Bondability

Articles fabricated from FEP resins can be made bondable by surface treatment with a solution of sodium in Hquid ammonia, or naphthalenyl sodium in tetrahydrofuran (64) to faciUtate subsequent wetting. Exposing the surface to corona discharge (65) or amines at elevated temperatures in an oxidizing atmosphere (66) also makes the resins bondable. Some of the more recent work is described in References 67—69. 

Fig. 11. Chemical treatment of Kevlar to increase hydrophilictty and bondability to epoxy resin matrices. Treatment with either strong base or strong acid causes chain scission at the surface. From ref. [57].

Although there is considerable evidence that chemical surface treatments improve the substrate bondability of stainless steels, there is no general agreement on which is the best. One etchant commonly used with stainless steels is an HNO3-HF mixture [128-131] others are chromic acid and ferric chloride/hydrochloric... 

In summary, preliminary studies indicate that plasma spray coatings show great potential for improving the bondability of steel. Potential drawbacks include the requirement for relatively expensive plasma spray equipment and the necessity to keep the substfate temperature below that which would lead to undesirable metallurgical changes. 

UV irradiation on a polymer surface produces chemical modification as well as wettability and bondability improvement. It causes chain scission and oxidation on polymer surfaces. -iven in the presence of an inert gas [45]. Carbonyls are found to be introduced onto polyethylenes on UV irradiation. Sivram et al. [46] have used photochemical treatments for surface modification of polymers. They have generated surfaces of vaying surface energies by simple organic reactions. 

Thermal aging is another simple pretreatment process that can effectively improve adhesion properties of polymers. Polyethylene becomes wettable and bondable by exposing to a blast of hot ( 500°C) air [47]. Melt-extruded polyethylene gets oxidized and as a result, carbonyl, carboxyl, and hydroperoxide groups are introduced onto the surface [48]. 

PVC plastisol proplnts are employed in sounding rockets, jets, aircraft, control motors, tactical weapons and ship models. However, they are not case-bondable (Ref 10)... 

Korai, H. (2001). Effects of low bondability of acetylated fibers on mechanical properties and dimensional stability of fiberboard. Journal of Wood Science, 47(6), 430-436. 

Just as wood may be impregnated with additives to improve physical properties, a variety of porous polymers also benefit from polymer impregnation. As more and more specialized applications arise, it is necessary to produce polymeric materials with very specific surface and bulk properties. The correct combination of properties may not be obtainable using a single polymer or copolymer. However, polymeric materials may be impregnated with an additive in order to modify the surface energy, bondability, hydro-philicity, and other important properties. 

Initial bondability of anodized surfaces was tested in the lap shear configuration using numerous commercial epoxy adhesives. With one exception, all surfaces proved to be bondable and gave acceptable lap shear values. That exception was an anodized film formed... 

The micro channel structure of the device is fabricated in a glass wafer by common procedures (Figure 4.14). To allow sealing of the channels, the whole surface is coated with CYTOP, a Teflon -like polymer. On the one hand it forms a bondable layer and on the other it makes the micro channel surface strongly hydrophopic. Bonding with a CYTOP-coated cover glass plate occurs under moderate pressure at 180 °C. Because sometimes the CYTOP layer peels off and disturbs the fluid flow behavior, the whole device is fabricated in polydimethylsiloxane (PDMS) [71]. 

TF1V has a unique combination of properties that include relatively low processing temperatures, bondability (to itself and other substrates), high flexibility, excellent clarity, low refractive index, and efficient electron-beam cross-linking.91 It also exhibits properties associated with fluoroplastics, namely, very good chemical resistance, weatherability, low friction, and low flammability. Typical properties of the dry grades are summarized in Table 3.9 and those of THV in aqueous dispersion form in Table 3.10. 

In many experiments, it appears that such drastic solvent extraction can remove the major part of the synthetic polymer, showing that the grafted polymer presents, in point of fact, a good "adhesive" bondability. However, in the case of surface modification, a heavy grafting is not necessary and the degre of permanence is a function of the insolubility of the homopolymer in the solvents used in the common course of subsequent treatments. So it can be inferred that this notion of grafting may be dependent on the efficiency of the solvent extraction. 

Flexible epoxy adhesives generally give good bond strengths to heated fluorocarbon surfaces. Table 16.11 shows the effect of surface treatments on the bondability of epoxy... 

TABLE 16.11 Effect of Surface Treatment on Bondability of Epoxy Adhesive to Teflon (Tetrafluoroethylene) and Kel-F (Chlorotrifluoroethylene)65... 

FIGURE 16.6 Bondability index of common and specialty elastomers.79... 

Plastics can also be combined with other materials such as aluminum, steel, and wood to provide specific properties. Examples include extruded PVC/wood window frames and extruded plastic film/ aluminum-foil packaging material. All combinations may require that certain aspects of compatibility such as processing temperature, bondability, and coefficient of expansion or contraction exist. 

Research into the properties and applications of Alcoa s rehydration bondable alumina powders (CP series) has been reported (12-14). The objective of this study was to determine if rehydration bondable aluminas could be successfully incorporated in the matrix of a conventionally formulated FCC catalyst. Success was based on meeting three criteria. First, addition of the alumina would not inhibit the fabrication of well-formed microspheres with diameters typical for FCC catalyst particles. 

---