Ticiane Sanches Valera

Kaolin is an abundant, low-cost filler for elastomeric compounds. The kaolin used here is primarily kaolinite, chemically clean, and contains a fine particle population. Although agglomeration is evident, it can be mitigated by appropriate physical processing and, when desired, by chemical coupling. This study evaluates kaolin in natural rubber (NR) and examines how adding bis(triethoxysilylpropyl) tetrasulfide (TESPT) during mixing affects filler–matrix compatibility, viscoelastic response, cure stability, and mechanical performance. Kaolin was structurally and morphologically characterized, and the compounds were prepared in a closed mixer coupled to a torque rheometer under controlled dispersion conditions. Part 1 assessed NR with kaolin without a coupling agent, and Part 2 assessed the NR–kaolin with TESPT added during mixing (0.5 and 5 phr). Small-amplitude oscillatory shear (SAOS) was used to probe viscoelastic behavior, while oscillating disk rheometry (ODR) and tensile tests quantified cure and mechanical properties. In Part 1, kaolin increased NR stiffness in SAOS and raised the 100% and 300% moduli by about 40% and 50%, respectively, relative to the unfilled NR compound, while reducing cure reversion from 30% to 10% at 150 °C. In Part 2, TESPT produced a threshold-like response: 0.5 phr caused only minor changes, whereas 5 phr led to pronounced stiffening and cure stabilization. At 5 phr, a low-frequency plateau in G′ below 0.1 Hz with no G′–G″ crossover was observed, accompanied by higher M_H and ΔM in ODR and reversion suppressed to 1% after 30 min. These trends indicate the formation of a more connected filler-rubber network, promoted by TESPT-assisted interfacial coupling/adhesion, while also reflecting the ability of TESPT (tetrasulfide) to contribute sulfur and modify the curing chemistry. Mechanically, kaolin produced marked stiffness increases, with the 100% and 300% moduli increasing by an additional 9% and 36%, respectively, at 5 phr TESPT. At the same time, ultimate tensile strength remained lower than that of neat NR, and elongation at break decreased slightly. Overall, adding TESPT during mixing enhances interfacial coupling and network connectivity and, at higher loading, also influences cure chemistry, yielding higher modulus and strongly improved reversion resistance without increasing ultimate tensile strength relative to neat NR.

Clay/natural rubber (Clay–NR) nanocomposites are a sustainable material class with a wide range of applications. The type and amount of the filler added to the rubber matrix promote significant changes in the matrix properties. Montmorillonitic clays (MMT) are mineral, natural fillers. This study investigates the effect of a modified Brazilian polycationic MMT on the nanocomposite rheology and mechanical properties. The MMT was incorporated into a NR matrix in its natural state, and after modification by cation exchange (MMT^Na) and organophilization (MMT^ORG), at concentrations of 2.5 and 5 phr (parts per hundred parts of rubber). The natural and modified clays were characterized by XRD, FTIR, BET, and SEM/EDS. Mechanical tests (tensile strength, elongation at break, and modulus at 100%) indicated that the use of MMT^Na led to increased strength and modulus, whereas a minor decrease in the elongation was observed. However, the use of MMT^ORG yielded the most significant improvements in the mechanical properties. The rheology tests indicated that the Payne effect was not observed, and the strain-dependent behavior arises from matrix-dominated mechanisms, rather than disruption of a filler network. Vulcanization curves showed that the NR-MMT^ORG composites exhibited higher torque values, corroborated by higher crosslink densities. These findings highlight the critical role of cation exchange modification in optimizing MMT dispersion and interfacial interactions within NR matrices, providing design principles for high-performance sustainable nanocomposites.

The UV-resistance performance of waterborne epoxy coatings with different aminic-curable substances was evaluated to solve the widely known problem of poor weathering resistance of coatings. Samples were evaluated by color and gloss changes, FTIR, thermal properties, and macroscopic morphology. Results indicated that higher aminic values in curing agents degraded faster than lower aminic values (increases of ~3% in delta b and delta E between 5 and 20%). All samples showed a gloss variation varying between 40 and 70 G.U. FTIR and Tg indicated the resin degradation when using curing agents of unmodified aliphatic amine because of its rapid chemical degradation under a UV environment, as confirmed by microscopy images. The curing agents with aminic values between 200 and 300 KOH/g and the equivalent weight of amine hydrogen higher than 120 g/eq showed the best performance in epoxy coatings and good stability against accelerated aging, being promising options for future applications.

This paper presents a comparison of traditional thermal and chemical reduction methods with more recent ionizing radiation reduction via gamma rays and electron beams (e-beams). For GO, all synthesis protocols were adapted to increase production scale and are a contribution of this work. The typical Raman D-band of the GO was prominent (I_D/I_G ratio increased sixfold). When comparing the GO reduction techniques, dramatic differences in efficiency and GO particle characteristics were observed. Although thermal and chemical reduction are effective reduction methods, as shown through the use of FTIR spectroscopy and the C/O ratio from EDS chemical analysis, the thermal process renders great weight losses, whereas chemical processing may involve the use of hazardous chemical compounds. On the other hand, comparing the gamma rays and e-beam for 80 kGy, the Raman spectra and chemical analysis suggested that the e-beam caused a greater GO reduction: C/O ratio from EDS of 5.4 and 4.1, respectively. In addition to being fast and effective, ionizing radiation reduction processes allow easier control of the reduction degree by adjusting the radiation dose. When the dose increased from 40 to 80 kGy, the Raman spectra and EDS showed that the I_D/I_G and C/O ratios increased by 15 and 116%, respectively.

This study investigated the effects of partial and total substitutions of fossil polypropylene (PP) for recycled plastic cap equivalents in the manufacture of signage labels used by the telephone industry. Four alternative scenarios to using virgin PP were evaluated considering recycled material in flake and pellet forms based on environmental performance, degree of circularity, and technical behavior. The environmental analysis was performed by the life cycle assessment (LCA) technique, and for all impact categories evaluated, using recycled material to replace the virgin reduced adverse effects on the environment. The most significant results in this dimension, with gains of 81% in the Global Environmental Indicator, occurred when recycled PP flakes entirely replaced the fossil polymer. Once again, the highest values of the Materials Circularity Indicator (MCI) were achieved by scenarios with full recycled resin in processing the tags; however, this product must also be reused. The mechanical behavior of the tags measured technical performance, and in this case, the product made with virgin PP outperformed the recycled options except for elongation. An analysis that integrated the three dimensions into a single performance index pointed to the complete substitution of virgin material for recycled as the most balanced option.

Cellulose nanocrystal (CNC) fillers have gained attention in research and industrial applications owing to their excellent properties and environmental bias. They can be added to natural rubber (NR) compounds to enhance properties such as the modulus of elasticity. CNCs can be extracted by different acid methods that promote singular features in interfacial adhesion, according to the type of acid used. This study addresses the feasibility of using cellulose nanoparticles in vulcanized NR composites. For this purpose, two different hydrolysis procedures using sulfuric acid and the less aggressive phosphoric acid were performed. These nanoparticles were then added to different amounts of NR compound. The effects of the CNCs on the vulcanization of the NR compound were evidenced by the formation of a zinc-cellulose-rubber complex, which reduced the optimal vulcanization time and increased the NR compound cure rate, particularly for the samples treated with phosphoric acid. In addition, the formation of this complex structure affected the morphology and mechanical properties of the composites. In particular, the tensile strength, elongation at break, and modulus at 300% of the composites with nanocellulose treated with phosphoric acid increased by 90%, 16%, and 51%, respectively, compared to the NR compound. Furthermore, the higher aspect ratio of the nanocellulose particles, mainly treated with phosphoric acid, favored the filler-matrix adhesion, making them a promising alternative to enhance the mechanical properties of NR compounds.

The mechanical and thermal properties of cryogels depend on their microstructure. In this study, the microstructure of hydroxypropyl methylcellulose (HPMC) cryogels was modified by the addition of ionic (bis (2-ethylhexyl) sodium sulfosuccinate, AOT) and non-ionic (Kolliphor^® EL) surfactants to the precursor hydrogels (30 g/L). The surfactant concentrations varied from 0.2 mmol/L to 3.0 mmol/L. All of the hydrogels presented viscous behavior (G″ > G′). Hydrogels containing AOT (c > 2.0 mmol/L) led to cryogels with the lowest compressive modulus (13 ± 1 kPa), the highest specific surface area (2.31 m²/g), the lowest thermal conductivity (0.030 W/(m·°C)), and less hygroscopic walls. The addition of Kolliphor^® EL to the hydrogels yielded the stiffest cryogels (320 ± 32 kPa) with the lowest specific surface area (1.11 m²/g) and the highest thermal conductivity (0.055 W/(m·°C)). Density functional theory (DFT) calculations indicated an interaction energy of −31.8 kcal/mol due to the interaction between the AOT sulfonate group and the HPMC hydroxyl group and the hydrogen bond between the AOT carbonyl group and the HPMC hydroxyl group. The interaction energy between the HPMC hydroxyl group and the Kolliphor^® EL hydroxyl group was calculated as −7.91 kcal/mol. A model was proposed to describe the effects of AOT or Kolliphor^® EL on the microstructures and the mechanical/thermal properties of HPMC cryogels.

A comparative study was conducted for three natural rubber (NR) composites: one containing raw jute fibers, one containing bleached jute fibers, and one containing cellulose nanocrystals (CNCs). The composites were prepared by adding each filler at 5 or 10 phr to the latex before chemical coagulation, and the composites were processed in a two-roll mixing mill. The mechanical, thermal, and vulcanization properties of the prepared composites were then determined. The NR stiffness increased with increasing fiber content, particularly when bleached fibers were added, as evidenced by the increased elastic moduli, maximum torques, glass transition temperature, and crosslinking density. Scanning electron microscopy showed agglomerates in the composite with 10 phr CNCs, which led to poorer mechanical performance compared to that of the bleached fiber-reinforced composite (10 phr). On the other hand, the addition of CNCs to the NR increased the cure rate index, thereby significantly advancing the optimum vulcanization time.