Effects of polymerization catalyst technology on the melt processing stability of polyethylenes. part 2. single stabilizer performance

Abstract

The effects of a range of thermal and light stabilizers on the melt stability (investigated via multiple pass extrusion) and color stability of three different polyethylenes (PEs) were examined. The PEs varied in terms of the catalyst system used to synthesize the polymers and included an HDPE produced by using a chromium‐based Phillips catalyst and two LLDPEs produced via chromium‐based metallocene and titanium‐based Ziegler‐Natta catalysts. The additive types included a range of phenolics of different functionality, phosphites, hindered piperidines, an hydroxylamine, and Vitamin E. The results obtained for the three PEs confirmed that primary antioxidants (AOs) such as highly hindered and less, hindered phenols or hydroxylamines promoted good melt stability but in some cases tended toward yellowing. The secondary AOs such as the phosphites or thioethers behaved in the opposite way; color suppression was good, but melt stabilization was poor. It was also shown that for different types of phenols (all with similar molar activity), reducing steric hindrance to the phenolic OH enhanced the tendency to form chromophoric groups and hence color led to better efficiency than high hindrance. Those phenol with higher molar activity (mol OH/kg AO) showed the best processing performance. J. VINYL ADDIT. TECHNOL., 2012. © 2012 Society of Plastics Engineers

Research perspectives and further studies on catalyst effects on the stability of different polyethylenes during multiple extrusion: Inter‐relationship of oxidation chemistry and antioxidant activity

“…Many of these outcomes are of course well reported, but the extensive analysis here and wide ranging additive and polymer types provides a more useful perspective and educational insight into the catalyst effects and a useful combined insight into the literature. From the additive consumption analysis, the catalysts do not appear to play a significant role if any as found earlier [ 42,43 ] although they do play a significant role in color development especially Ti levels. [ 41 ]…”

“…Catalyst effects and the role of vinyl unsaturations have attracted some interest since the development of the newer types of polyolefins. [ 24–43 ] However, not all the outcomes are consistent and although some of those reported here are not totally new the study outlined here provides a useful highly extensive and much wider evaluation and comparison of the chemistry and structural changes occurring during the multiextrusion of various unstabilized and stabilized (packages) polyethylene types of the HDPE, linear low density polyethylene (LLDPE), and LDPE. Standard stabilizer packages based on phenol/phosphite combinations are examined especially also with preformulated commercial nondust blends (NBDs).…”

“…The degree of branching may also be a significant factor related to the polymer chain structure that can affect the rate of degradation of polyethylenes. [ 24–43 ] Indeed, it has been often stated that short‐chain branched polyethylenes oxidize more readily than linear polymers. However, since the concentration of short‐chain branches is low they would not be expected to contribute significantly to the oxidation rate but more to the MFI changes.…”

Effect of polymerization catalyst technology on the melt processing stability of polyethylenes, Part 3: Additives blends performance

“…Figure shows a characteristic synergy curve for two different AO s. Note the average trend line was determined using the proportionally summed contributions of the single additives and trend line for the real blend was obtained from the actual processed samples containing the AO blend. Note the ♦ represents the MFR of the highly stabilized benchmark control sample containing 5000 ppm of L‐22IB46.…”

“…In this study, a similar behavior will be investigated. The results were compared with the performance of the additives when used in isolation .…”