Sheelakumari, Isac; Dr.George, K E(Cochin University of Science & Technology, August , 2001)
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Abstract:
The main aim of the study was to optimise the reactive extrusion
conditions in the conventional modification processes of polyethylenes in a
single screw extruder.The optimum conditions for peroxide crosslinking of low density
polyethylene (LDPE), linear low density polyethylene (LLDPE) and their blend
were determined in a torque rheometer. The actual reactive extrusion was
performed in a laboratory single screw extruder using the optimum parameters.
The influence of the coagent, triaUyl cyanurate (TAC), on the cross linking of low
density polyethylene in the presence of peroxide was also investigated. The
peroxide crosslinking was found to improve the mechanical properties and the
thermal stability of the polyethylenes. The efficiency of crosslinking was found
to be improved by the addition of coagent such as TAC.The optimum conditions for silane grafting viz temperature, shear rate,
silane and DCP concentrations were determined on a torque rheometer in the case
of LDPE, LLDPE and their blend. Silane grafting of LDPE in the presence of
peroxide was performed with and without addition of water. Compounding of such
mixtures in the melt at high temperatures caused decomposition of the
peroxide and grafting of alkoxy silyl groups to the polyethylene chains.The optimum parameters for maleic anhydride modification of LDPE,
LLDPE and their blend were determined. The grafting reaction was confinned by
FTIR spectroscopy. Modification of polyethylenes with maleic anhydride in the
presence of dicumyl peroxide was found to be useful in improving mechanical
properties. The improvement was found to be mainly due to the grafting of
carboxyl group and formation of crosslinks between the chains. The cross linking
initiated improvements indicate extended property profiles and new application
fields for polyethylenes.On the whole the study shows that the optimum conditions for
modifying polyethylenes can be determined on a torque rheometer and actual
modification can be performed in a single screw extruder by employing the
optimum parameters for improved mechanical! thermal behaviour without
seriously affecting their processing behaviour.
Description:
Department of Polymer
Science and Rubber Technology,
Cochin University of Science
and Technology