<p>Plastic waste from packaging materials has caused significant environmental harm. This has necessitated the development of industrially scalable upcycling techniques for mixed polyolefin waste streams. This review critically examines environmentally friendly and scalable techniques for upcycling waste polyolefin blends, polyethylene (PE)/polypropylene (PP), to protect the environment. In an endeavor to upcycle the waste PE/PP mixed polyolefins, the thermodynamic factors underlying the immiscibility of recycled PE/PP blends are examined. Industrially scalable techniques such as peroxide-induced modification, microwave-assisted reactive processing, ultrasonic-wave-assisted processing, and flash reactive extrusion are explored to determine their feasibility in compatibilizing polyethylene/polypropylene blends. Furthermore, the review explores the potential use of these upcycled blends in food-contact applications. For food-contact applications, much attention is paid to additive migration from recycled PE and PP polymers, regulatory requirements, and compliance issues. Overall, the review provides insight into advanced reactive processing techniques for converting mixed polyolefin waste (PE/PP) into valuable feedstock.</p>