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A low-temperature, atmospheric pressure helium and oxygen plasma has been used for the surface preparation of aluminum 2024 prior to adhesive bonding. The plasma converted the aluminum from a water contact angle (WCA) of 79° to down to 38° within 5 s of exposure, while sanding reduced the WCA to only 51°. Characterization of the aluminum surface by X-ray photoelectron spectroscopy revealed a decrease in carbon contamination from 70 to 36% and an increase in the oxygen content from 22 to 50% following plasma treatment. Similar trends were observed for sanded surfaces. Lap shear results demonstrated bond strengths of 30 ± 2 MPa for the sanded aluminum vs. 33 ± 1 MPa for plasma-treated aluminum, where sol–gel and primer coatings were added to the surface preparation. Following seven days of aging, wedge crack extension tests revealed cohesive failure percentages of 86, 92, and 96% for sanded, plasma-treated, and sanded/plasma-treated aluminum, respectively. These results indicate that atmospheric pressure pl...

In order to avoid using polyvinyl alcohol (PVA), an eco-friendly sizing technology with atmospheric pressure plasma treatment and green sizing recipes has been developed and evaluated with respect to sizing properties and desizing efficiency. The results show that the eco-friendly sizing technology can endow cotton yarn with better sizing properties, including significantly improved size-pick-up, breaking strength, breaking elongation, abrasion resistance and substantially reduced yarn hair, than the traditional sizing technology with the use of PVA. Compared with a typical traditional sizing technology using PVA and modified starch, the optimized eco-friendly sizing technology can impart the yarn an increase of 19.4%, 5.3%, 3.4% and 169.2% for the size-pick-up, breaking strength, breaking elongation and the abrasion resistance time, respectively, and a reduction of 59.3% for the yarn hairiness index value at level 1. The sizing properties can be obviously improved by the atmospheric pressure plasma treatment, which can roughen the fiber surface, etch away the hydrophobic cuticle layer and introduce polar groups. The glycerol in the green sizing recipes can effectively reduce the yarn hairiness and increase size-pick-up and abrasion resistance. The eco-friendly sizing technology has no observable negative influence on desizing of cotton fabrics. Furthermore, a better water diffusion in the fabric can be achieved because of the improved hydrophilicity by using the plasma treatment.

Adhesive bonding offers many advantages over mechanical fastening, but requires certification before it can be incorporated in primary structures for commercial aviation without disbond-arrestment features or redundant load paths. Surface preparation is widely recognized as the key step to producing robust and predictable adhesive bonds. Surface preparation by laser ablation provides an alternative to the expensive, hazardous, polluting, and less precise practices used currently such as chemical-dip, manual abrasion and grit blast. This report documents preliminary testing of a surface preparation technique using laser ablation as a replacement for the chemical etch and abrasive processes currently applied to Ti-6Al-4V alloy adherends. Surface roughness and surface chemical composition were characterized using interference microscopy and X-ray photoelectron spectroscopy, respectively. A technique for fluorescence visualization was developed which allowed for quantitative failure mode analysis. Wedge crack extension testing in a hot, humid environment indicated the relative effectiveness of various surface treatments. Increasing ablation duty cycle reduced crack propagation and adhesive failure. Single lap shear testing showed an increase in strength and durability as laser ablation duty cycle and power were increased. Chemical analyses showed trends for surface chemical species, which correlated with improved bond strength and durability.

A review is presented on the surface preparation of polymers and composites using atmospheric pressure plasmas. This is a promising technique for replacing traditional methods of surface preparation by abrasion. With sufficient exposure to the plasma afterglow, polymer and composite surfaces are fully activated such that when bonded and cured with epoxy adhesives, they undergo 100% cohesive failure in the adhesive. Depending on the material, the lap shear strength and crack delamination resistance (GIC) can be increased several fold over that achieved by either solvent wiping or abrasion. In some cases, a plasma-responsive layer must be incorporated into the top resin layer of the composite to achieve maximum bond strength to the adhesive. Adhesion does not correlate well with water contact angle or surface roughness. Instead it correlates with the fraction of the polymer surface sites that are oxidized and converted into active functional groups, as determined by x-ray photoelectron spectroscopy and infrared spectroscopy.

An atmospheric pressure helium and oxygen plasma has been used for the surface preparation of 410 stainless steel and carbon-fiber epoxy laminates prior to bonding to themselves or to each other. Lap shear results for stainless steel coupons and carbon-fiber epoxy laminates demonstrated an 80% and a 150% increase in bond strength, respectively, after plasma activation. Following 7 days of aging, wedge crack extension tests revealed a crack extension length of 7.0 mm and 2.5 mm for the untreated and plasma-activated steel. The untreated stainless steel had 30% cohesive failure compared to 97% for steel activated with the plasma. Surface analysis by X-ray photoelectron spectroscopy showed that carbonaceous contamination was removed by plasma treatment, and specific functional groups, e.g. carboxylic acids, were formed on the surface. These functional groups promoted strong chemical bonding to the epoxy film adhesive. Atmospheric pressure plasmas are an attractive alternative to abrasion techniques for surface preparation prior to bonding.

Summary form only given. Atmospheric pressure plasma treatment is a key process for surface preparation prior to adhesive bonding of plastics and composites for use in the aerospace, automotive, medical device, and electronics industries. A review is presented on methods for surface preparation of polymers and composites using low-temperature, atmospheric pressure radio frequency helium and oxygen plasmas. This is a promising technique for replacing traditional methods of surface preparation such as peel ply and abrasion. The plasma source generates an afterglow containing ∼1×1017 cm−3 oxygen atoms, ∼1×1017 cm−3 metastable oxygen molecules (1Δ g ), and ∼4×1014 cm−3 ozone molecules. With sufficient exposure to the afterglow, polymer and composite surfaces are fully activated such that when bonded and cured with epoxy adhesives, they undergo 100% cohesive failure. Depending on the material, lap shear strength and delamination resistance can be increased over 50% from that activated by solvent wiping or abrasion. Surface analysis by water contact angle and AFM indicates that there is no correlation between bond strength and surface energy or surface roughness. Instead, bond strength correlates with the fraction of the polymer surface sites that are oxidized and converted into carboxylic acid groups, as determined by x-ray photoemission and infrared spectroscopy. Polymers with aromatic groups in the backbone are especially suitable for activation with the atmospheric pressure plasma. The activation mechanism, surface characterization results, and bonding strength improvement are discussed in detail.