Development of pure poly vinyl chloride (PVC) with excellent 3D printability and macro‐ and micro‐structural properties

Unmodified polyvinyl chloride (PVC) has low thermal stability and high hardness. Therefore, using plasticizers as well as thermal stabilizers is inevitable, while it causes serious environmental and health issues. In this work, for the first time, pure food-grade PVC with potential biomedical applications is processed and 3D printed. Samples are successfully 3D printed using different printing parameters, including velocity, raster angle, nozzle diameter, and layer thickness, and their mechanical properties are investigated in compression, bending, and tension modes. Scanning electron microscopy is also used to evaluate the bonding and microstructure of the printed layers. Among the mentioned printing parameters, raster angle and printing velocity influence the mechanical properties significantly, whereas the layer thickness and nozzle diameter has a little effect. Images from scanning electron microscopy also reveal that printing velocity greatly affects the final part's quality regarding defective voids and rasters’ bonding. The maximum tensile strength of 88.55 MPa is achieved, which implies the superiority of 3D-printed PVC mechanical properties compared to other commercial filaments. This study opens an avenue to additively manufacture PVC that is the second most-consumed polymer with cost-effective and high-strength features

4D printing of polyvinyl chloride (PVC): a detailed analysis of microstructure, programming, and shape memory performance

In this research, polyvinyl chloride (PVC) with excellent shape-memory effects is 4D printed via fused deposition modeling (FDM) technology. An experimental procedure for successful 3D printing of lab-made filament from PVC granules is introduced. Macro- and microstructural features of 3D printed PVC are investigated by means of wide-angle X-ray scattering (WAXS), differential scanning calorimetry (DSC), and dynamic mechanical thermal analysis (DMTA) techniques. A promising shape-memory feature of PVC is hypothesized from the presence of small close imperfect thermodynamically stable crystallites as physical crosslinks, which are further reinforced by mesomorphs and possibly molecular entanglement. A detailed analysis of shape fixity and shape recovery performance of 3D printed PVC is carried out considering three programming scenarios of cold (Tg −45 °C), warm (Tg −15 °C), and hot (Tg +15 °C) and two load holding times of 0 s, and 600 s under three-point bending and compression modes. Extensive insightful discussions are presented, and in conclusion, shape-memory effects are promising, ranging from 83.24% to 100%. Due to the absence of similar results in the specialized literature, this paper is likely to fill a gap in the state-of-the-art shape-memory materials library for 4D printing, and provide pertinent results that are instrumental in the 3D printing of shape-memory PVC-based structures

Effects of TPU on the mechanical properties, fracture toughness, morphology, and thermal analysis of 3D‐printed ABS‐TPU blends by FDM

In this paper, blends of ABS-TPU with two different weight percentages of TPU were prepared using fused deposition modeling technology. The effect of adding TPU on the fracture toughness of ABS and mechanical properties was comprehensively studied. Tensile, compression, fracture toughness, and shear tests were conducted on the 3D-printed samples. Thermal and microstructural analyses were performed using dynamic mechanical thermal analysis (DMTA), and scanning electron microscope (SEM). The DMTA results showed that adding TPU decreased the storage modulus and the glass transition temperature of ABS, as well as its peak intensity. The mechanical test results showed that adding TPU decreased the strength but increased the formability and elongation of the samples. Fracture tests showed that the addition of TPU decreased the maximum force needed for a crack to initiate. The force required for crack initiation decreased from 568.4 N for neat ABS to 335.3 N for ABS80 and 123.2 N for ABS60. The ABS60 blend exhibited the highest strength against crack growth, indicating that TPU can change the behavior of ABS from brittle to ductile. Shear test results and SEM images also showed good adhesion strength between the printed samples for all three specimens, indicating their good printability. Adding TPU resulted in a reduction in the size and number of voids and holes between the printed layers

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

A new strategy for achieving shape memory effects in 4D printed two-layer composite structures

In this study, a new strategy and design for achieving a shape memory effect (SME) and 4D printed two-layer composite structures is unveiled, thanks to fused deposition modeling (FDM) biomaterial printing of commercial filaments, which do not have an SME. We used ABS and PCL as two well-known thermoplastics, and TPU as elastomer filaments that were printed in a two-layer structure. The thermoplastic layer plays the role of constraint for the elastomeric layer. A rubber-to-glass transition of the thermoplastic layer acts as a switching phenomenon that provides the capability of stabilizing the temporary shape, as well as storing the deformation stress for the subsequent recovery of the permanent shape by phase changing the thermoplastic layer in the opposite direction. The results show that ABS–TPU had fixity and recovery ratios above 90%. The PCL–TPU composite structure also demonstrated complete recovery, but its fixity was 77.42%. The difference in the SME of the two composite structures is related to the transition for each thermoplastic and programming temperature. Additionally, in the early cycles, the shape-memory performance decreased, and in the fourth and fifth cycles, it almost stabilized. The scanning electron microscopy (SEM) photographs illustrated superior interfacial bonding and part integrity in the case of multi-material 3D printing

4D printing and annealing of PETG composites reinforced with short carbon fibers

In this study, for the first time, post-heat treatment was applied to improve the stress recovery of short carbon fiber reinforced PETG (SCFRPETG). PETG and SCFRPETG composite were printed under optimal conditions, and constrained and free shape memory cycles were applied under compression and three-point bending loadings to assess shape and stress recovery. The results of the free shape memory test for both vertical and horizontal patterns showed that PETG composite also has a higher shape memory effect (SME) compared to PETG. The SME was significantly improved by performing heat treatment. The stress recovery values for pure PETG, reinforced PETG before and after annealing are 2.48 MPa, 3.04 MPa and 3.18 MPa, respectively. It showed that the addition of 1.5% carbon fiber increases the stress recovery by 22%. The increasing trend reaches 28% by performing post-heat treatment. Additionally, altering the printing pattern affects the programming and stress recovery values. For the SCFRPETG composite samples before and after annealing, changing the printing pattern from horizontal to vertical, resulted in a 16% and 7% increase in recovery stress, respectively. SEM results confirm that the annealing process removes the layered structure, micro-holes caused by shrinkage and 4D printing mechanism. Using the controlled heat treatment method can be a practical solution to solve the problem of adhesion and reduce the anisotropy of FDM 3D printed layers

Plasma PCSK9 level affects passively LAMP-2 expression; an evidence of transcription network

Free cholesterol accumulation in lysosomes is related to highly glycosylated membrane-protein functions, endogenous cholesterol synthesis and, LDL influx. The LAMP-1 and LAMP-2 are two lysosome proteins involved in cholesterol transport. The study aim was to investigate the associations between LAMP-2 expression level, LAMP-2/LAMP-1 expression ratio, blood PCSK9 protein and LDL-C values. One hundred twenty six healthy subjects were selected during a medical interview. The biochemical parameters were measured using routine laboratory techniques. The plasma PCSK9 level was identified by ELISA method. The LAMP-1/LAMP-2 expression levels were estimated by Real time qPCR technique. The PCSK9 and LAMP-2 expression networks were designed with Cytoscape software and, were enriched using transcription factor databases. Linear correlations were observed between PCSK9 and LDL-C levels (r = 0.34; p = 0.002) and, TC/HDL-C ratio (r = 0.35; p = 0.001). The LAMP-2 expression level and LAMP-2/LAMP-1 expression ratio were inversely related to LDL-C values (p = 0.02). The transcription factors were compartmented on the merged network and were strictly controlled the PCSK9 expression. The results suggested that the decreased LDL influx due to the increase of plasma PCSK9 level attenuates the LAMP-2 gene expression level. Furthermore, the merged network supported our findings that the LAMP-2 expression is not in relation to transcription factors involved with PCSK9 expression. © 2016 Elsevier Inc

Influence of programming and recovery parameters on compressive behaviors of 4D printed bio‐compatible PVC‐PCL blends

This paper introduces a new class of bio-compatible shape memory polymers (SMPs) through blending PVC and PCL. The compressive shape-memory behaviors of 4D-printed SMP PVC with 5 and 10%wt of PCL are studied in detail. In this respect, a set of experiments are carried out to understand thermo-mechanical responses of PVC-PCL blends under various shape memory parameters like programming temperature, load holding time, applied strain and recovery temperature. DMTA and SEM imaging are also performed to provide thermal and morphological analyses. It is found that by raising the recovery temperature from 45 to 65°C, the shape recovery ratio increases from 5.63MPa to 7.92MPa when the PVC-PCL10 is programmed via the hot programming protocol. The highest level of shape fixity (100%) and the best performance of stress relaxation are achieved for hot programming sample, while the highest shape recovery ratio (100%) is obtained for cold programming. By applying the load holding time, the amount of shape fixity can reach from 88.14% to 100%. Results of this research are expected to provide an insightful understanding of the shape memory behaviors of PVC-PCL and be instrumental for 4D printing and programming of shape adaptive structures like shape-memory intervertebral cages as spinal support devices