The research team, led by Luthfi and colleagues, fabricated composites containing five different volume fractions of sago pith waste, from 20 to 40 percent, in a commercial orthophthalic unsaturated polyester resin identified as SHCP 3315, cured with 1.5 weight percent methyl ethyl ketone peroxide hardener. Before any mixing began, the raw waste collected from facilities in Lhokseumawe had to be cleaned. The material was washed repeatedly in plain water, stirred and squeezed to strip away residual soil and sand, then sun-dried for five to seven days. Moisture content was verified with a gravimetric oven method at 60 degrees Celsius, and only batches drying below 2 percent moisture were accepted. During drying, the pith gradually shifted from white to light brown, a visual signature of moisture loss and natural oxidation.

Because dried sago pith tends to clump into soft agglomerates that could seed weak spots in a finished panel, the team sieved the material through a 20-mesh screen, capping particle size at roughly 0.841 millimeters. Notably, they skipped the glycerol plasticization used in earlier sago-waste studies, deliberately choosing a simpler and cheaper route. The apparent density of the sieved particles was estimated at 1.4286 grams per cubic centimeter using a simple ethanol displacement calculation, a value the authors candidly flag as an estimate rather than a validated true density, since no calibrated pycnometer or degassing was employed. That honesty matters, because the same number feeds into the theoretical density and porosity calculations that frame the entire mechanical analysis.

The composites themselves were mixed by hand, homogenized with a motorized mixer, and cast into 300 by 300 by 10 millimeter molds lined with aluminum foil, curing at room temperature for at least 24 hours. Three formulations, at 20, 30, and 40 percent sago pith waste, served most physical and thermal tests, while intermediate compositions at 25 and 35 percent were fabricated specifically to sharpen the mechanical trend analysis. Density measurements told the first part of the story: experimental density fell steadily from 1.08435 grams per cubic centimeter at 20 percent filler to 1.00232 at 40 percent, while estimated porosity climbed from 8.86 percent to 19.78 percent. In other words, more sago means a lighter panel, but also one riddled with more internal voids, as the resin increasingly struggles to wet and penetrate the growing mass of particles.

Flexural performance followed the same downward slope. In modified three-point bending tests on 200 by 15 by 10 millimeter specimens over a 160 millimeter span, average bending strength dropped from 3.87 kilograms-force per square millimeter for the 20 percent composite to 2.92 for the 40 percent version, and the maximum bending moment fell from 1.611 to 1.219 kilograms-force meters. A one-way analysis of variance confirmed these differences were statistically significant, with F values of 20.68 for moment and 19.06 for stress and p-values in the millionths. Strain at failure, intriguingly, showed a rising trend with more filler, from 1.19 to 1.35 percent, but the ANOVA returned p equal to 0.265, so the authors correctly decline to claim that sago content meaningfully changes how far the material bends before it breaks.

Scanning electron microscopy of the fractured surfaces explains why the strength falls. Micrographs of the 20 percent composite revealed residual sago starch granules roughly 20 to 30 micrometers across, cracked polyester matrix, and irregular voids with torn edges. Clean particle pull-out and interfacial gaps pointed to weak adhesion between the untreated lignocellulosic filler and the resin, meaning stress is not transferred efficiently across the interface. To separate failure damage from manufacturing defects, the team also imaged carefully cut, unfractured cross-sections, where voids appeared smoother and near-spherical, the classic fingerprint of air bubbles entrapped during mixing and molding. The 40 percent composite showed all of these features in greater abundance, consistent with its highest porosity, and the authors conclude that interfacial optimization, such as surface treatment of the particles, is the clearest path to better performance.

Fourier transform infrared spectroscopy added the chemical dimension. Using potassium bromide pellets, the team found all composites dominated by the polyester’s ester carbonyl stretch near 1730 inverse centimeters, with a broad hydroxyl band around 3533 to 3539 inverse centimeters growing more pronounced as sago content rose, reflecting the cellulose, hemicellulose, and absorbed water carried in with the biomass. Crucially, no new absorption bands unique to the composites appeared, indicating that sago pith and polyester interact primarily through physical rather than covalent chemical bonding. That chemical aloofness at the interface dovetails neatly with the pull-out features seen under the electron microscope.

Thermal analysis rounded out the picture. Differential scanning calorimetry showed the glass transition temperature sliding from 58 degrees Celsius at 20 percent sago to 54 at 30 percent and 50 at 40 percent, a shift the authors attribute to changes in crosslink density, interfacial region volume, and free volume when bio-filler particles enter the network. Because cured unsaturated polyester is a crosslinked thermoset, the broad high-temperature endotherms, which shifted from 165 to 200 degrees Celsius and grew in enthalpy from 3.74 to 5.86 joules per gram, reflect relaxation and thermally activated transitions rather than any true melting. Thermogravimetric analysis under nitrogen revealed multi-stage degradation: negligible moisture loss below 150 degrees Celsius, a 4 to 6 percent stage linked to hemicellulose decomposition up to 330 degrees, and a massive degradation stage between 331 and 490 degrees where more than 80 percent of the mass vanished. Final residues at 600 degrees Celsius ranged from 6.57 to 7.44 percent, with the 40 percent composite retaining the most, likely carbonaceous char from lignin plus natural mineral ash, though the authors caution the trend is not systematic.

Taken together, the study delivers a sober but genuinely useful verdict: sago pith waste can indeed be incorporated into unsaturated polyester as a renewable, nearly free filler, lightening the material while leaving the resin’s chemistry intact, but rising filler content drags in porosity and interfacial defects that erode bending strength. The authors frame the work as the integrating chapter of a broader program that previously examined tensile, acoustic, and thermal-conductivity behavior separately, and they point squarely at future work on particle-size optimization, improved processing, and surface chemical modification of the waste as the levers that could turn an agricultural liability into panels for insulation, construction, and other value-added uses. For Indonesia’s sago mills, the residue currently rotting behind the factory may be one sieve, one mixer, and one better interface away from a second life.

Subject of Research: Characterization of sago pith waste-filled unsaturated polyester composites

Article Title: The analysis of sago pith waste – unsaturated polyester composites by mechanical, SEM, FTIR, DSC, and TGA tests

Article References: Luthfi, Azhar, Jagodang, H., Riyadhsyah, T., Rihayat, T., & Setiawan, A. (2026). The analysis of sago pith waste – unsaturated polyester composites by mechanical, SEM, FTIR, DSC, and TGA tests. Environmental Challenges, 25, Article 101681. https://doi.org/10.1016/j.envc.2026.101681

Image Credits: AI Generated

DOI: Not provided

Keywords: sago pith waste, unsaturated polyester resin, natural fiber composites, flexural strength, porosity, FTIR, DSC, TGA, SEM, biomass waste utilization, Indonesia, thermal degradation

The team focused on linear low-density polyethylene, or LLD-PE, the workhorse polymer of artificial turf, chosen by manufacturers for its flexibility, chemical and thermal resistance, and low cost. Their source material came from a third-generation pitch with 50-millimetre pile length, installed in 2006 and used for football around 40 hours per week, year-round, until its removal in 2023. Over its lifetime the surface endured 1,825 hours of annual sunshine with 8.63 watts per square metre of UVA radiation, a mean temperature of 9.5 degrees Celsius, 74 percent mean humidity, and 920 millimetres of yearly precipitation. Because the average lifespan of such pitches is only 10 to 15 years, the 19-year service life represents an exceptionally high-exposure case, making it a stringent test of the polymer’s resilience.

Recovering the fibres was itself a technical challenge. The dismantled carpet was cleaned of its elastomeric performance infill and stabilising sand by tapping, shaking and vacuum cleaning, after which the polyethylene fibres were sheared from the backing and separated from sand and supporting polyester yarn by density separation in a water bath. Multiple cold-water washing cycles without surfactants removed residual mineral particles: washed fibres showed a residual mass of 4.3 percent after thermal degradation, compared with 6.9 percent for unwashed material, and a density of 0.98 grams per cubic centimetre versus 1.19 for the unwashed fibres. The cleaned fibres were then regranulated in a twin-screw extruder, pelletised, dried, and injection-moulded into standardised test specimens alongside two benchmarks: fibres from a new successor product from the same manufacturer, and a compound replicating the original material recipe with commercial LLD-PE grades and a masterbatch of antioxidants, UV stabilisers and pigments.

The first question was how badly the fibres had aged in place. Light and electron microscopy revealed unmistakable surface damage: cracks running along the fibre axis, pronounced curling, and discolouration. Energy-dispersive spectroscopy line scans across fibre cross-sections showed oxygen penetration up to 65 micrometres into the used fibres, compared with only 12 micrometres in new ones, indicating oxidative damage roughly five times deeper. Fourier-transform infrared spectroscopy confirmed surface oxidation, detecting hydroxyl stretching above 3,000 inverse centimetres, carbonyl bands near 1,714 and ether bands around 1,031, alongside signals from inorganic sand contamination below 600. On the face of it, the material looked tired and chemically battered.

But surface appearance proved deceptive. Because oxygen and water diffuse only slowly into polyethylene, ageing concentrates in the outer layers, and surface analysis alone can misrepresent the state of the bulk polymer. When the researchers measured wetting behaviour on injection-moulded plates, the recycled used turf showed a total surface free energy of 29.7 millinewtons per metre, barely below the 31.1 and 31.5 of the reference and new-turf materials, with virtually identical polar contributions. Reprocessing had effectively erased the polarity signature of oxidation. Differential scanning calorimetry revealed the characteristic double melting peak of LLD-PE in all materials, with the used material’s higher-temperature maximum shifted down by only about 2 to 3 degrees Celsius, and crystallinity of 40.2 percent against 43.0 for new turf and 45.2 for the reference, contrary to the increase expected from ageing-induced chain scission. Thermogravimetric analysis found decomposition temperatures essentially unchanged, with the only notable difference being a higher mineral residue in the used material, attributable to fine sand.

Mechanical testing delivered perhaps the most striking result. Tensile strengths of the recycled used turf, the new turf and the reference compound were statistically indistinguishable at 16.5, 16.9 and 16.7 megapascals respectively, with a p-value of 0.65. The used material did show a slightly higher tensile modulus, 318.7 versus 300.9 megapascals for new turf, but the researchers attribute this minor stiffening to residual mineral contamination restricting chain mobility rather than to structural degradation, noting it would be negligible in industrial compounding where mineral fillers are standard. Remarkably, the recycled material exhibited the smallest scatter in properties, defying the common perception that recyclates behave unpredictably. Melt flow rates of 3.3 to 3.7 grams per ten minutes across all materials confirmed that processability was preserved, with the used material’s slightly lower flow likewise explained by steric hindrance from sand rather than molecular damage.

High-temperature gel permeation chromatography added molecular-level nuance. The number-average molar mass of the recycled used fibres was 25,358 daltons, compared with 29,978 for recycled new turf and 34,391 for the reference compound, and the dispersity rose to 7.41 from 5.25 in the reference. Crucially, the reduction of about 4,620 daltons between recycled new and recycled used material was of the same magnitude as the 4,413-dalton drop caused by reprocessing alone. In other words, shredding, compounding and extrusion did as much molecular damage as nearly two decades of outdoor service. The broader distribution and lower average chain length had no measurable consequence for thermal, mechanical or rheological performance.

The spectroscopic extracts told a story of well-designed protection. Reference spectra identified the phenolic antioxidant Irganox 1010 and the hindered amine light stabilisers Chimasorb 2020 and Chimasorb 944 in the masterbatch, and traces of these stabilisers remained detectable in extracts of the used granules even after 19 years. No low-molecular-weight polymer fragments or degradation products appeared in the extract, indicating that the additive package had largely prevented bulk degradation throughout service. The authors conclude that the lifetime-limiting factor for high-quality artificial turf is not oxidative ageing of the polymer but mechanical wear, abrasion and bending from intensive use, and that a carefully balanced formulation can preserve performance almost indefinitely.

The implications reach well beyond football pitches. Europe hosted some 30,000 full-size and 70,000 small-size artificial turf pitches in 2021, covering more than 300 million square metres, and around 12,000 tonnes of the annual end-of-life waste stream is polyethylene. The study argues that from a materials standpoint there is no obstacle to closing the loop for several hundred thousand tonnes of this polymer; the real barriers are logistics, the availability of clean material streams, and the scarcity of advanced recycling facilities capable of separating the multi-layered turf construction and removing mineral contamination. It also cautions that the FTIR surface analysis routine in the recycling industry is insufficient to judge material condition, recommending supplementary differential scanning calorimetry to probe the bulk. With life cycle assessments showing mechanical recycling preferable to incineration, the authors call for political incentives to create demand for high-quality recyclates. If supported by better sorting, melt filtration and re-stabilisation, aged turf fibres could travel from field to feedstock, turning one of recycling’s most awkward waste streams into a genuine circular resource.

Subject of Research: Mechanical and chemical characterisation of aged linear low-density polyethylene fibres recovered from end-of-life artificial turf for high-value recycling.

Article Title: From field to feedstock: Mechanical and chemical behaviour of aged polyethylene fibres from artificial turf

Article References: From field to feedstock: Mechanical and chemical behaviour of aged polyethylene fibres from artificial turf. (n.d.). https://doi.org/10.1016/j.clet.2026.101321

Image Credits: AI Generated

DOI: 10.1016/j.clet.2026.101321

Keywords: artificial turf, polyethylene recycling, LLD-PE, polymer ageing, mechanical recycling, UV stabilisers, DSC, gel permeation chromatography, FTIR spectroscopy, tensile testing, circular economy, plastic waste