0000000000023865
AUTHOR
Fernando G. Torres
Development of self-assembled bacterial cellulose–starch nanocomposites
Abstract A bioinspired bottom-up process was developed to produce self-assembled nanocomposites of cellulose synthesized by Acetobacter bacteria and native starch. This process takes advantage of the way some bacteria extrude cellulose nanofibres and of the transport process that occurs during the gelatinization of starch. Potato and corn starch were added into the culture medium and partially gelatinized in order to allow the cellulose nanofibrils to grow in the presence of a starch phase. The bacterial cellulose (BC)–starch gels were hot pressed into sheets that had a BC volume fraction higher than 90%. During this step starch was forced to further penetrate the BC network. The self-assem…
Monitoring molecular dynamics of bacterial cellulose composites reinforced with graphene oxide by carboxymethyl cellulose addition
[EN] Broadband Dielectric Relaxation Spectroscopy was performed to study the molecular dynamics of dried Bacterial Cellulose/Carboxymethyl Cellulose-Graphene Oxide (BC/CMC-GO) composites as a function of the concentration of CMC in the culture media. At low temperature the dielectric spectra are dominated by a dipolar process labelled as a beta -relaxation, whereas electrode polarization and the contribution of dc-conductivity dominate the spectra at high temperatures and low frequency. The CMC concentration affects the morphological structure of cellulose and subsequently alters its physical properties. X-ray diffractometry measurements show that increasing the concentration of CMC promote…
Reversible stress softening of collagen based networks from the jumbo squid mantle (Dosidicus gigas).
Dosidicus gigas is the largest and one of the most abundant jumbo squids in the eastern Pacific Ocean. In this paper we have studied the muscle of the mantle of D. gigas (DGM). Morphological, thermal and rheological properties were assessed by means of atomic force microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, differential scanning calorimetry, thermogravimetry and oscillatory rheometry. This study allowed us to assess the morphological and rheological properties of a collagen based network occurring in nature. The results showed that the DGM network displays a nonlinear effect called reversible stress softening (RSS) that has been previously described for …
Molecular dynamics of carrageenan composites reinforced with Cloisite Na+ montmorillonite nanoclay
[EN] Nanocomposites comprising biodegradable carrageenan and glycerol(KCg) as the host polymer, with different contents of natural montmorillonite (MMT) as filler, were prepared by a solution casting process. Different techniques have been used to determine the interaction/behavior among the different components of the samples such as Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Transmission electron microscope (TEM) and, mainly, Dielectric relaxation spectroscopy (DRS). FTIR indicates hydrogen interaction between carrageenan matrix and silicate that is confirmed by the XRD data indicating some kind of carrageenan intercalation between the MMT layers. A rather ho…
Characterization of the nanocomposite laminate structure occurring in fish scales from Arapaima Gigas
In the present paper, the nanocomposite laminate structure of scales from the Amazonian fish Arapaima Gigas is investigated. The structure and composition of the scales were assessed by means of X-ray diffraction (XRD) and Fourier Transform Infrared spectroscopy (FTIR). The theory of Fickian diffusion is used and discussed in order to rationalize the water absorption and desorption behavior of the scales. Morphology studies and fracture analysis of the native scales were carried out using Transmission Electron Microscopy (TEM), Light Optical Microscopy (LOM) and Scanning Electron Microscopy (SEM). A fibrous layer of collagen and a plywood-like structure were observed. In order to study the …
Effect of Chitin Whiskers on the Molecular Dynamics of Carrageenan-Based Nanocomposites
[EN] Films of carrageenan (KC) and glycerol (g) with different contents of chitin nanowhiskers (CHW) were prepared by a solution casting process. The molecular dynamics of pure carrageenan (KC), carrageenan/glycerol (KCg) and KCg with different quantities of CHWs as a filler was studied using dielectric relaxation spectroscopy. The analysis of the CHW effect on the molecular mobility at the glass transition, T-g, indicates that non-attractive intermolecular interactions between KCg and CHW occur. The fragility index increased upon CHW incorporation, due to a reduction in the polymer chains mobility produced by the CHW confinement of the KCg network. The apparent activation energy associated…
Processing and Mechanical Properties of Natural Fiber Reinforced Thermoplastic Starch Biocomposites
Natural fiber reinforced starch polymers are processed by compression molding. Potato, sweet potato, and corn starch are used as matrices. Three types of natural fibers, namely sisal, jute, and cabuya, are used in concentrations varying from 2.5 to 12.5% w/w in the composites. Different plasticizers are used for the starch polymers, such as water and glycerol. Mechanical properties are assessed by tensile and impact tests. In both cases, improved mechanical properties are obtained at increasing fiber contents. Tensile strength appears to be markedly improved with the addition of 10% by weight of sisal fibers, while the best results for impact strength are obtained for cabuya fibers.
Nanocomposites of bacterial cellulose/hydroxyapatite for biomedical applications.
In the present work, a nanocomposite material formed by bacterial cellulose (BC) networks and calcium-deficient hydroxyapatite (HAp) powders was synthesized and characterized. The HAp nanoparticles were previously prepared by a wet chemical precipitation method, starting from aqueous solutions of calcium nitrate and di-ammonium phosphate salts. Energy-dispersive spectroscopy reveals that the prepared HAp corresponds to calcium-deficient hydroxyapatite. BC-HAp nanocomposites were prepared by introducing carboxymethylcellulose (CMC) into the bacteria culture media. HAp nanoparticles were then introduced and remained suspended in the culture medium during the formation of cellulose nanofibrils…
Optimization of Cell Growth on Bacterial Cellulose by Adsorption of Collagen and Poly-L-Lysine
Poly-L-lysine and collagen were separately added to bacterial cellulose (BC) nanofibers. The ionic surface charge had been previously modified in order to promote the adsorption of poly-L-lysine and collagen. Cell adhesion of Chinese hamster ovary (CHO) cells on BC surfaces was confirmed by removing unattached cells from the BC substrates. Cell viability was calculated and it was determined that both poly-L-lysine-BC and collagen-BC substrates are viable for cell growth. The results showed that the cell viability in poly-L-lysine modified BC substrate is similar to the one observed in polystyrene tissue culture plates.
Thermal and Structural Analysis of Natural Fiber Reinforced Starch-Based Biocomposites
This is the second part of a series of articles dealing with characterization of starch based biodegradable composites. Potato, sweet potato, and corn starch varieties were used as matrices of the biocomposites. Natural fibers including jute, sisal, and cabuya were used as discrete reinforcement. Water and glycols were used as plasticizers. Compression molded specimens were prepared and characterized by a variety of techniques. Differential Scanning Calorimetry (DSC) and Thermogravimetry (TGA) were used to characterize the thermal behavior of these composites. Processed specimens did not show the typical endothermic peak observed in DSC scans for native starch powder. No significant differe…
Reversible stress softening and stress recovery of cellulose networks
The mechanical properties of the plant cell wall play an important role in communication, differentiation and growth of plant cells. In particular, the expansive growth of plant cells is only possible because the material that forms the plant cell wall yields at a specific stress level, allowing for an increase in cell wall area. This process can be defined in mechanical terms as the relaxation of the wall stress. The current understanding of plant cell growth suggests that such relaxation behaviour occurs due to the presence of wall loosening agents rather than to the properties of the cellulose network itself. It is believed that certain nonenzymatic proteins, acting as wall loosening age…
Morphological Characterisation of Bacterial Cellulose-Starch Nanocomposites
Acetobacter sp. growing medium was modified in order to produce bacterial cellulose (BC) nanocomposites using a bottom-up technique that allowed starch to be introduced into the cellulose network. The BC-starch mats were hot-pressed to obtain nanocomposites sheets. Morphological characterisation was carried out using Atomic Force Microscopy and Environmental Scanning Electron Microscopy. The images obtained from microscopy were then processed using image analysis. Network properties, such as mesh size and fibre orientation were characterised. Fracture surfaces of these new nanocomposites were analysed.