{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,17]],"date-time":"2026-09-17T12:05:13Z","timestamp":1789646713153,"version":"4.0.0"},"reference-count":37,"publisher":"MDPI AG","issue":"18","license":[{"start":{"date-parts":[[2026,9,17]],"date-time":"2026-09-17T00:00:00Z","timestamp":1789603200000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Polymers"],"abstract":"<jats:p>This study investigates the effect of natural pumice filler content on the physical and mechanical performance of flexible polyester-based polyurethane (PU) composites. Composites containing 0, 2, 5, 10, and 20 wt.% pumice were produced using a constant PU matrix formulation and identical processing conditions. Microstructural and structural characteristics were examined using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and Fourier transform infrared spectroscopy (FTIR), while density, water absorption, tensile behavior, abrasion resistance, and cyclic flexural durability were evaluated. Increasing pumice content resulted in greater local microstructural heterogeneity and increased density and water absorption. Tensile strength exhibited a non-linear numerical response to filler content, with the highest mean value obtained at 5 wt.% pumice, although the differences among formulations were not statistically significant. In contrast, elongation decreased significantly overall with increasing filler content, while mean abrasion mass loss progressively increased with filler loading. Cyclic flexural testing revealed that the unfilled PU and 2 wt.% composite completed 30,000 cycles without measurable crack propagation at 20 and 0 \u00b0C, whereas higher filler contents exhibited severe crack growth or complete fracture. At \u221220 \u00b0C, all formulations fractured completely. Overall, pumice content produced a property-dependent response, revealing a trade-off among tensile response, deformability, abrasion resistance, and cyclic durability. These findings provide a basis for tailoring flexible PU composites for applications involving repeated deformation and mechanical contact, including footwear and cushioning components.<\/jats:p>","DOI":"10.3390\/polym18182270","type":"journal-article","created":{"date-parts":[[2026,9,17]],"date-time":"2026-09-17T11:41:35Z","timestamp":1789645295000},"page":"2270","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Natural Pumice-Filled Flexible Polyurethane Composites: Effect of Filler Content on Mechanical Performance and Cyclic Durability"],"prefix":"10.3390","volume":"18","author":[{"given":"Omer","family":"Uctu","sequence":"first","affiliation":[{"name":"Department of Mechanical Engineering, Institute of Science, Mersin University, Mersin 33343, T\u00fcrkiye"},{"name":"Department of Textile, Clothing, Footwear and Leather, Naci Topcuoglu Vocational School, Gaziantep University, Gaziantep 27600, T\u00fcrkiye"}],"role":[{"vocabulary":"crossref","role":"author"},{"role":"conceptualization","vocabulary":"credit"},{"role":"methodology","vocabulary":"credit"},{"role":"validation","vocabulary":"credit"},{"role":"formal-analysis","vocabulary":"credit"},{"role":"investigation","vocabulary":"credit"},{"role":"writing-original-draft","vocabulary":"credit"},{"role":"writing-review-editing","vocabulary":"credit"},{"role":"visualization","vocabulary":"credit"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-0019-3346","authenticated-orcid":false,"given":"Mehmet","family":"Ipekoglu","sequence":"additional","affiliation":[{"name":"Department of Mechanical Engineering, Faculty of Engineering, Turkish-German University, Istanbul 34820, T\u00fcrkiye"}],"role":[{"vocabulary":"crossref","role":"author"},{"role":"conceptualization","vocabulary":"credit"},{"role":"methodology","vocabulary":"credit"},{"role":"validation","vocabulary":"credit"},{"role":"formal-analysis","vocabulary":"credit"},{"role":"investigation","vocabulary":"credit"},{"role":"writing-original-draft","vocabulary":"credit"},{"role":"writing-review-editing","vocabulary":"credit"},{"role":"visualization","vocabulary":"credit"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-5918-3858","authenticated-orcid":false,"given":"Onder","family":"Albayrak","sequence":"additional","affiliation":[{"name":"Department of Mechanical Engineering, Faculty of Engineering, Mersin University, Mersin 33343, T\u00fcrkiye"}],"role":[{"vocabulary":"crossref","role":"author"},{"role":"conceptualization","vocabulary":"credit"},{"role":"methodology","vocabulary":"credit"},{"role":"validation","vocabulary":"credit"},{"role":"formal-analysis","vocabulary":"credit"},{"role":"investigation","vocabulary":"credit"},{"role":"visualization","vocabulary":"credit"},{"role":"writing-review-editing","vocabulary":"credit"},{"role":"writing-original-draft","vocabulary":"credit"}]}],"member":"1968","published-online":{"date-parts":[[2026,9,17]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"713","DOI":"10.1002\/pen.21315","article-title":"High-Strength Composites Based on Tung Oil Polyurethane and Wood Flour: Effect of the Filler Concentration on the Mechanical Properties","volume":"49","author":"Casado","year":"2009","journal-title":"Polym. Eng. Sci."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"2312816","DOI":"10.1002\/adma.202312816","article-title":"Fracture-Resistant Stretchable Materials: An Overview from Methodology to Applications","volume":"37","author":"Guo","year":"2025","journal-title":"Adv. Mater."},{"key":"ref_3","first-page":"311","article-title":"Optimum Calcium Carbonate Filler Concentration for Flexible Polyurethane Foam Composite","volume":"11","author":"Usman","year":"2012","journal-title":"J. Miner. Mater. Charact. Eng."},{"key":"ref_4","doi-asserted-by":"crossref","unstructured":"Paciorek-Sadowska, J., Borowicz, M., and Isbrandt, M. (2023). Evaluation of the Effect of Waste from Agricultural Production on the Properties of Flexible Polyurethane Foams. Polymers, 15.","DOI":"10.3390\/polym15173529"},{"key":"ref_5","doi-asserted-by":"crossref","unstructured":"Amo, J., Iswar, S., Vanbergen, T., Borreguero, A.M., De Vos, S.D.E., Verlent, I., Willems, J., and Rodriguez Romero, J.F. (2024). Polyurethane Composites Recycling with Styrene\u2013Acrylonitrile and Calcium Carbonate Recovery. Materials, 17.","DOI":"10.3390\/ma17122844"},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"e6313","DOI":"10.1002\/pat.6313","article-title":"Impact of Ambient and Vacuum Pressure on the Physico Mechanical Properties of Flexible Polyurethane Foam Reinforced with CaCO3","volume":"35","author":"Singh","year":"2024","journal-title":"Polym. Adv. Technol."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"147","DOI":"10.1016\/j.compscitech.2017.04.029","article-title":"Influence of Filler Surface Characteristics on Morphological, Physical, Acoustic Properties of Polyurethane Composite Foams Filled with Inorganic Fillers","volume":"146","author":"Sung","year":"2017","journal-title":"Compos. Sci. Technol."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"142","DOI":"10.1016\/j.polymdegradstab.2014.11.008","article-title":"Research on Highly Flame-Retardant Rigid PU Foams by Combination of Nanostructured Additives and Phosphorus Flame Retardants","volume":"111","author":"Xu","year":"2015","journal-title":"Polym. Degrad. Stab."},{"key":"ref_9","doi-asserted-by":"crossref","unstructured":"Lee, D.I., Ha, Y.H., Jeon, H., and Kim, S.H. (2022). Preparation and Properties of Polyurethane Composite Foams with Silica-Based Fillers. Appl. Sci., 12.","DOI":"10.3390\/app12157418"},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"7197","DOI":"10.1002\/pc.29424","article-title":"Improving the Interlaminar Shear Performance of Hybrid Nano-Filled 3D Woven Composites Using Response Surface Methodology","volume":"46","author":"Hussain","year":"2025","journal-title":"Polym. Compos."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"429","DOI":"10.1007\/s40544-020-0446-4","article-title":"A Review on Tribology of Polymer Composite Coatings","volume":"9","author":"Ren","year":"2021","journal-title":"Friction"},{"key":"ref_12","doi-asserted-by":"crossref","unstructured":"Demiral, M. (2025). Strength in Adhesion: A Multi-Mechanics Review Covering Tensile, Shear, Fracture, Fatigue, Creep, and Impact Behavior of Polymer Bonding in Composites. Polymers, 17.","DOI":"10.3390\/polym17192600"},{"key":"ref_13","doi-asserted-by":"crossref","unstructured":"Sudarisman, S., Haniel, H., Taufik, A.K., Tiopan, M., Himarosa, R.A., and Muflikhun, M.A. (2023). Tensile, Compressive, and Flexural Characterization of CFRP Laminates Related to Water Absorption. J. Compos. Sci., 7.","DOI":"10.3390\/jcs7050184"},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"357","DOI":"10.1177\/0021955X11398115","article-title":"Structure and Properties of Flexible Polyurethane Foams with Nano- and Micro-Fillers","volume":"47","author":"Javni","year":"2011","journal-title":"J. Cell. Plast."},{"key":"ref_15","first-page":"23","article-title":"Effects of Different Filler Treatments on the Morphology and Mechanical Properties of Flexible Polyurethane Foam Composites","volume":"8","author":"Latinwo","year":"2010","journal-title":"Nat. Sci."},{"key":"ref_16","first-page":"366","article-title":"Effect of Nanoclay on Mechanical Properties of Porous Flexible Polyurethane\/Clay Nanocomposites","volume":"23","author":"Ok","year":"2013","journal-title":"Korean J. Mater. Res."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"2248","DOI":"10.1002\/pc.23805","article-title":"Study of the Effect of Thermally Reduced Graphene Oxide on the Physical and Mechanical Properties of Flexible Polyurethane Foams","volume":"38","author":"Piszczyk","year":"2017","journal-title":"Polym. Compos."},{"key":"ref_18","first-page":"951","article-title":"Preparation of Kaolin-Modified Polyurethane Elastomer Composites and Synergistic Enhancement of Mechanical, Damping, and Sound Insulation Properties","volume":"57","author":"Zhang","year":"2026","journal-title":"Acta Polym. Sin."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"263","DOI":"10.1179\/1743289811Y.0000000035","article-title":"Effects of BaSO4, CaCO3, Kaolin and Quartz Fillers on Mechanical, Chemical and Morphological Properties of Cast Polyurethane","volume":"41","author":"Shahzamani","year":"2012","journal-title":"Plast. Rubber Compos."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"4932","DOI":"10.1002\/pc.26200","article-title":"High-Strain-Rate Mechanical Performance of Particle- and Fiber-Reinforced Polymer Composites Measured with Split Hopkinson Bar: A Review","volume":"42","author":"Graziano","year":"2021","journal-title":"Polym. Compos."},{"key":"ref_21","first-page":"12816","article-title":"Effect of CNT Filler and Temperature on Fracture Toughness of Epoxy Composites Reinforced with Carbon Fabric","volume":"6","author":"Kiran","year":"2024","journal-title":"Eng. Rep."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"41854","DOI":"10.1002\/app.41854","article-title":"Synthetic Ni-Talc as Filler for Producing Polyurethane Nanocomposites","volume":"132","author":"Prado","year":"2015","journal-title":"J. Appl. Polym. Sci."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"102187","DOI":"10.1016\/j.mtcomm.2021.102187","article-title":"Natural Fillers as Reinforcement for Closed-Molded Polyurethane Foam Plaques: Mechanical, Morphological, and Thermal Properties","volume":"27","author":"Husainie","year":"2021","journal-title":"Mater. Today Commun."},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"1092","DOI":"10.1177\/0892705718785692","article-title":"The Effect of Pumice Powder on Mechanical and Thermal Properties of Polypropylene","volume":"32","author":"Sever","year":"2019","journal-title":"J. Thermoplast. Compos. Mater."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"431","DOI":"10.29109\/gujsc.1279794","article-title":"Investigation of the Effect of Filling Ratio on Mechanical Properties of Pumice Filled Epoxy-Based Composites","volume":"11","author":"Kosedag","year":"2023","journal-title":"Gazi \u00dcniversitesi Fen Bilim. Derg. Part C Tasar. Ve Teknol."},{"key":"ref_26","doi-asserted-by":"crossref","unstructured":"Albayrak, O., Ipekoglu, M., Uctu, O., Batibay, G.S., Calik, A., and Pilipovic, A.P. (2026). Structure\u2013Property Relationships in Polyester-Based Polyurethane Foams with Varying Isocyanate Index for Footwear Midsole Applications. Polymers, 18.","DOI":"10.3390\/polym18151896"},{"key":"ref_27","unstructured":"(2000). Standard Atmospheres for Conditioning and Testing of Footwear and Components for Footwear (Standard No. TS EN 12222)."},{"key":"ref_28","unstructured":"(1988). Microporous Rubber Sheets, Soles and Heels (Standard No. TS 5501)."},{"key":"ref_29","unstructured":"(2000). Footwear\u2014Test Methods for Outsoles\u2014Abrasion Resistance (Standard No. TS EN 12770)."},{"key":"ref_30","unstructured":"(2019). Footwear\u2014Sampling Location, Preparation and Duration of Conditioning of Samples and Test Pieces (Standard No. TS EN ISO 17709)."},{"key":"ref_31","unstructured":"(2003). Footwear\u2014Test Methods for Outsoles\u2014Tensile Strength and Elongation (Standard No. TS EN 12803)."},{"key":"ref_32","unstructured":"(2006). Footwear\u2014Test Methods for Outsoles\u2014Flex Resistance (Standard No. TS EN ISO 17707)."},{"key":"ref_33","doi-asserted-by":"crossref","first-page":"3211","DOI":"10.1002\/app.32542","article-title":"Physical Properties of New Polyurethanes Foams from Benzene Polyols Synthesized from Erucic Acid","volume":"118","author":"Dumont","year":"2010","journal-title":"J. Appl. Polym. Sci."},{"key":"ref_34","doi-asserted-by":"crossref","unstructured":"Nordi, S.S., Noor, E.E.M., Kok, C.K., Julkapli, N.M., and Baig, M.F. (2025). Phase, Chemical, Thermal, and Morphological Analyses of Thermoplastic Polyurethane (TPU) Nanocomposites Reinforced with Jute Cellulose Nanofibers (CNFs). Polymers, 17.","DOI":"10.3390\/polym17070899"},{"key":"ref_35","doi-asserted-by":"crossref","first-page":"229","DOI":"10.1177\/0021955X02038003139","article-title":"Effect of Nano- and Micro-Silica Fillers on Polyurethane Foam Properties","volume":"38","author":"Javni","year":"2002","journal-title":"J. Cell. Plast."},{"key":"ref_36","doi-asserted-by":"crossref","first-page":"137286","DOI":"10.1016\/j.matlet.2024.137286","article-title":"Water Absorption of Polyurethane Foam Reinforced with Bio-Fillers","volume":"377","author":"Pieniz","year":"2024","journal-title":"Mater. Lett."},{"key":"ref_37","doi-asserted-by":"crossref","first-page":"e55846","DOI":"10.1002\/app.55846","article-title":"Assessment of Frequency and Amplitude Dependence on the Cyclic Degradation of Polyurethane Foams","volume":"141","author":"Foster","year":"2024","journal-title":"J. Appl. Polym. Sci."}],"container-title":["Polymers"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2073-4360\/18\/18\/2270\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,9,17]],"date-time":"2026-09-17T11:53:01Z","timestamp":1789645981000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2073-4360\/18\/18\/2270"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2026,9,17]]},"references-count":37,"journal-issue":{"issue":"18","published-online":{"date-parts":[[2026,9]]}},"alternative-id":["polym18182270"],"URL":"https:\/\/doi.org\/10.3390\/polym18182270","relation":{},"ISSN":["2073-4360"],"issn-type":[{"value":"2073-4360","type":"electronic"}],"subject":[],"published":{"date-parts":[[2026,9,17]]}}}