Lígia Passos Maia-Obi

Processes using CO₂ either as a solvent or as a reactant, for example, in catalyzed chemical reactions, are increasing in interest due to their green characteristics. Hyperbranched polyglycerols have the potential to be used as support for catalysts in these processes, allowing for an efficient separation of the products and the reutilization of the catalyst, but this requires them to absorb CO₂. Acetylating hydroxylated compounds has shown to be an efficient way to increase their CO₂-philicity, and this work aims to understand how acetylation increases the interaction of hyperbranched polyglycerols with different cores with supercritical CO₂. This involves the study of their kinetics of expansion in this media (from 10 to 25 MPa and at 35 °C and 45 °C) and, eventually, their solubility when it happens. The expansion of the acetylated polyglycerols reached up to 66% in volume, while that of non-acetylated ones, in general, do not exceed 10%. Acetylation plays an important role in increasing the expansion of these polymers in the presence of CO₂ and, therefore, in increasing their CO₂-philicity and CO₂ absorption, making them potential materials to be used in biphasic (polymer/CO₂) reaction systems.

Corrosion presents a significant challenge to various industries, compromising the integrity and longevity of materials like mild steel. This study explores the efficacy of a polyphenol-rich fraction extracted from the stem bark of Senegalia senegal (PRFSS) as a green corrosion inhibitor for mild steel in acidic environments. The PRFSS extract, containing tannins, phenols, and anthocyanins, was assessed for its corrosion inhibition capabilities through various experimental methods, including gravimetric weight loss, phytochemical screening, and potentiodynamic polarization measurements. Results indicated that increasing concentrations of PRFSS notably reduced the corrosion rate of mild steel and enhanced surface coverage, suggesting effective protective layer formation. Thermodynamic analyses confirmed that the adsorption process of PRFSS onto mild steel is exothermic and spontaneous, with the adsorption behavior fitting Langmuir, Freundlich, and El-Awady isotherm models. FT-IR spectrum analysis further validated the successful adsorption of PRFSS on the mild steel surface, while TGA highlighted the extract’s thermal stability. SEM images corroborated the protective role of PRFSS, showing a smoother and less corroded surface compared to untreated steel. The study demonstrates that PRFSS is a promising, environmentally benign alternative to conventional chemical inhibitors, offering significant corrosion protection for mild steel. These findings open avenues for its application in industries. Future research should investigate the long-term stability and performance of this green inhibitor under diverse operational conditions

(1) Background: The increasing generation of plastic and agricultural wastes is a critical environmental issue that requires urgent attention. Aiming to address this challenge, this study developed a sustainable waste-to-wealth system through the utilization of Zea mays husk as a reinforcing material in the production of green composites. (2) Methods: Delignification, de-hemicellulolysis, and bleaching were employed sequentially to improve the characteristics of the husk. Fourier-transform infrared spectroscopy and scanning electron microscopy confirmed the removal of lignin, hemicellulose, and impurities, and X-ray diffraction analysis determined the degree of crystallinity. Composites were made with treated and untreated husk and recycled low-density polyethylene (LDPE) at various husk-to-LDPE ratios. (3) Results: Mechanical characterization demonstrated that the treated husk composites exhibited superior tensile strength, flexural strength, and hardness compared to the untreated ones and pure LDPE. The treatment did not enhance the thermal stability of the composites, but it did lower their capacity for water absorption and improve their crystallinity. The economic assessment of the husk composite production indicated a total annualized cost of USD 0.9601 per kg, which is significantly lower than the estimated cost for LDPE (USD 1.2 to USD 1.4 per kg). Additionally, it has a much smaller carbon footprint compared to LDPE production. (4) Conclusions: The potential of utilizing treated Z. mays husk as a reinforcing agent in the development of sustainable and cost-effective green composites, improving their overall performance, was established. This approach offers a promising solution for the effective management of plastic and agricultural wastes, contributing to the transition towards a circular economy.

PH-sensitive degradable hydrogels are smart materials that can cleave covalent bonds upon pH variation, leading to their degradation. Their development led to many applications for drug delivery, where drugs can be released in a pH-dependent manner. Crosslinking hyperbranched polyglycerol (HPG), a biocompatible building block bearing high end-group functionality, using oxalic acid (OA), a diacid that can be synthesized from CO₂ and form highly activated ester bonds, can generate this type of smart hydrogel. Aiming to understand the process of developing this novel material and its drug release for oral administration, its formation was studied by varying reactant stoichiometry, concentration and cure procedure and temperature; it was characterized regarding gel percent (%gel), swelling degree (%S), FTIR and thermal behavior; impregnated using ibuprofen, as a model drug, and a release study was carried out at pH 2 and 7. Hydrogel formation was evidenced by its insolubility, FTIR spectra and an increase in T_d and T_g; a pre-cure step was shown to be crucial for its formation and an increase in the concentration of the reactants led to higher %gel and lower %S. The impregnation resulted in a matrix-encapsulated system; and the ibuprofen release was negligible at pH 2 but completed at pH 7 due to the hydrolysis of the matrix. A pH-sensitive degradable HPG-OA hydrogel was obtained and it can largely be beneficial in controlled drug release applications.

The development of active packaging for food storage containers is possible through impregnation of natural extracts by supercritical CO₂-assisted impregnation processes. The challenge of scCO₂-impregnation of natural extracts is to control the total loading and to ensure that the composition of the loaded extract may preserve the properties of the crude extract. This study aimed at investigating the scCO₂-impregnation of clove extract (CE) in polycarbonate (PC) to develop antibacterial packaging. A design of experiments was applied to evaluate the influences of temperature (35–60 °C) and pressure (10–30 MPa) on the clove loading (CL%) and on the composition of the loaded extract. The CL% ranged from 6.8 to 18.5%, and the highest CL% was reached at 60 °C and 10 MPa. The composition of the impregnated extract was dependent on the impregnation conditions, and it differed from the crude extract, being richer in eugenol (81.31–86.28% compared to 70.06 in the crude extract). Differential scanning calorimetry showed a high plasticizing effect of CE on PC, and high CL% led to the cracking of the PC surface. Due to the high loading of eugenol, which is responsible for the antibacterial properties of the CE, the impregnated PC is promising for producing antibacterial food containers.

Polymeric implants loaded with drugs can overcome the disadvantages of oral or injection drug administration and deliver the drug locally. Several methods can load drugs into polymers. Herein, soaking and supercritical CO₂ (scCO₂) impregnation methods were employed to load aspirin into poly(l-lactic acid) (PLLA) and linear low-density polyethylene (LLDPE). Higher drug loadings (DL) were achieved with scCO₂ impregnation compared to soaking and in a shorter time (3.4 ± 0.8 vs. 1.3 ± 0.4% for PLLA; and 0.4 ± 0.5 vs. 0.6 ± 0.5% for LLDPE), due to the higher swelling capacity of CO₂. The higher affinity of aspirin explained the higher DL in PLLA than in LLDPE. Residual solvent was detected in LLDPE prepared by soaking, but within the FDA concentration limits. The solvents used in both methods acted as plasticizers and increased PLLA crystallinity. PLLA impregnated with aspirin exhibited faster hydrolysis in vitro due to the catalytic effect of aspirin. Finally, PLLA impregnated by soaking showed a burst release because of aspirin crystals on the PLLA surface, and released 100% of aspirin within 60 days, whereas the PLLA prepared with scCO₂ released 60% after 74 days by diffusion and PLLA erosion. Hence, the scCO₂ impregnation method is adequate for higher aspirin loadings and prolonged drug release.