Deposition and evaluation of thermoplastic polyurethane on paper substrate for test specimen production

This work presents the development and characterization of a process for manufacturing test specimens using thermoplastic polyurethane (TPU) on paper substrates, which serve as elastomeric substrates for the manufacturing of piezoresistive sensor devices using the Graphite on Paper (GoP) technique. The study of piezoresistive sensor elements is based on their behavior in response to physical stimuli such as mechanical stress or compression, resulting in variations in electrical resistance obtained from the deposition of graphite films on paper, combined with the elastomer. By leveraging the piezoresistive effect of graphite, innovative technological solutions are sought, enabling the creation of different types of sensors for measuring and monitoring a wide range of physical quantities. The proposed process utilizes commonly available materials in the market and offers a low-cost alternative compared to traditional techniques used for semiconductor-based devices. To create the test specimens, a perforated matrix made of polylactic acid (PLA) was produced using 3D printing, with dimensions specified in ISO 1924-2/2008, and a thickness limitation of 2 mm. TPU is deposited into the perforated grooves of the developed matrix on the paper substrate, filling the spaces intended for the addition of the elastomeric polymer. The deposition process is carried out similar to silk-screen printing, ensuring uniform thickness of the test specimens. The curing process takes place over a period of 48 h at room temperature under the weight of granite structures covered with PVC sheets. After curing, the test specimens are demolded. The obtained results consist of TPU + Paper strips with an average thickness of approximately 2.1357 mm, with a mean thickness variation of 0.10688 mm, representing an average variation of 4.947 % among the strips. By disregarding the highest and lowest results from the measurement series, samples with an average thickness of 2.1327 mm and variations of 0.09250 mm were obtained, representing an average thickness variation of 4.328 %. These results are promising for the development of flexible sensor devices for applications in industrial equipment, soft robotic systems, healthcare, and bioengineering fields.