Klementina Khait

Solid-State Shear Pulverization of Plastics: A Green Recycling Process

Abstract A novel process called solid-state shear pulverization (S3P) has been developed at Northwestern University to recycle single or commingled postconsumer or preconsumer polymeric waste without sorting by type or color. This continuous, one-step process converts shredded plastic or rubber waste into controlled-particle-size powder ranging from coarse (10 and 20 mesh) to fine (80 mesh) or ultrafine (200 mesh). As a result, the pulverization product is usable in applications ranging from direct injection molding without prior pelletization, to rotational molding, to use in protective and decorative powder coatings, as well as to blending with virgin resins and compounding with additives. Scanning electron microscopy reveals that the fine particles have a unique elongated shape that is attributed to the high shear conditions occurring during the pulverization process. Injection-molded parts made from the powder product of the S3P process have mechanical and physical properties comparable to or better t...

Self-compatibilization of polymer blends via novel solid-state shear extrusion pulverization

The mechanochemistry of a novel economical solid-state shear extrusion (SSSE) pulverization is investigated. SSSE compatibilizes incompatible blends in situ; the process has great potential in recycling of post-consumer plastic waste (PCPW). It is proposed that SSSE causes this self-compatibilization of blends by rupturing polymer chains and allowing them to recombine with their neighboring chains. When this recombination involves dissimilar chains at an interface between powder particles, block copolymers are formed, and if the chain transfer reactions are possible, graft copolymers are formed. These copolymers at the interfaces in the phase-separated, incompatible blend lower the interfacial tension and increase the adhesion at the interfaces, thus compatibilizing the blend. Our nuclear magnetic resonance (NMR) and rheology studies reveal the formation of long chain branches (LCBs) in an linear low-density polyethylene (LLDPE), which is equivalent to the formation of graft copolymers in blends. With NMR, an increase from ∼ 0.2 to ∼ 2.0 of the number of LCBs per 1000 carbon atoms is observed due to pulverization of the LLDPE.

Trace levels of mechanochemical effects in pulverized polyolefins

This research investigated the structural changes that occur on different polyethylene polymer systems as a result of a novel pulverization process called solid-state shear pulverization (S3P). High-density polyethylene, low-density polyethylene, and two forms of linear low-density polyethylene were run through a pulverizer under high shear conditions as well as low shear conditions. The physical properties were examined before and after the pulverization via melt index, melt rheology, GPC, and DSC, techniques. The low shear pulverization did not noticeably alter the physical properties of the polymers. In contrast, high shear pulverization did result in an increase in viscosity as observed by melt index and oscillatory shear experiments, although solid-state and bulk properties as observed by DSC and GPC were not affected. These results indicate that a small amount of mechanochemically induced changes occur as a result of the pulverization process, including incorporation of a small amount of long-chain branches randomly placed on a few of the polymer chains. No evidence of short-chain branching resulting from S3P processing was found in these systems.