Biomedical Engineering Reference
In-Depth Information
OH
OH
O
O
HO
OH
O
OH
O
HO
O
OH
O
HO
OH
OH
OH
O
OH
O
O
O
O
O
O
O
O
O
OH
OH
OH
OH
HO
HO
HO
HO
Amylopectin
OH
OH
O
O
HO
OH
O
O
OH
HO
OH
O
OH
O
Glucose unit
HO
O
O
OH
HO
OH
O
Maltose repeat unit
Amylose
Figure 11.1
Chemical structure of starch.
cheapest and most abundant natural polymers (Mecking, 2004). The abundance and
degradability make starch interesting for several industrial applications.
Although starch is itself a thermoplastic polymer (thermoplastic starch, TPS) (Li
et al
.,
2008) and can be processed
via
extrusion or molding with the aid of a plasticizer (Chuayuljit
et al
., 2009), this natural polymer is a rapidly degrading material with minimal moisture
resistance. Application possibilities of TPS are as fillers or blends with other thermoplastics
(Arvanitoyannis
et al
., 1997, 1998). Chemical modification of starch, on the other hand
(Gandini, 2008 ; Lee
et al
., 2007), can be used to adjust degradation properties as well as the
water stability of the resulting materials.
For instance, blends of starch with polyethylene or other polyesters are manufactured by
Novamont on a scale of about 36 300 metric tons (tonnes) per year for packaging applications
(Mooney, 2009). Moreover, foam materials of starch blends are also used in packaging
applications. Firstly, the blend is prepared
via
the extrusion of TPS and a biodegradable
(Nabar
et al
., 2006 ) or non-biodegradable (Mihai
et al
., 2007 ; Biswas
et al
., 2006 ) polymer.
Subsequently, the blends are blown into foams in order to improve the hydrophobic character
and mechanical properties of starch foams and films (Yoon
et al
., 2007 ; Avella
et al
., 2005 ).
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