Gelatin rigidity

The second glass transition was associated with gelatin rigid blocks composed of sequences mainly made up of the imino acids proline and hydroxyproline including glycine at every third position which are predominant in mammalian gelatin. So the transition at -30 C can be attributed at the glass transition of plastified soft blocks in WG. 

In DSC traces of WGSCB20 the thermal transition associated with the Tg of plasticized gelatin soft blocks moved from -30 °C of WG to -35 °C (Fig. 4). The other two thermal events present in WG resulted in a single broad one with minimum at about 90°C. This thermal behavior results from the overlaying of the evaporation of volatile present in the composite with the transition related to the Tg of gelatin rigid blocks. 

Solution Filtration. The polymer solution, free of unacetylated ceUulose, rigid particle contaminants, and dirt, must pass through spinnerets with holes of 30—80 ]lni diameter. Multistage filtration, usuaUy through plate-and-frame filter presses with fabric and paper filter media, removes the extraneous matter before extmsion. Undesirable gelatinous particles, such as the hemiceUulose acetates from ceUulose impurities, tend to be sheared into smaller particles rather than removed. The solution is also aUowed to degas in hoi ding tanks after each state of filtration. 

Gelatin stmctures have been studied with the aid of an electron microscope (23). The stmcture of the gel is a combination of fine and coarse interchain networks the ratio depends on the temperature during the polymer-polymer and polymer-solvent interaction lea ding to bond formation. The rigidity of the gel is approximately proportional to the square of the gelatin concentration. Crystallites, indicated by x-ray diffraction pattern, are beUeved to be at the junctions of the polypeptide chains (24). 

Figure 2. Rigidity of gels from gelatin fractions as function of reduced viscosity...

Figure 4. Rigidity vs. time for a high standard rigidity (250 Bloom) calfskin gelatin at 10° C, pH 6.0, 0.1 sodium chloride...

The characteristic properties of the gels are dependent on the nature of the fibrils, the more coarse the fibrils the more moist and elastic the gel, the finer the fibril the drier and more rigid the resultant gel silica gel may be taken as representative of a dry rigid fine fibril gel and gelatine as that of the relatively coarse elastic type. 

---