Sven Saengerlaub and Karin Agulla found the sorption quality of calcium chloride and sodium chloride to be much higher than that of polar polymers such as polyamide, cellulose fibers and desiccants, such as silica gel.
The researchers said the novel polymer composite films stabilize the relative humidity (RH) in their environment so the undesired effects of humidity can be avoided, such as condensation in the packaging.
Polymers such as polypropylene (PP), polylactic acid (PLA), polyethylene terephthalate (PET) and polystyrene (PS) were investigated and stretched.
The most resistant film was polylactic acid (PLA) while sodium chloride (NaCI) in combination with PLA and PP worked best, Saengerlaub told FoodProductionDaily.com.
“In this case the water vapour absorption and desorption was much faster than for polypropylene (PP). PP has a lower water vapour transmission rate. Therefore the selection of the carrier polymer has a high impact on efficiency.
“The salt in the films absorb and desorb water vapour in high quantities. It is ten to one hundred times more than desiccants such as silica gel can absorb,” he said.
“One objective is the prevention of water vapour condensation in closed packets. The intention is a longer shelf life and better product appeal, because customers consider condensed water vapour as non-hygienic.”
Fluctuations of relative humidity (RH) and inappropriate storage often cause undesired effects. Examples are the condensation of water vapour during temperature fluctuations, agglomeration of powders, microbial growth at high RH and drying out of foods.
Possible solutions for these problems are films and moulded parts made of humidity regulating polymer composites containing salts as active substances, suggested the researchers, identifying fresh produce as the most promising application.
Saengerlaub said: “We got good results for champignons where our results indicate a shelf life extension by several days. Other products are powdery products or refrigerated products where temperature fluctuations cause water vapour condensation that needs to be prevented.
“When a desiccating salt such as calcium chloride is used the packed good can be protected from water vapour uptake. Possible application areas are dry hygroscopic products such as cereals.”
Water vapour prevention
Many salts absorb water vapour so they can regulate the RH in their environment and it is possible to prevent or at least reduce the impact of water vapour condensation and of dry environmental conditions but the integration of the salts into the polymer composites take more efforts than standard additives, according to Saengerlaub.
“The kind of selected polymer and the kind of selected salt have a big influence. Our development was scaled up to the industrial machines of our project partners.
“They produced films and we stretched them and they made thermoformed trays from them on production lines. The trials went quite well, i.e. we could show that the development runs in the industry.”
Saengerlaub added that further studies need to verify the benefit of quality preservation giving by the packaging materials and the migration of salts and sorption velocity should be examined.
“The selection of the salt sets the absorption and desorption behaviour. It is best to use polymers with a high water vapour transmission rate.
“Next we will examine migration behaviour, which is an important property. Other food products, such as cheese should be tested with our films and trays.”