Dynamic Mechanical Spectra Research Articles

Enhancing mechanical, self-healing and damping properties of dual-modified Eucommia ulmoides gum by introducing epoxy and perfluoroalkyl groups

Eucommia ulmoides gum (EUG) is a bio-based polymer with the structure of trans-1,4-polyisoprene, and easy to crystallize at room temperature, which limits its application in rubbery materials. The epoxidized EUG (E26EUG) with an epoxidation degree of 26% was readily prepared and further grafted with different contents of polar perfluoroalkyl groups by ring-opening reaction of epoxy group on the E26EUG backbone using perfluorocarboxylic acid as the nucleophilic reagent under mild conditions, affording the modified elastomers Em-xEUG-Fx with enhanced mechanical properties, good self-healing performance, and improved damping properties. The vulcanized elastomers VE26EUG and VEm-xEUG-Fx also exhibited excellent mechanical and damping properties. In addition, a high damping loss value at 0 °C in dynamic mechanical spectra indicated a good wet-skid resistance of the modified EUG elastomers before and after vulcanization. This research is of great significance for extending the applications of functional EUG rubbery materials.

Amplifying Mn Segregation and Enhancing Damping Capacity via Adding Sn in Mn–44Cu–1.5Al as‐Cast Alloys

As a metal functional material, the Mn–Cu‐based alloys are regarded to be able to cope with the vibration and noise from machines. In particular, the as‐cast alloys often exhibit an excellent damping capacity, which is attributed to the Mn segregation in the alloys. Herein, to amplify the kind of segregation, a trace of Sn is added in as‐cast Mn–Cu–Al alloys. The phase structures of the as‐cast Mn–44Cu–1.5Al alloys are analyzed in detail through X‐Ray diffraction (XRD). The distribution characteristics of face‐centered cubic (FCC) phases and face‐centered tetragonal (FCT) phases are observed using electron backscatter diffraction (BSE). The alloys’ dynamic mechanical spectra and internal friction (IF) are measured using an inverted torsion pendulum device. It is found that the addition of Sn promotes the Mn segregation in the as‐cast Mn–44Cu–1.5Al alloys. A large amount of FCT phases appears in the dendritic trunks, enhancing the damping capacity of the alloys. In the meantime, the Sn atoms enhance the twin boundary mobility in Mn‐rich dendritic trunks. As a result, the alloy containing 1 wt% Sn has the highest damping capacity in the alloys.

A Phenomenological Model for Enthalpy Recovery in Polystyrene Using Dynamic Mechanical Spectra.

This paper studies the effects of annealing time on the specific heat enthalpy of polystyrene above the glass transition temperature. We extend the Tool-Narayanaswamy-Moynihan (TNM) model to describe the endothermic overshoot peaks through the dynamic mechanical spectra. In this work, we accept the viewpoint that the enthalpy recovery behavior of glassy polystyrene (PS) has a common structural relaxation mode with linear viscoelastic behavior. As a consequence, the retardation spectrum evaluated from the dynamic mechanical spectra around the primary Tg peak is used as the recovery function of the endothermic overshoot of specific heat. In addition, the sub-Tg shoulder peak around the Tg peak is found to be related to the structural relaxation estimated from light scattering measurements. The enthalpy recovery of annealed PS is quantitatively described using retardation spectra of the primary Tg, as well as the kinetic process of the sub-Tg relaxation process.

Additive Effects of Solid Paraffins on Mechanical Properties of High-Density Polyethylene

In this work, two types of solid paraffins (i.e., linear and branched) were added to high-density polyethylene (HDPE) to investigate their effects on the dynamic viscoelasticity and tensile properties of HDPE. The linear and branched paraffins exhibited high and low crystallizability, respectively. The spherulitic structure and crystalline lattice of HDPE are almost independent of the addition of these solid paraffins. The linear paraffin in the HDPE blends exhibited a melting point at 70 °C in addition to the melting point of HDPE, whereas the branched paraffins showed no melting point in the HDPE blend. Furthermore, the dynamic mechanical spectra of the HDPE/paraffin blends exhibited a novel relaxation between -50 °C and 0 °C, which was absent in HDPE. Adding linear paraffin toughened the stress-strain behavior of HDPE by forming crystallized domains in the HDPE matrix. In contrast, branched paraffins with lower crystallizability compared to linear paraffin softened the stress-strain behavior of HDPE by incorporating them into its amorphous layer. The mechanical properties of polyethylene-based polymeric materials were found to be controlled by selectively adding solid paraffins with different structural architectures and crystallinities.

Cercidium praecox brea gum arabinoglucuronoxylans: A viscosant substitute for gum Arabic?

Brea gum, obtained from the cuts made in the trunk and branches of Cercidium praecox tree, has been traditionally collected and used as a substitute of gum Arabic (GA) in some regions of Argentina. The rheological performance of purified brea gum (BG) in water (20 °C) was thoroughly evaluated between 1 and 35% w/v. As we previously determined, BG is composed of highly branched arabinoglucuronoxylans (1:0.44:0.16:0.22 xylose:arabinose:glucuronic acid:4-O-methylglucuronic acid molar ratio) with 2.6% of acetyl groups bound to the O-3 of the xylan backbone. The deacetylated form (DBG) was also assayed at 10% w/v. Commercial GA was also considered for comparison. In flow assays (viscosity versus shear rate), BG (1–35%) showed pseudoplastic behavior, and higher initial thickening at very low shear rates (Newtonian viscosity, η0 ≈ 27.3–130 Pa⋅s) than 1–35% w/v GA (η0 ≈ 10–20 Pa⋅s), and 10% DBG (η0 ≈ 7 Pa⋅s). Dynamic mechanical spectra showed “solutions” for GA, and “weak-gel” type networks for BG, more frequency dependent at 35%, probably due to the lowest electrostatic repulsion at pH 3.77. Instead, 10% DBG showed a “dilute solution” spectrum. Heating and cooling ramps (5 °C/min) revealed a gelling temperature for 17.5% (24.2 °C) BG, but not for GA and DBG solutions. BG “weak-gels” were thermo-reversible. Thermal study revealed hydrophobic interactions between BG macromolecules, and hydrogen bonding between DBG macromolecules. BG macromolecules can have an extended hydrophobic (acetylated) side, absent in DBG. Like GA, rheological functionality can yield a commercial use of BG as food additive.

An In-Vitro Evaluation of the Characteristics of Zein-Based Films for the Release of Lactobionic Acid and the Effects of Oleic Acid.

Lactobionic acid (LBA) is widely used in different industrial sectors owing to its biocompatibility characteristics as well as antioxidant and antimicrobial properties. In this study, mixtures of the protein zein with LBA and with the addition of oleic acid (OA) as a ternary system were investigated as drug delivery films for the release of LBA. The chosen combinations exploit the vast difference in water solubility between LBA and the other two components (zein and OA). DSC thermograms and dynamic mechanical spectra, alongside electron microscopy images, were used to describe the microstructural features of the films and were found to provide insights for the release of LBA from the two examined zein-based films immersed in an aqueous physiological solution. For both film systems, a burst release behavior was observed, followed by a rapid and total extraction of LBA. The required immersion time for the total extraction of LBA was greatly reduced when oleic acid was added to the precursor solution mixture for producing the films. The LBA released from the zein-based films was found to exhibit both the expected antioxidant properties as well as exerting bacteriostatic effects towards Escherichia coli and Staphylococcus epidermidis.

Effects of Liquid Paraffin on Dynamic Mechanical Properties of Linear High-Density Polyethylene

We found that the dynamic mechanical spectra of linear high-density polyethylene (HDPE) can be controlled by swelling using liquid paraffin (LP) at 100 and 110 °C. The relaxation strength of α rela...

Reversible and irreversible β -relaxations in metallic glasses

The localized \ensuremath{\beta}-relaxation process is critical for understanding the complex dynamics and controlling the properties of glasses. However, the \ensuremath{\beta}-relaxation in most metallic glasses only appears in a form of excess wing or shoulder in dynamic mechanical spectra while the underlying mechanism of the \ensuremath{\beta}-relaxation remains elusive. In the present work, the \ensuremath{\beta}-relaxation of metallic glasses is systematically studied by calorimetry where the glass-transition temperature (${T}_{\mathrm{g}}$) is resolved. The key finding is that the long-time sub-${T}_{\mathrm{g}}$ annealing induces an endothermic peak upon heating prior to ${T}_{\mathrm{g}}$ with an activation energy of $\ensuremath{\sim}26R{T}_{\mathrm{g}}$. By using an annealing-scanning-annealing thermal protocol, we show that this distinct endothermic sub-${T}_{\mathrm{g}}$ peak is a reversible \ensuremath{\beta}-relaxation, indicating that the \ensuremath{\beta}-relaxation has both reversible and irreversible parts, which can be refined by the combination of calorimetry and the designed thermal protocol. The results might deepen our understanding of relaxation and the aging of metallic glasses.

Dynamic mechanical spectra of salep and casein mixtures.

In this study, a glucomannan based salep and casein were mixed in a solution at different concentrations (0-0.75% salep and 0-3.0% casein) according to the central composite rotatable design and their color, steady shear and dynamic shear rheological properties were characterized. All studied parameters were affected by the salep and casein levels significantly. Salep increased the apparent viscosity, consistency coefficient, storage modulus and complex modulus of the solution compared to casein and an interaction was observed between the salep and casein which shows a significant increasing effect on the parameters. Frequency dependency increased with the increase of casein in the mixtures. Regression equations having quite high coefficients of determination were constructed for the estimation of studied parameter levels. Optimization performed with desirability function showed that the maximum levels for the rheological parameters could be achieved by more increment of salep level in the solutions because sole effect of casein on the rheological parameters was limited compared to salep.

Soft interface dynamics in flax-fabrics/epoxy composites

In this work, we investigate the thermomechanical behavior of flax-fabric/epoxy composites by means of DMA experiments. Fabrics from flax fibers have undergone different chemical treatments: leaching, bleaching or mercerization. We study the influence of these chemical treatments on the dynamic mechanical relaxation spectra of the composites around the main relaxation mode. We construct master plots for the loss modulus for each sample using the time–temperature superposition (TTS) principle. The master curves were fitted with the Havriliak-Negami model and we show that both interface and interphase of composites are modified as a result of the chemical treatments. Best mechanical properties were found for mercerized treatment.

The structural relaxation in vanadium phosphate glass studied by DMA

The mechanism of structure evolution and microscopic hidden flow in glasses before yield and glass-to-liquid transition(GLT) remains unclear. In this work, the dynamic mechanical relaxation and stress relaxation spectra of vanadium-phosphate binary glass (V2O5-P2O5) when approaching the glass transition temperature T g were investigated by using the dynamic mechanical analysis (DMA). The β and α relaxation behaviors, occurring respectively at T β~ 483 K and T p~543 K and quite similar to those observed in the metal glass systems, were observed, which indicated the occurrence of the slowing-down microscopic localized flow in the investigated vanadium-phosphate glasses. This was further verified by the experimental observation and theoretical prediction of the linear logarithmic relation between the peak height of the β relaxation and the relaxation rate, i.e. ln( Δ ) µ −ln( v ). Furthermore, three stages during the structural evolution of the β and α relaxation in vanadium-phosphate glasses were observed from the temperature dependent curve of the non-exponential factor of β KWW obtained by the Kohlrausch-Williams-Watts (KWW) fitting: (I) β KWW β KWW β KWW>0.5, the region of macroscopic flow.

Effects of ball milling on the structural, thermal, and rheological properties of oat bran protein flour

Oat bran protein flour (OBPF), containing protein, starch, and lipid as major constituents, was ball milled and subsequently evaluated on structural conformation, thermal properties, particle size distributions, and rheological properties. Prior to ball milling, characterisation of OBPF were conducted by means of Fourier transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC) showing the existence of aggregated protein and starch-lipid complexes as predominant constituents of OBPF. Ball milling altered structural conformations of both protein and starch. Moreover, increase of ball milling time gradually decreased the transition enthalpy changes of amylose-lipid complexes upon heating which can be related to disruption of amylose-lipid complexes helical structure. Ball milling at higher speed resulted to smaller average particle size distributions of OBPF. Dynamic mechanical spectra of concentrated dispersions containing ball milled OBPF exhibited lower storage (G′) and loss (G″) moduli compared to control sample due to reduced particles volume packing. Moduli-frequency sweep data satisfactory fitted the Power Law’s model.

Structure and rheological characterization of konjac glucomannan octenyl succinate (KGOS)

Konjac glucomannan octenyl succinate (KGOS) has excellent emulsifying and thickening properties as a new polymeric surfactant. The reaction extent of KGOS was determined by using high-performance liquid chromatography. The molecular aggregation state of KGOS was observed and analyzed by transmission electron microscopy (TEM) and atomic force microscopy (AFM). The results showed that KGOS aggregated particles formed irregular spheres or ellipsoids, and the average particle diameter and height were approximately 30 nm and 5 nm, respectively. Thermal analysis indicated that the carbonization temperature of KGOS is slightly lower than that of konjac glucomannan (KGM). The steady shear rheology showed that KGOS solution fit to non-Newtonian fluid properties and the Carreau model, and the apparent viscosity increased with increase of KGOS concentration. The type and valence of the ions affected the apparent viscosity of KGOS solution. The trends of the dynamic mechanical spectra indicated KGOS solution could be an entanglement system. The ions had a similar effect on the dynamic modulus (G′, G″) and loss factor tanδ except for Fe3+ and H2PO4−.

Polymers in 2D confinement: A nanoscale mechanism for thermo‐mechanical reinforcement

Acrylate‐clay nanocomposites, a 2D confined system, exhibited unusual increase of thermo‐mechanical properties. The nature of this reinforcement can be ascribed to chain dynamics modification and therefore investigated via dynamic mechanical analysis. Transmission electron microscopy and dynamic light scattering showed a strong nanoconfined regime, 2Rh ≫ d001, whereRhis the polymer's hydrodynamic radius andd001is the clay gallery spacing. The geometrical constraints to polymer dynamics led to significantenhancementof the thermo‐mechanical properties. Adding only 1 wt% nanoclay, the glass transition temperature increased significantly,ΔTg = Tg − Tg,bulk ~ 10°C, and the dynamic modulusE′ increased 10‐fold. Analysis of dynamic mechanical spectra showed an increase of relaxation timeτ, ie, polymer dynamics retardation. Furthermore, the mechanical damping tanδwas strongly attenuated evidencing the reduction of viscous dissipation. The activation energyEaof theα‐transition increased as the confined macromolecules needed to overcome higher energy barriers to achieve configurational rearrangements. The considerable increase of mechanical modulus cannot be explained by polymer composite models, rather it was associated to a “nano‐effect,” scaling with the degree of confinement asE/Ematrix ~ (2Rh/d001)n. This study paves the road for further understanding of polymer dynamics under 2D confinement and the reinforcement mechanism of thermo‐mechanical properties.

Improvements in emulsion stability of dairy beverages treated by high pressure homogenization: A pilot-scale feasibility study

The impact of high pressure homogenization (HPH) on physical characteristics and emulsion stability of nutritional formulations were evaluated on a pilot scale HPH unit. Two products of industrial interest were used for these experiments. Manufactured formulations were analyzed using material characterization methods as particle size distribution, microscopy and dynamic mechanical spectra, compared to a control formula manufactured with conventional homogenization and heat treatments. Dynamic rheological measurements as strain and frequency sweeps exhibited increased product stability in parallel to increased homogenization pressures. Homogenization at elevated pressures yielded more shear thinning fluids evidenced by increased viscosities at low shear rates, ten fold greater compared to the control treatment, further evidence to increased physical stability. Experimental findings revealed the existence of a threshold pressure (100–150 MPa) for both formulations exhibiting significant correlation with product quality and physical stability. The study outcomes presents an opportunity for reducing stabilizer concentration in dairy beverages; in addition to shelf life and physical stability improvement for formulations treated at increased homogenization pressures.

Role of low melting point element Ga in pronounced β-relaxation behaviors in LaGa-based metallic glasses

In contrast to most metallic glasses (MGs) which exhibit weak β-relaxation peak in their dynamic mechanical spectra, the LaGa-based MGs we report here show a distinct β-relaxation peak with the ratio of β/α-relaxation peaks up to ∼0.32 in the mechanical relaxation measurements. Moreover, the β-relaxation behavior can be tuned by modification of the chemical composition and the concentration of flow units. The effects of gallium and structural origin of the β-relaxation in the MGs have been discussed. The LaGa-based MGs with pronounced slow β-relaxation could provide a model system to investigate some underlying issues of the relaxation and plastic mechanism of MGs.

Structural and physicochemical characteristics of a novel water-soluble gum from Lallemantia royleana seed

In this study, the structural information (monosaccharide compositions, molecular weight parameters & FTIR analysis), chemical composition (moisture, protein, ash, carbohydrate & uronic acids), rheological properties, and surface activity of Lallemantia royleana seeds mucilage (BSG) were determined. The results showed BSG contains 8.51% (w.b.) moisture, 8.24% (d.b.) ash, 2.71% (d.b.) protein, 75.87% (d.b.) carbohydrate and 20.33% (d.b.) uronic acids. Monosaccharide analysis revealed the presence of arabinose (37.88%), galactose (33.54%), rhamnose (18.44%), xylose (6.02%) and glucose (4.11%) in the BSG polysaccharide. Although BSG had similar molecular weight (1.294×106Da) compared to most seed gums, the intrinsic viscosity (23.06dL/g) and gyration radius (104.84nm) were higher. The BSG exhibited a strong shear-thinning behavior (n<0.29) over the shear rate range of 0.01 to 1000s−1. Flow behavior data was correlated with different time-independent models, which provided a good description of BSG rheological properties. Dynamic mechanical spectra demonstrated BSG is a typical of weak gel, which its rheological parameters were superior to those of many commercial gums. The FTIR spectra of the BSG polymer showed the presence of carboxyl groups, which may serve as binding sites for ions. BSG exhibited the ability to reduce the surface tension of water at concentrations lower than 0.75%.

The effects of wood flour content and coupling agent on the dynamic mechanical and relaxation properties of wood-plastic composites

This research studied the influence of formulations of wood-plastic composites on dynamic mechanical properties—storage modulus (E′), loss modulus (E′′) and mechanical loss factor (tan δ)—according to dynamic mechanical analysis spectra. The specimens were made with wood flour, high-density polyethylene (HDPE) and maleic anhydride polypropylene as a coupling agent. Generally, the presence of fillers and a coupling agent in polymer affect the relaxation processes and produce a more complex morphology, thereby influencing the mechanical and viscoelastic properties of the composites. In this work, the addition of a higher content of wood flour resulted in higher values of E′, indicating a better stiffness, but tan δ decreased. The bonding agent significantly improved E′, which can be attributed to an enhanced interface between the wood and the HDPE. Coupled products had better E′ retention at elevated temperatures than uncoupled samples. The addition of wood flour and a coupling agent increased the value of E′, but did not significantly change the range of relaxation transition.

Relaxation behavior of nanographite-reinforced silicon elastomer nanocomposites

Dynamic mechanical and dielectric relaxation spectra (DRS) of nanographite-reinforced silicon elastomer nanocomposites were studied. Scanning electron microscopic photomicrographs show well dispersion of nanographite in elastomer matrix. The primary relaxations (α transition and glass transition) have been studied by dynamic mechanical analysis as a function of temperature (−100 to 100°C) at a frequency of 1 Hz and at 1% strain. Irrespective of the nanographite loading, all nanocomposites show glass transition temperature in the range of −11 to −6°C, which was explained on the basis of the relaxation dynamics of silicon matrix. Storage modulus ( E′) shows elastic property and loss modulus shows viscous property of silicon nanocomposites as a function of temperature. Cole–Cole plots exhibit nonlinearity in the nanocomposite matrix. The nonlinearity in the plot between tan δ and E′ is explained by the concept of nanographite silicon interactions and the aggregation of the nanographite. The secondary relaxation (secondary, α* or β) has been studied using DRS in the frequency range of 10−1–106 Hz. The capacitance of the nanocomposite is expressed in terms of dielectric permittivity and explained on the basis of polarization of the nanographite in the silicon matrix. The dielectric modulus formalism has been utilized to further investigate the conductivity and relaxation phenomenon. Argand diagram confirms the existence of non-Debye/nonlinear relationship. The percolation threshold as studied by conductivity and dielectric permittivity measurements is found to be at 6 phr nanographite loading.

Detecting the Rouse and Sub-Rouse Modes in Poly(Butyl Acrylate) and Poly(Ethyl Acrylate) Through Two-Dimensional Dynamic Mechanical Spectra

The difficulties of observing sub-Rouse modes (SRM) and Rouse modes (RM) in acrylate polymers has resulted in many arguments and disputes concerning the nature of their glass-rubber transition. Because different modes have different sensitivity to external perturbations, the two-dimensional dynamic analysis mechanical spectra (2D-DMS) was introduced to detect the local segments motion (LSM), SRM, and RM in poly(butyl acrylate) (PBA) and poly(ethyl acrylate) (PEA). The results of the asynchronous spectra showed the LSM, SRM, and RM of PBA and PEA are located, respectively, at about (−46 ∼ −29°C), (−28 ∼ −10°C), (−4 ∼ 27°C), and about (−12 ∼ −5°C), (−3 ∼ 6°C), and (10 ∼ 44°C). Furthermore, the LSM and SRM of PBA and PEA have an overlap in the synchronous spectra. This is suggested to be caused by the higher coupling effect in PBA and PEA when compared with strong glass formation polymers, like polyisobutylene (PIB).