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Abstract. This work covers the synthesis and characterization of in-reactor Ultra-High Molecular Weight Polyethylene/High Density Polyethylene, UHMWPE/HDPE, blends by in situ polymerization in a single reactor, through dual catalyst immobilization. These blends are synthesized combining two different catalysts (one for each targeted molar mass) co-immobilized in mesoporous Santa Barbara Amorphous, SBA-15, particles. First, the ethylene polymerization behavior is investigated, under different polymerization conditions. Then, studies on the thermal, mechanical and rheological characteristics of the produced in-reactor blends are presented and their performance is compared and discussed in a comprehensive way. Moreover, the effect of different filler contents on the properties exhibited by the resulting materials is investigated.
Results have shown that these in-reactor UHMWPE/HDPE blends exhibit a complex thermal, mechanical and rheological behavior, which depends mainly on the proportion between the two polymer components and on the amount of SBA-15.
Keywords: polymer composites, in-reactor blends, UHMWPE
1.Introduction
The widespread uses of ultra-high molecular weight polyethylene, UHMWPE, lead to the urgent development of approaches aiming to improve its performance. This is essential to fulfill its continuous market demands with tailored mechanical and/or thermal properties. Among these methods, the melt blending of UHMWPE with other polymers, different mineral particles, or addition of reinforcements [1-4] have proved to be an interesting strategy to attain these goals. Between polymers, high density polyethylene, HDPE, is a low price commodity, with good flow properties and feasible transformation by traditional processes, like extrusion, injection, blow molding, and rotational molding. Consequently, blends of UHMWPE and HDPE seem to be very interesting since the outstanding properties of UHMWPE and the good processability of HDPE under conventional techniques could be combined. Nevertheless, homogeneous HDPE/UHMWPE blends are rather difficult to be obtained by melt transformation processes because of mismatch of both, HDPE and UHMWPE, viscosities [5, 6].
Another methodology to combine UHMWPE and HDPE polymers into a unique material is by in-reactor blending using a multisite polymerization catalysts approach. This offers considerable cost and energy savings with respect to melt compounding since an intimate blending takes place during polymerization, which occurs at much lower temperatures and enables the mixing of immiscible components at a nanometer scale without requiring high shear forces. Several studies from literature followed this route and have reported the use of homogeneous...