Processing and rheological behavior of cross‐linked polyethylene containing disulfide bonds

Abstract

Vitrimers are a new class of materials that consist of chemically cross‐linked networks that engage in thermoactivated associative exchange reactions. These exchange reactions can impart malleability, healing, and recyclability properties to thermosets. In this study, a one‐step protocol to prepare linear low‐density polyethylene (LLDPE) vitrimer‐like materials with disulfide exchange bonds via reactive blending is presented. The cross‐linking reaction of maleic anhydride‐grafted‐linear low‐density polyethylene (LLDPE‐MAH) and 4,4′‐dithiodianiline was followed in a torque rheometer. The degree of MAH‐functionalization and its impact on the melt rheology, dynamic mechanical properties, and thermal properties of the vitrimer was studied. The cross‐linked LLDPE possessed a mostly elastic behavior, with storage modulus (G′) higher than loss modulus (G′′) in the entire frequency range. The complex viscosity of cross‐linked LLDPE at high frequencies (>100 rad/s) was comparable to the thermoplastic LLDPE. The MAH‐groups and formation of cross‐links decreased the degree of crystallinity, which led to a decrease in the storage modulus at a temperature of 35°C. The storage modulus and dimensional stability of the materials improved with cross‐linking density, suggesting potential benefits of LLDPE vitrimers in secondary manufacturing processes. Finally, the reprocessing ability was demonstrated via internal mixing and the rheological and mechanical properties were retained.

Simple upcycling of virgin and waste polyethylene into covalent adaptable networks: catalyst-free, radical-based reactive processing with dialkylamino disulfide bonds

“…These include step-growth reactions between polymers made by free-radical polymerization (FRP) and small-molecule additives serving as cross-linkers. 60,61 Preparing dynamic networks with robust properties by exclusively addition-type polymerization methods, e.g., FRP and its variants 32,42,43,[48][49][50][51][52][62][63][64] or radicalbased reactive processing, [65][66][67][68][69][70][71][72][73][74][75][76][77][78][79] is a relatively untapped approach in CAN technology. It is important that methods to develop CANs via FRP and radical-based reactive processing are investigated because many thermosets with limited recyclability, e.g., PEX, are synthesized by such methods.…”

“…Radical-based reactive processing to modify polymers with dynamic graing units has recently gained traction as a method by which commodity plastics may be upcycled into CANs with enhanced properties and reprocessability. [65][66][67][68][69][70][71][72][73][74][75][76][77][78][79]85,86 Following the 2017 seminal study by Röttger et al 66 on the production of HDPE vitrimers by transesterication of boronic esters graed onto HDPE during reactive processing, a number of studies have been reported on polyethylene (PE) CANs. [67][68][69][70][71][72][73][74][75][76]78,79,85,86 However, few studies address the myriad of challenges that remain before the potential of PE CANs may be realized.…”

“…[65][66][67][68][69][70][71][72][73][74][75][76][77][78][79]85,86 Following the 2017 seminal study by Röttger et al 66 on the production of HDPE vitrimers by transesterication of boronic esters graed onto HDPE during reactive processing, a number of studies have been reported on polyethylene (PE) CANs. [67][68][69][70][71][72][73][74][75][76]78,79,85,86 However, few studies address the myriad of challenges that remain before the potential of PE CANs may be realized. For instance, most studies rely on external catalysis for bond exchange, use functionalized polyolens as precursors rather than virgin PE, or involve complex multistep syntheses.…”

“…60,61 Preparing dynamic networks with robust properties by exclusively addition-type polymerization methods, e.g. , FRP and its variants 32,42,43,48–52,62–64 or radical-based reactive processing, 65–79 is a relatively untapped approach in CAN technology. It is important that methods to develop CANs via FRP and radical-based reactive processing are investigated because many thermosets with limited recyclability, e.g.…”

Mechanochemical modification of crosslinked low‐density polyethylene: Effect of solid‐state shear pulverization on crosslinks, branches, and chain lengths

“…The development of LDPE vitrimers led to a material with reversible crosslinks. [ 24 ] While these works in the literature represent moderate success, there still is a need for simple, continuous, commercially scalable techniques to manage chemical crosslinks at the manufacturing stages.…”