Dynamic Mechanical Analysis Measurements Research Articles

Effect of multi-walled carbon nanotube on thermal decomposition, mechanical and heat-induced shape memory properties of crosslinked poly(vinyl alcohol)

Shape memory polymers are attractive smart materials that have many promising applications in a wide variety of fields. Here the multi-walled carbon nanotube (MWCNT) was used to adjust the performance of crosslinked poly(vinyl alcohol) (PVA), which had acetal reaction with glutaraldehyde (GA). The thermal degradation, mechanical strength and shape recovery properties of PVA/MWCNT/GA membranes were investigated by thermogravimetry, differential scanning calorimetry, x-ray scattering, dynamic mechanical analysis, tensile test and thermal-stimulus shape memory recovery measurements. The MWCNT embedded in the crosslinked PVA matrix accelerated the breaking of C–O bonds. The mechanical strength and shape recovery properties of PVA/MWCNT/GA composites were tunable. As the MWCNT loading increase in crosslinked PVA matrix, the yield strength increased from 3.85 MPa to 10.21 MPa, breaking elongation decreased from 230% to 50%, the 100% shape recovery time decreased from 27 s to 16 s, respectively.

Ultrasound regulated flexible protein materials: Fabrication, structure and physical-biological properties

Ultrasound can be used in the biomaterial field due to its high efficiency, easy operation, no chemical treatment, repeatability and high level of control. In this work, we demonstrated that ultrasound is able to quickly regulate protein structure at the solution assembly stage to obtain the designed properties of protein-based materials. Silk fibroin proteins dissolved in a formic acid-CaCl2 solution system were treated in an ultrasound with varying times and powers. By altering these variables, the silks physical properties and structures can be fine-tuned and the results were investigated with Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), gas permeability and water contact angle measurements. Ultrasonic treatment aids the interactions between the calcium ions and silk molecular chains which leads to increased amounts of intermolecular β-sheets and α-helix. This unique structural change caused the silk film to be highly insoluble in water while also inducing a hydrophilic swelling property. The ultrasound-regulated silk materials also showed higher thermal stability, better biocompatibility and breathability, and favorable mechanical strength and flexibility. It was also possible to tune the enzymatic degradation rate and biological response (cell growth and proliferation) of protein materials by changing ultrasound parameters. This study provides a unique physical and non-contact material processing method for the wide applications of protein-based biomaterials.

Toward mechanistic understanding the effect of aspect ratio of carbon nanotubes upon different properties of polyurethane/carbon nanotube nanocomposite foam

AbstractThis study investigated the carbon nanotube's aspect ratio's influence on the nanocomposite foams' cellular structure and mechanical, acoustic absorption characteristics. The free‐rising foaming process has been used for producing different flexible polyurethane (PU) foams embedded with other multi‐walled carbon nanotubes (MWCNT's). Dynamic mechanical and thermal analysis, flow resistivity, and compressive mechanical measurements were achieved on the prepared samples. The acoustic absorption coefficient in a wide range of frequencies was estimated for the prepared PU/CNT foamed nanocomposite samples. Results indicated that by increasing the aspect ratio of MWCNT, the absorption coefficient's peak shifts toward the lower frequencies and improved sound absorption characteristics of PU foam in the low‐frequency region. Moreover, the Young modulus of nanocomposite samples increases by increasing the aspect ratio of MWCNT's, whereas the stored strain energy or area under the stress–strain curve increases. Based on the obtained results, it is observed that the acoustic absorption coefficient of produced nanocomposite foams at the frequency of 800 Hz has been reported to have a 70% improvement in 2 cm samples and a 40% improvement in 3 cm samples compared to obtained results from pure PU foam.

Compositional effects on cure kinetics, mechanical properties and printability of dual-cure epoxy/acrylate resins for DIW additive manufacturing

Interest in 3D printing of thermoset resins has increased significantly in recent years. One approach to additive manufacturing of thermoset resins is printing dual-cure resins with direct ink write (DIW). Dual-cure resins are multi-component resins which employ an in situ curable constituent to enable net-shape fabrication while a second constituent and cure mechanism contribute to the final mechanical properties of the printed materials. In this work, the cure kinetics, green strength, printability, and print fidelity of dual-cure epoxy/acrylate thermoset resins are investigated. Resin properties are evaluated as a function of acrylate concentration and in situ UV exposure conditions. The acrylate cure kinetics are probed using photo-differential scanning calorimetry and the impacts of resin composition and UV cure profile on the acrylate extent of conversion are presented. Continuous and pulsed UV cure profiles are shown to affect total conversion due to variances in radical efficiency at different UV intensities and acrylate concentrations. The effects of acrylate concentration on the kinetics of the epoxy thermal cure and the final mechanical properties are also investigated using dynamic mechanical analysis and three-point bend measurements. The glass transition temperature is dependent on formulation, with increasing acrylate content decreasing the Tg. However, the room temperature shear moduli, flexural moduli, strength, strain-to-failure, and toughness values are relatively independent of resin composition. The similarity of the final properties allows for greater flexibility in resin formulation and in situ cure parameters, which can enable the printing of complex parts that require high green strength. We found that the in situ UV print intensities and exposure profiles that are necessary to achieve the best print quality are not, in most cases, the conditions that maximize conversion of the acrylate network. This highlights the importance of developing optimized resin compositions which enable complete cure of the acrylate network by promoting acrylate dark cure or thermal cure.

Thermal Degradation Behavior of Epoxy Resin Containing Modified Carbon Nanotubes.

Via the surface-grafting of carbon nanotubes (CNTs) with a silicon-containing flame retardant (PMDA), a novel flame retardant CNTs-PMDA was synthesized. The flame retardancy was tested by cone calorimeter. Compared with pure epoxy resin, the total heat release (THR) and peak heat release rate (PHRR) of epoxy resin containing CNTs-PMDA were significantly reduced, by 44.6% and 24.6%, respectively. Furthermore, thermal degradation behavior of epoxy resin based composite was studied by the thermogravimetric analysis with differences in heating rates. The kinetic parameters of the thermal degradation for epoxy resin composites were evaluated by the Kissinger method and Flynn-Wall-Ozawa method. The results suggested that activation energy values of epoxy resin containing CNTs-PMDA in thermal degradation process were higher than those of pure epoxy resin in the final stage of the thermal degradation process, which was closely related to the final formation of char layer residues. Finally, the results from Dynamic mechanical thermal analysis (DMTA) and Scanning electron microscopy (SEM) measurements exhibited that the functionalization of CNTs with PMDA obviously improved the dispersion of CNTs in the epoxy resin matrix.

Dynamic mechanical response of ZrCu-based bulk metallic glasses

The thermal stability and the dynamic mechanical relaxation behavior of (Zr50Cu40Al10)100-xDyx (at.%) (x = 0 or 2) metallic glasses were investigated by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). In the case of the (Zr50Cu40Al10)100-xDyx (x = 0 or 2) metallic glasses, atomic mobility increases by introduction of the Dy element. The activation energy of the the main a relaxation process and fragility index were discussed according to the DMA measurements. With the help of the time-temperature superposition (TTS) principle, the master curves of the model alloys were established, the Kohlrausch-Williams-Watts (KWW) function and quasi-point defects (QPD) theory were used to descirbe the master curves of the metallic glasses. The characteristic parameters related to microstructural heterogeneity in the KWW equation and the QPD model, Kohlrausch exponent βKWW and the correlation factor χ were evaluated. In parallel, the elastic, viscoelastic and viscoplastic responses of the model alloys have been analyzed based on the DMA results. Our investigations demonstrated that introduction of the Dy increases the structure heterogeneity of the (Zr50Cu40Al10)100-xDyx (x = 0 or 2) glassy system, which plays an important role in tailoring the dynamic relaxation behavior and mechanical properties of the metallic glasses.

The Influence of the Furan and Maleimide Stoichiometry on the Thermoreversible Diels–Alder Network Polymerization

In recent work, the thermoreversible Diels–Alder reaction between furan and maleimide functional groups has been studied extensively in the context of self-healing elastomers and thermosets. To elaborate the influence of the stoichiometric ratio between the maleimide and furan reactive groups on the thermomechanical properties and viscoelastic behavior of formed reversible covalent polymer networks, a series of Diels–Alder-based networks with different stoichiometric ratios was synthesized. Differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and dynamic rheology measurements were performed on the reversible polymer networks, to relate the reversible network structure to the material properties and reactivity. Such knowledge allows the design and optimization of the thermomechanical behavior of the reversible networks for intended applications. Lowering the maleimide-to-furan ratio creates a deficit of maleimide functional groups, resulting in a decrease in the crosslink density of the system, and a consequent decrease in the glass transition temperature, Young’s modulus, and gel transition temperature. The excess of unreacted furan in the system results in faster reaction and healing kinetics and a shift of the reaction equilibrium.

Investigation of the mechanical and electrical properties of SnS filled PVP/PVA polymeric composite blends

In the current work, the mechanical and electrical properties of SnS filled PVP/PVA polymeric composite blends have been investigated. SnS (0 to 10.0 wt%) filled PVP/PVA (50/50) polymeric composite blends were prepared via solution casting method. A scanning electron microscope instrument was used to examine the surface morphology of the prepared composite blends. A dynamic mechanical analyzer (DMA) was utilized to investigate the mechanical properties of the prepared samples over a temperature range from 298 to 450 K. DMA measurements reveal that the storage modulus and stiffness of the neat film are doubled via SnS filling. Also, the obtained glass transition temperature (Tg) values of all SnS filled PVP/PVA polymeric composite blends are shifted to higher ones as compared with that of the neat blend. The electrical properties of the prepared samples are studied over the temperature range from 298 to 450 K. The dc electrical conductivity (σ) of the neat PVP/PVA polymeric blend is also enhanced by SnS filling. Moreover at any temperature, σ of the prepared PVP/PVA polymeric composite blend increases as the concentration of SnS is increased up to 10.0%. The activation energy of the prepared composite blends is determined. The prepared SnS filled PVP/PVA polymeric composite blends could actively play a great role in industrial applications.

Tensile Strength of PMMA/n-ZrSiO<sub>4</sub> Composites Using Dynamic Mechanical Analyzer (DMA)

This study aimed to determine the tensile strength and strain properties of poly(methyl methacrylate) (PMMA)/nano-zircon (n-ZrSiO4) composites with various nano-zircon sizes. Wet milling method for 5 and 15 h without annealing treatment was used to obtain the nano-zircon powders. Results showed that milling for 15 hours can reduce zircon size up to 93 nm. Meanwhile, the composites were synthesized with zircon compositions of 1, 2.5, and 5 wt.%. Dynamic Mechanical Analyzer (DMA) measurement were carried out to characterize the tensile-strain dependence on filler compositions of the PMMA/n-ZrSiO4 composites. The PMMA/n-ZrSiO4 composite with 5 wt.% and 15h milling zircon exhibited the highest tensile strength, ca. 10.02 MPa or 2 times of the pure PMMA. The tensile strength of the composites can be explained from the mean size and size distribution of the filler.

Development of Toughened Flax Fiber Reinforced Composites. Modification of Poly(lactic acid)/Poly(butylene adipate-co-terephthalate) Blends by Reactive Extrusion Process.

The presented study focuses on the development of flax fiber (FF) reinforced composites prepared with the use of poly(lactic acid)/poly(butylene adipate-co-terephthalate)—PLA/PBAT blend system. This type of modification was aimed to increase impact properties of PLA-based composites, which are usually characterized by high brittleness. The PLA/PBAT blends preparation was carried out using melt blending technique, while part of the samples was prepared by reactive extrusion process with the addition of chain extender (CE) in the form of epoxy-functionalized oligomer. The properties of unreinforced blends was evaluated using injection molded samples. The composite samples were prepared by compression molding technique, while flax fibers reinforcement was in the form of plain fabric. The properties of the laminated sheets were investigated during mechanical test measurements (tensile, flexural, impact). Differential scanning calorimetry (DSC) analysis was used to determine the thermal properties, while dynamic mechanical thermal analysis (DMTA) and heat deflection temperature (HDT) measurements were conducted in order to measure the thermomechanical properties. Research procedure was supplemented with structure evaluation using scanning electron microscopy (SEM) analysis. The comparative study reveals that the properties of PLA/PBAT-based composites were more favorable, especially in the context of impact resistance improvement. However, for CE modified samples also the modulus and strength was improved. Structural observations after the impact tests confirmed the presence of the plastic deformation of PLA/PBAT matrix, which confirmed the favorable properties of the developed materials. The use of PBAT phase as the impact modifier strongly reduced the PLA brittleness, while the reactive extrusion process improves the fiber-matrix interactions leading to higher stiffness and strength.

Reinforcement of bio‐based network polymer with wine pomace

AbstractPolymer materials prepared using renewable resources such as agricultural and food wastes would lead to a sustainable society. Our target was a synthesis of fiber‐reinforced network polymer derived from citrus oil and wine pomace. Lignocellulose nanofiber (LCNF) was successfully prepared from wine pomace by mechanical fibrillation using disk mill grinder under wet condition, followed by freeze‐drying. The resultant LCNF with coarse powder‐like (the untreated LCNF) enabled to reinforce bio‐based network polymer derived from limonene oxide even though heterogeneously dispersed LCNF was observed in the polymer matrix. Polymer/LCNF composite material with almost homogeneously dispersed LCNF was obtained using LCNF prepared from alcohol‐exchange process prior to freeze‐drying (the alcohol‐exchanged LCNF). Tensile strength of the network polymer reinforced by 2% of alcohol‐exchanged LCNF was around 3.2 times higher than that of the polymer without any LCNF. Dynamic mechanical analysis measurement exhibited that cross‐link density of the network polymer reinforced by 2% of alcohol‐exchanged LCNF was around 1.4 times higher than that of the neat polymer. It is noted that the cross‐linker for bio‐based network polymer, branched polyethyleneimine, likely acted as a dispersing agent for LCNF.

Recrystallization Behavior and Mechanical, and Carbonizing Properties of Feather Keratin Resin Sheets Produced by Hot-Compression Molding

Resinification of milled waterfowl feathers was attempted via a conventional hot-compression molding and its resinification behavior and the physical properties of the resultant resin were investigated. The hot-compression molding using the wet feather powder was found to be effective to achieve full resinification of the feathers, suppressing its thermal decomposition. The starting milled feathers showed a halo X-ray diffraction (XRD) scattering, indicating the destruction by the milling of the four fold screw crystal structure embedded in the feather microfibrils. Fourier-transform infrared (FTIR) spectroscopic measurements revealed that the amide I peak of the pristine feathers was slightly shifted to the higher wavenumber side by milling or resinification, which means a decrease in the strength of hydrogen bonds between the adjacent β-strands. After the hot-press compression molding, a non-oriented crystalline WAXD peak was clearly recognized again, indicating the partial recrystallization of the feather keratin. The glass transition temperature of the feather keratin resin was estimated at around 120 °C from the onset of the increase of the loss modulus (E″) in the dynamic mechanical analysis (DMA) measurements. Further, it was confirmed that resinification of the milled feathers followed by the hydrothermal treatment could produce a carbonizing precursor having stacked polyaromatic carbon clusters which may be applicable to design a functional electrode.

Extruded PLA Nanocomposites Modified by Graphene Oxide and Ionic Liquid.

Polylactic acid (PLA)-based nanocomposites were prepared by twin-screw extrusion. Graphene oxide (GO) and an ionic liquid (IL) were used as additives separately and simultaneously. The characterization of the samples was carried out by means of Fourier transform infrared (FT-IR) and Raman spectroscopies, thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The viscoelastic behavior was determined using dynamic mechanical analysis (DMA) and rheological measurements. IL acted as internal lubricant increasing the mobility of PLA chains in the solid and rubbery states; however, the effect was less dominant when the composites were melted. When GO and IL were included, the viscosity of the nanocomposites at high temperatures presented a quasi-Newtonian behavior and, therefore, the processability of PLA was highly improved.

From Understanding Mechanical Behavior to Curvature Prediction of Humidity-Triggered Bilayer Actuators.

Nature will always be an endless source of bioinspiration for man-made smart materials and multifunctional devices. Impressively, even cutoff leaves from resurrection plants can autonomously and reproducibly change their shape upon humidity changes, which goes along with total recovery of their mechanical properties after being completely dried. In this work, simple bilayers are presented as autonomously moving, humidity-triggered bending actuators. The bilayers-showing reproducible bending behavior with reversible kinematics and multiway behavior-are studied in terms of their mechanical behavior upon humidity changes. The active layer consists of a highly conducting polymer film based on poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) with poly(dimethylsiloxane) (PDMS) as passive layer. The response to humidity is explored with dynamic mechanical thermal analysis and quartz crystal microbalance measurements. Introduction of a composite beam model allows to predict the curvature of the actuators with input from the rheological measurements. It is clearly demonstrated that volumetric strain and Young's modulus, both heavily influenced by the water uptake, dominate the bending behavior and therefore the curvature of the actuators. This loop of rheological characterization coupled with an analytical model allows to predict curvatures of in principle any complex geometry and material combination for moving parts in soft robotics.

Properties and Degradation of Novel Fully Biodegradable PLA/PHB Blends Filled with Keratin.

The utilization of keratin waste in new materials formulations can prevent its environmental disposal problem. Here, novel composites based on biodegradable blends consisting of poly(lactic acid) (PLA) and poly(3-hydroxybutyrate) (PHB), and filled with hydrolyzed keratin with loading from 1 to 20 wt % were prepared and their properties were investigated. Mechanical and viscoelastic properties were characterized by tensile test, dynamic mechanical thermal analysis (DMTA) and rheology measurements. The addition of acetyltributyl citrate (ATBC) significantly affected the mechanical properties of the materials. It was found that the filled PLA/PHB/ATBC composite at the highest keratin loading exhibited similar shear moduli compared to the un-plasticized blend as a result of the much stronger interactions between the keratin and polymer matrix compared to composites with lower keratin content. The differences in dynamic moduli for PLA/PHB/ATBC blend filled with keratin depended extensively on the keratin content while loss the factor values progressively decreased with keratin loading. Softening interactions between the keratin and polymer matrix resulted in lower glass transitions temperature and reduced polymer chain mobility. The addition of keratin did not affect the extent of degradation of the PLA/PHB blend during melt blending. Fast hydrolysis at 60 °C was observed for composites with all keratin loadings. The developed keratin-based composites possess properties comparable to commonly used thermoplastics applicable for example as packaging materials.

Design of epoxy-silica hybrids based on cycloaliphatic diol of natural origin for conservation of lithic materials

This work is focused on the development of sustainable stone conservation materials, based on BPA-free epoxy-silica hybrid resins, with consolidating and hydrophobic properties, for long-term treatments. For this purpose, a cycloaliphatic diol, with minor health and environmental associated issues with respect to classic phenolic derivatives, was selected to synthesize a BPA-free bio-based epoxy resins precursor, 2,2,4,4-tetramethyl-1,3-cyclobutanediol diglycidylether (CBDO-DGE). Fourier transform infrared (FT-IR) and Raman spectroscopies were employed to assess the synthesis and clean-up procedures. In addition, both 1H-NMR and 13C-NMR in solution were used to ascertain the structure and purity of the bio-based epoxy. The development of the epoxy thermosets by 1,8- diaminooctane (DAO), triethylenetetramine (TETA) and 5-amino-1,3,3-trimethylcyclohexanemethylamine (IPDA) curing agents was followed by attenuated total reflection infrared (ATR FT-IR) and Raman spectroscopies, whereas their suitability as organic counterpart of the hybrids was established by differential scanning calorimetry (DSC) and thermogravimetric (TGA) measurements. In addition, epoxy-silica hybrids were obtained by exploiting sol-gel technology, carrying out the epoxy hardening reactions also in the presence of (3-glycidyloxypropyl)trimethoxysilane (GPTMS) and octyltriethoxysilane (OcTES), as silica-forming additives. To investigate the properties of the resulting hybrid materials imparted by the selection of the different reactants, various blends were studied by a combination of scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM-EDS), ATR FT-IR and Raman analysis. Furthermore, the assessment of the hybrids tunability as materials for stone conservation was ascertained in terms of thermostability and hydrophobicity by TG-DTA, DSC, dynamic mechanical analysis (DMA) and contact angle measurements.

The role of ionic clusters in the determination of the properties of partially neutralized ethylene-acrylic acid ionomers

Ionomers with different degree of neutralization were prepared from an ethylene-acrylic acid copolymer of 8.5 wt% acrylic acid content. The ionomers were characterized by Fourier transform infrared spectroscopy, small angle X-ray scattering, differential scanning calorimetry and dynamic mechanical thermal analysis measurements as well as rheology and tensile testing. The main relaxing species in ionomers are the methylene groups and the ethylene-acrylic acid copolymer segments. The mobility of these latter decreases upon neutralization and above a critical degree of neutralization a phase consisting of polyethylene segments attached to ionic clusters forms. The crystalline structure of the polymer contains primary and secondary crystallites. The amount and regularity, i.e. lamella thickness, of the latter decrease with increasing neutralization. Multiplets form from ionic species already at a small degree of neutralization and then they associate into clusters with increasing size as ion content increases. The mechanical properties of the ionomers are determined by their crystalline structure and cluster formation. Clusters increase strength and modulus, while decrease deformability. The combined effect of the two factors (crystallinity, cluster size) on stiffness was successfully described by a simple model.

Synthesis, characterization and applications of poly(vinyl chloride) nanocomposites loaded with metal oxide nanoparticles

Metal oxide (i.e., Fe2O3, ZnO and TiO2) nanoparticles (NPs) have been prepared and investigated by various techniques with the objective of synthesis of nanocomposites thin films based on poly(vinyl chloride) (PVC) as a matrix. Different loadings of metal oxide NPs (i.e., 2.0, 5.0, 10.0 and 15.0 wt%) were incorporated in PVC followed by solution casting. The prepared film samples were characterized by X-ray diffraction (XRD), Raman spectra, scanning electron microscopy (SEM), dynamic mechanical analysis (DMA), thermal and electrical measurements. Also, the antibacterial activity was tested against Gram-positive (i.e., Bacillus subtilis and Staphylococcus aureus) and Gram-negative bacteria (i.e., Escherichia coli and Pseudomonas aeruginosa). The results were discussed in relation to metal oxide NPs content and type. XRD of the prepared nanocomposite films was almost the same as that of mixed ZnO metal oxide NPs with an amorphous region of PVC. Raman spectra suggested that ZnO NPs were just physically inserted into PVC matrix. SEM revealed a homogeneous distribution of the NPs on using 10 wt% in PVC matrix, while the NPs agglomerations at higher content (i.e., 15 wt%) were formed. The dynamic mechanical results, as a function in temperature, indicated an increase in the storage and loss moduli and a decrease in loss factor tan δ with shifting to higher glass transition temperature, with increasing metal oxide NPs content up to 10 wt%. Thermal gravimetric analysis revealed that utilizing Fe2O3 and TiO2NPs in PVC matrix improved thermal stability of PVC in comparison with ZnO NPs with catalytic behavior and polymer decomposition acceleration. Metal oxide Nps increased the electrical conductivity of PVC, the electrical conductivity values were found to be in the order of 10−13 for ZnO, while it is in the order of 10−11 for Fe2O3 and TiO2. This finding is highly recommended such composites to be used in antistatic applications as the needed range for such application is 10−9–10−14Ω−1 cm−1. Metal oxide nanocomposites improved the antibacterial activity of PVC toward both types of bacteria and can be used as an effective antibacterial agent in biomedical healthy applications.

Circular arc rules of complex plane plot for model parameters determination of viscoelastic material

We present a new approach to determine the rheological parameters of a mechanical model of viscoelastic materials. The fractional derivative solid model composed of a spring in series with a fractional derivative Kelvin–Voigt element has been employed to characterize the dynamic mechanical response of a real viscoelastic material. In dynamic mechanical analysis (DMA) measurements, the frequency-dependent loss modulus is plotted against the storage modulus in the form of complex plane plot. We find that the complex plane plot of the fractional derivative solid model is a depressed or distorted semicircle with its center below the real axis. The model parameters could be identified graphically via its complex plane curve, from which the spring constants can be obtained through the two intercepts of the extrapolated circular arc with the real axis, whereas the order of fractional dashpot can be estimated by the displacement of the semicircle center. The graphical method allows us to easily find rheological parameters, without using complicated calculation and special algorithms.

Influencing parameters on measurement accuracy in dynamic mechanical analysis of thermoplastic polymers and their composites

Long-term predictions of material properties such as stiffness and creep resistance are important in many engineering applications and require high reliability and accuracy. This is especially true for polymer materials and their composites as their viscoelastic nature results in time-dependent material behaviour and any measurement uncertainties or errors amplify in long-term predictions. To measure this behaviour at smallest loadings, Dynamic Mechanical Analysis (DMA) is frequently declared as an ideal method. However, the measurement accuracy and repeatability of this method is strongly influenced by (i) the testing fixture and corresponding loading mode, (ii) the sample preparation and (iii) the plotting scale to interpret the test results. In this study, relevant experimental parameters were found for DMA and a proper procedure was designed, which was then applied to measure the viscoelastic behaviour of a highly temperature and creep resistant thermoplastic polymer (polyethersulfone) and of a highly graphite filled polypropylene composite. In combination with finite element simulations and in-situ strain measurements by digital image correlation (DIC), the main influences on measurement accuracy of three-point-bending DMA were identified and subsequently used to determine measurement guidelines. Using these guidelines, DMA measurements allow quantitative determination of the viscoelastic response for rigid polymer and composite materials.