Article

Evaluating poly (ether ether ketone) powder recyclability for selective laser sintering applications

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Abstract

Poly(ether ether ketone) (PEEK) is increasingly used in selective laser sintering (SLS) due to its superior mechanical and thermal properties and biocompatibility. It is well known that the properties of selective laser sintering (SLS) powder govern the processability and quality of the parts. The SLS printing process exposes the PEEK bed/feedstock to variable elevated temperatures (above 300°C) for a prolonged time. The effect of this thermal history on the part quality is unknown. This work evaluates the changes that occur in thermally treated PEEK powder through spectroscopic, morphological, and rheological characterizations. It was found that crystallinity increased marginally within the first two hours, but particle size and shape remained virtually unchanged. The thermal treatment also resulted in a significant increase in the melt viscosity of the PEEK powder, and its flowability slightly improved. Understanding these changes could help to reduce waste through recycling of some portion of PEEK powders used in SLS printing.

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... [89] However, one of the main issues that come after SLS printing is the lack of recyclability of the used powder bed, which leads to a large amount of wastage of resources. [90] Annealing up to 340 C for 12 h increased the viscosity and crystallinity of the powder particles. ...
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... Whereas characteristics of a given trademark, for instance, DuraForm PA (3D-systems), can vary markedly when measured in different laboratories, our samples demonstrate properties typical of quality powders. For instance, they possess the angle of repose <40 • [92] and the Hausner ratio not exceeding 1.25 [29,87]. The advantages of our approach are much milder conditions of powder production and the use of phase diagram, which makes it possible to effectively tailor the mean size and dispersity of powder particles. ...
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The properties of dilute solutions of poly(oxy-l,4-phenyleneoxy-l,4-phenylenecarbonyl-l,4-phenylene) (PEEK) in strong acids such as H2SO4 and HSO3Cl have been investigated by static and dynamic light scattering, absorption spectroscopy, and viscometry. Chemical modification of the original polymer has been found to occur when it is dissolved in some acids. This modification has implications with respect to both the process of dissolution itself and the solution properties observed.
Article
Poly(aryl-ether-ether-ketone) (PEEK) has been heated at 400°C in both nitrogen and air. The extent of thermal degradation has been monitored by a variety of techniques including: solution viscometry, UV-visible spectroscopy, 13C high-resolution cross-polarization/magic angle spinning nuclear magnetic resonance and Fourier transform infrared spectroscopy. The results indicate, that in a nonoxidative environment such as nitrogen, PEEK is relatively stable at 400°C for periods up to 6 h. Under oxidative conditions chain scission reactions occur and crosslinks are formed causing a reduction in the crystallizability of the material and discoloration of the polymer. The spectroscopic evidence suggests that the chain cleavage occurs adjacent to the carbonyl functional groups. Subsequent hydrogen abstraction from the aromatic ring then leads to crosslinking between adjacent aryl rings.
Article
An economic survey of composite manufacturing was carried out to help to identify suitable fibre/resin systems for recycling trials. Three separate recycling strategies were also adopted. The first of these was the re-use of in-process polyester/glass prepreg offcuts, which were quantified and then reprocessed using a simple pressing technique. Three different panel types were pressed and subjected to comparative physical and mechanical testing. Solvent recycling trials were carried out on carbon fibre/PEEK APC-2. Initially methylene chloride proved successful, so concentrated sulphuric acid was used. Polymer recovered using the acid was checked for purity against 380-P moulding compound. The final process investigated was recovery of aramid fibre (Twaron™) from an epoxy matrix by solvent swelling, the solvent system used being 50% DMSO and 50% Toluene at 105°C. The recovered fibre was tested against virgin fibre to ascertain what degradation of the properties resulted from the process.
Article
Fourier transform infrared (FT-IR) spectroscopy was used to study the reactions which occur upon thermal degradation of films of poly(etheretherketone), or PEEK. Samples were exposed to temperatures in the range 400–485°C in both air and nitrogen atmospheres, and spectra were measured in both transmission and attenuated total reflection (ATR). The thermal degradation produces new carbonyl species, and the rate of growth of their IR peaks was used to determine activation energies for the reactions which produce them. In an inert atmosphere, the degradation involves a pyrolytic-type mechanism which produces a new carbonyl species absorbing in the IR at 1711 cm−1, possibly a fluorenone-type structure. The activation energy for this process is 236 kJ mol−1. In an oxidizing atmosphere, the same species is produced but at a faster rate, and the apparent activation energy is 211 kJ mol−1. In addition there is a second mechanism which requires the participation of oxygen and produces a species absorbing at 1739 cm−1, possibly ester groups. The activation energy for this reaction is 116 kJ mol−1. Because of the time required for oxygen to diffuse into the polymer, oxidative degradation is more pronounced at the surface, especially at higher temperatures. Thus ATR gives a more reliable value of the activation energies than transmission measurements on the bulk film.
Article
The molecular weight distribution of poly(aryl ether ether ketone) (PEEK) has been measured as a function of the melt holding temperature and time in air and in an inert environment. A branching mechanism was observed to occur in the usual melt processing conditions, which was much stronger in air than in vacuum or nitrogen. This degradation mechanism is correlated to a volatile emission observed with thermogravimetric analysis. The influence of the degradation on the PEEK crystallization is discussed. A considerable decrease in crystallization rate is observed associated with the decreased molecular mobility due to the molecular weight increase. and a crystallinity decrease associated with the structural defects introduced along the chains by the branching process. The self-nucleation in PEEK has also been examined through optical microscopy. It was concluded that to get rid of the self-nucleation phenomenon, it is necessary to bring the polymer to temperatures where degradation is already present.
Article
Thermogravimetry has been used to study the isothermal decomposition of poly(aryl ether ether ketone) and poly(aryl ether ketone) and the kinetics of decomposition established from the evolved volatiles. Both products and measured activation energies were consistent with a chain scission process occurring at ether and carbonyl linkages. The volatile decomposition products were analysed by mass spectroscopy and were found to contain various oligomers together with phenol and dibenzofuran. The volatile products were richer in hydrogen than the parent polymers, at the expense of a carbon-like insoluble residue. The degradation products are accounted for in terms of random chain scission and transfer reactions.
Article
This article investigates the fabrication of functionally graded materials (FGMs) by selective laser sintering (SLS) of Nylon-11 composites filled with different volume fractions of glass beads (0–30%). The investigation involved a combination of experimental studies, theoretical modeling and numerical analysis. Optimal processing parameters for each composition were developed by design of experiments (DOE). These parameters were then compared with parameters predicted by numerical modeling. Specimens for tensile and compressive testing for each composition and for a 1D FGM composition were fabricated and tested. The experimentally measured tensile and compressive moduli were compared with moduli predicted by Halpin's theoretical model and were found to be in excellent agreement. The results showed that the tensile and compressive modulus increases while strain at break and strain at yield decreases as a function of glass bead volume fraction. A finite element model for the compressive properties of the 1D FGM specimen showed good agreement with experimentally measured values. Finally, to demonstrate the SLS-based FGM approach, two components exhibiting a one-dimensional functional gradient of particulate-filled polymer composites were fabricated.
Article
This is an updated and edited version of a paper first published in Geiger, M. and Otto, A. (Eds) (2001), “Laser assisted net shape engineering 3”, Proceedings of the LANE 2001 Conference, 28‐31 August 2001, Erlangen, Germany, Meisenbach Bamberg. Many of the research results presented here benefited from financial support of Belgian national fund IUAP P4/33 and Flemish Science Foundation project FWO G.0216.00. © Prof. Dr. Ir. Jean‐Pierre Kruth
Article
This is a journal article. It was published in the journal, Materials Science and Engineering: A [© Elsevier] and the definitive version is available at: http://www.sciencedirect.com/science/journal/09215093 There currently exists the requirement to improve reproducibility and mechanical properties of SLS Nylon parts for Rapid Manufacturing (RM). In order to achieve this, further fundamental research is needed and this paper addresses this need by investigating effects of potential sources of the lack of reproducibility (i.e. build procedure/parameters and powder blend) and reports effects in relation to crystal structure, microstructure, chemical structure (molecular weight) and mechanical properties. Different γ crystal forms were identified and related to the un-molten particle cores and the molten/crystallised regions of the microstructure. The melt point of the γ form varied depending on processing conditions. Observable differences were also present when comparing the microstructure of the parts. Molecular weight of parts was significantly higher than virgin powder but used powder (powder already held at elevated temperature) also showed an increase in molecular weight. This was related to improved elongation at break of parts built from the used powder, consistent with previous studies. Tensile strength showed some increase with parameters selected for improved strength but Young’s modulus values were broadly similar.
Article
Rapid prototyping techniques, originally developed for building components from computer aided designs in the motor industry, are now being applied in medicine to build models of human anatomy from high resolution multiplanar imaging data such a computed tomography (CT). The established technique of stereolithography and the more recent selective laser sintering (SLS), both build up an object layer by layer. Models have applications in surgical planning, for the design of customised implants and for training. Preliminary experience of using the SLS technique for medical applications is described, addressing questions regarding image processing, data transfer and manufacture. Pilot models, built from nylon, included two skills (a child with craniosynoslosis and an adult with hypertetorism) and a normal femur which was modelled for use in a bioengineering test of an artificial hip. The dimensions of the models were found to be in good agreement with the CT data from which they were built-for the child's skull the difference between the model and the CT data was less than 1.0 +/- 0.5 mm in each direction. Our experience showed that, with care, a combination of existing software packages may be used for data conversion. Ideally, image data of high spatial resolution should be used. The pilot models generated sufficient clinical interest for the technique to be pursued in the orthopaedic field.
Article
Rapid Prototyping (RP) technologies provide the ability to fabricate initial prototypes from various model materials. Stratasys Fused Deposition Modeling (FDM) is a typical RP process that can fabricate prototypes out of ABS plastic. To predict the mechanical behavior of FDM parts, it is critical to understand the material properties of the raw FDM process material, and the effect that FDM build parameters have on anisotropic material properties. This paper characterizes the properties of ABS parts fabricated by the FDM 1650. Using a Design of Experiment (DOE) approach, the process parameters of FDM, such as raster orientation, air gap, bead width, color, and model temperature were examined. Tensile strengths and compressive strengths of directionally fabricated specimens were measured and compared with injection molded FDM ABS P400 material. For the FDM parts made with a 0.003 inch overlap between roads, the typical tensile strength ranged between 65 and 72 percent of the strength of injection molded ABS P400. The compressive strength ranged from 80 to 90 percent of the injection molded FDM ABS. Several build rules for designing FDM parts were formulated based on experimental results. Electronic access The research register for this journal is available at http://www.emeraldinsight.com/researchregisters The current issue and full text archive of this journal is available at http://www.emeraldinsight.com/1355-2546.htm 1.
Selective laser sintering using nanocomposite materials
  • A Manthiram
  • H L Marcus
  • D L Bourell
2 - Engineering Thermoplastics
  • Melton
A study of thermal degradation of poly (aryl-ether-ether-ketone) using stepwise pyrolysis/gas chromatography/mass spectrometry
  • Tsai