INTEMA   05428
INSTITUTO DE INVESTIGACIONES EN CIENCIA Y TECNOLOGIA DE MATERIALES
Unidad Ejecutora - UE
capítulos de libros
Título:
PRODUCTION, CHEMISTRY AND DEGRADATION OF STARCH-BASED POLYMERS
Autor/es:
ANALÍA VÁZQUEZ; LAURA FORESTI; VIVIANA CYRAS
Libro:
Films and coatings from renewable resources An applications perspective,
Editorial:
Wiley-Blackwell
Referencias:
Año: 2010; p. 15 - 42
Resumen:
As reflected in the number of publications, research on
starch and starch-based plastics is widespread and continuing to grow. The
characteristics of starch plastics are highly influenced by the amylase/amylopectin
ratio, humidity, type and content of plasticizer, processing method and final crystallinity.
In this respect, it is very important to monitor processing and storage conditions
because these will also influence the properties of starch-based plastics.
Thermoplastic starch is usually based on
starch with amylose content greater than 70% and is use of gelatinised starch.
The addition of specific plasticisers produces thermoplastic materials with
good performance properties and inherent biodegradability. Starch is typically
plasticised, destructured, and/or blended with other materials to obtain
products with useful mechanical properties. Importantly, thermoplastic starch
can be processed on existing plastic procesing equipment. High starch content
plastics are highly hydrophilic and readily disintegrate on contact with water.
The use of starch-polymer blends provides a route to materials with adjustable
degradation rates and the chemical modification of starch to form new materials
or for the purpose of compatibilization in blends is facilitated by the
availability of free hydroxyl groups in starch, which can undergo a number of
reactions such as acetylation, esterification and etherification. The fine
phase structure is an important parameter in terms of obtaining films with
useful properties and is determined by the interface and interphase, the weight
ratio of the components and features of the processing method such as shear,
residence time and temperature.
Biodegradation of starch and starch-based polymers has been studied by
means of laboratory tests using specific extracellular enzymes and also by means
of simulation tests, mainly in soil burial and compost environments. Even if
simulation tests do not entirely reflect the real biodegradation conditions in
a natural environment, these assays have proved suitable for assaying the
extent of polymer degradation in different environments whilst under
controlled conditions. In the case of starch granules, enzymatic hydrolysis has
been widely studied. The rate and extent of enzymatic degradation has proved to
be dependent on a number of factors, among which the botanical origin plays the
most important role by defining the granule size and shape, the amylose/amylopectin
ratio and the starch morphology. In blends, starch generally enhances the
degradation rate acting as the initial point of biological attack; and starch concentration
determines the extent of degradation of the blend. Although many research
groups have been interested in studying the degradation of starch-based
polymers they synthesize, the literature shows a wide diversity of assays and
conditions used to do so (e.g., time of exposure to degrading environment,
temperature, humidity, methods of measurement), sometimes making it difficult
to compare results for the degradation of starch-based blends.