https://repositorio.ufpb.br/jspui/handle/tede/440 PPGCEM Sun, 05 Jul 2026 09:24:55 GMT 2026-07-05T09:24:55Z http://repositorio.ufpb.br:443/jspui/retrieve/22187/ https://repositorio.ufpb.br/jspui/handle/tede/440 https://repositorio.ufpb.br/jspui/handle/123456789/38265 Título: Desenvolvimento de sistemas poliméricos à base de quitosana, breu e cera de carnaúba com potencial ação nematicida obtidos por ultrassom Autor(es): Almeida, Carolina Lima de Orientador: Medeiros, Eliton Souto de Abstract: The damage caused by plant-parasitic nematodes in agriculture represents a global challenge, with significant productivity losses in crops such as soybeans. Conventional control of these pathogens often relies on synthetic chemical nematicides, which, although effective, pose risks to human health and the environment. Given this scenario, the pursuit of sustainable and safe alternatives is urgently needed. This thesis explored the potential of chitosan in combination with bioactive components of natural origin, carnauba wax (Copernicia prunifera) and rosin (Pinus), to develop film-forming systems with potential nematicidal activity. The study innovated by employing ultrasound as a processing method to obtain homogeneous and stable suspensions, demonstrating that this technique not only considerably reduces preparation time (from 24 hours to 20 minutes) but also promotes significant morphological and surface modifications. DSC and FTIR characterizations confirmed that ultrasound processing does not chemically alter the components, preserving their thermal and functional properties. SEM analyses revealed that ultrasound directly influences film topography, and these morphological changes correlated directly with wettability assays, in which ultrasound-processed samples mostly exhibited a reduced contact angle, indicating increased hydrophilicity—a desirable characteristic for seed coating applications. Nematode tests showed that the film containing rosin achieved 50% mortality within 72 h, a value six times higher than the control. Carnauba wax also demonstrated nematicidal effectiveness, albeit to a lesser extent (20% at 72 h), contributing to a multifunctional approach. In summary, this research not only demonstrates the feasibility of using biopolymers and natural compounds as alternatives to traditional nematicides but also establishes well-founded correlations between processing, morphology, wettability, and biological activity. The results pave the way for future studies focused on active release kinetics and tests under real field conditions, contributing to more sustainable and safe agriculture. Editor: Universidade Federal da Paraíba Tipo: Tese Thu, 19 Mar 2026 00:00:00 GMT https://repositorio.ufpb.br/jspui/handle/123456789/38265 2026-03-19T00:00:00Z https://repositorio.ufpb.br/jspui/handle/123456789/38082 Título: Influência da adição de Nb e Cr nas propriedades microestruturais e mecânicas de uma liga CuAlMn Autor(es): Caluête, José de Queiroz Orientador: Oliveira, Danniel Ferreira de Abstract: This work investigates the effects of chromium (Cr) and niobium (Nb) additions on the microstructural, mechanical, electrochemical, and functional properties of Cu–Al–Mn shape memory alloys. The alloys were produced by induction furnace melting, followed by homogenization heat treatment and quenching, and characterized using techniques such as optical microscopy, scanning electron microscopy, corrosion resistance testing, and microhardness measurements. The results demonstrate that Cr and Nb promote significant grain refinement, the formation of Al–Cr- and Al–Nb-rich precipitates, an increase in the fraction of 18R martensite, and improvements in the structural stability of martensite. Microhardness tests and X-ray diffraction (XRD) confirmed hardening and changes in phase equilibrium, while energy-dispersive spectroscopy (EDS) validated the incorporation of the alloying elements. Electrochemical analyses showed that the isolated additions of Cr and Nb increase corrosive activity; however, when combined, these elements exhibit a synergistic effect, strengthening the passive film and improving corrosion resistance. The observed increase in electrical resistivity and in the e/a value reinforces the influence of these elements on the electronic behavior and martensitic stability. Thus, Cr and Nb demonstrate strong potential to enhance mechanical reliability, structural and chemical integrity, and to ensure the stability of the functional properties of the alloy. Editor: Universidade Federal da Paraíba Tipo: Tese Mon, 15 Dec 2025 00:00:00 GMT https://repositorio.ufpb.br/jspui/handle/123456789/38082 2025-12-15T00:00:00Z https://repositorio.ufpb.br/jspui/handle/123456789/38036 Título: Efeito de fibras de sisal em compósitos cimentícios impressos em 3D submetidos a elevadas temperaturas Autor(es): Medeiros, Fernanda Karolline de Orientador: Anjos, Marcos Alyssandro Soares dos Abstract: When exposed to high temperatures, 3D-printed cementitious composites (3DP-CC) often exhibit delamination and poor interlayer bonding. This study aims to develop a 3D-printable cementitious composite reinforced with sisal fibers (3DP-SFCC) and to experimentally evaluate the impact of elevated temperatures on the mechanical, physical, and microstructural behavior of both printed and cast specimens. The 3DP-SFCC mixtures were developed with appropriate buildability for extrusion-based printing systems, incorporating sisal fibers of 6 mm and 12 mm in length at volumetric contents of 0,5% and 1,0%. The mixes also included limestone filler and metakaolin. Extrudability, rheological properties, and green strength were evaluated, and physical, mechanical, and microstructural properties were assessed before and after exposure to 200, 400, 600, and 800 °C. The heat propagation through the printed composites was evaluated using thermocouples installed at eight different points of blocks heated to 400 and 600 °C. Incorporating sisal fibers improved green strength but reduced the mechanical performance of unheated 3DP-SFCC in the hardened state. However, at high temperatures, tests demonstrated that sisal fibers prevented interlayer adhesion loss up to 400 °C, while fiber-free mixtures showed a ~37% reduction in interlayer adhesion at the same temperature. Sisal fibers significantly reduced the losses in compressive strength with heating. Between room temperature and 600 °C, the compressive strength decreased by 34% in REF-C and by only 0.3% in SF05%12 in the Y direction. The damage caused by heating was mitigated, especially with the use of 12 mm fibers, and the impact of heating on the anisotropy induced by the 3D printing process was reduced, reinforcing that 3DP-SFCC exhibits improved performance in environments prone to elevated temperatures. The incorporation of sisal fibers altered the heat propagation through the printed composites, modifying the preferential heat transfer path from the interlayer region to the intralayer region, thereby reducing the thermal gradient across the material and minimizing its effects. Editor: Universidade Federal da Paraíba Tipo: Tese Fri, 31 Oct 2025 00:00:00 GMT https://repositorio.ufpb.br/jspui/handle/123456789/38036 2025-10-31T00:00:00Z https://repositorio.ufpb.br/jspui/handle/123456789/37896 Título: Caracterização e estudo do potencial de uso do residuo de gesso para a fabricação de gesso acartonado (drywall) Autor(es): Diniz, Rayane Karoline Melo Orientador: Lima Filho, Marçal Rosas Florentino Abstract: Gypsum is an industrial mineral produced worldwide. It is estimated that the generation of gypsum waste exceeds the amount of 15 million tons, which are dumped in landfills; furthermore, there are many other environmental impacts related to its production, usage and dumping. In view of the growing inclusion and influence of sustainability in the civil industries, the National Environment Council - CONAMA Resolution 307/2002), reclassified the plaster waste to Class B - waste that can be recycled to other destinations. In this way, this work proposes to investigate a new alternative for the reuse of gypsum residues, from the production of a drywall sealing element, without calcination, evaluating physical, mechanical, and microstructural properties. The raw materials used were kraft paper, plaster glue, commercial gypsum, and gypsum waste. The residue was comminuted and processed in a disc mill. The powders were characterized by XRF, XRD and laser granulometer. The XRF revealed the percentage of SO3 and CaO, which have limits determined by the standard. The XRD revealed to us the phases both qualitatively and quantitatively, indicating the quality of the material that resulted in the waste as well as the hydration process. The granulometry helped to determine the water/gypsum ratio for making the boards, which had the following variables: thickness of 9.5 and 15.0 mm, weight of 0 and 70 kg during molding, and curing temperature at 25° C and 50°C. The different boards were analyzed according to their geometric and visual characteristics, surface density, flexural strength, and SEM/EDS. The geometric and visual characteristics exposed the character of shrinkage, which was associated with the appearance of defects and influence on the boards interface. The surface density indicated to us how much the grain size of the gypsum residue (7,98 μm) can influence this characteristic, as well as the flexural strength. In the SEM/EDS analysis, it was observed the interface and its adhesion, the microstructure of the plaster residue resembling that of the commercial plaster, and also indicated the concentration of the components along the boards, mainly sulfur (S) and calcium (Ca), which are the main elements of the composition of plaster and gypsum. All these results indicate the possibility of reusing plaster waste with low energy expenditure. Editor: Universidade Federal da Paraíba Tipo: Dissertação Tue, 15 Dec 2020 00:00:00 GMT https://repositorio.ufpb.br/jspui/handle/123456789/37896 2020-12-15T00:00:00Z