Influence of Different Types of Peroxides on the Long-Chain Branching of PP via Reactive Extrusion

Abstract

Long-chain branching (LCB) is known as a suitable method to increase the melt strength behavior of linear polypropylene (PP), which is a fundamental weakness of this material. This enables the modification of various properties of PP, which can then be used—in the case of PP recyclates—as a practical “upcycling” method. In this study, the effect of five different peroxides and their effectiveness in building LCB as well as the obtained mechanical properties were studied. A single screw extruder at different temperatures (180 and 240 °C) was used, and long-chain branched polypropylene (PP-LCB) was prepared via reactive extrusion by directly mixing the peroxides. The peroxides used were dimyristyl peroxydicarbonate (PODIC C126), tert-butylperoxy isopropylcarbonate (BIC), tert-Butylperoxy 2-ethylhexyl carbonate (BEC), tert-amylperoxy 2-ethylhexylcarbonate (AEC), and dilauroyl peroxide (LP), all with a concentration of 20 mmol/kg. The influence of the temperature on the competitive prevalent reactions of degradation and branching was documented via melt mass-flow rate (MFR), rheology measurements, and gel permeation chromatography (GPC). However, via extensional rheology, strain hardening could be observed in all cases and the mechanical properties could be maintained or even improved. Particularly, PODIC C126 and LP signaled a promising possibility for LCB in this study.

Effect of Different Compatibilization Systems on the Rheological, Mechanical and Morphological Properties of Polypropylene/Polystyrene Blends

“…For 90:10 blends, the curve of PODIC is located above all other curves while for higher PS concentration it is located below LUC and SIS and in the low frequency range even below the uncompatibilized blend. In recently published work from our research group, similar behavior was observed for the reactive extrusion of PP at 240 C indicating the generation of a highly branched structure which was also confirmed by extensional rheology measurements [ 52 ]. A decrease in complex viscosity, as observed for 75:25 blends, is usually related to dominant chain scission during reactive extrusion with peroxides [ 25 ].…”

Strategic Approach Towards Plastic Waste Valorization: Challenges and Promising Chemical Upcycling Possibilities

“…[100] Here, the possibility of crosslinking also cannot be ruled out. [101] Chain scission is more prominent than recombination in the melt, whereas the reverse happens below the melting point. Hence, a stabilizing reagent is required during the extrusion process.…”

Al-alkenyl-induced formation of long-chain branched polyethylene via coordinative tandem insertion and chain-transfer polymerization using (nBuCp)2ZrCl2/MAO systems: An experimental and theoretical study

“…Nevertheless, it has been shown that these properties can be improved by introducing long-chain branching (LCB) to linear polyolefins [2][3][4]. Different methodologies have been developed, such as the ethylene copolymerization with vinylterminated polyolefins (macromonomers) [5,6], copolymerization with a non-conjugated α,ωdiene [7][8][9][10][11], as well as processes involving radical mechanisms [12][13][14][15][16][17][18]. Nevertheless, the materials produced with these methodologies generally exhibit complex molecular structures and/or uneven branch distribution.…”