bioplasticsMAGAZINE_0905

Basics
Fig.3: Mater-Bi technology: droplike structure
The products based on starch/EVOH show mechanical properties
good enough to meet the needs of specific industrial applications.
Their moldability in film blowing, injection molding, blow-molding,
thermoforming, foaming, etc is comparable with that of traditional
plastics such as PS, ABS, and LDPE [11]. The main limits of
these materials are in their high sensitivity to low humidities,
with consequent enbrittlement. The biodegradation of these
composites has been demonstrated in different environments [12].
A substantially different biodegradation mechanism for the two
components has been observed:
Fig. 5: Foamed loose fill
Bibliography
[1] G. J. L. Griffin, U.S. Pat. 4016117 (1977).
[2] G. Scott, U.K. Pat. 1,356,107 (1971).
[3] J. W. Donovan, Biopolymers 18, 263 (1979).
[4] P. Colonna and C. Mercier, Phytochemistry
24(8), 1667–1674 (1985).
[5] J. Silbiger, J. P. Sacchetto, and D. J. Lentz,
Eur. Pat. Appl. 0 404 728 (1990).
[6] C. Bastioli, V. Bellotti, and G. F. Del Tredici,
Eur. Pat. Appl. WO 91/02025 (1991).
[7] P. Le Bail, C. Rondeau, and A. Buléon,, Int.
Journal of Biological Macromolecules 35
(2005), 1-7
[8] J.L:Willett, B.K: Jasberg, C.L: Swanson,,
Polymer Engineering and Science 35 (2), 202-
210 (2004)
[9] F. H. Otey, U.S. Pat. 4133784 (1979).
[10] C. Bastioli, V. Bellotti, M. Camia, L. Del
Giudice, and A. Rallis “Biodegradable
Plastics and Polymers” in Y. Doi, K. Fukuda,
Ed., Elsevier, 1994, pp. 200–213.
[11] C. Bastioli, V. Bellotti, and A. Rallis,
“Microstructure and Melt Flow Behaviour of
a Starch-based Polymer,” Rheologica Acta
33, 307–316 (1994).
[12] C. Bastioli, V. Bellotti, L. Del Giudice, and
G. Gilli, J. Environ. Polym. Degradation 1(3),
181–191 (1993).
[13] C. Bastioli, V. Bellotti, G. F. Del Tredici, R.
Lombi, A. Montino, and R. Ponti, Internatl.
Pat. Appl. WO 92/19680, (1992).
• The natural component, even if significantly shielded by an
‘interpenetrated‘ structure of vinyl alcohol, seems, first,
hydrolysed by extracellular enzymes.
• The synthetic component seems biodegraded through a
superficial adsorption of micro-organisms, made easier by the
increase of available surface that occurred during the hydrolysis
of the natural component.
The degradation rate of 2–3 years in watery environments
remains too slow to consider these materials as compostable.
Aliphatic polyesters/thermoplastic starch
Starch can also be destructurised in the presence of more
hydrophobic polymers, totally incompatible with starch, such as
aliphatic polyesters [13].
It is known that aliphatic polyesters having a low melting point are
difficult to process by conventional techniques for thermoplastic
materials, such as film blowing and blow molding. It has been
found that the blending of starch with aliphatic polyesters allows
an improvement of their processability and their biodegradability.
Particularly suitable polyesters considered in the past have been
poly-e-caprolactone and its copolymers, or polymers at higher
melting point formed by the reaction of glycols as 1,4-butandiol
with succinic acid or with sebacic acid, adipic acid, azelaic acid,
dodecanoic acid, or brassilic acid. The presence of compatibilizers
between starch and aliphatic polyesters such as amylose/EVOH V-
type complexes [10], starch grafted polyesters, and chain extenders
such as diisocyanates, and epoxydes is preferred. Such materials
are characterised by excellent compostability, excellent mechanical
properties, and reduced sensitivity to water.
Thermoplastic starch can also be blended with polyolefines,
possibly in the presence of a compatibilizer. Starch/cellulose
derivative systems are also reported in the literature [12]. The
combination of starch with a soluble polymer such as polyvinyl
44 bioplastics MAGAZINE [05/09] Vol. 4