The melt flows of linear low‐density polyethylene (LLDPE) and branched low‐density polyethylene (LDPE) have been compared in a fully intermeshing co‐rotating twin‐screw extruder. The polyethylene melts were selected in order to investigate the effects of the melt rheology on the mixing. Their shear vicosity curves are quite similar, but the LDPE has a markedly higher apparent extensional viscosity over a wide range of stretch rates. The stagger of the paddles in the mixing zone of the extruder creates axial pressure‐driven axial flow can have significant extensional strain components. Residence time distributions obtained in the melt zones of the extruder with tracer dye reveal that the LDPE has a narrower residence time distribution than the LLDPE over a wide range of operating conditions. The axial dispersion for the LDPE is significantly lower than the axial dispersion for the LLDPE. This is attributed to the greater extensional viscosity of the LDPE. During the reactive extrusion process, solid maleic anhydride and polyethylene were added at the feed port but the peroxide provides better control of the crosslinking reaction. Residence time distributions measured for the chemically more reactive LLDPE melt indicate reduced levels of axial mixing with reaction. The reduction in mixing is due to a crosslinking reaction that occurs in parallel to the grafting reaction. This change in mixing is smaller than the difference in mixing between LDPE and LLDPE.

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The maleation of polypropylene melt with a peroxide as free radical initiator has been carried out isothermally in a continuous flow reactor and in a batch flow reactor. The continuous flow reactor is designed to provide significant levels of extensional strain in the fluid while the batch flow reactor provides a simple shear flow with uniform residence time. In both reactors, less than 1 part per hundred of dicumyl peroxide (dissolved in xylene) is added to a preblended single phase mixture of polymer melt and dibutyl maleate. The relative extent of maleation is much higher in the continuous flow reactor than in the batch reactor with comparable shear strain rates and mean residence times. As the feed rate and the rotation speed are varied at a fixed temperature in the continuous flow reactor, the highest degree of maleation is obtained under conditions where fluid dynamics computations show the stretching of a fluid element to be the greatest. Hence, increasing shear alone leads to rather limited increases in extent of maleation. These results emphasize the importance of the detailed deformation field for carrying out functionalization reactions on polymer melts.