Mechanical properties plastic body

The mechanical properties of these materials are too weak to use them in places in the body where much pressure is exerted. It is virtually impossible to achieve 100% polymerisation during the production process. Consequently the material contains impurities which may lead to toxic, allergic or carcinogenic processes. In future so-called biodegradable plastics will be used in applications such as artificial skin, synthetic blood, bone plates and in the controlled release of medication. 

Tensile and shear forces are not the only types of loads that can result in deformation. Compressive forces may as well. For example, if a body is subjected to hydrostatic pressure, which exists at any place in a body of fluid (e.g. air, water) owing to the weight of the fluid above, the elastic response of the body would be a change in volume, but not shape. This behavior is quantified by the bulk modulus, B, which is the resistance to volume change, or the specific incompressibihty, of a material. A related, but not identical property, is hardness, H, which is defined as the resistance offered by a material to external mechanical action (plastic deformation). A material may have a high bulk modulus but low hardness (tungsten carbide, B = 439 GPa, hardness = 30 GPa). 

In order to preserve the final compostabihty, different blends of biodegradable materials have been developed. There is a vast body of literature available in this domain. We find certain associations with agropolymers such as proteins [ARV 99, FIS 00, OTA 99] or pectins [FIS 00], but most research focuses on blends of plasticized starches and biodegradable polyesters PCL, PHA, PBSA, PBAT, etc. These polyesters, described previously, are produced industrially. They exhibit interesting properties such as a more hydrophobic natiue, limited water permeability and improved mechanical properties, in comparison to polysaccharides. However, the cost of biodegradable polyesters is generally higher than that of starch... 

In this respect, (thermoset) plastics composites with discontinuous fibre products are already mostly used in the car body applications, where polyester/E-glass is predominating (mostly because of polyesters, economy, ease of processability and reasonable mechanical properties provided), followed by use of phenolics (when fire retardance is required, in friction linings and engine compartments), and epoxies. Replacement by carbon or aramid fibre reinforcements can reduce body mass by 40% (compared to steel) and with more added strength, but the cost is unfavourable at the moment, as mentioned previously [12, 13]. 

Study of the mechanical properties of the boundary layers of reactive plastics, epoxy polymers in particular, is of special interest in that undercure of the compound is observed on the surface of the solid body the primary reason for this is selective adsorption of components of the reactive system, which results in violation of stoichiometry of the initial products close to the solid body surface. 

As commented, PVC plastisols are suspensions of emulsion PVC in a plasticizer. Formulations contain components such as pigments and thermal stabilizers, but plasticizers are by far the major component. PVC plastisols are rotomolded to obtain hollow soft articles, mainly in the toy industry. It could be deduced that mechanical properties of these parts are not important, but the finishing operations such as insertion of eyes and hair in dolls heads or mechanisms in arms and bodies, or final assembly, imply big loads apphed to the part, and consequently, the mechanical properties have to be developed to the full. Moreover, the molds used in these apphcations have very intricate shapes, pronounced ribs and comers, and aesthetics and details reproduction is very important in these parts. These complex shapes may involve high tensions in the moldings and corrrphcate the demolding process. To obtain a good thickness distribntion in snch a mold, variables involved in the process have to be at the optimnm. 

Careful consideration must be taken when selecting a sterilization method for SMPs. Though initial work has been promising, future studies are still needed. In particular, virtually all of the sterilization methods operate at temperatures above body temperature (Table 1), which may result in premature deployment if the device is sterilized in its temporary shape. Some researchers have proposed the use of water uptake, which can naturally occur in polymers in vivo, to act as a plasticizing agent to decrease the Tg of the device [118]. This would allow for the device to be stable against elevated temperatures during sterilization, and lower the Tg to activate via body temperature once implanted. Conversely, the mechanical properties of the device may be adversely lowered with the uptake of water [119]. Furthermore,... 

Poly(3-hydroxyalkanoates) (PHAs) are a family of polyesters accumulated as inclusion bodies (Fig. 1) by a wide variety of bacteria. They are water-insoluble, relatively resistant to aqueous hydrolysis but are readily biodegraded in any natural environment where microbial diversity exists. They can be produced from renewable resources and waste materials and, although temperature-sensitive, are potentially recyclable. Many PHAs have mechanical properties similar to those of common synthetic plastics. 

The wide range of forms (film, tube, or fiber) and mechanical properties available in plastics continues to make them attractive candidates for such uses (Fig. 4.57). These plastics are required to possess desired physical/mechanical properties and the assurance that they may be successfully utilized in the body. To be successful plastic implants involve the cross-fertilization of different disciplines (chemists, designers, physician, fabricator, etc.). 

For plastic materials, a conical plastometer can be used. The immersion of a cone with a defined apex angle into the body down to a depth h due to the action of force F can yield an area of contact, 5( and the tangential component of the force, f,. If the ratio FJS,=t is invariant with respect to the force applied, then the rheological behavior can be interpreted in terms of the Coulomb model and t = Inv is a critical shear stress. This is a common way to study the rheology of cement, flour, soils, etc. A conical plastometer was used in the evalnation of the mechanical properties of the surface of the Moon. 

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