The scale of the problem extends far beyond Korea. An estimated 8 to 12 million metric tons of plastic waste enter the world’s oceans each year, and projections suggest flows into aquatic ecosystems could climb from around 19 to 23 million metric tons in 2016 to 53 million metric tons annually by 2030. Marine aquaculture, which supports more than 20 million livelihoods worldwide, has emerged as a significant yet underrecognized contributor, because the very infrastructure that keeps shellfish suspended in nutrient-rich water degrades continuously in place. Expanded polystyrene is particularly vulnerable: its cellular structure creates preferential paths for crack propagation, its inherent brittleness worsens in cold water, and ultraviolet radiation reflected off the sea surface accelerates polymer chain scission, embrittling the material until it fragments. Visible breakdown can occur within just one to two years of deployment.

The consequences ripple through food webs and onto dinner plates. Pacific oyster larvae readily ingest polystyrene particles ranging from 20 to 70 micrometers, with uptake efficiency varying by particle size and developmental stage. Chemical additives embedded in the foam, including the flame retardant hexabromocyclododecane and other persistent organic pollutants, can transfer into oyster tissues and enter human food chains. Microplastic concentrations in Korean coastal sediments have reached up to 390 particles per kilogram of dry weight, levels reported to be 15 to 50 times higher than international maxima. Regulators have run out of patience: South Korea’s Ministry of Oceans and Fisheries banned new expanded polystyrene buoy installations effective November 2022 and mandated replacement with eco-friendly alternatives by 2025.

There is a catch, however. The current generation of alternative buoys costs two to three times more than conventional styrofoam while often showing reduced durability in marine conditions, a combination that has slowed adoption among farmers operating on thin margins. It is against this backdrop that Sun-Min Park and So Youn Mun of the Korea Institute of Ceramic Engineering and Technology, together with Jun Hwan Jang of Yuhan University, designed their thermoplastic-basalt composite buoy system, published in Advances in Industrial and Engineering Chemistry. Their central insight is that the reinforcement fiber matters as much as the matrix. Basalt fiber, drawn by melting volcanic rock at around 1500 degrees Celsius without chemical additives, offers tensile strengths of 2800 to 3200 megapascals and an elastic modulus of 85 to 95 gigapascals, comfortably exceeding the minimum requirements of 2000 megapascals and 70 gigapascals set for certified marine buoys.

Basalt also brings environmental credentials that glass fiber cannot match. Unlike E-glass production, essentially nothing is added during basalt fiber manufacture; the rock is simply washed and melted. The fibers show superior alkali resistance compared with glass, a critical property in seawater, and the composites exhibit higher tensile modulus and strength than E-glass panels made with the same resin, with interlaminar shear strength falling advantageously between glass and carbon fiber systems. Although basalt fiber costs 1.8 to 2.2 times more than E-glass, the researchers argue the lifecycle economics favor it decisively: extended service life, fewer replacements, and no regulatory penalties or remediation costs from fragmentation. Combined with a thermoplastic matrix rather than a thermoset, the composite can be melted and reformed at end of life, closing the material loop in a way that fragmented polystyrene never can.

The manufacturing pathway reads like an exercise in precision. Raw volcanic basalt, containing roughly 48 to 52 percent silica, 14 to 18 percent alumina, and 8 to 12 percent calcium oxide, is crushed, washed, and melted in electric resistance furnaces at 1500 to 1600 degrees Celsius for two to four hours. The molten rock is extruded through platinum-rhodium alloy bushings with orifices of 1.5 to 2.0 millimeters, then rapidly cooled by air and water sprays into continuous filaments 9 to 15 micrometers in diameter. Drawing speeds of 50 to 100 meters per minute are tuned to push tensile strength above 3000 megapascals, and batch-to-batch variation is held below 5 percent through tight control of melt temperature, drawing speed, and cooling rate. The fibers are then compounded with thermoplastic at 200 to 250 degrees Celsius to a 30 percent fiber volume fraction, and compression molding at 240 degrees Celsius and 15 megapascals consolidates the final buoy shell.

The team developed two buoy configurations, each with a 60-liter capacity and a 1.6-millimeter wall. Design 1 measures 666 millimeters long with a 390-millimeter maximum diameter, weighing 2.3 kilograms, and reinforces its shell with lateral grooves 30 millimeters wide and 20 millimeters deep. Design 2 shortens the body to 638 millimeters while widening it to 406 millimeters, adds six external tape reinforcement patches, and triples the connection openings to six, cutting the load on each attachment point by 66.7 percent for redundant mooring in harsh seas. To validate both, the researchers turned to finite element analysis, modeling the material as orthotropic and applying a uniform pressure of 0.125 megapascals, the most severe durability requirement with a 1.25 ultimate factor over the nominal 1.0 bar operating pressure. A knock-down factor of 0.8 accounted for manufacturing variability and environmental effects, yielding a design allowable flexural strength of 420 megapascals.

The results were decisive. Design 1 with a six-ply laminate showed a strength margin of safety of minus 0.08, a marginal failure under the harshest load, but adding two plies transformed the picture: the strength margin rose to plus 0.41 and the buckling margin leapt from plus 0.76 to plus 2.70. Design 2 fared worse in both configurations, with a six-ply strength margin of minus 0.39 and an eight-ply margin of just plus 0.28, suggesting that geometric optimization matters as much as laminate thickness. Drop-test simulations from a height of 1500 millimeters in three orientations added further confidence. Peak stresses in the six-ply laminate ranged from 180 to 489 megapascals depending on impact direction, with axial impact most critical, while the eight-ply [0/45/90/−45]s stacking sequence cut peak stresses by 6 to 21 percent across all directions, staying within the 400 to 600 megapascal ultimate strength range of basalt composites.

The environmental payoff is the headline figure: because the composite buoy maintains structural integrity under impacts that would shatter expanded polystyrene catastrophically, the researchers estimate a greater than 95 percent reduction in microplastic generation potential. Preliminary field data indicate durability exceeding five years, compared with the one to two years typical of EPS buoys, and the circular economy design recovers 85 to 90 percent of original fiber length and more than 95 percent matrix purity when retired buoys are shredded and thermally reactivated at 180 to 200 degrees Celsius. The framework reportedly delivers a 35 percent reduction in environmental impact relative to expanded polystyrene alternatives, with recovered materials feeding new buoys or higher-value construction products.

Challenges remain before volcanic-rock buoys blanket Korean longlines, which currently stretch 100 meters with 51 styrofoam floats apiece and support oyster strings hanging 3 to 7 meters deep through 18-to-30-month grow-out cycles. Certification requires 12 months of field testing across three distinct coastal regions, buoyancy retention of at least 95 percent after three years, and continuous monitoring, all under environmental extremes that include typhoon waves of 3 to 4 meters, winds above 25 meters per second, temperature swings from minus 5 to 35 degrees Celsius, and fouling loads of 5 to 10 kilograms per square meter annually. Yet with Korea producing over 300,000 tons of oysters annually as the world’s third-largest producer, and with roughly 990,000 styrofoam buoys lost or discarded into the sea each year, the stakes could hardly be higher. A buoy that survives the sea, recycles into its own successor, and leaves no microplastic legacy may be exactly what the industry, and the ocean, have been waiting for.

Subject of Research: Development and structural validation of a recyclable thermoplastic-basalt composite buoy to eliminate microplastic pollution in marine oyster aquaculture

Article Title: Eco-friendly thermoplastic-basalt composite buoy system: eliminating microplastic pollution in marine oyster farming

Article References: Park, S.-M., Mun, S. Y., & Jang, J. H. (2025). Eco-friendly thermoplastic-basalt composite buoy system: eliminating microplastic pollution in marine oyster farming. Advances in Industrial and Engineering Chemistry, 1(1), Article 31. https://doi.org/10.1007/s44405-025-00029-6

Image Credits: AI Generated

DOI: 10.1007/s44405-025-00029-6

Keywords: microplastics, oyster farming, basalt fiber, thermoplastic composite, aquaculture, marine pollution, recyclability, finite element analysis, expanded polystyrene, circular economy, South Korea, sustainable materials

The problem the researchers set out to solve is both familiar and severe. Expanded polystyrene, or EPS, buoys dominate marine aquaculture because they are cheap and buoyant, but their structure is inherently fragile. Ultraviolet radiation, wave action, and wind easily fragment them into particles smaller than five millimeters, the accepted definition of microplastics. In South Korea alone, more than twenty million EPS buoys are estimated to be in use on fish farms, and a 2023 report from the Ministry of Oceans and Fisheries found that buoy debris accounted for over forty percent of the plastic waste collected along the country’s coastlines. That debris has been detected not just on the ocean surface but along shorelines and in deep-sea sediments, where it is ingested by plankton, crustaceans, fish, and shellfish before entering the human food chain.

While Korea has already moved to restrict new EPS buoy installations in certain regions and has certified alternatives such as expanded polyolefin and expanded polypropylene, none of these plastic-based substitutes eliminates microplastic generation altogether. The researchers from the Korea Institute of Ceramic Engineering and Technology and Dongduk Women’s University took a fundamentally different approach. Rather than searching for a friendlier plastic, they turned to an inorganic material system in which microplastics simply cannot form, drawing on the same manufacturing principles used to produce foamed glass bricks.

The core of the new technology is the porous ceramic bead, sometimes called cellular or multicellular glass. Each bead is an inorganic material with a glassy matrix enclosing countless independent closed pores separated by thin glass walls. Because these pores trap air inside sealed cells, the beads float, much like the individual foam beads of an EPS buoy. To make them, the team selected soda-lime glass, the inexpensive material used in ordinary flat windows, as the base. Recycled waste glass was crushed and pulverized in an attrition mill without any washing or chemical pretreatment, then mixed with a binder and foaming agents before being shaped into spherical green granules on a disk-type pelletizer.

Choosing the right binder proved critical. The team tested four candidates: polyvinyl alcohol, basalt powder, kaolin, and water glass, or sodium silicate. Beads made with polyvinyl alcohol and water glass showed superior sphericity and lower densities, ranging from 0.23 to 0.28 grams per cubic centimeter, while kaolin and basalt produced irregular, partially fused shapes with densities up to 0.35 grams per cubic centimeter. Polyvinyl alcohol decomposes completely during foaming and leaves no residue, but water glass offered an added advantage: its water content evaporates during heating while the remaining silica vitrifies into the glass matrix, actually enhancing foaming behavior. Combined with easy handling, thermal stability, and low cost, this made water glass the optimal choice, requiring roughly twenty percent by weight in the mixture.

Particle size and temperature emerged as the twin levers controlling density. In the foaming process, fine glass particles partially fuse near their softening temperature, encapsulating the foaming agents whose decomposition or reaction generates gas that expands within the softened glass to form closed-cell pores. Smaller particles produce thinner pore walls and therefore lighter beads, and the experiments confirmed a dramatic effect. When glass powder was ground to below 25 micrometers, the foamed beads reached a bulk density of approximately 0.2 grams per cubic centimeter at foaming temperatures between 800 and 850 degrees Celsius. Particles larger than 45 micrometers were deemed unsuitable for buoy applications. The researchers paired petroleum coke carbon with calcium carbonate as a composite foaming agent, finding that 0.3 percent carbon and 0.5 percent calcium carbonate delivered the lowest density, while excess carbon caused over-foaming and structural collapse.

Preheating proved equally important. Working in a rotary kiln divided into preheating, foaming, and stabilization zones, the team found that a preheating temperature of 600 degrees Celsius produced the lowest-density beads. Below that threshold the foaming reactions were insufficiently activated, while above it premature softening and partial coalescence of glass particles increased density. After foaming, the beads were stabilized at 500 to 550 degrees Celsius and slowly cooled to 40 degrees to relieve thermal stress. To keep the molten, expanding beads from fusing together inside the kiln, the researchers added release agents such as clay, kaolin, or cement, each meeting a demanding set of criteria: melting points above that of the glass, chemical inertness, good flowability, and cost-effectiveness. With these agents in place, the finished beads showed smooth surfaces and densities between 0.19 and 0.21 grams per cubic centimeter.

Cross-sectional micrographs confirmed that the beads’ interiors consist of uniformly distributed, independent closed-cell pores, the architecture responsible for buoyancy. The beads were then consolidated into full buoys using white Portland cement as an inorganic binder, a route the team chose over sintering-based interfacial fusion for its simplicity and mechanical stability. Spherical beads two to five millimeters in diameter were mixed with cement, packed into molds, compacted, and dried for roughly nine to ten hours before demolding. The resulting buoys retained the spherical bead structure and the low density needed to float, and prototypes in a variety of shapes floated stably for more than sixty days without noticeable degradation.

Performance testing against Korean eco-friendly buoy certification standards underscored the technology’s practical promise. Two 40-liter cylindrical buoys, weighing 10.04 and 11.14 kilograms respectively, were verified by the Korea Conformity Laboratories to deliver buoyancies of 16.38 and 14.05 kilograms-force. Because water can partially fill the voids between beads, the researchers distinguished dry-basis and wet-basis weights; even accounting for the wet weight of about 18 kilograms, the buoys exceeded the certified buoyancy threshold. Critically, in the standard impact test, in which a 10-kilogram pendulum hammer is dropped from two meters, neither buoy fractured or ruptured, showing only shallow surface indentations. Because the individual beads are impermeable and the interconnected structure blocks water ingress, even damaged buoys retain their buoyancy, unlike hollow polymer floats that fail catastrophically when cracked.

The researchers, funded by the Korea Institute of Marine Science and Technology Promotion through the Ministry of Oceans and Fisheries, argue that with minor design optimization these ceramic buoys could satisfy existing certification requirements and become a next-generation, microplastic-free alternative to EPS systems. Because the beads are made from waste glass and bound with inorganic cement, the approach simultaneously recycles a major waste stream and eliminates a major microplastic source at its origin. If scaled, glass-turned-ceramic buoys could offer coastal aquaculture a permanent, durable answer to one of the ocean’s most visible pollution problems.

Subject of Research: Development of eco-friendly porous ceramic buoys made from waste glass to replace expanded polystyrene buoys and mitigate marine microplastic pollution

Article Title: Fabrication of porous ceramic buoys (Ⅰ): preparation of porous ceramic beads for buoy manufacturing

Article References: Park, S.-M., Hong, Y., Oh, C., Kim, J., & Lee, C.-T. (2025). Fabrication of porous ceramic buoys (Ⅰ): preparation of porous ceramic beads for buoy manufacturing. Advances in Industrial and Engineering Chemistry, 1(1), Article 38. https://doi.org/10.1007/s44405-025-00035-8

Image Credits: AI Generated

DOI: 10.1007/s44405-025-00035-8

Keywords: porous ceramic buoys, microplastics, soda-lime glass, foamed glass beads, buoyancy, marine pollution, expanded polystyrene, recycled glass, rotary kiln foaming, eco-friendly materials, aquaculture, ceramic beads