Saeed Fathi

Anionic polymerisation of caprolactam at the small-scale via DSC investigations

This work was part of a major project aiming to produce polyamide 6 parts using an additive manufacturing process. This is by manufacturing 3D parts layer by layer. The influence of heating strategy (heating rate, cooling rate and maximum temperature) on anionic polymerisation of caprolactam in a small-scale was investigated by means of differential scanning calorimetry (DSC). The relationship between heating rate and the polymerisation–crystallisation processes was determined. Two different catalyst/activator compositions were used to study the influence of a di-functional activator on polymerisation. Results showed that unlike cooling rate, the heating rate and maximum heating temperature had a major effect on the final properties of polymer such as crystallinity, monomer conversion and polymer chains regularity. Using a di-functional activator resulted in slowing down the crystallisation process due to the enhanced rate of branching.

Droplet characterisation of molten caprolactam for additive manufacturing applications

Droplet formation characteristics of molten caprolactam, the monomer of nylon 6, are reported in this article as part of research to develop a novel inkjet additive manufacturing process. Initial investigations confirmed the jettability of molten caprolactam at 80 °C with a printhead and recommended a range of parameters for a stable jet array. High-speed imaging was used to study the interactions between the melt and the printhead. Droplets were generated at voltages higher than 12.5 V. Nozzle wetting and crosstalk in adjacent nozzles were observed especially at higher voltages. Jetting frequency did not affect the droplet characteristics. By varying the jetting voltage though significant changes to the droplet shape, evolution and kinetics were observed. Satellite droplets were formed by disintegration of the tail at lengths of about 1 mm when a jetting voltage of 25.0 V was used. An increase of voltage from 15.0 V to 25.0 V increased the droplet velocity from 2 m/s to 8 m/s. Reynolds and Weber numbers predicted there would not be splashing upon droplet impact, which was confirmed by experiments when impinging molten caprolactam droplets on cold and heated substrates. The droplet formation study suggested a set of jetting parameters to be used for the next stage of the research on the inkjet process development.

Instability behaviours of a jet array in inkjet printing of molten caprolactam

Purpose – The purpose of this paper is to present the findings on jet array instabilities of molten caprolactam. Initial investigations showed that although a suitable range of parameters was found for stable jetting, there were cases where instabilities occurred due to external sources such as contamination.Design/methodology/approach – The inkjet system consisted of a melt supply unit, filtration unit and printhead with pneumatic and thermal control. A start‐up strategy was developed to initiate the jetting trials. A digital microscope camera monitored the printhead nozzle plate to record the jet array stability within the recommended range of parameters from earlier research. The trials with jet instabilities were studied to analyse the instability behaviour.Findings – It was found that instabilities occurred in three forms which were jet trajectory error, single jet failure and jet array failure. Occasionally, the jet with incorrect trajectory remained stable. When a jet failed, bleeding of melt from ...