Search

This study aimed to investigate the static and dynamic rheological properties of an ultra‐processed powdered goat milk beverage containing carboxymethyl cellulose (CMC), guar gum (GG), and xanthan gum (XG), using a mixture design. Fourteen samples were evaluated, in addition to the original beverage. The flow curves classified the fluids as non‐Newtonian and characterized all the reconstituted beverages with pseudoplastic behavior, precisely due to the addition of hydrocolloids that increased the viscosity, and the fresh beverage sample showed the behavior of a dilatant fluid. The stress sweep verified the changes in the storage module (G′) and the loss module (G″), the G′ ranged from 1.97 to 20.36 (Pa) and the G″ ranged from 5.94 to 11.30 (Pa), demonstrating that there was the formation of beverages with elastic and viscous behaviors. The results showed a synergistic effect between the texture improvers, and the formulations with GG identified a greater effect on the tension. The frequency sweep tests showed that the behavior of the samples was that of a weak gel; however, when subjected to a certain frequency, the values of G′ exceeded the value of G″, becoming a sample with more elastic characteristics and consequently, presenting the behavior of a stronger gel. Finally, according to the data presented, it is assumed that formulations containing GG and xanthan gum may produce desirable consumer properties for the reconstituted goat milk drink. Samples with a higher concentration of GG exhibited improved rheological performance, characterized by greater consistency, increased resistance to tension, and higher viscosity at low frequencies. Practical Application: The powdered goat milk drink is an innovative product that meets the demands of the food industry and consumers by offering a nutritious and sustainable beverage alternative. [ABSTRACT FROM AUTHOR]

This paper presents a comparative assessment of hygrothermal effects on the mechanical and thermomechanical properties of resin‐infused thermoplastic E‐glass fiber‐reinforced composites (FRC) in the marine environment. The thermoplastic FRCs were immersed in seawater at two different aging temperatures, that is, 35 and 70°C. The quasi‐static tests were conducted on unaged and aged FRCs, followed by scanning electron microscopy (SEM) to determine the effect of the marine environment on the mechanical properties and damage progression. The specimens immersed at 70°C showed a significant drop of 46.7%, 39.7%, 22.6%, and 16% in mechanical properties (tensile, compression, flexural, and ILSS) mainly due to plasticization, matrix cracking, and fiber/matrix debonding. The specimens immersed at 35°C showed a reduction in tensile, compressive, and flexural strength of 10%, 14.7% and 1.9% respectively, with no significant effect on ILSS. In addition, dynamic mechanical analysis (DMA) reveals that prolonged aging induces an increase in glass transition temperature Tg due to polymerization reactions. This work is intended to reveal the effect of extreme marine environment on the resin‐infused thermoplastic FRC and to provide a useful reference for their potential structural applications in the marine industry. Highlights: Influence of aging conditions on the long‐term performance of FRCs.Hygrothermal aging leads to an increase in the glass transition temperature.The marine environment degrades mechanical properties of FRCs by up to 50%.Matrix cracking and fiber‐matrix debonding evolved as dominant failure modes. [ABSTRACT FROM AUTHOR]

Gliadin and glutenin extracted from vital wheat gluten were studied using Large Amplitude Oscillatory Shear (LAOS) followed by stop-flow frequency sweep tests after being subjected to short (4 min) and prolonged (60 min) mixing times. The LAOS tests were conducted at up to two different strain amplitudes (γ: 0.1%, 200%; ω: 10 rad/s) to apply small and large deformations to the gliadin and glutenin after mixing for different time periods. Frequency sweep tests (ω: 0.01–100 rad/s, γ: 0.06%) revealed an increase in the elasticity of gliadin with respect to an increasing mixing time, as evidenced by a robust increase in G′(ω), coupled with a less robust increase in G″(ω). Consistent with the increase in elasticity, a progressively lower tanδ(ω) and G′(ω) slope were observed for the gliadin that underwent 60 min of mixing followed by large LAOS deformations. However, G′(ω), G″(ω), and η*(ω) remained constant for glutenin as the mixing time increased. Elastic decay with an increase in tanδ(ω) was found for glutenin when subjected to prolonged mixing followed by large LAOS deformations, which became apparent at high frequencies. The stop-flow LAOS (non-linear region)–frequency sweep (linear region) tests provided an understanding of how exposure to different mixing times and LAOS deformations of different magnitudes influence the mechanical/rheological properties of the main gluten proteins. [ABSTRACT FROM AUTHOR]

Several studies have demonstrated potential of cellulose nanofibers (CNF) in various applications. However, no protocols are available for the production of spray-dried CNF with high water redispersibility; interfibrillar hydrogen bonding that occurs during spray drying is believed to be responsible for such lack of redispersibility. The present study therefore aimed to develop a protocol that can be used to prepare CNF powders from Centella asiatica via spray drying, with maltodextrin (MD) at CNF-to-MD ratios of 1:0, 1:1, 1:1.5, 1:2 and 1:2.5 as the drying aid. Chlorophylls within such plant were also complexed with zinc in order to allow the resulting redispersed CNF to exhibit thermally stable green color. The resulting powders were analyzed for their morphology, XRD pattern and FTIR spectra to confirm the interaction between CNF and MD. Appropriate CNF-to-MD ratios were determined based on the sedimentation behavior, morphology, fiber sizes and viscoelasticity of the redispersed suspensions. Only spray-dried powders with CNF-to-MD ratios of 1:2 and 1:2.5 showed no sedimentation during the entire storage period. Suspensions prepared from the powders produced at these ratios were also capable of regaining morphology and nanofibrous widths (19–20 nm) comparable to those of freshly prepared CNF suspension, with gel-like behavior and viscoelasticity remained unchanged. Zinc-chlorophylls complex possessed thermal stability under the employed spray drying condition, as confirmed by the retention of chlorophylls in the powders. Green color of redispersed CNF suspensions was similar to that of freshly prepared CNF suspension. [ABSTRACT FROM AUTHOR]

Obtaining a polymer nanocomposite with optimum viscoelastic, thermal, and biocompatibility properties is the main objective when designing nanocomposite systems with potential applications in tissue engineering. For this purpose, a blend of Polycaprolactone (PCL) and Polyvinylidene fluoride (PVDF) in an 85/15 weight ratio, along with a nanocomposite reinforced by nanohydroxyapatite (nHA) particles, is fabricated using a solution casting method in a mold. The impact of nHA content on crystallinity, viscoelastic properties, thermal stability, and the properties–structure relationship of nanocomposites is evaluated using scanning electron microscopy (SEM). Dynamic mechanical thermal (DMTA) analysis is used to determine the William–Landel–Ferry (WLF) constants and the effect of nHA on the nanocomposite's viscoelastic behavior. The PCL/15PVDF/0.5 wt% nHA exhibits the maximum thermal stability (40% residual char value) and 95% increase in storage modulus at 90 °C (rubbery region) in comparison with PCL/15PVDF blend. Water contact angle (WCA) and biocompatibility tests are conducted on the PCL/15PVDF blend and nanocomposite scaffolds to design appropriate nanocomposite systems with potential applications in tissue engineering. The high hydrophilic properties are assigned to PCL/15PVDF/0.5 wt% nHA with a WCA of 67.5°. Finally, in vitro cell culture confirmed 0.5 wt% nHA significantly improves cell adhesion and cytotoxicity with MG‐63 cells. [ABSTRACT FROM AUTHOR]

Currently, principles of tissue engineering and implantology are uniformly applied to all bone sites, disregarding inherent differences in collagen, mineral composition, and healing rates between craniofacial and long bones. These differences could potentially influence bone quality during the healing process. Evaluating bone quality during healing is crucial for understanding local mechanical properties in regeneration and implant osseointegration. However, site-specific changes in bone quality during healing remain poorly understood. In this study, we assessed newly formed bone quality in sub-critical defects in the maxilla and femur, while impairing collagen cross-linking using β-aminopropionitrile (BAPN). Our findings revealed that femoral healing bone exhibited a 73 % increase in bone volume but showed significantly greater viscoelastic and collagen changes compared to surrounding bone, leading to increased deformation during long-term loading and poorer bone quality in early healing. In contrast, the healing maxilla maintained equivalent hardness and viscoelastic constants compared to surrounding bone, with minimal new bone formation and consistent bone quality. However, BAPN-impaired collagen cross-linking induced viscoelastic changes in the healing maxilla, with no further changes observed in the femur. These results challenge the conventional belief that increased bone volume correlates with enhanced tissue-level bone quality, providing crucial insights for tissue engineering and site-specific implant strategies. The observed differences in bone quality between sites underscore the need for a nuanced approach in assessing the success of regeneration and implant designs and emphasize the importance of exploring site-specific tissue engineering interventions. Accurate measurement of bone quality is crucial for tissue engineering and implant therapies. Bone quality varies between craniofacial and long bones, yet it's often overlooked in the healing process. Our study is the first to comprehensively analyze bone quality during healing in both the maxilla and femur. Surprisingly, despite significant volume increase, femur healing bone had poorer quality compared to the surrounding bone. Conversely, maxilla healing bone maintained consistent quality despite minimal bone formation. Impaired collagen diminished maxillary healing bone quality, but had no further effect on femur bone quality. These findings challenge the notion that more bone volume equals better quality, offering insights for improving tissue engineering and implant strategies for different bone sites. [Display omitted] [ABSTRACT FROM AUTHOR]

The thermomechanical and viscoelastic properties of a glass fiber polyethylene terephthalate glycol (GF/PETG) continuous unidirectional (UD) tape were investigated using differential scanning calorimetry (DSC), thermomechanical analysis (TMA), and dynamic mechanical analysis (DMA). This study identified five operational conditions based on the Army Regulation 70-38 Standard. The DSC results revealed a glass transition temperature of 78.0 ± 0.3 °C, guiding the selection of temperatures for TMA and DMA tests. TMA provided the coefficient of thermal expansion in three principal directions, consistent with known values for PETG and GF materials. DMA tests, including strain sweep, temperature ramp, frequency sweep, creep, and stress relaxation, defined the material's linear viscoelastic region and temperature-dependent properties. The frequency sweep indicated an increased modulus with rising frequency, identifying several natural frequency modes. Creep and stress relaxation tests showed time-dependent behavior, with strain increasing under higher loads and stress decreasing over time for all tested input values. Viscoelastic models fitted to the data yielded R2 values of 0.99, demonstrating good agreement. The study successfully measured thermomechanical and viscoelastic properties across various conditions, providing insights into how temperature influences the material's mechanical response under extreme conditions. [ABSTRACT FROM AUTHOR]

Incorporating nanoparticles into injectable hydrogels is a well-known technique for improving the mechanical properties of these materials. However, significant differences in the mechanical properties of the polymer matrix and the nanoparticles can result in localized stress concentrations at the polymer–nanoparticle interface. This situation can lead to problems such as particle–matrix debonding, void formation, and material failure. This work introduces boronic acid/boronate ester dynamic covalent bonds (DCBs) as energy dissipation sites to mitigate stress concentrations at the polymer–nanoparticle interface. Once boronic acid groups were immobilized on the surface of SiO2 nanoparticles (SiO2-BA) and incorporated into an alginate matrix, the nanocomposite hydrogels exhibited enhanced viscoelastic properties. Compared to unmodified SiO2 nanoparticles, introducing SiO2 nanoparticles with boronic acid on their surface improved the structural integrity and stability of the hydrogel. In addition, nanoparticle-reinforced hydrogels showed increased stiffness and deformation resistance compared to controls. These properties were dependent on nanoparticle concentration. Injectability tests showed shear-thinning behavior for the modified hydrogels with injection force within clinically acceptable ranges and superior recovery. [ABSTRACT FROM AUTHOR]

This research study was conducted to examine the effects of quenched biosilica on the composite material composed of cotton microfibers and vinyl ester. Examining the performance of quenched biosilica reinforced in a vinyl ester composite with cotton microfiber is the primary focus of this research. After the biosilica was quenched after being generated from hardly husk, a hand layup process was employed to create the composites. Adding quenched biosilica in silane-treated form significantly increases the load bearing characteristics, according to the comprehensive analysis of many composite materials. Results from the fatigue tests show that VCB3 has remarkable resilience to fatigue, with a maximum stress of 74 MPa maintained after 104 cycles and a subsequent decline to 16 MPa at 106 cycles. In the dynamic mechanical investigation, VCB3 showed the least amount of energy dissipation and highest stiffness with a peak loss factor of 0.38. This finding is supported by the creep test, which shows that VCB3 exhibits the best structural stability under continuous load, with creep strain values ranging from 0.0059 at 5000 s to 0.0084 at 15,000 s. When quenched silane-treated biosilica is included into the composite matrix, its resistance to deformation, propagation of fractures and energy loss is enhanced. These findings demonstrate the importance of quenched silane-treated biosilica in improving the mechanical performance of composite materials, making them suitable for demanding applications including drones, automobiles, homes, and sports that demand high levels of thermal stability and exceptional durability. [ABSTRACT FROM AUTHOR]

Simple Summary: Chicken liver pate is a smooth and spreadable product made from chicken meat, chicken livers, fat, seasoning and other optional ingredients (such as hydrocolloids). Hydrocolloids (polysaccharides or proteins) are commonly used in spreadable meat/poultry products (such as chicken liver pâté) to improve texture, stability and moisture retention, resulting in a product with desired functional and organoleptic properties. In general, the chicken liver pâté samples showed their highest hardness and viscoelastic moduli values when κ-carrageenan and furcellaran were used. Suggestions for producing a softer chicken liver pâté consistency involve utilizing ι-carrageenan at a level between 0.25% and 0.75% (w/w) or furcellaran at a 0.25% w/w concentration. We can conclude that the use of hydrocolloids in the manufacturing of chicken liver pâté could be an effective solution leading to the development of products with desired techno-functional properties. Hydrocolloids are used in spreadable meat or poultry products to improve consistency, emulsion stability and water retention, resulting in products with desired functional and organoleptic properties. The scope of the work was to evaluate the addition of three divergent algal hydrocolloids (κ-carrageenan, ι-carrageenan, furcellaran) at four different concentrations (0.25, 0.50, 0.75, and 1.00% w/w) on the physicochemical, textural, rheological and organoleptic properties of model chicken liver pâté (CLP) samples. Overall, the highest hardness and viscoelastic moduli values of the CLP samples were reported when κ-carrageenan and furcellaran were utilized at a concentration of 0.75% w/w (p < 0.05). Furthermore, increasing the concentrations of the utilized hydrocolloids led to increase in the viscoelastic moduli and hardness values of CLP. Compared to the control sample, an increase in spreadability was reported in the CLP samples with the addition of hydrocolloids. Finally, the use of algal hydrocolloids proved to be an effective way to modify the techno-functional properties of CLP. [ABSTRACT FROM AUTHOR]

Although the physical properties of a structure, such as stiffness, can be determined using some statical tests, the identification of damping parameters requires a dynamic test. In general, both theoretical prediction and experimental identification of damping are quite difficult. There are many different techniques available for damping identification, and each method gives a different damping parameter. The dynamic indentation method, rheometry, atomic force microscopy, and resonant vibration tests are commonly used to identify the damping of materials, including soft materials. While the viscous damping ratio, loss factor, complex modulus, and viscosity are quite common to describe the damping of materials, there are also other parameters, such as the specific damping capacity, loss angle, half-power bandwidth, and logarithmic decrement, to describe the damping of various materials. Often, one of these parameters is measured, and the measured parameter needs to be converted into another damping parameter for comparison purposes. In this review, the theoretical derivations of different parameters for the description and quantification of damping and their relationships are presented. The expressions for both high damping and low damping are included and evaluated. This study is considered as the first comprehensive review article presenting the theoretical derivations of a large number of damping parameters and the relationships among many damping parameters, with a quantitative evaluation of accurate and approximate formulas. This paper could be a primary resource for damping research and teaching. [ABSTRACT FROM AUTHOR]

The functionally graded composite structures with viscoelastic polymers inherits the excellent performance of functionally graded composites and also possesses large damping performance, which has broad application prospects in the aerospace and mechanical engineering fields. However, due to the complexity of the structure itself, there is limited literature available on its theoretical modeling for efficient solutions. To predict its dynamic performance, a simplified dynamic model of the functionally graded composite structures with viscoelastic polymers is established. This model takes into account the displacement transfer relationship between the functional graded composite layer and the viscoelastic polymer layer. The governing differential equations are obtained by applying the Navier method and complex modulus theory. These equations are then solved using the Rayleigh–Ritz method. The validity of the theoretical model is confirmed by comparing it with existing literature and the results obtained from ANSYS software. Additionally, the model that has been developed is used to analyze how the graded index and elastic modulus of the structure, as well as its geometric parameters, affect its vibration and damping characteristics. [ABSTRACT FROM AUTHOR]

In the current study, dental nanocomposite reinforced with silanized silicon dioxide nanoparticles was developed. The silicon dioxide nanoparticles were varied from 0 to 30 weight‐%. Polymer resin of bisphenol A‐glycidyl methacrylate/ triethylene glycol dimethacrylate (BisGMA/TEGDMA) was used along with camphorquinone and ethyl 4‐(dimethylamino) benzoate as polymerization initiator and accelerator respectively. The role of silicon dioxide nanoparticles in mechanical and viscoelastic properties of dental composites was evaluated. Physical properties like void content and water sorption were increased by 10 % and 25 % respectively. However, mechanical and viscoelastic properties were improved with the addition of silicon dioxide nanoparticles. Data were analyzed statistically with one‐way analysis of variance (ANOVA) and post hoc Tukey′s HSD test (α<0.05). The incorporation of 10 weight‐% of silicon dioxide nanoparticles increased the micro‐hardness by 126.1 %, compressive strength by 7.6 % and flexural strength by 28.8 %. The storage modulus was increased by 37 % and loss modulus was decreased by 1 % with the introduction of 10 weight‐% of silicon dioxide nanoparticles. [ABSTRACT FROM AUTHOR]

Elastic nonlinearity in sandstones is given by the combination of slow and fast effects, leading to hysteresis and relaxation of the viscoelastic properties after the sample is perturbed (conditioning). While a lot of experimental evidences of slow dynamics are available, quantification of nonclassical nonlinearity is still difficult: nonlinear indicators must be introduced which are independent of both experimental configuration and on conditioning strain amplitude, which is often difficult to quantify in an accurate way. In this contribution, we introduce and analyze some possible quantities describing nonlinear viscoelasticity in sandstones, derived from a non-equilibrium strain model. We will show that they identify real material properties, in the sense that they are not dependent on experimental details (such as experiment duration, conditioning protocol, frequency,...) and can be measured easily with good repeatability. Highlights: We quantify the temporal relaxation of viscoelastic properties of sandstones; We introduce measurable indicators allowing to quantify hysteresis, anisotropy, and relaxation in sandstones; We propose a non-equilibrium strain model to describe observed hysteresis and anisotropy in nonlinear hysteretic viscoelastic properties; We show a linear correlation exists between modulus and damping evolution during relaxation in sandstones. [ABSTRACT FROM AUTHOR]

Purpose: Musculotendinous stiffness (MTS) measurement is valuable for assessing stretch-induced effects for sports injury prevention. There is no consensus on whether there are sex-related differences in MTS reduction by stretching, and no effective stretching protocol exists. We aimed to investigate the sex-related differences in stretch-induced MTS changes. Methods: Fifteen healthy men (22.0 ± 1.0 years) and fifteen healthy women (22.3 ± 1.1 years) performed stretching of the ankle plantar flexors for four sets of 30 s each. MTS was measured before and after each set of stretching. Results: A significant two-way interaction (time × sex) was found for MTS (p = 0.021). MTS significantly decreased after one set of stretching in men (p = 0.024) and after three sets in women (p = 0.001). MTS after one and four sets of stretching was significantly higher in men than in women (p = 0.038 and p = 0.019, respectively). Conclusion: Fewer stretching sets are needed for men compared with that required for women to decrease MTS, and the MTS change is greater for men. Thus, the patient's sex should be considered when designing an optimum stretching protocol. [ABSTRACT FROM AUTHOR]

In this work, the effective behavior of viscoelastic composites with ellipsoidal reinforcements and imperfect interface or degraded interphase is investigated through the inclusion replacement concept. The concentration equations have been reformulated as to define the equivalent inclusion's behavior with imperfect interface or thin coating allowing to evaluate the effective behavior through different homogenization schemes. The correlation between interface and interphase descriptions is formulated in the context of anisotropic behavior of the inclusion and the matrix and for ellipsoidal inclusion shape. In the case of isotropic elasticity, the exact analytical solutions agree with the literature references for spherical and cylindrical inclusion morphologies and linear spring interface model. The replacement procedure was extended to viscoelastic behavior of the components with imperfect interface and/or interphase. Alternative descriptions of the interface behavior are proposed through Maxwell and Kelvin–Voigt models. The combined influence of shape of inclusions and interface parameters is analyzed on the effective relaxation modulus. [ABSTRACT FROM AUTHOR]

In this research, the morphology, rheology, and mechanical performance of polyamide 6/polylactic acid/acrylonitrile–butadiene–styrene (PA6/ABS/PLA) ternary blends were studied. The optimum ABS percentage in PA6/ABS binary blend to achieve highly toughened blend was determined around 35 wt.%. The spreading coefficient (Sij) predictions showed that each of PLA and ABS can form separate phase in the PA6 matrix. The evaluation of the interfacial interactions in the ternary blends revealed a higher tendency of PLA to interact with PA6 chains (Sij:−1.20) rather than ABS (Sij:−0.20) which is in comply with higher work of adhesion of PLA/PA6 than PLA/ABS and PA6/ABS. By adding PLA to the binary blends of PA6/ABS, it was found that the ABS domain size decreased due to rheological change. The localization of each component in the ternary blends observed in SEM analysis was in agreement with spreading coefficient predictions. Morphological evaluations revealed higher interfacial interactions between PA6 and PLA in the blends with up to 20 wt.% PLA. The optimized blend ratio of ternary blends showed higher complex viscosity at low shear rates and higher values than the mixing rule prediction. The optimum flexural modulus of 2 GPa and impact resistance of 47 kJ/m2 were achieved at 20 wt.% PLA in PA6/ABS/PLA ternary blend. Highlights: The optimum PA6/ABS blend ratio to achieve high toughness was determined.The phase localization in the blends predicted via Spreading Coefficient.The interaction of PA6 and ABS enhanced by the addition of PLA in the blends.The mechanical properties of blends are correlated with rheological behavior.The flexural modulus of blends was higher than Halpin–Tsai model predictions. [ABSTRACT FROM AUTHOR]

In this study, the creep behavior of semicrystalline polymers was investigated based on time‐dependent thermomechanical characteristics of the amorphous and crystalline sections. To this end, different equivalent box models (EBMs) with simple or complex structures were designed to interconnect the system components and cover all of their likely interactions. To induce time‐dependency to the model, a variety of viscoelastic models (e.g., Maxwell, Kelvin–Voigt, Maxwell representation of standard linear viscoelastic [SLV] model, Kelvin representation of SLV model, Burger and developed Bingham–Norton) were incorporated with the EBM structures as its crystalline/amorphous components. A specific strategy was devised in order to separately indicate the particular effects of crystalline and amorphous sections along with stress concentration on the temperature‐dependent creep behavior of the system. This approach combined with validating the theoretical data against the creep test results, performed at 20, 40, and 60°C, helped to indicate the most efficient structure for EBM and the best applicable viscoelastic model component. Accordingly, based on the findings of the present study, it was revealed that the series arrangement of the amorphous and crystalline model components, represented by the Burger viscoelastic model, could provide the best predictions regarding the temperature‐dependent creep in semicrystalline polymers. Highlights: Creep behavior of semicrystalline polymers at different temperatures.Representing the crystalline and amorphous sections using viscoelastic models.Evaluating different interactions in the semicrystalline polymers using EBMs.Comparison of the efficiency of different viscoelastic model components in EBM.Distinct impact of crystalline and amorphous sections on the system properties. [ABSTRACT FROM AUTHOR]

The effects of ultrasound (US) pretreatment, heat pump drying temperature and drying time on the water status and viscoelastic properties as well as the correlation between them of scallop adductors were investigated. As drying progressed, the transverse relaxation time (T2) of tightly and loosely bound water maintained a relatively stable state, while the T2 of free and immobilized water shifted leftwards with US pretreatment and increasing drying temperature. The creep compliance was increased, but the relaxation modulus decreased with US pretreatment and an increase in drying temperature. However, the creep compliance exhibited a decreasing trend, but the relaxation modulus showed an increase tendency as drying proceeded, viz., decreasing moisture content. Burger's model and the three-element generalized Maxwell model achieved the best fit to describe the creep behavior and stress relaxation, respectively. The storage modulus (G′) and loss modulus (G″) were decreased with US pretreatment, increasing the drying temperature and moisture content. The T2 of all water components and peak area fraction of immobilized water were positively correlated with the creep compliance but significantly negatively correlated with the stress relaxation modulus, G′ and G″. Low-field nuclear magnetic resonance provided reliable viscoelastic properties of scallop adductors by monitoring the water status during the drying process, which can be used to accurately control the final product quality. [ABSTRACT FROM AUTHOR]

Abstract New data analysis based on a spring‐dashpot model is developed to provide very close simulation of stress variation in polyethylene (PE) when subjected to a multi‐relaxation (MR) test. The model consists of a quasi‐static branch and two (long‐ and short‐term) viscous branches. The study shows that viscous stresses applied to the two dashpots and the model parameters can be quantified as functions of displacement (stroke) by simulating closely the stress variation in relaxation. Using these parameters, influences of stress triaxiality and material grade on PE's stress response at relaxation stages are examined, and along with experimental data at the loading stages, spring constants in the two viscous branches are determined. The results indicate that among three PE grades, spring constants and their trend of variation are similar in the long‐term viscous branch, but not in the short‐term counterpart. The results also show that by decreasing specimen gauge length 10 times to increase stress triaxiality, spring constants in the two viscous branches become closer to each other. The work concludes that the new data analysis can determine all parameters in the model, which can then be considered to quantify the role of the viscous stress response for PE's load‐carrying performance. Highlights Use a simple model to simulate complex, multiple relaxation behaviors of PE. Determine all model parameter values to characterize PE's relaxation behavior. Illustrate the effect of stress triaxiality on PE's viscous stress response. Show the similarity and difference of the viscous stress response among 3 PEs.

This paper presents the results of a study on the effect of the dispersed phase on the lubricating and rheological properties of selected lubricant compositions. A vegetable oil base (rapeseed oil) was used to prepare vegetable lubricants, which were then thickened with lithium stearate, calcium stearate, aluminum stearate, amorphous silica, and montmorillonite. Based on the results of the tribological tests of selected lubricating compositions, it was found that calcium stearate and montmorillonite have the most beneficial effect on the anti-wear properties of the tested lubricating greases, while silica thickeners (amorphous silica and montmorillonite) provide the effective anti-wear protection in compared to the lubricants produced on lithium and aluminum stearate. The lowest structural viscosity was found for grease thickened with montmorillonite. Much higher values of this parameter were observed for composition, where aluminum stearate was the dispersed phase, while the highest value of structural viscosity was observed for composition, where aerosol–amorphous silica was the thickener. The composition thickened with amorphous silica had the highest yield point value, while the composition in which montmorillonite was the dispersed phase had the lowest value. Dynamic viscosity decreases with temperature, which is characteristic of lubricants. No significant differences in dynamic viscosity were found for the lubricating compositions tested at temperatures above 50 [°C]. The most favorable rheological properties were observed for composition, which was produced using calcium stearate, as it allows the lowest dynamic viscosity at −20 [°C]. Lubricants produced with lithium stearate or aluminum stearate were characterized by higher viscosity at low temperatures. For grease, in which the lithium stearate was used as a thickener, the value of the elasticity index determines the weak viscoelastic properties of tested grease and a greater tendency to change structure under the influence of applied forces. For vegetable grease thickened with aluminum stearate, more than 15 times lower values of the MSD function were observed, and the calculated elasticity index value proves the stronger viscoelastic properties of the aluminum stearate grease in relation to grease thickened with the lithium stearate. The elasticity index value for grease thickened with amorphous silica was lower than for greases thickened with lithium and aluminum stearate, indicating its stronger viscoelastic properties in relation to these two greases. For grease composition prepared on the vegetable oil base and thickened with montmorillonite. The value of the elasticity index was lower than most of the tested grease compositions, without the composition, in which the calcium stearate was used as a thickener. Such results testify to moderately strong viscoelastic properties, which leads to the conclusion that the produced lubricant was a stable substance on changes in chemical structure under the influence of variable conditions prevailing during work in tribological joints. [ABSTRACT FROM AUTHOR]

Hyaluronic acid (HA) fillers are widely used in esthetic medicine and are categorized into biphasic and monophasic types based on their manufacturing processes. To evaluate the quality of these fillers, it is essential to understand their rheological properties, which reflect their viscoelastic nature. Rheology, the study of material deformation and flow, reveals how fillers behave under stress, combining properties of solids and liquids. This study explores the fundamental principles of elasticity and viscosity, rooted in Hooke's law of elasticity and Newton's law of viscosity, to explain the complex behavior of viscoelastic substances like HA fillers. The distinction between biphasic and monophasic fillers lies in their chemical cross-linking processes, which impact their molecular weight, structure, and ultimately, their clinical performance. Biphasic fillers with minimal cross-linking rely on natural molecular entanglements, exhibiting lower modification efficiency and greater elasticity. Conversely, monophasic fillers, which undergo extensive chemical cross-linking, demonstrate higher modification efficiency, firmer texture, and enhanced resistance to enzymatic degradation. The study emphasizes the importance of thoroughly removing residual cross-linking agents to ensure filler safety. Understanding these rheological characteristics aids clinicians in selecting appropriate fillers based on injection sites, tissue conditions, and desired outcomes, balancing viscoelastic properties and safety for optimal esthetic results. [ABSTRACT FROM AUTHOR]

Thermomechanical devulcanization of butyl rubber (BR1), bromobutyl rubber (BR2) vulcanizates, both prepared in laboratory, and a waste commercial butyl rubber (BR3) using a twin-screw extruder is reported. The commercial butyl rubber vulcanizate (BR3) was used as a tire curing bladder and the waste rubber received from a tire manufacturing company. The devulcanization process was carried out at various barrel temperatures and screw speeds (40, 80 and 120 r/min). The lowest sol fraction was obtained for devulcanized waste commercial butyl rubber (D-BR3). According to Horikx theory, devulcanized butyl rubber (D-BR1) presented mainly crosslink breakup while devulcanized bromobutyl rubber (D-BR2) and devulcanized waste commercial butyl rubber (D-BR3) showed a mixture of main chain and crosslink scission. As cure rheographs at 190°C indicated, the addition of devulcanized rubbers to the corresponding virgin ones influenced both scorch and optimal cure times. The tensile properties of devulcanized/virgin rubber blends changed depending on the blend type and virgin rubber. The stress relaxation experiment revealed that the addition of devulcanized rubber to virgin one mostly influenced short relaxation times and also decreased G0. BR1/D-BR3 blends exhibited higher elastic component than BR1/D-BR1 and BR2/D-BR2 samples. The Han plots revealed higher compatibility for BR2/D-BR2 blends. [ABSTRACT FROM AUTHOR]

This study emphasizes the influential role of rheology in decoding the viscoelastic properties of pressure-sensitive adhesives (PSAs) vital to predicting key application features such as shear, tack, and peel, depending on the flow characteristics of PSAs during bonding and debonding processes. By applying the principle of time–temperature superposition (TTS), we extend the scope of our frequency analysis, surpassing the technical constraints of the available apparatus. Our exploration aims to uncover the general correlations between PSAs' viscoelastic properties and their performance in end-use applications. Initially, the adhesive performance and viscoelastic properties of a UV-crosslinkable styrene-butadiene-styrene (SBS) model adhesive prior and subsequent to UV irradiation were examined. The subsequent crosslinking reaction increased cohesive strength and heat resistance, although tack and peel strength observed a substantial decline. We successfully demonstrated these effects by logging the viscoelastic properties, specifically the storage modulus G′ at lower frequencies, which mirrors the shear strength at higher temperatures and the shift in the tan δ peak to represent each PSA's tack. These correlations were partially reflected in three commercial UV crosslinkable acrylic PSA products, although the effect of UV irradiation was less distinctive. This study also revealed the challenges in predicting tack and peel strength, which result from a complex interplay of bonding and debonding processes. Our findings reinforce the necessity for more sophisticated analysis techniques and models that can accurately predict the end-use performance of PSAs across different physical structures and chemical compositions. Further research is needed to develop these predictive models, which may reduce the need for labor-intensive testing under real-life conditions. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Chongqing University of Technology (Natural Science) is the property of Chongqing University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Noninvasive in situ monitoring of viscoelastic characteristics of corneal tissue at elevated temperatures is pivotal for mechanical property-informed refractive surgery techniques, including thermokeratoplasty and photorefractive keratectomy, requiring precise thermal modifications of the corneal structure during these surgical procedures. This study harnesses Brillouin light scattering spectroscopy as a biosensing platform to noninvasively probe the viscoelastic properties of ovine corneas across a temperature range of 25–64 °C. By submerging the tissue samples in silicone oil, consistent hydration and immiscibility are maintained, allowing for their accurate sensing of temperature-dependent mechanical behaviors. We identify significant phase transitions in the corneal tissue, particularly beyond 40 °C, likely due to collagen unfolding, marking the beginning of thermal destabilization. A subsequent transition, observed beyond 60 °C, correlates with collagen denaturation. These phase transformations highlight the cornea's sensitivity to both physiologically reversible and irreversible viscoelastic changes induced by mild to high temperatures. Our findings underscore the potential of the Brillouin biosensing technique for real-time diagnostics of corneal biomechanics during refractive surgeries to attain optimized therapeutic outcomes. [ABSTRACT FROM AUTHOR]

Introduction: MyotonPRO technology is a clinically accessible tool for objectively monitoring the biomechanical and viscoelastic properties of musculoskeletal tissues. This study aimed to identify the level of accuracy needed for recording from specified measurement sites on the soleus muscle and plantar fascia (PF), which are important for postural control and gait. Methods: In 20 healthy adults, MyotonPRO measurements were taken 1 cm above and below a standardized point on the soleus and PF. Ultrasound scans were also taken at each site to measure subcutaneous tissue thickness to aid interpretation of MyotonPRO findings. Results: Biomechanical and viscoelastic properties of the soleus and PF, measured using the MyotonPRO, were not affected by the change in the recording site. Subcutaneous tissue thickness above the PF changed significantly (p < 0.001) by 0.61 cm when moving distally by 2 cm, whilst above the soleus, these did not differ significantly (p = 0.175) when moving distally by 2 cm. Conclusion: Changing the recording site 1 cm above or below the standardized site did not affect either the MyotonPRO results (soleus and PF) or ultrasound results for soleus, whilst this same distance affected ultrasound measurements of subcutaneous tissue thickness above the PF significantly. Moving away from the musculoskeletal junction reduces the need for precision in relocating the recording site for measuring soleus. These findings allow for quicker and easier measurement of soleus or PF using the MyotonPRO. [ABSTRACT FROM AUTHOR]

The description of various loading types within the frame of viscoelasticity, such as creep–recovery and stress relaxation in a wide time scale, by means of the same model and similar model parameters is always an interesting topic. In the present work, a viscoelastic model that was analyzed in previous works has been utilized to describe the main standard loading types of viscoelasticity with the same set of model parameters. The relaxation function of this model includes a distribution function followed by the energy barriers that need to be overcome by the molecular domains when a stress field is applied. This distribution function attains a decisive role in the analysis and it was shown that it can be determined on the basis of the loss modulus master curve experimental results. Thereafter, requiring no additional parameters, the creep compliance, the relaxation modulus of poly-lactic acid (PLA) in a wide time scale, as well as creep–recovery at various stresses could be predicted. It was also found that by employing the distribution function associated with the PLA matrix, the creep–recovery experimental data of PLA/hybrid nanocomposites could subsequently be predicted. Therefore, the proposed analysis was shown to be a useful method to predict the material's viscoelastic response. [ABSTRACT FROM AUTHOR]

Although various degradable gel materials have been developed for temporary plugging in oil fields, they often degrade too quickly in high-temperature environments. To address this issue, an unstable crosslinker was synthesized to prepare a high-temperature degradable gel. This gel does not degrade excessively fast at high temperatures. Temperature and crosslinker concentration are the primary factors influencing gel degradation time, followed by monomer and initiator concentrations. Increased temperature and decreased crosslinker concentration both reduce degradation time, which can be adjusted within the range of 90–130 °C by varying the crosslinker concentration. The molecular structure and thermal stability of the degradable gel were analyzed using FTIR, 13C NMR, and TG. Furthermore, the viscoelastic properties, compressive performance, plugging performance, and core damage performance of the gel were evaluated. Within the test range of 0.1–1000 Pa, the storage modulus is higher than the loss modulus. The gel prepared at 130 °C exhibited a compressive stress of 0.25 MPa at 50% strain. The plugging pressure of the gel in sand-filled tubes with varying permeabilities (538.2–2794.1 mD) exceeded 15 MPa while maintaining a core damage rate below 5%. SEM analysis indicated that the degradation mechanism of the gel may involve the collapse of its three-dimensional network structure due to the hydrolysis of amide groups in the crosslinker. The viscosity of the degradation liquid was below 11 mPa·s, enabling it to be brought back to the surface with the formation fluid without the need for further breaking operations. [ABSTRACT FROM AUTHOR]

Flax fibre-reinforced bio-composites are developed using both unmodified petroleum-based epoxy and Epoxy Methyl Ricinoleate (EMR) toughened epoxy modified with microcrystalline cellulose (MCC) as the base matrix. Base-catalyzed transesterification is employed for the synthesis of EMR as a low-viscosity reactive green monomer for the modification of petroleum-based epoxy. MCC is incorporated into the EMR-modified epoxy through mechanical stirring and subsequent sonication at loading rates of 1%, 3%, and 5% by weight. The compression molding technique was employed to prepare the composites. The results show an enhancement in tensile strength, modulus, impact strength, and inter-laminar shear strength values up to 19%, 34%, 34.2%, and 22.7%, respectively for MCC filled EMR toughened epoxy composite compared to neat epoxy composite. The storage and loss moduli, as revealed by the dynamic mechanical analysis (DMA), also demonstrate improvement for the 3% MCC-C composite signifying the improved fibre/matrix bonding. The low-velocity impact test at 10 J and 20 J for non-perforation and perforation conditions was also performed on the composites. The MCC-incorporated EMR-modified composite demonstrated the highest low velocity impact resistance among all other bio-composites, highlighting its potential for use in semi-structural applications due to the enhanced interfacial adhesion. The SEM analysis revealed that the fibre surface of MCC-modified EPEMR20 composites exhibited surface damage, and adherence of MCC fillers and matrix fragments, indicating superior adhesion to the matrix system. [ABSTRACT FROM AUTHOR]

Fine aggregate matrix (FAM), as the matrix phase in asphalt concrete (AC), significantly affects the fatigue behavior of AC. To accurately assess the mechanical properties of FAM, a newly designed experimental strategy for FAM testing was developed, and the viscoelastic continuum damage theory (VECD) theory was applied to analyze FAM's fatigue cracking characteristics. In this study, a dumbbell-shaped geometry for dynamic shear rheometer testing was designed and verified through the FE-aided method. Subsequently, three AC mixtures' FAM specimens with this special geometry were fabricated for the frequency sweep and linear amplitude sweep tests. Results showed that the specially designed specimens effectively capture the viscoelastic and fatigue properties of FAM with high replicability. Analyses based on the VECD theory indicated that FAM of porous asphalt (FAM(PA13)), featuring a higher asphalt content, exhibits a significant reduction in pseudo stiffness with increasing damage at the initial stage, but the reduction rate diminishes as damage progresses when compared to the other two FAMs. It was speculated that the higher aggregate content in FAM of dense-graded AC mixture (FAM(AC20) induces stress concentrations in the asphalt mastic near the protrusion areas of aggregates, thereby rendering the sample more susceptible to damage. The proposed methods will be readily extended to characterize other mechanical properties of FAM. [ABSTRACT FROM AUTHOR]

New data analysis based on a spring‐dashpot model is developed to provide very close simulation of stress variation in polyethylene (PE) when subjected to a multi‐relaxation (MR) test. The model consists of a quasi‐static branch and two (long‐ and short‐term) viscous branches. The study shows that viscous stresses applied to the two dashpots and the model parameters can be quantified as functions of displacement (stroke) by simulating closely the stress variation in relaxation. Using these parameters, influences of stress triaxiality and material grade on PE's stress response at relaxation stages are examined, and along with experimental data at the loading stages, spring constants in the two viscous branches are determined. The results indicate that among three PE grades, spring constants and their trend of variation are similar in the long‐term viscous branch, but not in the short‐term counterpart. The results also show that by decreasing specimen gauge length 10 times to increase stress triaxiality, spring constants in the two viscous branches become closer to each other. The work concludes that the new data analysis can determine all parameters in the model, which can then be considered to quantify the role of the viscous stress response for PE's load‐carrying performance. Highlights: Use a simple model to simulate complex, multiple relaxation behaviors of PE.Determine all model parameter values to characterize PE's relaxation behavior.Illustrate the effect of stress triaxiality on PE's viscous stress response.Show the similarity and difference of the viscous stress response among 3 PEs. [ABSTRACT FROM AUTHOR]

Conventional chemotherapeutic approaches currently used for brain tumor treatment have low efficiency in targeted drug delivery and often have non-target toxicity. Development of stable and effective drug delivery vehicles for the most incurable diseases is one of the urgent biomedical challenges. We have developed polymer nanoparticles (NPs) with improved temozolomide (TMZ) delivery for promising brain tumor therapy, performing a rational design of polyelectrolyte complexes of oppositely charged polysaccharides of cationic chitosan and anionic pectin. The NPs' diameter (30 to 330 nm) and zeta-potential (−29 to 73 mV) varied according to the initial mass ratios of the biopolymers. The evaluation of nanomechanical parameters of native NPs demonstrated changes in Young's modulus from 58 to 234 kPa and adhesion from −0.3 to −3.57 pN. Possible mechanisms of NPs' formation preliminary based on ionic interactions between ionogenic functional groups were proposed by IR spectroscopy and dynamic rheology. The study of the parameters and kinetics of TMZ sorption made it possible to identify compounds that most effectively immobilize and release the active substance in model liquids that simulate the internal environment of the body. A polyelectrolyte carrier based on an equal ratio of pectin–chitosan (0.1% by weight) was selected as the most effective for the delivery of TMZ among a series of obtained NPs, which indicates a promising approach to the treatment of brain tumors. [ABSTRACT FROM AUTHOR]

Background: Most rheological analyses in yam have been done on starch gels, which requires starch extraction from the tubers. In situ rheology bypasses the need of starch extraction and relies on the original cell structure and complex matrix organization under stress or strain. Dynamic rheological properties of tuber from 16 accessions belonging to four yam species (Dioscorea rotundata, D. alata. D. bulbifera and D. dumetorum) were investigated for potential use as a medium throughput phenotyping screening tool that can indicate the quality of yam food products or their industrial potentials. Results: Rheographs of the tubers illustrated differences in the structure of D. bulbifera compared to other yam species. High initial storage modulus (G′) of yam parenchyma indicated tubers with strong and rigid structure which do not lose their structural integrity easily on heating. Dioscorea rotundata and D. alata varieties exhibited a lower temperature at which gelatinization took place (Tgel) equivalent to the irreversible transition during starch gelatinization (75.3 and 79.8 °C) and took shorter time (867 and 958 s, respectively) to reach the G′ maximum, compared to other species. The stress relaxation test showed that the higher the dry matter of the tubers, the higher the work to rupture the structure. Conclusion: Rheological characteristics G′, loss modulus (G″), swelling capacity and Tgel showed potential as suitable quality indicators for yam products. In situ rheological characterization of yam tubers could be used as an instrumental screening tool to phenotype for quality in yam products. © 2023 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

This study aimed to investigate the effects of Himalayan salt on the physicochemical, microbiological, sensory and rheological properties of white cheese. For this purpose, five different brine solutions were prepared as follows; K (Control), B (White Himalayan Salt), K (Red Himalayan Salt), 1:1B (White: Rock salt), 1:1K (Red: Rock salt). While there was no significant difference between the value of dry matter, pH and ash content of the samples, the results of M17 agar were found the highest in the samples prepared with red Himalayan salt (p<0.05). The viscoelastic solid character (G’) of the samples increased with the addition of White and red Himalayan salt. The data obtained from frequency sweep test were fitted to power law model. The model parameters of K’ and K’’ were found to be 4184.04-9019.83 Pasn . The cheese samples produced with red Himalayan salt showed significantly higher K’ than the samples produced with white Himalayan salt and control sample (p<0.05). The using of different Himalayan salt color significantly increased the “a*” values of the samples, and the “b*” value decreased during storage period both two Himalayan salt usage. The results of this study indicated that the using of Himalayan salt could improve rheological properties of the white cheese samples without significant changing in sensorial and physicochemical properties. [ABSTRACT FROM AUTHOR]

To investigate the healing effect of microcapsules on microcracks in asphalt pavements, microcapsules were first prepared by in-situ polymerization from polyurea formaldehyde ( as microcapsule wall) and bio-oil ( as microcapsule heart). The appearance morphology and thermal stability of the microcapsules were investigated by scanning / transmission electron microscopy and thermo gravimetric analysis. Subsequently, these microcapsules were incorporated into styrene-butadiene-styrene (SBS) modified asphalt to create microcapsule / SBS-modified asphalt, and the effect of microcapsules on the performance of the composite modified asphalt pavement was investigated by dynamic shear rheometry and segregation tests. Finally, the healing effect of microcapsules was verified by ductility healing rate test and the healing mechanism was analyzed by a combination of macro and micro tests. The results show that the microcapsules exhibit a quasi-spherical shape with a relatively rough surface, increasing the contact area with asphalt. In addition, the microcapsules have better thermal stability and their microcapsules wall can withstand the high temperature environment during the asphalt mixture production. With the addition of microcapsules, the low temperature plasticity and heat resistance of the composite modified asphalt are both improved. In addition, the storage modulus and loss modulus of the composite modified asphalt are also improved, i. e., the incorporation of microcapsules enhance the viscoelastic properties of SBS modified asphalt, which can be attributed to the good compatibility of the added microcapsules with SBS and base asphalt. The microcapsules are uniformly dispersed within the asphalt and embedded in the network structure presented by SBS, which is confirmed in the segregation tests and fluorescence microscopy test. The highest healing rate of the composite modified asphalt is achieved when the content of microcapsules is 0. 4% . [ABSTRACT FROM AUTHOR]

Despite the common use of the standard linear solid model (SLSM) in viscoelasticity, the physical significance as well as the difference between the Maxwell and Kelvin forms of SLSM are still not clear. This paper demonstrates that each parameter of those two models has its specific physical meaning, and introduces the relationships allowing the transformations between those parameters. Regardless of their physical significance, those two models are equivalent in terms of their mathematical properties. Hence, no matter which model is chosen, consistent analysis results can always be obtained as long as the physical meaning of each parameter is accurately interpreted. [ABSTRACT FROM AUTHOR]

It is remarkable how teeth maintain their healthy condition under exceptionally high levels of mechanical loading. This suggests the presence of inherent mechanical adaptation mechanisms within their structure to counter constant stress. Dentin, situated between enamel and pulp, plays a crucial role in mechanically supporting tooth function. Its intermediate stiffness and viscoelastic properties, attributed to its mineralized, nanofibrous extracellular matrix, provide flexibility, strength, and rigidity, enabling it to withstand mechanical loading without fracturing. Moreover, dentin's unique architectural features, such as odontoblast processes within dentinal tubules and spatial compartmentalization between odontoblasts in dentin and sensory neurons in pulp, contribute to a distinctive sensory perception of external stimuli while acting as a defensive barrier for the dentin-pulp complex. Since dentin's architecture governs its functions in nociception and repair in response to mechanical stimuli, understanding dentin mechanobiology is crucial for developing treatments for pain management in dentin-associated diseases and dentin-pulp regeneration. This review discusses how dentin's physical features regulate mechano-sensing, focusing on mechano-sensitive ion channels. Additionally, we explore advanced in vitro platforms that mimic dentin's physical features, providing deeper insights into fundamental mechanobiological phenomena and laying the groundwork for effective mechano-therapeutic strategies for dentinal diseases. [ABSTRACT FROM AUTHOR]

This study investigated polyethylene glycol (PEG), as a polymer improver of the paraffinic oil viscosity index (VI). The characterization of PEG/paraffinic oil blends at different concentrations (0%, 1%, 2%, 3%, 5%, and 10%), was performed using Raman spectroscopy and optical microscopy. The rheological parameters as the viscosity index and activation energy were determined using the kinematic viscosity measurements. Results showed that the VI improvement reached an optimal value for the blend containing 3% PEG, with greater value for blends containing 2% PEG than 5 and 10% PEG. The presence of polymer particles was observed by optical microscopy, which confirmed the lack of PEG distribution in the blend containing 5%, and more, whereas mixtures with 3 and 2% PEG exhibited good particle distribution, evidenced by smaller polymer particle sizes. This finding was corroborated by Raman spectroscopy, which revealed the absence of polymer–oil intermolecular interactions in the PEG/paraffinic oil blends. The rheological tests showed that increasing the blend temperature from 40 to 80 ℃, improved the PEG chains dispersion in the paraffin oil, for the blends containing up to 3% PEG. The difference of the activation energy of the pure paraffinic oil and the PEG/paraffinic oil blends, (ΔEa) was calculated, and the correlation between the ΔEa and the viscosity index values was established. Therefore, adding PEG to paraffinic oil appeared to be promising for the viscosity index improvement and promote industrial applications of paraffinic oil. [ABSTRACT FROM AUTHOR]

Abstract Obtaining a polymer nanocomposite with optimum viscoelastic, thermal, and biocompatibility properties is the main objective when designing nanocomposite systems with potential applications in tissue engineering. For this purpose, a blend of Polycaprolactone (PCL) and Polyvinylidene fluoride (PVDF) in an 85/15 weight ratio, along with a nanocomposite reinforced by nanohydroxyapatite (nHA) particles, is fabricated using a solution casting method in a mold. The impact of nHA content on crystallinity, viscoelastic properties, thermal stability, and the properties–structure relationship of nanocomposites is evaluated using scanning electron microscopy (SEM). Dynamic mechanical thermal (DMTA) analysis is used to determine the William–Landel–Ferry (WLF) constants and the effect of nHA on the nanocomposite's viscoelastic behavior. The PCL/15PVDF/0.5 wt% nHA exhibits the maximum thermal stability (40% residual char value) and 95% increase in storage modulus at 90 °C (rubbery region) in comparison with PCL/15PVDF blend. Water contact angle (WCA) and biocompatibility tests are conducted on the PCL/15PVDF blend and nanocomposite scaffolds to design appropriate nanocomposite systems with potential applications in tissue engineering. The high hydrophilic properties are assigned to PCL/15PVDF/0.5 wt% nHA with a WCA of 67.5°. Finally, in vitro cell culture confirmed 0.5 wt% nHA significantly improves cell adhesion and cytotoxicity with MG‐63 cells.

Abstract The functionally graded composite structures with viscoelastic polymers inherits the excellent performance of functionally graded composites and also possesses large damping performance, which has broad application prospects in the aerospace and mechanical engineering fields. However, due to the complexity of the structure itself, there is limited literature available on its theoretical modeling for efficient solutions. To predict its dynamic performance, a simplified dynamic model of the functionally graded composite structures with viscoelastic polymers is established. This model takes into account the displacement transfer relationship between the functional graded composite layer and the viscoelastic polymer layer. The governing differential equations are obtained by applying the Navier method and complex modulus theory. These equations are then solved using the Rayleigh–Ritz method. The validity of the theoretical model is confirmed by comparing it with existing literature and the results obtained from ANSYS software. Additionally, the model that has been developed is used to analyze how the graded index and elastic modulus of the structure, as well as its geometric parameters, affect its vibration and damping characteristics.

Employment of distinct fibres (glass/carbon etc.) in Fibre Metal Laminates (FMLs) is one way of enhancing the durable life of an FML and its performance under dynamic loads. In the present work, carbon fibre is employed in GLARE (Glass/Aluminium laminated epoxy) to enhance the vibration (natural frequency) and viscoelastic (storage modulus (E ′), loss modulus (E ″) and Tan δ) properties. Similarly, the influence of 1 wt% of Al2O3 (alumina), ZrO2 (zirconium oxide) and TiO2 (titanium oxide) nano particles are also studied in hybrid (carbon/glass) FML. The mean particle size of Al2O3 (5.1 nm), ZrO2 (25.3 nm) and TiO2 (63.2 nm) were estimated using the Scherer equation with the aid of X-ray diffractometer analysis. Hybridisation resulted in a 22%, 10% and 2% increase of natural frequencies from mode 1 to mode 3 and 36.3%, 15% and 13.2% of E ′, E ″ and Tanδ, respectively, when compared to GLARE (glass fibre reinforced aluminium laminated epoxy). TiO2-reinforced hybrid FML shows the highest natural frequencies among all nanohybrid FMLs. The results summarise that natural frequencies and viscoelastic properties of nanohybrid FMLs are sensitive to the type of fibre, nano particle reinforcement and its size. A stereo microscope and a scanning electron microscope (SEM) were used to analyse the defects at the interface and the nanoparticle dispersion in the matrix, respectively. Further, a numerical model was developed to perform free vibration analysis, and it was noticed that the results were similar to experimental values. [ABSTRACT FROM AUTHOR]

Carbon nanotube (CNT) has fostered research as a promising nanomaterial for a variety of applications due to its exceptional mechanical, optical, and electrical characteristics. The present article proposes a novel and comprehensive micromechanical framework to assess the viscoelastic properties of a multiscale CNT-reinforced two-dimensional (2D) woven hybrid composite. It also focuses on demonstrating the utilisation of the proposed micromechanics in the dynamic analysis of shell structure. First, the detailed constructional attributes of the proposed trans-scale composite material system are described in detail. Then, according to the nature of the constructional feature, mathematical modelling of each constituent phase or building block's material properties is established to evaluate the homogenised viscoelastic properties of the proposed composite material system. To highlight the novelty of this study, the viscoelastic characteristics of the modified matrix are developed using the micromechanics method of Mori–Tanaka (MT) in combination with the weak viscoelastic interphase (WI) theory. In the entire micromechanical framework, the CNTs are considered to be randomly oriented. The strength of the material (SOM) approach is used to establish mathematical frameworks for the viscoelastic characteristics of yarns, whereas the unit cell method (UCM) is used to determine the viscoelastic properties of the representative unit cell (RUC). Different numerical results have been obtained by varying the CNT composition, interface conditions, agglomeration, carbon fibre volume percentage, excitation frequency, and temperature. The influences of geometrical parameters like yarn thickness, width, and the gap length to yarn width ratio on the viscoelasticity of such composite material systems are also explored. The current study also addresses the issue of resultant anisotropic viscoelastic properties due to the use of dissimilar yarn thickness. The results of this micromechanical analysis provide valuable insights into the viscoelastic properties of the proposed composite material system and suggest its potential applications in vibration damping. To demonstrate the application of developed novel micromechanics in vibration analysis, as one of the main contributions, comprehensive numerical experiments are conducted on a shell panel. The results show a significant reduction in vibration amplitudes compared to traditional composite materials in the frequency response and transient response analyses. To focus on the aspect of micromechanical behaviour on dynamic response and for the purpose of brevity, only linear strain displacement relationships are considered for dynamic analysis. These insights could inform future research and development in the field of composite materials. [ABSTRACT FROM AUTHOR]

To describe the evolution of residual stresses in epoxy resin during the curing process, a more detailed characterization of its viscoelastic properties is necessary. In this study, we have devised a simplified apparatus for assessing the viscoelastic properties of epoxy resin. This apparatus employs a confining cylinder to restrict the circumferential and radial deformations of the material. Following the application of load by the testing machine, the epoxy resin sample gradually reduces the gap between its surface and the inner wall of the confining cylinder, ultimately achieving full contact and establishing a continuous interface. By recording the circumferential stress–strain on the outer surface of the confining cylinder, we can deduce the variations in material bulk and shear moduli with time. This characterization spans eight temperature points surrounding the glass transition temperature, revealing the bulk and shear relaxation moduli of the epoxy resin. Throughout the experiments, the epoxy resin's viscoelastic response demonstrated a pronounced time-temperature dependency. Below the glass transition temperature, the stress relaxation response progressively accelerated with increasing temperature, while beyond the glass transition temperature, the stress relaxation time underwent a substantial reduction. By applying the time-temperature superposition principle, it is possible to construct the relaxation master curves for the bulk and shear moduli of the epoxy resin. By fitting the data, we can obtain expressions for the constitutive model describing the viscoelastic behavior of the epoxy resin. In order to validate the reliability of the test results, a uniaxial tensile relaxation test was conducted on the epoxy resin casting body. The results show good agreement between the obtained uniaxial relaxation modulus curves and those derived from the bulk and shear relaxation modulus equations, confirming the validity of both the device design and the testing methodology. [ABSTRACT FROM AUTHOR]

Carbon fiber/epoxy tow prepreg is an intermediate material for filament winding, consisting of fibers pre-impregnated with a matrix resin in a specific ratio. This study predicted the long-term viscoelastic properties of tow prepreg using DMA and TTSP. Typically, DMA involves applying a wound or laminated flat specimen, but a strand specimen was attempted to predict the characteristics of tow prepreg. The long-term viscoelastic properties were storage modulus, creep compliance, and relaxation modulus. Three test modes were performed in DMA to obtain each result. Smoothly overlapped master curves were obtained in all results. From the master curves, the viscoelastic properties of the material were predicted for 1 year, 10 years, and more extended periods. For 10 years, it was estimated that the storage modulus, creep compliance, and relaxation modulus changed by 7%, 132%, and 48%, respectively. When tests are conducted, considering future design variables, such as temperature, humidity, and out time, the results can be utilized to predict the long-term performance of tow prepreg and optimize composite manufacturing processes. [ABSTRACT FROM AUTHOR]