Investigation of the effect of zinc borate on the performance and flammability of polypropylene in additive manufacturing

Additive manufacturing is a production method that use has increased in recent years due to the many advantages it provides. Many materials such as polymers, metals and ceramics can be produced with different techniques of this production method. The use of polymers is increasing due to lightness, design flexibility, chemical resistance, easy processing, etc. day by day. However, low thermal and mechanical properties are the main weaknesses of polymers. It is a very common method to prepare composites with various additives to improve the properties of polymers. Polypropylene (PP) is the second most widely used polymer globally. Although, its low strength and elongation against tensile force is one of its weaknesses. Nowadays, flame retardant additives play an important role for improving the flame resistance of polymers. Zinc borate (ZB) is an additive that acts as a fire retardant in polymer materials. In this study, composites have been prepared by adding ZB to polypropylene at different rates (5, 10, 15 and 20 wt.%). In the preparation of the composites, the melt mixing method with a twin-screw extruder was used. Test samples were produced using an open source 3D printer of the Prusa 3D model type. Mechanical, thermal, impact and non flammability tests were carried out to see the effect of ÇB which has flame retardant properties on PP. In addition, studies have been carried out with different infill ratios (50%, 75%, 100%) for pure PP and 10% ZB filled PP composites. It was observed that the densities and the melt flow index (MFI) results of the samples increased with increasing ZB ratio. The melting temperatures (Te), melting enthalpies (ΔHe) and crystallinity degrees (Xk) of the samples were determined using a differential scanning calorimetry (DSC) device. While Te showed similar results, ΔHe and Xk results decreased with the increase in the contribution ratio. Tensile test specimens were produced according to ISO 527-2 standard and tensile strength, elongation at break and elastic modulus values were determined by applying a tensile test with a universal tensile test machine. From the experimental results, it was observed that the tensile strength values decreased and the elongation at break values increased with increasing ZB ratios. The tensile strength and elongation at break decreased in pure PP and 10% ZB added PP composites with decreasing infill ratio at different infill ratios. There was no significant difference in elastic modulus values. According to the 3-point bending tests, the bending strengths showed similar results with the tensile strength values, and the strengths decreased with increasing ZB. According to the result in the infill ratios, the decreasing infill ratio decreased the bending strength. 10% ZB added PP composites had the highest displacement result. The bending modulus decreased with the addition of ZB. For different infill ratios, this situation is similar with flexural strengths and decreased with decreasing infill ratio. When the results of the impact tests were examined, it was determined that the ZB additive reduced the impact energy of the samples. Impact energies also decreased for decreasing infill ratios. The addition of ZB to the PP matrix decreased the heat deflection temperature (HDT) of the composite up to a certain rate and increased it after a certain rate. The flammability tests were tested by determining the burning rate with a horizontal flammability tester. While pure PP has a burning rate of 66,60 mm/min, the burning rate of 20% ZB added PP composites is 49,18 mm/min. With increasing ZB ratio, a decrease in burning rate was observed. According to the results at different infill ratios, the burning rate of 10% ZB added PP composites for all infill ratios is lower than that of pure PP. It was determined that with decreasing infill ratios, the burning rate increased due to the voids in the sample. The dimensional stability of the samples was obtained by measuring the warpage angles and improved by 68,6% with increasing ZB ratios. When the different infill ratios are examined, all infill ratios of 10% ZB added PP composite gave the best results compared to pure PP.