Clarifying effect of multimodal polymerization on thermal, rheological, and mechanical properties of HDPE pipe resin

In order to clarify the multimodal polymerization effect on the microstructural properties of high-density Polyethylene (HDPE), multi and bimodal samples were synthesized in a lab-scale reactor by manipulating a set of polymerization parameters. For better insight, the synthesized resins were fully characterized by thermal, rheological, and mechanical analysis. Rheological measurements demonstrated that multimodal HDPE is easy to process in compression with bimodal HDPE due to its higher shear thinning index (SHI) and broad molecular weight distribution (MWD). On the other hand, zero shear viscosity (eta(0)), as a critical point in the sagging evaluation, reveals that multimodal HDPE has more resistance to sagging. Also, strain hardening modulus (SHM) was calculated by tensile test and reflected possible suppression of long-term resistance of the multimodal sample to slow crack growth(SCG). Furthermore, isothermal crystallization showed that a multimodal process led to highly crystallizable segments and faster crystallization kinetic than bimodal resins. These results were justified by higher Mz and polydispersity (PDI) values directly related to more tie-molecules and broad MWD, respectively. In this research, we found that a multimodal process can effectively govern the microstructure of HDPE resin to tailor properties in the production of large diameter pipes.