Methylcellulose, hydrated

Combining thermal- with pH-dependent gelation, Kumar et al. [86] developed a combination of methylcellulose 15% and carbopol 0.3%. This composition exhibited a sol-to-gel transition between 25 and 37 °C with a pH increase from 4 to 7.4 [203], A possible mechanism for the thermal effect could be the decrease in the degree of the methylcellulose hydration, while the polyacrylic acid can transform into a gel upon an increase in pH due to the buffering properties of the tear fluid [1]. 

The stabilizing effects of methylcellulose and hydrated magnesium silicate were applied to calamine lotion. Sample 1 was the U.S.P. XV calamine lotion, and sample 2 the U.S.P. XV calamine lotion with 0.5% of methylcellulose. Sample 1 showed 50% separation, while sample 2 showed 12% separation after 24 hours at room temperature. 

For methylcellulose, increased matrix material concentration did not affect the release profile (Table 4). The sustained action can be directly attributed to the formation of a hydration layer by this polymer. This hydration layer, however, did not resist attrition and remain intact. Consequently, attrition becomes more important than diffusion the hydrated layer dissolves away almost as rapidly as it is formed. On the contrary, the dibasic calcium phosphate dihydrate did not diffuse outward, but rather became entrapped within the matrix and effected an increase in release of drug because its presence necessarily decreased the polymer concentration. 

Katzhendler, I. Mader, K. Friedman, M. Structure and hydration properties of hydroxypropyl methylcellulose matrices containing naproxen and naproxen sodium. Int. J. Pharm. 2000, 200, 161-179. 

The swelling properties of HPMC as a sustained relea.se, hydrophilic matrix binder in tablets are well known. This polymer also has the ability to form a gel network to delay drug release (30,32.34.36,137). The use and efficiency of HPMC as a tablet and granule binder is comparable with methylcellulose. HPMC is available in a variety of grades with different solution viscosities and it is soluble in both water and hydroalcoholic solutions. However, HPMC is more soluble in cold water than hot but more dispersible in hot water than cold. Therefore, it is recommended to hydrate the HPMC powder in very hot water first, under agitation, and then to cool the solution down as quickly and as low as possible in order to avoid lumping problems. 

Katzhendler I, Mader K, Azoury R, et al. Investigating the structure and properties of hydrated hydroxypropyl methylcellulose and egg albumin matrices containing caihamazepine EPR and NMR study. Pharm Res 2000 17(10) 1299-1308. 

Recently, we have measured the partial molar heat capacity Cp of hydrated samples of methylcellulose and elastin at temperatures ranging from 110°K to 330 K (37). For both, just as for collagen, at any temperature, the partial molar heat capacity of water appears to be independent of water content. Its values is equal to that of ice from 110°K to 150°K, where it starts to increase over that of ice and then increases virtually linearly with temperature to values close to that of liquid water at room temperature. Schematically, the results are given in... 

Hardening of cement mortars modified with water-soluble polymers comprises both cement hardening by hydration as well as polymer solidification by coagulation and film formation. Whereas the effect of polymer dispersions on the microstructure formation is frequently studied [1], only little information is available about the effect of polymer solutions. In contrast to polymer dispersions, water-soluble polymers are dissolved in the mixing water on a molecular scale and no surfactants are needed. However, the addition of small amounts of water-soluble polymers (usually below 4%) also influences the properties of the hardened material [2], This paper deals with the effect of the presence of water-soluble polymers on the microstructure. The study is made by means of SEM investigation. Polyvinyl alcohol-acetate (PVAA), Methylcellulose (MC) and Hydroxyethylcellulose (HEC) are applied in a 1 % polymer-cement ratio. This study was part of the doctoral research of E. Knapen [3],... 

Sarker N, Walker LC (1995) Hydration-dehydration properties of methylcellulose and hydroxy-propylmethylcellulose. Carbohydr Polym 27 177-185 Schadler LS, Brinson LC, Sawya- WG (2007) Polymer nanocomposites a small part of the story. JOM 59(3) 53-60... 

Finally, the cellulose derivatives are mosdy used as matrix formers for sustained release pellets due to their hydration and gel formation ability, with formation of a diffusion layer around the drug particles and delays its release into the dissolution medium. Certain cellulose esters, such as hydroxypropyl methylcellulose acetate succinate (Aqoat-AS ) or cellulose acetate phthalate, are used for the production of enteric release pellets, because they are soluble in the mildly basic intestinal fluid. 

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