Thermal stability, polysaccharide polymers

A significant limitation in the use of polysaccharide polymers in water-based drilling fluids is their temperature stability. The polysaccharide polymers are prone to thermal-oxidative breakdown that reduces their molecular weight. Thomas (33) has observed that the upper temperature limit of starch is about 100 °C and 135 °C for CMC. Darley and Gray (25) have quoted comparable limiting temperatures. Other polysaccharide polymers are restricted to even lower temperatures. Guar gum, for example, is not used at temperatures above 70 °C (25), which limits its use to shallow wells. 

A number of additional examples of protein delivery via polysaccharides are available in the scientific and patent literature. Edman et al. (1980) have demonstrated release of carbonic anhydrase, catalase, human serum albumin, and immunoglobulin G from cross-linked biodegradable polyacryl dextrans having molecular weights ranging from 10,000 to 2,000,000. Thermal stability of carbonic anhydrase was found to be enhanced via entrapment in microspheres of the above polymer. Schroder (1984) has shown that... 

Martin (1983) examined many commercially available polymers, including HPAMs, polysaccharides and other polymers. He developed a very wide range of screening tests which examine most of the properties discussed above, including thermal stability and shear stability. He showed that some of the modified acrylamide polymers exhibit improved performance compared with conventional HPAM, in so far as these modified materials generate higher viscosities in brine. In this work, a very large number of new... 

Thermal Stability of Polysaccharide Polymers. Several long-term (16- to 22-month) polymer stability tests were conducted with the four brine systems used in the laboratory investigation. The results showed that polysaccharide polymers had good stability at reservoir temperature even in the presence of oxygen. In the particular case of FIB, oxygen was excluded because of its reaction with H2S. PS(P) solution viscosity actually increased slightly during the tests where FIB was used as the solvent. 

---