A new method for systematic identification of nontoxic gels is described. It is based on fundamental chemical reactions between organic compounds containing different functional groups, here called X and Y. Such reactions are found in most textbooks on organic chemistry. The next step is to identify polymers with either X or Y as a functional group. The crosslinker can than be selected from a usually large group of molecules containing at least two X groups (for the Y polymer) or at least two Y groups (for the X polymer).
Using catalogues listing the toxicity of organic chemicals, both the polymers and crosslinkers can be screened, and the least toxic and least costly can be selected for further studies. In these studies the gelant can be optimized regarding gelation time, including the effect of pH and temperature, gel appearance as a function of concentration of both polymer and crosslinker, and the behavior of the gelant and gel in cores.
In this study we report results from experiments carried out on gelant systems based on the ester reaction between a carboxylate group (X) and an alcohol group (Y). Here both polymers containing carboxylate groups (hydrolyzed polyacrylamide) and alcohol groups (polyvinylalcohol) can been used. The corresponding crosslinkers are di- and polycarboxylic acids (X) and di- and polyols (Y). This paper focuses on the system polyvinylalcohol and polycarboxylic acids.