DMA measurements

The DMA characterization was made of the series of polymers denoted PU 1 to PU 5 as listed in Table 3.11. The samples were tested in the tensile mode with a starting distance between the clamps of 45 mm. The cooling conditions were room temperature till -60°C cooling rate of 10 K/minute, -60°C to -120°C 3.5 K/min and -120°C to -140°C 2 K/min. The test started at -140°C and the complex modulus , storage modulus loss modulus E and the loss factor were measured as function of temperature at a heating rate of 1 K/min. The instrument was operated with controlled sinusoidal force with a frequency of 1 s  

Depending on the material structure and on the conformation of diisocyanate, there were observed large differences between the modulus and tan (5 loss factors respectively. The material 3, obtained with MDI via the one shot technique in melt (Table 3.11), showed an amorphous structure. The modulus above Tg was the lowest of all the materials, and correspondingly the loss factor tan in the glass transition region was the highest. For the samples PU 1, 2, 4 and 5 (DBDI, one shot), the Tg values ranged between -28°C (PU 2) and -14°C (PU 3), while tan varied between 0.127 (PU 2) and 0.394 (PU 3). 

Example selected DMA curves of selected materials listed in Table 1.1 are shown in Fig. 3.19-3.22. 

---

Dynamic mechanical anlaysis (DMA) measurements were done on a Rheometrics RDS-7700 rheometer in torsional rectangular geometry mode using 60 x 12 x 3 mm samples at 0.05% strain and 1 Hz. Differential scanning calorimetry (DSC), thermomechanical analysis (TMA), and thermogravimetric analysis (TGA) were performed on a Perkin-Elmer 7000 thermal analysis system. 

Glass transition temperatures as obtained from DMA measurements (no = 10 Hz)... 

The investigated polypropylenes are difficult to categorize. While PE 5031 L fits in the above findings and apparently is mainly attrited by sliding friction as expected from analysis of the DMA measurements, PE 2420 H does not fit into this scheme. Here different mechanisms like adhesion might play an important role, which can be neglected for the other polymers. 

Tg for a linear, high-molecular-mass PPO, which was prepared from a polypropylene glycol precursor (with a molecular mass of 4000 g/mol) using a chain extender with a chemical structure similar to that of the crosslinker, is -62.5 °C. The Tg was determined from DMA measurements performed at 0.215 Hz [43]. 

Tg values can be determined via either calorimetric, dynamic scanning calorimetry (DSC) or mechanical dynamic mechanical analysis (DMA) measurements. However, since three dimensional highly crosslinked systems have relatively small amounts of molecular motion, the DSC method is not particularly sensitive for Tg determination [131,132]. Fry and Lind have reported that DSC is misleading, as reactive groups are often sufficiently entrapped in the vitrified structure to give spurious results [133]. 

Figure 5.16 Modulus of elasticity (E ) of simple fatty esters and mixed acetic-fatty triesters of cellulose (DMA measurements)...

Scanning electron micrographs were taken with an ISIDS-130 microscope. Thermogravimetric analysis (TGA) was performed with an SDT Q600 (TA Instruments). A Seiko DMS 210 dynamic-mechanical analyzer was used for DMA measurements. For water content determination samples were allowed to equilibrate over saturated salt solutions in sealed jars at controlled relative... 

Figure 10.12. Temperature dependence of the storage modulus E and loss modulus E" of different PEEK/SWCNT nanocomposites with 1 wt% CNT content, obtained from DMA measurements performed in the tensile mode at frequency 1 Hz and heating rate of 2°C/min. The inset is a magnification showing the increment in Tg for the nanocomposites. From ref 11.

A Fortran based program was developed to generate nomograph plots directly from data generated by fixed frequency multiplex DMA measurements. The program can be executed on any IBM XT or compatible and requires a Hewlett Packard plotter to generate the nomographs. 

One instmment capable of measuring the dynamic shear modulus is a dynamic mechanical analyzer (DMA). A DMA measures the viscoelastic properties of a material by measuring the mechanical response that is deformed under periodic stress. Operation of a DMA tool offered by TA Instruments is as follows The sample is clamped between the ends of two parallel arms, which are mounted on low-force flexure pivots, allowing motion only in the horizontal plane. The distance between the two arms is adjustable by means of a precision mechanical slide to accommodate a wide range of sample lengths (from < 1 mm up to 65 mm). An electromagnetic motor attached to one arm drives the arm/sample to a strain (amplitude) selected by the operator. As the arm/sample system is displaced, the sample undergoes a flexural deformation [as depicted schemati-... 

In a study of initially incompatible blends of SAN and PC (30 70) extrusion at a high shear rate of up to 10 s produced a blend in the first extrusion run in which the minor constituent (SAN) was present as small spherical particles in PC (Takahashi et al, 1988). The apparent volume fraction of the spherical SAN decreased with the shear rate and repeated extrusion. The DMA measurements showed that the maximum of tan (5 for PC shifted to lower temperatures with repeated extrusion, which is consistent with some SAN being mixed with PC in a compatible form. This result suggests that compatibility is enhanced in extremely-high-shear-rate processing. Because of the rapid quench from an elevated temperature that occurs after processing, this new structure may be retained. 

Readers interested in a more in-depth understanding of data obtained from DMA measurements can refer to pol mier rheology textbooks. Some of the available helpful books published in this area as listed in Refs. 14-16. 

DMA measurements are intensively used to investigate the amorphous phase transitions of polymers. The results of DMA studies were published by authors like Schmieder and Wolf [2], Nielsen and Buchdahl [3] and Heijboer [4]. Neat polymers, but also polymer blends and polymer systems blended with fillers, plasticisers or impact improvers were investigated by DMA. An example of such an application is given for toughened polypropylene in 4.1.2. 

The rubber addition results, as expected, in the presence of a low temperature rubber loss maximum. The DMA measurements also show, however, that a part of the added rubber phase influences the intensity of both PP relaxation effects. Such an effect might be important for the toughening efficiency of the used type of rubber. 

The results of the DMA measurements on a PK terpolymer sample after 720 hours of ageing in an exsiccator under vacuum and a temperature of about 21°C... 

Results of DMA measurements on a Vectra B950 compression moulded (5 min / 290°C) sample... 

The measurements were performed with an automated torsion pendulum (DMA) apparatus working at a frequency of about 0.5 Hz. (varying frequency system, see Chapter 4). The use of a low-stiffness suspension wire permitted stiffness measurements as low as 5H4 N/m2. These DMA measurements were performed from 50°C up to 250°C using a heating rate of l°C/minute the samples were, during these experiments, purged with nitrogen. 

DMA measurements on a series of UHMW-PP/J-grade PP showed that such a physical network is able to "carry" a considerable amount the standard J-grade PP before the rubbery plateau of the UHMW-PP collapses. The results in Figure 10.10 show that for a blend of UHMW-PP/J-grade PP (60/40) the rubbery plateau is still present up to 250°C. This rubbery plateau starts to disappear quickly for J-grade concentrations higher than 40 %wt. 

So, if the interfacial regions have to be considered, we must differentiate the amorphous/crystal polymer interface from the amorphous polymer/mineral interface (29). By DMA measurements, a decrease in Tg matrix from 7°C for the PP/talc composites and also for the neat PP processed under similar conditions while a decrease upto 13°C was found for PP/mica composites. A higher fraction of free amorphous phase on the PP/mica system than on the PP/talc composites was evidenced. This free amorphous phase appeared to participate in the cooperative segmental free-rotation motion, well accepted (30) to be responsible for glass transition for the polymer matrix as fully discussed in Reference 29. 

Right-hand plots in the same Fig. 13.6 allows to conclude the well-optimized material performance from the macroscopic up to the mesoscales by the correspondence between the elastic modulus component obtained from the tensile tests and the elastic component of complex modulus from the DMA measurements performed at room temperature and which ratio results to be independent of the grafting level in the interfacial modifier (32,55). 

Figure 16.34 Representative sample probe shapes for TMA and DMA measurements. (Courtesy of PerkinElmer, Inc. Shelton, CT, www.perkinelmer.com.)...

T s, 10-20. Kean deviations shown are fron the average of 2 experiicents bUatlve DMA measurements at 32 0. 

The authors are grateful to HASYLAB for beamtime within the projects 11-20060086 and I-20100280 and A. Timmann, J. Perlich and M. A. Kashem for local support, and N. Stribeck (University of Hamburg) for the support in the course of data evaluation. They thank their colleagues from the IFF for support, in particular V. Korber for the construction of the tensile rig, W. Jenschke for the software support for the tensile rig, R. Boldt for SEM micrographs, R. Vogel and R. Jurk for DMA-measurements, and D. Krause for sample preparation. 

The viscoelastic behavior of biomaterials is typically measured using DMA. In rheological terms, viscoelastic is the concomitance of viscous (fluid-like) and elastic (solid-like) elements. The proportion of viscous and elastic properties is depending on the used material as well as on the measuring conditions such as the temperature. In DMA measurements, a sinusoidal shear load is applied to the sample while measuring the shear stress (cr ) with a stress transducer. The strain induced... 

In addition, Tg determined through DMA measurements is obtained at a prescribed heating rate and dynamic loading frequency (see Table 2.2). It is found that the Tg values may change with the heating rate [3] or frequency [13], therefore it is necessary to specify the heating rate and frequency for the T value measured. 

DMA measures the ability of the material to store and dissipate mechanical energy. DMA properties of the elastomeric materials are important because they often correlate to actual field performance. This method determines the storage modulus (G, elastic behaviour), loss modulus G", energy dissipation), tan 8, loss compliance (J ) and Tg values. In this work, the DMA method was effectively utilised to understand the advantages of HER over the butanediol extended elastomer. The results are summarised in Table 8.18. 

Dynamic mechanical analysis (DMA) is a sensitive method for glass transition temperature measurement, for detection of side-chain and main-chain motions, and for local mode relaxation measurements. Loeal mode relaxation can not be measured by DSC. DMA can give information about the crosslinking process of modified phenolic prepolymer [218] and about the erosslinked material [132]. During DMA measurements, sinusoidally varying stress of frequency is applied to the sample. Frequency and the stress are connected by equation 57, where is the maximum stress amplitude and is the phase angle at which the stress proceeds the strain. 

The DMA measures the deformation of a material in response to vibration forces or sinusoidal wave. The storage modulus E refers to stiffness of material and tan 5 gives the amount of energy dissipated as heat during deformation (Nielsen Landel 1974). The investigation of dynamic storage modulus and internal friction over a wide range of temperature and frequencies has proven to be... 

The specimens for the DMA measurements were prepared as graphite-fiber reinforced resin composite sheets in which the fibers were in the form of a woven cloth, designated as T300-3000, 13 X 13 weave (Union Carbide Thornel 300 yarn, woven by Hexcel). To prepare a specimen, four thicknesses of cloth, in a bidirectional fiber lay, were saturated with resin, vacuum-pumped to remove trapped air, laid smoothly between two sheets of 0.025 mm polyethylene and irradiated to a total dose of 100 kGy. The irradiation was performed at the NRL Van de Graaff accelerator facility with electrons having an energy of 2 MeV. The composites, thus made were approximately 1 mm thick and contained approximately 60 wt percent resin. The specimens cut from these sheets were approximately 10 x 12.5 mm and were measured to the nearest 0.1 mm before inserting into the clamps of the DMA. 

---