## 1 Introduction  
Previous investigations demonstrated the potential optimization of a functionally filled polymer for additive manufacturing, by adjusting the particle size distribution of calcium carbonate as a mineral filler [1]. Additive manufacturing (AM) continues to develop rapidly, with a particular focus on three-dimensional layer-by-layer processing, in which each layer is bonded/fused together by one of the various different techniques, such as sintering, melting, chemical reaction, curing, etc. [2]. The technique has shown its suitability for constructing complex geometries; in some cases, impossible to achieve using subtractive techniques [3]. Applications have also grown, ranging from automotive and aerospace to biomedicine and art design [3; 4; 5; 6]. Current materials commonly used in AM are frequently plastic or metal-based [7; 8]. A major sector of AM employs selective laser sintering (SLS), which readily interfaces with computer-aided design (CAD) as the print template formed from a powder bed by fusing the layers of powder together adopting a laser beam of material-selective absorbing wavelength. Engineering thermoplastics and metals are used [4]. Polyamides/nylons, typically polyamide 12, are among the commonly used thermoplastics [5]. Prior work has identified the process limitations, which can prevent successful processing in selective laser sintering [5; 6; 7; 8; 9; 10; 11]. The most important factors are the crucial need for consistent, optimized thermal properties and the physical flow and layering properties defined by the particle size of the polymer/composite powder [12]. [PERSON] et al. described how it is possible to reduce manufacturing and material costs, including increasing energy efficiency, by adding an environmentally friendly filler material, such as calcium carbonate, into the polymer matrix [13]. Following this adoption of filler, our own previous work [1; 14], among others, addressed the potential for further reduction of the current high energy consumption involved in selective laser sintering [15; 16; 17]. This is achieved by introducing filler with controlled thermal capacity and conductivity. By increasing the thermal conductivity above that of PA12 alone, the laser power needed to sinter the polymer is reduced. In parallel, the increase in thermal capacity offered by the filler opens the possibility of employing greater total energy density without subsequent material bulk distortion during re-crystallization [1]. In addition, if a filler can be used that enhances laser radiative absorption, further energy utilization could be supported. Calcium carbonate, in the form of limestone, can be employed as a functional filler in that its properties can be adjusted to enhance both the melting and crystallization behavior [1]. Calcium carbonate was chosen in this work to represent a commonly used high brightness filler in polymer applications. Advantages of using natural ground calcium carbonate include the lower resistance to flow offered by isometric granular particles of crystalline calcite, as opposed to anisometric platelets or needle-like structures of high aspect ratio typical of kaolin, talc or mica and precipitated scalenohedral or aragonitic calcium carbonate, respectively. The relatively low hygroscopy of calcium carbonate--in comparison with, say, gypsum (calcium sulfate), which exists with thermally unstable crystal water (hemihydrate versus dihydrate), with the anhydrous form being particularly problematic due to its desiccant behavior--is a suitably optimal choice when among the various calcium salts in respect to maintaining consistent humidity and surface energy as a function of temperature in application with a lipophilic polymer, such as polyamide 12.