Poly(lactic acid) is a biobased polymer and known to biodegrade reasonably quickly in
commercial compost. There has been a growing interest in using it as a replacement for petrochemical
based polymers due to its environmental-friendliness.
Zeolites are crystalline hydrated aluminosilicates of alkali and alkaline earth elements. They can
be natural minerals or produced synthetically. Depending on their framework they can have different
structures and different pore sizes which makes them sorption-specific systems for various volatiles.
There is a growing interest in their application in food packaging as they can adsorb and absorb gases
crucial for extending shelf life of fresh produce, like ethylene and CO2.
Active packaging systems are efficiently used in food packaging. Studies show that PLA and
zeolites can be combined into one material by extrusion. Now the question is if they can act as an
efficient active packaging system
Results obtained showed that two chosen zeolites, natural clinoptilolite and synthetic type 4A,
have high sorption capacities for ethylene and carbon dioxide. Experimental conditions were varied,
temperatures of 23⁰C and 7⁰C, relative humidities of 0% and 100%, headspace gases composed of
varying combinations and concentrations of ethylene, carbon dioxide, nitrogen, and oxygen. Although
low temperature and the presence of water in the system decreased sorption capacities of the zeolites,
most measured amounts of adsorbed ethylene and carbon dioxide were relevant to concentrations
produced and higher than concentrations tolerated by fresh produce, and were promising enough to
continue investigating these two zeolites when incorporated into/onto PLA films
Two techniques to produce PLA/zeolite films were tested, extrusion (followed by injection
molding and compression)and bar solution coating. The second method resulted in films with higher
sorption potential for the two investigated gases since extrusion resulted in the zeolites being too
deeply incorporated into the polymer matrix and having PLA as the polymer with good barrier
properties towards ethylene did limit their sorption capacities. Further development of the most
efficient coating solution and coating method resulted in production of two zeolite coated PLA films.
The newly developed films were compared in sorption studies to two commercially available
bags that are claimed to be ethylene scavengers and as a result to extend fresh produce shelf life. PLA
films proved to be comparable to one of the commercial bags comprised of LDPE impregnated with
zeolites. The second commercial product did not show significant sorption of either of the two gases of
interest. All film samples were tested in two conditions (23⁰C, 0% RH and 7⁰C and 100% RH).Although in
both cases sorption of ethylene and carbon dioxide was smaller than for powder zeolites, with even
higher decrease in low temperature and in the presence of water, the resulting sorbed amounts were
still relevant to real life situations. Experiments designed to determine whether those films could be
reused showed that both zeolite coated PLA films could be successfully reused in room temperature, the
same as for the commercial film.