Mechanical analysis, dynamic

Dynamic mechanical analysis is carried out to analyze the viscoelastic properties of polymers and dynamic moduli of polymers and composite materials. In DMA, an oscillatory force is applied on the composite or neat polymer samples and the response to force is recorded in terms of strain to obtain the complex modulus and the variation in complex modulus is 

1 Dynamic Mechanical Analysis of Clay-Polymer Nanocomposites 

Studies by Becker et al. reveal that the glass transition temperature (T of the nanocomposites decreases gradually with the rise in clay concentration for all the epoxy systems irrespective of the functionality of the epoxy resin [32]. A lot of factors may contribute to such a decrease in glass transition temperature. Certain studies show significant improvement in T on the incorporation of clay platelets [85-86]. Interestingly some studies s ow a decrease in values on clay incorporation [87-88]. The following factors maybe responsible for the decrease in glass transition temperature [32]  

Clay may change the chemistry of the reaction and the organo-ions may catalyze the homo-polymerization even though it is unlikely to produce high crosslink density of epoxy-amine reaction  

The unreacted resin plasticization and low crosslinking density may result in decrease in T values. 

DMA is an analysis technique used to determine the dynamic properties of the elastomers [13, 14]. Dynamic properties of the elastomeric materials are important because they influence the performance of certain parts such as wheels and tyres. This method determines the storage modulus G (elastic behaviour), loss modulus G (energy dissipation), tan 8, loss compliance ] and glass transition temperature (Tg) values. The Tg of the soft segment can determine the low temperature behaviour of polyurethane elastomers. This is not only influenced by the nature of the soft 

The thermal stability of urethane elastomers can be determined by the DMA method. The temperature at which the storage modulus (G ) decreases significantly in the rubbery region is considered to be the limit of thermal stability of the elastomers [16]. From the G values of the elastomers, it was determined that HER extended materials were stable up to 160 °C whereas HQEE extended elastomer showed a 10 °C higher stability. 

In the temperature range between 0 and 160 °C, the loss modulus decreases into a long plateau and then starts to increase when the temperature reaches beyond 170 °C and 180 °C. This might be due to the melting of the hard segments. 

Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA) are the most widely-used techniques for characterization of thermal properties of polymers and composites. 

or DMTA (dynamic mechanical thermal analysis) as it can also be called, measures the modulus (stiffness) and damping (energy dissipation) properties of polymers as a function of temperature as they are deformed under a periodic stress. This latter criterion distinguishes this technique from the closely related one of TMA, which is a static technique. Because DMA is able to provide information on the viscoelastic properties of polymers, it has a greater capability than TMA and this is why the latter will not be included in this section, but is covered in Section 6.3.6. 

In common with most thermal analysis techniques, DMA analyses can be performed under both ramped and isothermal temperature programmes. The outputs from an experiment are elastic (storage) modulus and viscous (loss) modulus, and tan 8, which is the ratio of viscous modulus over the elastic modulus. 

The operator in a DMA experiment has a number of variables that can be set prior to running an experiment, namely the following  

Temperature programme, i.e. heating rate or isothermal conditions. 

In addition to this, the instrument can be operated using a number of different configurations to enable data to be collected on a variety of polymeric samples  

DMA is more sensitive to material transitions than traditional thermal analysis techniques (e.g., DSC, TMA). Detection of major transitions such as the Tg, for example, by DMA, is easier in highly filled or reinforced materials because the material modulus changes by several orders of magnitude at the Tg, while the material heat capacity (the basis for DSC detection) and expansion coefficient (the basis for TMA detection) changes less significantly. Moreover, the detection of weak secondary transitions is possible only by using DMA. 

Grenet, S. Marais, M.T. Legras, P. Chevalier and J.M. Saiter, Journal of Thermal Analysis and Calorimetry, 2000, 61, 3, 719. 

Kosar and Z. Gomzi, Polymer Plastics Technology and Engineering, 2004,43, 5, 1277. 

Schilling, V.L. Colvin, A. Hale and NJ. Levinos in Proceedings of the ACS Polymeric Materials Science and Engineering Conference, Dallas, TX, USA, Spring 1998, 78, 230. 

Influence of the amount of PEDOT-PSS on mechanical properties was studied using d3mamic mechanical anatysis in tension mode. Uniaxial tensile tests were carried out at 30 1°C with TA Q800 Dynamic Mechanic Analyzer. Elastic modulus and breaking points were measured by increasing ramp force 0.1 N/min to 18.0 N/min. Composite nanofibers were electrospun for three hours to measure mechanical properties. At least four specimens were tested for each measurement and the average values are presented. 

PEDOT-PSS/PVAc composites showed brittle mechanical property. A decrease in tensile strength was observed for each composition in comparison to the PVAc and tensile strength decreased with increasing PEDOT-PSS content in the composition. However, afterward PI.00 sample yield decreases, leading to more brittle fractures due to a high value of PEDOT, which has a typical mechanical property of conductive polymers (brittleness). 

The area under the stress-strain curve is toughness, which represents the total strain energy per unit volume in the material induced by the applied stress. It was seen that the toughness increases with increasing content of PEDOT-PSS in the composites up to P0.75. Increase in toughness is indicated in Table 5.2. 

Analyses show that sample P0.75 has the best mechanical properties compared to the other samples (Fig. 5.18]. The modulus strength of PVAc is improved with the addition of PEDOT-PSS. However, the increment of modulus values decreases with a high amount of PEDOT-PSS, whereas the strength is increased with increased PEDOT-PSS content, it has been observed that the modulus of PEDOT-PSS/PVAc composites is higher than that of neat PVAc. it is also observed that the average value of the maximum modulus is reduced by increased PEDOT-PSS content, revealing the limited deformation and decreased ductility of PVAc. 

The DMA of rubber-based nanocomposites has been the subject of recent research. Many literature reports describe the dynamic mechanical behavior of rubber-based nanocomposites [155, 156]. Das et al. have studied the DMA of CR nanocomposites based on montmorillonite clay and LDH [157]. The montmorillonite clay is 

On the other hand, Bhattacharya et al. have reported the plasticization effect of organically modified layered silicates on dynamic mechanical properties [13]. In this work, nanocomposites of SBR have been prepared using various nanofillers like modified and unmodified montmorillonite, SP, hectorite etc. It has been observed that the Tg shifts to lower temperature in all the nanocomposites, except for systems from hectorite and NA. This is due to the fact that clay layers form capillaries parallel to each other as they become oriented in a particular direction. Due to wall slippage of the unattached polymer through these capillaries, the Tg is lowered, which could be even more in the absence of organo-modifiers [13]. A similar type of plasticization effect is also noted in the case of the low 

Tfr is transition zone relaxation time, rte is terminal relaxation time, is reptation time 

Since the mechanical response of materials is related to the time or frequency of the imposing stress, one can measure the hierarchical characteristic relaxation times of the materials via continuous scan of imposing frequency. Often, the solid materials are characterized by the dynamic mechanical spectroscopy or dynamic viscoelastic spectroscopy, while the liquid materials are characterized by the rheometer. Nowadays, advanced instmments can measure the continuous change from liquid to solid. 

In a typical case of dynamic mechanical analysis, a small stress oscillates periodically in a sinusoidal mode with amplitude cr and frequency co, and the small strain e follows the modulation with a certain phase lag The sinusoidal stress is the imposed stimulation, and in a complex form. 

The sinusoidal strain is the detected response with a phase lag, as 

The dielectric relaxation spectroscopy can effectively measure the relaxation processes of dipoles in the polymers. Like the dynamic mechanical spectroscopy, the sinusoidal electric field is the imposing stimulation, and again in a complex form. 

Correspondingly, s is the storage dielectric constant, and e is the loss dielectric constant. The dielectric loss factor is 

The physical properties of barrier dressings were evaluated using the Seiko Model DMS 210 Dynamic Mechanical Analyzer Instrument (see Fig. 2.45). Referring to Fig. 2.46, dynamic mechanical analysis consists of oscillating (1 Hz) tensile force of a material in an environmentally (37°C) controlled chamber (see Fig. 2.47) to measure loss modulus (E ) and stored modulus (E ). Many materials including polymers and tissue are viscoelastic, meaning that they deform (stretch or pull) with applied force and return to their original shape with time. The effect is a function of the viscous property (E ) within the material that resists deformation and the elastic property (E ) 

The data in Table 2.9 represents a composite list of pertinent thermal and viscoelastic properties for barrier dressing materials, and the following observations can be drawn these data. The tensile (pull) testing results of barrier dressing are listed in Table 2.10. 

(7) Immersed in water 48 h in water 9. Porcine skin (kept moist in saline solution) 0.19 0.20 0 

The Standard Test Method for Strength Properties of Tissue Adhesive in T-Peel by Tension Loading, ASTM F 2256-03, was not employed for testing barrier dressings only porcine tissue was available in 15 cm strips that possessed thick hair on the epidermis side and a thick fat layer on the underside that was not conducive to testing. Removal of the fat layer to isolate the dermis will be necessary before testing by the T-Peel method. 

The barrier dressings were tested in tensile mode, adhered at ends, as discussed in Sect. 2.3. These tests provided good relative adhesive values (kPa) for comparing the barrier dressings for their ability to adhere to tissue. 

Under viscoelastic measurements poly(cycloalkyl methacrylates) show a loss maximum (designated y), located in the very low temperature range (T -60 °C), as illustrated in Fig. 6 in the case of poly(cyclohexyl methacrylate). Such a series of polymers has been extensively studied by Heijboer in his Ph.D. thesis [5], by performing viscoelastic studies at 1 Hz (sometimes 180 kHz) as a function of temperature and exploring quite a large number of cycloalkyls, either substituted or not. In cyclopentyl, cyclohexyl, cyclohep-tyl derivatives, the y transition was shown to occur at ca. - 185 °C (180 Hz), - 80 °C (1 Hz), - 180 °C (1 Hz), respectively. The associated activation energies, a are 13, 47, 26kJmol 1 for the cyclopentyl, cyclohexyl, cycloheptyl derivatives, respectively. 

These y transitions were assigned to motions within the alkyl cycles. In the specific case of poly(cyclohexyl methacrylate), in order to identify the pre- 

Later on, when high-resolution solid-state 13C NMR became available, these questions concerning motions within the rings of poly(cycloalkyl methacrylates) and the assignment of the specific motion occurring in the case of poly(cyclohexyl methacrylate) were revisited [6]. 

Applications General method also used in filler applications. The results give information on mobility of molecules in the presence of filler, changes in the structure of the matrix due to interaction with filler, the effect of fillers on matrix degradation, microphase separation, and other related phenomena. 

Testing procedure DMA is mostly used as a scientific tool therefore the testing procedure is selected depending on the requirements of the studies conducted. Standard methods none 

The theory and instrumentation of this technique are discussed in Section 10.1. 

DMA has also been used in curing studies on 2,2-bis(4-(2-hydroxy-3 methacryloxy propoxy)phenyl) propane and triethylene glycol dimethacrylate [15], and bisphenol A epoxy diacrylate [16]. 

1 Effect ofKenaf Whiskers Reinforcement on Storage and Loss Modulus 

The main objective of this study was to evaluate chemical, thermal and dynamic mechanical properties of the resulted nanocomposite from kenaf and cellulose acetate butyrate (CAB). Whiskers-matrix compatibility was evaluated by all of the characterizations to see the interaction between whiskers and matrix. Based on the findings, FTIR analysis showed no intermolecular hydrogen bonding between CAB and whiskers. Thermal analysis foxmd that whiskers reinforcement did not affect the decomposition temperature of resulted nanocomposite. However, good miscibility was detected 

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Other PDMS—sihca-based hybrids have been reported (16,17) and related to the ceramer hybrids (10—12,17). Using differential scanning calorimetry, dynamic mechanical analysis, and saxs, the microstmcture of these PDMS hybrids was determined to be microphase-separated, in that the polysiUcate domains (of ca 3 nm in diameter) behave as network cross-link junctions dispersed within the PDMS oligomer-rich phase. The distance between these... 

The volatile content of the treated paper is important because moisture acts as a temporary plasticizer to promote resin flow during early stages of pressing (9). Dynamic mechanical analysis of the treated paper is a very useful means to study the initial flow stages of a resin and the cure time required to complete cross-linking (10). 

Glass-transition temperatures are commonly determined by differential scanning calorimetry or dynamic mechanical analysis. Many reported values have been measured by dilatometric methods however, methods based on the torsional pendulum, strain gauge, and refractivity also give results which are ia good agreement. Vicat temperature and britde poiat yield only approximate transition temperature values but are useful because of the simplicity of measurement. The reported T values for a large number of polymers may be found ia References 5, 6, 12, and 13. 

The principal techniques for determining the microstmcture of phenoHc resins include mass spectroscopy, proton, and C-nmr spectroscopy, as well as gc, Ic, and gpc. The softening and curing processes of phenoHc resins are effectively studied by using thermal and mechanical techniques, such as tga, dsc, and dynamic mechanical analysis (dma). Infrared (ir) and electron spectroscopy are also employed. 

Dynamic mechanical analysis provides a useful technique to study the cure kinetics and high temperature mechanical properties of phenoHc resins. The volatile components of the resin do not affect the scan or limit the temperature range of the experiment. However, uncured samples must be... 

Thermal analysis iavolves techniques ia which a physical property of a material is measured agaiast temperature at the same time the material is exposed to a coatroUed temperature program. A wide range of thermal analysis techniques have been developed siace the commercial development of automated thermal equipment as Hsted ia Table 1. Of these the best known and most often used for polymers are thermogravimetry (tg), differential thermal analysis (dta), differential scanning calorimetry (dsc), and dynamic mechanical analysis (dma). 

Changes in heat capacity and measurement of T for blends have been used to determine components of copolymers and blends (126—129), although dynamic mechanical analysis has been found to give better resolution. Equations relating T of miscible blends and ratios of components have been developed from dsc techniques, eg, the Fox equation (eq. 1), where f the blend, or is the weight fraction of component 1 or 2,... 

In a similar fashion. Thermally Stimulated Current spectrometry (TSC) makes use of an appHed d-c potential that acts as the stress to orient dipoles. The temperature is then lowered to trap these dipoles, and small electrical currents are measured during heating as the dipoles relax. The resulting relaxation maps have been related to G and G" curves obtained by dynamic mechanical analysis (244—246). This technique, long carried out only in laboratory-built instmments, is available as a commercial TSC spectrometer from Thermold Partners L.P., formerly Solomat Instmments (247). 

Table 9. ASTM Standards on Dynamic Mechanical Analysis...

Thermal Properties. Spider dragline silk was thermally stable to about 230°C based on thermal gravimetric analysis (tga) (33). Two thermal transitions were observed by dynamic mechanical analysis (dma), one at —75° C, presumed to represent localized mobiUty in the noncrystalline regions of the silk fiber, and the other at 210°C, indicative of a partial melt or a glass transition. Data from thermal studies on B. mori silkworm cocoon silk indicate a glass-transition temperature, T, of 175°C and stability to around 250°C (37). The T for wild silkworm cocoon silks were slightly higher, from 160 to 210°C. 

The thermal glass-transition temperatures of poly(vinyl acetal)s can be determined by dynamic mechanical analysis, differential scanning calorimetry, and nmr techniques (31). The thermal glass-transition temperature of poly(vinyl acetal) resins prepared from aliphatic aldehydes can be estimated from empirical relationships such as equation 1 where OH and OAc are the weight percent of vinyl alcohol and vinyl acetate units and C is the number of carbons in the chain derived from the aldehyde. The symbols with subscripts are the corresponding values for a standard (s) resin with known parameters (32). The formula accurately predicts that resin T increases as vinyl alcohol content increases, and decreases as vinyl acetate content and aldehyde carbon chain length increases. 

Shock isolation is also possible usiag the dampiag characteristics of FZ elastomer. Dynamic mechanical analysis iadicates multiple transitions and a broad dampiag peak. This dampiag can be enhanced usiag formulatioas containing both siUca and carbon black fillers. 

In dynamic mechanical analysis of plastics, the material is subjected to a sinusoidal variation of stress and the strain is recorded so that 1, 2 and S can be determined. The classical variation of these parameters is illustrated in Fig. 2.55. 

The dynamic mechanical analysis of the ternary blends with 75 25 PVC-ENR bl6nd showed single Tg at all levels of XNBR concentrations, which indicates the miscibility of the system. In the 50 50 PVC-ENR blend, when the concentration of XNBR increased, the blend becomes progressively miscible. 

Thermal and thermomechanical analyses44 are very important for determining die upper and lower usage temperature of polymeric materials as well as showing how they behave between diose temperature extremes. An especially useful thermal technique for polyurethanes is dynamic mechanical analysis (DMA).45 Uiis is used to study dynamic viscoelastic properties and measures die ability to... 

A number of analytical techniques such as FTIR spectroscopy,65-66 13C NMR,67,68 solid-state 13 C NMR,69 GPC or size exclusion chromatography (SEC),67-72 HPLC,73 mass spectrometric analysis,74 differential scanning calorimetry (DSC),67 75 76 and dynamic mechanical analysis (DMA)77 78 have been utilized to characterize resole syntheses and crosslinking reactions. Packed-column supercritical fluid chromatography with a negative-ion atmospheric pressure chemical ionization mass spectrometric detector has also been used to separate and characterize resoles resins.79 This section provides some examples of how these techniques are used in practical applications. 

A difunctional bisphenol-A-based benzoxazine has been synthesized and characterized by GPC and 1II NMR (Fig. 7.39). A small of amount of dimers and oligomers also formed. Thermal crosslinking of bisphenol-A benzoxazine containing dimers and oligomers resulted in networks with relatively high Tgs. Dynamic mechanical analysis of the network showed a peak of tan 8 at approximately 185°C. 

Dynamic DSC, 409. See also Differential scanning calorimetry (DSC) Dynamic mechanical analysis (DMA), 138, 163, 241-242, 407, 409... 

Mechanical properties. See also Dynamic mechanical analysis (DMA) of polyamides, 138 of polyester LCPs, 52 of polyurethanes, 242-244 of semicrystalline aromatic-aliphatic polyesters, 45 Mechanical recycling, 208 Medical applications, for polyurethanes, 207... 

Dynamic mechanical analysis of siloxane-urea copolymers show a sharp loss peak around —110 °C corresponding to the Tg of the siloxane segment. The transition in... 

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