Hydrolases in Polymer Chemistry: Part III: Synthesis and Limited Surface Hydrolysis of Polyesters and Other Polymers - Enzymatic Polymerisation - page 120

Fig. 3 To p ro w : Hydrolysis of PET with 7% crystallinity with a Humicola insolens cutinase for
( a )0,( b )12and( c ) 48 h resulting in weight losses of 0, 18% and 54%, respectively. Bottom row :
Hydrolysis of PET with ( a ) 34.8% crystallinity (blank), ( b ) a lipolytic enzyme (no weight loss)
and ( c ) 1 M NaOH (modified from [ 14 , 18 ])

Several methods, including DSC and FTIR, have been used to demonstrate in-
creases of crystallinity during hydrolysis of PET [ 14 , 18 ] . This indicates that PET
hydrolases preferably attack the amorphous regions of PET [ 13 - 15 , 44 , 66 , 67 ] .
Indeed, a cutinase from T. fusca released up to 50-fold higher amounts of oligomers
and terephthalic acid from amorphous fibres than from semi-crystalline fibres [ 1 ] .
Likewise, a lipase displayed higher hydrolytic activity towards amorphous PET,
as shown by the decrease in the WCA values [ 14 ]. In the same way, NaOH titra-
tion at constant pH indicated a tenfold increase in activity of cutinases on PET
with 7% crystallinity compared to PET with 35% crystallinity [ 18 ] . Similar results
were obtained with PTT (polytrimethyleneterephthalate), which is gaining increas-
ing importance because, apart from attractive properties, one of the building blocks
(namely 1,3-propanediol) can be produced by microbial fermentation from renew-
able sources [ 15 ] .

4 Polyacrylonitrilases

PAN was for a long time thought to be resistant to microbial attack. However,
various bacteria that produced nitrile-converting enzymes were isolated from waste-
waters of factories producing PAN fibre. For example, a nitrile hydratase/amidase
enzyme system was studied from Mesorhizobium sp. F28 [ 68 ]. Also, bacteria
(namely Ralstonia solanacearum and Acidovorax avenae )wereusedforthere-
moval of acrylic acid from such waste-waters [ 69 ]. Later, on the basis of NMR