Search Results (189)

The aim of the work was to obtain poly(butylene succinate)—a PBS biocomposite material with an addition of natural sodium montmorillonite (Na-MMT) modified with two selected terpenes: pinene (P) and limonene (L) or their mixture (PL)—and examine their physico-chemical, rheological, and antiviral properties. Na-MMT was effectively hydrophobized and intercalated (confirmed with FTIR, TGA, and XRD analysis results) with the terpenes via the solventless method. The materials were obtained via extrusion, and the films were formed using thermo-compression molding. The addition of the fillers slightly increased mechanical properties, but barrier properties towards oxygen and water vapor were significantly improved (OTR from 52 to 28 cm³/m²∙24 h and WVTR 21 to 11 g/m²∙24 h for PBS and composite, respectively) without alteration of polymer morphology (SEM, XRD, FTIR) or thermal and thermomechanical properties, despite high filler content (10 wt%) in the polymer matrix. Surface contact angle values of PBS/M, PBS/M-L, and PBS/M-PL exhibited antiviral properties and were tested using Φ6 bacteriophage. The composites can be used for materials in medical and food packaging applications. Full article

This study provides a comprehensive quantitative comparison of three structurally distinct epoxy prepolymers—cycloaliphatic, novolac, and bis-aromatic (BADGE)—cured with a single hardener, methyl nadic anhydride (MNA), and catalyzed by 1-methylimidazole under strictly identical stoichiometric and thermal conditions. Each formulation was optimized in terms of epoxy/anhydride ratio and catalyst concentration to ensure meaningful cross-comparison under representative cure conditions. A multi-technique approach combining differential scanning calorimetry (DSC), dynamic rheometry, and thermogravimetric analysis (TGA) was employed to jointly assess cure kinetics, network build-up, and long-term thermal stability. DSC analyses provided reaction enthalpies and glass transition temperatures (Tg) ranging from 145 °C (BADGE-MNA) to 253 °C (cycloaliphatic ECy-MNA) after stabilization of the curing reaction under the chosen thermal protocol, enabling experimental fine-tuning of stoichiometry beyond the theoretical 1:1 ratio. Isothermal rheology revealed gel times of approximately 14 s for novolac, 16 s for BADGE, and 20 s for the cycloaliphatic system at 200 °C, defining a clear hierarchy of reactivity (Novolac > BADGE > ECy). Post-cure thermomechanical performance and thermal aging resistance (100 h at 250 °C) were assessed via rheometry and TGA under both dynamic and isothermal conditions. They demonstrated that the novolac-based resin retained approximately 93.7% of its initial mass, confirming its outstanding thermo-oxidative stability. The three systems exhibited distinct trade-offs between reactivity and thermal resistance: the novolac resin showed superior thermal endurance but, owing to its highly aromatic and rigid structure, limited flowability, while the cycloaliphatic resin exhibited greater molecular mobility and longer pot life but reduced stability. Overall, this work provides a comprehensive and quantitatively consistent benchmark, consolidating stoichiometric control, DSC and rheological reactivity, Tg evolution, thermomechanical stability, and degradation behavior within a single unified experimental framework. The results offer reliable reference data for modeling, formulation, and possible use of epoxy–anhydride thermosets at temperatures above 200 °C. Full article

During deep and ultra-deep well drilling operations, the throttling performance of the hydraulic-while-drilling jar is significantly affected by the combined influence of temperature-induced differential thermal expansion among components and changes in the rheological properties of hydraulic oil. These effects often lead to unstable jarring behavior or even complete failure to trigger jarring during stuck pipe events. Here, we propose a high-temperature degradation evaluation model for the throttling performance of the throttle valve in an HWD jar based on thermal expansion testing of individual components and high-temperature rheological experiments of hydraulic oil. By using the variation characteristics of the throttling passage geometry as a linkage, this model integrates the thermo-mechanical coupling of the valve body with flow field simulation. Numerical results reveal that fluid pressure decreases progressively along the flow path through the throttle valve, while flow velocity increases sharply at the channel entrance and exhibits mild fluctuations within the throttling region. Under fluid compression, the throttling areas of both the upper and lower valves expand to some extent, with their spatial distributions closely following the pressure gradient and decreasing gradually along the flow direction. Compared with ambient conditions, thermal expansion under elevated temperatures causes a more pronounced increase in throttling area. Additionally, as hydraulic oil viscosity decreases with increasing temperature, flow velocities and mass flow rates rise significantly, leading to a marked deterioration in the throttling performance of the drilling jar under high-temperature downhole conditions. Full article

High-Density Polyethylene (HDPE) plays a crucial role in the life of every human being due to its properties such as chemical resistance, light weight, and ease of forming, among others. Its usage ranges from bottles for beverages and other liquids, to pipes, wire and cable insulation, and prosthetics. As it undergoes several thermal cycles during its life cycle, it is essential to maintain its qualities, even after undergoing thermal and thermo-oxidative degradation. Here, various dosages of synthetic (Irganox 1010) and natural (vitamin E) antioxidants are added to HDPE formulations to study their impacts on HDPE stability. The antioxidants are mixed physically with HDPE before the mixtures are melt-mixed three times to represent their life cycles. Samples are taken after each time and used to analyze the molecular weight distribution, rheological behavior, mechanical properties, and thermal stability. The results show that vitamin E is superior to Irganox 1010 in these tests, as vitamin E performance exceeds that of Irganox 1010, even at lower doses. The only drawback of using vitamin E is the yellow color it causes, which may necessitate the addition of another additive to enhance the color stability of HDPE in color-sensitive applications. Full article

Wood–plastic composites (WPCs) are polymeric materials, usually thermoplastic, filled with wood flour or fibers. They are relatively durable and stiff and resistant to water. They are also, importantly, relatively cheap compared to materials with similar properties. The WPCs market has grown significantly in recent years, mainly thanks to the increasing construction and automotive markets. Currently, the global WPCs market is forecasted to reach about USD 15 billion by 2030, increasing at an impressive compound annual increase rate of about 12% until 2030. There are some review articles on WPCs written from many different points of view, e.g., the type of materials used (polymers, fillers, auxiliaries), the method of manufacturing and processing, processing properties (thermal and rheological) and functional properties, methods of designing composite products and designing (modeling) forming processes. In this article, we will summarize these different points of view and will present a thorough literature review of rheology and material processing, and more specifically, the modeling of WPCs processing. This work will be presented in relation to state-of-the-art research in the field of modeling the processing of other polymeric materials, i.e., standard (neat) polymers and polymer blends. The WPCs’ processing is significantly different from that of standard plastics due to the differences in thermo-rheological properties, diverse structures, etc. So far, the global WPCs processing models have only been developed for both gravity-fed and starve-fed single-screw extrusion. The models for twin-screw extrusion, both co-rotating and counter-rotating, as well as for injection molding, have still not been developed. WPCs show a yield stress and wall slip when extruding, which must be considered when modeling the process. As the slippage on the screw and barrel grows, the process throughput and pressure diminish, but as the slippage on the die grows, the throughput grows and the pressure diminish. As the yield stress in the screw grows, the process throughput and pressure grow, whereas as the yield stress in the die grows, the throughput diminishes and the pressure grows. Full article

This study investigates the processability—via Fused Deposition Modeling (FDM) 3D printing—and mechanical performance of biocomposites based on polylactic acid (PLA), polybutylene succinate (PBS), and their 50/50 wt% blend, each reinforced with hemp shive at 3 and 5 wt%. Blending PLA with PBS represents a straightforward and encouraging strategy to enhance both the printability and mechanical properties of the individual resins, expanding the range of their potential applications. The addition of hemp shive—a by-product of hemp processing—not only enhances the biodegradability of the composites but also improves their thermo-mechanical performance, as well as aligning with circular economy principles. The rheological characterization, performed on all the systems, evidenced that the PLA/PBS blend possesses viscoelastic properties well suited for FDM, enabling smooth extrusion through the nozzle, good shape stability after deposition, and effective interlayer adhesion. Moreover, the constrain effect of hemp shives within the polymer matrix reduced the extrudate swell, a key factor affecting the dimensional accuracy of the printed parts. Optimal processing conditions were identified at a nozzle temperature of 190 °C and a printing speed of 70 mm/s, providing a favorable compromise between print quality, final performances and production efficiency. From a mechanical perspective, the PLA/PBS blend exhibited an 8.6-fold increase in elongation at break compared to neat PLA, and its corresponding composite showed a ductility nearly three times higher than the PLA-based counterpart’s. In conclusion, the findings of this study provide new insights into the interplay between material formulation, rheological behavior and printing conditions, supporting the development of sustainable, hemp-reinforced biocomposites for additive manufacturing applications. Full article

Constitutive models and deformation behaviors for polymer materials have long been complex and are always a hot research focus. As a typical semi-crystalline polymer, polyethylene (PE) gas pipes exhibit pronounced nonlinearity, strain dependence, and time dependence during long-term service. Simple material models fail to capture the scale-dependent characteristics of the PE pipes, resulting in difficulties in accurately describing and simulating their deformation and damage behavior. Currently, some PE gas pipes have entered the mid-to-late stages of service life, so it is necessary to propose a constitutive model representing their complex mechanical behavior for simulation and performance evaluation purposes. Based on results from aging tests, tensile tests, differential scanning calorimetry, and Fourier-transform infrared spectroscopy, this study proposes a method to select a rheological framework and a constitutive model that couples thermo-oxidative aging effects in PE gas pipes. The model is developed within the widely recognized rheological framework and is grounded in continuum mechanics, continuum damage mechanics, and the aging behavior of polymer materials. This method and model are suitable for characterizing the mechanical dependency of PE pipes and demonstrate strong fitting performance. According to the calculation results, the goodness of fit of this constitutive model for the uniaxial tensile test results at the different aging times ranges from 0.982 to 0.999. The findings provide theoretical support for the simulation and service life prediction for PE pipelines. Full article

In high-slope substrates, special requirements are imposed on sprayed ecological soil, which needs to exhibit high rheological properties before spraying and rapid curing after spraying. Traditional stabilizers are often unable to meet these demands. This study developed a thermo-responsive hydrogel stabilizer (HSZ) and applied it to ecological soil. The effects of HSZ on the rheological, mechanical, and vegetation performance of ecological soil were investigated, and the mechanism of the responsive carrier in the stabilizer was explored. The experimental results show that the ecological soil containing HSZ has high flowability before response, but its flowability rapidly decreases and consistency sharply increases after response. After the addition of HSZ, the 7 d unconfined compressive strength of the ecological soil reaches 1.55 MPa. The pH value of the ecological soil generally ranges from 6.5 to 8.0, and plant growth in a simulated vegetation box is favorable. Conductivity and viscosity tests demonstrate that the core–shell microcarriers, upon thermal response, release crosslinking components from the carrier, which rapidly react with the precursor solution components to form a curing system. This study provides a novel method for regulating ecological soil using a responsive stabilizer, further expanding its capacity to adapt to various complex scenarios. Full article

Gelatin is a commonly used protein-based hydrogel. However, the thermo-reversible nature of gelatin makes it unstable at physiological and higher temperatures. Therefore, this study adopted phosphates and glutaminase transaminase (TG) to modify gelation and studied the effects of combining sodium hexametaphosphate (SHP) and TG on the structure and gel properties of TG-crosslinked gelatin. This study focused on the effects of different SHP concentrations (0, 0.4, 0.8, 1.2, 1.6, 2.0, 2.4, 2.8 mmol/L) on the water distribution, textural properties, rheological properties, and microstructure of the TG-crosslinked gelatin gels. Results showed that the free water content in the TG-crosslinked gelatin gel declined with the increasing SHP addition when the concentration of SHP was kept below 2.0 mmol/L. The gel of TG-crosslinked gelatin at the SHP concentration of 1.6 mmol/L exhibited the highest hardness (304.258 g), chewiness (366.916 g) and η₅₀. All the TG-crosslinked gelatin gels with SHP modification were non-Newtonian pseudoplastic fluids. The G′ and G″ of TG-crosslinked gelatin increased before the SHP concentration reached 1.6 mmol/L, and the TG-crosslinked gelatin with 1.6 mmol/L SHP exhibited the largest G″ and G′. The fluorescence intensity of TG-crosslinked gelatin with SHP concentration above 1.6 mmol/L decreased with the increasing SHP concentration. SHP modified the secondary structure of TG-crosslinked gelatin gels. The gel of TG-crosslinked gelatin with the SHP concentration of 1.6 mmol/L exhibited a porous, smooth, and dense network structure. This research provides references for modifying gelatin and the application of gels in the encapsulation of bioactive ingredients and probiotics. Full article

This article analyzes the residual stresses generated during the curing process of thermoset composites. Specifically, a numerical procedure is developed and implemented in Ansys 18.0 to evaluate, at the micromechanical level, the residual stresses in a carbon epoxy composite that undergoes the process of curing. The viscoelastic behavior of the epoxy material is modeled using a formulation recently published by the same authors. It accounts for the concurrent effect of curing and structural relaxation on epoxy’s relaxation times, assuming thermo-rheological and thermo-chemical simplicities. The model validated for the neat epoxy matrix is now tested against the composite application. Various representative volume element (RVE) arrangements and fiber fractions are examined. The proposed procedure can predict the evolution of mechanical properties (apparent stiffness and creep compliance) and the residual stresses that develop in each composite constituent during the cure. It demonstrates that the residual stresses in the matrix are a consistent fraction of an epoxy’s nominal strength and significantly influence the transverse mechanical properties of the composite. Full article

Direct ink writing (DIW) is an attractive, extrusion-based, additive manufacturing method for fabricating scaffold structures with controlled porosity using custom composite inks. Polycaprolactone–bioactive glass (PCL-BG) inks have gained attention for bone applications, but optimizing the formulation and fabrication of PCL-BG-based inks for improved printability and desired mechano-biological properties remains a challenge. This study employs a two-step design to systematically evaluate the effect of three factors in terms of PCL-BG composite printability and mechano-biological properties: ink preparation (acetone or dichloromethane (DCM) as the solvent, and mechanical compounding), the extrusion temperature (90 °C, 110 °C, and 130 °C), and the BG content (0%, 10%, and 20% BG). Pure PCL was used as the control. Rheological, calorimetric, and thermo-gravimetric analyses were conducted before printing. Cylindrical scaffolds and solid wells were printed to evaluate the printability, mechanical properties, and cytocompatibility. The scaffold porosity and pore size were carefully examined. Mechanical tests demonstrated that composite formulations with added BG and higher printing temperatures increased the elastic modulus and yield strength. However, PCL-DCM-BG combinations exhibited increased brittleness with higher BG content. Despite concerns about the toxic solvent DCM, the cytocompatibility was comparable to pure PCL for all ink preparation methods. The results suggest that the interaction between the ink preparation solvent, the BG content, and the printing temperature is critical for material design and fabrication planning in bone tissue engineering applications, providing insights into optimizing PCL-BG composite ink formulations for 3D printing in bone tissue engineering. Full article

Gluten-free flour blends, consisting of quinoa and sorghum flours, were used in the present study to prepare sourdough samples, which were characterized in terms of physical–chemical properties, the thermo-mechanical behavior of dough and bread making performance. The quinoa–sorghum flour blends (100:0, 75:25, 50:50) were fermented using two different starter cultures, consisting of Lacticaseibacillus rhamnosus, Levilactobacillus brevis and Lactiplantibacillus plantarum (SC1), and Lactobacillus acidophilus, Bifidobacterium lactis and Streptococcus thermophilus (SC2). After 20 h of fermentation at 30 °C, the acidity of the sourdoughs prepared with SC1 and SC2 was significantly higher in respect to the corresponding spontaneously fermented sample. The use of the starter culture for sourdough fermentation resulted in sourdoughs with higher glycerol and lactic acid contents, and lower ethanol and acetic acid. The empirical rheological measurements indicated that the behavior of the proteins and starch within the complex dough matrix, during mixing and heating, is influenced by both sorghum level and starter culture type. The use of the sourdough allowed the preparation of gluten-free breads with good texture and high contents of bioactive compounds. In conclusion, sourdough fermentation can be successfully used for boosting the quality of the gluten-free bread products. Full article

The aim of this study was to evaluate the effect of multi-walled carbon nanotubes (CNTs) on various material properties of the polyamide 66 (PA66) nanocomposites. This is achieved first by investigating the effect of CNTs (0.1–5 wt.%) on the material properties of PA66 pellets, and second, on the injection-molded PA66/CNT nanocomposites. Thermal analysis revealed that CNTs do not have a significant effect on the melting behavior and melting temperature of PA66/CNT nanocomposites, but they increase the crystallization temperature of the nanocomposites. Rheological analysis showed that the melt shear viscosity of the PA66 increased with increasing CNT content particularly above 1 wt.%. Additionally, the PA66 nanocomposites exhibit shear-thinning behavior, and this effect is more significant at higher CNT contents. The FT-IR analysis revealed the absence of chemical bonds between PA66 and CNTs and, consequently, the uniform dispersion of CNTs in the PA66 matrix. Mechanical testing indicated that the inclusion of CNTs (0.1 to 5 wt.%) in PA66 matrix could not improve the tensile modulus to a great extent, while it decreased the ultimate tensile strength of PA66 nanocomposites under tension. On the other hand, CNTs positively influenced the mechanical behavior under bending (+15% increase at 5 wt.%). Among the nanocomposites, PA66 filled with 5 wt.% CNTs exhibited the optimal mechanical performance in terms of tensile strength (58 MPa), tensile modulus (2689 MPa), bending modulus (2072 MPa), and bending strength (104 MPa). The experimental results also showcase the significant improvement in the tensile and bending mechanical properties of the injection-molded PA66 nanocomposites after thermal annealing at −40 °C and 180 °C for one hour. This experimental study provides guidelines for the structure–property–processability of the PA66 nanocomposites, revealing the complex relationship between the CNTs and the enhancement of mechanical properties, while highlighting the potential of thermal annealing in improving the mechanical performance of PA66 nanocomposites. This will be further investigated to promote the use of PA66 nanocomposite in industrial applications. Full article

This study investigates the stiffening phenomena caused by aging and low-dosage Kraft lignin addition on a soft bitumen (PG58S–28)- used in cold climate regions. Through a combination of physico-chemical and rheological analyses, including Fourier-transform infrared spectroscopy (FTIR), Brookfield rheometer viscosity (BRV), dynamic shear rheometer (DSR), multiple stress creep recovery (MSCR), bending beam rheometer (BBR), and complex shear modulus (G*) tests, the impacts of lignin modification and thermo-oxidative aging are evaluated. In particular, the anti-aging potential of lignin is scrutinized. The results indicate that while the carbonyl index effectively tracks bitumen aging, the sulphoxide index is less reliable due to high initial S=O bond content in Kraft lignin and greater repeatability variability. Standard rheological tests (BRV, DSR, MSCR, and BBR) show that long-term aging significantly increases bitumen stiffness, while lignin modification leads to a moderate stiffening effect but does not exhibit any noticeable anti-aging properties. The G* analysis confirms that aging strongly influences bitumen rigidity, particularly at low and intermediate equivalent frequencies, while lignin acts similarly to an inert filler, with minimal effects on linear viscoelastic (LVE) behaviour. Overall, the study concludes that the addition of Kraft lignin at low dosage does not alter the fundamental aging mechanisms of bitumen, nor does it provide significant antioxidant benefits. These findings contribute to the ongoing discussion on bio-based bitumen modifiers and their role in sustainable pavement materials. Full article

Oleogels must replicate the rheological behavior of saturated fats at processing and consumption temperatures to maintain their physical stability and sensory acceptance. Thus, multicomponent oleogels present a promising approach since oleogelators can exhibit structuring and melting at different temperatures. The aim of the study was to produce a mixture of ultra-chain-long esters capable of structuring and modulating rheological behavior in response to temperature exposure. Therefore, enzymatic transesterification between sorbitol and fully hydrogenated crambe oil (FHCO) was performed to produce a mixture of ultra-long-chain sorbitan esters (SB) for efficient structuring of sunflower oil. SB generated in a reaction medium consisting exclusively of ethanol (60 °C, 200 rpm, 1:1 molar ratio) was selected for its high sorbitol consumption (~95%). While SB oleogels exhibited higher gel strength at 5 °C, at 25 °C, FHCO oleogels were stiffer, showing the gradual melting of SB oleogels evaluated by temperature-dependent rheological analyses and thermal properties. Oleogelation inhibited hydroperoxide formation compared to sunflower oil over 30 days. Results highlight the potential of multicomponent oleogels based on ultralong-chain esters for healthier and more stable high-lipid products. Modulating rheological thermoresponsiveness ensures physical stability under refrigeration while providing a texture similar to saturated fats during spreading and swallowing. Full article