The Mechanical Properties of Polymers General Considerations

In the Institute of Mechanics of Metal—Polymer Systems, Byelorussian SSR Academy of Sciences, USSR a method MR 74—82 (20) for evaluating the tribotechnical properties of polymer-based materials had been developed based on the generalization of techniques and talcing into consideration the friction behavior of polymers and polymer—based composites... 

Additional TMDSC study of other vinyl polysiloxane, polyether and polysulfide impression materials is important to verify if the polymer transitions shown in Figures 16 to 19 generally exist in different products and to investigate the effects of other temperature modulation conditions. Complementary research on correlations with clinically relevant mechanical properties of the elastomeric impression materials is needed to verify if these thermal analyses have useful predictive power. Interestingly, when compared at apparently similar viscosities, the reported values of the elastic modulus [3] are highest for the vinyl polysiloxane silicone impression materials, intermediate for the polyether impression materials, and lowest for the polysulfide impression materials, in reverse order to the relative values of Tg fovind in our thermal analyses [45]. Our X-ray diffraction and scanning electron microscopic study [47] of these impression materials has shown that they contain substantial amounts of crystalline filler particles in the micron size range, which are incorporated by manufacturers to achieve the clinically desired viscosity levels. Tliese filler particles should have considerable influence on the mechanical properties of the impression materials. 

With regards to the mechanical properties of substituted polyacetylenes, aromatic polymers like poly(diphenylacetylene) derivatives are generally hard and brittle, whereas aliphatic polymers with long alkyl chains like poly(2-octyne) are soft and ductile.Considerations of mechanical properties are especially important when polymer membranes or fibers are required for the specific application. 

As already indicated above, what one may consider a surface depends on the property under consideration. Adhesion is very much an outer atomic layer issue, unless one is dealing with materials like fibreboard in which the polymer resin may also be involved in mechanical anchoring onto the wood particles. Gloss and other optical properties are related to the penetration depth of optical radiation. The latter depends on the optical properties of the material, but in general involves more than a few micrometer thickness and therewith much more than the outer atomic layers only. It is thus the penetration depth of the probing technique that needs to be suitably selected with respect to the surface problem under investigation. Examples selected for various depths (< 10 nm, 10 s of nm, 100 nm, micrometer scale) have been presented in Chapter 10 of the book by Garton on Infrared Spectroscopy of Polymer Blends, Composites and Surfaces... 

Mechanical properties of solid polymers generally become considerably "softer" in the corresponding foams. This is particularly true in open-cell foams. In closed-cell foams, properties per unit area or unit volume are also generally somewhat softer but properties per unit weight in the expanded polymer may be considerably harder and stronger than in the solid polymer because of the principles of sandwich structures. 

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