Macromolecular Insights into the Altered Mechanical Deformation Mechanisms of Non-Polyolefin Contaminated Polyolefins

Abstract

Current recycling technologies rarely achieve 100% pure plastic fractions from a single polymer type. Often, sorted bales marked as containing a single polymer type in fact contain small amounts of other polymers as contaminants. Inevitably, this will affect the properties of the recycled plastic. This work focuses on understanding the changes in tensile deformation mechanism and the related mechanical properties of the four dominant types of polyolefin (PO) (linear low-density polyethylene (LLDPE), low-density polyethylene (LDPE), high-density polyethylene (HDPE), and polypropylene (PP)), contaminated with three different non-polyolefin (NPO) polymers (polyamide-6 (PA-6), polyethylene terephthalate (PET), and polystyrene (PS)). Under the locally elevated stress state induced by the NPO phase, the weak interfacial adhesion typically provokes decohesion. The resulting microvoids, in turn, initiate shear yielding of the PO matrix. LLDPE, due to the linear structure and intercrystalline links, is well able to maintain high ductility when contaminated. LDPE shows deformation similar to the pure material, but with decreasing ductility as the amount of NPO increases. Addition of 20 wt% PA-6, PET, and PS causes a drop in strain at break of 79%, 63%, and 84%, respectively. The typical ductile necking of the high-crystalline HDPE and PP is strongly disturbed by the NPO phase, with a transition even to full brittle failure at high NPO concentration.

Assessment of Commercially Available Polyethylene Recyclates for Blow Molding Applications by a Novel Environmental Stress Cracking Method

“…As rPE-A shows a higher level of contamination than rPE-B, as shown in Figure 5 and Figure 8 , for rPE-A, it is more likely to have random occurring contamination agglomerates. These agglomerates can act as crack initiators and lead to premature failure of the specimen, which subsequently can lead to a high standard deviation in strain at break values [ 50 ]. This can also be seen in Figure 9 , which shows that three out of five samples from rPE-A showed low strain at break values of around 45% while two samples had very long strain at break values of above 80%.…”

Recycling of polyamides: Processes and conditions

“…For tensile properties, significant differences were observed depending on the PO resin The necking behavior is controlling the deformability of this recycled system. 91 T A B L E 4 Overview of the information available on the mechanical recycling of PA.…”

“…Finally, Demets et al 91 presented a molecular investigation on the recycling of four PO (HDPE, LDPE, LLDPE, and PP) with three nonpolyolefins (NPO) (PA6, PET, and PS). All materials were of different origin, but the PA6 was from films and injection molded samples.…”

“…Effect of nonpolyolefin (NPO) content in (A) LLDPE, (B) LDPE, (C) HDPE and (D) PP on the elongation at break of PA6. The necking behavior is controlling the deformability of this recycled system 91 …”

Gaining control over conjugated polymer morphology to improve the performance of organic electronics

“…That is followed by lamellae separation, cavity formation, and eventual lamellae fracture. 42 At low temperatures, chain movement is restricted, hence, brittle semicrystalline materials tend to fracture faster at low temperatures. On the contrary, chain flexibility increases at elevated temperatures.…”