RESUMEN

The forest industry produces several low-value by-products, such as bark, sawdust, limbs, and leaves, that are not ultimately disposed of and remain in the forests and sawmill facilities. Among these by-products are leaves, which contain not only cellulose fibers and lignin but also essential oils such as terpenes. These are biosynthesized in a similar way as cis-1,4-polyisoprene. In this context, this work evaluates the use of screened and unscreened dried Eucalyptus nitens leaves in natural rubber. Among the most relevant results of this work is a significant increase in mechanical properties, such as tensile strength and elongation at break, reaching values of 9.45 MPa and 649% of tensile strength and elongation at break, respectively, for a sample of natural rubber containing sieved dried leaves of Eucalyptus nitens. In addition, it is observed that the content of this vegetable filler allows for inhibiting the antibacterial effect of vulcanized rubber against several bacteria, such as Bacillus subtilis, Staphylococcus aureus, Escherichia coli K 12, Escherichia coli FT 17 and Pseudomonas fluorescens. These results are promising because they not only add value to a by-product of the forestry industry, improving the mechanical properties of natural rubber from a sustainable approach but also increase the affinity of rubber with bacterial microorganisms that may play a role in certain ecosystems.

RESUMEN

The mechanical, thermal and gamma radiation attenuation properties of ethylene-propylene-diene monomer (EPDM)-based composites containing graphene nanoplatelets (GNs) and bismuth (III) oxide nanoparticles (B) were investigated. The use of polyethylene glycol (PEG) as a compatibilizer to improve the dispersion of the fillers was also investigated. The results showed that the combined use of these fillers resulted in a drastic increase in mechanical properties, reaching 123% and 83% of tensile strength and elongation at break, respectively, compared to those of EPDM. In contrast, the addition of PEG to composites containing EPDM GNs and B resulted in composites with lower values of mechanical properties compared to the EPDM/B/GN-based composite. However, the presence of PEG leads to obtaining a composite (EPDM/B/GNP) with a mass attenuation coefficient to gamma radiation (137Cs, 662 keV) superior to that composite without PEG. In addition, the composite EPDM, B and PEG exhibited an elongation at break 153% superior to unfilled EPDM. Moreover, the binary filler system consisting of 100 phr of bismuth (III) oxide and 10 phr of GN leads to reaching 61% of the linear damping coefficient of the EPDM composite compared to that value of the unfilled EPDM. The study of the morphology and the state of filler dispersion in the polymer matrix, obtained using scanning electron microscopy and energy-dispersive X-ray spectroscopy, respectively, provides a useful background for understanding the factors affecting the gamma radiation attenuation properties. Finally, the results also indicated that by adjusting the formulation, it is possible to tune the mechanical and thermal properties of EPDM composites reinforced with bismuth oxide and graphene nanoplatelets.

RESUMEN

The size and shape of nanoparticles have a profound effect on the properties of nanocomposites. For instance, the lateral dimensions of graphene oxide (GO) platelets affect several properties, including their antibacterial and pharmacokinetic functions. However, the impact of lateral dimensions has been poorly studied in nanocomposites, and their effect on hydrogels is still unknown. The current study aims to determine the effect of GO lateral dimensions on the mechanical, rheological, thermal, and antibacterial properties of gelatin hydrogels. The hydrogels were fabricated via photopolymerization of methacrylated gelatin and GO derived from the oxidation of commercial graphene. The observations indicate that an increase in GO sheets improves the mechanical strength with an increase in compressive modulus and a low mechanical hysteresis (<10%). Furthermore, low mechanical energy is dissipated even after several deformation cycles. The nanocomposite hydrogels demonstrated bactericidal effects on two clinical strains with an extensively drug-resistant phenotype, primarily through contact. Additionally, an increment in lateral dimensions increased the bactericidal capacity of Gram-negative strains. Thus, the significant effect of the lateral dimensions of GO sheets on the properties of hydrogels is demonstrated.

Asunto(s)

Gelatina , Grafito , Nanogeles , Hidrogeles , Antibacterianos

RESUMEN

The electrical properties of nanocomposites based on polyetherimide (PEI) filled with reduced graphene oxide (rGO) and a graphene oxide hybrid material obtained from graphene oxide grafted with poly(monomethyl itaconate) (PMMI) modified with barium titanate nanoparticles (BTN) getting (GO-g-PMMI/BTN) were studied. The results indicated that the nanocomposite filled with GO-g-PMMI/BTN had almost the same electrical conductivity as PEI (1 × 10-11 S/cm). However, the nanocomposite containing 10 wt.% rGO and 10 wt.% GO-g-PMMI/BTN as fillers showed an electrical conductivity in the order of 1 × 10-7 S/cm. This electrical conductivity is higher than that obtained for nanocomposites filled with 10% rGO (1 × 10-8 S/cm). The combination of rGO and GO-g-PMMI/BTN as filler materials generates a synergistic effect within the polymeric matrix of the nanocomposite favoring the increase in the electrical conductivity of the system.

RESUMEN

This paper revises the use of polymer nanocomposites to attenuate high-energy electromagnetic radiation (HE-EMR), such as gamma radiation. As known, high-energy radiation produces drastic damage not only in facilities or electronic devices but also to life and the environment. Among the different approaches to attenuate the HE-EMR, we consider the use of compounds with a high atomic number (Z), such as lead, but as known, lead is toxic. Therefore, different works have considered low-toxicity post-transitional metal-based compounds, such as bismuth. Additionally, nanosized particles have shown higher performance to attenuate HE-EMR than those that are micro-sized. On the other hand, materials with π-conjugated systems can also play a role in spreading the energy of electrons ejected as a consequence of the interaction of HE-EMR with matter, preventing the ionization and bond scission of polymers. The different effects produced by the interactions of the matter with HE-EMR are revised. The increase of the shielding properties of lightweight, flexible, and versatile materials such as polymer-based materials can be a contribution for developing technologies to obtain more efficient materials for preventing the damage produced for the HE-EMR in different industries where it is found.

Asunto(s)

Nanocompuestos/química , Polímeros/química , Bismuto/química , Fenómenos Electromagnéticos , Rayos gamma , Ensayo de Materiales/métodos , Tamaño de la Partícula , Protección Radiológica/métodos

RESUMEN

A study addressed to develop new recyclable and/or biodegradable magnetic polymeric materials is reported. The selected matrices were polypropylene (PP) and poly (lactic acid) (PLA). As known, PP corresponds to a non-polar homo-chain polymer and a commodity, while PLA is a biodegradable polar hetero-chain polymer. To obtain the magnetic nanocomposites, magnetite supported on thermally reduced graphene oxide (TrGO:Fe3O4 nanomaterial) to these polymer matrices was added. The TrGO:Fe3O4 nanomaterials were obtained by a co-precipitation method using two types of TrGO obtained by the reduction at 600 °C and 1000 °C of graphite oxide. Two ratios of 2.5:1 and 9.6:1 of the magnetite precursor (FeCl3) and TrGO were used to produce these nanomaterials. Consequently, four types of nanomaterials were obtained and characterized. Nanocomposites were obtained using these nanomaterials as filler by melt mixer method in polypropylene (PP) or polylactic acid (PLA) matrix, the filler contents were 3, 5, and 7 wt.%. Results showed that TrGO600-based nanomaterials presented higher coercivity (Hc = 8.5 Oe) at 9.6:1 ratio than TrGO1000-based nanomaterials (Hc = 4.2 Oe). PLA and PP nanocomposites containing 7 wt.% of filler presented coercivity of 3.7 and 5.3 Oe, respectively. Theoretical models were used to analyze some relevant experimental results of the nanocomposites such as mechanical and magnetic properties.

RESUMEN

This work consists of studying the influence of two thermally reduced graphene oxides (TRGOs), containing oxygen levels of 15.8% and 8.9%, as fillers on the barrier properties of thermoplastic polyurethane (TPU) nanocomposites prepared by melt-mixing processes. The oxygen contents of the TRGOs were obtained by carrying out the thermal reduction of graphene oxide (GO) at 600 °C and 1000 °C, respectively. The presence and contents of oxygen in the TRGO samples were determined by XPS and their structural differences were determined by using X-ray diffraction analysis and Raman spectroscopy. In spite of the decrease of the elongation at break of the nanocomposites, the Young modulus was increased by up to 320% with the addition of TRGO. The barrier properties of the nanocomposites were enhanced as was evidenced by the decrease of the permeability to oxygen, which reached levels as low as -46.1%.

RESUMEN

Electrospun meshes (EM) composed of natural and synthetic polymers with randomly or aligned fibers orientations containing 0.5% or 1% of thermally reduced graphene oxide (TrGO) were prepared by electrospinning (ES), and their hyperthermia properties were evaluated. EM loaded with and without TrGO were irradiated using near infrared radiation (NIR) at 808 nm by varying the distance and electric potential recorded at 30 s. Morphological, spectroscopic, and thermal aspects of EM samples were analyzed by using SEM-EDS, Raman and X-ray photoelectron (XPS) spectroscopies, X-ray diffraction (XRD), and NIR radiation response. We found that the composite EM made of polyvinyl alcohol (PVA), natural rubber (NR), and arabic gum (AG) containing TrGO showed improved hyperthermia properties compared to EM without TrGO, reaching an average temperature range of 42-52 °C. We also found that the distribution of TrGO in the EM depends on the orientation of the fibers. These results allow infering that EM loaded with TrGO as a NIR-active thermal inducer could be an excellent candidate for hyperthermia applications in photothermal therapy.

RESUMEN

Poly(monomethyl itaconate) is outstanding because it is a glassy and dielectric polymer obtained from sustainable feedstock. Consequently, the study of the properties of its nanocomposites has gained importance. Herein, the electrical properties of nanocomposites based on poly(monomethyl itaconate) and functionalized few-layer graphene oxide (FGO) in the presence and absence of lithium ions (Li+) are studied. Not only did the electrical conductivities of the nanocomposites present values as high as 10-5 Scm-1, but also the dielectric permittivity of nanocomposites with (FGO) content lower than the percolation threshold was twice that of the pristine polymer, without presenting a drastic increase of the loss tangent. By contrast, nanocomposites containing Li+ ions presented significant increases of the permittivity with concomitant increases of the loss tangent. Moreover, it was determined that the presence of Li+ ions influenced the charge transport in the composites because of its ionic nature.

RESUMEN

Itaconic acid (IA) is an organic acid produced by the fermentation of sugars with aspergillus. It has been identified as one of the top 12 building-block chemicals. Here, we report the use of IA as a possible substitute to petroleum-based compatibilizers in polymer composite. We applied this study to thermoplastic elastomers based on styrene copolymers, since they are commonly used in blends and composites. Poly(styrene-b-ethylene-butylene-b-styrene) (SEBS) was grafted with 2.6 wt.% of itaconic acid (SEBS-g-IA) prepared by a reactive melt-mixing process, and was subsequently used to prepare composites filled with BaTiO3.). IA was successfully grafted as demonstrated by FTIR and XRD. SEBS-g-IA composites presented better mechanical properties, achieving an increase of Young modulus up to 80% compared with the neat polymer. This was ascribed to better dispersion and compatibility with the filler. Additionally, SEBS-g-IA showed increased dielectric permittivity, i.e., showed increased polarity, which indicates that it could potentially be used as a modifier for specialized polymers.

RESUMEN

Multiwalled carbon nanotubes (MWCNTs) are interesting high-tech nanomaterials. MWCNTs oxidized and functionalized with itaconic acid and monomethylitaconate were demonstrated to be efficient additives for controlling nucleation of calcium carbonate (CaCO3) via gas diffusion (GD) in classical as well as nonclassical crystallization, yielding aragonite and truncated calcite. For the first time, all amorphous calcium carbonate (ACC) proto-structures, such as proto calcite-ACC, proto vaterite-ACC and proto aragonite-ACC, were synthesized via prenucleation cluster (PNC) intermediates and stabilized at room temperature. The MWCNTs also showed concentration-dependent nucleation promotion and inhibition similar to biomolecules in nature. Incorporation of fluorescein-5-thiosemicarbazide (5-FTSC) dye-labeled MWCNTs into the CaCO3 lattice resulted in fluorescent hybrid nanosized CaCO3. We demonstrate that functionalized MWCNTs offer a good alternative for controlled selective crystallization and for understanding an inorganic mineralization process.