Shape-memory polymers (SMPs) and their composites (SMPCs), as a kind of smart materials, can respond to particular external stimulus and recover the original shape. They present outstanding features encompassing shape-memory effect, deformability, biocompatibility, variable stiffness, lightweight, and so on. They have attracted considerable research interest in recent years. Several stimulation methods to actuate the deformation of SMPs and SMPCs, of which the thermal stimulation is the common one, and many types of reinforcements have been developed over the past few years. It is revealed that the SMPC thermal and mechanical properties can be improved by introducing a number of reinforcements. Therefore, to well investigate the SMPC characteristics upon exposure to a specific external stimulus, a deep knowledge and understanding of the potential reinforcements as well as the available stimulation methods are crucial. In this review, reinforcements such as fibers, ceramics, and nanocarbons are first concisely presented. Next, numerous novel stimulation methods used to trigger the memory effect of the SMPCs are introduced, where the mechanisms of electrical, magnetic, thermal, light, and solution stimulations are briefly discussed. Finally, considering the increase of the number of interesting reinforcements as well as the efficient stimulation methods, SMPCs are expected to have great potential applications in different fields.
In the recent few years, fused filament fabrication technique have seen extensively used to produce complex-geometry objects. However, the relatively restricted range of 3D printable biocomposites decelerated its adoption in the biomedical sector as a conventional manufacturing technique. In this method, the introduction of biofillers with unique properties to produce high performance composites as printing feedstocks are increasingly recommended. The interest in using eco-friendly fillers from waste as reinforcing agents for producing lightweight and low-cost poly(lactic acid) (PLA) composites is recently increased. In this work, a series of PLA biocomposites filled with calcined seashell (CSh) particles have been prepared by melt mixing technique using a twin-screw extruder, and characterized by different morphological, thermal, and mechanical methods. The visco-elastic parameters have been determined for these biocomposites to optimize their processing conditions. The morphological analysis revealed a homogenous dispersion of CSh fillers within the biopolymeric matrix, which was responsible for the enhancement of the various mechanical properties. Where, by adding 10 wt% of treated CSh, the tensile modulus and strength were significantly increased from 183.8 ± 4.7 MPa and 29.81 ± 1.8 MPa to 241.9 ± 63 MPa and 49.06 ± 8.87 MPa, respectively, compared to the virgin PLA. In addition, respected to PLA matrix, the compressive moduli of the printed specimens of PLA/5CSh and PLA/10CSh biocomposite filaments exhibited improvements of 5% and 14%, respectively. Moreover, the thermal analysis showed a marked improvement in the thermal stability of the elaborated biocomposites, where the degradation temperature (Td50) have been upgraded by 4 C for the biocomposite containing 10 wt% of CSh biofiller. These outstanding properties of PLA/CSh composites make them very suitable for 3D printing applications in the biomedical field.
Nanocomposites of polypyrrole/reduced graphene oxide (PPy/rGO) and polypyrrole/ functionalized reduced graphene oxide with aryl 4-carboxybenzene diazonium salt (PPy/rGO-aryl-COOH) were prepared through covalent bonding by simple one-step chemical oxidative synthesis. The as-prepared nanocomposites were deposited on BOPET substrate by spin coating to test their chemiresistive sensitivity properties on a homemade modular for online detection of (NO 2 ) vapors at ambient temperature. Results showed that PPy/rGO-aryl-COOH forms a homogeneous nanocomposite within the size of 80 nanometers and improvement of the crystalline ordering. The more enhanced NO 2 sensing properties have been shown by PPy/rGO-aryl-COOH in terms of higher sensitivity (1.01%/ppm), the faster response time (129 s), and the detection limit of (2ppm). Reproducibility features were also investigated. Moreover, humidity rates and temperature effects were also tested. Finally, impedance spectroscopy is conducted in the fresh air and in the presence of gas. These results highlight the paramount role of functionalization of reduced graphene oxide (rGO-aryl-COOH).
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.