Tensile modulus of polymers

Efforts of polymer scientists and fuel cell developers alike are driven by one question What specific properties of the polymeric host material determine the transport properties of a PEM, especially proton conductivity The answer depends on the evaluated regime of the water content. At water content above kc, relevant structural properties are related to the porous PEM morphology, described by volumetric composition, pore size distribution and pore network connectivity. As seen in previous sections, effective parameters of interest are lEC, pKa, and the tensile modulus of polymer walls. In this regime, approaches familiar from the theory of porous media or composites (Kirkpatrick, 1973 Stauffer and Aharony, 1994), can be applied to relate the water distribution in membranes to its transport properties. Random network models and simpler models of the porous structure were employed in Eikerling et al. (1997, 2001) to study correlations between pore size distributions, pore space connectivity, pore space evolution upon water uptake, and proton conductivity, as will be discussed in the section Random Network Model of Membrane Conductivity. ... 

Fertig III R S and Gariiich M R (2004) Influence of Constituent Properties and Micro-structural Parameters on the Tensile Modulus of Polymer/Clay Nauocomposites, Compos Sci Technol 64 2577-2588. 

Figure 9.3. A schematic representation of the dependence of tensile modulus of polymers on temperature [8],...

It may be prepared in two stereo-regular forms, cis- and trans-. The cii-polymer, which crystallises in zig-zag form, has a of 235°C, whilst the fran -polymer, which crystallises in helical form, melts at the much lower temperature of 145°C. Tensile strengths of both forms are reportedly similar to that of Penton whilst the tensile modulus of 2300 MPa is about twice as high. Unfortunately the material is rather brittle with an impact strength only about half that of polystyrene although this may be improved by orientation. 

Some viscoelasticity results have been reported for bimodal PDMS [120], using a Rheovibron (an instrument for measuring the dynamic tensile moduli of polymers). Also, measurements have been made on permanent set for PDMS networks in compressive cyclic deformations [121]. There appeared to be less permanent set or "creep" in the case of the bimodal elastomers. This is consistent in a general way with some early results for polyurethane elastomers [122], Specifically, cyclic elongation measurements on unimodal and bimodal networks indicated that the bimodal ones survived many more cycles before the occurrence of fatigue failure. The number of cycles to failure was found to be approximately an order of magnitude higher for the bimodal networks, at the same modulus at 10% deformation [5] ... 

Figure 20.12 The tensile modulus of the LCP/PEN blends as a function of the LCP content at draw ratios of 10 ( ) and 20 ( ) [13]. From Kim, S. H., Hong, S. M., Hwang, S. S. and Yoo, H. O., J. Appl. Polym. Sci., 74, 2448-2456 (1999), Copyright (1999, John Wiley Sons, Inc.). This material is used by permission of John Wiley Sons, Inc...

Stiffness-Temperature - One simple tensile test of polymers involves the measurement of a modulus as a function of temperature. Figure 5 illustrates the characteristics of such a measurement. 

FIG. 13.62 Tensile strength of polymers, correlated with modulus. 

Another striking example concerns the polymer poly(p-xylylene) (PPX). It is obtained by condensation at room temperature of the gaseous monomer. A clear foil may be obtained in that way. The melting point of PPX is 427 °C and it crystallises immediately after polymerisation, so that entanglement cannot be formed. Van der Werff and Pennings (1988, 1991) have shown that hot drawing of such a material at 420 °C yields a material with a tensile strength of 3 GPa and a tensile modulus of 100 GPa. 

Du et al. (50) reported the synthesis of butadiene styrene rubber nanocomposites with halloysite nanotubes. The tensile properties of the composites containing various amounts of nanotubes are depicted in Table 2.2. The tensile properties were observed to significantly increase as a function of increasing amount of nanotubes in the composites. For the maximum loading of the nanotubes, a tensile modulus of 5.56 MPa was observed as compared to 1.52 MPa for the pure polymer. 

The tensile modulus of polysulphide polymers is enhanced with additional cross-linking agent and filler loading. It decreases with plasticisation. The presence of suitable reinforcing pigments gives adequate tensile and elongation properties. 

Table 6 Tensile modulus of several ordered polymers...

Figure 15.11. Tensile modulus of composites made from nylon and different fillers (montmorillonite, saponite, hectorite and mica) vs. N-NMR chemical shifts of model compounds of fillers. [Adapted, by permission, from Usuki A, Koiwai A, Kojima Y, Kawasumi M, Okada A, Kurauchi T, Kamigaito O, J. Appl. Polym. Sci., SS, No.l, 1995, 119-23.]...

Figure 16.24 shows the schematic representation of dispersed clay particles in a polymer matrix. Conventionally dispersed clay has aggregated layers in face-to-face form. Intercalated clay composites have one or more layers of polymer inserted into the clay host gallery. Exfoliated polymer/clay nanocomposites have low clay content (lower than intercalated clay composites which have clay content -50%). It was found that 1 wt% exfoliated clay such as hectorite, montmorillonite, or fluorohectorite increases the tensile modulus of epoxy resin by 50-65%. ... 

For the majority of plastics (within the same group) the tensile modulus of elasticity increases approximately linearly with the degree of crystallinity [5], The data for linear and branched polymers follow the same approximate relationship. It is not clear whether the same molecular principles is applicable to WPCs (Table 8.13), but their tensile modulus of elasticity vary between different brands quite significantly. 

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