A comparative study on the 3D printing process of semi-crystalline and amorphous polymers using simulation

Polymers have been widely used in the field of fused deposition modelling (FDM). The part integrity of the final printed part is affected by parameters such as processing conditions and the material properties of the polymer. Build-up of residual stresses are the main cause of shrinkage and warpage (i.e., part distortion) in the FDM parts. Among the thermoplastic polymers, semi-crystalline polymers are more prone to part distortion due to crystallisation. Therefore, it is important to understand and predict part distortion in FDM of polymers to achieve good quality prints with desirable mechanical properties. Several studies have investigated the resulting part distortion in FDM parts through empirical, analytical, and numerical approaches. In most cases, the simulation results are not quantitatively validated, mainly because the temperature dependent properties of the polymers and the crystallinity of semi-crystalline polymers are often overlooked. In this study, the thermal-mechanical properties of the polymer of study such as specific heat capacity, thermal conductivity and density and the crystallisation kinetics are invoked as a function of temperature. Furthermore, an amorphous polymer was also simulated with consideration of its respective material properties. Both the semicrystalline and the amorphous polymer models were simulated under various layer thickness (0.1 and 0.5mm), in order to investigate the effect of layer thickness on the induced thermal stress and resulting warpage. Based on the simulation results, for 0.1mm layer thickness, the amorphous polymer model exhibited a warpage drop of 77%. And for 0.5mm, the warpage noted was found to decrease by 63%, on comparison with the warpage noted from semi-crystalline polymer model. These warpage values from the simulated models were then measured against the 3D scan results of the printed samples for quantitative validation. An excellent agreement was observed between the experimental and the simulated samples.</div

Additive Manufacturing and Injection Moulding of High-Performance IF-WS 2 /PEEK Nanocomposites: A Comparative Study

In this study, PEEK nanocomposites with 0, 0.5, 1, and 2wt% IF-WS2 were manufactured by injection moulding and Fused Deposition Modelling (FDM). To compare the impact of the two processing methods and the incorporated nanoparticles on the morphology, crystallization and final mechanical properties of the nanocomposites, SEM, DSC and tensile testing were performed. In general, a good distribution of nanoparticles was observed in PEEK, although larger agglomerates were visible at 2 wt% IF-WS2. The crystallization degree of PEEK increased with increasing loading of IF-WS2 nanoparticles up to 1wt% and then declined at 2 wt%, due to lower level of particle dispersion in this sample. The 3D printed samples showed slightly higher crystallinity at each IF-WS2 loading in relation to the injection moulded samples and extruded filaments, because of multiple reheating effect from subsequent layer deposition during FDM, causing recrystallization. In general, incorporation of IF-WS2 nanoparticles increased the mechanical properties of pure PEEK in both 3D printed and injection moulded samples. However, this increment was more noticeable in the 3D-printed nanocomposite samples, resulting in smaller gap between the mechanical properties of the 3D-printed samples and the injection moulded counterparts, in respect to pure PEEK, particularly at 1 wt% IF-WS2. This effect is ascribed to the increased inter-layer bonding of PEEK in the presence of IF-WS2 nanoparticles in FDM. In general, the lower mechanical properties of the 3D printed samples compared with the injection moulded ones are ascribed to poor interlayer bonding between the deposited layers and the presence of voids. However, addition of just 1 wt% of IF-WS2 nanoparticles into PEEK increased the tensile strength and Young’s modulus of the FDM PEEK materials to similar levels to those achieved for unfilled injection moulded PEEK. Therefore, incorporation of IF-WS2 nanoparticles into PEEK is a useful strategy to improve the mechanical performance of FDM PEEK

Influence of Ambient Temperature on Part Distortion: A Simulation Study on Amorphous and Semi-Crystalline Polymer

Semi-crystalline polymers develop higher amounts of residual stress and part distortion (warpage) compared to amorphous polymers due to their crystalline nature. Additionally, the FDM processing parameters such as ambient temperature play an important role in the resulting residual stresses and part distortion of the printed part. Hence, in this study, the effect of ambient temperature on the in-built residual stresses and warpage of amorphous acrylonitrile-butadiene-styrene (ABS) and semi-crystalline polypropylene (PP) polymers was investigated. From the results, it was observed that increasing the ambient temperature from 50 °C to 75 °C and further to 120 °C resulted in 0.22-KPa and 0.37-KPa decreases in residual stress of ABS, but no significant change in the amount of warpage. For PP, increasing ambient temperature from 50 °C to 75 °C led to a more considerable decrease in residual stress (0.5 MPa) and about 3% increase in warpage. Further increasing to 120 °C resulted in a noticeable 2 MPa decrease in residual stress and a 3.4% increase in warpage. Reduction in residual stress in both ABS and PP as a result of increasing ambient temperature was due to the reduced thermal gradients. The enhanced warpage in PP with increase in ambient temperature, despite the reduction in residual stress, was ascribed to crystallization and shrinkage

3D printed PEEK/HA composites for bone tissue engineering applications: effect of material formulation on mechanical performance and bioactive potential

Polyetheretherketone (PEEK) is a biocompatible polymer widely used for biomedical applications. Because it is biologically inert, bioactive phases, such as nano-hydroxyapatite (HA), have been added to PEEK in order to improve its bioactivity. 3D printing (3DP) technologies are being increasingly used today to manufacture patient specific devices and implants. However, processing of PEEK is challenging due to its high melting point which is above 340 °C. In this study, PEEK-based filaments containing 10 wt% of pure nano-HA, strontium (Sr)- doped nano-HA and Zinc (Zn)-doped nano-HA were produced via hot-melt extrusion and subsequently 3D printed via fused deposition modelling (FDM), following an initial optimization process. The raw materials, extruded filaments and 3D printed samples were characterized in terms of physicochemical, thermal and morphological analysis. Moreover, the mechanical performance of 3D printed specimens was assessed via tensile tensing. Although an increase in the melting point and a reduction in crystallization temperature was observed with the addition of HA and doped HA to pure PEEK, there was no noticeable increase in the degree of crystallinity. Regarding the mechanical behavior, no significant differences were detected following the addition of the inorganic phases to the polymeric matrix, although a small reduction in the ultimate tensile strength (~14%) and Young's modulus (~5%) in PEEK/HA was observed in comparison to pure PEEK. Moreover, in vitro bioactivity of 3D printed samples was evaluated via a simulated body fluid immersion test for up to 28 days; the formation of apatite was observed on the surfaces of sample surfaces containing HA, SrHA and ZnHA. These results indicate the potential to produce bioactive, 3DP PEEK composites for challenging applications such as in craniofacial bone repair