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      Characterisation of UHMWPE Polymer Powder for Laser Sintering

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          Abstract

          Ultra-high molecular weight polyethylene (UHMWPE) is a thermoplastic semicrystalline polymer that has outstanding mechanical properties, low friction coefficient, excellent wear resistance, and is highly resistant to corrosive chemicals. UHMWPE is found in many applications including artificial joints and filtration. However, UHMWPE parts cannot be produced easily by traditional techniques, such as injection moulding and extrusion because of its very high melt viscosity owing to the extremely long polymer chains. Few attempts were made to process UHMWPE by additive manufacturing, particularly laser sintering. This is due to the lack of understanding of the powder properties of UHMWPE. Therefore, the aim of the powder characterisation process in this study is to gain a better understanding of the material requirements and provide a detailed insight on whether UHMWPE is a suitable material for laser sintering. The characterisation process includes powder morphological and flow characteristics, thermal behaviour and stability, and crystallinity of UHMWPE. The study reveals that the sintering behaviour of polymers is controlled by the morphology of the particles in addition to the viscous flow of UHMWPE. There are still difficulties of processing UHMWPE due to highly agglomerated structure of smaller particles with the presence of fibrils in the UHMWPE particles.

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          A comparison of micro CT with other techniques used in the characterization of scaffolds.

          The structure and architecture of scaffolds are crucial factors in scaffold-based tissue engineering as they affect the functionality of the tissue engineered constructs and the eventual application in health care. Therefore, effective scaffold assessment techniques are required right at the initial stages of research and development so as to select or design scaffolds with suitable properties. Various techniques have been developed in evaluating these important features and the outcome of the assessment is the eventual improvement on the subsequent design of the scaffold. An effective evaluation approach should be fast, accurate and non-destructive, while providing a comprehensive overview of the various morphological and architectural characteristics. Current assessment techniques would include theoretical calculation, scanning electron microscopy (SEM), mercury and flow porosimetry, gas pycnometry, gas adsorption and micro computed tomography (CT). Micro CT is a more recent method of examining the characteristics of scaffolds and this review aims to highlight this current approach while comparing it with other techniques.
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            Preparation of a Carbon-Based Solid Acid Catalyst by Sulfonating Activated Carbon in a Chemical Reduction Process

            Sulfonated (SO3H-bearing) activated carbon (AC-SO3H) was synthesized by an aryl diazonium salt reduction process. The obtained material had a SO3H density of 0.64 mmol·g−1 and a specific surface area of 602 m2·g−1. The catalytic properties of AC-SO3H were compared with that of two commercial solid acid catalysts, Nafion NR50 and Amberlyst-15. In a 10-h esterification reaction of acetic acid with ethanol, the acid conversion with AC-SO3H (78%) was lower than that of Amberlyst-15 (86%), which could be attributed to the fact that the SO3H density of the sulfonated carbon was lower than that of Amberlyst-15 (4.60 mmol·g−1). However, AC-SO3H exhibited comparable and even much higher catalytic activities than the commercial catalysts in the esterification of aliphatic acids with longer carbon chains such as hexanoic acid and decanoic acid, which may be due to the large specific surface area and mesoporous structures of the activated carbon. The disadvantage of AC-SO3H is the leaching of SO3H group during the reactions.
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              The use of bulk density measurements as flowability indicators

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                Author and article information

                Journal
                Materials (Basel)
                Materials (Basel)
                materials
                Materials
                MDPI
                1996-1944
                25 October 2019
                November 2019
                : 12
                : 21
                : 3496
                Affiliations
                [1 ]Department of Mechanical Engineering, University of Sheffield, Sheffield S3 7HQ, UK
                [2 ]Xaar 3D Ltd, 5-6 William Lee Buildings, Science Park, Nottingham NG7 2RQ, UK
                [3 ]Unilever plc, R & D Port Sunlight Laboratory, Wirral CH63 3JW, UK
                Author notes
                [* ]Correspondence: y.khalil@ 123456leeds.ac.uk
                Author information
                https://orcid.org/0000-0002-1813-6120
                https://orcid.org/0000-0002-1675-5219
                Article
                materials-12-03496
                10.3390/ma12213496
                6862515
                31731427
                ba1ba9d8-ea2a-401b-8353-ee58aebbbb86
                © 2019 by the authors.

                Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license ( http://creativecommons.org/licenses/by/4.0/).

                History
                : 30 September 2019
                : 21 October 2019
                Categories
                Article

                uhmwpe,laser sintering,powder flow,hot stage,crystallinity
                uhmwpe, laser sintering, powder flow, hot stage, crystallinity

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