Virtual Dynamic Mechanical Analysis

A series of polyurethane networks were prepared from MDI (4,41-diphenyl methane diisocyanate), ethylene glycol and a polyoxyethylene-tipped polyoxypropylene triol. The phase separation and phase inversion phenomena of these polyurethane networks were investigated by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and measurement of their tensile properties. The DSC and DMA data indicate that the segmented copolyurethanes possess a two-phase morphology comprising soft and hard segments. It can be found from DSC data that the polyether soft segments exhibit a Tg (glass transition temperature) of −60 °C, and the aromatic hard segments display a Tg of about 128 °C. Two Tgs corresponding to the comprised segments can also be found by DMA for some segmented polyurethanes. Varying the content of aromatic hard segments over the range from 0 to 80 wt% changes the material behavior from a soft rubber through a highly extensible elastomer to a brittle semi-ductile glassy material. Based on the property-composition plots, phase inversion appears to occur at a hard segment content of about 50 wt%.

In order to study the glass transition temperature and low temperature performance of foam warm mix asphalt (FWMA), we have prepared the FWMA samples with different asphalt types and different foaming water contents (FWC). Glass transition temperatures of the samples are determined by using dynamic mechanical analyzer (DMA) and differential scanning calorimetry (DSC) methods, and their low temperature performancesare evaluated by using bending beam rheometer (BBR) method. Results show that for different asphalt types and FWC, the behaviors of glass transition temperatures determined by DMA and DSC are different, but their changing trends are similar.With the increase of FWC, the glass transition temperature of asphalt increases gradually.The addition of foam water damages the low temperature cracking resistance of asphalt to a certain extent.Foaming water with a mass fraction of 6% could not meet the low temperature requirement below -12 °C, and could not satisfy the application scope of the non-foaming asphalt at low temperature.In order to ensure good pavement performance of FWMA, the low temperature cracking resistance must be taken as the priority consideration for choosing the optimal FWC.

Determination of the glass transition temperature of latex films: Comparison of various methods

ABSTRACTThis work applies different thermal analysis methods to polymer based materials degradation, studying the degradation process itself and evaluating the degree of material damage as a consequence of chemical degradation by thermal or radiation effects. On the one hand, thermal degradation in varied atmospheres is investigated by means of thermogravimetric analysis (TGA) in dynamic experiments. The authors find that the evolution of the sample mass follows a mixture of logistics models, and these can fit an overall TGA curve. The fitting parameters have important physical meaning related to the kinetics of the different processes involved and to the relative amount of each component in the sample. The method itself entails separating overlapping processes. Other improvements made by the authors are related to reducing the noise and smoothing the TGA and differential scanning calorimetry (DSC) data, particularly when estimating TGA derivatives through logistic regression.Analyzing many materials by means of TGA results in more or less complex traces that do not allow a simple parametric fit like the one described above. Although it reproduces asymptoticity at the beginning and end of the reaction, there are times when many processes overlap, resulting in a complex trace that would need a high number of logistic components to be adequately fitted. However, it is possible to use a local polynomial regression model instead. This is also applicable to DSC traces, whose shapes are totally different from those found in TGA. The authors propose a model based on a nonparametric estimation, where the fit's suitability very much depends on the bandwidth selection, especially where derivatives are concerned. The proposed model gives a satisfactory fitting. It smoothes noise and always provides reliable values, different from those obtained by other methods strongly dependent on user choice.On the other hand, to evaluate the degree of damage by thermal analysis methods, dynamic mechanical analysis (DMA) is applied to polyamides. The glass transition temperature is measured before and after exposure to varying doses of proton radiation, emulating the space environment. Other examples show how exposure over long periods at moderately elevated temperatures results in reduction of some mechanical properties. Additionally, the effect of different nanofillers on styrene-isoprene-styrene block copolymers is evaluated by DMA. A shift in the glass transition temperature seems to be dependent on nanofiller content. The degradation of some materials suitable for space applications, such as polyethylene and polyamide, are also briefly reviewed.

ABSTRACTThermal behavior of a coextruded microlayer composite with 388 alternating layers of polycarbonate and polymethyl methacrylate (PMMA) was investigated using differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). Two distinct glass transition temperatures were observed with DSC for the coextruded composite, however both were shifted very slightly towards each other, compared to the glass transition temperatures of the pure components, indicating limited miscibility. Adhesion between the alternating microlayers appeared to be very good; delamination did not occur after the microlayer composite was subjected to a high speed impact test. Adhesion is attributed to limited miscibility since little mixing resulted from the laminar flow which was required in the coextrusion process. DMA results revealed an additional damping peak, which was not observed with DSC, at a temperature between the glass transitions of the two components. This intermediate transition peak is more sensitive to change in frequency compared to the response for the individual pure components.

Acid surface modified carbon nanotube (MCNT)‐, carbon nanotube (CNT)‐filled fluoroelastomer (FE), and unfilled‐FE were prepared (MCNT/FE, CNT/FE, and FE). Dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC) showed that the glass transition temperature (Tg) of MCNT/FE is less than that of CNT/FE and FE. The storage modulus of CNT/FE is higher than that of MCNT/FE over the whole temperature range. Storage modulus in rubbery state is higher in the case of MCNT/FE when compared to FE, however, in glassy state, it is slightly higher. For MCNT/FE at glassy and rubbery state, loss modulus is less than that of CNT/FE. Loss modulus in rubbery states is higher in the case of MCNT/FE compared to FE and in glassy states for both are the same. The DSC, DMA, and X‐ray diffraction (XRD) results confirmed that the FE and filler/FE is partially crystalline mostly in γ‐form. MCNT and CNT together with shear and high temperature, induced γ‐crystallinity in the FE, γ‐phase melting of MCNT/FE is higher than that of CNT/FE and FE. Most probably MCNT/FE obeys behaviors of thin films with high surface energy substrate interactions, while in CNT/FE the substrate surface energy is lower. XRD and DSC showed that MCNT causes more γ‐crystallinity in FE compared to others. Tetrafluoroethylene segments crystals have the degree of crystallinity in the order of CNT/FE > MCNT/FE > FE. The γ–phase crystal size is in the order of FE > CNT/FE > MCNT/FE. XRD, DSC, and DMA results for FE and filler/FE confirmed each other. POLYM. COMPOS., 37:3341–3353, 2016. © 2015 Society of Plastics Engineers

A dynamic mechanical thermal analysis (DMTA) was performed on allylester polymers and composites filled with alumina. We determined the glass transition temperatures and the values of the storage moduli in both the glassy and rubbery states in each system and compared the mechanical-thermal behavior of pristine allylester polymers with that of composites filled with alumina. To supplement the result of DMTA, we also carried out viscometry, gel permeation chromatography, and differential scanning calorimetry. The molecular structures had an influence on the viscosity, the glass transition temperature, and the storage modulus. Allylester composite filled with 20 phr alumina showed peculiar mechanical—thermal behavior. © 1996 John Wiley & Sons, Inc.

A study of the effect of absorbed water on the Tg of a poly(amideimide) using DMA and DSC

In this work, the cure kinetics and through‐the‐thickness cure shrinkage upon curing of a carbon fiber‐epoxy composite (AS4/8552) were studied. The study is composed of two major parts. Firstly, dynamic and isothermal Differential Scanning Calorimeter (DSC) scans were performed to develop a new cure kinetics model. The most appropriate kinetic model that produces a nearly perfect fit of all data sets corresponds to a process with two single‐step parallel autocatalytic reactions with diffusion control. Multivariate kinetic analysis was used to evaluate the parameters. In the second part of the study, the coefficients of thermal expansion (CTEs), the glass transition temperatures (Tg), and the through‐the‐thickness cure shrinkage strain values of the partially cured unidirectional and cross‐ply composite samples were measured by using a dynamic mechanical analyzer (DMA). Cure strains were measured throughout the Manufacturer's Recommended Cure Cycle (MRCC) with the same method. Results indicate that glass transition temperatures of partially cured samples can be measured very closely by the two methods (DSC and DMA). The methods proposed were proved to be very reliable to predict the degree of cure and to measure the through‐the‐thickness strains during the cure cycle. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers

Effects of physical aging on the submicroscopic structure and dynamic mechanical properties of amorphous poly(ether sulfone) copolymer film were studied by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and electron‐microscopy measurements. Heat flow responses were measured after annealing the amorphous samples obtained, by quenching the melt into an ice‐water bath close to but below the glass transition temperature. The extent of aging is related to the supercooling from the glass transition temperature and to the aging time. The activation energy of the aging process was estimated by the Williams–Watt expression (Williams and Watts, Trans Faraday Soc 1970, 66, 80). A systematic study of the influence of aging on the dynamic mechanical properties of poly(ether sulfone) copolymer has also been made. During isothermal annealing, the increase of the temperature of tan δ peak for the α and β′ relaxation with aging time has been observed. The aging in the zone of the β peak has also been investigated and an interpretation of the results was proposed on the basis of foregone theories. The result of electron‐microscopy investigation indicates that poly(ether sulfone) copolymer has formed a local order structure during the physical aging. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 530–534, 2006

Synthesis of the liquid crystalline (LC) diol 6,6′-[ethylenebis(l,4-phenylene-oxy)]-dihexanol (I) is described. The structure of polyurethanes prepared from diol I and 4,4′-methylenedi(phenyl isocyanate) (MDI), 4,4′-methylenedi(cyclohexyl isocyanate) (HMDI), or 2(4)-methyl-l,3-phenylene diisocyanate (TDI) at 1:1 molar ratios of isocyanate and hydroxy groups is studied by dynamic mechanical spectroscopy, differential scanning calorimetry (DSC), polarizing microscopy, and x-ray scattering. The polymer prepared from HMDI and the diol (I/HMDI) shows, on cooling, thermal behavior typical of amorphous polymers. A frequency-temperature superposition could be applied to the mechanical data, and the horizontal shift factor satisfied the Williams-Landel-Ferry (WLF) equation. A more-complex thermal behavior was found for I/HMDI polymer during subsequent heating; above 70°C, the formation of an ordered structure takes place, and this structure melts at about 120°C. Complex thermal behavior is exhibited by I/TDI polymer. On cooling its melt, the polymer forms a nematic phase at about 80°C, which freezes into the LC glassy state. On heating, the mesophase melts, and. subsequently, a better-ordered smectic phase is formed at 95°C, which melts at 120°C. This structure buildup is accompanied by a rapid increase in storage modulus G′, and the sample shows thermorheologically complex mechanical behavior. The polymer formed from the diol and MDI (I/MDI) exhibits a most-complex thermal behavior. On cooling and heating, four transitions can be detected in its thermal mechanical behavior, and the structure of the polymer is strongly dependent on its thermal history.

Direct digital manufacturing of continuous fiber-reinforced thermoplastics exhibits the potential to relieve many of the constraints placed on the current design and manufacture of composite structures. At present, the additive manufacturing of continuous fiber-reinforced thermoplastics is demonstrated to varying extents; however, a comprehensive investigation of manufacturing defects and the quality of additively manufactured high fiber volume fraction continuous fiber-reinforced thermoplastic composites is limited. Considering the preliminary nature of the additive manufacturing of continuous fiber-reinforced thermoplastics, composites processed in this manner are typically subject to various manufacturing defects, including excessive void content in the thermoplastic matrix. Generally, quality evaluation of processed composites in the literature is limited to test methods that are largely influenced by the properties of the continuous fiber reinforcement, and as such, defects in the thermoplastic matrix are usually less impactful on the results and are often overlooked. Hardware to facilitate the direct digital manufacturing of continuous fiber-reinforced thermoplastic matrix composites was developed, and specimens were successfully processed with intentionally varied void content. The quality of the additively manufactured specimens was then evaluated in terms of the measured maximum storage modulus, maximum loss modulus, damping factor and the glass transition temperature by means of dynamic mechanical analysis (DMA). DMA allows for thermomechanical (i.e., highly matrix sensitive) evaluation of the composite specimens, specifically in terms of the measured elastic storage modulus, viscous loss modulus, damping factor and the glass transition temperature. Within the tested range of void contents from roughly 4–10%, evaluation by DMA resulted in a distinct reduction in the maximum measured storage modulus, maximum loss modulus and glass transition temperature with increasing void content, while the damping factor increased. Thus, the results of this work, which focused on the effect of void content on DMA measured properties, have demonstrated that DMA exhibits multi-faceted sensitivity to the presence of voids in the additively manufactured continuous fiber-reinforced thermoplastic specimens.

The objective of this investigation is to prepare the shape memory hydrogenated epoxy resin used for asphalt mixtures (SM-HEP-AM) and study its properties. The shape memory hydrogenated epoxy resin (SM-HEP) is prepared using hydrogenated bisphenol A epoxy resin (AL-3040), polypropylene glycol diglycidylether diacrylate (JH-230), and isophorone diamine (IPDA). The formulations of the SM-HEP-AM are obtained by the linearly fitted method. The thermo-mechanical property, molecular structure, and shape-memory performance of the SM-HEP-AM are studied. The glass-transition temperature (Tg) is determined using the differential scanning calorimeter (DSC). The results proved that the Tg level increased when the JH-230 content decreased. The thermo-mechanical property of the SM-HEP-AM is measured by dynamical mechanical analysis (DMA). The storage modulus of the SM-HEP-AM decreased with the increase in the JH-230 content. The above phenomena are attributed to the change in the JH-230 content. The shape memory performance results of the SM-HEP-AM indicate that specimen deformation can completely recover after only several minutes at Tg + 10 °C and Tg + 20 °C. The shape recovery time of the SM-HEP-AM increases with increased JH-230 content, and the change between the shape recovery time and JH-230 content gradually decreased as the temperature increased. The deformation recovery performance of asphalt mixture with and without the SM-HEP-AM (Tg = 40 °C) was tested by the deformation recovery test. This was used to prove that the SM-HEP-AM helps to improve the deformation recovery performance of the asphalt mixture.

It is crucial to adapt the processing of forest bio-resources into biochemicals and bio-based advanced materials in order to transform the current economic climate into a greener economy. Tall oil, as a by-product of the Kraft process of wood pulp manufacture, is a promising resource for the extraction of various value-added products. Tall oil fatty acids-based multifunctional Michael acceptor acrylates were developed. The suitability of developed acrylates for polymerization with tall oil fatty acids-based Michael donor acetoacetates to form a highly cross-linked polymer material via the Michael addition was investigated. With this novel strategy, valuable chemicals and innovative polymer materials can be produced from tall oil in an entirely new way, making a significant contribution to the development of a forest-based bioeconomy. Two different tall oil-based acrylates were successfully synthesized and characterized. Synthesized acrylates were successfully used in the synthesis of bio-based thermoset polymers. Obtained polymers had a wide variety of mechanical and thermal properties (glass transition temperature from –12.1 to 29.6 °C by dynamic mechanical analysis, Young's modulus from 15 to 1 760 MPa, and stress at break from 0.9 to 16.1 MPa). Gel permeation chromatography, Fourier-transform infrared (FT-IR) spectroscopy, matrix-assisted laser desorption/ionization-time of flight mass spectrometry, and nuclear magnetic resonance were used to analyse the chemical structure of synthesized acrylates. In addition, various titration methods and rheology tests were applied to characterize acrylates. The chemical composition and thermal and mechanical properties of the developed polymers were studied by using FT-IR, solid-state nuclear magnetic resonance, thermal gravimetric analysis, differential scanning calorimetry, dynamic mechanical analysis, and universal strength testing apparatus.

Polymer electrolyte membranes from fluorinated polyisoprene-block-sulfonated polystyrene: Structural evolution with hydration and heating