Aidan Vogel*a and Joseph Moniodis b
Recycled PC-ABS was infused with talc (hydrous magnesium silicate) to enhance the chemical resistance of the resulting filament. Talc was added at ratios of 2%, 3%, 4% and 5% and all ratios were successfully extruded. A ratio of 2% was found to be the ideal concentration for filament consistency and diameter. At higher talc concentrations (4-5%), the diameter of the filament was not consistent. Testing is required to measure the chemical resistance at each concentration of talc and determine whether an appropriate level of chemical resistance is achievable with no observed decrease in mechanical strength.
A polymer composite is a multiphase material made from two or more components.[1] The resulting mixture can have characteristics that are different and often superior to the individual components through a synergistic effect.
Talc (talcum) is a hydrated magnesium silicate clay mineral with the chemical formula Mg3Si4O10(OH)2.[2] It is a monoclinic mineral with stacked platelets consisting of thousands of elemental sheets.[1] It has high thermal stability.[1] The addition of talc can enhance the physical and mechanical properties of a resulting polymer composite by:[3], [4]
Increasing stiffness and impact resistance
Increasing thermal conductivity allow for faster production rates
Improving creep resistance
Preventing water vapour and oxygen transmission
Enhancing chemical resistance.
PC-ABS is an engineering grade polymer that exhibits high strength, high stiffness, high heat resistance, and high impact resistance, even at low temperatures.[5] However, it has poor weatherability and low fatigue endurance, as well as low chemical, UV and oxidation resistance. Our previous communication studied the extrusion of PC-ABS with titanium dioxide, which was added to improve weatherability and UV resistance.[6] In this experiment, we aim to test the effect of adding between 2-5% talc on the tensile strength of our upcycled PC-ABS 3D printing filament to determine whether the addition of talc has a measurable impact on the tensile strength of the polymer blend.
Results and Discussion
Table 1 shows the measured tensile strengths of the filament resulting from the addition of between 2-5% talc to upcycled PC-ABS.
The results in the above table show a general decrease in the tensile strength as the concentration of talc is increased, with the ideal concentration being 2%. At 2% w/w, tensile strength did not decrease appreciably. At concentration levels of 4-5%, some of the talc did not melt in the extruder, leaving specs in the resulting filament. Further experiments will involve raising the extrusion temperature at 4-5% and examining the impact on the extrusion process. While this may melt the remaining talc, it may also impact the extruded filament, which may be harder to spool.
The filament diameter variation increased as the concentration of talc increased. Up to a concentration of 3% talc, the filament diameter was reasonably consistent, to within approximately ±0.10 mm and averaged around 1.75 mm. However, at concentrations of 4-5%, it varied up to ±0.20 mm with a significant increase in diameter, to around 1.90 mm. Further work is needed to obtain consistent filament diameter, particularly at higher concentrations.
In this experiment, silicone spray was used as an adhesive. When talc is mixed with PC-ABS, the talc is not evenly distributed. It does not coat the surface of the polymer in the same way as other additives. Experiments conducted without silicone spray were abandoned because of poor dispersion and resulting inferior filament. The silicone spray resulted in an even distribution and successful extrusion, although as can be seen from the table, the silicone spray reduced the tensile strength of the filament.
Further experiments are required to test the impact on other properties of the polymers. This experiment has demonstrated that successful extrusion can be achieved at low percentages (2-3%). This is in line with our previous experiments involving titanium dioxide.[6] Higher percentages would require the use of a twin screw extruder to form PC-ABS-talc pellets prior to extrusion.[7]
Materials and Methods
Recycled PC-ABS pellets were purchased from Carl’s Industrial Salvage Store. No material data sheet was provided for the polymer blend. Pellet size was an average of 3mm. Talc was purchased from Fasco Expoxies Inc and was of 100% purity with a median particle size of 10µm. Samples of PC-ABS were dried at 90◦C in a conventional oven for 2 hours. After cooling, Silicone spray was applied to the PC-ABS to facilitate the adhesion of the talc powder. For each experiment, a total of 50g of material was used, with the following weight ratios of talc to PC-ABS mixed by mechanical shaking for approximately 5 minutes until the mixture was evenly dispersed:
2% - 1.0g Talc | 49.0g PC-ABS
3% - 1.5g Talc | 48.5g PC-ABS
2% - 2.0g Talc | 48.0g PC-ABS
2% - 2.5g Talc | 47.5g PC-ABS
For each experiment, the mixtures were loaded into a Filabot EX2 Extruder with a 1.75mm nozzle. A Filabot Airpath was used to cool the mixture once it extruded from the nozzle and a Filabot Filament Spooler collected and spooled the resulting filament. The extrusion temperature was set at 245◦C with the extrusion rate at 100% and the airpath speed at 83%, and these were varied as required throughout the experiment. The filament thickness was measured using a Filabot Filameasure and was consistent to within 0.1 mm, except at higher concentrations where consistency decreased. The tensile strength was then measured using a ShenCe Digital Force Gauge.
Conclusions
The extrusion of talc infused upcycled PC-ABS 3D printing filament was successfully achieved for 2-5% talc added. The tensile strengths of the resulting materials showed a slight decrease as the concentration of talc increased from 2-3%, with a marked decreased observed at 4-5%. Chemical resistance testing is needed to determine the ideal concentration of talc required to achieve adequate chemical resistance at a reasonable cost. Further tests may also be needed to ensure the observed trend is reproducible and attain a more accurate measure of the slope of the observed decrease.
Notes and references
[1] C. Lee, M. M. Pang, S. C. Koay, H. L. Choo, and K. Y. Tshai, “Talc filled polylactic-acid biobased polymer composites: tensile, thermal and morphological properties,” SN Appl Sci, vol. 2, no. 3, Mar. 2020, doi: 10.1007/s42452-020-2172-y.
[2] Wikipedia, “Talc,” https://en.wikipedia.org/wiki/Talc, 2022.
[3] Avani Group, “Talc in Plastics and Polymers,” https://avanitalc.com/applications/talc-plastics-polymers/, 2022.
[4] Bandhan Calchem Pvt. Ltd, “Talc in the Plastic Industry,” Bandhan Calchem Website, 2022.
[5] R. Krache and I. Debah, “Some Mechanical and Thermal Properties of PC/ABS Blends,” Materials Sciences and Applications, vol. 02, no. 05, pp. 404–410, 2011, doi: 10.4236/msa.2011.25052.
[6] A. Vogel and J. J. Moniodis, “Extruding Titanium Dioxide Infused Upcycled PC-ABS for Improved UV Resistance,” Swyftlyt Communications, 2022.
[7] Jim Johnson, “Polymeric Compatibilizers for Blends and Recycled Compounds,” https://www.youtube.com/watch?v=JyCC94CJ8IQ. 2021.