FAIR-CT98-4416 BIONANOPACK: Biodegradable nanocomposite food packaging

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Biopolymers/Gums : FAIR Area 1.2 - Green Chemicals and Polymers Chain : Nanotechnology : Packaging : Paints/Coatings/Plastics : Starch

	Contract No:	FAIR-CT98-4416
	Date Prepared:	July 2001
	Source:	Final Report

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Final Report

Source: Progress Report, January 2001

Consortium: The project was co-ordinated by the TNO Institute of Industrial Technology, Eindhoven (The Netherlands), in partnership with Research and Technology of Plastic materials Institute of CNR, Naples (Italy), BIOP Biopolymer GmbH, Dresden (Germany), Laviosa Chimica Mineraria SPA, Livomo (Italy), Interchem Hellas S.A, Athens (Greece), Ortobell s.r.l., Bergamo (Italy), National Center For Scientific Research, Institute of Physical Chemistry, Paraskevi (Greece), Conzorzio Interuniversitario Nazionale Per La Chimica Dei Materiali, Florence (Italy).

Abstract

Objectives The overall aim of the project is to develop a new biodegradable food packaging material with a low permeability for oxygen, carbon dioxide nitrogen and water vapour, by homogeneously dispersing functionalised layered silicates (clay minerals) in thermoplastic starch via polymer melt processing techniques. The specific objectives of this project are:

• Modification of layered silicates, i.e. clay minerals, with a new class of non- ionic modifying agents in order to compatibilise the clay with thermoplastic starch.
• Development of a polymer melt process, compatible with current polymer processing techniques, to homogeneously disperse modified clay particles in thermoplastic starch in order to be able to produce starch-clay nanocomposite films.
• Characterisation of nanocomposite films, particularly with respect to mechanical properties, thermal stability, biodegradability and permeability towards oxygen, nitrogen, carbon dioxide and water vapour.
• Optimisation of the polymer melt processing and the mechanical properties, thermal stability and permeability of the starch-clay nanocomposites by adjusting the chemical structure of the starch, the clay modification agents and the clay content.
• Development of prototype, packaging film material for food packaging applications, including a full characterisation of the packaging materials, its permeability in modified atmosphere applications and its biodegradability. Barrier specifications of prototypes depend on application demands. Verification of food packaging film for food application according to EEC directives.
• Scaling up of the modification of the clay minerals and the dispersion of the modified clay minerals in thermoplastic starch via polymer melt processing to a 5 kilogram pilot plant scale, in order to produce prototype packaging films.

Activities It is expected to attain the above described objectives through the following tasks:

• Modification of clay particles
• Preparation of starch-clay nanocomposites
• Starch modification to optimise the compatibility of the starch component in the polymer-clay nanocomposites.
• Complete characterisation of prototype starch-clay nanocomposite films,
• Biodegradable prototype packaging development
• Scaling up of raw materials preparation.

Progress The progress of the project, is reviewed task by task.

Task 1. Two more clays have been selected for testing. The modification of clay 7 with modifier 2 resulting, in "Clay modified 4" has been optimised and up-scaled to 100 litres. Work has been done on the cationic starch modifier but most of the work has been successfully focused on the possibility to use only water as a modifier for the clay samples. It was shown to be possible to use a "wet" clay alone as starting material for making nanocomposites. An optimised procedure has been found for using a clay/water mixture alone as modified clay for the incorporation into the starch matrix. Several clay-types with different chemical exchange capacities (CECs) and counter-ions have been used in order to find the optimal clay-type for modification with the starch-compatibilising agents.

Task 2. The possibility of using water alone as plasticiser and modifier together with glycerol in the starch/clay mixing process has been divided into three different steps at laboratory scale:

• modification of the clay by extrusion
• incorporation of clay into starch by extrusion, and
• production of films.

In particular a significant effort was made to get the experimental conditions correct for incorporation of clay into starch. What is now obtained is a true nanocomposite with water resistant properties. The polymer melt processing is going very well and the starch shows good processibility even at temperatures as low as 90°C. Physical properties of the starch-based products and films have been examined by microscopy, ESEM, thermal analysis, mechanical analysis (tensile strength), water absorption properties and X-Ray diffraction. The analysis of the samples indicate some crucial differences regarding the distribution of the clay within the starch matrix depending on the concentration of ingredients used and the temperature regime in the extruder. Furthermore, the amount of clay was found to influence the degree of gelatinisation.

Task 3. A process for making starch acetate has been investigated and an acceptable standard for pilot plant production has been achieved. For films a suitable plasticiser must be found. At TNO the manufacturing of thermoplastic starch/clay composites in an extruder has been optimised. Attempts have been made to transfer this to conditions at BIOP. The three basic steps were investigated in detail for the up-scaling process. General mixing theory indicates that dispersion is best accomplished at high viscosity where interparticulate shear is greatest. Under these conditions maximum break-up of clusters and gelatinisation of starch is caused and chances for polymer intercalation between the clay layers is increased. In the extruder the polymer (starch) is plastizised (thermoplastic starch - THPS) by the combined action of plasticiser (water and glycerol), temperature and shear forces. This causes a rapid melting of the polymer, minimising the temperature variation. The barrel temperature profile is of great importance in improving transport and dissipating heat if necessary. BIOP used screw geometry with 2 kneading zones, one at the beginning and one at the end. However, many of the much results have been obtained using only one kneading zone. In order to measure all the required physical properties for the blends and to compare them with other starch-based materials, films had to be produced. This was accomplished by re-extruding the granulates through a slot die resulting in flat films.

Task 4. The synthesis of the modifier amino-dodecanoic acid out of lauryl lactam is more difficult than assumed from laboratory experiments in the first year. It is not possible to obtain a pure product at the moment. Three series of samples have been examined in the laboratory. The samples have undergone a thermal, mechanical and a moisture absorption test. Despite the presence of clay in some series the water absorption is still quite high. Regarding biodegradability a series of films are still under evaluation under different incubation conditions in the presence of various microbial populations.

Task 5. The biodegradation tests on nanocomposite films under soil burial conditions provide strong indications for the possible classification of the tested samples as biodegradable within the EN standards on packaging and packaging waste. There is still a considerable difference between permeability of the starch-based samples and commercial polypropylene films. The effects of packaging with these commercial films on produce quality have been estimated through comparative observations of the product cycle under selected conditions of storage.

Task 6. For scaling up production of the clay sample no 12, the process conditions for the centrifugal machine used in the pilot plant have been investigated. TPhS-clay composites were produced by extrusion of potato starch with clay, water and glycerol according to two recipes that differ in water/glycerol ratio. The production of starch/clay composites was shown to be possible under the chosen conditions. The compound can be extruded in pilot plant scale using a twin screw extruder to produce flat films with a thickness of 500 microm. However, as yet production on industrial scale seems not possible.

Achievements The main advances made are as follows:

• A new modifier of clay and an easy procedure to obtain a modified clay has been developed. The modification of the clay as well as the clay purification can be carried out at pilot scale.
• The polymer extrusion process has been optimised and can be translated to larger scale experiments. Proper nanocomposite films, although still very thick, have been made and can be used for testing.
• The biodegradability of the material has been confirmed and thermal, mechanical and permeability test have been carried out
• Shelf life tests, using commercial films have been performed.
• The scale up of purified or modified clay has been shown to be possible.
• Flat films have been produced, but with a thickness of 500 microm.

Future actions This project is somewhat behind the work plan scheduled in the technical annex. It was anticipated that by this time flat films would have become available. The relation between water stability, permeability and mechanical properties still needs to be assessed thoroughly. The production of thin flat films remains the first priority. The work to be carried out on food packaging and analytical evaluation depends on the samples produced. One partner has difficulties in synthesising a modifier for the clay, but this is expected to be solved in the near future. Possibilities for scaling up the production processes for clay, modified clay, starch-clay granulate and formulations have been discussed by the partners at a project Steering Committee meeting.