Moisture and Solvents

Moisture can be important by acting as a plasticizer or by acting as a solvent for some catalytic species. UV light and oxygen usually will have different effects on a polymer depending on the humidity. This is especially true when the polymer has a 

FIGURE 12.3 Four stages observed in oxygen absorption measurements on elastomers. 

FIG U RE 12.4 Concentration of peroxide, carbonyl, and ester groups as a function of oxygen absorbed in oxidation of 5-phenyl-2-pentene at SOX. (Data from Shelton, J. R., Rubber Chem. Technol. 30, 1251, 1957.) 

The overall view of chemical attack is impossible to condense because of the wide variety of chanical species and polymeric substrates. Whenever a polymer is suggested as a material of construction in a chemical plant, a thorough consideration of resistance to specific chemicals is desirable. Polymeric pipes and tank liners are used for acids and alkalis, oxidizing and reducing agents, and all kinds of organic reactants. In each case the most economical solution will be specific, because factors of initial cost, versatility, and maintenance may enter in. 

Swelling of rubbers and polymers was mentioned in Section 2.6 in connection with cohesive energy density. Solvents may extract portions of polymer systems, for example, the plasticizer from a polyfvinyl chloride)-based system. Swelling at a surface may set up a stress that is relieved by crazing. Craze lines consist of oriented polymers. They become evident by their opacity in glassy polymers stressed by a purely mechanical couple or by surface absorption of a liquid (see Section 10.7). 

---

Process validation should be extended to those steps determined to be critical to the quality and purity of the enantiopure drug. Establishing impurity profiles is an important aspect of process validation. One should consider chemical purity, enantiomeric excess by quantitative assays for impurity profiles, physical characteristics such as particle size, polymorphic forms, moisture and solvent content, and homogeneity. In principle, the SMB process validation should provide conclusive evidence that the levels of contaminants (chemical impurities, enantioenrichment of unwanted enantiomer) is reduced as processing proceeds during the purification process. 

Both are stable metallocarbene complexes, but they have very different reactivity profiles. The molybdenum catalyst is highly reactive and is effective widi sterically demanding olefins. Its drawbacks are diat it is not highly tolerant of diverse functional groups and has high sensitivity to air, moisture, and solvent impurities. The ruthenium system, on die odier hand, is catalytically active in die presence of water or air, and it exhibits a remarkable functional group tolerance. It is not a reactive as the molybdenum catalyst, particularly toward sterically bulky substrates. However, it is readily available and is die reagent of choice for all but die most difficult substrates. 

Definition of the API in terms of its critical quality attributes. Among the attributes that should be considered are chemical purity qualitative and quantitative impurity profiles physical characteristics such as particle size, bulk and tap density polymorphic forms moisture and solvent content homogeneity and microbial quality (if the product is susceptible to microbial contamination). 

The mechanical properties of polymers are further influenced by external conditions such as temperature, the pressure of the test environment and the presence of other additives or impurities such as moisture and solvents. The tensile strength, modulus and hardness decrease with an increase in temperature, but the elongation at break will increase. The effect of temperature on the mechanical properties of polymers is much greater than in any other category of materials. 

This is a technique used to measure the change in weight of a material as a function of temperature in a controlled atmosphere based on material thermal stability, filler content in polymer, moisture and solvent content, and the percent composition with different components. 

Packaging easy machineability, high strength, dimensional stability over a broad temperature range, crystal clarity, printability, moisture and solvent resistance, barrier against oxygen and water vapor... 

Properties. Since nrethanes are polymerized and cross-linked in plac they have excellent resistance to chemical, moisture and solvents. They are available in hardnesses ranging from tough, abrasion-resistant varieties to low-modulus versions suitable for extreme temperature ranges (see Fig. 41.1). 

Most versatile adhesive available excellent tensile-shear strength poor peel strength excellent resistance to moisture and solvents low cure shrinkage variety of curing agents/hardeners results in many variations... 

No aging and subsequent testing were performed beyond those in Table 13. Resorcinol dicyanate is one of many examples where excellent potential was demonstrated but no further results are available. Problems such as availability, toxicity, moisture and solvent resistance, low shelf life, processability, etc. often discourage further adhesive development. ResorcinoMicyanate is unavailable but a few other dicyanates are commercially available. No adhesive properties have been reported on these dicyanates. The adhesive work on resorcinol dicyanate is representative of company funded research that is not readily available to the public. 

Lactic acid and its salts act as inhibitors of bacterial spoilage and are used in the disinfection process (Datta and Henry, 2006). Polyactide may be also used as a fiber for clothing, carpets, and industrial applications. Lactic acid is also used for cosmetic and pharmaceutical purposes (eg, lotions preparation, dialysis, calcium deficiency therapy, and antiacne treatments, respectively). Long chain esters have been applied as moisturizers and solvents. 

---