## 1 Introduction
Due to the subsequent deposition of molten polymer on top of a previously printed layer, the layer temperature will strongly change over time, making the FFF process highly non-isothermal. As a consequence, the development of interlayer strength and crystallization will become time-dependent [26; 27]. Thermal monitoring of the FFF process to extract the non-isothermal temperature profile of a printed layer has been extensively reported in the literature, either by utilizing a thermocouple [28; 29; 30] or through infrared (IR) thermography [31; 32; 33; 34; 35; 36; 37; 38]. Other authors have successfully attempted to model the temperature profiles within consecutively deposited layers [32; 39; 40; 41; 42]. The discussion above has illustrated the great significance of gaining insight in the behavior of semi-crystalline thermoplastics during FFF as a function of thermal history to possibly predict or tailor both the extent and gradient of crystallinity within a printed part and the resulting part quality in terms of mechanical strength and dimensional stability. Few studies, of which most are mainly focused on PLA, have investigated the influence of material properties or processing parameters, such as print speed and liquefier temperature, on the degree of crystallinity attained through printing. By using conventional Differential Scanning Calorimetry (DSC) and X-ray Diffraction (XRD), the crystallinity in the final printed part is examined showing little impact of the liquefier temperature, yet a large effect of increasing the build plate temperature. Annealing the printed part, either by the build plate heated sufficiently above the glass transition temperature (T\({}_{\text{g}}\)) or as a follow-up treatment, has been proven to enhance crystallinity strongly [43; 44; 45; 46; 47]. The continuous successive deposition of new molten polymer onto previously printed layers results in consecutive annealing cycles, ultimately producing a gradient of crystallinity in the printed part with upper layers, having been exposed to fewer annealing cycles, being less crystalline. A slower print speed is also suggested to contribute to a higher degree of crystallinity. For PLA, both a high L-enantiomeric purity and low molecular weight have been shown to greatly intensify crystallization kinetics, indicating the possibility to alter crystallization during FFF on a molecular level [30]. The presented research aimed at studying the effect of processing parameters, including print speed as well as liquefier and build plate temperature, on the thermal history and the resulting degree of crystallinity at different heights above the build plate for two PA 6/66 random copolymers with distinct molecular weights. By monitoring the layer temperatures during printing through IR thermography, temperature profiles as a function of time were obtained, which were then simulated in a Fast Scanning Chip Calorimetry (FSC) device. FSC has proven itself to be able to mimic the fast heating and cooling rates, which are typically experienced by the extruded polymer during the FFF process and cannot be achieved with conventional DSC [48]. Hence, by replicating the thermal conditions in the FSC device, the progression of crystallinity in a layer during printing and the contribution of each print setting can be monitored, once the layer temperature profile is known.