Adhesive, improving wettability

Film and paper Surface adhesion improved wettability ... 

Tackifying resins enhance the adhesion of non-polar elastomers by improving wettability, increasing polarity and altering the viscoelastic properties. Dahlquist [31 ] established the first evidence of the modification of the viscoelastic properties of an elastomer by adding resins, and demonstrated that the performance of pressure-sensitive adhesives was related to the creep compliance. Later, Aubrey and Sherriff [32] demonstrated that a relationship between peel strength and viscoelasticity in natural rubber-low molecular resins blends existed. Class and Chu [33] used the dynamic mechanical measurements to demonstrate that compatible resins with an elastomer produced a decrease in the elastic modulus at room temperature and an increase in the tan <5 peak (which indicated the glass transition temperature of the resin-elastomer blend). Resins which are incompatible with an elastomer caused an increase in the elastic modulus at room temperature and showed two distinct maxima in the tan <5 curve. 

The application of surface treatments to mbbers should produce improved wettability, creation of polar moieties able to react with the adhesive, cracks and heterogeneities should be formed to facilitate the mechanical interlocking with the adhesive, and an efficient removal of antiadherend moieties (zinc stearate, paraffin wax, and processing oils) have to be reached. Several types of surface preparation involving solvent wiping, mechanical and chemical treatments, and primers have been proposed to improve the adhesion of vulcanized SBR soles. However, chlorination with solutions of trichloroisocyanuric acid (TCI) in different solvents is by far the most common surface preparation for mbbers. 

The reason for surface modification of a polymer is in most cases a wish to improve wettability and adhesion towards more hydrophilic materials. Both adhesion and wettability are interfacial phenomena. 

The common polymers are composed of a small number of elements whose XP spectra are simple (generally C Is plus one or two peaks from Ols, Nls, FIs and Cl 2s, 2p). Common contaminants contain additional elements such as S, P, Si, A1 and heavy metals, and the presence of these elements, even in low concentrations, can be detected very easily. Polymer surface modification is an area in which XPS has been fruitfully applied, notably in the study of commercial pretreatments aimed at improving wettability and general adhesion characteristics. 

Plasma oxidation of fibers is an example of a treatment aimed at chemically modifying the surface to improve a surface property. These treatments have wide application in industry and are used to improve wettability and printability of plastics, the adhesion of materials to surfaces including tissue culture cells, and a variety of other applications (36). 

Thermoplastic materials often have a lower surface energy than do thermosetting materials. Thus, physical or chemical modification of the surface is necessary to achieve acceptable bonding. This is especially true of the crystalline thermoplastics such as polyolefins, linear polyesters, and fluoropolymers. Methods used to increase the surface energy and improve wettability and adhesion include... 

Strong joints with epoxy adhesives can be made to polyethylene surfaces which have been oxidized by a variety of techniques (4, 5). The general belief has been that the presence of polar groups on the polymer surface creates an affinity for the polar epoxy adhesive which improves wettability and results in a strong adhesive joint. 

It has been well known that weak interfaces between the inorganic fillers and the organic matrix reduce the mechanical strength of bone cement [38,40,44,45]. The interfacial adhesion strength can be enhanced by plasma treatment, which is generally due to the improved wettability and possibly to the chemical bonds between the filler and the resin [46,47]. Especially in acrylic bone cement, chemical bonds may have an important role in improving the mechanical strength by the plasma treatment. 

The surface chemisfry of flame-freafed polypropylene closely correlates wifh fhe weffabilify of the surface. Figure 22.8 also shows fhe ESCA O/C atomic ratio of flame-freafed polypropylene as a function of fhe equivalence ratio. The amounf of surface oxidation generated by the flame follows fhe same trend as the wettability. The maximum O/C ratio of 0.18 is obtained at q) = 0.92 - 0.94. Within this range, the gas phase concentrations of surface oxidizers in fhe flame are high. This surface oxidation is fhe reason for the improved wettability and adhesion properties of flame-treated polypropylene. A detailed discussion of the flame and surface chemistry involved in surface freafing is presented in Section 22.4. 

Polymer surface restructuring has become a topic of considerable interest in recent years. It is of particular interest in efforts to increase the surface energy of relatively hydrophobic materials including silicone polymers. This can give benefits such as improved adhesion, better wettability, etc. but such efforts are often frustrated by a progressive hydrophobic recovery once the treatment ceases. The two most important areas of this type in the organosilicon polymer field are plasma treatment and corona discharge treatment. These two treatments are closely related. The former is often used to improve adhesion of... 

Plasma technologies have been investigated for quite some time with the aim of improving wettability and thus the adhesion of coatings. However, a much broader range of applications is feasible with plasma (Buyle, 2009) these apphcations include the improvement of printability and dyeability (Rahman and Nur, 2014), and antishrink treatment of wool, the scouring of wool (Rahman and Nur, 2014), sterilization, and the desizing of cotton. 

To enhance the adhesive strength, the surface properties of substrate are very important. The surface treatments are often used to enhance the adhesive strength between the coating and the substrate, as well as to enhance the surface energy of substrate - improving wettability of coating. If adhesive problem occurs, check out the surface treatment processes such as flame, plasma, or corona. Corona treatment does not persist permanently, therefore it should be done in-line, the corona is often applied directly before the coating station. 

The results on wettability showed that water wettability was lower on the heat-treated wood, but wettability with the PF adhesive improved with the heat treatment of the wood. It was found that the difference in the effective penetration of PF adhesive due to the heat treatment did not have crucial effect on the shear strength of the bonded specimens. 

Porous PE membranes on which a layer of acrylonitrile was deposited were treated with argon plasma. The modified membranes used as a separator for a lithium-ion battery showed improved wettability, electrolyte retention, and interfacial adhesion between the electrodes and the separator, and hence the performance of the battery was also better (Kim et al. 2009). 

For this reason, the polymer substrate treatment represents a very important step in the technology of metallic or ceramic coating on the polymer substrate. Therefore, noble metals and other low reactivity metals do not wet the untreated polymer surfaces, forming three-dimensional spherical clusters growing in a Volmer-Weber mode. Surface modification of the hydrophobic polymer surface onto a hydrophilic one can be achieved by wet (acid, alkali), dry (plasma), and radiation treatments (ultraviolet radiation and laser), without affecting the bulk properties. Consequently, application of different pretreatment methods represents an efficient way to improve wettability and thin metal adhesion. 

Kusano [40] found that neither corona nor plasma treatments improved peel strength with a polyurethane adhesive despite improved wettability as indicated by water contact angles. FTIR indicated substantial oxidation after the corona treatment but only minor oxidation after the plasma treatment. 

In 1994 Uchida et al. grafted polyfethylene glycol) methacrylate onto the surfaces of PET film by a simultaneous UV irradiation-grafted polymerization to improve wettability, antistatic property, and adhesion, and presumed that the model for the grafted surface in direct contact with a solvent of grafted chains was just like brushes (Figure 5.3) [49]. Subsequently, Uchida and Ikada also confirmed that the topography of water-soluble polymer... 

The cold-plasma treatment improved the fibers superficial properties, such as adhesion of the epoxydic resin for the realization of composite materials [419 23] and improved wettability and rewettability [424-426]. 

---