Hybrid composites based on synthetic thermoplastics (STP) are a prospect for replacing traditional plastics in various sectors of the national economy: crop production (composite hydroponic substrates, containers, etc.), water treatment (composite biofilter loads), packaging industry, etc. The purpose of the work is to assess the destruction of composites based on STP, modified with prooxidants (PR) and polysaccharides (PS), in various external conditions that mimic environmental factors (thermal, photochemical (UV radiation), chemical, biochemical effects). As objects of research, we used prototypes based on a copolymer of ethylene with vinyl acetate and high-pressure polyethylene, modified with microcellulose and cobalt stearate. The time of exposure to external factors is 3 months. The work also assessed the degree of influence of the compounding technology (one-stage, two-stage) of the three-component system "STP: PR: PS" on the degree of destruction of the composite. It has been established that effective destruction of polyolefins modified by prooxidants is observed only under conditions of thermal and ultraviolet exposure. When the content of polysaccharides in the polyolefin matrix is 40 vol.% Or less, the composites are not significantly affected by chemical and biological environmental factors. Simultaneous modification of polyolefins with a prooxidant and a polysaccharide does not lead to a synergistic effect of destruction during the studied period of exposure. Under conditions of heat exposure and UV irradiation, the behavior of the three-component composite is similar to the behavior of the PO modified with the prooxidant, but with a less pronounced aging effect, and in aqueous media such materials behave as the PO polysaccharides modified, but also with less pronounced destruction. One-stage compounding of the three-component system "STP: PR: PS" significantly reduces the efficiency of composite destruction