Alessandra Lavoratti

Dynamic-mechanical and thermomechanical properties of cellulose nanofiber/polyester resin composites.

Composites of unsaturated polyester resin (UPR) and cellulose nanofibers (CNFs) obtained from dry cellulose waste of softwood (Pinus sp.) and hardwood (Eucalyptus sp.) were developed. The fiber properties and the influence of the CNFs in the dynamic-mechanical and thermomechanical properties of the composites were evaluated. CNFs with a diameter of 70-90 nm were obtained. Eucalyptus sp. has higher α-cellulose content than Pinus sp. fibers. The crystallinity of the cellulose pulps decreased after grinding. However, high values were still obtained. The chemical composition of the fibers was not significantly altered by the grinding process. Eucalyptus sp. CNF composites had water absorption close to the neat resin at 1 wt% filler. The dynamic-mechanical properties of Eucalyptus sp. CNFs were slightly increased and the thermal stability was improved.

Drying techniques applied to cellulose nanofibers

Nanotechnology applied to cellulosic fibers has quickly become an interdisciplinary field with great interest in the application as reinforcement in polymer composites, mainly due to the abundance of these raw materials, and to their mechanical properties and multifunctionality. However, one of the critical points to obtain individualized cellulose nanofibers is the drying technique (dehydration), since most of the nanofiber processes are performed in the liquid phase. According to the methodology applied to the cellulose water dehydration process, various morphologies and properties can be obtained in the cellulose fibers. This review study aims to discuss the main processes used to obtain nanocellulose (chemical and mechanical) and the drying techniques applied to nanocellulose structures, such as conventional oven drying, freeze drying (lyophilization), supercritical extraction, and spray drying.

Aerogel preparation from short cellulose nanofiber of the Eucalyptus species

Wood is the main industrial source for obtaining cellulose. It is a natural composite, constituted by cellulose, polyoses, lignin, small amounts of extracts and mineral salts, wherein cellulose is the most abundant component. Many studies are being developed for obtaining materials based on natural fibers, which combine interesting properties such as renewability, biodegradability, low density and low cost. Aerogels are solid, lightweight materials with high porosity and high internal surface area. These features combined in one single material make the aerogels a differentiated product with potential for use as an adsorbent. In this context, aerogels made of cellulose nanofibers obtained from short-fiber cellulose of Eucalyptus sp. were made. The cellulose suspension was first disintegrated by a mechanical grinder, and the aerogels were undergone to freeze-drying. The characterization of the samples was performed by apparent density, porosity, scanning electron microscopy, Fourier transform infrared spectroscopy and thermogravimetric analyses. According to the micrographs obtained by scanning electron microscopy and field emission gun scanning electron microscopy, it was observed the formation of pores formed by the interconnection of cellulose fibers. The apparent density of the starting cellulose fibers (pressed plates) was 0.6998 g.cm−3 and the aerogel density decreased to 0.0240 g.cm−3. The values for aerogel porosity were about 97%, which benefits the passage of liquids and gases from the external environment to the internal structure of the material. Fourier transform infrared spectroscopy and thermogravimetric analyses showed no change in the chemical composition or in the thermal stability of the obtained aerogels in comparison to their starting materials.

INFLUENCE OF SILANE TREATMENTS ON THE PROPERTIES OF GRAPHITE NANOPLATELET/EPOXY NANOCOMPOSITES

Epoxy resins are used in composite applications due to their good mechanical properties. To further enhance their performance, the use of nanofillers such as graphite nanoplatelets (GrNP) has been proposed, which can be surface treated for extra improvement. This study aims to evaluate the influence of GrNP content and treatment on the mechanical and dynamic-mechanical properties of GrNP/epoxy composites. GrNP was treated with (3glycidyloxypropyl)trimethoxysilane and (3-aminopropyl)triethoxysilane, and later dispersed in epoxy resin aided by sonication. Composites reinforced with 0.25 wt% GrNP displayed increased tensile strength compared to the neat resin. Silane treated fillers showed an improvement in tensile strength and dynamic-mechanical properties compared to both neat resin and GrNP/epoxy composites at the same wt% of reinforcement, evidencing that the silane treatment was advantageous.

Evaluation of the degradation of HDPE hybrid composites using wood flour from CCA-treated poles, and recycled ceramic insulators

Waste from the maintenance of electricity distribution networks is generated every day, in repairing and replacement of components used in electricity distribution networks. Among the most dangerous residues, wood poles treated with chromated copper arsenate are distinguished by the toxicity of the chemical treatment it has been submitted to, as well as its ceramic insulators, due to the difficult recyclability of this material. Thus, an alternative may be the reuse of these components as reinforcing elements in polymeric composites. Based on this, two residues were used as fillers for the production of high-density polyethylene (HDPE) hybrid composites, wood powder, and insulating ceramic powder. Degradation by ultraviolet (UV) exposure in controlled environments of the composites was also evaluated, and toxicity tests were carried out based on the leaching of these loads with increased exposure time to degradation. Composites presented higher tensile and flexural properties than pure HDPE, and after the exposure to the UV degradation process, the composites presented fewer cracks when compared to HDPE. After exposure to the simulated degradation environment, the levels of chromium, copper, and arsenic leached were within the limits allowed by the standard that provides classification and means of disposal of these materials.

Obtaining Hydrophobic Aerogels of Unbleached Cellulose Nanofibers of the Species Eucalyptus sp. and Pinus elliottii

The use of natural fibers from renewable and biodegradable sources in oleophilic sorbents, such as cellulose, has become an interesting alternative due to their excellent properties and sustainability. In addition to that, the low density of the aerogels obtained from cellulose is favorable for their use as sorbents. In this context, the objective of this study is to develop hydrophobic aerogels of unbleached cellulose nanofibers of the Eucalyptus sp. and Pinus elliottii. Cellulose samples were submitted to mechanical fibrillation to obtain cellulose nanofiber suspensions, followed by a chemical treatment with methyltrimethoxysilane and dried by freeze-drying to prepare the aerogels. The aerogels presented hydrophobic and oleophilic characteristics, including a water contact angle of 134°, sorption capacities in a heterogeneous medium of above 21.0 g·g−1, and oil removal efficiency greater than 88.5%. The Pinus elliottii nanofiber aerogels showed higher compressive strength when compared to the nanofiber aerogels of Eucalyptus sp.