Naked alpaca wool works better with silicone elastomers

Washed, naked wool fiber works is an efficacious reinforcing agent for silicone elastomers. The reinforcement depends both on total wool loading and the fiber length. Silicone elastomers must be filled/reinforced with fillers, typically fumed silica, as they are otherwise soft and/or weak and prone to tearing. Fumed silica, produced from waste chlorosilanes by combustion, is relatively expensive and involves the challenge of managing HCl. We report an investigation of alternative reinforcing agents based on waste wool fibers, a renewable resource. Chemical modification of the wool surface, by base etch, exposed free thiols that were used to chemically graft to silicone polymers using a thio-Michael addition. The reinforcement of such chemisorbed silicones was compared to physisorbed silicones or no pretreatment, except for washing, of the wool at all. Tensile tests evaluating the Young's modulus, tensile strength and elongation at break demonstrated a significant improvement of elastomer physical properties when modified with the chemisorbed silicone. The efficiency of reinforcement was found to depend both on the loading of wool in the silicone elastomer and on fiber length. More surprising, however, was the facile incorporation in silicone elastomers, and excellent reinforcement by, naked (chemically unmodified) short wool fibers in loadings up to 50 wt%. Significantly better reinforcement than fumed silica at the same loading – 10% – was provided by the use of long, naked alpaca wool fibers.