Ana Paula Lemes

Review of Cellulose Nanocrystals Patents: Preparation, Composites and General Applications

This review attempts to visualize the actual impact of nanocellulose-based materials in different areas. A detailed search in recent patent databases on nanocellulose showed the importance of this material, as well as relevant topics concerning its technological preparations to obtain versatile new composites materials, and the applications of nanocellulose in different domains. At the present moment, the most common techniques for nanocellulose preparation were found to be acid and enzymatic procedures, oxidation, electrospinning, high pressure homogenization, and steam explosion processes. Concerning nanocellulose composites, several aspects were found in recent patents ranging from simple to complex structures with different properties. As unique materials, nanocellulose can be used in different areas of expertise, such as in biomedical and technical applications. This review is a useful tool for researchers to provide an update on nanocellulose patents in an expanding and interesting field of nanotechnology.

A MINIREVIEW OF CELLULOSE NANOCRYSTALS AND ITS POTENTIAL INTEGRATION AS CO-PRODUCT IN BIOETHANOL PRODUCTION

Cellulose nanocrystals appeared as important bio-based products and the collected information in term of production, characterization and application suggest that this nanomaterial could be easily extrapolated to bioethanol production. This review describes recent published syntheses using chemical and enzymatic hydrolyses and different preparations such as high pressure homogenization. Their industrial and medical applications, such as controled of delivery carriers, suggest a large projection of this nanomaterial. The most important aspect in this collected data is the potential to decrease significantly the final cost of the enzymes or the hydrolysis pre-treatment of lignocellulosic materials of all bioethanol processes in such a way that it could be economically feasible from materials such as bagasse, straw or wood resources.

Processing and characterization of composites of poly(3-hydroxybutyrate-co-hydroxyvalerate) and lignin from sugar cane bagasse

A biodegradable polymer composite containing lignin from sugarcane bagasse and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) was produced and characterized in terms of its thermal, morphological, and mechanical properties. For comparison with the properties of the composites, the properties of the isolated composite components (lignin and PHBV) were also determined. The characterizations were carried out by Fourier transformed infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and mechanical properties. In the micrograph images, no physical contact between filler and matrix was verified. The thermal decomposition profiles of composites depend on the lignin/PHBV proportions, and their residual mass increased as a function of lignin amount. Higher temperatures were necessary to promote PHBV crystallization in the presence of lignin. However, the crystalline degree of composites was not affected by the lignin. The results obtained in the mechanical tests showed that the lignin addition caused a decrease of mechanical properties.

Preparation and Characterization of Maleic Anhydride Grafted Poly(Hydroxybutirate-CO-Hydroxyvalerate) – PHBV-g-MA

A compatibilizer agent was successfully produced by grafting maleic anhydride (MA) to poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) chains on a reactive processing by mechanical mixing, using a mixture of PHBV, MA and dicumyl peroxide (DCP) as initiator. The resulting PHBV grafted MA (PHBV-g-MA) was characterized by Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and gel permeation chromatography (GPC), and its properties were compared to neat PHBV. FTIR showed an absorption band at 699 cm-1 for PHBV-g-MA, related to CH group of grafted anhydride ring. The initial thermal degradation temperature of the compatibilizer agent was reduced when compared to neat PHBV. DSC analysis showed that after grafting MA onto PHBV the crystallization temperature was about 20oC higher than neat PHBV, and the degree of crystallinity was increased. GPC analysis showed that MA when grafted onto PHBV led to a reduction of molecular weight and polydispersity.

Nanocomposites of Polyhydroxyalkanoates Reinforced with Carbon Nanotubes: Chemical and Biological Properties

The polyhydroxyalkanoates (PHA) is one of the most investigated polymers in the development of eco-friendly nanocomposites. Biotechnology is used for their production and the mechanisms of their biodegradation make them very interesting polymers to replace conventional polymers in applications where the biodegradability is a desirable characteristic. PHA applications include medical field (suture fasteners, staples, screws, valves, orthopedic pins, etc.) besides agriculture and packaging sectors. The introduction of nanofillers in the polyhydroxyalkanoates matrixes is one of the ways used in an attempt to improve their properties or to reach new properties. With this goal, PHA/carbon nanotubes (CNT) nanocomposites have been quite studied. The remarkable properties shown by carbon nanotubes such as high Young’s modulus, high thermal stability and electrical conductivity, and their low chemical reactivity is the key to achieve excellent properties from PHA nanocomposites, and to maintaining the matrix biodegradability. CNT cause changes in PHA characteristics that can affect the biodegradation rate as crystallinity degree, porosity, surface roughness, and hydrophilicity of polymer matrix. Many researches have shown the effects and advances caused by CNT filler in the mechanical resistance, crystallinity degree, thermal properties, and other important characteristics of PHA nanocomposites. However, these works have disregarded the study of the biodegradation of PHA/CNT nanocomposites, what is essential to define the application field of final product.

Effect of Graphite Nanosheets on Properties of Poly(3-hydroxybutyrate-co-3-hydroxyvalerate)

The influence of different contents, 0.25, 0.50, and 1.00 wt%, of graphite nanosheets (GNS) on the properties of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) nanocomposites obtained by solution casting method has been studied. GNS were prepared by three steps: intercalation (chemical exfoliation), expansion (thermal treatment), and the GNS obtainment (physical treatment by ultrasonic exfoliation). X-ray diffraction (XRD), Raman spectroscopy, and field emission gun-scanning electron microscopy (FE-SEM) showed that the physical, chemical, and thermal treatments preserved the graphite sheets structure. XRD and Raman results also showed that GNS were dispersed in the PHBV matrix. The degree of crystallinity (X) of the nanocomposites did not change when the graphite nanosheets were added. However, the GNS acted as nucleation agent for crystallization; that is, in the second heating the samples containing GNS showed two melting peaks. The addition the GNS did not change the thermal stability of the PHBV.

Electrospun poly(ethylene oxide)/chitosan nanofibers with cellulose nanocrystals as support for cell culture of 3T3 fibroblasts

Abstract Chitosan/poly(ethylene oxide) (PEO) (5:1) nanofibers with cellulose nanocrystals (CNCs) were produced using an electrospinning technique. The addition of CNCs to the chitosan/PEO solutions allowed the production of uniform fibers (without beads) with a high proportion of chitosan. The fiber diameters were influenced by the concentration of CNCs in the chitosan/PEO solutions. The solutions containing 10% (w/w) of CNCs produced thinner fibers compared to solutions containing 5% (w/w) of CNCs. Thermogravimetric analysis indicated that the nanofibers were thermally stable, despite the CNCs having an effect on the PEO decomposition. Results from the cell assay in cultures of 3T3 fibroblasts indicated that the chitosan/PEO nanofibers (with 10% CNCs) promoted cell attachment with changes in the cytoskeletal organization. The results obtained in this work highlight the favorable effect of CNCs in electrospinning of chitosan/PEO. As expected, the influence of nanofibers on 3T3 fibroblasts F-actin and β-tubulin network revealed alterations in cytoskeleton, leading to changes in cell morphology and spreading.

Bacterial remediation from effluent containing multi-walled carbon nanotubes

Multi-wall carbon nanotubes (MWCNT) were functionalized with functional groups containing oxygen, mainly carboxylic groups (-COOH), through reaction with a mixture of H2SO4/HNO3 (3:1 v/v). The oxidized multi-wall carbon nanotubes (MWCNTOOH) were used to prepare an effluent, 2 mg L−1 in a saline solution of NaCl (0.9%), to study of remediation of MWCNTOOH in aqueous suspension by utilization of Escherichia coli. The suspensions of E. coli (4.5 × 105 CFU mL−1 and 4.5 × 108 CFU mL−1) in test tubes with MWCNTOOH effluent caused the precipitation of a large amount of MWCNTOOH and supernatant clearing. The scanning electron microscopy (SEM) analysis of the precipitate and supernatant showed the adhesion and interlace of MWCNTOOH in bacteria surface. Although the precipitate consist of a large quantity of MWCNTOOH and bacteria, it was verified their presence in the supernatant. The spread plate technique showed that MWCNTOOH caused no cellular death of E. coli in the supernatant.

PHBV-TiO2 mats prepared by electrospinning technique: Physico-chemical properties and cytocompatibility

One of the most important challenges in tissue engineering research is the development of biomimetic materials. In this present study, we have investigated the effect of the titanium dioxide (TiO2) nanoparticles on the properties of electrospun mats of poly (hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV), to be used as scaffold. The morphology of electrospun fibers was observed by scanning electron microscopy (SEM). Both pure PHBV and nanocomposites fibers were smooth and uniform. However, there was an increase in fiber diameter with the increase of TiO2 concentration. Thermal properties of PHBV and nanocomposite mats were characterized by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). DSC analysis showed that the crystallization temperature for PHBV shifts to higher temperature in the presence of the nanoparticles, indicating that TiO2 nanoparticles change the process of crystallization of PHBV due to heterogeneous nucleation effect. TGA showed that in the presence of the nanoparticles, the curves are shifted to lower temperatures indicating a decreasing in thermal stability of nanocomposites compared to pure PHBV. To produce scaffolds for tissue engineering, it is important to evaluate the biocompatibility of the material. Cytotoxicity assay showed that TiO2 nanoparticles were not cytotoxic for cells at the concentration used to synthesize the mats. The proliferation of cells on the mats was evaluated by the MTT assay. Results showed that the nanocomposite samples increased cell proliferation compared to the pure PHBV. These results indicate that continuous electrospun fibrous scaffolds may be a good substrate for tissue regeneration.