Tan Delta Curves Research Articles

Hygrothermal effect and statistical analysis of the interfacial performance of nano and microscale polymer composites

ABSTRACT Hygrothermal exposure significantly impacts polymer composite (PMC) performance, affecting various industries. This study evaluated the short-term hygrothermal effects on PMCs by examining interfacial shear strength (IFSS), water uptake, glass transition temperature (Tg), and morphology. Data-driven techniques minimized experimental time while analyzing multiple factors. Specimens were immersed in water at 25°C and 70°C for 3, 7, and 14 days. The IFSS between carbon nanotube yarns and carbon fiber with epoxy (EPON™ 862) was measured before and after exposure. Statistical analysis indicated that fiber type significantly influenced IFSS, while time had a marginal effect and temperature had no impact. The IFSS decreased by 4.14% for CF/epoxy and 14.9% for CNT/epoxy. Water uptake analysis revealed weight gains of 0.465% and 1.566% for epoxy after 14 days at 25°C and 70°C, respectively. Morphological studies showed moisture penetration between 7 and 14 days. Thermomechanical analysis (TMA) indicated that pristine epoxy expanded by 0.318% of its original height. After 14 days, the Tg of epoxy decreased by 6.4% at 25°C and 9.7% at 70°C. Dynamic mechanical analysis (DMA) on dried epoxy samples showed similar Tg but varied tan delta curves due to plasticization. Short-term hygrothermal evaluation revealed degradation in interface quality and viscoelastic properties.

Tensile properties and dynamic mechanical analysis of kenaf/epoxy composites

Kenaf fibre-reinforced polymer composites could offer low-cost, biodegradable, recyclable, and renewable materials. The hydrophilic kenaf fibres exhibit poor compatibility with the hydrophobic epoxy matrix as compared to their synthetic counterparts and ultimately, this may severely constrain their potential as a green composite material. This work aims to evaluate the tensile properties and dynamic mechanical analysis (DMA) of kenaf fibre composites reinforced with two epoxy systems as matrices, B and M resins. Neat epoxy samples and kenaf-reinforced composites with varying fibre loading, 15% and 45% were fabricated in the study. It was found that the tensile properties of kenaf composites are dependent on the epoxy resin systems and higher with reinforcement content. The tensile strength of M-15% and M-45% are 16.3% and 12.0% stronger than their counterparts. Determination of interfacial shear strength using a modified micromechanical model was employed showing that M-45 has a higher value than B-45%, 107.09 kPa and 90.28 kPa respectively. By DMA, in general, an increase in the storage modulus and peak height in the loss modulus was always higher with kenaf composites that were manufactured with the M resin system. The adhesion factor, A calculated from tan delta curves and cole-cole plot has shown the state of fibre/matrix adhesion level in each epoxy resin system. The SEM analysis indicates the presence of void spaces around fibres and matrix may attributed to the lower compatibility of the B resins system used in kenaf composites fabrication.

Exploring shape memory and self-healing behavior in sodium and zinc neutralized ethylene/methacrylic acid (EMAA) ionomers

Polymeric materials with self-healing and shape memory capabilities have gained increasing attention for their potential applications across various industries. In this study, zinc and sodium ionomers were systematically investigated using a multi-faceted approach, including rheological analysis, Fourier-transform infrared spectroscopy (FTIR), dynamic mechanical thermal analysis (DMTA), X-ray diffraction (XRD), and self-healing and shape memory assessments. Rheological analysis revealed distinct viscosity profiles among the ionomers, with EMAA-Zn 1706 exhibiting higher viscosity at low frequencies and a pronounced thinning behavior across the frequency range. FTIR analysis provided insights into the ionomers' molecular structures and functional groups. DMTA results illuminated the viscoelastic behavior and phase transitions of the ionomers. Peaks in the tan delta curve indicated order-disorder transitions and crystalline melting temperatures, influencing their mechanical properties. XRD patterns revealed low-angle peaks associated with clusters or localized regions within the ionomers. Additionally, characteristic peaks pointed to degrees of crystallinity and ordered packing. Self-healing assessments demonstrated varying healing efficiencies, with values ranging from 40 % to 60 % for EMAA-Zn 9945 and EMAA-Na 2000, while EMAA-Zn 1706 exhibited lower healing efficiency, not surpassing 20 %, attributed to its distinct rheological characteristics. Shape memory experiments were conducted in both torsion and fold-deploy modes, revealing remarkable shape fixations, with all ionomers exceeding 99 % in torsion and 95 % in the fold-deploy method. In aqueous environments, shape memory returns remained above 90 %, underscoring the water's influence on the shape memory effect. The exceptional shape memory performances and varying self-healing efficiencies of these ionomers highlight their versatility and significance in addressing practical challenges, paving the way for tailored materials with promising applications in numerous fields.

Flexural, Dynamic and Thermo-Mechanical Analysis of Pineapple Leaf Fiber/Epoxy Composites

ABSTRACT The properties of pineapple leaf fiber composites drawn from the vastly untapped Yankee pineapple plant variant were tested in this study. The properties of silane treated (T-PALFC) and untreated (UT-PALFC) samples were evaluated using flexural testing, dynamic mechanical analysis (DMA), and thermomechanical analysis (TMA). In this study, the T-PALFC sample was specifically treated in silane for 3 hours. The results show that the bending strength is improved by up to 97% in PALF composite compared to epoxy composite.The DMA results show that the UT-PALFC possess 7.1% higher storage modulus than T-PALFC, indicating untreated fiber attribute to high dynamic property in composite. The TMA finding shows the sequence of linear coefficient of thermal expansion (CTE) as follows: T-PALFC > Neat epoxy > UT-PALFC. Furthermore, this research shows T-PALFC displayed lower properties compared to UT-PALFC because the composite had low cross-linked network. This is because T-PALFC had low glass transition temperature, Tg as shown in tan delta curve and was further supported in differential scanning calorimetry analysis. Moreover, morphological analysis of the cross-section image of the T-PALFC shows the existence of a wide gap between the PALF and the matrix compared to UT-PALFC.

Antibiotic loaded electrospun poly (lactic acid) nanofiber mats for drug delivery system

Active material-loaded nanofibers becoming more important, because of their applications in many areas such as wound healing, skin engineering, and drug release. This study was conducted to compare the release kinetics of three different antibiotics loaded on nanofibers in Phosphate-buffered saline (PBS) solution and their inhibition properties against bacteria. The three different commercial antibiotics; vancomycin (VAN), ceftriaxone (CFT), and cefpodoxime (CFD) were loaded into Polylactic acid (PLA) nanofibers via electrospinning process with different percentages; 5%, 7.5%, and 10% weight ratios of PLA. The SEM images of PLA/Antibiotic nanofibers and pure PLA nanofiber revealed an increase in diameters with the presence of antibiotics embedded in PLA nanofiber. The TGA analysis showed that the thermal degradation of CFD and VAN-loaded nanofibers were higher than neat PLA, while the thermal stability of CFT loaded nanofibers was the lowest. In the Tan Delta curves, the Tg temperatures of CFD, VAN, CFT loaded nanofibers and pure PLA nanofiber were determined as 54.56 °C, 54.57 °C, 53.86 °C, and 53.55 °C, respectively. As can be seen from the results, the variation of the glass transition temperatures supports the DSC data. Drug releasing behaviors of PLA/Antibiotic nanofibers were investigated by Ultraviolet–Visible Spectroscopy at 280, 242 and 230 nm wavelength for VAN, CFT, and CFD antibiotics, respectively. Drug-releasing amounts were gradually increased by increasing the drug loading amounts from 5% to 10%. PLA-VAN, PLA-CFT, and PLA-CFD nanofibers which contain 10% of drugs were delivered about 79%, 75%, and 29% of drugs linearly within nearly 380 h, 500 h, and 360 h, respectively. The formulations including CFT at different concentrations were found to be effective against Staphylococcus aureus and Escherichia coli in a dose-dependent manner. The formulations including CFD and VAN at different concentrations have also inhibited the growth of S. aureus.

Viscoelastic analysis of oat grain within linear viscoelastic region by using dynamic mechanical analyzer

Abstract The stress relaxation, creep-recovery, temperature, and frequency sweep tests were performed within the linear viscoelastic region by using a dynamic mechanical analyzer to investigate the viscoelastic characteristic of oat grain. The result showed that 5-element Maxwell and Burgers model were able to describe viscoelastic behaviors better. The relaxation stress decreased with the increasing moisture content from 6.79 to 23.35%, while the creep strain increased as well as the final percentage recovery decreased from 58.61 to 32.50%. In frequency sweep, storage modulus increased with the increasing frequency. In temperature sweep, there was a clear turning point in storage modulus, loss modulus, and tan delta curves with increasing temperature. The turning value of 167.47, 147.44, 134.27, 132.41, 110.28, and 92.62 °C detected in the tan delta were regarded as the best glass transition temperatures. This temperature was found to be lower than gelatinization heating temperature and decrease with the increase of moisture content. The crystalline structure of oat exhibited a typical A-type pattern and corresponding crystallinity increased from 22.03 to 31.86% with increasing moisture content. The scanning electron microscopy (SEM) micrograph of oat section was found that the size and adhesive effect of starch granules increased due to hydration.

Effect of the addition of thiourethane oligomers on the sol⿿gel composition of BisGMA/TEGDMA polymer networks

ObjectivesThiourethane oligomers have been shown to increase the fracture toughness and reduce the polymerization stress of methacrylate-based materials. However, network formation has not been elucidated in these materials yet. The aim of this study was to evaluate how the addition of a thiourethane oligomer (TU) influences the sol/gel composition and network structure of methacrylate-based materials using dynamic mechanical analysis and extraction methods. Materials and methodsBisGMA/TEGDMA at systematically varied mass ratios (20/80 to 80/20wt%) were mixed with pre-polymerized thiourethane oligomers at 0 (control) or 20wt%, synthesized by combining pentaerythritol tetra-3-mercaptopropionate with dicyclohexylmethane 4,4⿲-Diisocyanate, at 1:2 isocyanate:thiol. 0.1wt% of 2,2-Dimethoxy-2-phenylacetophenone was added as the photoinitiator and 0.3wt% of 2,6-di-tert-butyl-4-methylphenol was added as a free radical inhibitor. Disk specimens (0.8ÿ10mm in diameter, n=3) were photoactivated at 270mW/ (320⿿500nm) for 1min. The degree of conversion (DC) was measured in near-IR (˿6165cm⿿1). Specimens were immersed in two different solvents (water for 7 days or dicholoromethane for 48h). Water sorption (WS) and solubility (SL) were obtained according to ISO 4049. The leachates for both solutions were analyzed with 1H-NMR (400MHz, CDCL3). Bar specimens (1ÿ3ÿ25mm, photocured and then post-processed at 180°C for 8h to DC>95%) were subjected to dynamic mechanical analysis (⿿30 to 230°C) to obtain glass transition temperature (Tg), tan delta curves and crosslinking density (ν). Data was analyzed with two-way ANOVA/Tukey⿿s test (95%). ResultsIn general, the presence of TU increased the overall conversion. The WS was similar for all groups, but the SL decreased by 2-fold with the addition of the TU oligomer for all compositions, except BisGMA/TEGDMA 80/20. The BisGMA concentration of the leachates increased with increasing BisGMA in the initial mixture, and with the presence of thiourethane. This compositional drift of the gel with the presence of TU was attributed to the preferential dissolution of TEGDMA into the TU network. Tg and ν decreased with the addition of TU, as expected. The addition of TU produced more homogeneous networks, as evidenced by narrower breadth of the tan delta curve. ConclusionThe addition of TU affected the composition of the sol/gel in crosslinked networks, which were more homogeneous and presented 2-fold less potentially toxic leachates than the methacrylate controls. Clinical significanceThe addition of TU may produce less cytotoxic materials based on the increased conversion and reduced amount of unreacted extractables from its network after water storage.

Correlations between dynamic fragility, activation energy and glass transition temperature in polymeric composite materials: An overview from literature

Here, it is compiled data from literature for glass transition temperature (Tg) and activation energy (Ea) for different types of polymeric composite materials. A correlation among both parameters and dynamic mechanical curves is analyzed in terms of reinforcement effect and its correlation with the glassy and elastomeric moduli, as well the wideness of the main transition region. Besides, all results are discussed in terms of dynamic fragility. The results indicate that the glass transition temperature has not a direct relation with reinforcement effect promoted both in the glassy and/or elastomeric moduli. Moreover, the dynamic fragility concept seems do not be applied in polymeric composite materials since in the glass transition region the format of the storage, loss and tan delta curves vary strongly, depending on the specific polymeric composite material family.

Uniaxial tensile tests and dynamic mechanical analysis of satin weave reinforced epoxy shape memory polymer composite

The utilization of epoxy shape memory polymer composite (SMPCs) as engineering materials for deployable structures has attracted considerable attention in recent decades due to high strength and satisfactory stiffness in comparison with shape memory polymers (SMPs). Knowledge of static and dynamic mechanical properties is essential for analyzing structural behavior and recovery properties, especially for new epoxy SMPCs. In this paper, a new weave reinforced epoxy shape memory polymer composite was prepared with satin weave technique and resin transfer molding technique. Uniaxial tensile tests and dynamic mechanical analysis were carried out to obtain basic mechanical properties and glass transition temperatures, respectively.The tensile strength and breaking elongation of warp specimens were comparable with those of weft specimens. The increment of elastic modulus and hysteresis loop areas became smaller with loading cycles, meaning that cyclic tests could obtain approximate stable mechanical properties. For dynamic mechanical properties, glass transition temperature (Tg) obtained from storage modulus curves was lower than that determined from tan delta curves and Tgs in the warp and weft directions were similar (29.4 °C vs 29.7 °C). Moreover, the storage modulus in response to Tg was two orders of magnitude less than that with respect to low temperature, which demonstrated the easy processibility of epoxy SMPCs near glass transition temperature. In general, this study could provide useful observations and basic mechanical properties of new epoxy SMPCs.

Dynamic mechanical analysis of ethylene tetrafluoroethylene (ETFE) foils in use for transparent membrane buildings

Glass transition temperature and tan delta (the ratio of loss modulus to storage modulus) are indispensable parameters for determining appropriate application range of ETFE foils. In this study, ETFE foils in terms of specimen number, material direction and thickness were investigated with dynamic mechanical analysis (DMA) over a temperature range of -70-100 °C at frequencies of 0.1, 1, and 10 Hz. Glass transition temperatures were obtained with storage modulus, loss modulus and tan delta curves. It is found that frequency effect on glass transition temperature was proportional and that frequency effect was more significant than material direction effect. Moreover, a comparison study showed that elastic modulus determined with quasi-static experiments was greater than storage modulus calculated with dynamic mechanical experiments. To propose suitable glass transition temperature ranges for engineering application, an approach to determine confidence interval based on statistical analysis was employed. The resulting intervals with confidence coefficient of 95% were 31.2–32.7 °C, 60.5–66.4 °C and 79.6–83.3 °C for storage modulus, loss modulus and tan delta, respectively. In general, this study could provide useful observations and values for evaluating dynamic mechanical properties of ETFE foils.

The effect of radiation exposure on the mechanical behavior of Rohacell foams used in composite structures

Rohacell foam is being utilized on a number of composite structures used for space applications. The effect of radiation exposure on these materials has been evaluated to determine the degree of structural degradation that may occur in a space environment. A 60Co source was used on Rohacell 31HFHT, Rohacell 110WF, and Rohacell HERO 110. The exposure levels varied from 0 to 15 Mrad, in both an inert and an air environment. Tensile tests were then performed to determine the failure strength and strain. Mechanical testing of the 31HFHT specimens showed a significant decrease in strength of 50% after only a 4‐Mrad exposure. The failure strain also exhibited a 75% decrease over the same range. The 15‐Mrad specimens continued to decrease in strength, losing 95% of the initial strength. The rate of tensile strength degradation with radiation increased as the foam cell pore diameter increased. Dynamic mechanical analysis indicated an increase in the peak intensity of the tan delta curve as a function of radiation exposure, which has been attributed to radiation‐induced polymer chain fragmentation. The fracture behavior of the radiated specimens also exhibited embrittlement of the polymer cells consistent with the mechanical properties. Thermal gravimetric analysis showed a decrease in the temperature for the onset of mass loss with radiation exposure, which is consistent with chain scission of the polymer network. Even though the chemical structure of all polymethacrylimide foams is susceptible to radiation degradation, a smaller foam cell pore diameter may provide additional margin with respect to the rate of mechanical property degradation. POLYM. COMPOS., 39:2181–2189, 2018. © 2016 Society of Plastics Engineers

Dynamic mechanical properties and correlation with dynamic fragility of sisal reinforced composites

In this study, the reinforcement effect in sisal/polyester composites containing distinct reinforcement content was studied ranging from fragile to strong classification. The results indicate that the reduced storage modulus changes steadily, and the loss modulus and the tan δ peak are broader for composites containing more fiber (dynamically strong composites). As more fiber was incorporated in the resin, lower peak height for the tan delta curve was obtained, which may be indicative of lower energy dissipation due to a greater relative amount of interface. Also, the use of reduced dynamic mechanical curves (similar to dynamic fragility) is an alternative to facilitate the study of the material behavior. POLYM. COMPOS., 36:161–166, 2015. © 2014 Society of Plastics Engineers

STUDIES ON THE INFLUENCE OF TESTING PARAMETERS ON DYNAMIC AND TRANSIENT PROPERTIES OF COMPOSITE SOLID ROCKET PROPELLANTS USING A DYNAMIC MECHANICAL ANALYZER doi: 10.5028/jatm.2012.04044012

Dynamic mechanical analysis is a unique technique that measures the modulus and damping of materials as they are deformed under periodic stress. Propellants, which are viscoelastic in nature, are subjected to time, temperature, and frequency effects during the analysis to determine their dynamic and transient properties. The choice of parameters during the experiments like temperature, frequency, strain (%), and stress level is very crucial to the results obtained since the propellant behaves differently under different conditions. A series of experiments like strain and temperature ramp/frequency sweeps, creep, stress relaxation, etc. have been conducted using high burning rate composite propellant (burn rate ~20 mm/s at 7,000 kPa), in order to determine the precise effects of such parameters on the results obtained. The evaluated data revealed that as the temperature increases the storage modulus, loss modulus, and tan delta curves with respect to the frequency shift towards the lower side. Moreover, there is equivalency between the increase in the temperature and the decrease in the frequency, which can be used for the time-temperature superposition principles. Further, in transient tests, the relaxation modulus has been found to decrease when increasing strain levels in the given time range. Also, relaxation modulus versus time curves were found to shift towards the lower side with increasing temperature while creep compliance decreases with the increase in stress and decrease in temperature. The glass transition value of the composite propellant increases when there is an increase in the heating rate.

Interfacial Interaction and Morphology of EVOH and Ionomer Blends by Scanning Thermal Microscopy and Its Correlation with Barrier Characteristics

In a blend, the interfacial interaction between the component phases can be effectively utilized to bring about homogeneous mixing and unique performances. While in conventional blends, preserving the morphology of the melt mixed state is unfeasible because of the strong thermodynamic tendency of the components to phase separate, herein, we report the intermolecular interaction of two hydrogen bonded polymers such as a barrier polymer poly(ethylene-co-vinyl alcohol) (EVOH) with an ionic polymer in their blends, which work symbiotically to achieve the desirable characteristics. We demonstrate the creation of a unique ellipsoid microfibrilliar morphology and melt exfoliation of one polymer in the blends through intermolecular interaction and achieve high oxygen barrier characteristics. Scanning thermal microscopy and scanning electron microscopy investigations confirm the presence of such unique morphology. The interfacial interaction and formation of interphase was evident from the local thermal analysis results combined with photoacoustic Fourier transform infrared spectroscopy (PA-FTIR). PA-FTIR confirms the chemical nature of the interaction, while the differential scanning calorimetry results indicate modification of the EVOH phase by the ionomer. The shift of Tg and broadening of the tan delta curve is evident from dynamic mechanical analysis confirming the interaction of the blend components. The blend B(60) with microfibrillar morphology shows fourfold drop in oxygen permeability indicating the role of interfacial interaction and desired morphology.

Development of dynamic mechanical methods to characterize the cure state of phenolic resole resins

AbstractWe are interested in using dynamic mechanical analysis (DMA) to measure the degree of cure achieved by aqueous phenol‐formaldehyde (PF) resole resins as a result of previous exposures to various temperature‐humidity‐time regimes. We developed procedures that permit the obtaining of data that properly characterize and quantify the DMA behavior of these aqueous systems. Particularly important factors are substrate selection, sample clamping geometry, and sample humidification prior to analysis. In this report, we illustrate the problems encountered and the steps that we adopted to resolve them. We also present preliminary DMA data that illustrate some approaches for measuring the degree of cure achieved during previous resin exposures. One especially promising approach employs the area under the tan delta curve during isothermal scanning as an inverse measure of precure. © 1993 John Wiley & Sons, Inc.

Phenol-Formaldehyde Resin Curing and Bonding in Steam-Injection Pressing. Part II. Differences Between Rates of Chemical and Mechanical Responses to Resin Cure

Summary Dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC) were applied to samples of phenol-formoldehyde resole resins that had been previously exposed to dry precure conditions. The area under tan delta curves during DMA isothermal scans of such samples decreased as the degree of precure increased; this area was used as an empirical measure of the rate of mechanical cure for phenolic resins. Similarly, the DSC exotherm area decreased with greater sample precure; this area was used to measure the rate of chemical cure. Rates of mechanical and chemical cure differed for different resins and with temperature. Under dry precure conditions at 115° and 140°C, a high degree of mechanical cure was achieved at a low degree of chemical cure.