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Effect and characterization of plasma treatments on adhesively bonded joints for automotive applications

Andrea Iadarola

Effect and characterization of plasma treatments on adhesively bonded joints for automotive applications.

Rel. Giovanni Belingardi, Raffaele Ciardiello, Davide Salvatore Paolino. Politecnico di Torino, Corso di laurea magistrale in Ingegneria Meccanica (Mechanical Engineering), 2021

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In the present study the effect of low-pressure vacuum plasma and cold atmospheric pressure plasma surface treatments of polypropylene samples with 12% of talc addition substrates is analysed in order to find an efficient procedure which is able to increase the adhesion with a polyolefin hot-melt adhesive typically used in automotive industry. The polymeric substrates were treated at first using different plasma gas mixtures and varying some process parameters such as power and working distance of the jet in order to find the most suitable configuration considering the process gas to be used. Once identified the most effective plasma treatment for both low-pressure and atmospheric pressure plasma treatments, a deeper and more precise analysis of the process is carried out, taking into account both the chemical and mechanical effect of plasma on bonded joints and on the polymeric substrates. The effect of these treatments was studied through a chemical and optical surface characterization, analysing the outermost surface of the substrates by means of Optic Microscopy, Micro-Raman spectroscopy, Micro-IR spectroscopy and Attenuated Total Reflection (ATR) analysis. The critical issue in this case study was that the adhesive under investigation is a non-polar polyolefin and, for this reason, the plasma treatment should not produce polar functional groups on the surface of the substrates; therefore, the oxygen amount on the surface has to be as low as possible and the most commonly used treatments using air or nitrogen plasma are not suitable for our purpose. After the chemical and optical characterization, untreated and plasma treated specimens were used to create single lap joints and subsequently tested by lap shear test in order to evaluate the mechanical characteristics of the bonded joint. Experimental results show that low-pressure plasma treatment is a more effective solution with respect to the atmospheric pressure plasma jet treatment when a polyolefin hot-melt adhesive is used to bond a polyolefin substrate, such as polypropylene. Despite the several efforts in order to obtain a cohesive failure of the bonded joints, we obtained only an increase of the maximum load and shear strength from the lap shear tests after low-pressure plasma treatments, meaning that the maximum strength of the hot-melt adhesive has not been totally exploited. Using atmospheric plasma resulted to be a less effective solution, probably due to its better ability to make the surfaces richer in oxygen and other polar functional groups.

Relators: Giovanni Belingardi, Raffaele Ciardiello, Davide Salvatore Paolino
Academic year: 2020/21
Publication type: Electronic
Number of Pages: 104
Corso di laurea: Corso di laurea magistrale in Ingegneria Meccanica (Mechanical Engineering)
Classe di laurea: New organization > Master science > LM-33 - MECHANICAL ENGINEERING
Aziende collaboratrici: UNSPECIFIED
URI: http://webthesis.biblio.polito.it/id/eprint/19525
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