Dynamic Mechanical Analysis Method Research Articles

Correlation between mechanical properties and thermochemical behaviours of waste papers in their early devolatilization stage

This article details a correlation study on early devolatilization behaviors (drying & volatile emission at 25–240 °C) and the change in mechanical properties (expressed by viscoelasticity) of four types of waste papers. The early stage of devolatilization was investigated using the TG-FTIR and mechanical properties using the dynamic mechanical analysis (DMA) method. The results show that the elastic and viscous mechanical properties showed obvious correlations with free and bound water evaporation and volatile emission. The storage modulus (E′) and loss modulus (E″) of the papers decreased as temperature increased and at the two important temperatures, namely 100 °C, the start of bound water evaporation, and 150 °C, the start of devolatilization in TG & DTG curves, E′ showed extrema. Especially the relative storage modulus (E′r) exhibited a sudden decrease at around 150 °C, where the activation energy of thermochemical conversion jumps from low values to high values, indicating the start of devolatilization. CO2 is the major compound of the volatiles and it is well correlated with E′r in exponential function model and can be used as an index for predicting the E′r of the waste papers in their early devolatilization stage; while during the drying stage, mass loss ratio can be used to predict E′r of the waste papers.

Segmental Dynamics and Cooperativity Length of PMMA/SAN Miscible Blend Intercalated in Organically Modified Nanoclay.

The effect of nanoconfinement on the segmental dynamics of a poly(methyl methacrylate) (PMMA)/poly(styrene- ran-acrylonitrile) (SAN) miscible blend, intercalated into the interlayer spacing of the organically modified nanoclay (OMNC), was investigated using dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC) methods. We reported an unusual phenomenon in which the weak interfacial interactions between the polymer chains and OMNCs was responsible for increase in segmental mobility at the glass-transition temperature ( Tg). Remarkably, we found a positive correlation between dynamic fragility and thermodynamic fragility, in which both fragilities decreased under nanoconfinement. The cooperative length of segmental motions, or length of cooperatively rearranging regions, ξCRR, decreased from 2.64 nm for the PMMA/SAN blend to 1.86 nm for the PMMA/SAN/OMNC nanocomposite. The segmental mobility of the PMMA/SAN/OMNC model was also studied using the molecular dynamics simulations. The simulation results showed the increased segmental mobility of the PMMA/SAN chains in the presence of OMNCs, which is in agreement with the DMA and DSC results.

Extracting elastic modulus at different strain rates and temperatures from dynamic mechanical analysis data: A study on nanocomposites

Viscoelastic nature of polymers makes their properties strongly dependent on temperature and strain rate. Characterization of material properties over a wide range of strain rates and temperatures requires an expensive and time consuming experimental campaign. While viscoelastic properties of materials are widely tested using dynamic mechanical analysis (DMA) method, the frequency dependent component of the measured properties is underutilized due to a lack of correlation between frequency, temperature, and strain rate. The present work develops a method that can extract elastic modulus over a range of strain rates and temperatures from the DMA data for nanocomposites. Carbon nanofiber (CNF) reinforced high-density polyethylene (HDPE) matrix nanocomposites are taken as the study material. Four different compositions of CNF/HDPE nanocomposites are tested using DMA from 40 to 120 °C at 1–100 Hz frequency. First, time-temperature superposition (TTS) principle is used to develop an extrapolation for the results beyond the test parameter range. Then the TTS curve is transformed to a time domain relaxation function using integral relations of viscoelasticity. Finally, the strain rate sensitive elastic modulus is extracted and extrapolated to room temperature. The transform results are validated with tensile test results and the error found to be below 13.4% in the strain rate range 10−5 to 10−3 for all four nanocomposites. Since the materials are tested with the aim of finding a correlation among the test methods, the quality of the material is not a study parameter and the transform should yield accurate results for any material regardless of composition and quality.

Determining elastic modulus from dynamic mechanical analysis: A general model based on loss modulus data

Dynamic mechanical analysis (DMA) method is used to measure viscoelastic properties such as storage and loss moduli of materials. The present work is focused on developing a generalized model that allows transforming the storage and loss moduli obtained from DMA to time domain elastic modulus values. The model is capable of transforming the loss modulus data that may have multiple transition peaks in the test temperature range into elastic modulus over a wide range of temperatures and frequencies. In order to develop the model, the storage modulus is divided into frequency dependent and independent components, which are analyzed separately to build a general transform for strain rate sensitive and insensitive material properties. To test the accuracy of the model, the model is validated with experimental data obtained on ethylene-vinyl acetate (EVA). The secant moduli obtained from tensile tests and loss modulus transform are compared and the average error is found to be 1.1% in the strain rate range of 10−6/s to 10−2/s, which provides validation for the model. The proposed method eliminates the need for conducting numerous tensile tests to obtain modulus over various temperatures and strain rates and replaces them with a single DMA experiment.

Thermal Properties of Salt and Base Forms of Chitosan

The temperature dependences of elastic and relaxation properties of films of salt and base forms of chitosan were obtained by methods of dynamic mechanical analysis. It was estimated that the presence of two maxima on the temperature dependence of mechanical loss tangent tanδ at T1 = 150–160°C and T2 = 250–270°C is typical of the salt form of chitosan. The maximum at 150–160°C on tanδ curves is reduced or even eliminated after thermal or alcohol–alkali treatment of chitosan acetate films, while the high-temperature maximum is preserved. The results of IR spectroscopy and thermogravimetric analysis allow supposing that the low-temperature maximum of molecular mobility in films of chitosan salt form is related to the removal of absorbed water and residues of acetic acid as well as to dehydration of macromolecules. The maximum at 259°C determines the glass transition temperature of the chitosan base form.

The effect of surface modification of microfibrillated cellulose (MFC) by acid chlorides on the structural and thermomechanical properties of biopolyamide 4.10 nanocomposites

Microfibrillated cellulose (MFC) has recently been identified as an innovative product of wood and agriculture industry with potential applications as reinforcement and carrier for functional properties of polymer composite materials, such as improved barrier and optical properties. The widespread commercial application of MFC in polymer technology still requires the development of new methods of MFC surface modifications in order to provide stong interfacial adhesion and good dispersibility of additive in polymer matrix. In this work microfibrillated cellulose was modified by acid chlorides arranged in a homologous series that showed high efficiency in changing the surface properties of the material. The modified MFC displayed hydrophobic character combined with preserved fibrillar morphology and high crystallinity. Chemical modification of MFC was assessed by Fourier transformed infrared spectroscopy (FTIR) and X-ray Photoelectron Spectroscopy (XPS) analyses. Despite the fact that the reactivity of acid chloride slightly decreased with increasing chain length the total effect on MFC wetting with water was most pronounced for the modifier with the longest alkyl chain. Completely bio-based engineering nanocomposites of biopolyamide 4.10 (PA4.10) and surface modified MFC were prepared by melt blending. Structural, morphological and thermomechanical analysis by scanning electron microscopy (SEM), atomic force microscopy (AFM) and dynamic mechanical analysis (DMA) methods evidenced clear dependence of composite performance on the length of alkyl chain attached to the MFC surface. The modification of MFC by hexanoyl chloride produced nanofiller with good dispersibility in PA4.10 matrix and was favorable in terms of dynamic mechanical properties of composites. While PA4.10 composites containing MFC functionalized by longer alkyl chains (more than 10 carbon atoms) showed a decrease of storage modulus due to insufficient interfacial interactions or plasticization effect.

One‐Step Electrodeposition Method to Prepare Robust Flexible PEDOT‐Based Films for Ultra‐Stable Supercapacitors

AbstractUltra‐long cycling stability is essential for conducting polymers (CPs) in the practical application of organic electronics. However, CPs usually exhibit poor cycling stability and fragile mechanical properties. Herein, through two alkyl‐bridged monomers, freestanding, flexible conducting P(EDOT‐co‐BEDTH) films based on the copolymerization of EDOT and 1,6‐bis((2,3‐dihydrothieno[3,4‐b][1,4]dioxin‐2‐yl)methoxy)hexane (BEDTH) are easily prepared through a one‐step electrodeposition process in CH2Cl2 containing 0.1 M Bu4NBF4. Both the homopolymers and copolymers are characterized by using SEM, FTIR and UV/Vis spectroscopy, dynamic mechanical analysis (DMA), thermogravimetry (TG), and electrochemical methods. The results of DMA and TG indicate that the copolymer films show better mechanical flexibility and thermal stability than the corresponding homopolymers. Electrochemical results of P(EDOT‐co‐BEDTH) films with a capacitance of 23.6 mF cm−2 at 10 mV s−1 present ultra‐stable cycle life with a cycling capacitance retention of 99 % after 30 000 cycles. Furthermore, all‐solid‐state supercapacitors based on flexible P(EDOT‐co‐BEDTH) films exhibit the practical ability to light a red light‐emitting‐diode, demonstrating great promise in flexible energy‐storage devices.

Development of Epoxy Grout Containing Fine Waste from Production of Mineral Wool Board Insulation

Within this work, it was experimentally verified that the waste from mineral wool board insulation production (WIRG) with high portion of glass recyclate (> 80%) and no organic material seems like ideal filler for polymer grouting materials. The main objective was to develop a progressive grout on epoxy basis with as high content of this secondary raw material as possible, while achieving physical and mechanical properties as e.g. very fast strength increase and high thermal resistance. With regard to the consistency of epoxy grout in the fresh state, three different filling were tested, namely 60%, 65% and 70%. The grout with lower filling is too fluid, and it is also disadvantageous from an economic point of view because a large amount of epoxy resin is used. On the other hand, at higher filing, it is not possible to mix the filler into epoxy resin properly. Setting of an optimal filler content in the mixture was performed mostly on the basis of the results of compressive and three-point flexural strength test. It was found out that the optimal amount of the filler is 65%. In case of the best formulation with optimal filler content (65% WIRG), the thermal resistance was monitored by determination of the glass transition temperature (Tg) by the dynamic mechanical analysis (DMA) method. Furthermore, the optical microscope with high resolution was used to monitor filler distribution and homogeneity of the hardened developed epoxy grout.

Key acceptability attributes of orodispersible films

The features rendering orodispersible films (ODFs) patient-centric formulations are widely discussed in the scientific literature. However there is a lack of research studies exploring ODF characteristics with a potential impact on end-user acceptability. The aim of this study was to identify the key ODF characteristics affecting end-user acceptability by developing in vitro test methods for the prediction of ODFs acceptability and correlate these formulation characteristics with the data obtained from a human panel study. Four drug-free single-polymer films were prepared by solvent casting. Solutions of poly(vinyl) alcohol (PVOH) 39 KDa (P1), PVOH 197 KDa (P2), carboxymethylcellulose (CMC) 395 KDa (C1), and CMC 725 KDa (C2) were prepared. Texture analysis and Dynamic Mechanical Analysis (DMA) were used to assess film tack. Petri dish and drop methods were used to assess disintegration time. A human panel of 24 healthy young adults was employed to identify end-user acceptability criteria of the four study film samples. Texture analysis data of ODF tack were not found to be in agreement with the in vivo perceived stickiness in the mouth. However, measurement of the area under the adhesive force curve obtained by DMA correlated with in vivo perceived stickiness data for all samples. The disintegration times obtained by drop method were more comparable to human panel data than the petri dish method. Hence DMA and drop methods proved to be promising methodologies for the prediction of the end-user acceptability. The type and molecular weight of the film-forming polymer had a strong influence on stickiness perception, whereas only polymeric molecular weight influenced perceived disintegration time. The human panel study showed that Participant Reported Outcomes (PROs) for the perceived stickiness in the mouth and disintegration time of test films received significantly different scores between samples, and thus were identified as the key attributes with the potential to affect the end-user acceptability. ODF stickiness and disintegration time should therefore be evaluated at an early stage of the drug product design.

Uticaj neutralizacije na svojstva poroznih hidrogelova na bazi hidroksiapatita i poli(metakrilne kiseline) sintetisanih slobodno-radikalskom polimerizacijom

Goals. The goal of this study was a development of biocompatible composite hydrogels, structurally similar to native bone tissue, by incorporation of ~60 wt % of calcium hydroxyapatite (HA) into a matrix of hydrogels. Also, a possibility to control swelling kinetic and equilibrium swelling degree (SDeq) of hydrogels, by altering the degree of neutralization of the precursor (DN) was examined. Methods. Composite hydrogels, based on HA and poly(methacrylic acid) (PMAA), were synthesized by free-radical polymerization with different DN. Theoretical content of HA in synthesized composites was 60 wt %. Composites were synthesized by methods of dynamic mechanical analysis and scanning electron microscopy. SDeq and swelling kinetic were examined in distilled water and simulated body fluid. Results. Morphological observations revealed uniform distribution and strong bond of spherical HA particles within the polymer matrix. Swelling analyses demonstrated that SDeq is directly proportional to DN, while rheological examinations indicated inverse proportion between DN and storage modulus, but due to the HA particles inclusion, mechanical properties of composites were significantly better compared to monophasic PMAA hydrogels. Significance. Simple method of synthesis of composite hydrogels with high content of filler nanoparticles is presented. Incorporation of HA nanoparticles significantly improved mechanical properties of hydrogels, while at the same time was demonstrated a possibility to control swelling kinetic by influencing the DN.

Study of selected thermoplastics using dynamic mechanical analysis

The aim of given paper is to study selected polymers using dynamic mechanical analysis method (DMA). DMA is one of the most useful techniques for the study of the viscoelastic behaviour of thermoplastic polymers. In relation to DMA, an oscillatory stress and strain is applied to the material at specific frequencies and temperatures and based on this mentioned fact hereinbefore, the resulting changes after the loading in the material are measured. This technique allows detecting the melting temperature and the glass transition temperature of the thermoplastic materials. Furthermore, some spectroscopy techniques, such as energy dispersive X-ray spectroscopy (EDX) and infrared spectroscopy (IR), were also used for the investigation of the thermoplastics. The thermoplastics used for examination, namely polyethylene, polystyrene, polypropylene and polyethylene terephthalate, were gained from the waste of the packaging.

Effect of outdoor exposure on the moisture diffusion and mechanical properties of epoxy polymers

Specimens of epoxy polymers of four compositions based on 2,2 di-(4-hydroxyphenyl) propane cured by a cycloaliphatic amine hardener were exposed during 3, 6, 9, and 12 months on an open bench in a moderately warm marine climate of Gelendzhik. In the initial state and at various stages of exposure the moisture diffusion coefficient and maximum moisture content of flat rectangular specimens-coupons are determined for drying and humidification at a temperature of 60 °C. Properties of polymers in three states have been studied: after a stop of climatic tests without conditioning and after additional stages of humidification and drying using stress-strain tensile tests, dynamic mechanical analysis, optical microscopy, fractography. After the exposure in the climatic conditions, different amounts of moisture accumulate in the specimens depending on relative air humidity and precipitation amounts in different year seasons. At the drying stage, moisture transfer obeys Fick's second law. At the humidification stage, a change of mass of specimens depends on sorption of moisture and desorption of hydrolysis products. Tensile strength decreases after the climatic action and differs by a value of 20–66% for the dried and moistened specimens. A method of dynamic mechanical analysis revealed processes of post-curing and destruction depending on the polymer composition and duration of exposure. The humidification also affected a failure mode of specimens. In the initial state and after different exposure times in open climatic conditions after the humidification on fractographs an area of a mirror zone corresponding to plastic fracture increases. After drying, an area of a rough (relief) zone increases. It is shown that in order to obtain reliable information about mechanisms of climatic aging of epoxy polymers it is necessary to compare the properties of controlled specimens taking into account the moisture content to determine a degree of reversible plasticizing action of moisture against the background of irreversible changes.

Temperature dependency of dynamic mechanical properties of cement asphalt paste by DMTA method

We investigated the temperature dependency of the dynamic mechanical properties of cement asphalt paste by the dynamic mechanical thermal analysis (DMTA) method. The experimental results show that the dynamic mechanical properties of cement asphalt pastes are sensitive to temperature due to the inclusion of asphalt, and may go through different states within a temperature range of -40 °C to 60 °C, which is different from that of pure cement and asphalt. As the temperature of the cement asphalt paste increases, a considerable change of dynamic mechanical properties, including storage modulus (E’), loss modulus (E”) and loss factor (tanδ) is observed. Moreover, the influence of asphalt to cement (A/C) ratio on the temperature sensitivity of the dynamic mechanical properties of cement asphalt composites was investigated. The temperature dependency of cement asphalt composites is ascribed to the temperature dependency of the asphalt and its interaction with cement paste. A simple fractional model is proposed to describe the viscoelastic behavior of cement asphalt composites.

Thermomechanical insight into the reconfiguration of Diels–Alder networks

Relating thermoreversible bond kinetics to temperature and mechanical stress is essential to for the ongoing development of melt-processable, reconfigurable networks. Here, we apply the dynamic mechanical analysis methods to study the kinetics and equilibrium behavior of dynamic polymer networks above their gel point. Thermoreversible Diel–Alder (DA) adducts are installed as linking groups to create well-defined poly(caprolactone) networks. Stress relaxation studies at various strains are performed to differentiate how temperature and stress influence the rate of bond breaking, i.e., the rate of the retro-DA reaction. The resulting thermal activation energies of stress relaxation are nearly independent of applied stress over the experimental range studied. The forward, more sluggish, DA reaction is studied by continuously monitoring the response in Young's modulus (E′) following different temperature reductions. Equilibrium values of E′ are used to establish the temperature dependence of the DA equilibriu...

Effect of fabric weaves on the dynamic response of two-dimensional woven fabric composites

This study investigated the effect of two-dimensional fabric weaves (plain, twill, and satin) on the vibrational characteristics (natural frequency and damping) of woven carbon/epoxy composites. Natural frequencies of woven composites were measured by experimental modal analysis for plain weave, twill weave, and satin weave composites. The experimentally measured natural frequency results were compared with the ones predicted by numerical free vibration analysis. Numerical analysis was performed using a multiscale modelling approach. First, the impregnated fiber tow properties were predicted using periodic boundary conditions assuming that fibers are perfectly bonded. Then, the homogenized impregnated fiber tow properties and matrix properties were used to predict the natural frequencies of woven composite beams. The experimental and numerical results revealed that satin weave composites possess higher natural frequencies than plain weave composites. Flexural loss factor of woven composites was measured experimentally by dynamic mechanical analysis and half-power bandwidth method. Results from both analyses showed that plain weave composites have higher flexural loss factor as compared to satin weave composites.

Effect of electron beam irradiation on thermal and mechanical properties of aluminum based epoxy composites

The epoxy resins are widely used in nuclear and aerospace industries. The certain properties of epoxy resins as well as the resistance to radiation can be improved by the incorporation of different fillers. This study examines the effect of electron beam irradiation on the thermal and mechanical properties of the epoxy composites filled with aluminum nanoparticles at percentage of 0.35wt%. The epoxy composites were exposed to the irradiation doses of 30, 100 and 300 kGy using electron beam generated by the linear electron accelerator ELU-4. The effects of the doses on thermal and mechanical properties of the aluminum based epoxy composites were investigated by the methods of thermal gravimetric analysis, tensile test, and dynamic mechanical analysis. The results revealed that the studied epoxy composites showed good radiation resistance. The thermal and mechanical properties of the aluminum based epoxy composites increased with increasing the irradiation dose up to 100 kGy and decreased with further increasing the dose.

Supercritical processing of starch aerogels and aerogel-loaded poly(ε-caprolactone) scaffolds for sustained release of ketoprofen for bone regeneration

Bone regeneration requires scaffolds with a suitable nanostructured 3D-network and decorated with bioactive functionalities to promote cell ingrowth and induce the intended biological responses. In this work, highly porous poly(ε-caprolactone) (PCL) scaffolds containing biodegradable mesoporous microparticles (starch aerogel microspheres) and a bioactive compound (ketoprofen, a NSAID) were designed and produced using supercritical technologies (scCO2 impregnation/deposition and foaming) for bone regeneration purposes. One-micron-sized starch aerogel microspheres were processed for the first time. The effects of the incorporation of aerogel powders in the synthetic PCL-based scaffolds on the morphological, physico-chemical and mechanical properties of the construct were evaluated by N2 adsorption-desorption analysis, scanning electron microscopy, mercury intrusion porosimetry, 3D-modeling, dynamic mechanical analysis and differential scanning calorimetry methods. Scaffolds containing starch aerogels presented an increased porosity and pore interconnectivity to promote the bone tissue growth processes at the expense of a minor decrease in the mechanical properties. The scaffolds showed sustained release of ketoprofen (37°C, pH 7.4) in the timeframe of days with faster release rate in the case of scaffolds containing starch aerogels. Therefore, scaffolds containing starch aerogel microspheres and obtained by supercritical foaming are an attractive solution to obtain drug-loaded scaffolds with accurate pore structure (porosity, pore size distribution, interconnectivity) for cell in-growth and with sustained release profiles of bioactive compounds.

Evolution of polymer matrix structure in carbon-fiber-reinforced plastic based on polycyanurate and polyarylsulfone during accelerated climatic tests

By methods of dynamic mechanical analysis and electron microscopy, has been carried out an investigation of evolution of the polymer microstructure in carbon-fiber-reinforced plastic based on polycyanurate and polyarylsulfone in accelerated climatic tests. Has been discovered that, under the impact of heat and moisture factors, more densely packed structural formations are disintegrated and the morphology of microstructure transforms from a mutually continuous to dispersed structure. It is shown that the structural characteristics of polymer matrix depend on the type and duration of climatic impact on carbon-fiber-reinforced plastic.

Effect of electron beam irradiation on thermal and mechanical properties of epoxy polymer

This study investigates the thermal and mechanical properties of epoxy polymer after exposure to different doses of electron beam irradiation. The epoxy polymer was prepared using epoxy-diane resin ED-20 cured by polyethylenepolyamine. The irradiation of the samples was carried out with doses of 30, 100 and 300 kGy. The effects of doses on thermal and mechanical properties of the epoxy polymer were investigated by the methods of thermal gravimetric analysis, tensile test, and dynamic mechanical analysis. The thermal properties of the epoxy polymer slightly increased after irradiation at the heating in air. The tensile strength and Young’s modulus of the epoxy polymer increased by the action of electron beam up to dose of 100 kGy and then decreased. The elongation at break decreased with increasing the irradiation dose.

Mechanical Analysis of the Industrial Robot to Upgrade to the Gaming Robot

In order to explore the value of traditional industrial robots, a solution was discussed to upgrade a 5R series joint industrial robot into a desktop lightweight game robot by transforming some components. Based on the dynamic analysis, the forward kinematics equations and inverse kinematics equations of the robot were solved by using the traditional method and the double quaternion method. Based on the mechanical analysis, the static equilibrium equation and kinematic equation of the robot system were obtained. As a result, the upgrade of the robot can complete the basic functions of the game. However, an universal significance of dynamic analysis and mechanical analysis method can be obtained from the article.