May 15, 2020 by admin 0 Comments

Exfoliated graphene/thermoplastic elastomer nanocomposites with improved wear properties for 3D printing

Authors
Hyerin Jeon a,b,1, Youn Kim b,1, Woong-Ryeol Yu a, Jea UkLee b
Abstract
Although three-dimensional (3D) thermoplastic elastomer printing has been studied, the unsatisfactory mechanical properties of 3D-printed elastomers, especially their substandard wear characteristics, make it difficult to use them in industrial products or processes. In this study, thermoplastic elastomer nanocomposites with improved wear properties were fabricated using thermoplastic polyether elastomer (TPEE), with surface-modified carbon black (CB), or electrochemically exfoliated graphene through multiple extrusion processes. The surface-modified CB/TPEE composite showed about four times more wear resistance and 26% improvement in tensile strength as compared to bare TPEE resin. The graphene/TPEE composite with only 1 wt% graphene exhibited an elevenfold increase in wear resistance and 43% improvement in the tensile strength owing to the high dispersibility and lubricating effect of the two-dimensional graphene filler. Graphene/TPEE composites were extruded into filaments for 3D printing. Three-dimensional printed products made from the nanocomposites have much higher wear resistance than 3D products of bare TPEE resin, demonstrating that graphene and TPEE nanocomposites are well suited for manufacturing a wide variety of complex electronic and mechanical components with excellent wear characteristics.

January 5, 2020 by admin 0 Comments

Biobased thermoplastic elastomer with seamless 3D-Printability and superior mechanical properties empowered by in-situ polymerization in the presence of nanocellulose

Authors
Jun Mo Koo (a, b, 1), Jaeryeon Kang (a, 1), Sung-Ho Shin (a), Jonggeon Jegal (a), Hyun Gil Cha (a), Seunghwan Choy (c), Minna Hakkarainen (b), Jeyoung Park (a, d), Dongyeop X. Oh (a, d), Sung Yeon Hwang (a, d)
Abstract
A biobased and biocompatible thermoplastic elastomer (TPE) with superior 3D printability was demonstrated with great potential for customized manufacturing technologies and fabrication of biointegrated devices. The inherent structural and stereochemical disadvantages of biobased monomers, such as 2,5-furandicarboxylic acid, in comparison with today used petroleum based monomers like terephthalic acid generally lead to lower mechanical performance for the biobased replacement polymers. This is additionally enhanced by poor interfacial adhesion and fusion commonly encountered during customized manufacturing technologies like 3D printing. Herein, we demonstrate that in-situ polymerization in the presence of trace amounts of cellulose nanocrystals (CNCs) can homogeneously distribute the nanofiller leading to dramatically strengthened thermally 3D-printable bio-furan-based TPE. This TPE exhibited a tensile strength of 67 MPa which is 1.5–7-fold higher than the values reported for silicone and thermoplastic urethane, which are widely used in biomedical applications. In addition, the TPE had an impressive extensibility of 860% and negligible in vivo cytotoxicity; such properties have not been reported to date for bio-based or petrochemical TPEs. While a petrochemical 3D printed TPE counterpart retained only half of the tensile strength compared to the hot-pressed analogue, the 3D-printed biobased TPE in-situ modified with nanocellulose maintained 70–80% of its strength under the same experimental conditions. This is explained by inter-diffusion between interfaces facilitated by the nanocellulose and the furan rings. Using the ergonomic shape of a wrist as a 3D-printable design, we successfully manufactured a wearable thermal therapeutic device from the nanocellulose modified biobased TPE, giving promise for wide variety of future applications.

January 1, 2018 by admin 0 Comments

Design, fabrication and evaluation of a hybrid biomanufacturing system for tissue engineering

Authors
Fengyuan Liu
Abstract
Plasma-assisted Bio-extrusion System (PBS System) is an innovative hybrid bio-manufacturing system to produce complex multi-material and functionally graded scaffolds combining multiple pressure-assisted and screw-assisted printing heads and plasma jets. This approach, which represents a step forward regarding the current state of the art technology in the field of biomanufacturing, enables to design and fabricate more effective scaffolds matching the mechanical and surface characteristics of the surrounding tissue, enabling the incorporation of high number of cells uniformly distributed and the introduction of multiple cell types with positional specificity. The system requires complex control software to manipulate different materials, scaffold designs and processing parameters. This software, developed using MATLAB GUI, is detailed in this paper. It provides high freedom of design allowing the users to create single or multi-material constructs with uniform pore size or pores size gradients by changing the operation parameters, such as geometric parameters, lay-down pattern, filament distance, feed rate and layer thickness. Functionally graded scaffolds can also be designed considering different layer-by-layer coating/surface modification strategies using the multi-jet plasma system. Based on the user definition, G programming codes are generated enabling fully integration and synchronization with the hardware of the PBS system. Examples will be provided describing the design of single, multi-material and functionally graded scaffolds.

October 17, 2016 by admin 0 Comments

The effects of moisture and temperature on the mechanical properties of additive manufacturing components: fused deposition modeling

Authors
Eunseob Kim, Yong-Jun Shin, Sung-Hoon Ahn
Abstract
Purpose This paper aims to investigate the water absorption behaviors and mechanical properties, according to water absorption and temperature, of components fabricated by fused deposition modeling (FDM) and injection molding. The mechanical properties of FDM and injection molded parts were studied under several environmental conditions. Design/methodology/approach FDM components can be used as load-carrying elements under a range of moisture and temperature conditions. FDM parts show anisotropic mechanical properties according to build orientation. Components were fabricated from acrylonitrile-butadiene-styrene in three different orientations. The mechanical properties of parts fabricated by FDM were compared to injection molded components made from the same material. Water absorption tests were conducted in distilled water between 20 and 60°C to identify the maximum water absorption rate. Both moisture and temperature were considered as environmental variables in the tensile tests, which were conducted under various conditions to measure the effects on mechanical properties. Findings The water absorption behavior of FDM components obeyed Fickian diffusion theory, irrespective of the temperature. High temperatures accelerated the diffusion rate, although the maximum water absorption rate was not affected. The tensile strength of FDM parts under dry, room temperature conditions, was approximately 26-56 per cent that of injection molded parts, depending on build orientation. Increased temperature and water absorption had a more significant effect on FDM parts than injection molded components. The tensile strength was decreased by 67-71 per cent in hot, wet environments compared with dry, room temperature conditions. Originality/value The water absorption behavior of FDM components was investigated. The quantitative effects of temperature and moisture on tensile strength, modulus and strain were also measured. These results will contribute to the design of FDM parts for use under various environmental conditions.