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Chitosan coating/compounding of PLA materials

Two very interesting features of chitosan in relation to food packaging are its very high gas barrier and antimicrobial properties.

The following chitosan forms were evaluated:

Initial chitosan, microcystalline chitosan (MCCh), chitosan salts (lactate, acetate, glutamate, maleate), and modified chitosan salts (lactate, acetate, glutamate). Chitosan coating blends made of modified chitosan lactate and modified MCCh. These forms were prepared according to procedures elaborated at IWCh.

Selected chitosan forms were used for:
- Coating of PLA film surface;
- Compounding with PLA granulate.

In the process of coating PLA film surface, the chitosan was applied as a one-sided coating, double-sided coating, and by inserting chitosan between two layers of PLA film and pressing the layers together. Chitosan was successfully coated on PLA-based materials.

All chitosan forms displayed a distinct effect on the oxygen permeability of coated PLA with a resultant OTR below 4cm3/m2/24h at 23 degrees Celsius, 0% RH (100mm thick materials). The OTR was lowered considerably in comparison to uncoated, flexible PLA materials. Earlier studies on mechanical properties of modified PLA/chitosan films showed poor adhesion of chitosan to the PLA film surface and heterogeneity of the coating, but the moisture sensitivity of the latest modified MCCh coating on PLA showed a significant improvement compared to these earlier chitosan types tested, as no disintegration was seen even after the chitosan coating was conditioned at 38 degrees Celsius and 100% RH. Chitosan seemed not to influence the WVTR, which was 101g/m2/24h for the chitosan-coated PLA films.

The selected chitosan types exhibited antimicrobial activity. It was found that both chitosan salts and modified chitosan salts demonstrated high bacteriostatic and bactericidal activity against E. coli. In the case of MCCh only bacteriostatic action was observed.

All chitosan forms exhibited biological activity within the investigated incubation times and temperatures. Among the tested microorganisms, the highest relative inhibition (80-100%) was found for Penicillium roqueforti and Penicillium nalgiovense, and for Kluyveromyces marxianus and Debaromyces hansenii. These fungi and yeast are associated with the cheese microflora.

Evaluation of chitosan-coated PLA films proved that the antimicrobial effect against the tested yeast and mold strains, i.e. P. nalgiovense, P. roqueforti, P. commune, P. caseifulvum, and K. marxianus was regained during processing of the films.

Chitosan lactate is biodegradable. Further evaluation of the other modified chitosan forms is required.

Finally, compounding of PLA granulate with chitosan powder was evaluated. It was noted that only chitosan preparates characterized by good thermo-stability could be applied for preparation of PLA/chitosan composites with suitable properties. The investigations on thermal properties proved very good thermo-stability for initial chitosan but some chitosan forms displayed a little worse thermo-stability. In most cases the degradation occur in temp. 200-299 degrees Celsius so these values are acceptable for manufactures of PLA/chitosan composites (temp. not higher than 180 degrees Celsius are used).

The mechanical and barrier properties of chitosan compounded PLA films were not sufficient to meet the requirements with respect to cheese packaging, and the compounding process should be further optimised.

The PLA/chitosan materials are recommended for products requiring medium and high oxygen barriers, and where the water vapour transmission rate is not critical.

Informations connexes

Reported by

Institute of Chemical Fibres (IWCh)
ul. Sklodowskiej-Curie 19/27
90-570 Lodz
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