Hydrolases in Polymer Chemistry: Part III: Synthesis and Limited Surface Hydrolysis of Polyesters and Other Polymers - Enzymatic Polymerisation - page 115

1.2 Monitoring Surface Hydrolysis

For various applications of synthetic polymers, such as in textiles, limited enzymatic
surface hydrolysis should ultimately bring increases in hydrophilicity. Conse-
quently, quantification of this parameter was the main target of early studies on
enzymatic surface hydrolysis. Thereby, simple and fast analysis methods primarily
involved measurement of the water contact angle (WCA) and the rising height,
and the drop dissipation test. In addition, dye binding on textile fabrics was used
as a measure to quantify success of the enzyme treatment (Table 1 ) . However,
besides enzymatic hydrolysis, enzyme protein adsorption can also increase the
hydrophilicity and, consequently, the dye binding on synthetic polymers. For
example, treatment of PET with a cutinase from Fusarium solani and a lipase
from Candida antarctica resulted in protein layers with thickness of 1.6-2.6 nm
and 2.5-2.8 nm, respectively, according to angle-resolved X-ray photoelectron
spectroscopy (XPS) [ 13 ]. Therefore, either complete protein removal (e.g. via ex-
traction, detergents or proteases) [ 1 , 14 ] or the use of enzyme inhibitors in control
experiments is an experimental prerequisite when the above analysis methods are
used [ 15 ]. XPS was also used for monitoring PAN hydrolysis based on increasing

Tabl e 1 Monitoring enzymatic surface hydrolysis of polymers

Method Target Polymers References

FTIR Crystallinity PET, PA [ 14 , 19 ]

Amino and amide groups [ 16 ]

DSC Crystallinity PET, PTT [ 15 , 18 ]

XPS (ESCA) Atomic composition PET, PTT [ 1 , 2 , 13 , 16 , 17 ]

Carboxyl and hydroxyl
groups, nitrogen content

PA N

MALDI-TOF Changes in DP PET [ 2 ]

Oligomers formed

SEM Morphology PET, PA, PAN Various

WCA, drop test,
rising height

Hydrophilicity PET, PA, PAN Various

Tensiometry Surface charge PET, PA [ 11 , 20 ]

Dye binding Indirect measure for

functional groups

PET, PA, PAN Various

Derivatisation Quantification of carboxyl

and hydroxyl groups with
2-(bromoniethyl)naphthalene
and sulphobenzoic acid
anhydride, respectively

PET [ 11 , 14 ]

Titration Quantification of carboxyl

groups

PET, PA [ 18 , 21 ]

HPLC, LC-MS,
other

Quantification of oligomers
and monomers released

PET, PA, PAN Various

Weight loss Solubilisation of oligomers PET, PA Various

Tensile strength Bulk properties PET, PA, PAN Various