In order to get homogeneous solutions, the Tylose® must first be dispersed. It is advisable to use a variety of methods to prepare aqueous cellulose ether solutions, depending on the type of ether concerned and the physical form of the particular Tylose product. A number of well-established processes are described below, but need to be adapted to the requirements of each individual case.
1. How to dissolve non delayed solubility Tylose grades
Even though cellulose ethers are soluble in a given solvent, they may tend to form lumps while being dissolved. This is due to the fact that cellulose ether particles form aggregates during the dispersing process and thus cannot be fully wetted with water. Furthermore, these aggregates are quickly covered by a swollen layer of gel of already dissolved Tylose particles, which further hinders the dissolving process. However, depending on the type of etherification and the physical form (powder or granules), a complete and lump-free dispersing of Tylose can be ensured.
Generally it is recommended (independent of etherification and physical form) to sprinkle the Tylose uniformly into the solvent during intensive stirring. While dissolving, the viscosity of the solution increases continuously so that already after a few minutes the intensity of the stirring can be decreased in order to avoid too many air bubbles in the solution. Stirring should be continued until the solution is homogeneous. For the preparation of aqueous cellulose ether solutions it is recommended to read the following, specific instructions:
→ Tylose MH and Tylose MO powder grades
How to prepare solutions on laboratory scale
The powder grade MHEC or MHPC is dispersed in a part of the water needed for the complete dissolving process and which has been heated to about 80°C. Next, by adding the remaining cold water, the required concentration and temperature are reached. For some applications it may be advantageous to heat the entire amount of water, disperse the Tylose in the hot water and cool down the resulting dispersion, until the Tylose has dissolved completely.
→ Tylose MH and Tylose MO granular grades
MHEC or MHPC in granular form is easier to disperse than pulverized products, but needs longer stirring time for complete dissolution. Granular Tylose MH and Tylose MO grades can be dispersed in cold water without forming any lumps. Dispersion in hot water is possible, although not necessary. Depending on the stirring intensity, the dissolution process of granular Tylose MH and Tylose MO grades is usually completed within 60 minutes.
→ Tylose H granular grades
Tylose H grades in granular form can be dispersed in cold and in hot water, no matter how finely ground/granulated the Tylose is. However, lumps may form if the temperature is too high (> 80 °C). The time needed for complete dissolution of Tylose H grades is similar to that of Tylose MH and Tylose MO grades.
→ Tylose H powder grades
Tylose grades in powder form (except Tylose H...N grades) are of the delayed solubility type. For these types, the delayed solubility feature is less pronounced than with the “Y” grades, which is the reason why Tylose H powder grades are not denoted with an additional “Y”. The Dispersion of Tylose H grades is described in the following section “Simplified Dispersion by Delayed Solubility”
2. Simplified dispersion by delayed solubility
Tylose products with delayed solubility are denoted with an additional “Y”, for example Tylose H 6000 YP2 (see chapter Nomenclature of Tylose). Besides Tylose products, which are denoted with a “Y”, all Tylose H powder grades show (slight) delayed solubility, unless they are produced for pharmaceutical applications.
Using a stirrer delayed solubility Tylose grades can easily be suspended in pH neutral water without forming any lumps. For delayed solubility Tylose, the dissolving process only begins after all the Tylose particles are completely dispersed. This effect is due to a chemical surface treatment of Tylose. While the Tylose is not yet completely dissolved, the surface treatment prevents the Tylose from quickly being covered by a coat of gel, which would considerably hinder the dissolution process.
Adjusting the pH to alkaline values can eliminate the delayed solubility. Please note that the ph value should be adjusted after the Tylose is completely dispersed. Raising the pH value before the dispersion results in lumps.
Adjusting the pH value between values of 3 and 6 is not recommended for Tylose grades with delayed solubility, since this would considerably prolong the dissolution time (up to several hours). Extreme pH values (<3 and >12) can result in the chemical decomposition of the cellulose ether molecules.
Please see more information about processing hints for Tylose with delayed solubility (Y-grades).
