Low mechanical properties

The most commonly measured mechanical properties for films are tensile strength, tear strength, and impact resistance. The first two are generally measured in both the machine and transverse directions (MD and TD). The last one is a biaxial test, examining MD and TD simultaneously. 

The magnitude of these properties in any film depends on several factors. The primary factor is the type of polymer used to make the film. All polymers can be ranked by then-inherent strength. Some, such as nylon, are generally very high, and others, such as low-density polyethylene, are relatively low. Of course, one must always keep in mind that there are property trade-offs to make when evaluating materials to perform a job, and strength is not always the most important quality characteristic. Nevertheless, the base polymer is what primarily determines film strength. 

There are several other process variables that affect mechanical properties. The frostline height, which is a measure of polymer cooling rate, has a large influence on crystal structure for semicrystalline materials such as polyethylene. (Process stretching also 

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Connectivity of hydrophilic phase at high sulfonic acid content yields membranes with very high water swelling and thus low mechanical properties... 

At metallographic research of structure melted of sites 2 mechanisms of education of spherical particles of free carbon are revealed. In one of them, sold directly at the deformed graphite the formed particles became covered by a film austenite, that testifies to development abnormal eutectic crystallization. In other sites containing less of carbons and cooled less intensively, eutectic crystallization the education numerous dispersed dendrites austenite preceded. Crystallization of thin layers smelt, placed between branches austenite, occured to complete division of phases, that on an example of other materials was analyzed in job [5], Thus eutectic austenite strated on dendrites superfluous austenite, and the spherical inclusions of free carbon grew in smelt in absence austenite of an environment. Because of high-density graphite-similar precipitates in interdendritic sites the pig-iron is characterized by low mechanical properties. 

The changes in mechanical properties, YS, UTS and creep resistance (CR), of fully aged cast lead—calcium—tin alloys with two different Sn concentrations (0.5 wt% Sn or 1.5 wt% Sn) as a function of Ca content are presented in Fig. 4.36. Data from Ref. [66] were used to plot these dependences. The alloys with low-Ca content (0.02 and 0.03 wt% Ca) have low mechanical properties which improve with an increase of the Ca content up to the peiitectic concentration, pass through a maximum and decrease thereafter. All three measured parameters (YS, UTS and CR) have higher values when the alloys contain 1.5 wt% Sn (higher r value) than at the lower 0.5 wt% Sn level. Tin accelerates the precipitation reaction to completion. This holds for the whole range of calcium concentrations but proceeds at different rates. 

These low-melting-point alloys were the first alloys to be die-cast, originally for printer s type. Lead alloyed with antimony, sometimes with small additions of tin, has a melting point of about 315 C and can be cast to very close tolerances and in intricate shapes. The castings have low mechanical properties and are used mainly for their density, e.g. car-wheel balance masses, and corrosion-resistance, e.g. battery-lead terminals. 

The reaction temperatures are about 200-250 °C. The PEEK so produced, however, exhibits a low molecular weight with an intrinsic viscosity (IV) smaller than 0.7dlg and comparatively low mechanical properties. 

Based on clinical experience and retrieval analyses, implant geometries should have a sphericity of less than 1 jum and a radius tolerance between components of 7 to 10 /rni (Boutin et al., 1988). These specifications are based on the rationale that too small a gap between the components does not provide sufficient room for necessary lubrication or an escape route for alumina particles, whereas too large a gap increases contact pressures. To design around the low mechanical properties, a 32-mm femoral head and an acetabular cup with a minimum 44-mm outside diameter are recommended (Boutin et al., 1998). 

One of the possible solutions to overcome low mechanical properties of thermogelling copolymer systems must be enlargement of their total molecular weights. But elongation of each segment (hydrophobic and hydrophilic) with keeping their hydrophobic/hydrophilic... 

Polyester Low temperature limit Medium/low mechanical properties Low cost Production of styrene... 

Hydrogel Does not require specialized equipment Easily customizable based on monomer and cross-linking agent concentration Low mechanical properties Shrinkage when dried >10... 

Polycaprolactone is semicrystalline, with very low glass transition temperature (approximately 60°C) and low mechanical properties, but with high elongation at rupture. Because of the high hydrophobicity of e-caprolactone, the polymer is slowly degraded. 

Physical gelation Relative simple design use of natural polymers able to respond to in vivo stimuli Weak stability low mechanical properties lack of control upon injection 29,79,81,86,105... 

Pitch-based fibers can be divided in two groups (a) the isotropic pitch fibers, which have low mechanical properties and relatively low cost, and (b) he mesophase-pitch fibers, which have very high modulus but are more expensive. Pitch-based fibers are produced by a simple process and their cost should eventually rival that of glass fibers. Their potential is yet to be fully reetlized. 

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