Helena Oliver-Ortega

Effective and simple methodology to produce nanocellulose-based aerogels for selective oil removal

Spilled oil in seas has a direct impact on the environment and biodiversity. Moreover, there is no clear relationship between the amount of oil in the aquatic environment and its impact, since it mainly depends on the time and season that the oil is spilled. Nowadays, there are several techniques to clean up and recover oil from the sea, including the use of microorganisms, chemicals, controlled burning, dispersants and solidifiers, among others. Sometimes, unfortunately, the best option is to watch and wait for natural attenuation. Cellulose nanofibers have potential environmental applications due to their availability, light weight, mechanical and optical properties, and renewability. Several studies have dealt with modification of their hydrophilic character through silanation and acetylation. Both treatments, despite having a significant impact on the environment, are not plausible on a large scale because of the cost of chemicals and complexity of the modification. In this sense, the present work aims to develop hydrophobic nanocellulose-based aerogels from bleached kraft eucalyptus fibers modified with alkyl ketene dimers. For this, an experimental batch of 24 aerogels was prepared, including three types of CNF (TEMPO-oxidized, enzymatically hydrolyzed and mechanical) and eight modification degrees. The obtained aerogels were characterized in terms of morphology, hydrophilicity and water–oil absorption capacity under static and dynamic conditions, as well as their suitability for recycling and reuse for selective oil removal. The results showed that it is possible to obtain 3D-structured aerogels with a high oil absorption capacity by a simple and presumably low-cost methodology.

Evaluation of Thermal and Thermomechanical Behaviour of Bio-Based Polyamide 11 Based Composites Reinforced with Lignocellulosic Fibres

In this work, polyamide 11 (PA11) and stone ground wood fibres (SGW) were used, as an alternative to non-bio-based polymer matrices and reinforcements, to obtain short fibre reinforced composites. The impact of the reinforcement on the thermal degradation, thermal transitions and microstructure of PA11-based composites were studied. Natural fibres have lower degradation temperatures than PA11, thus, composites showed lower onset degradation temperatures than PA11, as well. The thermal transition and the semi-crystalline structure of the composites were similar to PA11. On the other hand, when SGW was submitted to an annealing treatment, the composites prepared with these fibres increased its crystallinity, with increasing fibre contents, compared to PA11. The differences between the glass transition temperatures of annealed and untreated composites decreased with the fibre contents. Thus, the fibres had a higher impact in the composites mechanical behaviour than on the mobility of the amorphous phase. The crystalline structure of PA11 and PA11-SGW composites, after annealing, was transformed to α’ more stable phase, without any negative impact on the properties of the fibres.

Towards More Sustainable Material Formulations: A Comparative Assessment of PA11-SGW Flexural Performance versus Oil-Based Composites

The replacement of commodity polyolefin, reinforced with glass fiber (GF), by greener alternatives has been a topic of research in recent years. Cellulose fibers have shown, under certain conditions, enough tensile capacities to replace GF, achieving competitive mechanical properties. However, if the objective is the production of environmentally friendlier composites, it is necessary to replace oil-derived polymer matrices by bio-based or biodegradable ones, depending on the application. Polyamide 11 (PA11) is a totally bio-based polyamide that can be reinforced with cellulosic fibers. Composites based on this polymer have demonstrated enough tensile strength, as well as stiffness, to replace GF-reinforced polypropylene (PP). However, flexural properties are of high interest for engineering applications. Due to the specific character of short-fiber-reinforced composites, significant differences are expected between the tensile and flexural properties. These differences encourage the study of the flexural properties of a material prior to the design or development of a new product. Despite the importance of the flexural strength, there are few works devoted to its study in the case of PA11-based composites. In this work, an in-depth study of the flexural strength of PA11 composites, reinforced with Stoneground wood (SGW) from softwood, is presented. Additionally, the results are compared with those of PP-based composites. The results showed that the SGW fibers had lower strengthening capacity reinforcing PA11 than PP. Moreover, the flexural strength of PA11-SGW composites was similar to that of PP-GF composites.

Reducing the Amount of Catalyst in TEMPO-Oxidized Cellulose Nanofibers: Effect on Properties and Cost

Cellulose nanofibers (CNF) are interesting biopolymers that find numerous applications in different scientific and technological fields. However, manufacturing costs are still one of the main drawbacks for the industrial production of highly fibrillated, transparent CNF suspensions. In the present study, cellulose nanofibers were produced from bleached eucalyptus pulp via TEMPO-mediated oxidation with varying amounts of NaClO and passed through a high-pressure homogenizer. The CNFs were chemically and physically characterized; cellulose nanopapers were also produced to study tensile properties. Production costs were also calculated. Results indicated that CNF properties are strongly dependent on the carboxyl content. Manufacturing costs showed that chemicals, in particular TEMPO catalyst, represent a large part of the final cost of CNFs. In order to solve this problem, a set of samples were prepared where the amount of TEMPO was gradually reduced. Characterization of samples prepared in this way showed that not only were the costs reduced, but also that the final properties of the CNFs were not significantly affected when the amount of TEMPO was reduced to half.

The role of lignin on the mechanical performance of polylactic acid and jute composites

The present work shows the feasibility of incorporating properly treated jute strands into a polylactic acid (PLA) thermoplastic matrix. The role of lignin in the interaction between jute strands and PLA was assessed by means of gradually decreasing the amount of lignin and producing composites. Five different lignin contents were studied and the resulting strands were incorporated into the PLA matrix at the ratio of 30 wt%. Composites were produced in a discontinuous extruder and standard specimens were injected and characterized at tensile. It was found that as the amount of lignin was decreased, the interface between the matrix and the reinforcement was properly improved, since tensile strength was increased up to 46% and FTIR analysis revealed the existence of H-bonds however they cannot be clearly related with an interaction between both phases. Both macro and micromechanical analysis showed that jute strands with a lignin content of 4% were the most suitable to be used as PLA reinforcement, mainly due to their higher intrinsic mechanical properties, better interaction with PLA and dispersion within the matrix. Overall, it was found that it is possible to obtain high-performance bio-based and presumably biodegradable composites with potential to substitute current oil-based commodities.

Combined effect of sodium carboxymethyl cellulose, cellulose nanofibers and drainage aids in recycled paper production process

The present work shows the suitability of using recovered cardboard boxes for the development of high-performance papers through the use of cellulose nanofibers (CNF) and sodium carboxymethyl cellulose (CMC-Na). CNF were prepared by enzymatic hydrolysis using bleached kraft hardwood pulp, while a commercial grade of CMC-Na was used. Both were added in bulk together with polyethylenimine (PEI) as wet-end additive to improve pulp drainability. The combination of 3 wt% CNF and 7.5 wt% CMC-Na double the breaking length of paper. In addition, the use of 0.4 wt% of PEI significantly decreased the Schopper - Riegler degree, while mechanical properties remained almost at the same level. It was found that it is possible to recover and even increase the properties of recycled papers, with the added advantage that no structural damages were caused on the fibres, increasing the life span and recyclability of paper products.

Immobilization of antimicrobial peptides onto cellulose nanopaper

In this work we report the production of cellulose nanopapers modified with alkyl ketene dimer (AKD) in order to allow the immobilization of antimicrobial peptides (AMPs) to produce surfaces with antimicrobial properties. Cellulose nanofibers (CNF) were prepared from softwood bleached pulp via high pressure homogenization after chemical pretreatment of fibers via TEMPO oxidation. Nanopapers were then prepared after a casting technique and functionalized with alkyl ketene dimer before AMPs were immobilized. The immobilization process was performed by submerging the samples into AMP aqueous solutions and then dried at room temperature. Antimicrobial activity was tested against B. subtilis. Results indicated that AMPs were bound onto the nanopaper surface and released when the nanopaper was put in contact with the culture medium, which effectively demonstrates the viability of the immobilization process.