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 similar to 0.2 to similar to 2.0 of the number of LCBs per 1000 carbon atoms is observed due to pulverization of the LLDPE.