Design of biodegradable composite films for food packaging

Desalination 199 (2006) 331333

Presented at EUROMEMBRANE 2006, 2428 September 2006, Giardini Naxos, Italy.

0011-9164/06/$ See front matter 2006 Elsevier B.V. All rights reserved.

Design of biodegradable composite films for food packaging

Vtor Alvesa*, Nuno Costab, Loic Hillioub, Fbio Larotondab,Maria Gonalvesb, Alberto Serenob, Isabel Coelhosoa

aREQUIMTE-CQFB, Departamento de Qumica, Faculdade de Cincia e Tecnologia,Universidade Nova de Lisboa, Quinta da Torre, 2829-516 Caparica, Portugal

email: [email protected], Departamento de Engenharia Qumica,

Faculdade de Engenharia da Universidade do Porto, Rua Dr. Roberto Frias, s/n, 4200-465 Porto, Portugal

Received 22 October 2005; accepted 4 March 2006

1. Introduction

The materials most used for food packaging arethe petrochemical-based polymers, due to theiravailability in large quantities at low cost andfavourable functionality characteristics, such as,good tensile and tear strength, good barrier proper-ties to O2 and heat sealability [1]. However, thesematerials are totally non-biodegradable, leading toserious ecological problems. As a consequence,the consumer demand has shifted to eco-friendlybiodegradable materials, especially from renew-able agriculture by-products, food processingindustry wastes and low cost natural resources.

The biopolymers commonly used to producefilms are carbohydrates, often vegetal starchy andpectic materials and proteins, vegetal and animal[2,3]. Usually, these biopolymers require thattheir mechanical and rheological properties beimproved by molecular restructuring or by theinclusion of food grade additives. In addition tothe appropriate mechanical properties, the filmsmust have also the adequate permeability to watervapour and gases. The specific barrier requirements

of the packaging depend upon the products charac-teristics and the intended end-use application. In thecase of a packaged product whose deterioration isrelated to its moisture content, the barrier proper-ties of the package relating to water vapour willbe of major importance in extending shelf life.Similarly, the oxygen concentration in a perme-able package will affect the rate of oxidation ofnutrients such as vitamins, proteins and fattyacids.

The required specific permeability propertiesof the films can be obtained by inclusion of inertimpermeable barriers and/or reactive compoundsin the polymer matrix. The inert barriers canreduce permeability by increasing the diffusionpath, while the reactive compounds interactselectively with the diffusing species increasingthe time before a significant permeability occurs.

The objective of this work is to develop modelcomposite films based on commercial pectin andk-carrageenan, and characterize them in terms oftheir hygroscopic and mechanical properties, andpermeability to gases (oxygen and carbon diox-ide) and water vapour. In order to design filmswith specific permeability properties, reactive com-pounds (ascorbic acid and/or calcium hydroxide to*Corresponding author.

doi:10.1016/j.desal.2006.03.078

332 V. Alves et al. / Desalination 199 (2006) 331333

interact with oxygen and carbon dioxide, respec-tively) are added to the polymer matrix, while micaflakes are used as impermeable barriers.

2. Experimental

Commercial k-carrageenan (SKW Biosys-tems, France) and pectin from citrus fruit(SigmaAldrich, Spain) were used to preparemodel carrageenanpectin aqueous mixtures,with different proportions of the two compo-nents. The films were prepared by wet casting ofthe aqueous solutions and further drying. Theirmechanical properties were studied using aTAXT2 (Stable Micro Systems, England) inaccordance with ASTM D-882-91 (1996), andthe glass transition temperature (Tg) was mea-sured using a Shimadzu DSC-50 differentialscanning calorimeter. Water sorption isothermswere determined by placing the samples in des-iccators with different relative humidities,imposed by the use of saturated saline solutions,and weighed periodically until they reachedconstant weight. The water vapour permeancewas measured gravimetrically, based on theASTM E-96-80. In order to determine the gaspermeability, the films were placed between twosealed chambers containing nitrogen at the sametemperature and pressure. A known quantity ofthe test gas was injected in one of the chambers(feed chamber) and the solute flux across themembrane came indirectly from measuring thetotal pressure increase with time in the perme-ate chamber.

3. Results and discussion

In the water sorption experiments, the amountof water at equilibrium in the film was higher forfilms with pure carrageenan, which indicates thatcarrageenan is more hydrophilic than pectin. It wasalso observed that the amount of carrageenan inthe films leads to a decrease in the glass transitiontemperature (Tg). This result can be explained by

the plasticizing effect of carrageenan itself, sincethe 100% carrageenan film revealed a lower Tgthan the pure pectin film. Alternatively, theincreased hygroscopic properties of the pure carra-geenan film and the inherent water plasticizingeffect could be at the origin of the observeddepressed Tg.

The addition of carrageenan resulted also onan improvement of the films mechanical proper-ties, by decreasing the Young modulus andincreasing the strain at break. These results arein agreement with the observed plasticizingeffect of carrageenan.

It was also observed that, the films becomemore permeable to water vapour as the carrag-eenan content increases, until a plateau is reached.This increase in the water vapour permeance canbe explained by the higher hydrophilic character ofcarrageenan when compared to pectin, alreadyobserved in the water sorption experiments. How-ever, beyond a critical content of about 67%,a further increase in films carrageenan content hasnot a significant influence on the water vapour per-meance. The inclusion of mica flakes in the poly-mer matrix (10% w/w in a dry basis) led to a watervapour permeance decrease of about 27%. Theflakes act as impermeable barriers that increase thediffusional path of the water molecules.

Ongoing work is focused on the characteriza-tion of the films in terms of permeability togases (oxygen and carbon dioxide). The resultssuggest that these films are more permeable towater than to oxygen and carbon dioxide, and itis anticipated a decrease of the gas permeabilitywith the inclusion of mica flakes. Moreover, theinclusion of ascorbic acid, which reacts withoxygen, leads to an improvement of the filmsselectivity (CO2/O2).

4. Conclusions

The model carrageenanpectin films stud-ied showed increased mechanical properties,lower glass transition temperatures, increased

V. Alves et al. / Desalination 199 (2006) 331333 333

water permeability and hydrophilic propertieswith increased carrageenan content. The waterpermeability was significantly reduced byincluding mica flakes in the polymer matrix,which act as impermeable barriers. These filmsrevealed to be more permeable to water vapourthan to oxygen and carbon dioxide, and the filmsselectivity (CO2/O2) was enhanced by addingascorbic acid to the polymer matrix. The perme-ability properties obtained can be advantageousfor the preservation of fresh fruit and vegetables.

References

[1] R.N. Tharanathan, Biodegradable films andcomposite coatings: past, present and future,Trends Food Sci. Technol., 14 (2003) 7178.

[2] L. Vermeiren, F. Devlieghere, M. van Beest, N.de Kruijf and J. Debevere, Developments in theactive packaging of foods. Trends Food Sci.Technol., 10 (1999) 7786.

[3] M. Alvarez, Review: active food packaging,Food Sci. Technol. Int., 6(2) (2000) 97108.

EUR117.pdf

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Design of biodegradable composite films for food packaging