A. Buchman

Toughening of Epoxy Adhesives by Nanoparticles

With the emergence and commercialization of nanoparticles, new opportunities have emerged for toughening of epoxy adhesives using nanoparticles without sacrificing strength, rigidity and glass transition temperature, as is the case with conventional elastomeric tougheners. Inorganic Fullerene-like tungsten disulfide (IF-WS2) nanoparticles and functionalized nano-POSS (Polyhedral-Oligomeric-Sil-Sesquioxane) were used to study the effects of nanoparticles on the toughening and mechanical properties of low and high temperature curing epoxy systems. Experimental results indicated that IF-WS2 increased the fracture toughness by more than 10 fold in both epoxy systems at very low concentrations (0.3–0.5 wt%) while increasing its storage modulus and preserving its glass transition temperature. Epoxy functionalized POSS demonstrated an increase in toughness in addition to preserving rigidity and thermal properties at higher concentrations (3 wt%). It was postulated that chemical interaction of the sulfide and the epoxy matrix and the inherent properties of WS2 were the decisive factors with respect to the outstanding nano-effect in the case IF-WS2.

Pre-bonding technology based on excimer laser surface treatment

Abstract The application of ArF excimer laser for surface pre-treatment of polycarbonate, polyetherimide, polyaryl ether–ether–ketone (PEEK) composite, fiberglass, aluminum, copper and fused silica was investigated. Various substrates were tested with excimer laser irradiation using various parameters, such as: intensity, repetition rate, and number of pulses. The optimal laser treatment parameters were found for each material needed for achieving maximum adhesional strength of the corresponding bonded joints. Experimental results indicated that UV laser surface treatment improved significantly the adhesion strength compared to conventional treated substrates for all the materials tested. The improved adhesion was correlated with the roughening of the irradiated surface, chemical modification and removal of contamination.

Improved Adhesives Containing CNT/SP1 Nano Fillers

Carbon nanotubes (CNT) have stimulated research due to their wide range of applications. However, their existence as aggregates and the difficulty in debundling and dispersion limits the improvement of properties when used as fillers. Many techniques have been employed to obtain such dispersions including mechanical, ultrasonic, and solution mixing, resulting in limited effect. Attaching a protein moiety such as SP1 showed promising results. SP1 is a thermally stable protein, originally isolated from poplar trees, which self-assembles to an extremely stable 11-nm ring-shape dodecamer. Linkage of CNT to specific peptides on SP1 N-terminus by genetic engineering resulted in 12 CNT binding sites per ring. It was demonstrated by us that the CNT/SP1 complex prevents CNT aggregation and allows its homogenous mixing in water at rather low CNT/protein weight ratio (20:1). In order to obtain homogenous CNTs in a polymer matrix, the dehydrated complex was redispersed in epoxy resin. The CNT/SP1 is covalently bound to epoxy groups prior to polymerization with the curing agent. Dispersion and uniformity were improved by using a speed-mixer and a 3-roll mill. CNT/SP1 in epoxy resin exhibited improved mechanical properties compared with pure unfilled epoxy (EPON® 828/Versamide® 140). CNT/SP1 filler in epoxy adhesive at less than 1% wt. improved peel strength by 50% and shear strength by 24%. In addition, HR-SEM images of 0.7% wt. CNT/SP1 nano-filled epoxy adhesive fracture surfaces demonstrates efficient load transfer and crack arrest by the CNT/SP1 particles. Moreover, comparing the thermal properties of neat epoxy with those of 0.35% and 0.7% wt. CNT/SP1 filled nano-composite was tested using three methods: differential scanning calorimetry (DSC), thermomechanical analysis (TMA), and thermogravimetric analysis (TGA) showed a dramatic improvement increasing Tg by 20°C.

Laser-induced adhesion enhancement of polymer composites and metal alloys

Proper surface treatment of an adherend is among the decisive factors concerning the final quality and durability of an adhesive joint. Various surface treatments are applied to plastic and metal adherends; among them are abrasive treatment, chemical treatment, and plasma etching. An alternative method is presented here which utilizes an excimer UV laser as a new technique for preadhesion surface treatment. Experimental results indicated that preadhesion laser surface treatment improved significantly the shear strength of adhesively bonded aluminum joints as compared with untreated or anodized substrates. Laser treatment also improved the adhesion strength of polycarbonate, polyetherimide, and composite adherends as compared with untreated or simply abraded substrates. Optimal laser treatment parameters (intensity, repetition rate, and number of pulses) depend on the substrate material and its chemical nature. As a result of laser treatment, the mode of failure changed from interfacial to cohesive as long...

Improvement of adhesive bonding strength in sealed anodized aluminium through excimer laser prebond treatment

The feasibility of using an excimer laser as a prebond treatment of sealed anodized aluminium alloys has been demonstrated. Irradiation of sealed chromic acid anodized aluminium by means of pulsed ultraviolet laser (193 nm wavelength, energy density of 0.2–7 J cm−2 per pulse and duration of 24 ns) improved bonding strength by more than 100% compared to that of the sealed anodized but non-treated alloy (using modified epoxy adhesive). The influence of laser treatment on the sealed anodic layer was investigated by various techniques, including scanning electron microscopy, X-ray diffraction and Fourier transform-infrared spectroscopy. Various phenomena, such as morphological changes, ablation, crater formation, melting, gas evaporation, water removal and crystallization, were observed following the laser treatment. The magnitude of these changes was found to depend on both laser-beam energy density and number of pulses.

Preadhesion treatment of thermoplastic adherends using excimer laser

Abstract Preadhesion treatment of two thermoplastic substrates (Lexan polycarbonate and Ultem polyetherimide) by means of ArF excimer laser has been evaluated by comparing the lap shear strengths of polyurethane-bonded joints with untreated, laser-treated and SiC abraded adherends. Experimental results showed a significant increase in lap shear strength following ArF laser treatment. Different laser conditions were needed to achieve the same level of bond strength improvement for both thermoplastic adherends. Surface analysos of the ArF laser-treated adherends and the fractured polyurethane joints revealed morphological and chemical modifications due to the intense ultra-violet laser irradiation. For best results laser irradiation intensity, dose and operating atmosphere should be further studied.

Preadhesion Laser Surface Treatment of Carbon Fiber Reinforced PEEK Composite

Abstract An excimer UV laser (193 nm) was used for preadhesion surface treatment of PEEK (polyetheretherketone) composite. This method presented an alternative to other limited and polluting conventional surface treatment methods. Experimental results indicated that laser preadhesion treatment significantly improved the shear and tensile adhesion strength of structural epoxy FM 300 2K bonded PEEK composite adherends compared with untreated and SiC blasted substrates. Best results were obtained with laser energies of 0.18 or 1 J/P cm.2 Shear strength of laser-treated joints was improved by 450% compared with that of untreated PEEK composite and by 200% compared with SiC-blasted pretreatment at ambient and at extreme temperatures. An order of magnitude of improvement was found in the tensile strength-of laser-treated PEEK composite in a sandwich structure compared with non-treated or abraded sandwich joints. The mode of failure changed from adhesive to cohesive as the number of pulses or laser energy increa...

Preadhesion Laser Treatment of Aluminum Surfaces

Abstract An excimer laser may be used for preadhesion treatment of aluminum alloys. This method presents an alternative to the use of ecologically unfriendly chemicals involved in conventional anodizing pretreatments. Experimental results indicate that preadhesion laser surface treatment significantly improved the shear strength of modified-epoxy bonded aluminum specimens compared with untreated and anodized substrates. The best results were obtained with laser energy of about 0.2 J/Pulse/cm2 where single lap shear strength was improved by 600-700% compared with that of untreated Al alloy, and by 40% compared with chromic acid anodizing pretreatment. The mode of failure changed from adhesive to cohesive as the number of laser pulses increased during treatment. The latter phenomenon has been correlated with morphology changes as revealed by electron microscopy, and chemical modification as indicated by Auger and infrared spectroscopy. It can be concluded that the excimer laser has potential as a precise, c...

Preadhesion laser surface treatment of polycarbonate and polyetherimide

Abstract The effects of carbon dioxide (10.6 μm) and argon fluoride excimer (193 nm) lasers as preadhesion surface treatments for polycarbonate and polyetherimide were studied. Single lap shear specimens bonded with a flexible polyurethane adhesive were utilized to investigate the effect of the various laser treatments on final shear properties and mode of failure. Experimental results based on mechanical properties, scanning electron microscopy and Fourier transform infra-red have indicated that the excimer laser is more effective than the carbon dioxide laser with respect to shear properties and the level of adhesion obtained with the thermoplastic adherends and polyurethane adhesive studied. Polycarbonate with its lower glass transition temperature T g was affected by the carbon dioxide laser to a higher extent than the higher T g polyetherimide. Furthermore, polycarbonate exhibited enhanced shear properties and a higher level of chemical modification following excimer laser irradiation compared to polyetherimide.

Microstructure Characterization of Laser Treated Surfaces

Abstract Excimer laser UV radiation presents a new technology for preadhesion surface treatment of various material adherends. The application of an ArF Excimer laser (193 nm) for surface pretreatment of polycarbonate, polyetherimide, PEEK composite, glass reinforced epoxy composite, aluminum, copper, magnesuim. PZT and fused silica was investigated. Experimental results indicated that UV laser surface treatment improved the adhesional strength significantly compared with conventionally-treated substrates for all the materials tested. The improved adhesion correlated with changes in morphology of the irradiated surface, chemical modification and removal of contaminants, which contributed to a strong and durable adhesive bond. This paper will concentrate only on the connection between the mechanical and morphological effect. The most common microstructure features on the surface after laser irradiation (examined by SEM and AFM) were small conical structures randomly distributed on the irradiated areas. Other features were periodic surface ridges or flat smoothened areas with spread arrays of microcracks. All these morphologies increase the roughness of the surface, enabling mechanical interlocking of the adhesive. It should be noted that the roughness is micronsized, and uniformly spread on the surface, which presents an advantage over abrasive treatments. The distribution of the features and their size were dependent on the laser parameters (intensity and number of pulses). Some mechanisms are presented, and these interesting phenomena are discussed.