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

Abstract

This article considers the interaction between additives that occur during the stabilization process. The simultaneous effects of the additives and associated interactions on melt processing stability and processing discoloration were of particular interest. Melt stability is an important factor to consider because physical changes in the processed polymer can occur during the compounding and fabrication steps. Furthermore, discoloration is one of the most important problems affecting commercial polymers. Most discoloration manifests itself as yellowing, especially in the case of polyolefins. Although yellowing can often be associated with degradation processes caused by various agents, such as light or heat, this is not always the case; yellowing can also be due to the interaction of additives in the stabilizer packages. Blends of primary antioxidants (AOs), secondary AOs, and hindered amine light stabilizers have been studied with the intention of further improving stabilization performance together with cost reduction of the stabilized polymer. Although synergism between AOs and a stabilizer is fairly common, antagonism was also observed in terms of melt flow protection and in color stability in some of the AOs tested. 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 a high‐density polyethylene (HDPE) produced by using a chromium‐based Phillips catalyst and two linear low‐density polyethylenes (LLDPEs) produced via chromium‐based metallocene and titanium‐based Ziegler‐Natta catalysts. The apparent lack of influence of polymerization catalyst system on the mode of stabilizer interaction should lead to the reassessment of stabilizer formulation strategies in relation to PE type/catalyst system and associated commercial/economic considerations. J. VINYL ADDIT. TECHNOL., 22:117–127, 2016. © 2014 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.…”

Simulating the recycling of milk bottles in the UK: Influence of blending virgin and repeatedly melt-extruded high-density polyethylene

“…HDPE that has been subjected to 50 repeated melt-extrusion cycles (rHDPE-50) showed the darkest hue. It is worth mentioning that previous works on the discolouration of repeatedly melt-processed HDPE focused on the effect of antioxidant (del Teso Sánchez et al, 2016, 2012. In our work, the HDPE used was pure without any antioxidant.…”

Effect of type of polymerization catalyst system on the degradation and stabilization of polyethylenes in the melt state—Part 4: Comparative antioxidant effectiveness on organoleptic extractables

“…The aim of this study is to identify the nature of products involved in these types of processes to establish if VOCs formed in the process are toxic or not as organoleptics (i.e., extractables) as well as the influence of the catalyst type on their structure and relative concentrations and follows on from our previous series in this work. Here, the effectiveness of different antioxidants has been considered assessing if the results of the GC–MS correlate with the results of previous work done using melt flow rate [ 10,11 ] and chemiluminescence techniques. [ 12 ] Here, the catalyst type and stabilizer exhibit a complex interplay in controlling the type and distribution of oxidation and breakdown products during extrusion.…”