Hardness crystallinity, dependence

Poly(ether ester) (PEE) copolymers were consisted of soft segments of polyethers and hard crystalline segments of polyesters. Depending on the polyether/polyester ratio, PEE copolymers exhibit a wide range of mechanical behavior combined with solvent resistance, thermal stability, and ease of melt process ability. 

Chemical methods can sometimes be used to distinguish between stone artifacts that are made with very similar materials. Lithic raw materials were chosen because of properties, such as hardness, that depend upon crystallinity and chemical composition. Geochemical processes determine both the chemical composition and physical properties of the rock. In many cases, lithic artifacts do not require chemical analysis to show that they are made from different materials. A simple visual examination is frequently sufficient. 

This NMR analysis is particularly useful as the block TMPS-DMS copolymers exhibit a wide range of properties depending upon the composition and average sequence lengths of the soft dimethylsiloxane segments and the hard crystalline silphenylene blocks. 

Recently, a random copolymer of 3HB and 4-hydroxybutyrate (4HB) (Figure Ic) is produced by A. eutrophus from 4-hydroxybutyric acid [9,10], or Y-bulyrolactone [11,12], This copolyester can be made in a wide variety of materials, from hard crystalline plastic to very elastic rubber, depending on the copolymer composition. More recently, the... 

Diamonds are in fact an exceptional precious stone because of their extreme hardness and light refraction, the second of which makes it sparkle beautifully. A common, but not completely accurate view is that diamonds are the hardest of all known substances. This statement is not easy to prove or disprove as most crystalline substances are anisotropic, which means that their properties (hardness included) depend on the orientation in which they are studied. Ciystals of rhenium diboride (ReB2) are harder in certain orientations than diamonds are in any orientation. The same is true for another substance called ultra-hard fullerene, which—no small irony involved—is another, very rare form of carbon, and can be metastable under any conditions. 

PHAs demonstrate a wide range of physical and mechanical properties depending on the number of carbon atoms in the constituent monomer units of the polymer chain. There are two main types of PHAs. SCL-PHAs have three to five carbon atoms in their monomer units whereas medium chain length PHAs or MCL-PHAs have 6-14 carbon atoms in their monomer units. SCL-PHAs tend to be hard, crystalline, and brittle polymers with high melting points whereas MCL- LCL-PHAs are usually soft and elastomeric with lower melting points compared to SCL-PHAs. 

The family of polyhydroxyalkanoates (PHA) exhibits a wide variety of mechanical properties from hard crystalline to elastic, depending on the composition of monomer units [12]. Solid-state poly(3-hydroxybutyrate) (P(3HB)) is a compact right-handed helix with a two-fold screw axis (i.e. two monomer units complete one turn of the helix) and a fibre repeat of 0.596 nm [13]. The stereoregularity of P(3HB) makes it a highty crystalline material. Its melting point is around 177°C close to that of polypropylene, with which it has other similar properties, although the biopolymer is stiffer and more brittle. 

Crystallization. Raw natural mbber may freeze or crystallize during transit or prolonged storage, particularly at subzero temperatures. The mbber then becomes hard, inelastic, and usually much paler in color. This phenomenon is reversible and must be differentiated from storage hardening. The rate of crystallization is temperature-dependent and is most rapid at —26° C. Once at this temperature, natural mbber attains its maximum crystallinity within hours, and this maximum is no more than 30% of the total mbber. 

The density of the polymer will clearly depend on the density of the soft phase (usually low), and the density of the hard phase (generally higher with crystallisable polar blocks) and the ratio of the soft and hard phases present. It will also clearly depend on the additives present and to some extent on the processing conditions, which may affect the crystalline morphology. 

In conclusion, the different thermal histories imposed to PTEB have a minor effect on the /3 and y relaxations, while the a. transition is greatly dependent on the annealing of the samples, being considerably more intense and narrower for the specimen freshly quenched from the melt, which exhibits only a liquid crystalline order. The increase of the storage modulus produced by the aging process confirms the dynamic mechanical results obtained for PDEB [24], a polyester of the same series, as well as the micro-hardness increase [22] (a direct consequence of the modulus rise) with the aging time. 

The present review shows how the microhardness technique can be used to elucidate the dependence of a variety of local deformational processes upon polymer texture and morphology. Microhardness is a rather elusive quantity, that is really a combination of other mechanical properties. It is most suitably defined in terms of the pyramid indentation test. Hardness is primarily taken as a measure of the irreversible deformation mechanisms which characterize a polymeric material, though it also involves elastic and time dependent effects which depend on microstructural details. In isotropic lamellar polymers a hardness depression from ideal values, due to the finite crystal thickness, occurs. The interlamellar non-crystalline layer introduces an additional weak component which contributes further to a lowering of the hardness value. Annealing effects and chemical etching are shown to produce, on the contrary, a significant hardening of the material. The prevalent mechanisms for plastic deformation are proposed. Anisotropy behaviour for several oriented materials is critically discussed. 

Microindentation hardness normally is measured by static penetration of the specimen with a standard indenter at a known force. After loading with a sharp indenter a residual surface impression is left on the flat test specimen. An adequate measure of the material hardness may be computed by dividing the peak contact load, P, by the projected area of impression1. The hardness, so defined, may be considered as an indicator of the irreversible deformation processes which characterize the material. The strain boundaries for plastic deformation, below the indenter are sensibly dependent, as we shall show below, on microstructural factors (crystal size and perfection, degree of crystallinity, etc). Indentation during a hardness test deforms only a small volumen element of the specimen (V 1011 nm3) (non destructive test). The rest acts as a constraint. Thus the contact stress between the indenter and the specimen is much greater than the compressive yield stress of the specimen (a factor of 3 higher). 

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