4D Printing-Encapsulated Polycaprolactone–Thermoplastic Polyurethane with High Shape Memory Performances

There are a few shape memory polymers (SMPs) like polylactic acid (PLA) and polyurethane (PU) that are 4D printable, and other SMPs must be synthesized with a complicated chemical lab effort. Herein, considering dual-material extrusion printing and microscopic mechanism behind shape memory effect (SME), bilayer-encapsulated polycaprolactone (PCL)–thermoplastic polyurethane (TPU) shape memory composite structures are 4D printed for the first time. The SME performance is investigated by assessing fixity, shape recovery, stress recovery, and stress relaxation under bending and compression loading modes. PCL, TPU, and melting temperature of PCL play the role of switching phase, net point, and transition temperature, respectively. Due to the destruction and dripping of molten PCL in contact with water, PCL is encapsulated by TPU. Encapsulation successfully solves the challenge of bonding/interface between printed layers, and the results show that the SME performance of the encapsulated structures is higher than bilayer PCL–TPU one's. Experiments reveal that maximum stress recovery in 4D-printed composites remains constant over time. This is a great achievement compared to the previous extrusion-based SMP structures that have great weakness in stress relaxation due to weak and low crystalline fractions and the unraveling of molecular entanglements in semicrystalline and amorphous thermoplastic SMPs, respectively.     

Microstructure and Mechanical Properties of CP-Titanium Processed by ECAP Followed by Warm Caliber Rolling

In this study, microstructural evolution and mechanical properties of commercial purity titanium after a combined equal channel angular pressing (ECAP) and warm caliber rolling (WCR) was investigated. The ECAP process was applied to enhance the hardness and strength of the specimen by decreasing the grain size and producing UFG microstructure. WCR was applied to reduce cross-section and increase the ductility of the ECAPed specimens. Results show that WCR reduces the work-hardening rate by increasing grain size and also increases elongation and workability while it reduces the yield and ultimate tensile strength. It has been shown that the strength ratio (\({{\sigma_{UTS} } \mathord{\left/ {\vphantom {{\sigma_{UTS} } {\sigma_{y} }}} \right. \kern-0pt} {\sigma_{y} }}\)) and strain ratio (\({{\varepsilon_{UTS} } \mathord{\left/ {\vphantom {{\varepsilon_{UTS} } {\varepsilon_{t} }}} \right. \kern-0pt} {\varepsilon_{t} }}\)) of the processed samples are comparatively larger than all previously post processed ECAPed materials at lower temperatures.     

Toughening PVC with Biocompatible PCL Softeners for Supreme Mechanical Properties,Morphology, Shape Memory Effects,and FFF Printability

In this article, a first of its kind blend of polyvinyl chloride (PVC) and biocompatible polycaprolactone (PCL) is introduced by melt mixing and then 3D printed successfully via Fused Filament Fabrication (FFF). Experimental tests are carried out on PCL-PVC blends to assess thermo-mechanical behaviors, morphology, fracture toughness, shape-memory effects and printability. Macro and microscopic tests reveal that PVC-PCL compounds are miscible due to high molecular compatibility and strong interaction. This causes extraordinary mechanical properties specially for PVC-10 wt% PCL. In addition to the desired tensile strength (45 MPa), this material has a completely rubbery behavior at ambient temperature, and its total elongation is more than 81%. In addition, due to the high formability of PVC-PCL at ambient temperature, it has capability of being programed via different shape-memory protocols. Programming tests show that PVC-PCL blends have an excellent shape-memory effect and result in 100% shape recovery. SEM results prove a high improvement of PVC printability with the addition of 10 wt% PCL. Toughened PVC by PCL is herein added to the materials library of FFF 3D printers and expected to revolutionize applications of PVC compounds in the field of biomedical 3D and 4D printing due to its appropriate thermo-mechanical properties, supreme printability, and excellent biocompatibility.