Mechanical properties in polymers

L. Chazeau, C. Gauthier, G. Vigier and J.-Y Cavaille, "Relationships between microstructural aspects and mechanical properties in polymer based nanocomposites", in H.S. Nalwa, ed., Handbook of Organic-Inorganic Hybrid Materials and Nanocomposites, American Scientific Publishers, 2003. 

Wilkes, G.L. Mechanical properties. In Polymer Characterization and Analysis Brady, R.F., Ed. American Chemical Society/Oxford University Press New York, 2003 624—668. 

The cross-linking of polymers during vulcanization was an example of chemical reaction affecting mechanical properties in polymers. The sensitivity of the mechanical properties of nylon to atmospheric moisture was considered. Polymers are also reactive with various organic solvents. This is an important consideration in those industrial processes in which such solvents are part of the material s environment. 

Acknowledgement This paper was stimulated by an EPRI workshop in Baltimore (March 1989) and was prepared under support from EPRI. Many of the specific results were drawn from earlier work. In particular, I thank Prof S. Kivelson for many important discussions and many detailed results. Any insight on the relationship of electrical and mechanical properties in polymers is due to my interactions with Prof Paul Smith. 

An important development in Raman spectroscopy has been the coupling cf the spectrometer to an optical microscope. This allows the chemical and structural analysis described above to be applied to sample volumes only 1 across [38]. No more sample preparation is required than that for optical microscopy, and the microscope itself can be used to locate and record the area which is analyzed. This has obvious practical application to the characterization of small impurities or dispersed phases in polymer samples. This instrument, which may be called the micro-Raman spectrometer, the Raman microprobe or the Molecular Optics Laser Examiner [39] has also been applied to the study of mechanical properties in polymer fibers and composites. It can act as a non-invasive strain gauge with 1 fim resolution, and this type of work has recently been reviewed by Meier and Kip [40]. Even if the sample is large and homogeneous, there may be advantages in using the micro-Raman instrument. The microscope... 

Heckmann, W., McKee, G.E., Ramsteiner, F. in Michler, G.H., Balta-Calleja, F.J. (Eds.), Mechanical Properties in Polymers Based on Nanostructure and Morphology (2005) Taylor Francis, Boca Raton, Florida, Chapter 11, pp. 435-485... 

Polydiacetylenes allow a unique opportunity to study the relationship between structure and mechanical properties in polymer crystals. The technique of solid state polymerization 11] enables highly-perfect poiydiacetylene single crystals to be produced with macroscopic dimensions. For example single crystal fibres can be grown with lengths in excess of 50 mm 12.3]. Crystalline polymers produced by crystallization from both dilute solution and the molten state are invariably only semi-crystalline 14]. Melt-crystallized... 

The improved mechanical properties in polymer/clay nanocomposites are associated with particle geometries of high aspect ratio and the resulting high interfacial area per unit volume. In this work, an elastic Finite Element analysis of idealized clay platelet configurations was carried out identifying which platelet characteristics are important in producing the property enhancement. 

Some authors " observed improved mechanical properties in polymer electrolytes with added nanofiUers. The rheological behaviour of filled and unfilled PEO-LiTFSI electrolytes was studied at 85 °C. A significant... 

In this section we resume our examination of the equivalency of time and temperature in the determination of the mechanical properties of polymers. In the last chapter we had several occasions to mention this equivalency, but never developed it in detail. In examining this, we shall not only acquire some practical knowledge for the collection and representation of experimental data, but also shall gain additional insight into the free-volume aspect of the glass transition. 

In describing the various mechanical properties of polymers in the last chapter, we took the attitude that we could make measurements on any time scale we chose, however long or short, and that such measurements were made in isothermal experiments. Most of the experimental results presented in Chap. 3 are representations of this sort. In that chapter we remarked several times that these figures were actually the result of reductions of data collected at different temperatures. Now let us discuss this technique our perspective, however, will be from the opposite direction taking an isothermal plot apart. 

Molecular Weight. The values of the mechanical properties of polymers increase as the molecular weight increases. However, beyond some critical molecular weight, often about 100,000 to 200,000 for amorphous polymers, the increase in property values is slight and levels off asymptotically. As an example, the glass-transition temperature of a polymer usually follows the relationship... 

And we are still learning how best to fabricate and use them. As emphasised in the last chapter, the mechanical properties of polymers differ in certain fundamental ways from those of metals and ceramics, and the methods used to design with them (Chapter 27) differ accordingly. Their special properties also need special methods of fabrication. This chapter outlines how polymers are fabricated and joined. To understand this, we must first look, in slightly more detail, at their synthesis. 

The greater the degree of crystallinity the less the water absorption and hence the less will be the effect of humidity on the properties of the polymer. The degree of crystallinity also has an effect on electrical and mechanical properties. In particular high crystallinity leads to high abrasion resistance. 

In general, physico-mechanical properties of polymers depend on the molecular weight. However, the physico-mechanical properties of PSs decreased in the presence of cationic catalysis, but increased in the case of the binding of functional groups to the aromatic ring in spite of the destruction of PS. Therefore, new properties such as adhesion and photosensitive capability increase... 

The mechanical properties of polymers are of interest in all applications where they are used as structural materials. The analysis of the mechanical behavior involves the deformation of a material under the influence of applied forces, and the most important and characteristic mechanical property is the modulus. A modulus is the ratio between the applied stress and the corresponding deformation, the nature of the modulus depending on that of the deformation. Polymers are viscoelastic materials and the high frequencies of most adiabatic techniques do not allow equilibrium to be reached in viscoelastic materials. Therefore, values of moduli obtained by different techniques do not always agree in the literature. 

The opportunity to synthesize new conjugated polymers with improved properties began to attract the attention of a larger number of synthetic chemists in the 1980s. Equally important was the subsequent development of stable, processible metallic polymers. As a result of these efforts, we now have a class of materials which exhibit a unique combination of properties the electronic and optical properties of metals and semiconductors in combination with the processing advantages and mechanical properties of polymers. 

Usually, crystallization of flexible-chain polymers from undeformed solutions and melts involves chain folding. Spherulite structures without a preferred orientation are generally formed. The structure of the sample as a whole is isotropic it is a system with a large number of folded-chain crystals distributed in an amorphous matrix and connected by a small number of tie chains (and an even smaller number of strained chains called loaded chains). In this case, the mechanical properties of polymer materials are determined by the small number of these ties and, hence, the tensile strength and elastic moduli of these polymers are not high. 

As an organic polymer, poly(tetramethylene oxide) was also used for the preparation of ceramers. The mechanical properties in these cases were much improved in comparison with those for hybrids from polysiloxanes. In these poly (tetramethylene oxide)-silica hybrids, the effect of the number of functional triethoxysilyl groups was examined [13]. As shown in Fig. 2, more multifunctional organic polymer produced more crosslinked hybrid networks. This means that the more rigid the structure in the hybrids is, the higher the modulus and the lower swelling property. 

Most suggestions for further reading are given in full in the Bibliography at the end of this book. However, in view of the specialised nature of the topics discussed in this chapter it is worth citing a list of further reading which concentrates on mechanical properties of polymers. They are ... 

Liquid membranes consist of an organic phase, which by its hydrophobic nature is relatively impermeable to ions. Originally organic solvents such as decanol were used in conjunction with a porous hydrophobic membrane. These have been replaced by plasticized polyvinyl chloride membranes which behave like liquids yet have improved mechanical properties Other polymers such as silicone, polyurethane and ururshi, a... 

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