Study of alternative fillers, which are created like a secondary product of industry, gives important information about their properties as well as possibilities of their further application. Compared to commonly use industrial fillers, they often represent not only
a more ecological, but also a more economical production option. After a thorough study
of the effect on the properties of polymer blends, alternative fillers (AF) are often suitable for use in further industrial production. Biodegradability is an important parameter that specific types of alternative fillers can bring to the industrial production of polymer composite materials. This study deals with the possibility of innovative application of walnut shells
as alternative filler in polymer composite blends based on natural rubber and the preparation
of a new type of ecological polymer composite. Alternative filler based on walnut shells after treatment for samples with particle size >40µm; 40-32µm; 32-25µm and 25-0µm were applied into natural rubber (NR) in quantities of 0; 10 and 20 phr. The effect of particle size and shape (studied by SEM scanning electron microscopy) on the properties of polymer composite blends was investigated. Samples of the resulting polymer composites after vulcanization were tested for their physical and mechanical properties such as hardness, tensile strength, elongation at break and abrasion resistance. This research work was created within the project „Biodegradable alternative fillers and their application in a new type of ecological polymer blends“, code of the project MVP06_2024, based on the financial support from the Internal Grant Scheme of the Alexander Dubček University of Trenčín (Call for proposals: Early Stage Grants),  it has been also supported by the Operational Program Integrated Infrastructure, co-financed by the European Regional Development Fund by the project: Advancement and support of R&D for "Centre for diagnostics and quality testing of materials" in the domains of the RIS3 SK specialization, Acronym: CEDITEK II., ITMS2014+ code 313011W442 and by Scientific Grant Agency VEGA 1/0265/24 and KEGA 001TnUAD-4/2022.