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Ultra High Molecular Weight Polyethylene (UHMWPE) is a semi-crystalline polymer that has remarkable properties of high mechanical properties, excellent wear resistance, low friction and chemical resistance, and it is found in many applications such sporting goods, medical artificial joints, bullet proof jackets and armours, ropes and fishing lines...
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... DSC curve for un-sintered UHMWPE powder is shown in Fig. 2. The melting temperature of the UHMWPE is around 141 • C and the peak for solidification is around 117 • C. This temperature was used to assist with the determination of the build temperature of the powder bed (i.e. processing window). UHMWPE processing window appears to be extremely narrow and could show a signif- icant issue for ...Citations
... The range of materials processed through polymeric SLS is currently limited to polyamide 12 (PA12) [23] and to a smaller extent to polyether ether ketone [24,25], thermoplastic polyurethane (TPU), other polyamides such as polyamide 6 (PA6) and polymers such as ultra high molecular weight polyethylene [26]. ...
The optimisation of selective laser sintering (SLS) of polymeric materials, based on analytical equations providing fast predictions, can broaden the SLS application area. However, the selection of SLS polymeric materials is currently rather limited, due to specific requirements regarding sufficient flowability and limited molecular degradation. The present work highlights that upgrading existing analytical equations, by incorporating a well-calculated overlay factor and correcting for pre-heating starting at ambient conditions, can accelerate SLS screening. Model validation is performed based on density, colorimetric, morphological and mechanical analysis of printed parts, focusing on the prediction of the laser power which corresponds to the onset of degradation, taking polyamide powder as a reference case. Furthermore, the optimised model is successfully applied for two other polymer powders, namely thermoplastic co-polyester and thermoplastic polyurethane powder, to highlight a better overall description of the SLS degradation mechanism.
... The laser wavelength is 10.6 µm, and the spot size is 0.2 mm. It is well known that laser energy density has a great impact on the manufacturing quality of LPBF-fabricated specimens, which can be defined by the following equation 53 : ...
SiC ceramic lattice structures (CLSs) via additive manufacturing (AM) have been recognized as potential candidates in engineering fields owing to their various merits. Compared with traditional SiC CLSs, SiC triply periodic minimal surface (TPMS) CLSs could possess more outstanding properties, making them more promising for wider applications. Since SiC CLSs are hard to be fabricated through stereolithography techniques because of inferior light performance, the laser powder bed fusion (LPBF) process via selective sintering is an effective method to prepare near‐net‐shaped SiC TPMS lattices. As the mechanical performances of lattice structures are the foundation for future practical applications, it is of great significance to optimize the preparation process, thus improving the mechanical properties of SiC TPMS structures. In this work, the optimal printing parameters of the LPBF and liquid silicon infiltration process for SiC ceramic TPMS CLSs with three different volume fractions were systematically illustrated and analyzed. The effects of the printing parameters and carbon densities on the fabrication accuracy, microstructure, and mechanical performance of SiC TPMS CLSs were defined. The mechanism of the reactive sintering process for the SiC TPMS lattice structure was revealed. The results reveal that Si/SiC TPMS CLSs with optimum preparation have superior manufacturing accuracy (most less than 6%), relatively high bulk densities (about 2.75 g/cm³), low residual Si content (6.01%), and excellent mechanical properties (5.67, 15.4, and 44.0 MPa for Si/SiC TPMS CLSs with 25%, 40%, and 55% volume fractions, respectively).
... The laser power is the rate of change of thermal energy that the laser applies on the powder as it scans; the scan spacing is the distance between two parallel laser scan lines; and the scan speed is the velocity at which the laser travels along the surface of [86], which describes the energy transferred from the laser to the powder. The laser energy density should be set by adjusting these three parameters to provide adequate heat to melt the materials [1], [6], [7], [45], [48], [52], [67], [ The ideal ED needed for each material is different and varies between different LS systems, although, there are some generalities that apply to all powders and systems [6]. ...
... Apart from the parameters related to the energy input, there are also other important factors that influence processing with respect to the properties of the final sintered parts and should be taken under consideration for increased efficiency. As such is the layer thickness, the laser spot size, the beam offset, the delay time, and the part build orientation and placement [1], [6], [7], [30], [45], [49], [52], [67], [79]. ...
... After that step, the laser scanned on the surface of the last layer spread to initiate sintering. For the tests, square parts of 20 x 20 x 2 mm were designed to be built flat (x-y orientation) at fixed places in the middle of the build area, to minimise anisotropy [6], [48], [52], [67], [132]. ...
Additive Manufacturing (AM) of medication has offered great potential to the pharmaceutical industry in recent years, specifically for its revolutionary potential for personalised medicine. The replacement of conventional drug manufacture and distribution could provide patients with customised drug dosages fabricated at the point of care to reduce cost and enhance therapy adherence. Laser Sintering is a powder-based AM technique with potential for use in pharmaceutical applications. It is a solvent-free process that does not require support structures compared to other AM processes, providing increased stability and productivity in comparison to other AM techniques such as extrusion. Laser Sintering relies on consolidation mechanisms achieving high mechanical properties, and further it offers unlimited design freedom and industrial scale opportunities. However, there are limitations that prevent rapid deployment of Laser Sintering in pharmaceutics mainly due to the narrow variety of applicable polymer based excipient materials, which results from the complex thermal processing conditions. Most materials do not make it through the development stages in Laser Sintering, which makes it necessary to understand the most important factors that influence processing and part properties to enable design and development of drug dosage forms by this technology. This PhD studied the potential of using Laser Sintering for the fabrication of oral solid dosage forms (tablets) using placebo formulations. To achieve this, characterisation and processing of several pharmaceutical grade polymers was performed to identify candidate materials. Primarily, Laser Sintering showed potential for processing pharmaceuticals, however all the investigated materials presented important incompatibilities that impacted their processability. Materials with high moisture content experienced dehydration, which led to degradation upon the application of the laser beam. Furthermore, increased moisture levels induced cohesiveness and prevented the deposition of uniform layers of powder. Processing materials consisting of large and irregular particles introduced porosity and shrinkage, while processing of fine particle grades generated high electrostatic forces causing agglomeration and limiting powder flow. However, among the tested materials, Eudragit L100-55, a methacrylic acid ethyl acrylate copolymer known for its use as a coating agent in drug dosage forms, although an amorphous polymer it exhibited acceptable sinter-ability due to its ideal particle morphology and distribution that resulted in high packing efficiency and part density. Eudragit L100-55 and Avicel 101, a microcrystalline cellulose grade pharmaceutical popularly used as a diluent, were used for the development of preliminary formulations for the preliminary assessment on Laser Sintering of oral solid dosage forms. Avicel 101 demonstrated poor sinter-ability due to its unfavourable thermal characteristics, which resisted particle fusion and experienced degradation. Processing of the two materials together was proved viable by direct sintering of Eudragit L100-55 as a matrix to bind together the solid particles of Avicel 101. However, the presence of unmolten Avicel 101 particles increased the number of voids and promoted structural porosity. The increased porosity enhanced fragility of the parts, which impacted the mechanical properties resulting in poor strength, friability and stiffness. The poor mechanical performance significantly reduced the tablet integrity, which was translated in poor pharmaceutical functionality, demonstrating rapid disintegration. To enhance the processability of the powders and enable the production of oral solid dosage forms with increased functionality, an alternative approach was taken to produce an optimal pharmaceutical material for Laser Sintering. Exploiting the pH-dependent solubility of Eudragit L100-55, polymer precipitation and evaporation methods were used in a simple cost-effective system to create a film coating on Avicel 101 particles. The methods proved suitable to produce a film on the surface of Avicel 101 particles and they were simple and easy to reproduce. The development of a coated cellulose-base material aimed at the production of parts with increased density and mechanical strength, compared to the powder blends. This coating approach could have wide implications for Laser Sintering providing a new route for materials development for Laser Sintering that can open the way for innovative opportunities in pharmaceutics and broader, enabling the selection of a greater list of materials for further adoption of Laser Sintering in a wider range of applications.
... SLS of PE is challenging, due to its narrow sintering window, which can impact the printing accuracy [134]. Without fine tuning the energy density, laser energy can broadly radiate into surrounding particles, leading to lateral growth and warping; in turn, filling voids [135] and reducing part porosity [136]. Additionally, in its native state, PE is white or semi-transparent, making it highly reflective to visible (445 nm) or near infrared (1064 nm) light. ...
The adoption of additive manufacturing (AM) techniques into the medical space has revolutionised tissue engineering. Depending upon the tissue type, specific AM approaches are capable of closely matching the physical and biological tissue attributes, to guide tissue regeneration. For hard tissue such as bone, powder bed fusion (PBF) techniques have significant potential, as they are capable of fabricating materials that can match the mechanical requirements necessary to maintain bone functionality and support regeneration. This review focuses on the PBF techniques that utilize laser sintering for creating scaffolds for bone tissue engineering (BTE) applications. Optimal scaffold requirements are explained, ranging from material biocompatibility and bioactivity, to generating specific architectures to recapitulate the porosity, interconnectivity, and mechanical properties of native human bone. The main objective of the review is to outline the most common materials processed using PBF in the context of BTE; initially outlining the most common polymers, including polyamide, polycaprolactone, polyethylene, and polyetheretherketone. Subsequent sections investigate the use of metals and ceramics in similar systems for BTE applications. The last section explores how composite materials can be used. Within each material section, the benefits and shortcomings are outlined, including their mechanical and biological performance, as well as associated printing parameters. The framework provided can be applied to the development of new, novel materials or laser-based approaches to ultimately generate bone tissue analogues or for guiding bone regeneration.
... chemical resistance, good toughness, high durability, low friction, excellent abrasion resistance, low moisture absorption and non-toxicity etc. [1][2][3]. It is also used for the development of armor and bullet proof jackets [4][5][6]. However, it has low flame resistance and relatively low thermal stability, therefore, it decomposes into olefins and paraffins at high temperatures [7][8][9]. ...
Thermal decomposition of UHMWPE (ultra-high molecular weight polyethylene) sheet is studied at 5 °C/min heating rate, utilizing TGA/DTA technique. The measurements are performed in the temperature region 50–500 °C, in the presence of nitrogen environment. The decomposition of UHMWPE shows four different stages. The present measurements are used to find various kinetic parameters like activation energy, pre- exponential and thermodynamic factors by adopting two different kinetic models (Flynn-Wall-Ozawa (FWO) and Coats and Redfern (CR)).
... Fabrics are constructed of strands that are aligned in two perpendicular directions: one is called the warp, and the other is called the fill (or weft) [1]. The fill yarns pass between the warp yarns in a predictable order, indicating that the fibres are woven together as shown in Figure 1 [2]. ...
Due to their qualities and advantages, such as light weight, high rigidity, and high performance, composite materials have been used in a wide variety of industries and sectors. For example, carbon fibres are used in the construction of aircraft, while ultrahigh-molecular-weight polyethylene (UHMWPE) is used in the fabrication of medical artificial joints. In this study, the blade dimensions were estimated using side profiles from a European patent specification and the mechanical properties of numerous layers of composite materials (UHMWPE, carbon, glass fibre, and Perlon) utilized in the fabrication of sports prosthesis were investigated experimentally, theoretically, and numerically, and the results were compared, as well as the theory of failure calculated. The influence of data entered into the ANSYS programme was also investigated in the case of isotropic or orthotropic materials. The findings indicate that longitudinal young modules are experimentally and theoretically equivalent. While the material ISO or Ortho is considered and its information is entered into the ANSYS programme for the same lamina, similar results are obtained under the same boundary condition, as was demonstrated when computing the theory of failure. Additionally, it was demonstrated in this research that layering woven carbon fibre on top of layers of UHMWPE woven fabrics had a greater effect than layering woven glass fibre when fabricating the sports prosthetic foot.
... Nevertheless, Caulfield et al. [6] and Goodridge et al. [7] suggested that high laser power values may result in excess heat, which will result in damaged or burnt powder, shear stresses between layers, and part distortion. Khalil et al. [8] have also studied the influence of energy density in the range from 0.016 J.mm −2 to 0.032 J.mm −2 on flexural properties of ultra-high molecular weight polyethylene (UHMWPE). e elastic modulus and flexural stress increase with an increase in laser energy density. ...
A statistical analysis of the response of the parameters has been led by a design of experiments to extract the most influential parameters in the selective laser sintering process. The parametric study was carried out by varying five parameters on the SLS machine and by looking at their influence on five groups of responses relating to the physical, mechanical, and thermal properties as well as to the printing duration. The mathematical models of the response surfaces were established by linking the responses to factors and their interactions. The model of regression uses not only the interaction between regressors but also nonlinear logical functions. These statistical models were used to define an optimal set of parameters. The geometry and density of specimens made of polyamide 12 confirm that increasing the distance between successive laser beam passes allows a significant manufacturing time reduction. The mechanical properties depend mostly on laser power and scan count. We conclude that a low laser power applied twice can improve the properties of the printed part. By optimizing the laser parameters, the targeted mechanical properties are obtained with over 33% of production time savings.
... The most commonly used materials are polyamide 11 (PA11) (e.g., Duraform EX natural, 3D-Systems), polyamide 12 (PA12; e.g., PA2200, EOS GmbH), and a few thermoplastic elastomers [17,18]. Some studies have been performed in order to develop new materials suitable for SLS technology, such as ultrahigh molecular weight polyethylene (UHMWPE), polypropylene (PP), and polystyrene (PS) [12,19]. However, the demand for very specific material properties for the development and optimization of new polymeric materials limits the number of available materials for SLS. ...
... With Equation (19), the values of the energy for degradation (E deg ), energy melt ratio for degradation (EMR D ), and laser power for degradation (P D ) for the polyester material were recalculated (see Table 5). ...
... When comparing the data from Table 4 with those in Table 5, one can observe that the application of Equation (19) resulted in lower values for E deg , EMR D , and P D , as expected. ...
Additive manufacturing (AM) of polymeric materials offers many benefits, from rapid prototyping to the production of end-use material parts. Powder bed fusion (PBF), more specifically selective laser sintering (SLS), is a very promising AM technology. However, up until now, most SLS research has been directed toward polyamide powders. In addition, only basic models have been put forward that are less directed to the identification of the most suited operating conditions in a sustainable production context. In the present combined experimental and theoretical study, the impacts of several SLS processing parameters (e.g., laser power, part bed temperature, and layer thickness) are investigated for a thermoplastic elastomer polyester by means of colorimetric, morphological, physical, and mechanical analysis of the printed parts. It is shown that an optimal SLS processing window exists in which the printed polyester material presents a higher density and better mechanical properties as well as a low yellowing index, specifically upon using a laser power of 17–20 W. It is further highlighted that the current models are not accurate enough at predicting the laser power at which thermal degradation occurs. Updated and more fundamental equations are therefore proposed, and guidelines are formulated to better assess the laser power for degradation and the maximal temperature achieved during sintering. This is performed by employing the reflection and absorbance of the laser light and taking into account the particle size distribution of the powder material.
... It possesses high resistance against impact, fatigue, chemical corrosion and abrasion, which stemmed from effective load transfer to its long linear backbone. This polymer also has a remarkable self-lubricating, low friction coefficient and good biocompatibility [2][3][4] that enable its application in various fields including aerospace and industrial machineries (i.e., pipes, panels, bars, gears), microelectronics and joint replacement or also known as arthroplasty (i.e., hip liner, tibial inserts) [5][6][7]. However, relatively low Young's modulus and surface hardness of UHMWPE could limit the sustainability of this polymer against wear as a result of contact and slip with harder counterpart such as metal under repeated motion [8]. ...
The major hurdle in melt-processing of ultra-high molecular weight polyethylene (UHMWPE) nanocomposite lies on the high melt viscosity of the UHMWPE, which may contribute to poor dispersion and distribution of the nanofiller. In this study, UHMWPE/cellulose nanofiber (UHMWPE/CNF) bionanocomposites were prepared by two different blending methods: (i) melt blending at 150 °C in a triple screw kneading extruder, and (ii) non-melt blending by ethanol mixing at room temperature. Results showed that melt-processing of UHMWPE without CNF (MB-UHMWPE/0) exhibited an increment in yield strength and Young’s modulus by 15% and 25%, respectively, compared to the Neat-UHMWPE. Tensile strength was however reduced by almost half. Ethanol mixed sample without CNF (EM-UHMWPE/0) on the other hand showed slight decrement in all mechanical properties tested. At 0.5% CNF inclusion, the mechanical properties of melt-blended bionanocomposites (MB-UHMWPE/0.5) were improved as compared to Neat-UHMWPE. It was also found that the yield strength, elongation at break, Young’s modulus, toughness and crystallinity of MB-UHMWPE/0.5 were higher by 28%, 61%, 47%, 45% and 11%, respectively, as compared to the ethanol mixing sample (EM-UHMWPE/0.5). Despite the reduction in tensile strength of MB-UHMWPE/0.5, the value i.e., 28.4 ± 1.0 MPa surpassed the minimum requirement of standard specification for fabricated UHMWPE in surgical implant application. Overall, melt-blending processing is more suitable for the preparation of UHMWPE/CNF bionanocomposites as exhibited by their characteristics presented herein. A better mechanical interlocking between UHMWPE and CNF at high temperature mixing with kneading was evident through FE-SEM observation, explains the higher mechanical properties of MB-UHMWPE/0.5 as compared to EM-UHMWPE/0.5.
... The investigation of processing conditions on parts obtained from SLS has been the object of extensive experimental studies [48][49][50][51][52][53][54][55][56][57][58][59][60][61][62][63][64]. Part density is unanimously recognised as the principal variable affecting the mechanical behaviour of laser-sintered components. ...
... defined as the ratio between the laser beam diameter and the scan spacing OL ¼ D b =s, has been shown to play a fundamental role on the mechanical properties of the printed components and was recently included in the definition of the surface energy density [58]. In general, all the experimental studies confirm a positive correlation of E b with mechanical properties such as Young's modulus, yield stress, ultimate tensile strength and elongation at break [48][49][50][51][52][53][54][55][56][57][58][59][60] (Fig. 3). The motivation is imputed to the increased density of parts processed at high energy densities: by contrast, at lower energies the sintering process is incomplete and parts usually show a porous structure with interconnected voids [48]. ...
Additive manufacturing (AM) is a broad definition of various techniques to produce layer-by-layer objects made of different materials. In this paper, a comprehensive review of laser-based technologies for polymers, including powder bed fusion processes [e.g. selective laser sintering (SLS)] and vat photopolymerisation [e.g. stereolithography (SLA)], is presented, where both the techniques employ a laser source to either melt or cure a raw polymeric material. The aim of the review is twofold: (1) to present the principal theoretical models adopted in the literature to simulate the complex physical phenomena involved in the transformation of the raw material into AM objects and (2) to discuss the influence of process parameters on the physical final properties of the printed objects and in turn on their mechanical performance. The models being presented simulate: the thermal problem along with the thermally activated bonding through sintering of the polymeric powder in SLS; the binding induced by the curing mechanisms of light-induced polymerisation of the liquid material in SLA. Key physical variables in AM objects, such as porosity and degree of cure in SLS and SLA respectively, are discussed in relation to the manufacturing process parameters, as well as to the mechanical resistance and deformability of the objects themselves.
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