Now showing 1 - 7 of 7
  • Publication
    Evaluation of the protective performance of hydrophobic coatings applied on carbon-fibre epoxy composites
    Carbon-fibre epoxy composites are widely used for high performance structural applications, where they are often exposed to harsh environments. The result of moisture ingress has been extensively studied, causing significant deterioration in the mechanical properties of these composites. This study evaluates the performance of five commercial hydrophobic coatings as protective layers, to inhibit moisture ingress into the composite. The coatings evaluated were: NeverWet, HydroBead, SHC, Aculon and LiquidGlass. These coatings were characterised and compared in terms of hydrophobicity, surface energy, roughness and chemical composition. This study also evaluated two atmospheric plasma pre-treatments as a means of enhancing the adhesion performance of these coatings. The pre-treatments involved the use of an air plasma for the activation of the epoxy, as well as the plasma deposition of a nanometre thick SiOx interlayer coating. The durability and protective performance of the coatings, with and without the pre-treatments were then compared using an abrasion test as well as a water immersion study. The use of both plasma pre-treatments was found to enhance the adhesion and the abrasion performance of four out of the five coatings. Of the coatings and pre-treatments investigated, the LiquidGlass in conjunction with an SiOx coating interlayer was found to exhibit the highest abrasion resistance. This was followed by the composite which was plasma activated prior to the application of the Aculon coating. Only minor differences were observed when comparing the total moisture ingress (M%) of the epoxy, coated with the different hydrophobic layers. The composite coated with the Aculon and SiOx interlayer exhibited the least amount of moisture ingress, at 0.90 %, compared to 1.08 % of the uncoated specimen. The shear strength of epoxy composite, coated with the LiquidGlass, NeverWet and the activated Aculon combination, were within the range of the uncoated specimens, therefore the moisture ingress was reversible upon heating and no permanent damage to the epoxy-fibre interface was observed. It is concluded that, of the five coatings investigated, both the Aculon coating and LiquidGlass in combination with an SiOx interlayer coating, exhibit the greatest potential as protective layers for carbon fibre epoxy composites.
      234Scopus© Citations 5
  • Publication
    Low‐pressure additive manufacturing of continuous fiber‐reinforced polymer composites
    Continuous fibre reinforced polymer composites have found a wide range of applications in the automotive and aerospace industry, due to their lightweight properties. Recently the use of additive manufacturing (AM) has been developed for the fabrication of these composites. This study investigates the use of both atmospheric and for the first time, low-pressure (1 Pa) processing conditions, for the AM of continuous carbon, glass and Kevlar fibre reinforced nylon composites. DSC was used to compare the thermal properties of the three types of fibre reinforced filament, prior to printing. It was found that the melting peak was dependent on filament type, which can be related to the polymer processing conditions used during their fabrication. Based on computed tomography measurements, it was found that the use of low-pressure printing conditions yielded a reduction in porosity for the carbon, glass and Kevlar printed composites of 5.7, 1.0 and 1.7 % respectively. The mechanical properties of the composites were compared, using a short beam shear test, which assisted in the measurement of interlaminar properties. An increase in interlaminar shear strength of 33, 22 and 12% was obtained for the carbon, glass and Kevlar fibre reinforced polymer composites respectively, when printed under low-pressure, compared with that obtained at atmospheric pressure.
      330Scopus© Citations 39
  • Publication
    3D printing of PEEK reactors for flow chemistry and continuous chemical processing
    Chemically resistant parts for flow chemistry, with integrated mixing elements have been produced using the 3D printing process of fused filament fabrication, from poly(etheretherketone). Poly(etheretherketone) has greater chemical resistance than common fused filament fabrication materials such as acrylonitrile butadiene styrene, polypropylene, or even high-performance plastics like poly(etherimide), in addition to having superior thermal resistance and excellent mechanical strength. Printed reactors were demonstrated to be suitable for liquid–liquid extraction and flow chemistry and to be capable of withstanding pressures of at least 30 bar allowing superheated solvents to be used. Burst tests in simple geometries of 20 minute duration have indicated that increased operating pressures of up to 60 bar could be accommodated in future reactor designs. The ability to use fused filament fabrication for these reactors allows highly customisable, cost effective flow reactors and equipment to be fabricated on relatively inexpensive benchtop scale printers. X-ray microcomputed tomography was utilised to non-invasively image and verify the internal structure of the prints to ensure fidelity in reactor fabrication. This non-invasive method of equipment validation shows potential in helping to demonstrate regulatory compliance for bespoke additively manufactured components, for example in continuous pharmaceutical manufacturing where the methods and printer used in this work should be sufficient to produce, (continuous) manufacturing scale equipment.
      370Scopus© Citations 29
  • Publication
    Comparison between the properties of polyamide 12 and glass bead filled polyamide 12 using the multi jet fusion printing process
    This study investigates the material and mechanical properties of both polyamide 12 (PA12) and reinforced glass bead PA12 composites, fabricated using a production scale additive manufacturing (AM) process. The printing studies were carried out using the production scale, Multi Jet Fusion powder bed fusion process. The study demonstrated that the chemical functionality and the thermal properties of the printed PA 12 parts and the glass bead composite, were similar. Almost identical infrared spectra were obtained demonstrating the same chemical functionality. Based on DSC measurements, the melting temperature was 184°C and 186°C and the associated cooling cycle temperature was 150°C and 146°C for the composite and the PA12 respectively. The percentage crystallinity of the glass bead composite was 24 %, compared with the 31% obtained for the PA12 only parts. Based on mechanical tests, the addition of glass beads increased the tensile and flexural modulus by 85% and 36% and lowered the tensile and flexural strength by 39% and 15% respectively. The effect of print orientation during the MJF process was evaluated based on porosity and mechanical performance. Using X-ray micro computed tomography, it was demonstrated that the porosity of the PA12 and composite parts were less than 1%. Polymer and composite parts printed in the ZYX orientation were found to exhibit both the lowest porosity and highest mechanical strengths
      929Scopus© Citations 49
  • Publication
    Evaluation of the mechanical performance of polymer parts fabricated using a production scale multi jet fusion printing process
    Additive manufacturing (AM) is rapidly becoming one of the most popular manufacturing techniques for short run part production and rapid prototyping. AM encompasses a range of technologies, including powder bed fusion (PBF) process. The purpose of this paper is to evaluate and benchmark the mechanical performance of polyamide 12 (PA12) parts, fabricated using a production scale powder bed fusion printing process (HP Multi Jet Fusion printing process). This system has a build volume is 380 × 254 × 350 mm. The printed polymer parts were examined to determine their hydrophobicity, morphology, porosity and roughness. Chemical and thermal properties of the PA12 parts were also evaluated using attenuated total reflection infrared spectroscopy (ATR FT-IR), x-ray photoelectron spectroscopy (XPS) and differential scanning calorimetry (DSC). The study highlights the influence of build orientation on the tensile (ISO 527-1:2012) and flexural (ISO 178:2010) properties. In terms of tensile strength, the parts exhibited isotropic behaviour with a maximum tensile strength of 49 MPa. In terms of flexural testing, the build orientations had a significant effect on the strength of the printed part. The Z orientation exhibited a 40% higher flexural strength, when compared to that of the X orientation. The maximum flexural strength observed was 70 MPa. The results of this rapid, production scale AM study are compared with previous studies that detail the mechanical performance of PA12, fabricated using PBF processes, such as selective laser sintering.
      541Scopus© Citations 116
  • Publication
    Evaluation of the influence of low pressure additive manufacturing processing conditions on printed polymer parts
    The properties of 3-D printed polymeric parts depend significantly on the processing conditions under which they are fabricated. This study aims to determine how the use of low-pressure additive manufacturing (AM) processing conditions, influences the mechanical performance of printed polymeric parts. This polymer material extrusion (PME) study was carried out using an open-source desktop printer, under both low pressure (1 Pa) and at atmospheric pressure. The printing study was carried out using acrylonitrile butadiene styrene (ABS), polylactic acid (PLA) and a nylon co-polymer (PA6). The resultant polymer parts were compared based on their printed mass, density, volume, porosity, surface energy, ATR-IR analysis and thermal properties (DSC). As expected only minor differences in chemical functionality were observed between parts printed under the two processing pressures. Under low-pressure printing conditions, the polymer parts exhibited some physical changes, when compared to those, printed under atmospheric conditions, such as an increase in density and a decrease in porosity. This was observed in particular with the low-pressure printing of PA6 parts, which exhibited an increase in density from 1.095 to 1.113 g/cm3 and a decrease in porosity by 8%. Comparing low-pressure printed type V dog bones (ASTM D-638), with those printed at atmospheric pressure, it was observed that the ABS, PLA and PA6 exhibited an increase in Ultimate Tensile Strength of 9%, 13% and 42% respectively. It is proposed that the superior mechanical properties obtained for polymers printed under low pressure conditions, may be due to a combination of two factors. These are the reduction in porosity of the printed part and the reduction in heat loss at the printed polymer surface, yielding enhanced bonding between the polymer layers. In a further printing study carried out at atmospheric pressure in a nitrogen atmosphere, it was also demonstrated that any oxidation of the polymer layers during printing, did not significantly influence the mechanical properties of the resultant printed parts.
      246Scopus© Citations 21
  • Publication
    Concentric Annular Liquid-Liquid Phase Separation for Flow Chemistry and Continuous Processing
    A low-cost, modular, robust, and easily customisable continuous liquid-liquid phase separator has been developed that uses a tubular membrane and annular channels to allow high fluidic throughputs while maintaining rapid, surface wetting dominated, phase separation. The system is constructed from standard fluidic tube fittings and allows leak tight connections to be made without the need for adhesives, or O-rings. The units tested in this work have been shown to operate at flow rates of 0.1 – 300 mL/min, with equivalent residence times from 80 to 4 seconds, demonstrating the simplicity of scale-up with these units. Further scale-up to litre per minute scales of operation for single units and tens of litres/minute through limited numbering up should allow these low cost concentric annular tubular membrane separators to be used at continuous production scales for pharmaceutical applications for many solvent systems. In principle this approach may be sufficiently scalable to be utilized in-line, in batch pharmaceutical manufacturing also, through further scale-up and numbering up of units. Several solvent systems with varying interfacial tensions have been investigated, and the critical process parameters affecting successful separation have been identified. An additively manufactured diaphragm based back pressure regulator was also developed and printed in PEEK, allowing highly accurate, adjustable, and chemically compatible pressure control to be accessed at low cost.
      157Scopus© Citations 2