A Novel Polyoxymethylene Fiber-Based Artificial Muscle Enabled Stable Actuating Behavior

Due to superior water/chemical resistance, constructing novel polyoxymethylene (POM) fiber-based artificial muscles (AM) is significant for developing advanced flexible actuating devices with high stability. However, strong crystallizing ability and low amorphous content of POM fibers were disadvantageous for them to achieve ideal actuating performance as artificial muscles. Herein, thermoplastic polyurethane elastomer (TPU) was blended with POM to regulate its crystalline behavior widely, while POM/TPU fibers were prepared by melt spinning-hot drawing/heat setting, and a mandrel-coiled POM fiber-based AM was constructed for the first time by further merged/twisted/coiled processes. With increasing fiber draw ratio/TPU content, the increased orientation factors/amorphous content of stretched POM fibers substantially enhanced the actuation properties of muscles. Meanwhile, by controlling merging/twisting/coiling geometries, the actuating properties of muscles are further optimized. Under 14 V actuating voltage/200 load-to-weight ratio, the max shrinkage strain/work capacity of POM/20T-600%f AM achieve 40.23%/34.69 J kg^-1, reaching 201%/434% of those of typical mammalian skeletal muscle. Moreover, POM fiber-based AM exhibit superior cyclic actuating stability due to thermal stable oriented crystalline structures of fiber during the actuating process, while in alkali resistance tests, the maximum shrinkage strain retention reach 94.11%, much higher than that of nylon 66 sewing threads AM (53.56%).