Sheep-Wool-Fiber-Reinforced Rigid Polyurethane Composites: Comparative Effects of Alkaline, Oxidative, and APTES Treatments
DOI:
https://doi.org/10.12974/2311-8717.2026.14.11Keywords:
Sheep wool fiber, Rigid polyurethane, Surface treatment, APTES, Tensile properties, Density-derived porosity, Water absorptionAbstract
Coarse sheep wool is a low-value byproduct whose use as reinforcement in rigid cast polyurethane remains less studied than its use in insulation products. This study compares untreated, alkaline-treated, oxidatively treated, and 3-aminopropyltriethoxysilane (APTES)-treated wool fibers in the same two-component polyurethane matrix (NEUKADUR MultiCast 1 / Hardener ISO 2, 100:100 by mass). Five series of twenty ASTM D638 Type I specimens were prepared: unreinforced polyurethane (P0) and four composites containing 10 wt% wool (approximately 8.0 vol%) cut to 10 ± 2 mm (T0-T3). Relative to P0, washed wool reduced tensile strength from 32.66 ± 0.59 to 26.00 ± 0.87 MPa and increased the apparent Young's modulus, determined from crosshead displacement, from 727 to 793 MPa. All treatments increased strength relative to T0, with the ranking T3 > T1 > T2 (Tukey HSD, adjusted p < 0.001). T3 reached 30.40 ± 0.68 MPa and had the highest apparent modulus (911 MPa) and the lowest 24 h water absorption among the reinforced series (1.24%). Density-derived porosity differed among series and covaried with strength; however, an exploratory covariance model retained a large series effect after adjustment. Because porosity was estimated indirectly and surface chemistry and fiber orientation were not measured directly, the results support an association between APTES treatment and improved composite performance but do not demonstrate a specific interfacial bonding mechanism or long-term moisture resistance. Under the tested formulation and processing conditions, APTES provided the best overall measured response, although none of the reinforced series recovered the tensile strength of the neat matrix.
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