologia de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingenieria. Instituto de Investigaciones en Ciencia y Tecnologia de Materiales; Argentina