Experiments
> Which experiment and why ?
For this project a virtual budget of 4000 € was available to characterize the different materials used to print the drone which are ABS and Flexifil.
First, a Differential Scanning Calorimetry (DSC) was performed on both materials after printing. It is a thermal method used to analyze the change in physical and chemical properties (glass transition temperature and solid-state reactions) of the polymer according to temperature. Indeed, the DSC measures the difference in heat flow between a sample and an inert reference in function of the temperature. [1] This experiment was performed to check if the polymer is amorphous or semi-crystalline. Moreover, it allowed us to determine the phase transition temperatures such as glass transition or melting transition (if semi-crystalline). Therefore, we could know if the material of the drone will sustain high temperatures such as 120 °C. Moreover, it allows us to study the percentage of crystallinity and the heat of fusion. These two experiments cost us 800€.
Then, a Fourier transform infrared spectroscopy (FTIR) [2] was done on the Flexifil material in order to identify its composition. In this technique, an infrared radiation is sent on the sample. A part of this radiation is absorbed by the sample and an other one is transmitted. The detector analyses the transmitted signal and transforms it into a spectrum. This spectrum allows us to identify the different functional groups present in the polymer. This experiment costs us 400€.
Next, a Scanning transmission electron microscopy (STEM) was performed on the ABS to analyse its structure at the micro and nano scales. The STEM focuses a beam of high-energy electrons at the surface of a sample. The signals which derive from this interaction are composed of secondary electrons, backscaterred electrons, diffracted backscattered electrons, photons, visible light and heat. They are collected by the transmission detector and give information about the morphology, the composition and the structure. [3] It allows us to determine the fabrication method of ABS and the origin of its properties. This experiment costs us 400 €.
Besides, a thermogravimetric analysis (TGA) was performed on both polymers. This is a method which analyzes the evolution of the mass (with a micro-thermobalance), in function of the temperature, which can be due to adsorption of oxygen, thermal degradation, oxidation or other heterogeneous reactions. [4] The polymer samples were put at 120 °C during 2 hours and the evolution of their mass was measured. This test allows us to determine the degradation of the sample during this time. These two experiments cost us 800 €.
Finally, some mechanical tests were realized on both ABS and Flexifil. For the ABS, tensile tests before and after printing were performed at 120 °C. This allows us to compare the mechanical properties before and after printing and to study the mechanical properties in extreme conditions (120 °C) of ABS. For the Flexifil, only a tensile test after printing was done. During a tensile test, the sample is placed between two grips. Then, the machine pull on the sample with an increasing force. The evolution of the length in function of this weight is measured. [5] This can give information about the tensile strength and the Young’s modulus. These experiments cost us 1200 €.
> Bibliography
[1]”Differential scanning calorimetry”, Derrick Dean, University of Alabama, https://www.uab.edu/engineering/home/images/downloads/DSC_UAB_TA_May_2014_Compatibility_Mode.pdf, accessed on 22/04/2017.
[2]”Introduction to FTIR spectroscopy”, ThermoFisher scientific, https://www.thermofisher.com/be/en/home/industrial/spectroscopy-elemental-isotope-analysis/spectroscopy-elemental-isotope-analysis-learning-center/molecular-spectroscopy-information/ftir-information/ftir-basics.html, accessed on 22/04/2017.
[3]”Scanning electron microscopy”, Susan Swapp, University of Wyoming, http://serc.carleton.edu/research_education/geochemsheets/techniques/SEM.html, accessed on 22/04/2017.
[4] ”Thermogravimetric Analysis (TGA) & Differential Scanning Calorimetry (DSC)”, Mark McKinnon, University of Maryland, http://www.fpe.umd.edu/sites/default/files/documents/LMD-TGA-DSC.pdf, accessed on 22/04/2017.
[5]”Tensile test experiment”, Michigan technological university, http://www.mtu.edu/materials/k12/experiments/tensile/, accessed on 22/04/2017.
In conclusion, different experiments were performed for a total of 4000 €. They allowed us to determine the thermal behaviour of our polymer, the types of functional groups present in their structure, the morphology of the ABS after printing and their mechanical properties.
A last experiment was performed on Flexifil in order to identify its microstructure: AFM. In Atomic Force Microscopy, a lever vibrated above the surface of the studied sample and interacts with it. As the interaction with the lever is different for each block of the copolymer (because there is a soft block and a hard block), it is possible to map the microstructure of the different phases in the polymer. This experiment costs us 400€.
By Julie
> What can we conclude from these experiments ?
Through all these experiments, we have learned a lot about the composition, the microsctructure and the properties of both materials.
For ABS, the composition found in the literature was verified not only by DSC, but also by analysing its microstructure with SEM. From the microscopy observations, it was also possible to conclude that this type of ABS was fabricated through a hybrid process, mixing emulsion and bulk polymerization, thus resulting in a bimodal distribution of butadiene in the SAN matrix. Concerning its properties, a DSC measurement after printing enable to say that the thermal properties to not change after impression. Also, thanks to TGA measurements, we know that there is no degradation of the material at 120°C. For the mechanical properties, a proper comparison before and after printing was not possible due to a different infill. We were however able to deduce that the drone would not undergo a plastic deformation during its use.
For Flexifil, the exact composition of the material was not documented in the literature. We therefore performed an FTIR in order to discover its main constituents, with the help of the glass transition measurements of the DSC. We were able to find a copolymer with a similar spectra and with similar Tg’s: PBT-PTMEG, where PBT is a hard block and PTMEG a soft block that could be responsible for the elastomeric properties of the materials. To verify this, we analysed the microsture with AFM and found that we had a matrix of one phase, with dispersed grains of a second phase. The elastomeric properties thus come from the matrix, which is the amorphous soft block. Concerning its thermal properties, they remain mostly unchanged after impression. The mechanical test indicates that even at 120°C, Flexifil maintains excellent properties.
By Roselien