Additive Manufacturing (AM) describes a powerful set of techniques which have the potential to become a reliable method for the manufacture of complex and accurate parts. Laser Sintering (LS) is one of the most promising AM techniques, capable of manufacturing 3-dimensional (3D) products from polymer powders. However, some key challenges still limit their widespread applications. The most common key challenges, specifically for the Laser Sintering AM process are limited availability of different materials, inconsistent or poor mechanical properties and surface quality, each of which is currently still restricting the functions of the end-use parts.
In some cases, nanoclay reinforcement of polymers has been shown to provide performance benefits, improving part quality, and offering new applications. However, the dispersion of those nano-sized materials still remains a critical issue for the preparation of Laser Sintering nanocomposites. A novel method of using plasma treatment to tackle these challenges was developed in this study. Plasma treatment was used to increase the surface area of nanoclay particles and with the expectation of simultaneous surface functionalisation aiming for increased homogeneity after dry mixing of polymer and nanoclay powders. SEM images of treated composite powders confirmed this expectation as the plasma treatment reduce agglomerations and improved nanoclay dispersion in the powders.
To consolidate these powders into parts a novel methodology, i.e. Downward Heat Sintering (DHS) method was initially used as a powerful replication method for the Laser Sintering technique. DHS process was employed with a hot press to process small quantities of PA12 and dry mixed composite powders into tensile test specimens after optimisation attempts based on differential scanning calorimetry (DSC) and hot-stage microscopy (HSM). SEM images of the heat sintered specimens showed clearly the plasma treatment prevented the aggregation of the nanoclay resulting in an improved elastic modulus of treated composite compared with neat PA12 and untreated composites. Moreover, the reduction in elongation at break for the treated composite was less pronounced than untreated composite.
Further work resulted in successfully LS parts with different complex and accurate shapes. No significant deterioration in LS processibility was observed and complex LS parts could be produced when including the plasma treated nanoclay. SEM images of the cross-sections of the fabricated parts that the layer by layer structure were successfully consolidated and relatively uniform. In addition, the introduction of the plasma treated nanoclay was found to improve the elastic modulus of the LS composite parts. Most notably however, a substantially improved surface quality in part’s appearance and microstructure was found as a result of incorporating plasma treated nanoclay compared to the nontreated nanoclay.
PA12 exposed to Low Pressure Air Plasma Treatment showed an increase in wettability, was relatively porous, and possessed a higher density, which resulted from surface functionalisation and materials removal during the plasma exposure. However, it showed poor melt behaviour under heating conditions typical for Laser Sintering. In contrast, brief Plasma Jet treatments demonstrated similar changes in porosity, but crucially, retained the favourable melt characteristics of PA12 powder.
To summarise, this is a unique study on the use of plasma treatment and polymer/polymer nanocomposites in LS applications, demonstrating for the first time that plasma treatment has the potential to provide crucial performance benefits for laser sintered nanocomposites.
