Chemistry Reference
In-Depth Information
The Effect of Feed Composition of Styrene and
Acrylic Acid on the Properties of Modified
Low Density Polyethylene
Shenglong Ding, Mingzhu Liu
*
Summary: Low density polyethylene (LDPE) was functionalized with different molar
ratios of styrene (St) to acrylic acid (AA) in the presence of dicumyl peroxide (DCP) in
the molten state. The resultant LDPE was characterized by gel content and torque
analysis. The results showed that the gel content of polymers grafted with small
molar ratios (St/AA
¼
0.5) was always higher than those grafted with the equimolar
St/AA ratio. The effect of DCP amount and AA concentration on the grafting degree of
AA was investigated. The suitable DCP amount and AA concentration was obtained.
Functionalized LDPE [LDPE-
-(AA-St)] was characterized by Fourier transform infrared
spectroscopy (FTIR), melt flow rate (MFR), water contact angle and capillary rheo-
metry. The results showed that both MFR and grafting degree of AA of LDPE-g-(AA-St)
was the highest when an equimolar AA/St ratio was used, but when mixtures of St
and AA (St/AA
g
¼
1/10) were loaded, the water contact angle of the film prepared from
the LDPE-
-(AA-St) was the smallest, which indicated that the hydrophicity of the film
surface not only depended on the grafting degree, but also the molar ratios of the
hydrophobic/hydrophilic groups.
g
Keywords: acrylic acid; graft copolymers; modified polyethylene; rheology; styrene
Introduction
From an industrial point of view, free
radical initiated functionalization of poly-
olefins in the molten state had received
much attention over the past decades.
Acrylic acid (AA),
[1,2]
glycidyl methacryl-
ate (GMA),
[3,4]
and maleic anhydride
(MAH) were employed widely as mono-
mers to enhance polarity and reactivity of
polyolefin.
[5-7]
Grafting copolymerization
of LDPE with AA was investigated by
Ghosh
[8]
and the conclusion was drawn that
the grafting reaction in the molten state was
first order with respect to AA concentra-
tion. Besides, the information of pendant
structures of LDPE-g-AA suggested that
AA monomers grafted onto the LDPE
backbone were several units long
[9]
and that
the grafted AA could act as a nucleating
agent for crystallization of LDPE.
[10]
Styrene (St) as a second monomer in the
melt-grafting system not only increases the
graft degree of most monomers on poly-
olefin, but also reduces crosslinking of
Low density polyethylene (LDPE) is a
commodity polymer used in extrusion opera-
tions such as blown film, coating, blow mold-
ing, and foaming for its low cost. However,
its application is greatly limited due to its
lack of polarity and lower reactivity.
Chemical modification of LDPE is an
important method to expand the applica-
tions of LDPE and generate value-added
materials with improved mechanical, ther-
mal, polar, and chemical properties.
Modified LDPE can react with chemical
coupling agents to increase the polymer
interfacial interactions with inorganic fillers
and its miscibility with polar polymers as
well as to produce polyolefin with improved
adhesion and dyeability.
