Effects of polymerization parameters on the slow crack growth resistance and rheological properties of bimodal polyethylene resins

Abstract

In this paper, using a comprehensive study, we have investigated the effect of various polymerization parameters during the synthesis of bimodal polyethylene resins on their rheological and mechanical properties. Bimodal polyethylene resins were synthesized in two subsequent stages in a lab-scale reactor by manipulating a set of parameters such as C 2 /H 2 ratios in the first and second stages, the split value, and the comonomer type. The results showed that the comonomer type and C 2 /H 2 ratio of the second stage of the polymerization are the most critical parameters that control the final resins' slow crack growth resistance properties. On the other hand, the shear-thinning behavior of the resins is mainly controlled by the first-stage polymers. Although the C 2 /H 2 ratio of the first stage results in a moderate effect on the rheological properties of the final resins, its split value governs the flow characteristics of the final molten polymers under high shear rates.

Demystifying the two-sided role of inorganic halides in the structure and performance of Ziegler–Natta catalysts

“…In other words, as a PE100 grade is expected (based on standard methods) to retain its mechanical properties for more than 50 years, SCG resistance is a determining factor when we are comparing different polymers for prolonged applications. 30,39,40,[62][63][64] Although there are many ways to assess the SCG resistance of polymers, comparing their strain hardening modulus (SHM) has been accepted as a speedy and reliable method. The test is identical to a simple tensile test, but it is done at 80 °C using a standard methodology mentioned in the Experimental section.…”

“…2,27 For example, LyondellBasell, one of the most famous licensors of polyethylene production line, disclosed a hugely popular recipe for ZNCs used in synthesizing PE100 grade (a polyethylene grade used in the production of polymeric pipes for water and gas transportation industries). 3,[28][29][30] The innovations have updated their old ZNC recipe by adding a small amount of SiCl 4 to their base formulation. By doing so, they have claimed that the amount of wax produced in their polymerization reaction has plunged from 8.5% to 5.5%, which is a brilliant feature from a practical point of view.…”

Chlorination of Mg(OEt)2 with Halocarbons: A Promising Approach for Eliminating Chlorine-Containing Activators from Ziegler–Nattas’ Recipes

“…At first glance, industrially favorable ZNCs usually consist of magnesium chloride and TiCl 4 . While different types of donors, promotors, and so forth are frequently added to the base formulation, MgCl 2 and TiCl 4 can be considered the backbone of all ZNCs’ recipes. ,− In addition, MgCl 2 can be used as a starting material or produced in situ during ZNC synthetic approaches. − The second choice is strongly preferable, especially when a morphology-less catalyst is targeted. Most slurry-based polymerization technologies use Mg­(OEt) 2 -based ZNCs to produce their products due to their low price and ease of handling. − …”

“…The chlorinating agent can be TiCl 4 or chlorinated alkylaluminium cocatalysts (CACs) such as ethylaluminum sesquichloride (EASC), ethylaluminum dichloride (DEAC), and diethylaluminum chloride (DEAC). ,− Unfortunately, chlorination of Mg­(OEt) 2 with TiCl 4 decreases the performance of ZNCs in terms of activity and hydrogen response due to the formation of titanium islands. Because of this, the catalysts are not perfect options for producing highly effective polyethylene grades such as PE100 (a bimodal polyethylene grade used in the production of polyethylene pipes for the transportation of water and gases). , …”

“…Because of this, the catalysts are not perfect options for producing highly effective polyethylene grades such as PE100 (a bimodal polyethylene grade used in the production of polyethylene pipes for the transportation of water and gases). 15,16 On the other hand, chlorination of Mg(OEt) 2 using CACs is very challenging. CACs are very dangerous to use in petrochemical industries not only from the handling and transportation points of view but also because of their corrosion risks.…”