Treatments to improve adhesion

Buchman, A. and Dodiuk-Kening, H., Laser surface treatment to improve adhesion. In Mittal, K.L. and Pizzi, A. (Eds.), Adhesion Promotion Techniques — Technological Applications. Dekker, New York, 1999, pp. 205-244. 

Heat treatment to improve adhesion on aluminium and its alloys is normally carried out at 120-140°C for 1 h. 

Historically, surface treatments to improve adhesion of coatings to plastics consisted of mechanical abrasion, solvent wiping, solvent swell that was followed by acid or caustic etching, flame treatment, or corona surface treatment. Each of these treatments has limitations, thus providing a strong driving force for the development of alternative surface preparation methods. Many of the common methods mentioned are accompanied by safety and environmental risks, increased risk of part damage, and expensive pollution and disposal problems. 

The use of plasma surface treatment to improve adhesion is well known [5-19] and several literature sources provide an in-depth discussion of the nature of gas plasmas and their chemistries [1,5,7,10-12]. Although any gas can be ionized using RF excitation, gases such as O2, N2, He, Ar, NH3, N2O, CO2, CF4, and air or some combination of these gases are generally used for surface treatment. 

Film thickness is usually monitored during the process. A beta gauge detects the passage of beta rays through the film bubble, while capacitance gauges measure the increase in thickness as increased capacitance. Blown film lines may also include corona or flame treatment to improve adhesion, sealing operations for bags, and slitters. 

Custodio, J., et al. (2009b). Activation of timber surfaces by flame and corona treatments to improve adhesion. International Journal of Adhesion and Adhesives, 29, 167-172. 

The plasma surface treatment of ETEE to improve adhesion has been studied (34). 

CAA. Chromic acid anodization [74-76]. was developed initially as a treatment to improve the corrosion resistance of aluminum surfaces, but it is also used as a surface treatment for adhesive bonding especially in Europe where it is used extensively in aerospace applieations [29,77],... 

The use of chlorination as surface treatment to improve the adhesion of mbbers to polyurethane adhesives was proposed in 1971. The employ of chlorination in the industry is due to its high effectiveness in improving the adhesion of several types and formulations of mbbers, it is cheap and easy to apply. Furthermore, chlorination makes the mbber surface compatible with many adhesives... 

Not all modified starches are suitable for removal by aqueous dissolution alone. Such modifications of natural starches are carried out to reduce solution viscosity, to improve adhesion and ostensibly to enhance aqueous solubility. Commercial brands vary [169], however, from readily soluble types to those of limited solubility. Indeed, some may be as difficult to dissolve as potato starch if they have been overdried. It is thus very important to be sure of the properties of any modified starch present. If there are any doubts about aqueous dissolution, desizing should be carried out by enzymatic or oxidative treatment. Even if the size polymer is sufficiently soluble, it is important to ensure that the washing-off range is adequate. Whilst the above comments relate to modified starches, other size polymers such as poly(vinyl acetate/alcohol) and acrylic acid copolymers vary from brand to brand with regard to ease of dissolution. 

Metal ions that diffuse to the surface react with atmospheric gases to form hydroxides in a thin layer of high pH [36]. Fowkes improved adhesion of a basic polymer to glass with an acid wash [6, 7] a similar treatment also improved adhesion to epoxy [37], an acidic polymer. The former effect was attributed to replacement of sodium silicate with silanols by ion exchange the latter may result from removing a corrosive layer of metal hydroxides from the interface. IGC and PTD measurements in this study demonstrate a measurable basicity on bare fibers, which other investigators also noted [6,14,17],... 

Surface treatment also improves adhesion to the polymer matrix and resulting physical properties. The combination of particle size and surface treatment is critical in the selection of precipitated calcium carbonate fillers to obtain desired properties. Often graded combinations of ultrafine precipitated CaC03 and larger CaC03 particles are used for optimum properties and value. 

When a corrosive medium contacts the edge of a bonded joint and finds an extremely active surface, such as that produced by a fresh acid treatment of the metal substrate to improve adhesion, corrosion at the metal-adhesives interface can occur. This initial corrosion and the subsequent penetration can take several forms. 

Surface modification (texturing) of polyimide through a metal clustering and migration process is reported. This process involves heat treatment of polyimide coated with a thin copper layer. Subsequent metallization of the textured surface leads to improved adhesion due to mechanical anchoring. Adhesion values of 7-10 lbs/in (ambient) and 4-6 lbs/in (after solder float) have been obtained. 

Surface modification of a polymer prior to metallization is widely used to improve adhesion. The most common surface modifications employed are electric discharge (corona and plasma) and, more recently, ion-beam treatments QJ- Several mechanisms have been proposed for the improved adhesion after such surface modifications (2). These include mechanical interlocking, the elimination of weak boundary layers, electrostatic attractions, and chemical bonding. All of these can play a role in adhesion depending on the surface modification used, metal/polymer system, type of metal deposition, and the extent of polymer preparation employed. However, for low power, short exposure modifications, the formation of new chemical species which can provide nucleation and chemical bonding sites for subsequent overlayers is considered to be of prime importance (3-51. 

Plasma treatment is widely used commercially for polymer surface modification. Plasma discharge treatments are used to improve adhesiveness and printing properties, to improve cell adhesion to tissue culture substrates (1 ) and to etch or clean the surfaces of materials (removal of photoresist materials on semiconductors, for example ( ). The surface characterization of plasma-modified surfaces is important in order to provide greater insight into how the properties are changed. 

Different surface treatments such as peel ply make it possible to roughen and clean composite surfaces and consequently to improve adhesion performance. However, like many other treatments, it is limited by the cohesive failure that may occur in the material. As an alternative, laser ablation appears to be quite an interesting surface pretreatment for polymer composites since it fadhtates efficient control of the surfaces to be adhesively bonded. Furthermore, surface properties must be suitably defined by taking into account the nature of the composite material and the adhesive used. 

The most widespread methods to manufacture the PHB scaffolds for tissue engineering by means of improvement of cell adhesion and growth on polymer surface are change of PHB surface properties and microstructure by salt-leaching methods and enzymatic/chemical/physical treatment of polymer surface [40, 89, 98, 113]. Adhesion to polymer substrates is one of the key issues in tissue engineering because adhesive interactions control cell physiology. One of the most effective techniques to improve adhesion and growth of cells on PHB films is the treatment of polymer surface with enzymes, alkali, or low-pressure plasma [40, 113]. Lipase treatment increases the viable cell number on the PHB film from 100 to 200 times compared to the untreated PHB film. NaOH treatment on PHB... 

Primers are also used in conjunction with a surface treatment either to improve adhesive performance or to increase production flexibility in a bonding operation. Isocyanates have been used for over 50 years as primers on substrates such as rubber. 

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