Polypropylene surface modification by low pressure plasma to increase adhesive bonding: Effect of process parameters

The purpose of this study is to evaluate the effect of a cold plasma surface treatment of polypropylene substrates with the aim of increasing their adhesion characteristics. These substrates were treated with plasma, using different process parameters such as power, time and working gas. The effect of the treatment has been studied through a surface characterization, analyzing the chemical species created on the topmost layer of the substrates thanks to the plasma treatment and evaluating the surface energy, through contact angle measurements. Then, untreated and plasma treated samples with various parameters were used to create single overlapping bonded joints and evaluate the effect of the surface treatment on the mechanical characteristics of the joints. Experimental results show that plasma treatment is an effective treatment for the surface preparation of polypropylene adhesive bonding. In fact, the increase in surface energy and the formation of chemical bonds between oxygen and carbon have favored the adhesion, thus increasing the mechanical strength of the joint

A Response Surface Methodology Approach to Improve Adhesive Bonding of Pulsed Laser Treated CFRP Composites

In this work, a response surface-designed experiment approach was used to determine the optimal settings of laser treatment as a method of surface preparation for CFRP prior to bonding. A nanosecond pulsed Ytterbium-doped-fiber laser source was used in combination with a scanning system. A Face-centered Central Composite Design was used to model the tensile shear strength (TSS) of adhesive bonded joints and investigate the effects of varying three parameters, namely, power, pitch, and lateral overlap. The analysis was carried out considering different focal distances. For each set of joints, shear strength values were modeled using Response Surface Methodology (RSM) to identify the set-up parameters that gave the best performance, determining any equivalent conditions from a statistical point of view. The regression models also allow the prediction of the behavior of the joints for not experimentally tested parameter settings, within the operating domain of investigation. This aspect is particularly important in consideration of the process optimization of the manufacturing cycle since it allows the maximization of joint efficiency by limiting the energy consumption for treatment

Low-pressure plasma treatment of CFRP substrates for epoxy-adhesive bonding: an investigation of the effect of various process gases

This work reports a systematic and quantitative evaluation of the effects induced on the adhesive properties of carbon fiber reinforced polymer (CFRP) substrates by various vacuum cold-plasma treatments. In particular, surface activation of the CFRP substrates was performed using several combinations of exposure time, plasma power, and processing gas (air, O 2 , Ar and N 2 ). By comparing these plasma treatments with conventional techniques of abrasion and peel ply, it was possible to substantially increase the performance of the adhesively bonded joints made by overlapping the CFRP substrates with a structural epoxy resin. On each differently treated surface, measurements of roughness and of wettability were performed, allowing the evaluation of the increase in surface energy after the plasma treatment. XPS analyses allowed the identification of the chemical state of the substrates and showed an in-depth functionalization of the outer layer of the CFRP material. The experimental results show that an engineered plasma treatment of the CFRP substrates allows one to modify the surface morphology and both wetting and chemical activation properties of the treated surfaces, resulting in an increased mechanical shear strength of the joints

Improved Bond Strength of Cyanoacrylate Adhesives Through Nanostructured Chromium Adhesion Layers

The performance of many consumer products suffers due to weak and inconsistent bonds formed to low surface energy polymer materials, such as polyolefin-based high-density polyethylene (HDPE), with adhesives, such as cyanoacrylate. In this letter, we present an industrially relevant means of increasing bond shear strength and consistency through vacuum metallization of chromium thin films and nanorods, using HDPE as a prototype material and cyanoacrylate as a prototype adhesive. For the as received HDPE surfaces, unmodified bond shear strength is shown to be only 0.20 MPa with a standard deviation of 14 %. When Cr metallization layers are added onto the HDPE at thicknesses of 50 nm or less, nanorod-structured coatings outperform continuous films and have a maximum bond shear strength of 0.96 MPa with a standard deviation of 7 %. When the metallization layer is greater than 50 nm thick, continuous films demonstrate greater performance than nanorod coatings and have a maximum shear strength of 1.03 MPa with a standard deviation of 6 %. Further, when the combination of surface roughening with P400 grit sandpaper and metallization is used, 100-nm-thick nanorod coatings show a tenfold increase in shear strength over the baseline, reaching a maximum of 2.03 MPa with a standard deviation of only 3 %. The substantial increase in shear strength through metallization, and the combination of roughening with metallization, may have wide-reaching implications in consumer products which utilize low surface energy plastics

Ti 6Al-4V FSW weldability: mechanical characterization and fatigue life analysis

Friction stir welding (FSW) is an innovative solid-state process, patented in 1991 by The Welding Institute, which avoids solidification problems associated with conventional fusion welding, providing joints having excellent mechanical and metallurgical properties. Due to its many advantages, FSW is successfully applied to weld various aluminium, magnesium and copper alloys. In recent years, FSW of high melting temperature materials such as steels and titanium alloys has become a key research topic. However, the high softening temperature of high melting temperature materials result in extreme stress of the pin tool during FSW, which adds to the difficulty in creating defect-free joints, especially for titanium alloys. This work is a preliminary investigation of FSW application on titanium alloy Ti\u20136Al\u20134V. The research focused on optimization of tool material and geometry, as well as process parameters. Complete microstructural and microhardness evaluations were conducted in addition to surface examinations. In order to evaluate the service behaviour of the joints realized with the optimized parameters, an in-depth investigation was also conducted on the fatigue properties of FSW joints

Resistenza a invecchiamento di un adesivo per impiego navale

Gli adesivi presentano numerosi vantaggi, che possono essere ottimamente sfruttati nella costruzione e riparazione di navi e imbarcazioni di qualunque tipo

Trattamento delle superfici - Il plasma freddo migliora l'incollaggio

I plasmi sono mezzi chimicamente attivi. In relazione alle modalit\ue0 di attivazione e alla loro potenza di lavoro possono generare temperature molto alte o basse; nel primo caso si parla di plasma termico, nel secondo di plasma freddo. L\u2019ampio intervallo di temperatura consente una grande variet\ue0 di applicazioni. Il plasma termico, grazie alle elevatissime temperature generate, \ue8 ampiamente utilizzato in ambito metallurgico per il taglio e la saldatura dei metalli. Le applicazioni industriali della tecnologia del plasma freddo, pur essendo le pi\uf9 svariate, possono essere tutte ricondotte a operazioni di modifica superficiale: attivare, pulire, rivestire le superfici. Un trattamento in plasma freddo consente, infatti, di ricerca ottenere superficialmente dei composti chimici reattivi che non sono ottenibili con procedimenti chimici tradizionali. Un considerevole vantaggio consiste nel fatto di poter realizzare un trattamento che coinvolge solo gli strati superficiali di materiale, che lascia quindi inalterate le propriet\ue0 meccaniche generali, adottando tra l\u2019altro temperature di processo poco elevate che non danneggiano eventuali substrati degradabili. Proprio quest\u2019ultimo vantaggio offre una possibile soluzione ai problemi di bagnabilit\ue0 e, conseguentemente, di incollaggio di alcune tipologie di polimeri, tra cui per esempio il polietilene o il polipropilene, che presentano scarsissime propriet\ue0 di adesione ma un vasto campo di impiego. Queste le ragioni alla base di una ricerca finalizzata alla valutazione dell\u2019effetto di un trattamento in plasma freddo sulle caratteristiche di adesione del polietilene. L\u2019obiettivo \ue8 quello di individuare i parametri di macchina \u2013 potenza e tempo di esposizione \u2013 pi\uf9 idonei a garantire il miglior risultato in termini di resistenza a taglio di un giunto incollato

Saldatura Laser di componenti in Inconel 718 per usi aeronautici

Le leghe di nichel rappresentano un gruppo di materiali molto particolare, caratterizzato da elevate qualit\ue0 meccaniche e di resistenza alla corrosione. La capacit\ue0 di mantenere inalterate tali caratteristiche, anche a temperature estremamente elevate, rende questi materiali idonei all\u2019utilizzo nelle applicazioni pi\uf9 estreme. La saldatura delle leghe di nichel viene genericamente realizzata mediante processi ad arco elettrico. Tuttavia, per minimizzare le alterazioni subite dal materiale, sta prendendo sempre pi\uf9 campo l\u2019applicazione di tecniche pi\uf9 avanzate, come quella basata sull\u2019uso di sorgenti laser. Nel presente lavoro, viene affrontato il problema della realizzazione, mediante tecnologia laser, di giunti a sovrapposizione tra lamiere di diverso spessore di una lega Ni-Cr-Fe denominata Inconel 718, caratterizzata da eccellente resistenza alla corrosione e da elevate caratteristiche meccaniche

Effetto dei parametri di processo e dell'apporto termico sulla qualit\ue0 di pannelli saldati per uso navale

I processi di saldatura ad arco sono tra le tecniche pi\uf9 utilizzate per la giunzione di grandi strutture in acciaio, specialmente nel settore della costruzione navale. In particolare, la saldatura ad arco sommerso trova ampio impiego nella giunzione di lastre piane di svariati spessori. La sua flessibilit\ue0 si adatta bene al fatto che, negli ultimi anni, ai progettisti \ue8 stato imposto di utilizzare strutture pi\uf9 leggere e quindi lamiere pi\uf9 sottili per ridurre i pesi, incrementare il risparmio di carburante e soprattutto aumentare il carico utile. Il principale svantaggio di tutte le tecniche di saldatura per fusione \ue8 che la generazione dell\u2019arco elettrico crea un riscaldamento locale del pezzo, che provoca severi gradienti termici nel componente, e il rapido raffreddamento che segue genera tensioni residue e distorsioni. Nella costruzione navale, dove la saldatura per la realizzazione di pannelli rinforzati \ue8 di larghissimo impiego, le tensioni residue possono portare ad un cedimento prematuro in alcune zone. Inoltre, le distorsioni possono essere particolarmente problematiche nel caso di assemblaggio di pannelli di basso spessore, nei quali l\u2019eccessiva deformazione pu\uf2 comportare disallineamento delle parti e spesso richiede costosi e lunghi accorgimenti, come le calde di ritiro, per rientrare nei criteri di accettabilit\ue0 previsti. Scopo del presente studio \ue8 la valutazione dell\u2019effetto dei parametri di saldatura, ed in particolare dell\u2019apporto termico, sulla distorsione di pannelli rinforzati

Effect of cold plasma treatment on surface roughness and bonding strength of polymeric substrates

For an effective application of polymers, it is essential to have good adhesion behaviour to ensure good mechanical properties and durable components. Unfortunately, in general terms, polymers are characterized by high chemical inertness, which leads to very low surface energy values and, consequently, poor adhesive properties; this is particularly true for polyolefins. In this study, the effects of low pressure plasma treatment on surface roughness of polyethylene and polypropylene samples and on shear properties of adhesive bonded joints based on these substrates have been investigated. In particular, the optimization of three plasma process parameters, exposure time, voltage and working gas, were studied performing roughness measurement, contact angle evaluation and lap-shear tests. The experimental results show that the optimized plasma process may remarkably change the surface morphology, increasing wettability properties of the surfaces and shear strength of the bonded joints. These good properties remain almost unchanged even after some days of storage in the laboratory