Chemistry Reference
In-Depth Information
naturally occurring polysaccharide. Both of them are cheap, renewable, non-toxic, and
biodegradable. The starch/chitosan blend exhibits good film forming property, which
is attributed to the inter- and intramolecular hydrogen bonding that formed between
amino groups and hydroxyl groups on the backbone of two components. The mechani-
cal properties, water barrier properties, and miscibility of biodegradable blend films
are affected by the ratio of starch and chitosan. Extrusion of the mixture of corn starch
and microcrystalline cellulose in the presence or absence of plasticizers (polyols) is
used to produce edible films. By increasing the content of the cellulose component, the
rupture strength is increased, whereas the elongation at break and the permeability of
films for water vapor are decreased. Starch can form thermodynamically compatible
blend films with water-soluble CMC when the starch content is below 25 mass%. Such
films are biodegradable in presence of microorganisms. Starch-based nanocomposite
film is obtained by casting the mixture of PS and flax cellulose nanocrystals. The me-
chanical properties and water resistance are greatly improved. The tensile strength of
nanocomposite and unreinforced films are 498.2 and 11.9 MPa, respectively.
Chemical derivatives
One problem for starch-based blends is that starch and many polymers are non-misci-
ble, which leads to the mechanical properties of the starch/polymer blends generally
become poor. Thus, chemical strategies are taken into consideration. Chemical modifi-
cations of starch are generally carried out via the reaction with hydroxyl groups in the
starch molecule. The derivatives have physicochemical properties that differ signifi-
cantly from the parent starch but the biodegradability is still maintained. Consequent-
ly, substituting the hydroxyl groups with some groups or chains is an effective means
to prepare starch-based materials for various needs. Graft copolymerization is an often
used powerful means to modify the properties of starch. Moreover, starch-g-polymer
can be used as an effective compatibilizer for starch-based blends. PCL and PLA are
chemically bonded onto starch and can be used directly as thermoplastics or com-
patibilizer. The graft-copolymers starch-g-PCL and starch-g-PLA can be completely
biodegraded under natural conditions and exhibit improved mechanical performances.
To introduce PCL or PLA segments onto starch, the ring opening graft polymerization
of ε-caprolactone or L-lactide with starch is carried out. Starch-g-poly(vinyl alcohol)
can be prepared via the radical graft copolymerization of starch with vinyl acetate
and then the saponification of the starch-g-poly(vinyl acetate). Starch-g-PVA behaves
good properties of both components such as processability, hydrophilicity, biodegrad-
ability, and gelation ability.
Starch can be easily transformed into an anionic polysaccharide via chemical func-
tionalization. For instance, a carboxylic derivative of starch, maleic starch half-ester
acid (MSA), has been prepared via the esterifi cation of starch with maleic anhydride
in the presence of pyridine. MSA is an anionic polyelectrolyte, consequently it can
perform ionic self-assembly with chitosan in aqueous solution and forms a polysac-
charide-based polyelectrolyte complex.
Thermoplastic Starch-clay Nanocomposites and their Characteristics
Biodegradable polymers such as starch, poly(lactide) and poly(3-caprolactone), have
attracted considerable attention in the packaging industry. Starch is a promising raw
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