Chemistry Reference
In-Depth Information
OAc
OAc
CH
2
OAc
CH
2
OAc
OAc
OAc
O
O
O
O
O
O
O
O
O
OAc
OAc
CH
2
OAc
CH
2
OAc
OAc
OAc
> 250
o
C
HOAc
CH
2
OAc
CH
2
OAc
OAc
O
O
OO
O
O
O
O
O
OAc
glycosidic
scission
> 250
o
C
CH
2
OAc
O
CH
2
OAc
O
OOAc
tar
O
O
O
+
O
OAc
O
OAc
The mechanism of thermal degradation of cellulose appears to include two reactions. The first
reaction consists of dehydration and the second one of scission of C-O bonds in the chains between
the rings or within the rings [
457
]. This can give rise to levoglucosan [
457
]:
CH
2
OH
O
OH
OH
OH
OH
OH
O
O
+
O
O
O
OH
OH
O
O
O
O
OH
CH
2
OH
CH
2
OH
OH
9.9.9 Hydrolytic Degradation of Polymers at Elevated Temperatures
Hydrolytic degradation is only significant in polymers with chain links that can react with water, such
as polyesters. A recent study reports on depolymerization of poly(ethylene terephthalate) during
processing, if the material is not dried thoroughly, prior to melting [
530
]. The hydrolytic depolymeri-
zation of poly(ethylene terephthalate) was carried out in a stirred batch reactor at 235, 250, and 265
C
above the polymer melting point and under autogenous pressure. The solid products were mainly
composed of terephthalic acid. The liquid products were mainly composed of ethylene glycol and a
small amount of its dimer. Moreover, an autocatalytic mechanism was detected. That indicates that
