Mechanical properties of polymeric materials

In an overwhelming majority of investigations into the effect of fillers on the mechanical properties of polymeric materials (cf., e.g. [234]) it was noted that the... 

When we consider the mechanical properties of polymeric materials, and in particular when we design methods of testing them, the parameters most generally considered are stress, strain, and Young s modulus. Stress is defined as the force applied per unit cross sectional area, and has the basic dimensions of N m in SI units. These units are alternatively combined into the derived unit of Pascals (abbreviated Pa). In practice they are extremely small, so that real materials need to be tested with a very large number of Pa... 

It Is well known that mechanical properties of polymeric materials are greatly deteriorated by UV exposure (2-j)). The nature of this deterioration was determined using non-strained samples which were photooxidized at 37°C. Engineering stress-strain curves as a function of UV exposure are shown in Figure 1. The numbers next to each curve represent days of UV exposure. In terms of degradation, the points of interest are ... 

Dynamic properties Mechanical properties of polymeric materials exhibited under repeated cyclic deformation. 

This mechanism appears to be most commonly reported for transition-metal-catalyzed autoxidation of organic substrates. However, at least a few other possibilities exist (23). The effect of oxygen absorption and subsequent oxidation and cleavage of cellulosic chains on the permanence as well as the appearance of paper can be very significant. The absorption of even the smallest amounts of oxygen is known to produce a substantial loss in mechanical properties of polymeric materials. In the case of paper, oxygen absorption leads to a decrease in the degree of polymerization, color reversion, and a loss in mechanical properties. 

Tensile properties are one of the most important single indications of the strength of a material. Mechanical properties of polymeric materials are often measured using standard test sample configurations. In these studies, a tensile dumbbell-shaped test specimen which conforms to ASTM D638 was used for all measurements. 

When we consider the mechanical properties of polymeric materials, and in particular when we design methods of testing them, the parameters most generally considered are stress, strain, and Young s modulus. Stress is defined as the force applied per unit... 

The physical properties including the mechanical properties of polymeric materials depend on their molecular characteristics, highly ordered structures, fillers, and material morphology. Table 8.1 [8] and Figure 8.9 [125] summarize the physical properties of PLA and other representative commercial polymers. In the following sections, some crucial parameters that significantly alter the mechanical properties are discussed. 

Molecular weight is an important parameter to determine the mechanical properties of polymeric materials and is given by the following empirical equation ... 

The mechanical properties of polymeric materials are of considerable importance for their engineering applications. In this respect the understanding of the molecular mechanisms involve in polymer deformation is a necessary prerequisite for a reasonable structure-property correlation. 

Hengl, R., and Gust, H. Influence of Loading History on the Mechanical Properties of Polymeric Materials. Kunststoffe, pp. 31-33, Mar. 1989. 

The positron annihilation technique is quite promising for studying free-volume holes (FVH) in polymer structure. Information on free-volume holes is useful for imder-standing many physical and mechanical properties of polymeric materials. However, some problems of rationalizing the annihilation characteristics obtained by measiuing positron lifetimes still remain unsolved. 

The mechanical properties of polymeric materials including blends are reported in detail in commercial product literature and provide a basis of comparison of the engineering properties of materials for various end-use applications. The specific mechanical properties of interest include the modulus (tensile, flexural or bulk), strength (tensile, flexural or compressive), impact strength, ductility, creep resistance as well as the thermomechanical properties (e.g., heat distortion temperature). The mechanical property profile can be employed to determine the compatibility of the blend by comparison with the unblended constituents. Compatibi-lization methods can be evaluated easily by comparison of the mechanical property profile with and without compatibihzation. 

Polymeric roofing membranes are evaluated using various test methods developed for assessment of durability. Mechanical properties of polymeric materials have two facets one is related to the macroscopic behavior and the other to the molecular behavior. PI Engineers are concerned only with the description of the mechanical behavior (physical properties) under the design conditions. Evaluation of the mechanical properties of roofing membranes (tensile properties at different temperatures, load at break, elongation at break, and energy to break) provides information about the material structural failures and how it can be improved, but does not offer an explanation. If the failure is related to molecular activity, additional information is necessary to comprehend the problem fully. 

As a consequence of autoxidation, the most important mechanical properties of polymeric materials may undergo a sudden breakdown during continuous exposure to light. This is shown in Figure 3.8, where the impact strength of an ABS polymer is seen to fall drastically after a certain exposure time [108]. 

Considered individually, these interactions are not stronger than those observed in a system composed of simple molecules. However, in polymeric systems, the multiplicity of interactive groups and the forces resulting from their repetition along the same macromolecular chain lead to considerable cohesion energies that are in turn responsible for the peculiar mechanical properties of polymeric materials. 

Composite materials contain two or more distinct constituent materials or phases, on microscopic or macroscopic size scale. The use of composite materials is motivated by the fact that they can provide more desirable material properties than those of homogeneous materials. For example, mechanical properties of polymeric materials may be improved by reinforcement (e.g., silica particles in silicone implants) and the biocompatibilities of metallic implants may be improved by coating with carbon. 

The list of items along the left side of Table I are those which strongly influence the mechanical properties of polymeric materials. Most are quite well known and subject to measurement with varying degrees of accuracy and precision. Filler and plasticizer concentration must also be considered in combination with their specific nature, such as filler particle size and surface, or plasticizer type. However, for the purposes of this discussion we may restrict them to non-polar, or non-interacting materials, and concentration will be the measurable quantity. 

The mechanical properties of polymeric materials are of considerable importance to their engineering applications. Apart... 

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