Recycling of many polymers has gained a spectacular importance mainly because of its environmental and economical benefits. Ethylene vinyl acetate is one of the thermoplastics used directly as a final product and indirectly as an additive within many other polymeric materials. There has been limited research work on recycling of polymers even though recycling in industry has shown a spectacular growth in the last decade. It is the aim of this study to investigate and to evaluate the rheological behaviour of an ethylene-vinyl acetate copolymer resin upon recycling. For this purpose, original ethylene vinyl acetate granules were processed five cycles by using a twin-screw extruder and their rheological analysis was performed by means of an AR-G2 rheometer (TA Instruments), with a parallel-plate geometry, under a steady state condition. It was found that the rheological measurements of copolymer ethylene vinyl acetate exhibited a shear thinning constitutive behavior, obeying Carreau-Yasuda rheological constitutive model. The changes in flow and oscillatory shear measurements under different processing conditions were also determined in detail and results are reported in the paper.
In order to survive the competition, the processing cycle time and the energy consumption of the rotational foam molding process must be reduced to a fraction of its current levels without compromising product quality. This paper introduces a novel extrusion-assisted rotational foam molding process for the manufacture of rotational moldings having adjacent, but clearly distinct, layers of an integrated solid (non-cellular) skin boundary layer encapsulating a cellular core structure, consisting of identical or compatible polyolefin grades, that achieves significant savings in processing cycle time duration and energy consumption. It introduces non-chilled extruded foam as a foamed core-forming material, in real time, directly into a uni-axially rotating hot mold through a dedicated mold "injection" port onto the already formed un-foamed soft skin layer.
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