Specific mechanical properties

One can find the specific tensile strength and tensile modulus ranges for the different biopolymers. These values were obtained by dividing the original mechanical properties by the density. If either density or the mechanical property was not available within the same reference, no specific data were calculated. This restriction was necessary since it is likely that the polymers density is related to its mechanical properties. If one would like to use the biopolymers as a structural element without using reinforcement, specific properties become important as they determine the dimensions necessary for a certain mechanical strength or stiffness. Contrary to the usefulness as composite matrix, in this case, PGA and 1-PLA seem the best choices, whilst PCL and also PHO (polyhydroxyoctanoate, s =8.8 MPa and E =7.8 MPa) are clearly the worst ones [40]. 

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As normally polymerized, PVF melts between IH5 and 210 °C and contains 12 18% inverted monomer units ft is normally considered a thermoplastic, but because of its instability above its melting point, it cannot be processed by conventional thermoplastic techniques Instead it is generally extruded into films in a solvent swollen (organosol) form and the solvent is subsequently evaporated and recovered Such films can be onented further to achieve specific mechanical properties PVF films are exceptionally weather and radiabon resistant considenng their modest fluonne content PVF is insoluble below 100 °C but, at higher temperatures, it dissolves in polar solvents like amides, ketones, tetramethylene sulfone, and tetramethylurea Resistance to acids and bases at room temperature IS good [1, 29 ... 

In the preparation and processing of ionomers, plasticizers may be added to reduce viscosity at elevated temperatures and to permit easier processing. These plasticizers have an effect, as well, on the mechanical properties, both in the rubbery state and in the glassy state these effects depend on the composition of the ionomer, the polar or nonpolar nature of the plasticizer and on the concentration. Many studies have been carried out on plasticized ionomers and on the influence of plasticizer on viscoelastic and relaxation behavior and a review of this subject has been given 119]. However, there is still relatively little information on effects of plasticizer type and concentration on specific mechanical properties of ionomers in the glassy state or solid state. 

The specific mechanical properties take account of the density and consider the performance to density ratio (performance/density). 

As for the specific mechanical properties, the high densities of metals modify the classification (Table 1.11 and Figure 1.9) of the various materials. 

Moulded plastic Specific mechanical property bearing inserts... Overmoulding, post-moulding insertion by means of pressure (and heat)... 

Aramid fibres have high specific mechanical properties and are used for their attractive characteristics such as ... 

Plastics and polymer composites are much more expensive than metals, even more-specialized ones such as nickel. As for the specific mechanical properties, the high densities of metals modify the classification of the various materials. According to the cost per volume, plastics are competitive. Only the very high performance plastics or composites are more expensive than metals. 

Fillers are solid materials that are dispersed in plastics and elastomers. One distinguishes between inactive fillers that are used in the first place to make the plastics less expensive and active fillers (reinforcing fillers) that improve specific mechanical properties and thus effect a reinforcement . With the aid of these fillers, the elastic modulus, hardness, and thermostability are enhanced predominantly, whereas the impact strength of thermoplastic niaterials is re-... 

The description of the physical properties of fluoroelastomers is necessarily less precise than that of fluoroplastics because of the major effect of adding curatives and fillers to achieve useful cross-linked materials of a given hardness and specific mechanical properties Generally, two parameters are varied increasing cross-link density increases modulus and decreases elongation, and raising filler levels increases hardness and decreases solvent swell because of the decreased volume fraction of the elastomer In addition to these two major vanables, the major determinants of vulcanizate behavior are the chemical and thermal stabilities of its cross-links The selection of elastomer, of course, places limits on the overall resistance to fluids and chemicals and on its service temperature range... 

In addition to dense monolithic ceramics, porous silicon nitrides are gaining more importance in technological applications [24], Some porous silicon nitrides with high specific surface area have already been applied as catalysis supports, hot gas filters and biomaterials [25], There is an emerging tendency to facilitate silicon nitride as biomaterial, because of specific mechanical properties that are important for medical applications [25], Moreover, in a recent study it was shown that silicon nitride is a non-toxic, biocompatible ceramic which has the ability to propagate human bone cells in vitro [25], Bioglass and silicon nitride composites have already been realized to combine... 

Table 9.2. Specific mechanical properties of solid and microcellular PLA and PLA-MWCNT nanocomposites (35)... 

In general, polishing pads are composed of either a matrix of cast polyurethane foam with filler material to control hardness or polyurediane impregnated felts. Polyurethane is utilized because urethane chemistry allows the pad characteristics to be tailored to meet specific mechanical properties needs. Jairath et al. describe the manufacture of pad material as follows ... 

Conceptually, the problems associated with the optimization of specific mechanical properties by variations of structure and morphology are the same in rubber-filled systems, ass-bead filled systems and semicrystalline polymers. When the fracture properties are singled out, our understanding of the relationships between macroscopic failure and local failure is hampered by the limited knowledge of stress transfer in statistically nonhomogeneous structures. The increased use of composites theory and micromechanics to address these problems would appear to be appropriate. 

Figure 13 illustrates the elongation profile of the composition when three different plasticizers are used at increasing concentrations (37). Dioctyl adipate emerges from the antiplasticization area at relatively low concentrations and the elongation property builds steeply. The composition responds intermediately with increasing amounts of dioctyl phthalate, and dicyclohexyl phthalate is quite inefficient. When different plasticizers are substituted in a vinyl composition that must still maintain specific mechanical properties, the concentration of the substitutions must be adjusted to accommodate each particular plasticizer s "efficiency factor."... 

Similarly to condensed phases, the adsorption layers have some specific mechanical properties characteristic of their phase state. The investigation of mechanical properties of adsorption layers can be performed using the torque pendant technique (Fig. 11-28). A disk attached to a thin elastic thread is... 

This chapter contains three case studies. The first one on climbing rope illustrates the technology of fibre production and rope construction to meet specific mechanical property targets. There are some similarities between rope and the much smaller scale braided sutures used in surgery. Further sport case studies, on polymer foam protective gear and materials in running shoes, are mentioned in the Further Reading section. 

Favourable specific mechanical properties of continuous fibre-reinforced plastics have made them attractive materials for application to many engineering structures. 

As already mentioned, specific mechanical properties are decisive when using natural fibres in composite materials. The fact that hemp, flax, and ramie natural fibres can compete with technical fibres is demonstrated in Fig 1. 

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