Characteristics of Composite Materials of the Type: TPU/PP/BaTiO3 Powder for 3D Printing Applications

Composite materials are materials with anisotropic properties that are created by combining several different components in a way that allows the best qualities of each component to be used. In this paper, raw materials were used to obtain composite materials of the type TPU/PP/BaTiO3 powder. The thermogravimetric analysis, dynamic differential calorimetry, and scanning electron microscopy were carried out. The preliminary tests for making specific filaments for 3D printing with a diameter of 1.75 mm were carried out on a laboratory extruder. The purpose of the experiment was to develop the optimal extrusion temperatures and the speed of drawing the filament to make filaments with rigorously constant dimensions, and the variation in diameter had a maximum of 10%.

Some researchers have tried various techniques for obtaining the composite polymer matrix. [39][40][41][42][43][44][45]. Among these techniques, we mention in situ polymerization and meltmixing. It is difficult to achieve a universal technique for obtaining polymer composites due to the physical and chemical differences between the systems and the various types of equipment available to researchers. Thus, these different techniques will determine obtaining different results [46].
The addition of rigid filler particles increases the modulus of elasticity proportional to the volume percentage of the filler. The effective fracture surface energy is higher in the composite than in the unfilled polymer. The causes are numerous. The dispersed particles make the crack propagation path longer, increase the plastic deformation of the matrix, and part of the energy is absorbed. So the strength of the composite should increase with increasing filler content. But in reality it doesn't happen like that because the value of c and the interactions between the neighboring voids predominate.
The value of c represents the size of the voids formed when the matrix detaches from the particles of the filler material due to deformation. Naturally, the larger the particle size of the filler material, the larger the voids will be. It can be concluded that using small particle fillers, finely dispersed, is indicated. Another important conclusion is the anticipation of a considerable statistical dispersion of the strength data for the composite samples because a single void that has acquired a critical size can initiate the main crack.
Practice has also demonstrated the existence of a large number of factors that lead to complications, such as the morphology of the matrix in the composite, dispersed particles as additional crosslinks, the particle structure of the dispersed filler material, porosity, the agglomeration of dispersed filler particles, molecular restructuring of the matrix, and the residual stresses in the composite.
The most noticeable effect of the dispersed filler material on the matrix morphology is expected in the case of semi-crystalline polymers, where the filler largely affects the crystallization conditions. In certain cases, the experimentally observed strengthening effect can be explained by variations in the morphology of the matrix. This problem has been studied most intensively in the case of elastomers, being found in many publications. It has been established experimentally that a dispersed filler material has a reinforcing effect only if its particle sizes are very small. Obviously, the filler particles are adsorbed by the macromolecules and act as additional points of the macromolecular network. This is realized through a reinforcement of the material. However, it is not possible to explain this effect only by additional crosslinks.
Most researchers believe that the structured particles of the filler interfere with the development of cracks during the deformation of the material.
A secondary side effect of the production process of filled systems is the high void content. Since the presence of voids is due to the initiation of cracks during deformation, it follows that they reduce the strength of the composite. The void content is high in many composites due to poor wetting of the filler particles by the polymer. The presence or release of water on the surface of the particles also favors the formation of voids.
Agglomeration of dispersed filler particles is reflected in the decrease in the mechanical strength of the composite due to the increase in the particle size of the filler material and the low strength of the agglomerates themselves.
In general, processing compositions with a high degree of filling with high viscosity requires high shearing forces and high temperatures. These two factors initiate degradation processes in the matrix, varying the molecular mass distribution of the matrix during the formation process. These effects must be considered when studying the properties of thermoplastic materials with and without filler.
On average, the coefficients of thermal expansion of polymers and mineral fillers differ by a factor of ten. This fact is responsible for the residual stresses that remain in the composite after hardening. Concerning dispersed fillers, the stresses are compressive. Under a tensile force applied, the compressive stresses should manifest an additional resistance to the detachment of the polymer matrix from the filler material, thus improving the strength of the composite. But, in real materials, the structural inhomogeneities give a complex tensional state, which means that at certain points, shear and tensile stresses are present. They can facilitate the propagation of the crack and cause the reduction of the material's strength.
Thermoplastic Polyurethanes (TPU), due to their high abrasion resistance, strength, chemical resistance, and good fireproof properties, are widely used as insulation for lowvoltage electrical cables and for making various profiles by extrusion. [47].
TPUs are linear copolymers with alternating soft and hard segments. The hard segment is composed of diisocyanate (diol or diamine) molecules, while the soft segment consists of a long linear diol chain.
Phase separation occurs in TPU due to the thermodynamic incompatibility of hard and soft segments. The segments aggregate into micro-domains and result in a structure consisting of hard glassy or semi-crystalline and soft rubbery domains, which are below and above the glass transition temperatures (Tg) at room temperature, respectively. The hard domains act as physical crosslinks and impart elastomeric properties to the soft phase. Due to the absence of chemical crosslinking, TPUs can be processed by melting and by solution [48].
Barium titanate (BaTiO 3 ) is widely used to manufacture embedded film capacitors. It has relatively low thermal conductivity, very high dielectric constant, and high density, making it unattractive for the preparation of high thermal conductivity dielectric composites [49].
Huang X et al. measured the thermal conductivity of the ethylene-vinyl acetate elastomer with BaTiO 3 particles (100 nm). They presented a 300% increase in thermal conductivity for an addition of 50% BaTiO 3 compared to the TPU polymer matrix.
Much research has been carried out to obtain composite materials to improve the properties of TPUs. In one of these studies, TPU/kenaf-type composites were prepared, and the composites showed better mechanical properties than natural TPU [50].
In another study, a new elastomeric composite material based on polystyrene butadienestyrene (SBS), ester-type polyurethane, and melt-blended polyurethane materials was made. This material presented thermal, dynamic, and mechanical resistance to a large amount of TPU [51].
Other research highlighted the obtaining of new TPU/nano clay composite materials that were characterized after accelerated aging, finding that the TPU/nano clay composite has better mechanical properties than the natural TPU polymer [52].
Recent studies described obtaining flexible transparent electromagnetic interference shielding films with silver mesh fabricated using electric-field-driven microscale 3D printing [53].
Black phosphorus and MXene nanosheets were combined by hydrogen bonding and π-π stacking under ultrasound. Then the as-prepared BP-MXene nanohybrids were coated via the in situ polymerization of dopamine to improve the fire safety and mechanical properties of TPU [54]. Also, a new material 4D printing-encapsulated polycaprolactonethermoplastic polyurethane with high shape memory performance was obtained by combining the microscopic concept of shape-memory polymers and multimaterial printing of a thermoplastic elastomer with fused deposition modeling without extra operations, such as synthesis and blending [55].
Other researchers obtained antibacterial masterbatches by doping nano-Si 3 N 4 ceramic materials into PP with a twin-screw extruder. They transferred those masterbatches as raw material into antibacterial meltblown nonwovens during the meltblown process, which were further finished with superhydrophobicity on one side. The as-prepared nonwovens have applications in air filtration, including respirators and masks with a high-efficiency filtration performance and good antibacterial properties [56].
In this paper, composite materials were obtained from TPU/PP/BaTiO 3 powder and characterized by different methods. The PP + TPU filament variant with 35% BaTiO3 turned out to be the easiest deposition process, with no clogging of the nozzle, no problems with multilayer deposition, and no 3D printing defects. Very good precision structures were obtained experimentally by adjusting the deposition parameters. Precision mesh structures were also made at an angle of 90 compared to the initially planned one of 45 and at deposition densities higher than 50%.

Materials and Methods
To obtain composite polymers, the following raw materials were used: polypropylene TIPPLEN H 318, thermoplastic polyurethane Estane 58,887 TPU, and BaTiO 3 powder maximum 2 microns from Sigma Aldrich.
The experimental models were obtained on the KETSE laboratory extruder. In Figure 1, the raw materials used to obtain composite materials of the type TPU/PP/BaTiO 3 powder are presented. The experimental models were obtained on the KETSE laboratory extruder. In Figure  1, the raw materials used to obtain composite materials of the type TPU/PP/BaTiO3 powder are presented. To obtain good homogenization, the polymers (TPU and PP) and the BaTiO3 powder were homogenized by mixing for one hour in a cylindrical mixer with a 1,3l capacity TUR-BULA T2F type with a rubber ring holding device, and the rotation speed was 40 rpm. In this way, we sought to obtain a uniform distribution of the components of the mixtures throughout the structure without using specific additives or adhesives for compatibility. Processing conditions involved a rotation speed (in counter-rotation) of the extruder of 95 rpm and a feed speed from the feed hopper of 450 rpm. The main characteristics of the machine are a screw diameter of 28 mm, L/D ratio of 18,6 mm, calculated injection capacity of 58,5 cm 3 , maximum material pressure of 2200 bar, and real injection capacity min 500 mm.
The obtained experimental models have the following codes: M1-120 g powder of BaTiO3 51 g granules of PP and 829 g granules of TPU (12%) M2-160 g powder of BaTiO3 49 g granules of PP and 791 g granules of TPU (16%) M3-200 g powder of BaTiO3 47 g granules of PP and 753 g granules of TPU (20%) M4-240 g powder of BaTiO3 45 g granules of PP and 715 g granules of TPU (24%) M5-280 g powder of BaTiO3 43 g granules of PP and 677 g granules of TPU (28%) M6-320 g powder of BaTiO3 41 g granules of PP and 639 g granules of TPU (32%) The hydrostatic density was determined by a Mettler Toledo Analytical Balance with these characteristics: maximum capacity 220 g; precision: 0.1 mg; linearity ±0.2 mg; internal calibration; density kit for solids and liquids; the RS 232 interface.
The working temperature was 23.9 °C. The density was determined as the average value between 3 measurements performed on 3 different samples with the exclusion of values outside the range and a confidence level of 95%.
The thermogravimetric analysis and dynamic differential calorimetry (TG/DSC) were carried out with the help of the Simultaneous thermal analyzer TG-DSC type STA 449 F3 (Jupiter, NETZSCH, Germany). This equipment works in the temperature range of −150 °C −1550 °C in an inert, oxidizing, reducing, static, or dynamic working atmosphere. The device is provided with a vacuum system that provides a maximum of 10-2 mbar. (Operating Instructions-Simultaneous TG-DTA/DSC Apparatus (STA 449F3), Jupiter, Selb, October 2008, NETZSCH Gerätebau GmbH).
The conditions of the TG/DSC measurements performed on solid samples of composite polymer materials (10-15 mg) were as follows: temperature range: 25-700 °C, heating speed: 10 K/min, working atmosphere: nitrogen + oxygen, reference substance: alumina. To obtain good homogenization, the polymers (TPU and PP) and the BaTiO 3 powder were homogenized by mixing for one hour in a cylindrical mixer with a 1.3 L capacity TURBULA T2F type with a rubber ring holding device, and the rotation speed was 40 rpm. In this way, we sought to obtain a uniform distribution of the components of the mixtures throughout the structure without using specific additives or adhesives for compatibility. Processing conditions involved a rotation speed (in counter-rotation) of the extruder of 95 rpm and a feed speed from the feed hopper of 450 rpm. The main characteristics of the machine are a screw diameter of 28 mm, L/D ratio of 18.6 mm, calculated injection capacity of 58.5 cm 3 , maximum material pressure of 2200 bar, and real injection capacity min 500 mm.
The obtained experimental models have the following codes: M1-120 g powder of BaTiO 3  The hydrostatic density was determined by a Mettler Toledo Analytical Balance with these characteristics: maximum capacity 220 g; precision: 0.1 mg; linearity ±0.2 mg; internal calibration; density kit for solids and liquids; the RS 232 interface.
The working temperature was 23.9 • C. The density was determined as the average value between 3 measurements performed on 3 different samples with the exclusion of values outside the range and a confidence level of 95%.
The thermogravimetric analysis and dynamic differential calorimetry (TG/DSC) were carried out with the help of the Simultaneous thermal analyzer TG-DSC type STA 449 F3 (Jupiter, NETZSCH, Germany). This equipment works in the temperature range of −150 • C-1550 • C in an inert, oxidizing, reducing, static, or dynamic working atmosphere. The device is provided with a vacuum system that provides a maximum of 10-2 mbar. (Operating Instructions-Simultaneous TG-DTA/DSC Apparatus (STA 449F3), Jupiter, Selb, October 2008, NETZSCH Gerätebau GmbH).
The conditions of the TG/DSC measurements performed on solid samples of composite polymer materials (10-15 mg) were as follows: temperature range: 25-700 • C, heating speed: 10 K/min, working atmosphere: nitrogen + oxygen, reference substance: alumina.
Before introducing the sample to be analyzed into the device, it is weighed on a digital balance type Precisa XT 220 A (Switzerland), with digital display, precision class 0.1 mg.
Polymer swelling capacity depends on the amount of liquid that the material can absorb when immersed in the liquid. To determine the swelling capacity (swelling) in water and solvent (acetone) for the studied composite materials, the procedure was as follows [57]: It weighed approx. 0.06 g of composite material and placed in plastic ampoules with tight caps (tubes for micro-centrifuges with a diameter of 10 mm and a length of 40 mm); -Two sets of samples were made, one to determine the degree of swelling in water and the other set to determine the degree of swelling in solvent (acetone); - The ampoules with composite material, thus made, were filled with deionized water and respectively with solvent (acetone) and then were maintained for 72 h at a temperature of 22 • C (atmospheric) and a humidity of 41%.
The following formula was used to determine the degree of swelling: where: Q-degree of swelling; X 2,3,4 -the mass of the inflated/swollen polymer (after each 72-h cycle); X 1 -dry polymer mass.

Results and Discussion
From the interpretation of the obtained results, it is found that the melting temperatures vary in the range of 163-166 • C. The temperatures at the beginning of the first oxidation process vary between 190-213 • C.
In Figures 2-10, the results of the TG/DSC variation curves as a function of temperature (25-700 • C) are presented for all the studied materials.
Before introducing the sample to be analyzed into the device, it is weighed on a digital balance type Precisa XT 220 A (Switzerland), with digital display, precision class 0.1 mg.
Polymer swelling capacity depends on the amount of liquid that the material can absorb when immersed in the liquid. To determine the swelling capacity (swelling) in water and solvent (acetone) for the studied composite materials, the procedure was as follows [57]: -It weighed approx. 0.06 g of composite material and placed in plastic ampoules with tight caps (tubes for micro-centrifuges with a diameter of 10 mm and a length of 40 mm); -Two sets of samples were made, one to determine the degree of swelling in water and the other set to determine the degree of swelling in solvent (acetone); - The ampoules with composite material, thus made, were filled with deionized water and respectively with solvent (acetone) and then were maintained for 72 h at a temperature of 22°C (atmospheric) and a humidity of 41%.
The following formula was used to determine the degree of swelling: where: Q-degree of swelling; X2,3,4,-the mass of the inflated/swollen polymer (after each 72-h cycle); X1-dry polymer mass.

Results and Discussion
From the interpretation of the obtained results, it is found that the melting temperatures vary in the range of 163-166 °C. The temperatures at the beginning of the first oxidation process vary between 190-213 °C In Figures 2-10, the results of the TG/DSC variation curves as a function of temperature (25-700 °C) are presented for all the studied materials.                       In Figure 3, the TG/DSC variation curves for the TPU (Thermoplastic Polyurethane) material studied in the temperature range of 25-700 °C are presented. This material presents two transformation processes: -Glass transition (phase transition of the second order), when the state of rubber changes to the glassy-solid state, with the starting temperature of the transformation at 241.8°C and variation of Cp of 4017 J/g • K, a process that occurs due to the presence of amorphous areas in the sample; -Four chemical oxidation processes with maximum temperatures on the DSC curve at 334.1 °C, 375.9 °C, 408.5 °C , and 523.7 °C , respectively, with corresponding oxidation points on the DTG variation curve, at minimum temperatures of 328.5 °C, 366.4 °C, 409.8 °C , and 528.5 °C , respectively, and with partial mass losses of 32.49%, 23.25%, 19.02%, and 24.70%, respectively, the resulting total mass loss being 99.54%. BaTiO3 is an inorganic compound with a high melting temperature (1625 °C), which does not present phase transformations in the studied temperature range (25-700 °C), as seen in Figure 6.
In Table 1, the values resulting from the transformation processes (melting, glass transition, oxidation) from the analysis of the TG/DSC variation curves, shown in Figures  2-10, are presented BaTiO 3 is an inorganic compound with a high melting temperature (1625 • C), which does not present phase transformations in the studied temperature range (25-700 • C), as seen in Figure 6.
In Table 1, the values resulting from the transformation processes (melting, glass transition, oxidation) from the analysis of the TG/DSC variation curves, shown in Figures 2-10, are presented. Composite materials M1-M6 are materials based on BaTiO 3 powder with the addition of PP (Polypropylene) granules and TPU granules in a constant ratio (approx. 6.2%). In these materials, the concentration of BaTiO 3 increased from 12% (M1) to 32% (M6), while the addition of thermoplastic polyurethane (TPU) decreased from 88% (M1) to 68% (M6). The composite materials M1 and M2 present a thermal analysis behavior similar to that of the TPU material, showing both a glass transition process starting around 230 • C and chemical oxidation processes, with the difference that the second process of oxidation that appears in the TPU material at the maximum DSC temperature of 375.9 • C is no longer present in the composite materials M1 and M2 (Figures 7 and 8).
For composite materials M3-M6, in addition to glass transition processes and chemical oxidation processes, there is also a first-order phase transformation process-melting, due to the polypropylene (PP) melting process. The maximum melting temperature is around 164-167 • C.
Composite material M4 shows the most oxidation chemical processes (5 processes) among all composite materials M1-M6, suffering a total mass loss of 81.38%, which means that this material contains more intermediate products.
Following the TG/DSC analyses performed on materials M1-M6, we can conclude: -M1 and M2 present a thermal analysis behavior somewhat similar to that of the TPU material, showing both a glass transition process starting around 230 • C and chemical oxidation processes, with the difference that the second process of oxidation that occurs in the TPU material at the maximum DSC temperature of 375.9 • C is no longer present in the composite materials M1 and M2; -M3-M6, in addition to the glass transition and chemical oxidation processes, there is a first-order phase transformation process-melting using the polypropylene (PP) melting process. The maximum melting temperature is around 164-167 • C; -M4 presents the most oxidation chemical processes (5 processes) among all composite materials M1-M6, suffering a total mass loss of 81.38%, which means that this material contains more intermediate products.
The results of the swelling tests in water for materials M1-M6 are presented in Table 2 and Figure 11.  It is found that starting from 360 h of immersion in distilled water the samples no longer absorb water. Then at 432 h their saturation is observed, and at this moment, the test stops. The results of swelling tests in acetone for materials M1-M6 are presented in Table 3 and Figure 12. It is found that starting from 360 h of immersion in distilled water the samples no longer absorb water. Then at 432 h their saturation is observed, and at this moment, the test stops.
The results of swelling tests in acetone for materials M1-M6 are presented in Table 3 and Figure 12.   The degree of swelling was determined by measuring the variation in the mass of the sample. The measurement cycle was 72 h.
Swelling times in acetone were 72, 144, 216, and 288 h. From the experimental results (Table 3), the following classification of the studied composite materials can be made according to the swelling degree increase in solvent (ac- The degree of swelling was determined by measuring the variation in the mass of the sample. The measurement cycle was 72 h. Swelling times in acetone were 72, 144, 216, and 288 h. From the experimental results (Table 3) The structure of the polymer can be seen in SEM pictures. In the case of PP, a melting process can be seen ( Figure 13). For the BaTiO3 powder, the micrographs are shown in Figure 14. A large dispersion of particle sizes is found. For the BaTiO 3 powder, the micrographs are shown in Figure 14. A large dispersion of particle sizes is found.
The evidence of the differences in the granulation of the BaTiO 3 powder particles is highlighted in Figure 14. The results of 10 measurements of powder particles are presented, with the following values: 814,4 nm, 1112 nm, 868.8 nm, 841.3 nm, 780.5 nm, 1482 nm, 513.1 nm, 743.7 nm, 767.5 nm, and 661.3 nm. This nano-powder has an average size of 858.46 nm.
From Figures 15 and 16, the micrographs of TPU/PP/BaTiO 3 composite materials (M1-M6), powder particles of BaTiO 3 are observed to be present but not perfectly uniformly dispersed. They form small conglomerates in the polymer structure due to the irregular morphology of the BaTiO 3 powder that was embedded in the polymer. Analyzing the TPU/PP/BaTiO 3 type experimental models of composite materials, it is found that M6 is the most homogeneous (respectively, the agglomerations are less). For the BaTiO3 powder, the micrographs are shown in Figure 14. A large dispersion of particle sizes is found.  The evidence of the differences in the granulation of the BaTiO3 powder particles is highlighted in Figure 14 From Figures 15 and 16, the micrographs of TPU/PP/BaTiO3 composite materials (M1-M6), powder particles of BaTiO3 are observed to be present but not perfectly uniformly dispersed. They form small conglomerates in the polymer structure due to the irregular morphology of the BaTiO3 powder that was embedded in the polymer. Analyzing the TPU/PP/BaTiO3 type experimental models of composite materials, it is found that M6 is the most homogeneous (respectively, the agglomerations are less). From Figures 15 and 16, the micrographs of TPU/PP/BaTiO3 composite materials (M1-M6), powder particles of BaTiO3 are observed to be present but not perfectly uniformly dispersed. They form small conglomerates in the polymer structure due to the irregular morphology of the BaTiO3 powder that was embedded in the polymer. Analyzing the TPU/PP/BaTiO3 type experimental models of composite materials, it is found that M6 is the most homogeneous (respectively, the agglomerations are less).   (e) (f)

Preliminary Processing of Filaments
In Figure 17, the appearance of the granules obtained after one and two passes through the extruder is presented. The filament from the TPU/PP/BaTiO3 composite material resulting from the extrusion operation is very elastic, close to the elasticity of rubber, which made the granulation operation difficult and discontinuous (Figure 17c), but the filament itself provided good features to be used for 3D printing applications. The composition of the material (with up to 35% BaTiO3) makes it a good candidate for achieving 3D-printed piezoelectric flexible materials for energy harvesting, and the electrical properties are now under evaluation.

Preliminary Processing of Filaments
In Figure 17, the appearance of the granules obtained after one and two passes through the extruder is presented. The filament from the TPU/PP/BaTiO 3 composite material resulting from the extrusion operation is very elastic, close to the elasticity of rubber, which made the granulation operation difficult and discontinuous (Figure 17c), but the filament itself provided good features to be used for 3D printing applications. The composition of the material (with up to 35% BaTiO 3 ) makes it a good candidate for achieving 3D-printed piezoelectric flexible materials for energy harvesting, and the electrical properties are now under evaluation. through the extruder is presented. The filament from the TPU/PP/BaTiO3 composite material resulting from the extrusion operation is very elastic, close to the elasticity of rubber, which made the granulation operation difficult and discontinuous (Figure 17c), but the filament itself provided good features to be used for 3D printing applications. The composition of the material (with up to 35% BaTiO3) makes it a good candidate for achieving 3D-printed piezoelectric flexible materials for energy harvesting, and the electrical properties are now under evaluation. The preliminary tests for making specific filaments for 3D printing with a diameter of 1.75 mm were carried out on a laboratory extruder. The purpose of the experiment was to develop the optimal extrusion temperatures and the speed of drawing the filament to make filaments with rigorously constant dimensions, and the variation in diameter should be a maximum of 10%. The principle of structural models is presented in Figure 18. The preliminary tests for making specific filaments for 3D printing with a diameter of 1.75 mm were carried out on a laboratory extruder. The purpose of the experiment was to develop the optimal extrusion temperatures and the speed of drawing the filament to make filaments with rigorously constant dimensions, and the variation in diameter should be a maximum of 10%. The principle of structural models is presented in Figure 18.
The images with the data and the optimal products obtained are reproduced below. For all the recipes tested, the optimal temperatures were around 190 °C with a firing speed of 15 cm/min. The preliminary 3D printing tests with the realization of structural models involved using a laboratory 3D thermal printer.
The work stages included the following: -Creation of CAD models on specialized software that are then transferred to the laboratory 3D thermal printer. 2 structural models were designed, one 45 × 30 × 0.5 mm grid type and one 25 × 25 × 1 mm mesh type ( Figure 19). The images with the data and the optimal products obtained are reproduced below. For all the recipes tested, the optimal temperatures were around 190 • C with a firing speed of 15 cm/min. 5 types of filaments were made, with the following characteristics: The preliminary 3D printing tests with the realization of structural models involved using a laboratory 3D thermal printer.
The work stages included the following: -Creation of CAD models on specialized software that are then transferred to the laboratory 3D thermal printer. 2 structural models were designed, one 45 × 30 × 0.5 mm grid type and one 25 × 25 × 1 mm mesh type ( Figure 19).  Preliminary testing of the 3D printing parameters listed in Table 4, with a comparison between the experimental filaments and the commercial ScotchBlue™ Original Painter's Tape-type PLA filaments, and with compatibility testing for successive depositions of the two filaments, since the base deposition support can be made with the commercial one ( Figure 20). Preliminary testing of the 3D printing parameters listed in Table 4, with a comparison between the experimental filaments and the commercial ScotchBlue™ Original Painter's Tape-type PLA filaments, and with compatibility testing for successive depositions of the two filaments, since the base deposition support can be made with the commercial one ( Figure 20). Preliminary testing of the 3D printing parameters listed in Table 4, with a compar between the experimental filaments and the commercial ScotchBlue™ Original Pain Tape-type PLA filaments, and with compatibility testing for successive depositions o two filaments, since the base deposition support can be made with the commercial (Figure 20).  PP + TPU filament variant with 35% BaTiO3 turned out to be the easiest deposi process, with no clogging of the nozzle, no problems with multilayer deposition, and 3D printing defects.
In the end, very good precision structures were obtained experimentally by adjus the deposition parameters. Even precision mesh structures were made at an angle o compared to the initially planned one of 45 and at deposition densities higher than 5  PP + TPU filament variant with 35% BaTiO 3 turned out to be the easiest deposition process, with no clogging of the nozzle, no problems with multilayer deposition, and no 3D printing defects.
In the end, very good precision structures were obtained experimentally by adjusting the deposition parameters. Even precision mesh structures were made at an angle of 90 compared to the initially planned one of 45 and at deposition densities higher than 50% ( Figure 21). PP + TPU filament variant with 35% BaTiO3 turned out to be the easiest deposition process, with no clogging of the nozzle, no problems with multilayer deposition, and no 3D printing defects.
In the end, very good precision structures were obtained experimentally by adjusting the deposition parameters. Even precision mesh structures were made at an angle of 90 compared to the initially planned one of 45 and at deposition densities higher than 50% ( Figure 21). The filament from the TPU/PP/BaTiO3 composite material resulting from the extrusion operation is very elastic, close to the elasticity of rubber, a good feature in 3D printing applications. Considering the composite receipt, the material can be a good candidate for achieving 3D-printed piezoelectric flexible materials for energy harvesting.

Conclusions
In this paper, obtaining and characterizing composite materials from raw materials of the type TPU/PP/BaTiO3 powder was presented. The main observations are as follows: − M1 and M2 present a thermal analysis behavior somewhat similar to that of the TPU material, showing both a glass transition process starting around 230 °C and chemical oxidation processes, with the difference that the second process of oxidation that occurs in the TPU material at the maximum DSC temperature of 375.9 °C is no longer present in the composite materials M1 and M2; − M3-M6; in addition to the glass transition processes and chemical oxidation processes, there is also a first-order phase transformation process-melting due to the The filament from the TPU/PP/BaTiO 3 composite material resulting from the extrusion operation is very elastic, close to the elasticity of rubber, a good feature in 3D printing applications. Considering the composite receipt, the material can be a good candidate for achieving 3D-printed piezoelectric flexible materials for energy harvesting.

Conclusions
In this paper, obtaining and characterizing composite materials from raw materials of the type TPU/PP/BaTiO 3 powder was presented. The main observations are as follows: -M1 and M2 present a thermal analysis behavior somewhat similar to that of the TPU material, showing both a glass transition process starting around 230 • C and chemical oxidation processes, with the difference that the second process of oxidation that occurs in the TPU material at the maximum DSC temperature of 375.9 • C is no longer present in the composite materials M1 and M2; -M3-M6; in addition to the glass transition processes and chemical oxidation processes, there is also a first-order phase transformation process-melting due to the polypropylene (PP) melting process. The maximum melting temperature is around 164-167 • C; -M4 presents the most oxidation chemical processes (5 processes) among all composite materials, M1-M6, suffering a total mass loss of 81.38%, meaning that this material contains more intermediate products; -In the case of water inflation, using the M1 composite material is recommended, which has the lowest degree of swelling in water; -in the case of acetone inflation, the composite materials begin to degrade (dissolve) after immersion for 144 h. Composite M6 disaggregated after immersion for 144 h in acetone; -Analyzing the TPU/PP/BaTiO3 type experimental models of composite materials, it is found that M6 is the most homogeneous (respectively, the agglomerations are less).
The filament from the TPU/PP/BaTiO3 composite material resulting from the extrusion operation is very elastic, close to the elasticity of rubber, a good feature in 3D printing applications. Taking into account the composite receipt, the material can be a good candidate for achieving 3D-printed piezoelectric flexible materials for energy harvesting.