(161j) Producing and Modeling Ldpe/Hdpe Blends Based on Their Kinetics

Polyethylene (PE) is of great importance within the chemical industry with its large share of the overall global plastic material demand. Low-density PE (LDPE) and high-density PE (HDPE) are two main types and differ in their density which is given by variations of the microstructure. In particular, the degree and length of branching of the backbone influences the density and mechanical properties. The branching of the polymer is determined by the chosen production process.

HDPE is produced using a catalytic system, mainly a heterogeneous Ziegler-Natta or homogeneous metallocene catalyst, at temperatures up to 300 °C and pressures up to 200 bar. This leads to the characteristic structure of linear chains with almost no branching. LDPE is produced under pressures up to 3000 bar and temperatures up to 300 °C in a free radical polymerization leading to short-chain and long-chain branching of the polymer backbone. The differences in degree and length of branching reflects directly in the physical and mechanical properties of the polymer. By blending these polymers their physical and mechanical properties can be altered depending on the chosen blending ratio.

In this work, metallocene catalyzed HDPE produced in a solution polymerization mini-plant and LDPE produced in a high-pressure mini-plant set-up are blended in different ratios using two different methods. Firstly, a two-screw mini extruder is used to blend the two polymer types. Secondly, the polymers are solved and mixed under high pressures and temperatures using a high-pressure view cell.

In addition, the microstructure and molecular weight distribution (MWD) of HDPE and LDPE are modeled separately using a hybrid approach consisting of a deterministic and a stochastic model.[1] In a next step the simulated polymeric microstructures of HDPE and LDPE are blended virtually by a stochastic selection process according to their respective MWD and the blending ratios. By that topological information and the MWD of the blends can be obtained. Further using the topological information their rheological properties using the software BoB[2] can be modeled. By modeling blends starting with the kinetics of the respective polymer, it is possible to investigate them with varying polymers and blending ratios theoretically and reduce thereby the experimental expense.

[1] E. Neuhaus, T. Herrmann, I. Vittorias, D. Lilge G. Mannebach, A. Gonioukh, M. Busch, Macromol. Theory Simul. 2014, 23 (7), 415-428.

[2] D. J. Read, D. Auhl, C. Das, J. den Doelder, M. Kapnistos, I. Vittorias, T. C. B. McLeish, Science 2011, 333 (6051), 1871-1874.