Functional packaging materials: factors affecting the capacity and rate of water adsorption in desiccant composites

Abstract

Ten different polymers were selected as possible matrices for zeolite-containing desiccant composites utilized in the preparation of functional packaging materials. Water uptake was determined at 100 % RH and the results were analyzed to identify factors influencing the capacity and rate of water adsorption. The results showed that the desiccant was able to adsorb a considerable amount of water in its free pores. The adsorption capacities of the composites depended linearly on the amount of desiccant present in the composite, but were independent of the type of polymer used. Water initially diffused rapidly into the composites, but this diffusion slowed over time and also with increasing desiccant content. The latter effect can be explained by the increase in the diffusion path as the zeolite content increases. The initial rate of diffusion depended solely on the specific free volume of the matrix, and this factor also strongly influenced the overall rate of water adsorption. However, the latter characteristic also depended on other factors, such as the dispersion of the desiccant in the matrix. Matrix type and zeolite content must be selected according to the task to be fulfilled; fast adsorption can only be achieved by using polymers with large free volumes.