15.3 Chemistry of Cutin
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present state of the technology are still inferior to those of the fossil-based polymers
widely used in industry. The elongation at break, young modulus and tensile strength
measured for cutin is 27%, 45 and 12.3 MPa (Heredia-Guerrero et al. 2017a, b;
López-Casado et al. 2007). Much lower than that of the petroleum-based polymers
such as polyethylene, polystyrene and polypropylene where elongation at break is
in the hundreds and the young modulus in multiple GPa. On the other hand, cutin
has a relatively high thermal degradation temperature of 200 °C, similar to that of
rubbers and polyethylene. Polymers such as polystyrene, polyvinyl chloride and
polystyrene have lower degradation temperatures. Cutin shows no melting point in
thermogravimetry analysis, thus confirming that it is a thermoset polymer. This is
expected of its cross-linked structure. It has a transition temperature of −22 °C.
Cuticle composition and cutin content vary from plant to plant. Factors which
determine cutin content include developmental stage of the plant, species, part of
the plant and the environmental conditions within which the plant is grown (Yeats
et al. 2012). Although there is a significant variation in the monomers making up the
cutin from different species and different parts of the plant, the species and anatomy
structure relation is well defined enough to allow obtaining a biomass with uniform
cutin composition. This is important in order to achieve standard controlled processes
and uniform products.
15.3.1 Biodegradation of Cutin
As a biodegradable polymer, it is essential that cutin decomposes into harmless
monomers which further decomposes into smaller molecules and finally carbon,
nitrogen and hydrogen compounds (Angst et al. 2016). Unlike other commonly
used fossil-derived polyesters such as polyethylene terephthalate that take over three
decades to degrade, cutin can be fully degraded within 3–8 months when buried in
soil (De Vries et al. 1967). The degradation of cutin by microorganisms such as
bacteria and fungi and other microorganisms involves the cleavage of ester linkages
catalyzed by cutinases released by the organisms (Kolattukudy 2001a, b; HerediaGuerrero et al. 2017a, b). Understanding of the mechanism of degradation of cutin
by these organisms using cutinase is key to the development of processes for degradation of the fossil fuel-derived polyesters into monomers or oligomers with faster
degradation rate or further applications.
15.4 Availability of Raw Materials
Although cutin which is present in the cuticle, is a more common feature in terrestrial
plants, cutin is also present in a diverse range of aquatic plants such as duckweed,
sea grasses and water hyacinth (Borisjuk et al. 2018). The cutin from these plants has
been shown to contain the same monomeric unit as those in land plants. Therefore,
337
present state of the technology are still inferior to those of the fossil-based polymers
widely used in industry. The elongation at break, young modulus and tensile strength
measured for cutin is 27%, 45 and 12.3 MPa (Heredia-Guerrero et al. 2017a, b;
López-Casado et al. 2007). Much lower than that of the petroleum-based polymers
such as polyethylene, polystyrene and polypropylene where elongation at break is
in the hundreds and the young modulus in multiple GPa. On the other hand, cutin
has a relatively high thermal degradation temperature of 200 °C, similar to that of
rubbers and polyethylene. Polymers such as polystyrene, polyvinyl chloride and
polystyrene have lower degradation temperatures. Cutin shows no melting point in
thermogravimetry analysis, thus confirming that it is a thermoset polymer. This is
expected of its cross-linked structure. It has a transition temperature of −22 °C.
Cuticle composition and cutin content vary from plant to plant. Factors which
determine cutin content include developmental stage of the plant, species, part of
the plant and the environmental conditions within which the plant is grown (Yeats
et al. 2012). Although there is a significant variation in the monomers making up the
cutin from different species and different parts of the plant, the species and anatomy
structure relation is well defined enough to allow obtaining a biomass with uniform
cutin composition. This is important in order to achieve standard controlled processes
and uniform products.
15.3.1 Biodegradation of Cutin
As a biodegradable polymer, it is essential that cutin decomposes into harmless
monomers which further decomposes into smaller molecules and finally carbon,
nitrogen and hydrogen compounds (Angst et al. 2016). Unlike other commonly
used fossil-derived polyesters such as polyethylene terephthalate that take over three
decades to degrade, cutin can be fully degraded within 3–8 months when buried in
soil (De Vries et al. 1967). The degradation of cutin by microorganisms such as
bacteria and fungi and other microorganisms involves the cleavage of ester linkages
catalyzed by cutinases released by the organisms (Kolattukudy 2001a, b; HerediaGuerrero et al. 2017a, b). Understanding of the mechanism of degradation of cutin
by these organisms using cutinase is key to the development of processes for degradation of the fossil fuel-derived polyesters into monomers or oligomers with faster
degradation rate or further applications.
15.4 Availability of Raw Materials
Although cutin which is present in the cuticle, is a more common feature in terrestrial
plants, cutin is also present in a diverse range of aquatic plants such as duckweed,
sea grasses and water hyacinth (Borisjuk et al. 2018). The cutin from these plants has
been shown to contain the same monomeric unit as those in land plants. Therefore,