Extrusion De Almidones Termoplasticos

TEKA Kom. Mot. Energ. Roln., 2006, 6A, 138–144

INVESTIGATIONS OF THERMOPLASTIC STARCH EXTRUSION
COOKING PROCESS STABILITY
Marcin Mitrus
Department of Food Process Engineering, Agricultural University of Lublin
Doświadczalna Str. 44, 20-236 Lublin, Poland,
e-mail: marcin.mitrus@ar.lublin.pl

Summary. Results of thermoplastic starch (TPS) extrusion cooking process stability investigationsare presented in the paper. Research showed that the use of additional cooling system in modified
single screw extruder TS-45 allowed to keep constant process temperature for almost all the trials
at the appropriate level within the range 80–100°C. There was recorded an evident influence of the
screw rotation speed, the mixture composition and the moisture content of raw materials ontemperature profile along the barrel of the extruder. It was found out that changes of the TPS temperature at the slit die depended predominantly on the screw rotation speed used.
Key words: thermoplastic starch, extrusion cooking, process stability

INTRODUCTION
An interest in starch as material to be incorporated into packaging industry was recorded to rise drastically in the 1970`s along with thegrowth of ecological awareness of
the society. Quite important proved to be a possibility to reduce manufacture cost of
synthetic plastics due to relatively low starch price.
Unfortunately, the materials obtained from traditional synthetic polymers with addition of starch are not fully biodegradable. After starch biodegradation, they undergo only
strong fragmentation into small pieces thatoccasionally gives an impression of material
disappearance.
Considering both the fact that starch biodegrades to carbon dioxide and water in a
relatively short time compared with most synthetic polymers, and some drawbacks of the
existing technologies of biodegradable materials manufacture, in the recent years there
have been started large-scale researches to increase amount of starch instarch-plastic
composites to the highest possible level. The final objective of these investigations is to
obtain disposable commercial items produced from pure starch and to exclude synthetic
polymers from the formulation. Thermoplastic starch (TPS) seems to be perfect solution
that can be processed with conventional technologies used in synthetic plastic manufacture
(extrusion, injection moulding)[Wiedmann et al. 1991, Shogren et al. 1993].

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MATERIALS AND METHODS
Materials
The basic material for investigations was made by potato starch Superior type produced by the Food Industry Plant PEPEES S.A. in Lomza (Poland), Potato Industry
Plant in Braniewo (Poland) and AVEBE b.a. from the Netherlands.
To make comparative studiesthere were used wheat starch Excelsior MB type
manufactured by AVEBE b.a. in Holland and corn starch Cargill 2000 type produced by
Hanseland B.V. in the Netherlands.
Glycerol of 99% purity was used in the tests as a plasticizer, being added in the
amount of 15–30% of starch dry mass [Mitrus 2005b, 2006].
Blend preparation
All the starch types were blended and, after their mixing and damping,made 20 kg
of the sample material. As a result of the repeated trials there was established the effective agitation time in a bakery kneading pan, i.e. 20 min, that assured loose and friable
blend structure.
The obtained mixture was stored for 24h in air-tight polyethylene bags at room
temperature to make the whole sample material homogeneous, to facilitate penetration of
additions intostarch granules and prevent from moisture absorption.
The prepared mixtures were delivered to the feeding device of the modified extruder to undergo baro-thermal treatment [Mitrus 2005b, 2006].
Extrusion cooking
The preliminary investigations on starchy biopolymers extrusion cooking were run
on a standard food extruder TS-45 produced by Z.M.Ch. Metalchem in Gliwice
equipped with the plastifying...