Daniel Pasquini

Mechanical properties of natural rubber nanocomposites reinforced with high aspect ratio cellulose nanocrystals isolated from soy hulls.

Cellulose nanocrystals (CNCs) were isolated from soy hulls by acid sulfuric hydrolysis. The resulting CNCs were characterized using TEM, AFM, WAXS, elemental analysis and TGA. The CNCs have a high crystallinity, specific surface area and aspect ratio. The aspect ratio (around 100) is the largest ever reported in the literature for a plant cellulose source. These CNCs were used as a reinforcing phase to prepare nanocomposite films by casting/evaporation using natural rubber as matrix. The mechanical properties were studied in both the linear and non-linear ranges. The reinforcing effect was higher than the one observed for CNCs extracted from other sources. It may be assigned not only to the high aspect ratio of these CNCs but also to the stiffness of the percolating nanoparticle network formed within the polymer matrix. Moreover, the sedimentation of CNCs during the evaporation step was found to play a crucial role on the mechanical properties.

Physical Vapor Deposited Thin Films of Lignins Extracted from Sugar Cane Bagasse: Morphology, Electrical Properties, and Sensing Applications

The concern related to the environmental degradation and to the exhaustion of natural resources has induced the research on biodegradable materials obtained from renewable sources, which involves fundamental properties and general application. In this context, we have fabricated thin films of lignins, which were extracted from sugar cane bagasse via modified organosolv process using ethanol as organic solvent. The films were made using the vacuum thermal evaporation technique (PVD, physical vapor deposition) grown up to 120 nm. The main objective was to explore basic properties such as electrical and surface morphology and the sensing performance of these lignins as transducers. The PVD film growth was monitored via ultraviolet-visible (UV-vis) absorption spectroscopy and quartz crystal microbalance, revealing a linear relationship between absorbance and film thickness. The 120 nm lignin PVD film morphology presented small aggregates spread all over the film surface on the nanometer scale (atomic force microscopy, AFM) and homogeneous on the micrometer scale (optical microscopy). The PVD films were deposited onto Au interdigitated electrode (IDE) for both electrical characterization and sensing experiments. In the case of electrical characterization, current versus voltage (I vs V) dc measurements were carried out for the Au IDE coated with 120 nm lignin PVD film, leading to a conductivity of 3.6 × 10(-10) S/m. Using impedance spectroscopy, also for the Au IDE coated with the 120 nm lignin PVD film, dielectric constant of 8.0, tan δ of 3.9 × 10(-3), and conductivity of 1.75 × 10(-9) S/m were calculated at 1 kHz. As a proof-of-principle, the application of these lignins as transducers in sensing devices was monitored by both impedance spectroscopy (capacitance vs frequency) and I versus time dc measurements toward aniline vapor (saturated atmosphere). The electrical responses showed that the sensing units are sensible to aniline vapor with the process being reversible. AFM images conducted directly onto the sensing units (Au IDE coated with 120 nm lignin PVD film) before and after the sensing experiments showed a decrease in the PVD film roughness from 5.8 to 3.2 nm after exposing to aniline.

Comprehensive morphological and structural investigation of cellulose I and II nanocrystals prepared by sulphuric acid hydrolysis

Cellulose nanocrystals (CNCs) were produced from eucalyptus wood pulp using three different methods: (i) classical sulphuric acid hydrolysis (CN-I), (ii) acid hydrolysis of cellulose previously mercerized by alkaline treatment (MCN-II), and (iii) solubilization of cellulose in sulphuric acid and subsequent recrystallization in water (RCN-II). The three types of CNCs exhibited different morphologies and crystalline structures that were characterized using complementary imaging, diffraction and spectroscopic techniques. CN-I corresponded to the type I allomorph of cellulose while MCN-II and RCN-II corresponded to cellulose II. CN-I and MCN-II CNCs were acicular particles composed of a few laterally-bound elementary crystallites. In both cases, the cellulose chains were oriented parallel to the long axis of the particle, although they were parallel in CN-I and antiparallel in MCN-II. RCN-II particles exhibited a slightly tortuous ribbon-like shape and it was shown that the chains lay perpendicular to the particle long axis and parallel to their basal plane. The unique molecular and crystal structure of the RCN-II particles implies that a higher number of reducing chain ends are located at the surface of the particles, which may be important for subsequent chemical modification. While other authors have described nanoparticles prepared by regeneration of short-chain cellulose solutions, no detailed description was proposed in terms of particle morphology, crystal structure and chain orientation. We provide such a description in the present paper.

Mechanical, thermal, and barrier properties of methylcellulose/cellulose nanocrystals nanocomposites

In this work, the effects of incorporating cellulose nanocrystals from soy hulls (WSH 30 ) on the mechanical, thermal, and barrier properties of methylcellulose (MC) nanocomposites were evaluated. MC/WSH 30 nanocomposite films with different filler levels (2, 4, 6, 8, and 10%) were prepared by casting. Compared to neat MC film, improvements in the mechanical and barrier properties were observed, while thermal stability was retained. The improved mechanical properties of nanocomposites prepared may be attributed to mechanical percolation of WSH 30 , formation of a continuous network of WSH 30 linked by hydrogen interactions and a close association between filler and matrix.

New biphasic mono-component composite material obtained by partial oxypropylation of bacterial cellulose

Abstract The present work evaluates the partial oxypropylation of dried bacterial cellulose (BC) performed by grafting propylene oxide with potassium hydroxide as the catalyst. Samples were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, differential scanning calorimetry, and thermogravimetric analysis. Partial transformation of BC was observed, with cellulose fibers being covered by the thermoplastic phase, leading to a new biphasic mono-component composite material. This synthesis can be considered a green chemical process, since it does not require the use of solvents nor the application of any processing operation, given the fact that the final product is ready for further exploitation as it is removed from the reactor. The obtained material can be used in various applications in the polymer field, i.e. composites, reinforced rigid polyurethane foams, and others.

NANOCRISTAIS DE CELULOSE A PARTIR DE CELULOSE BACTERIANA

Bacterial cellulose produced from Gluconacetobacter xilinus was used to produce cellulose nanocrystals by sulfuric acid hydrolysis. Hydrolysis was performed with 64% sulfuric acid at 50 oC with the hydrolysis time ranging between 5 and 90 min. The production of nanocrystals was observed to have size distributions that were dependent on hydrolysis times up to 10 min, after which time the suspensions showed distributions closer in size. Results from thermal analysis and X-ray diffraction showed that the amorphous cellulose was removed, leaving only the crystalline portion. Self-supported films were formed from the suspension of nanocrystals and had iridescence characteristics. The films were characterized by microscopy measures and specular reflectance.

Nanocellulose: Extraction and application as a sustainable material for wastewater purification

Abstract With the increase in water quality regulations and decrease in available fresh water supplies, scientists around the world are focusing on renewable raw materials and environmentally friendly, cost-effective materials for water purification. Among these, nanocellulose has gained considerable interest because of its excellent properties. Many laboratory operations depend on the filtration process that is performed with cellulose-based filter papers. Nanocelluloses inherent fibrous nature and remarkable mechanical properties, including low cost and bio-compatibility make nanocellulose a huge potential component in water filtration membranes. Nanocellulose is a very promising adsorbent for removing heavy metals, viruses, dyes, etc. due to its high surface area-to-volume ratio, low cost, high natural abundance, and inherent environmental inertness. Moreover, the surface of nanocellulose has easily functionalizable OH groups, and this facilitates the incorporation of chemical moieties that may increase the binding efficiency of pollutants to the nanocellulosic materials. The materials based on cellulose and its derivatives have been used for more than 150 years in a wide variety of applications, such as food, paper production, biomaterials, and pharmaceuticals. In recent years, nanotechnologies have been promoted as having great potential for reducing costs and developing efficiency in pollution prevention, treatment, and clean up. Two applications for cellulose nanomaterials in this area that have achieved interest are as an active sorbent material for contaminants and as a stabilizer for other active particles. Cellulose nanofibers (CNF) are one of the types of cellulose nanomaterials. CNFs are a promising substitute adsorbent due to their high surface area to-volume ratio, low cost, high natural abundance, and inherent environmental inertness. Furthermore, CNFs readily functionalized surface facilitates the incorporation of chemical moieties that may enhance the binding efficiency of pollutants to the CNF.

Biomass sorghum as a novel substrate in solid-state fermentation for the production of hemicellulases and cellulases by Aspergillus niger and A. fumigatus

We investigated the role of carbon and nitrogen sources in the production of cellulase and hemicellulase by Aspergillus strains.

Cellulose Nanofiber-Based Polyaniline Flexible Papers as Sustainable Microwave Absorbers in the X-Band

A series of flexible, lightweight, and highly conductive cellulose nanopapers were fabricated through in situ polymerization of aniline monomer on to cellulose nanofibers with a rationale for attenuating electromagnetic radiations within 8.2-12.4 GHz (X band). The demonstrated paper exhibits good conductivity due to the formation of a continuous coating of polyaniline (PANI) over the cellulose nanofibers (CNF) during in situ polymerization, which is evident from scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction analysis. The free hydroxyl groups on the surface of nanocellulose fibers promptly form intermolecular hydrogen bonding with PANI, which plays a vital role in shielding electromagnetic radiations and makes the cellulose nanopapers even more robust. These composite nanopapers exhibited an average shielding effectiveness of ca. -23 dB (>99% attenuation) at 8.2 GHz with 1 mm paper thickness. The fabricated papers exhibited an effective attenuation of electromagnetic waves by a predominant absorption mechanism (ca. 87%) rather than reflection (ca. 13%), which is highly desirable for the present-day telecommunication sector. Unlike metal-based shields, these demonstrated PANI/CNF papers have given a new platform for designing green microwave attenuators via an absorption mechanism. The prime novelty of the present study is that these robust PANI/CNF nanopapers have the ability to attenuate incoming microwave radiations to an extent that is 360% higher than the shielding effectiveness value reported in the previous literature. This makes them suitable for use in commercial electronic gadgets. This demonstrated work also opens up new avenues for using cellulose nanofibers as an effective substrate for fabricating conductive flexible papers using polyaniline. The direct current conductivity value of PANI/CNF nanopaper was 0.314 S/cm, which is one of the key requisites for the fabrication of efficient electromagnetic shields. Nevertheless, such nanopapers also open up an arena of applications such as electrodes for supercapacitors, separators for Li-S, Li-polymer batteries, and other freestanding flexible paper-based devices.

Produção, caracterização e utilização de membranas de poliestireno sulfonado e polissulfona como catalisadores na reação de esterificação do ácido oleico.

O biodiesel e um biocombustivel renovavel e nao toxico que pode ser produzido pela reacao de esterificacao. Nesta reacao, sao usados catalisadores acidos e, devido as inumeras vantagens, os catalisadores heterogeneos estao ganhando espaco. Membranas de polissulfona (PSF) e poliestireno sulfonado (PSS) foram preparados para catalisar a reacao de esterificacao do acido oleico com metanol, produzindo biodiesel. Foram obtidos varios tipos morfologicos de membranas: densas, porosas e eletrofiadas. As condicoes de reacao foram: temperatura de 100 ° C, razao molar de 10:1 (metanol:acido oleico), 5% de catalisador e tempo de 2 horas. Atraves dos metodos BET e BJH foi possivel obter a area superficial das membranas, volume e tamanho do poro. O consumo de acido oleico e a formacao do ester sao confirmados pelas analises de CGMS e pelas bandas FTIR, respectivamente. Para as membranas que apresentaram o PSS, 2 horas de reacao foram suficientes para o consumo quase total do acido oleico, com excecao da membrana densa.