Thermal Aging Research Articles

Provides Efficient Shear Bond Strength and Durability Between Lithium Disilicate Glass-ceramic and Resin Cement: A Potential Alternative to the Conventional Hydrofluoric Acid Protocal

Objectives: This study investigated the effects of two surface treatment protocols on the shear bond strength, bond durability, and failure mode at the interface between lithium disilicate glass-ceramic and resin cement. The protocols compared were a self-etching ceramic primer and the conventional hydrofluoric acid (HF) etching followed by silane. Methods: Fifty lithium disilicate specimens were randomly divided into five surface treatment groups (n=10 each). A control group received no treatment. The remaining 4groups included: 5% HF etch with Monobond Plus thermocycled and non-thermocycled, Monobond Etch & Prime (MEP), thermocycled and non-thermocycled. Microshear bond strength (microSBS) was assessed before and after thermocycling to evaluate bond durability. Failure modes (adhesive, mixed, cohesive in resin/ceramic) were recorded under a stereomicroscope. Results: Both surface treatment protocols exhibited comparable microSBS for both pre- and post-thermocycling results. Moreover, bone durability obtained from the two treatment protocols seemed to be comparable. Most groups displayed adhesive/mixed failures. Notably, the self-etching ceramic primer group showed cohesive failure in half of the specimens initially, persisting in 20% after thermal aging. Conclusions: Compared with the conventional HF protocol, the self-etching ceramic primer protocol provided similar microSBS and bond durability between lithium disilicate glass-ceramic and resin cement. The data suggest a self-etching ceramic primer is a viable option for the conventional HF protocol in bonding to glass-ceramic, minimizing the HF hazard and simplifying the clinical procedure.

Combined Effect of Ambient Temperature and Relative Humidity on Skin Aging Phenotypes in the Era of Climate Change: Results From an Indian Cohort Study.

Background: There is no doubt that global warming, with its extreme heat events, is having an increasing impact on human health. Heat is not independent of ambient temperature but acts synergistically with relative humidity (RH) to increase the risk of several diseases, such as cardiovascular and pulmonary diseases. Although the skin is the organ in direct contact with the environment, it is currently unknown whether skin health is similarly affected. Objective: While mechanistic studies have demonstrated the mechanism of thermal aging, this is the first epidemiological study to investigate the effect of long-term exposure to heat index (HI) as a combined function of elevated ambient temperature and RH on skin aging phenotypes in Indian women. Methods: The skin aging phenotypes of 1510 Indian women were assessed using the Score of Intrinsic and Extrinsic Skin Aging (SCINEXA™) scoring tool. We used data on ambient temperature and RH, combined into an HI with solar ultraviolet radiation (UVR), and air pollution (particulate matter <2.5 µm [PM2.5]; nitrogen dioxide [NO2]) from secondary data sources with a 5-year mean residential exposure window. An adjusted ordinal multivariate logistic regression model was used to assess the effects of HI on skin aging phenotypes. Results: HI increased pigmentation such as hyperpigmented macula on the forehead (odds ratios [OR]: 1.31, 95% confidence interval [CI]: 1.12, 1.54) and coarse wrinkles such as crow's feet (OR: 1.17, 95% CI: 1.05, 1.30) and under-eye wrinkles (OR: 1.3, 95% CI: 1.15, 1.47). These associations were robust to the confounding effects of solar UVR and age. Prolonged exposure to extreme heat, as indicated by high HI, contributes to skin aging phenotypes. Conclusion: Thus, ambient temperature and RH are important factors in assessing the skin aging exposome.

Comparative Analysis of Modern 3D-Printed Hybrid Resin-Ceramic Materials for Indirect Restorations: An In Vitro Study

The study investigated the impact of aging on surface roughness, color stability, and biocompatibility of hybrid resin-ceramic materials. A total of 225 specimens were produced from three three-dimensional (3D)-printed (HarzLabs Dental Sand Pro (HL), BEGO VarseoSmile Crown plus (BV), Voco V-Print c&amp;b temp (VV)) and one milled material (Voco Grandio Blocs (VG)). Specimens were grouped into untreated, polished, and glazed surfaces. 5000 thermal cycles simulated aging. Surface roughness and color stability were analyzed, and surface topography was observed using scanning electron microscopy (SEM). Biocompatibility was evaluated with L929 cells. Surface roughness differed significantly between untreated and other groups, with no changes before and after artificial aging. Untreated milled samples were significantly smoother than 3D-printed ones. SEM analysis revealed roughest surfaces in untreated 3D-printed specimens. Polished and glazed specimens were smoother than untreated ones. Color values showed significant differences between untreated and treated/aged groups. No material showed cytotoxicity. In summary, untreated VG was smoother than 3D-printed materials, but polishing and glazing reduced roughness to levels comparable to VG. Surface treatments induced color changes, with glazing causing more changes than polishing. Aging affected color stability and biocompatibility but not surface roughness. All materials showed acceptable color changes and good biocompatibility.

Investigation of Thermal Aging Behaviour on Silane Treated White Fumed Silica/Glass Fiber Reinforced Vinyl Ester Composite

Investigation of Thermal Aging Behaviour on Silane Treated White Fumed Silica/Glass Fiber Reinforced Vinyl Ester Composite

Investigation of Combined Aging and Mullins Stress Softening of Rubber Nanocomposites

The present study investigated the effects of thermal aging, ultraviolet radiation (UV), and stress softening on the performance properties of rubber modified with Cloisite Na+ or Cloisite 20A. Tensile strength (TS), strain at break (SB), modulus, and the retention coefficient were measured before and after aging. Results showed that TS and SB decreased by about 50% after 7 days of aging for all tested samples due to the breakage of the chemical bonds between rubber and nanoparticles. The modulus at 300% elongation increased by 20%, 15%, and 7% after thermal aging for the unmodified sample, nanocomposites with Cloisite Na+, and Cloisite 20A, respectively. The shape retention coefficient of all samples was not affected by heat, except for the virgin rubber sample, which exhibited a decrease of about 15% under thermal aging. The virgin matrix and nanocomposites showed different values of aging coefficient during thermal aging and UV radiation. The dissipated energy of samples that were aged after stretching was slightly higher than that of samples that were aged after stretching due to the breakdown of the bonds within the nanocomposites. Loading-reloading energy results showed that the level of stress softening was lower when Mullins was applied after the aging of the samples. Differential scanning calorimetry results indicated a slight decrease in Tg1 in the aged and stretched samples and an increase in the temperature of the first endothermic peak due to the addition of nanofillers in the stretched and aged samples. Thermogravimetric analysis revealed that all tested samples exhibited similar thermograms, regardless of their state of stretching or aging. Scanning electron microscopy analysis showed that the fracture surface of the virgin unaged sample was rough with some holes, while it was flatter and less rough after aging.

STUDY OF THE INFLUENCE OF HDPE AND UHMWPE ON THE PROPERTIES OF ETHYLENE PROPYLENE DIENE VULCANIZATES

Introduction of small additives of thermoplastic polymer into the elastomer matrix is one of the simple and effective ways to improve the complex of physical and mechanical properties of rubbers. This article is devoted to the study of the effect of low-density polyethylene (HDPE) grade 273-83 and ultra-high molecular weight polyethylene (UHMWPE) grade GUR 4113 on the vulcanization characteristics of rubber compounds, physical and mechanical properties and resistance to thermal aging of vulcanizates based on ethylene propylene diene rubber grades SKEP-40 and SKEP-50. The use of HDPE and UHMWPE as additives is of interest not only due to their properties, but also due to their similar chemical nature to SKEP. It is shown that the introduction of polyethylene additives leads to some increase in the duration of the rubber compounds in the viscous flow state and the vulcanization optimum. Vulcanizates containing polyethylene additives are charac-terized by an increase in the conventional stress at 100 % elongation and a decrease in the relative elongation at break, which indicates an increase in the rigidity of the vulcanizates. In the presence of PE, wear resistance and the ability to elastic-elastic recovery of vulcanizates after compression also increase significantly. The frost resistance coefficient of rubber samples containing UHMWPE remains at the level of the original vulcanizates, and in the case of HDPE it decreases significantly, which can be explained by the better ability of UHMWPE to maintain its flexibility at low temperatures. According to the results of accelerated thermal aging, it was found that the presence of polyethylene additives leads to a significant increase in the stability of the elastic-strength properties of vulcanizates based on SKEP-50. Moreover, the higher the molecular weight of polyethylene, the higher its efficiency. It should be noted that in the DOT-4 environment, vulcanizates are characterized by a greater degree of preservation of elastic-strength indicators compared to the air environment, which is due to their high resistance to this working environment. It was found that UHMWPE, compared to HDPE, results in the production of an elastomeric material based on EPDM with a more optimal set of physical and mechanical properties and increased stability of elastic strength indicators after thermal aging.

End‐Extended Conjugation Strategy to Reduce the Efficiency‐Stability‐Mechanical Robustness Gap in Binary All‐Polymer Solar Cells

AbstractConcurrently achieving high efficiency, mechanical robustness and thermal stability is critical for the commercialization of all‐polymer solar cells (APSCs). However, APSCs usually demonstrate complicated morphology, primarily attributed to the polymer chain entanglement which has a detrimental effect on their fill factors (FF) and morphology stability. To address these concerns, an end‐group extended polymer acceptor, PY‐NFT, was synthesized and studied. The morphology analysis showed a tightly ordered molecular packing mode and a favorable phase separation was formed. The PM6 : PY‐NFT‐based device achieved an exceptional PCE of 19.12 % (certified as 18.45 %), outperforming the control PM6 : PY‐FT devices (17.14 %). This significant improvement highlights the record‐high PCE for binary APSCs. The thermal aging study revealed that the PM6 : PY‐NFT blend exhibited excellent morphological stability, thereby achieving superior device stability, retaining 90 % of initial efficiency after enduring thermal stress (65 °C) for 1500 hours. More importantly, the PM6 : PY‐NFT blend film exhibited outstanding mechanical ductility with a crack onset strain of 24.1 %. Overall, rational chemical structure innovation, especially the conjugation extension strategy to trigger appropriate phase separation and stable morphology, is the key to achieving high efficiency, improved thermal stability and robust mechanical stability of APSCs.

The Characterization of Natural Resins and a Study of Their Degradation in Interactions with Zinc Oxide Pigment

In the last few years, the role of science in Cultural Heritage has assumed greater significance since diagnostics have become essential for the characterization of artworks. The development of conservation strategies involves growing the study of artworks and the knowledge of the materials used against the degradation plaguing the painted surfaces. This work focuses on the investigation of the degradation processes involving paintings on canvas, in particular delamination and progressive deterioration of the painted surfaces. The main causes of the degradation are attributable to the formation of metal soaps, which originate from the interaction between binders and pigments; as a result, the process leads to the progressive fracturing of the paint film. Using various characterization techniques allowed us to acquire information on the structural and morphological properties of the binder resins and study the binder/pigment interaction during the degradation process to understand the quantity and quality of the acid sites present in the binders and, consequently, the potential reactivity with the cationic part of the pigments. The binders were also analyzed within paint layers in contact with zinc oxide to study the interactions and the possible formation of new species as metal soaps and metal oxalates that can modify the boundary among the painting layers and, consequently, the appearance of the artwork and its artistic value. Modifications after UV and thermal aging processes were observed using Infrared spectroscopy and thermogravimetric analysis. Zinc soap formation was observed after 7 h of a UV aging process and was correlated to the acidity of the resins.

Carbon microspheres prepared from soluble starch hydrothermal carbonization for extending thermal stability of water-based drilling fluid

This study employed hydrothermal carbon microspheres (HCMs) as high-temperature stabilizers in drilling fluids. The HCMs were synthesized through a green hydrothermal carbonization method, using soluble starch as the precursor. The impact of HCMs on the thermal stability of xanthan, polyanionic cellulose and synthetic polymer solutions was assessed by comparing their rheological changes before and after thermal aging. The rheology and filtration properties of a polymer-based drilling fluid in the presence of HCMs were recorded before and after dynamic thermal aging at various temperatures for 16 h and static thermal aging at 200 °C for 96 h. The results demonstrated that HCMs effectively maintained stable rheology and low filtration loss following dynamic hot rolling at various temperatures and prolonged static thermal aging, surpassing the performance of conventional Na2SO3 and nano-SiO2 stabilizers. Mechanistic studies, including dissolved oxygen measurements, free radical detection, and cryo-scanning electron microscopy observations, revealed that HCMs can consume dissolved oxygen, scavenge free radicals, and physically crosslink polymers. This process prevents polymer thermo-oxidative degradation and ensures the stability of the drilling fluid. HCMs are novel, stable, sustainable, and highly effective high-temperature stabilizers for water-based drilling fluids. This study introduces a new application of biomass-derived hydrothermal carbonaceous materials for high-temperature drilling.

Green and synergistic effects of buton rock asphalt and styrene-butadiene-styrene on asphalt performance: Focus on resistance to thermal oxygen aging

The enhancement of asphalt properties was investigated through utilizing the Buton rock asphalt (BRA) and styrene–butadiene–styrene (SBS) in this study. Despite of the splendid high-temperature resistance of the BRA-modified asphalt, it could be liable to low-temperature cracking. Hence, a composite BRA/SBS-modified asphalt was explored. The rheological tests, Fourier transform infrared spectroscopy (FTIR), and differential scanning calorimetry (DSC) were employed for analyzing the rheological, thermal, and chemical stability properties of the samples. The findings demonstrated that SBS promoted the low-temperature crack resistance of the BRA-modified asphalt, and BRA improved the thermal stability and thermal oxygen aging resistance of the SBS-modified asphalt. Considering the overall anti-aging and anti-fatigue effectiveness, 2 % SBS and 10 % BRA were proposed as the appropriate dosages for the modified asphalt. The analysis of correlation revealed that the BRA could be introduced to mitigate the influence of aging on the performance of SBS-modified asphalt to resist the irreversible deformation. This study could address the limitations of the BRA-modified asphalt and promote its application in road constructions.

Revisiting Unaddressed Safety Concerns Regarding Intense Pulsed Light Treatment: Past and Present Perspectives.

The light spectrum of intense pulsed light (IPL) comprises visible to near-infrared light. It has been widely employed in the field of aesthetics for approximately 30 years. However, several studies have demonstrated the appearance of various undesirable biomarkers on the skin after IPL irradiation, which remain elucidated. We reviewed the evolving concepts and explored the potentially harmful effects of IPL that may have been neglected in the past. Increased levels of reactive oxidative stress, p53, p16, proliferating cell nuclear antigen, interleukin-6, C-reactive protein, and cleaved caspase 3 and decreased albumin levels in human or mouse skin have been observed after IPL treatment. Visible and infrared light can exert harmful and beneficial effects on human skin. If perform improperly, IPL treatment may lead to cellular senescence, photoaging, photocarcinogenesis, thermal aging, and inflammaging. Further studies are required to verify the significance of the changes in the relevant biomarkers. The selection of treatment candidates, optimal parameters, and standardized protocols for IPL therapy are necessary.

Does short-span chemical oxidation induce more weathering than prolonged thermal aging on polypropylene microplastics? Its consequence during the interaction with cadmium

Weathering and degradation of plastics in the environment are evident in almost all conditions. However, the difference is the changes in the polymer properties, which varies with the aging mechanism, polymer type, and other prevailing environmental conditions. Aging is an essential factor that further determines the fate and transportation of smaller plastics. Apart from UV radiation for microplastics (MPs) aging, other mechanisms also play a crucial role in changing the physicochemical properties of polymers in natural environments. Other aging mechanisms, such as chemical and thermal oxidation, were used in this study. Also, thermally stable and chemical resistant polypropylene MP is used in this study to understand the oxidation mechanisms and to know the breakpoint where it becomes susceptible to the reactions. From the results, the aged MPs showed roughness, pore formation, and cracks on the surface; more specifically, PP MPs were more weathered during thermal oxidation, revealed in both physicochemical characterizations of MPs. However, the chemical oxidation reached almost half the aging of the thermal process within a short period. The additives in the PP MPs make it resistant to the treatment, where it takes time to break during the thermal treatment, which was contradictory with Fenton aging. Further, the adsorption study was conducted to determine its interaction with Cd2+ and which aged MPs adsorb more. It can be concluded that PP MPs are more vulnerable towards chemical aging within a short duration, but it takes time to stimulate weathering under increased temperature.

Mechanical, optical and surface properties of 3D-printed and conventionally processed polyamide 12.

Polyamide-based materials are suitable for three-dimensional (3D) printing. The aim of the study is to examine the impact of aging on the mechanical, surface and optical properties of polyamide 12. A total of 116 specimens were examined, comprising 58 conventionally processed polyamide 12 (PA12_C) specimens and 58 3D-printed polyamide 12 (PA12_3D) specimens. The modulus of elasticity was determined before and after mechanical and thermal aging with 1,000, 3,000, 9,000, and 1,000, 3,000 and 7,000 cycles, respectively. The surface roughness (Ra), Ra change (ΔRa) and color change (ΔE) were examined before and after chemical aging (1, 12 and 36 days, with artificial saliva, coffee and red wine) using surface profilometry and color spectroscopy. The Kruskal-Wallis test, Mann-Whitney U test and Bonferroni-Holm correction were employed, with a significance level of p < 0.05. Before and after mechanical aging, the modulus of elasticity for PA12_3D showed significantly higher values (761 MPa and 747 MPa, respectively) in comparison to PA12_C (515 MPa and 455 MPa, respectively; adjusted p < 0.001). Additionally, before and after thermal aging, the modulus of elasticity for PA12_3D exhibited significantly higher values (833 MPa and 705 MPa, respectively) compared to PA12_C (516 MPa and 458 MPa, respectively; adjusted p < 0.001). The Ra of PA12_3D was higher than that of PA12_C at the baseline (0.41 μm compared to 0.31 μm, respectively), and remained higher during the aging process. The ΔRa values were small for both groups. The ΔE was significantly higher for PA12_3D compared to PA12_C after 12 days (6.2 (PA12_3D) compared to 4.8 (PA12_C), adjusted p = 0.003) and 36 days of storage in red wine (8.2 (PA12_3D) compared to 6.8 (PA12_C), adjusted p = 0.003). After 36 days of coffee storage, the observed changes were found to be statistically significant (8.6 (PA12_3D) compared to 6.7 (PA12_C), adjusted p < 0.001). The 3D-printed polyamide 12 demonstrated higher rigidity, Ra and discoloration compared to the conventionally processed polyamide 12. However, not all of the observed parameter differences were significant or clinically relevant. These differences may impact clasp retention, biofilm formation and aesthetic appearance. Nevertheless, the clinical efficacy of 3D printing may be significant.

Characterization of CL-20/HMX cocrystallization and its effects on GAP-based propellants during thermal aging process

The incorporation of HMX and CL-20 as component particles can greatly improve the energy efficiency of composite propellants. Nevertheless, the occurrence of cocrystallization arises when HMX and CL-20 exists together. Further investigation is needed to determine the effects of the CL-20/HMX cocrystallization on the aging features of the propellants. The present study examines the evolutionary trends and effects of the CL-20/HMX cocrystal on the process of solid propellant aging. Experimental thermal aging studies were carried out on GAP-based composite propellants at temperatures of 60 °C/180-day and 70 °C/90-day. An investigation of density bottle, differential scanning calorimetry, X-ray diffraction, Fourier transform infrared spectroscopy, and uniaxial tensile testing were performed on the samples. The results indicate that the cocrystallization behaviours of CL-20/HMX undergo three distinct stages during propellant aging. The reaction rate accelerates most during the middle aging stage. As the GAP-based propellant ages, the recently developed cocrystal structure deteriorates the interfacial characteristics between the propellant particles and the matrix, leading to the formation of cavities inside the material. This will further enhance the decrease in elastic modulus, ultimate strength, and maximum elongation of the propellants. Among them, the most notable distinction from the aging behaviours of propellants without the addition of particles is the increase of the elastic modulus. Furthermore, a strong linear correlation was observed between variation of the elastic modulus and the cocrystal content of CL-20/HMX. This correlation offers a reliable indicator for monitoring the extent of cocrystallization phenomena.

Solid‐phase synthesis of grafted carbon black for superior aging resistance in biodegradable poly(butylene adipate‐co‐butylene terephthalate) composite films

AbstractBiodegradable films mitigate plastic pollution but often lack UV‐aging resistance, shortening their lifespan. While anti‐aging additives can boost the films' durability, small molecule migration constrains the extension of their service life. This study introduces a straightforward solid‐phase reaction for producing carbon black (CB) grafted with the UV absorber UV531, termed CB‐UV531. This material was then blended with the biodegradable polymer PBAT and transformed into a film via blow molding, yielding a durable UV‐resistant biodegradable film (PBAT/CB‐UV531). This solid‐phase grafting reaction does not require any solvents, thereby reducing solvent contamination and waste, and it is simple to operate, allowing for scalable production. Compared to the unmodified CB, the obtained CB‐UV531 exhibits significantly improved thermal stability, which can effectively reduce the loss of UV531 during the subsequent high‐temperature film‐blowing process. Furthermore, the chemically bonded UV absorber on the surface of CB‐UV531, coupled with its reduced particle size, promotes enhanced dispersibility and consistent stability within the PBAT/CB‐UV531 film, markedly improving its long‐term resistance to UV aging. This method is expected to enhance the anti‐aging effects of various commercial light stabilizer additives and can be used to extend the lifespan of different biodegradable materials.Highlights A simple solid‐phase reaction method was developed to prepare CB‐UV531. CB‐UV531 reveals smaller size and superior dispersibility. Biodegradable PBAT/CB‐UV531 film was prepared via a blowing process. UV531 migration loss in PBAT/CB‐UV531 film is significantly reduced. PBAT/CB‐UV531 film shows enhanced thermal stability and aging resistance.

Enhanced reliability of Cu-Sn bonding through the microstructure evolution of nanotwinned copper

Kirkendall voids are detrimental to the Cu-Sn bonding interface, causing the failure of the high-density package. Herein, the perpendicularly aligned nanotwinned Cu (p-ntCu) and the horizontally aligned nanotwinned Cu (h-ntCu) are prepared by controlling the electrodeposition procedure. The p-ntCu shows advantages both in fast-bonding process and in void suppression through the in-situ microstructure evolution. Compared with h-ntCu, the abundant perpendicularly aligned twin boundaries in p-ntCu provide fast interdiffusion paths to build a bonding interface. In the bonding process, p-ntCu grows to ultra-large-grained Cu with an average grain size of 6.68 μm. The reduced density of normal grain boundaries in p-ntCu lowers the Cu diffusion rate and contributes to more balanced interdiffusion at the bonding interface, which is confirmed by molecular dynamics simulation and kinetic calculations of intermetallic compound (IMC) growth. In addition, the low impurity content in p-ntCu further reduces the diffusion flux imbalance and limits the nucleation of Kirkendall vacancies. Consequently, the p-ntCu/Sn interface keeps void-free during 150 °C long-term thermal aging due to the synergistic effect of reduced grain-boundary diffusion and lower impurity content, which will be beneficial for achieving high-reliability Cu-Sn bonding.

Effects of ultraviolet and thermal oxygen ageing on the rheological properties of SEBS/MWCNTs composite-modified asphalt

To enhance the anti-ageing properties of asphalt binder, multiwalled carbon nanotubes (MWCNTs) and styrene-ethylene-butylene-styrene (SEBS) were used to create a composite-modified asphalt (CMA). The ageing resistance was assessed through rheological property changes, using a dynamic shear rheometer (DSR) for various tests. FTIR spectroscopy analyzed the ageing mechanism. The results showed that CMA exhibited significantly better rutting resistance than matrix and SBS asphalt. Although the fatigue life of CMA was lower than SBS asphalt, ist was still dramatically higher than matrix asphalt. MWCNTs reduced the low-temperature relaxation performance of unaged asphalt. Notably, CMA showed superior ageing resistance against both thermal oxygen and UV ageing, with decreases of about 30% and 28% in the UV ageing index and long-term ageing index, respectively, compared to matrix asphalt. The carbonyl and sulfoxide indices increased after ageing, with the composite containing 3% SEBS demonstrating optimal ageing resistance and road performance.

High-Temperature Behavior of Pd/MgO Catalysts Prepared via Various Sol–Gel Approaches

A series of Pd/MgO catalysts based on nanocrystalline MgO were prepared via different sol–gel approaches. In the first two cases, palladium was introduced during the gel preparation, followed by drying it in supercritical or ambient conditions. In the third case, aerogel-prepared MgO was impregnated with an ethanol solution of Pd(NO3)2. The prepared catalysts differ in particle size and oxidation state of palladium. The catalytic performance and thermal stability of the samples were examined in a model reaction of CO oxidation at prompt thermal aging conditions. The as-prepared and aged materials were characterized by low-temperature nitrogen adsorption, UV-vis spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, and ethane hydrogenolysis testing reaction. The highest initial activity (T50 = 103 °C) was demonstrated by the impregnated sample, containing Pd0 particles of 3 nm in size. The lowest T50 value (215 °C) after aging at 1000 °C was demonstrated by the impregnated Pd/MgO-WI sample. The high-temperature behavior of the catalysts was found to be affected by the initial oxidation state and dispersion of Pd. Two deactivation mechanisms, such as the agglomeration of Pd particles and migration of small Pd species into the bulk of the MgO support with the formation of Pd-MgO solid solutions, were discussed.

Investigating the Effect of Nano-Crystalline Cellulose in Nitrile Butadiene Rubber Matrix for Improved Thermo-Mechanical Properties

The escalating demand for sustainable rubber products has spurred research into alternative reinforcing fillers, driven by concerns regarding the detrimental effects of using conventional fillers like carbon black and silica. In this investigation, nano-crystalline cellulose (NCC), derived from micro crystalline cellulose (MCC), sourced from sugarcane bagasse via acid hydrolysis, serves as a bio-filler to reinforce Nitrile Butadiene Rubber (NBR) matrices. NBR-NCC nano-composites were prepared using a two-roll mill, varying NCC from 1–5 parts per hundred rubber matrices, followed by hot press curing. NCC and NBR-NCC nano-composites were characterized using Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), curing characteristics, thermo-mechanical testing, thermal aging and motor oil resistance. Chemical interactions between the NCC and NBR matrix were verified with FTIR. The SEM images of the NCC showed a combination of rod-like and spherical morphologies and a homogenous dispersion of NCC in NBR-NCC nano-composites with some agglomeration, notably at higher percentages of NCC. It is shown that the cure time decreases with increasing NCC loading which mimics a shorter industrial production cycle. The results also showed an increase in tensile strength, hardness, oil resistance and a rise in degradation temperature when compared to NBR at approximately 34%, 36%, 38% and 32 °C, respectively, at 3 phr NCC loading. Furthermore, NBR-NCC nano-composites showed a lower decrease in mechanical properties after aging when compared to NBR. The findings of this research suggest that the NBR-NCC nano-composites may find applications in high oil resistance seals and rubber gloves where higher thermal stability is strictly required.

Different adhesive approaches for the bonding of a new universal resin cement to a disilicate glass-ceramic.

This study aimed to evaluate the shear bond strength (SBS) when bonding a universal resin cement to a disilicate glass-ceramic using different adhesive protocols. Sixty specimens were etched with 10% hydrofluoric acid (HF) for 20s and assigned to one of four treatment protocols (n=15): The Positive control protocol comprised use of a universal adhesive system+adhesive resin cement; the Test1 protocol comprised use of a new universal adhesive system+universal resin cement; the Test2 protocol comprised use of a silane coupling agent+universal resin cement; and the use of a universal resin cement without adhesive and silane served as the Negative control. One of the two resin cement cylinders built on each specimen in each group was used to test for 24-h SBS, while the other was thermocycled and then tested for SBS. Data were submitted to two-way ANOVA, Tukey's test, and Weibull analysis. The negative control (24h) showed the lowest SBS mean value. The Test2 protocol resulted in the highest SBS mean value after thermocycling. Adhesive and mixed failures were prevalent in all groups. No statistical difference in m values was observed among the groups at 24h. After thermocycling, the two Test protocols showed the highest m values. The m values were significantly lower after thermocycling than at 24h for all groups. After thermal aging, The Test2 protocol resulted in a statistically significantly higher SBS mean value after thermal aging than seen for the other groups.