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This paper aims to identify the creep mechanisms of high tenacity (HT) polyester industrial fiber under different loads. In-situ synchrotron small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS) tests were conducted on a 1000 D HT fiber during the creep and creep recovery process with a low load (15 N) and a medium load (50 N) as well as creep rupture process with a high load (60 N). The measured creep strain-time curves comprised tensile zone (I), creep deformation zone (II) and creep recovery/rupture zone (III). The SAXS indicated that the macroscopic initial creep strain in zone I and creep deformations in zone II were attributed to conformation transition from gauche to trans in amorphous region, increasing the amorphous orientation and long period. Irreversible portion of conformation changes accounts for the small unrecoverable plastic creep strain after removing 15 N load in zone III. The initial creep strain in zone I and creep deformations in zone II of the 50 N creep process were bigger than the microscopic long period strain, because amorphous layers had conformational transformation and microfibril slippage which also produced a higher unrecoverable plastic creep strain in zone III. The long period increased significantly at the beginning of rupture zone with 60 N due to fragmentation of amorphous tie molecular. The disappearance of lamellar peaks at the end of rupture zone implied destruction of periodic lamellar structures, for the entire breakage of amorphous chains. The WAXS suggested that the crystal structure was stable under the creep loads. [ABSTRACT FROM AUTHOR]

[Display omitted] • This work develops a strain sensor that is insensitive to humidity and temperature changes. • The sensor shows a linear sensing feature throughout the whole sensing range. • It provides a new route for enhancing the sensing reliability of wearable sensors. Wearable and stretchable strain sensors have attracted much attention for their unique applications in monitoring human motion and health. However, state-of-the-art sensors lack sensing reliability on temperature and humidity changes at the wearable microinterface, leading to suboptimal sensing accuracy in body area sensing networks. For that, we design and fabricate a strain sensor using silk/polyurethane composite yarns with a core-sheath structure. The silk is modified using graphene with the assistance of 3-glycidyloxypropyl trimethoxy silane as coupling agent. The sensor exhibits fast response speed (i.e., 80 ms), high durability (>1500 cycles), remarkable linear sensing feature (R2 = 99.8 %) throughout the whole working range, and negative resistance response towards strain deformation. More importantly, the sensor performance will not be affected by temperature and humidity changes in typical use conditions. Testing is conducted and sensor responses in various body motions are also reported. In addition, a demonstration for the real-time body area sensing network using the fabricated sensor is provided. Experimental results from this study show that the fabricated strain sensor will have huge potentials for future personalized healthcare and public health management. [ABSTRACT FROM AUTHOR]