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3038868 
Journal Article 
ACTION AND OPTIMIZATION OF PLASTICIZERS IN SOFT GELATIN CAPSULES 
Reich, G 
1994 
56 
10 
915-920 
WOS:A1994PQ07000002 
When manufacturing soft gelatin capsules it is necessary to use an external plasticizer, because the internal plasticization of gelatin is very low. In this respect the different mechanism of action of varies polyols has been comprehensively investigated. Differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA) were used to quantify the effectivity and compatibility of the plasticizers and to optimize the type and the concentration of a plasticizer with respect to the mechanical properties of the capsule shell. With additional measurements of hardness and pliability it could be demonstrated that the effect of the plasticizer depended not only on the reduction of the glass transition temperature but also on its effect on the gelatin gel structure. In this respect, glycerol which has been used by the capsule manufacturers for many years turned out to be the most suitable plasticizer for soft gelatin capsules. This is because it combines the advantages of a high effectivity, a sufficient compatibility and a low volatility with the ability to interact specifically with the gelatin. In this way it forms a stable thermoreversible gel network. For the sorbitol specifications it was shown by chemical analyses of varies products that plasticizer effectivity and compatibility strongly decrease with an increase in the content of hydrogenated oligosaccharides. This explains why Karion 83/70 should only be used in the capsule shell in combination with glycerol. Although 1,2-propylene glycol is superior to glycerol regarding its plasticizer effectivity, it cannot be used to replace glycerol as a plasticizer in soft gelatin capsules. This is due to its high solvent power for gelatin which has a negative effect on the formation of the gel structure comparable with that of a structure breaker such as urea. This together with its higher volatility compared with glycerol leads to a considerable deterioration in the mechanical strength of the capsules.