# Thermal and Mechanical Assessment of PLA-SEBS and PLA-SEBS-CNT Biopolymer Blends for 3D Printing
## 1 Introduction  
Rapid prototyping, or as it is increasingly referred to today, 3D printing, has changed the product design process. Thanks to the printed prototype, the time from the idea of the product to its production was shortened. In addition to hand-held, view-only models, there is a growing need for functional prototypes for the industry, with which the automotive industry, for example, can also perform assembly tests [1, 2]. There are several types of 3D printing processes, of which FDM (Fused Deposition Modelling) technology is one of the simplest and most cost-effective. Thanks to these advantages, it is widespread, and even smaller companies can afford it, so the range of suppliers can expand. In the FDM process, the coiled thermoplastic fiber is pushed into the heated print head by a pair of rollers, where it melts. At the end of the print head, there is a small cross-section nozzle; the molten fiber exits this and it is placed on the print-table in the direction specified by the software. After one layer is completed, for some printer types, the print table sinks by one layer and printing of the next layer begins; for other printer types, the nozzle is moved in the \(Z\) direction and the table does not move [1, 2]. One of the most common raw materials in the FDM process is PLA, polylactic acid. PLA is thermoplastic, semi-crystalline polyester and it is a biopolymer that can be made from natural materials, such as starch and sugar, and it can be decomposed by composting under industrial conditions [3, 4]. Nowadays, environmental protection is very important, so biopolymers such as PLA have become the center of interest [5]. The elevated environmental awareness and the good properties (high tensile strength and Young's modulus,good flexural strength) have resulted in the expanded use of PLA for consumer goods and packaging applications; furthermore, it is expected that novel technological advances will lead to the biopolymer market boom in the transportation and automotive industries [6]. Due to its high mechanical strength and good processability, it has great potential to replace conventional materials; however, it also has some disadvantages. Its impact resistance is poor, tensile elongation is low, it behaves in a brittle manner, its heat resistance is low, and its crystallization rate is slow [7; 8; 9]. There have been many attempts to improve the disadvantages of PLA. The brittleness was reduced by the addition of a plasticizer or impact modifier. Even further improvement can be achieved by using nano-clay, which also increases the crystallinity of PLA [7]. Another way to overcome the disadvantages is to make blends with polymers with better impact resistance [10]. The advantage of using a polymer is that the blooming problem of small molecule additives will not occur. Natural rubbers or thermoplastic elastomers are used as toughening agents for thermoplastic polymers, so one of the simplest solutions is to use them to increase the impact resistance and flexibility of PLA [11; 12]. The styrene-ethylene-butylene-styrene (SEBS) copolymer is a thermoplastic elastomer that has a low production cost but good processability, aging resistance, and excellent thermal stability [13; 14]. It is often used as a toughness agent for polymer blends and nanocomposites. It is also used as a compatibilizer for immiscible polymers [15; 16]. Due to these good properties, several studies have been published on the study of PLA and SEBS mixtures [13; 14]. In most cases, a SEBS copolymer grafted with maleic anhydride (MA) was used [13; 15; 16; 17]. It has been found that mixing 5% or more of SEBS into PLA significantly increases impact strength and flexibility [18]. To date, the effect of less than 5% of SEBS (without MA) on 3D-printed PLA specimens has not been studied. Another very important area is nanocomposites, because the addition of nanomaterials can achieve significant property modification in the case of PLA [19; 20].