Composites natural origin

Rased on the above data, it would seem unusual if reactivity of the propagating species in copolymerization were insensitive to the nature of the last added monomer units. However, while there are ample experimental data to suggest that copolymerizations should be subject to penultimate unit effects that affect the rate and/or copolymer composition, the origin and magnitude of the effect is not always easily predictable. 

The Components of Materials. The composition of most materials -whether of natural origin, such as minerals, rocks, wood, and skin, or made by humans, as for example, pottery, glass and alloys - includes several kinds of components major, minor, and trace elements (see Textbox 8). 

Thus, three types of components can be distinguished in most substances, whether of natural origin or made by humans major, minor, and trace components (see Table 8). The major components, also known as the main or matrix components, are those that determine the chemical nature and properties of a substance. The major components occur in the substance in high concentration, generally exceeding 1 % of the total weight. In minerals and biological substances, for example, the major components are those that appear in the chemical formula that expresses their composition. 

Vermilion and cinnabar are two bright red, toxic minerals that share an identical composition (they are both composed of mercury sulfide) but have different crystal structures. Two kinds of vermilion are known one of natural origin and another made artificially. Finely ground natural vermilion may vary in hue from red to liver-brown and even to black. Artificial vermilion was made from mercury and sulfur the method of preparation seems to have been developed by the Chinese and was introduced into Europe only during the eighth century c.e. (Gettens et al. 1972). 

The nature of the material to be studied, which means its degree of crystallinity and perfectness of crystal structure, may have a significant effect on the thermoanalytical behavior. In spite of identical chemical composition of a certain material the variations with respect to structure, imperfections, grain boundaries, etc. are almost infinite. Of course many of these will not show in normal thermogravimetric analysis, with very sensitive apparatus characteristically different TG curves18, 19 may be obtained however. As an example Fig. 26 shows the thermal decomposition of hydrozincite, Zn5(OH)6(003)2, whereby equal amounts of samples from natural origin and synthetic preparations are compared. 

The chemical composition of petroleum also varies over a wide range. A broad functional definition of petroleum hydrocarbons is that hydrocarbons are composed primarily of many organic compounds of natural origin and low water solubility. 

Gelatin is a biopolymer it is denaturated collagen. Due to its natural origin, differences exist between the molecular composition... 

Corrections of relative order (Za) connected with the nonelementarity of the nucleus are generated by the diagrams with two-photon exchanges. As usual all corrections of order (Za), originate from high (on the atomic scale) intermediate momenta. Due to the composite nature of the nucleus, besides intermediate elastic nuclear states, we also have to consider the contribution of the diagrams with inelastic intermediate states. 

Elastomeric Closures Closures for pharmaceutical products are generally made of polymeric materials, which may be of either a synthetic or natural origin. While brittle closures such as screw caps are made of conventional thermoplastics with a single composition, elastomeric closures are made of complex mixtures of many... 

The elemental composition and related atomic ratios of HAs and FAs isolated from some representative organic amendments of various nature and source, and unamended and amended soils are shown in Table 4.2. Although the elemental composition of HAs and FAs show significant variability on dependence on the nature, origin, and treatment of the amendment, they generally feature larger H, N,... 

The majority of the new drugs approved and the most often prescribed drugs in the United States have at least one asymmetric center [169]. Approximately half of these chiral drugs are of a racemic composition. Many of the optically pure drug substances are of natural origin, while the majority of the synthetically derived products are in racemic form [172]. Enantiomers can differ in their pharmacological activity or one may be inactive or... 

Meyer, H. O. A. Boyd, F. R. (1972) Composition and origin of crystalline inclusions in natural diamonds. Geochim. Cosmochim. Acta, 36,1255-73. 

The processing will affect the composition and quality of an essential oil. The plant material used for extraction is dead, and is subjected to conditions including heat, solvents and pressure, all of which can have an effect on composition of the final product. The products formed are products of natural origin-, they are not necessarily natural products that are present in the living plant. 

In the case of aromatherapy, which uses genuine products of natural origin, there are additional features that make it difficult to apply rigorous research methodology. The composition of an essential oil from a specific species can vary for a number of reasons. This is the reason why chemical compositions... 

The composition of commercially available essential oils cannot be artificially controlled as they are products of natural origin. However, when the essential oils are analyzed their composition should be within a range of acceptable values. If these values are not met, the oil should be rejected. This ensures a standard in the product supplied so that it should perform in a consistent manner when used therapeutically. QC is necessary to protect supplier, practitioner and client from any unforeseen effects of aromatherapy performed with oils that might present risks due to unknown properties. 

Analysis of an essential oil will tell us what compounds are present (qualitative analysis) and in what amounts (quantitative analysis). However, when considering the composition of any named oil it is difficult to lay down precise criteria. As with all products of natural origin, there will be variations according to growing conditions and how they are harvested, extracted and stored. Even if the species of plant is defined and the parts used for oil production are carefully controlled, variation in composition will occur. This has previously been explained in terms of chemotypes and will be examined in more detail for other essential oils later in this chapter. Even when examining a particular chemotype there will be differences in the amounts of constituents, although these are usually within a fairly narrow range. 

The LD values are known for most essential oils, but they represent a measure of acute oral value. It is one of many measures quoted when describing properties of essential oils. Aromatherapists do not practise the use of oral administration but full tables of LD50 values can be found in established texts and on safety data sheets. As essential oils are products of natural origin with variations in composition the values will also show some variations due to this. Also oils from different parts of a plant will have different chemical compositions and this will be reflected in the different LD50 values. For example... 

Naturally occurring AFm phases, called hydrocalumite. appear to vary in composition. The original specimen was reported to have a composition near to C AHij with some CO 3 and a monoclinic unit cell similar to that of a-CjA CaClj-lOHjO (T31), but others have proved to be either the a or the p polymorph of that compound or members of a CjA CaCl2 l0H2O-C4AH,3 solid solution series (F26). 

From Table 3 data it follows that in the course of the first 10 days after the submarine sinking radionuclide composition of bottom sediments was determined (99%) by " k -natural-origin radionuclide the remaining 1% was due to man-caused Cs which concentrations (3-5 Bq/kg) were attributed to global fallouts. That conclusion was confirmed by the results of radiation background measurements and independents surveys (see Reference [8]). 

In spite of the composite nature of the stratum corneum, its water sorption isotherm is qualitatively identical to those of the more simple protein systems shown, suggesting that water interacts predominately with the protein components of the corneum. This conclusion is supported further by the results of chloroform-methanol (3/1 by volume) extraction which removed as much as 25% of the original dry weight (lipids and low molecular weight water-soluble components) but did not quantitatively alter the isotherm in the low relative humidities (18). The application of the Zimm-Lundberg cluster theory (56, 57) to the isotherm yields additional information as to the state of the sorbed water in the corneum. The tendency of water to cluster is expressed in this theory by the cluster function CiGn ... 

Bao H., Campbell D. A., Bockheim J. G., and Theimens M. H. (2000a) Origins of sulphate in Antarctic dry-valley soils as deduced fro anomalous compositions. Nature 407, 499-502. 

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