Chemistry Reference
In-Depth Information
LDPE. However, the addition of St will
decrease the hydrophobicity of the LDPE-
g
taken from the chamber and quenched with
liquid nitrogen to stop further reactions.
-(AA-St) surface.
Grafting AA onto LDPE has been
reported in the literature, but there are
few articles that study the effect of the
amount of St on the hydrophilicity and
rheological properties of LDPE-
Purification and Characterization of
the LDPE-
g
-(AA-St)
About 3.0 g of gross grafted products were
dissolved in 150 mL boiling xylene and
precipitated in 500 mL acetone to remove
unreacted monomers and homopolymers
formed during grafting. Then the polymer
was extracted with acetone for 6 hours once
again. All purified polymer samples were dried
to a constant weigh at 50
8
C under vacuum.
The Fourier transform infrared (FTIR)
spectra of the purified polymers were record-
ed with a FTIR spectrometer (AVATAR
360 FTIR, Nicolet, US). The resolution was
4.0 cm
1
, and the scanned wave number
ranged from 4000 to 400 cm
1
. The purified
products were pressed into thin films at
180
-(AA-St).
In this work, the effects of feed composition
of St and AA, and concentrations of initiator
and monomer on the grafting degree of AA
and extent of crosslinking of modified LDPE
were systematically studied. LDPE-g-(AA-
St) would be used as compatibilizer for
blends of LDPE and nylon 6.
g
Experimental Part
Materials
LDPE with MFR
C,
2.16 kg) was supplied by Lanzhou Petro-
Chemical Co. (China). Reagent-grade acrylic
acid (AA, 99% purity) and styrene (St,
99% purity) were purchased from Tianjin
Institute of Chemical Reagents (China)
and used without further purification.
Dicumyl peroxide (DCP), purified by re-
crystallization from ethanol prior to use,
was purchased from Shanghai Reagent Co.
(China). DCP has a half-time of about
1.45 min at 175
¼
2 g/10 min (190
8
C for FTIR measurement. From the
FTIR spectrum, the absorbance ratio (R
a
)
of the area of the bands at 1709 cm
1
and
1467 cm
1
represents the relative grafting
degree of the AA.
8
R
a
was calculated with
the following equation:
R
a
¼ A
1709
=
A
1467
(1)
where A
1709
is the peak area of absorbance
at 1709 cm
1
, characteristic of the carbonyls
from AA, and A
1467
is that of the absor-
bance at 1467 cm
1
, characteristic of
the CH
2
groups.
The melt flow rates (MFR) of the
purified polymers were determined using
XRZ-400 type MFR equipment at 190
8
C
with a load of 2.16 kg according to the
ASTM 1238-89 standard.
The gel content was obtained by the
following measurement: An unpurified
sample (100-120 mg) was packed in a
preweighed nickel net (120 mesh) and put
into a Soxhlet extractor, extracted with
boiling xylene for 24 hours, then dried in a
vacuum oven at 60
C. The modified LDPEs
using AA, and St and AA, were designated
LDPE-
8
-(AA-St), respec-
tively. St/AA represents the molar ratio of
styrene to acrylic acid.
g
-AA and LDPE-
g
Melt Grafting
The grafting reactions were carried out in a
Haake Rhemix 600P batch mixer, equipped
with roller blades and a mixing head with a
volumetric capacity of 69 cm
3
. A 45 g
charge of the vacuum-dried LDPE at 60
C
was blended with the desired amount of St,
AA and DCP, then fed into the mixer which
had already been adjusted to the optimum
conditions, which for processing in the
Haake Rhemix 600P was selected from our
previous work:
[11]
8
C until its weight was a
constant. The gel content was calculated
with the following equation:
8
C,
mixing speed of 80 rpm, and reaction time
of 10 min. After mixing, the samples were
temperature of 170
8
Gel content
ð
%
Þ
¼ðW
s
W
n
Þ
=
W
p
100
%
(2)
