Flexible crosslinking of polyurethane using grafted poly(dimethylsiloxane) with Epichlorohydrin and Bisphenol A end groups and its impact on the mechanical properties and low-temperature flexibility

Poly(dimethylsiloxane) (PDMS) was grafted onto polyurethane (PU), and Epichlorohydrin and Bisphenol A were attached to the free ends of PDMS groups and used to link the grafted PDMS to thereby introduce flexible crosslinks between the PU chains. The flexible crosslinks enhanced the crosslink density and solution viscosity of PU but did not change the melting and crystallization behaviors of the soft segments of PU. In particular, the flexible PDMS crosslinks increased the maximum tensile stress by up to 300% and the maximum tensile strain up to 180%. The shape recovery capability at 10°C and the shape retention capability at −25°C were maintained above 90% with the flexible crosslinking. Grafted PDMS moderately improved the low-temperature flexibility of PU due to its flexibility at low temperature. The flexible crosslinks of grafted PDMS successfully improved the tensile strength, shape recovery, and low-temperature flexibility of the PU.

Engineering the shape memory parameters of graphene/polymer nanocomposites through atomistic simulations: On the effect of nanofiller surface treatment

This paper aims to comprehend the mechanisms underlying the shape memory behavior of polylactic acid infused with graphene functionalized by four groups of -OH, -CH3, -NH2, and tethered polymer layer. Applying molecular dynamics simulation, it is revealed that the graphene surface treatment enhances the shape fixity ratio of nanocomposites monotonically by increasing the physical cross-linking points within the polymer matrix. The improvement would be even more pronounced by increasing the coverage degree of small functional groups and grafting density of the covalently bonded polymer chains. Monitoring the key parameters illustrates that contrary to the OH groups, which improve the shape recovery value, the other functional groups degrade it by prohibiting the polymer chains mobility. Attempts to explore the governing mechanism demonstrate that shape fixity is improved when the difference between the potential energy variations in the loading and unloading stages increases. Interestingly, shape recovery is only under the influence of conformational entropy, and it is not affected by the potential energy. As such, we also probe variations of the radius of gyration during the recovery stage to address the role of different functionalization procedures on the reported shape recovery parameter.

Development of multi-angle fiber array for accurate measurement of flexion and rotation in human joints

Herein, we have proposed a method that uses a highly stretchable and conductive fiber-based multi-angle fiber array, which precisely measures human joint motion in various degrees of freedom (flexion and rotation) at the shoulders, knees, and wrists in real time. By embedding conductive carbon nanotubes (CNTs) within spandex fibers of high elasticity and shape recovery ratio, we monitored joint motion stably without degrading the fiber’s conductivity even during repeated stretching and contraction of different lengths. The strain occurring in a specific direction was monitored using mapping images generated due to the change in resistance that occurred when 12 CNT-embedded spandex fibers arranged in radial lines at intervals of 15° were stretched or contracted by an external force. The proposed high-precision joint-monitoring technology measures human motion accurately and is applicable for use in wearable healthcare devices that require precise measurements.

On PVC-PP composite matrix for 4D applications: Flowability, mechanical, thermal, and morphological characterizations

Thermoplastics such as; polyvinyl chloride (PVC) and polypropylene (PP) have applications in different sectors such as; automobile, aerospace, biomedical, textile etc. due to cost-effectiveness, biodegradability, high mouldability, easy availability and good mechanical properties. The shape memory performances of these thermoplastics are crucial for extending the four-dimensional (4D) printing applications. But hitherto little has been reported on flowability, mechanical, thermal, morphological and shape memory properties of PVC-PP composite. In this study, twin-screw compounding has been employed on PVC and PP thermoplastics (in single and blended form) to prepare feedstock filaments for fused filament fabrication (FFF). The investigations have been made for flowability (melt flow index (MFI), mechanical (tensile strength and elongation), thermal (melting point) morphological, Fourier transform infrared spectroscopy (FTIR) analysis, and shape memory effect on different feedstock filaments (prepared with neat PVC, 75%PVC-25%PP, 50%PVC-50%PP, 25%PVC-75%PP, and neat PP). The results have been supported by fracture analysis of photomicrographs obtained from scanning electron microscopy (SEM). The results of the study suggested that tensile strength was maximum for 50%PVC-50%PP (23.57 MPa) and minimum for neat PP (8.89 MPa). Further percentage shape recovery was observed maximum for neat PVC and minimum for neat PP.