Microstructural Contributions of Different Polyolefins to the Deformation Mechanisms of Their Binary Blends

Abstract

The mixing of polymers, even structurally similar polyolefins, inevitably leads to blend systems with a phase-separated morphology. Fundamentally understanding the changes in mechanical properties and occurring deformation mechanisms of these immiscible polymer blends, is important with respect to potential mechanical recycling. This work focuses on the behavior of binary blends of linear low-density polyethylene (LLDPE), low-density polyethylene (LDPE), high-density polyethylene (HDPE), and polypropylene (PP) under tensile deformation and their related changes in crystallinity and morphology. All of these polymers plastically deform by shear yielding. When unmixed, the high crystalline polyolefins HDPE and PP both exhibit a progressive necking phenomenon. LDPE initiates a local neck before material failure, while LLDPE is characterized by a uniform deformation as well as clear strain hardening. LLDPE/LDPE and LLDPE/PP combinations both exhibit a clear-cut matrix switchover. Polymer blends LLDPE/LDPE, LDPE/HDPE, and LDPE/PP show transition forms with features of composing materials. Combining PP in an HDPE matrix causes a radical switch to brittle behavior.

Mechanical Recycling of Packaging Plastics: A Review

“…[ 131,147,148 ] These adhesion issues prevent the use of these blends for manufacturing purposes due to lower Young's moduli and reduced elasticity (iPP:PE blends shown in Figure ). [ 89,149–151 ] Poor adhesion can be explained by presence of noncrystallizable oligomers at the interphases generated during synthesis. [ 148 ] Appropriate choice of catalyst during polyolefin synthesis can minimize the presence of these oligomers and promote adhesion across MPO interphases.…”

“…[ 148 ] The mechanical behavior of polyolefin blends can be altered by modifying the majority phase as shown by research conducted by Van Belle et al. [ 150 ] Blends of LDPE/HDPE, LDPE/PP and LLDPE/HDPE have transitional tensile behavior in which tensile behavior will transfer to the majority phase. Blends of PP/HDPE cause brittle behavior, unlike the shear yielding seen for the mono‐polymers.…”

The Feasibility of Using the MFC Concept to Upcycle Mixed Recycled Plastics

“…Although R MPO is already a recycled blend, quite a high impact strength was noted for this sample. On the one hand, this is not a surprising result for R MPOs, as PE is often added to PP to increase its toughness [36,64,65,79], so the same effect will be present in the recycled mixtures too. On the other hand, it is disappointing to notice the decrease in impact strength for the RMPO IMB and RMPO MFC.…”

“…With multilayer films, adhesive layers can often be present between the different polymer layers [36]. At this moment, no industrial solution is available for a highly efficient separation of these multilayers [31].…”

“…However, since MPO consists of PPs and PEs, which are considered to be compatible but only partially miscible [39], their blends tend to separate at the interface. Therefore, these blends may achieve limited mechanical properties, such as a reduced ductility, due to the immiscibility of the components [36,40,41]. Attempts to improve the properties of MPOs have proven challenging so far [40][41][42].…”