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.
Highlights
Powder characterisation is an essential step for processing polymers by laser sintering (LS).Laser sintering is well suited process to manufacture a variety of polymeric materials including non-standard laser sintering materials
This result indicates that the average particle size of UHMWE is larger than that of the standard powders used in laser sintering
These powders have a good powder flow properties that are desirable for laser sintering [40]
Summary
Powder characterisation is an essential step for processing polymers by laser sintering (LS).Laser sintering is well suited process to manufacture a variety of polymeric materials including non-standard laser sintering materials (i.e., off-the-shelf powders). Powder characterisation is an essential step for processing polymers by laser sintering (LS). Powder characteristics and properties, such as particle size, shape and powder flow, can greatly influence the quality of the parts produced as well as the processing of the powder [1]. No single analytical method alone can be used to reliably characterise a powder Methods such as x-ray powder diffraction, scanning electron microscopy, density, thermal analysis, hot stage microscopy, and X-ray diffraction (XRD) analysis all contribute to define the powder characteristics that best suited for laser sintering. Particle size distribution and morphology influence the packing density of the powder, whereas the thermal behaviour and stability define the laser energy density required in laser sintering [2]. Understanding the thermal stability of ultra-high molecular weight polyethylene (UHMWPE) powder is essential for the simulation of laser sintering process
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