Characterization of PDMS (Sylgard 184)

 Ana Catarina Gomes, Ana Rita Simões, João Magalhães, Rita Gomes

Abstract (Part I)

The main objective of the work developed during the “i9MASKS” project consisted in the characterization of the primary material of the innovative facial mask, the polydimethylsiloxane (PDMS).

The viscoelastic behaviour of the material (storage modulus, loss modulus and tangent delta) was studied by a dynamic mechanical analysis (DMA), its transmittance was measured through spectrophotometry and its contact angle was determined in a wettability test. In addition to this, an elementary analysis of the elastomer was carried out, as well as the obtainment of its calorific value, in order to assess what could happen to the mask at the end of its life cycle. Finally, an alternative material to the PDMS, HB SKIN 30 silicone, was studied because of its economic interest (lower cost). To determine whether the silicone would have the same transparency characteristics as the PDMS, it was also evaluated in a spectrophotometry test.

The results showed that PDMS is a material that presents mostly a elastic behaviour, with excellent transparency characteristics, due to its high transmittance values, whose surface is hydrophobic. Furthermore, the elemental chemical composition of this polymer is essentially made up of carbon, with a relatively high calorific value. To validate the conclusions presented previously, all results were compared with the ones already described by the available literature. Regarding the HB Skin 30 silicone, it was found that it is a translucent material and, therefore, not a viable alternative to PDMS.

The participation and collaboration in this summer course allowed to acquire multidisciplinary practical and theoretical knowledge, especially in Mechanics of Materials, which represents one of the most interesting fields from the point of view of Mechanical Engineering students.

Abstract (Part II)

Within the scope of the summer project “i9Masks”, financed by the FCT (Fundação para a Ciência e Tecnologia) in partnership with Universidade do Minho, we aimed to measure the mechanical properties of PDMS that could be used in protection face masks due to the shortage in PPE (Personal Protection Equipment) caused by the coronavirus Sars-Cov-2 pandemic.

The tests conducted to our material (PDMS) consisted in the measurement of properties such as the storage modulus, loss modulus, tangent delta (the relation between both of the previous referenced), transparecy, calorific value, as well the percentual composition in elements of our sample.

We started with the viscoelastic properties of PDMS (Sylvard 186). For that, it was used the DMA (Dynamic Mechanical Analysis). Our samples were divided between two different cure temperatures (25ºC and 40ºC), which included each one of them four ratios of pre-polymer and cure agent (5:1, 10:1, 15:1 and 20:1). The transparacy of the various samples with diferent ratios was tested using a qualitative method . The calorific value was measured through a calorimeter, and the percentual composition in elements of PDMS in a multimelementar analyzer.

The results showed that viscoelasticity proprieties of our analysed PDMS are coherent with the bibliographic ones. With the qualitative transparency analisys we concluded that, no matter the ratio we used, the transparancy of PDMS is very good. Furthermore, the elemental chemical composition of this polymer is essentially made up of carbon, hydrogen and oxygen. As for the calorific value analysis, since it was just a preliminar test, we could not state any conclusion. 

This summer course allowed us to acquire practical and theoretical knowledge in various engeneering areas, such as Mechanics (CAD softwares), Mechanics of Materials (measurement of numerous materials properties), which will be very helpful for our future as Materials Engenniers. 

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Characterization of PDMS (Sylgard 184)

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