Chemistry Reference
In-Depth Information
monoacrylate) (NCO-PCLA) onto cellulose diacetate (CDA) and determined from
the soil burial tests and active sludge tests that graft copolymers have good
biodegradability in natural conditions.
2.3.6 Confirmation of Grafting
The proof of grafting can be checked by various methods such as swelling, thermal
(by DTA/TGA) and mechanical property measurements, FTIR, DSC, XRD, NMR,
SEM, and XPS.
Grafting has been confirmed mostly by FTIR analysis which is performed by
ATR or KBr technique. While ATR technique gives information about the changes
due to grafting in the surface of graft copolymer [
107
], KBr technique indicates the
changes occurred both inside and in the surface of graft product [
4
]. The band in the
FTIR spectrum of graft product, which is not present in the spectrum of graft
substrate, is the proof of grafting if substrate has no FTIR band at the same wave
number. In the case of a graft copolymer consisting of a vinyl monomer such as
acrylamide or acrylic acid and cellulose, FTIR band assigned to the stretching
vibration of carbonyl (
ν
C
¼
O
) is generally used for the confirmation of grafting. An
example for the characteristic band positions and assignments used in the charac-
terization of various graft products by FTIR was listed in Table
2.2
with their
references.
The grafting also leads to changes in the thermal properties. As known, the
original cellulose has no glass transition temperature (
T
g
) and melting temperature
(
T
m
) due to strong inter- and intramolecular hydrogen bondings [
108
]. For that
reason, depending on structure the polymer grafted and the lengths of graft chains, a
slight deviation in baseline in the DSC curve of graft copolymer will be a good
indicator for both the presence of a
T
g
due to the graft side chains on the cellulose
backbone and for the proof of grafting. For example, Zhe et al. [
53
] determined in
the grafting of methyl acrylate onto carboxymethyl cellulose (CMC) that while
CMC does not display any transition between
40 and 60
C, poly(methyl
acrylate)-grafted CMC and poly(methyl acrylate) have
T
g
's at 19.2 and 13.75
C,
respectively. Wang et al. [
57
] reported that the grafting of poly(caprolactone
monoacrylate) (PCLA) onto isocyanate-terminated cellulose diacetate (CDA)
decreased the flow temperatures of graft copolymers in comparison to that of
CDA, and the processibility of CDA-g-PCLA copolymers was easier than that of
original CDA. The introduction of PNIPAM onto cellulose backbone by grafting
increased the
T
g
of graft copolymer [
30
]. Thermal degradation or stability of
cellulose can also change with grafting. Dahou et al. [
109
] reported that the thermal
stability of cellulose-g-PAN or cellulose-g-PAA is higher than that of ungrafted
cellulose. A similar improvement in the thermal stability observed by grafting was
determined for polyacrylamide-grafted carboxymethyl cellulose [
51
] and
N
-isopropylacrylamide- and methyl acrylate-grafted cellulose [
84
], poly(acrylic
acid)-grafted
cellulose
microfiber
[
105
],
cellulose-graft-poly(
N
,
N
-
