André R. Fajardo

Bio: André R. Fajardo is an academic researcher from Universidade Federal de Pelotas. The author has contributed to research in topics: Self-healing hydrogels & Adsorption. The author has an hindex of 31, co-authored 84 publications receiving 3220 citations. Previous affiliations of André R. Fajardo include State University of Campinas & University of Grenoble.

Chitosan- graft -poly(acrylic acid)/rice husk ash based superabsorbent hydrogel composite: preparation and characterization

Abstract: Rice husk ash (RHA), an industrial waste, was incorporated in the preparation of high performance chitosan (CTS) and poly(acrylic acid) (PAA) based superabsorbent hydrogel. Hydrogels filled with RHA previously calcinated at 900 °C (RHA900) showed better water uptake (225 gwater/gabsorbent) than those with husk calcinated at 400 °C (RHA400) (198 gwater/gabsorbent) due to the higher purity and crystallinity, at same composition. The hydrogel composite at 5 wt-% of RHA900 showed the best water uptake (255 gwater/gabsorbent). A clear reduction in swelling degree is observed by increasing the amount of crosslinker from 1 to 3 wt-% due to the increase in the crosslinking density forming more rigid hydrogels. On the other hand, an increase in the initiator amount from 1 to 3 wt-% increased the water uptake due to the formation of greater numbers of active sites increasing the number of PAA chains grafted into CTS backbone. Furthermore, the hydrogel composites presented responsive behavior in relation to both pH and sat solution. The data shows it is possible to obtain high performance materials by incorporating an industrial waste, rice husk ash, in the preparation of hydrogel composites.

Reaction of glycidyl methacrylate at the hydroxyl and carboxylic groups of poly(vinyl alcohol) and poly(acrylic acid): is this reaction mechanism still unclear?

Abstract: Transesterification and epoxide ring-opening reactions are two mechanism routes that explain chemical modifications of macromolecules by glycidyl methacrylate (GMA). Although the coupling reaction of the GMA with macromolecules has widely been investigated, there are still mechanisms that remain to be explained when GMA is processed in an aqueous solution at different pH conditions. To this end, reaction mechanisms of poly(vinyl alcohol) (PVA) and poly(acrylic acid) (PAAc) by GMA in water in acidic and basic conditions were investigated thoroughly. The presence of hydroxyl groups in PVA and carboxyl groups in PAAc allowed for a better evaluation of the reaction mechanisms. The analysis of the 1H and 13C NMR spectra clearly demonstrated that the chemical reactions of GMA with carboxyl groups and alcohols of the macromolecules in an aqueous solution are dependent on pH conditions. At pH 3.5, the GMA reacts with both the carboxylic and the hydroxyl groups through an epoxide ring-opening mechanism. At pH 10.5...

Lignocellulosic biomass: a sustainable platform for the production of bio-based chemicals and polymers

Abstract: The demand for petroleum dependent chemicals and materials has been increasing despite the dwindling of their fossil resources. As the dead-end of petroleum based industry has started to appear, today's modern society has to implement alternative energy and valuable chemical resources immediately. Owing to the importance of lignocellulosic biomass being the most abundant and bio-renewable biomass on earth, this critical review provides insights into the potential of lignocellulosic biomass as an alternative platform to fossil resources. In this context, over 200 value-added compounds, which can be derived from lignocellulosic biomass by various treatment methods, are presented with their references. Lignocellulosic biomass based polymers and their commercial importance are also reported mainly in the frame of these compounds. This review article aims to draw the map of lignocellulosic biomass derived chemicals and their synthetic polymers, and to reveal the scope of this map in today's modern chemical and polymer industry.

Review of Hydrogels and Aerogels Containing Nanocellulose

Abstract: Naturally derived cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs) are emerging nanomaterials that display high strength, high surface area, and tunable surface chemistry, allowing for controlled interactions with polymers, nanoparticles, small molecules, and biological materials. Industrial production of nanocelluloses is increasing rapidly with several companies already producing on the tons-per-day scale, intensifying the quest for viable products across many sectors. While the hydrophilicity of the nanocellulose interface has posed a challenge to the use of CNCs and CNFs as reinforcing agents in conventional plastics, it is a significant benefit for creating reinforced or structured hydrogel composites (or, when dried, aerogels) exhibiting both mechanical reinforcement and a host of other desirable properties. In this context, this Review describes the quickly growing field of hydrogels and aerogels incorporating nanocelluloses; over 200 references are summarized in comprehensive tables ...