The growing amount of waste worldwide requires new solutions for its management. Agricultural by-products account for almost 10% of the waste generated. One of them is sheep wool, a natural fibre with beneficial physicochemical properties. Currently, sheep wool production amounts to approximately 1–2 million tonnes per year, of which 60% is used in the manufacture of clothing. Nevertheless, it poses a considerable challenge in terms of disposal due to its keratin-rich composition and slow biodegradability. This review analyses the chemical and physical properties of sheep wool and assesses its potential as biomass based on its carbon content and other elemental components. This allows us to provide a critical comparative analysis of the main technological pathways for the use of waste sheep wool as biomass, including anaerobic digestion, pyrolysis, direct combustion and gasification. The review highlights both the opportunities and limitations of these processes, comparing sheep wool in terms of energy potential and carbon footprint with other biomass. The review shows that the calorific value of sheep wool (19.5 MJ/kg) is competitive with traditional plant-based biofuels and the use of waste sheep wool as biomass source can contribute to reduction in CO₂ emissions of 2.1 million tonnes per year. The use of sheep wool as biomass can not only contribute to waste reduction but also supports the goals of sustainable agriculture and climate neutrality. The selected methods may offer a new and effective way of reducing waste and allow all sheep wool produced to be introduced into the circular economy.

Amid increasing demand for energy efficiency and reduced CO₂ emissions in the building sector, natural fibres such as sheep wool are gaining attention as a sustainable raw material for low-impact insulation materials. This review summarises the current state of research on the thermal and acoustic properties of sheep wool-based composites and their applications in low-carbon construction. The fibre structure, thermal conductivity, hygroscopicity, heat storage capacity, and sound absorption coefficient are discussed, highlighting the competitiveness of sheep wool compared to conventional synthetic and mineral materials. The review also addresses the use of wool fibres in cement composites, insulation panels, sound-absorbing materials, and sorption mats, emphasising their potential in humidity regulation, acoustic comfort, and circular economy strategies. A literature analysis indicates that utilising sheep wool waste can reduce environmental impact, lower the carbon footprint of building materials, and enhance local agricultural value. The review provides an overview of current knowledge on sustainable sheep wool-based insulation materials and focuses on an interdisciplinary and quantitative approach to the thermal, acoustic, and environmental performance of composites based on waste sheep wool, combined with an analysis of their applicability in low-carbon construction and circular economy frameworks. Future research should focus on assessing long-term durability, material ageing under real service conditions, and standardised life cycle assessment (LCA) methodologies to enable reliable comparison with conventional insulation materials.

Biocomposites based on natural fibres represent a promising solution for the circular economy. The aim of this study was to develop and characterise a biodegradable composite based on sheep wool from herds raised in the Kyrgyz Republic and polylactide (PLA 4032D). Composite samples with a wool–PLA ratio of 50:50 were fabricated by thermoforming at a temperature of 168 °C for 30 s (n = 10). Mechanical properties tests were performed (PN-EN ISO 604—compression tests), for impact resistance (Charpy method), differential scanning calorimetry (DSC), and measurements of density and thermal conductivity. Biodegradation samples were subjected to enriched soil conditions for 6 weeks in two variants (with and without irrigation). The results showed that the addition of sheep wool to the PLA matrix significantly increased compressive strength (23.56 ± 5.23 MPa) and impact energy absorption (226.2 ± 23.8 kJ/m²) compared to neat PLA. After biodegradation, a 59% reduction in compressive strength was observed while maintaining an increase in fracture energy, suggesting a change in the failure mechanism. The density (0.27 ± 0.02 g/cm³) and the thermal conductivity (0.127 W/m·K) comparable to polymer foams indicate potential for thermal insulation applications. Microscopy and DSC analysis confirmed complete biodegradation under soil conditions. The developed biocomposite from Kyrgyz sheep wool demonstrates the potential for valorisation of local fibrous waste for biodegradable materials with functional insulation properties.

Modern photovoltaic technologies are increasingly evaluated not only in terms of power conversion efficiency and cost, but also with respect to resource origin, toxicity, recyclability, and overall life-cycle impacts. Within this broader sustainability framework, bio-based and bio-inspired materials derived from biomass or mimicking biological structures have emerged as promising candidates for a wide range of photovoltaic components, including active layers, interfacial modifiers, substrates, encapsulants, and natural dyes. This review provides a layer-by-layer overview of such materials implemented or proposed in dye-sensitized, organic, perovskite, biohybrid, and silicon solar cells, linking their molecular structures and optoelectronic properties to representative device performances and key degradation pathways. Cross-cutting challenges related to moisture and thermal stability, barrier performance, feedstock variability, and the risk of “greenwashing” are highlighted, emphasizing that sustainability claims must be supported by quantitative metrics such as life-cycle assessment, circularity indicators, and durability studies. Finally, we outline promising research directions in molecular engineering, hybrid biosynthetic architectures, and advanced encapsulation concepts that could enable bio-based materials to make a meaningful contribution to low-impact photovoltaic technologies.

This study reports the physicochemical characterization and structure–property relationships of rigid sheep wool/phenolic novolac panels developed as bio-based thermal insulation for building envelopes. Mixed Polish sheep wool was washed, mechanically opened, and formed into nonwoven mats, then impregnated with either neat or flame-retardant novolac resin to obtain lightweight boards with a fiber content of about 50 wt%. Elemental analysis, ICP-OES, FTIR spectroscopy, and laser and electron microscopy were used to evaluate the fiber composition, keratin structure, morphology, and fiber–matrix interfaces. Mechanical performance under three-point bending and shear, differential scanning calorimetry, thermogravimetric analysis, and transient hot-probe thermal-conductivity measurements were applied to link microstructure with functional behavior. Novolac impregnation transformed the compliant wool mat into self-supporting panels, increasing the flexural modulus to the 0.8–1.4 GPa range and flexural strength to approximately 48–52 MPa, while the shear modulus and work to failure rose by more than an order of magnitude relative to the loose wool reference. Thermal conductivity remained in a typical range for natural-fiber insulations (λ = 0.061 W·m⁻¹·K⁻¹ for the wool mat and 0.071–0.074 W·m⁻¹·K⁻¹ for the composites), although higher than that of expanded polystyrene. DSC and TGA confirmed that wool fibers remain thermally stable up to about 200–220 °C, that the novolac resin cures around 140 °C, with typical phenolic reaction enthalpies, and that both formulations generate high char residues of roughly 60–80 wt% at 600 °C under nitrogen, evidencing a strong charring propensity rather than directly quantifying fire resistance. Overall, the results position sheep wool/novolac panels between conventional bio-based insulation and structural composites and highlight their potential as sustainable, circular insulation materials for energy-efficient building envelopes.

Low-grade sheep wool is an underused, keratin-rich by-product whose cystine-derived sulphur could be returned to agricultural soils. Carded wool was bonded with sprayed poly(lactic acid) (PLA) hot-melt to obtain porous wool–PLA biocomposite mats, which were exposed in field soil, in a pasture-grass composter and under soil-free outdoor conditions. The elemental composition of the wool, soil, forage, composting material and exposed mats was determined by ICP-OES after 60 days of exposure; each reported value is the mean of at least three analytical determinations, whereas the field layout comprised one plot per treatment. Forage from the plot with buried mats contained 47.8% more S and 21.9% more K than forage from the untreated plot, whereas Ca, Mg, B and Mo concentrations were lower; because the plots were not replicated, these differences are reported as preliminary observations rather than as demonstrated treatment effects. After composting, the mats retained only 17–23% of their initial storage modulus between −30 and 50 °C, while the relaxation of the PLA phase shifted by 7–10 °C towards higher temperatures. The water contact angle decreased from 72.3 ± 10.0° to 55.7 ± 12.1° (six droplets on one mat per condition), while the stylus roughness did not change appreciably. Digital microscopy revealed swelling, fissuring, cavities and fibre exposure along wool–PLA interfaces. A coupled mechanism of PLA ester hydrolysis and keratinolytic release of sulphur is proposed as a working hypothesis that is consistent with, but not yet proven by, the present data. The results support wool–PLA mats as temporary, degradable carriers of keratin-bound sulphur; replicated field trials with yield, nutrient uptake and soil measurements, together with direct degradation markers, are required before any fertilising or soil-improving effect can be claimed.