Effects of plasma treatments of polypropylene adhesive joints used in the automotive industry

Abstract

Plasma treatment has been used in recent years to activate the surfaces of adhesive substrates and thus as an adhesion promoter between adhesive and substrates. The use of plasma treatments is widely adopted in the automotive industries especially for polymers that present low surface energy, such as polypropylene. In this work, polypropylene substrates used in the automotive industries have been treated with two different techniques: vacuum and atmospheric plasma. Then, polyurethane and methacrylate adhesives have been used to bond single lap joints (SLJs). Typically, these two adhesives cannot bond polypropylene substrates without surface treatments. An experimental plan has been designed to investigate the process parameters that can increase the functional polar groups (FPGs) maximizing the adhesion strength. Besides the types of plasma, two different gas carriers (air and nitrogen) and different treatment times have been investigated. The substrates, treated and not treated, have been assessed through scanning electron microscopy, energy-dispersive X-ray analysis, and Fourier-transform infrared spectroscopy to quantitatively assess the increment of FPGs after the different treatments. The experimental plan shows that the atmospheric plasma can improve the surface of the substrates by using a smaller time. Mechanical tests on SLJs show that methacrylate and polyurethane cannot bond polypropylene substrates without the plasma treatment. On the other hand, the treated substrates can form a strong bonding with the adhesive since all SLJs exhibit a substrate failure. Mechanical tests have been also carried out after three different aging cycles showing that the adopted plasma treatment is not affected by the aging cycles.

Effect of the Atmospheric Plasma Treatment Parameters on the Surface and Mechanical Properties of Carbon Fabric

“…The oxygen of the surrounding air reacted with carbon: free radicals, which had not yet decayed, acted by binding to oxygen in the air since a certain distance was set between the plasma jet and fabric. This result was also noted by Ciardiello et al [ 25 ] who showed that polypropylene surfaces treated with nitrogen-based plasma exhibited a high content of oxygen that was related to the reaction with the air in the environment of the plasma treatment. Nonetheless, the induced polar functional groups and radicals formed onto the surface after combination with oxygen allow the wettability of strongly nonpolar carbon fabrics to be increased by working in parallel with the direct functionalization achieved with the nitrogen-based gas.…”

“…The oxygen of the surrounding air reacted with carbon: free radicals, which had not yet decayed, acted by binding to oxygen in the air since a certain distance was set between the plasma jet and fabric. This result was also noted by Ciardiello et al [25] who showed The spectra illustrate particular differences between treated and untreated samples. The peaks detected between 2875 and 2972 cm −1 , typical of CH 2 and CH 3 bonds, are ascribed to an unsaturated polyester, poly(4,4-dipropoxy-2,2-diphenylpropane fumarate) since high compatibility of the chemical composition has been found in the software database, LabSolutions IR [23].…”

Quality Analysis of Bonded Joints in the Renovation of Plastic Automotive Parts

“…The activation of adhesive substrate surfaces by plasma treatment of polypropylene joints used in the automotive industry was studied by Ciardiello [18], who applied this method to polymers that have low surface energy and are widely used in the automotive industry. In his experiment, he used two techniques, namely vacuum and atmospheric plasma, for the treatment of polypropylene substrates and applied polyurethane and methacrylate adhesives for the purpose of forming a bonded joint.…”

Experimental Study on the Effect of Bonding Area Dimensions on the Mechanical Behavior of Composite Single-Lap Joint with Epoxy and Polyurethane Adhesives

“…Although there are international standards that define the geometry and testing conditions for various materials [23], different geometries and boundary conditions are used to take into account the effective working condition of the adhesive joints. These parameters include substrate materials, adhesive type [24], overlap length [25], adhesive thickness [26,27], joint width [18], fillets at the edges [28][29][30], and surface treatment [31,32], and play roles in a joint which are difficult to predict.…”