Solid state properties

Solid-state characterization is one of the most important functions of the preformulation group, which is assigned the responsibility of making recommendations for further formulation work on a lead compound. Physical properties have a direct bearing on both physical and chemical stabilities of the lead compound. Much of the later work on formulation will depend on how well the solid state is characterized from the decisions to compress the drug into tablets to the selection of appropriate salt forms. The studies reported in this section, of course, apply to those drugs that are available in solid form, crystalline or amorphous, pure or amalgamated. 

The stability of the salt could also be an important issue, and depending on the pKa, many properties can change, including indirectly related physical characteristics, such as volatility (e.g., hydrochloride salts are often more volatile than sulfate salts). Discoloration of the salt form of drugs is also prominent for some specific forms, as the oxidation reactions (often accompanied by hydrolysis) are a result of factors, such as affinity for moisture, surface hydrophobicity, and so on. Hydrolysis of a salt back to the free base may also take place if the pK of the base is sufficiently weak. 

Oriented films are obtained by extrusion (for a temperature around 250 °C) through a flat die. After the die the film is amorphous with a T, of 30 MPa and a e. of 500 %. After monoorientation by stretching a. increases up to 500 MPa but the film is very brittle. 

On the other hand, after biorientation and thermal treatment, a film with good mechanical properties is obtained (E = 3-4.2 GPa and e. of 70-130 %). 

These films present excellent resistance to biological agents and are autoextinguishable. Their main applications are in the electric field (condenser, insulation, etc) and sterilizable packaging. They don t need to be plasticized. 

Mechanical properties of PET fibers commonly used in the textile field are characterized by high values of both Young s Modulus (2-2.7 GPa) and and by low values. In the case of normal tenacity PET fibers, is 3400-6350 MPa with of 19-40 % and for high tenacity PET fibers increases up to 7300-11550 MPa with values of 10-13 % (5-7). 

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Although it is required to refine the above condition I in actuality, this rather simple but impressive prediction seems to have much stimulated the experiments on the electrical-conductivity measurement and the related solid-state properties in spite of technological difficulties in purification of the CNT sample and in direct measurement of its electrical conductivity (see Chap. 10). For instance, for MWCNT, a direct conductivity measurement has proved the existence of metallic sample [7]. The electron spin resonance (ESR) (see Chap. 8) [8] and the C nuclear magnetic resonance (NMR) [9] measurements have also proved that MWCNT can show metallic property based on the Pauli susceptibility and Korringa-like relation, respectively. On the other hand, existence of semiconductive MWCNT sample has also been shown by the ESR measurement [ 10], For SWCNT, a combination of direct electrical conductivity and the ESR measurements has confirmed the metallic property of the sample employed therein [11]. More recently, bandgap values of several SWCNT... 

V. EFFECT OF CHAIN BRANCHING ON SOLID STATE PROPERTIES... 

The effect of MW and MWD on the solid state properties have been extensively studied [11,12,82]. These studies have been made both on fractionated and whole polymer samples. Attempts have also been made to correlate the solution viscosity, melt viscosity, MFI and other related parameters, which represent the MW and MWD of the polymers, with the solid state properties. Table 6 summarizes the results of various studies on effect of MW and MWD on the properties of PEs. 

Block copolymers have become increasingly important in recent decades. This importance is due to the fact that their special chemical structure yields unusual physical properties, especially as far as solid-state properties are concerned. Block copolymers are applied in various fields, they are used as surfactants, adhesives, fibres, thermoplastics, and thermoplastic elastomers. 

Solid solutions are very common among structurally related compounds. Just as metallic elements of similar structure and atomic properties form alloys, certain chemical compounds can be combined to produce derivative solid solutions, which may permit realization of properties not found in either of the precursors. The combinations of binary compounds with common anion or common cation element, such as the isovalent alloys of IV-VI, III-V, II-VI, or I-VII members, are of considerable scientific and technological interest as their solid-state properties (e.g., electric and optical such as type of conductivity, current carrier density, band gap) modulate regularly over a wide range through variations in composition. A general descriptive scheme for such alloys is as follows [41]. 

The phenomenon of pseudopolymorphism is also observed, i.e., compounds can crystallize with one or more molecules of solvent in the crystal lattice. Conversion from solvated to nonsolvated, or hydrate to anhydrous, and vice versa, can lead to changes in solid-state properties. For example, a moisture-mediated phase transformation of carbamazepine to the dihydrate has been reported to be responsible for whisker growth on the surface of tablets. The effect can be retarded by the inclusion of Polyoxamer 184 in the tablet formulation [61]. 

Rheological studies explore the flow of a material as an external force acts upon it. This flow depends not only on the magnitude and directionality of the external force, but also on the molecular composition and structure of the material that experiences the force. In this chapter, we will focus on the flow behavior of molten polymers, as it relates to their molecular structure. It is important to note that the molecular characteristics that determine a molten polymer s behavior also define the polymer s solid state behavior. Therefore, many of the concepts introduced in this chapter will reappear in Chapter 8, Solid State Properties of Polymers., ... 

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