# Tribological Analysis of PETG Fire-Retardant Samples Manufactured by FFF
## 1 Introduction
In all cases, these materials achieve the V-0 rating [21] under the UL94 standard, indicating the highest level of flame resistance according to this classification:  
* The maximum after-flame time after removing the material from the flame is 10 s or less. * No dripping of flaming particles occurs. * Afterglow combustion does not last more than 30 s after removing the flame source. These characteristics make such materials ideal for industrial applications. However, their original drawbacks remain: ABS, although strong, emits toxic compounds during printing and has a greater environmental impact [22]; PLA is biodegradable but moisture-sensitive, limiting its durability in certain environments [23]; and PC, despite its thermal and mechanical strength, poses printing challenges due to the high temperatures required and its tendency to warp from shrinkage [24]. In contrast, PETG offers an excellent alternative, combining good mechanical strength, ease of printing, and a lower environmental impact [25], making it especially suitable for functional applications across different industries [26]. Nonetheless, there are very few studies on the fire-resistant additivated materials and they focus on traditional mechanical properties, such as those found in the material manufacturers' data. In the case of fire-resistant PETG, only certain mechanical properties are known, and no other mechanical aspects of great relevance are known. Nevertheless, recent studies [27; 28; 29] demonstrate that tribological properties can be decisive in material selection, particularly for parts in motion, or subject to friction and vibrations. For this reason, evaluating these properties is a matter of special interest. Polymer tribology has gained increasing attention in recent decades as the use of polymeric materials in functional applications has grown--particularly due to the rise in polymer additive manufacturing. Although this field is still less explored than that of metallic materials, it is crucial in sectors requiring low-friction, high wear-resistance components. Polymers exhibit unique tribological behavior due to their viscoelastic nature, low hardness, and adaptability to the contact surface. Wear in polymers usually results from a combination of friction and plastic deformation, and their coefficient of friction (CoF) tends to be high due to the increased contact area caused by material deformability [30; 31; 32; 33]. In this context, the most commonly used materials in FFF exhibit varied behavior. PLA, for instance, has a lower CoF than other polymers such as ABS, but it suffers greater wear--although this can be improved with reinforcements like copper or aluminium [34; 35; 36]. ABS, on the other hand, has greater wear resistance than PLA and offers more consistent performance in humid environments, especially when reinforced with carbon fibers [37; 38]. PETG has gained popularity due to its good wear resistance, combining hardness and flexibility. Compared to unreinforced PLA and ABS, PETG shows up to 40% less wear, and its performance improves in humid conditions [34; 35]. However, there are no existing studies on PETG materials enhanced with fire-resistant additives. In this context, the present study aims to analyze the tribological behavior of parts manufactured using PETG with flame-retardant additives via FFF technology. Through a series of tests designed to evaluate the coefficient of friction, wear resistance, and surface roughness, this work seeks to determine the extent to which additive incorporation affects the material's functional properties. A comparison with conventional PETG will allow for objective criteria to be established for its potential application in industrial settings where fire safety requirements coexist with mechanical demands related to contact and friction. This study will help to decide the possible industrial applications of PETG with flame-retardant additives in applications where there is relative motion between different objects.