Poly adhesives initial viscosity

Figure 5. The change in dynamic viscosity of Halthane 87-1 segmented poly(urea-urethane) adhesive with time increases dramatically with temperature. Since the initial viscosity decreases with temperature, the plot cross through each other.

Figure 6. Because of the rapid increase in dynamic viscosity of Halthane 88-2 poly(urea-urethane) adhesive caused by a higher concentration of HMDI- aromatic diamine chain extender, the initial viscosities are difficult to determine accurately.

Figure 7. The inverse temperature dependence of initial viscosity and direct dependence of cure chemorheology for poly(urea-urethane) adhesives yield activation energies of 9-12 Kcal/mole for viscous flow and 6-8 Kcal/mole for overall cure, respectively.

Poly(vinyl alcohol) is employed as a modifier of thermosetting resins used as adhesives in plywood and particle board manufacture (314,315). The polymer is added to urea-formaldehyde or urea—melamine—formaldehyde resins to improve initial grab, to increase viscosity, and, in general, to improve the characteristics of the board. 

When water-soluble initiators and surface-active agents are used, relatively stable latices are formed from which the polymer cannot be separated by filtration. In the case of vinyl acetate, the distinctions are more blurred. Our description of Procedure 3-3 above represents a transitional situation between a solution and a suspension process since the product separated from the reaction medium. Between the true suspension and the true emulsion polymerization, we find, according to Bartl [4], the processes for formation of reasonably stable dispersion of fine particles of poly(vinyl acetate) using reagents which are normally associated with suspension polymerization. The product is described as creme-like. The well-known white, poly(vinyl acetate), household adhesives may very well be examples of these creamy dispersions. The true latices are characterized by low viscosities and particles of 0.005-1 /im diameter. The creme-like dispersions exhibit higher viscosities and particle diameters of 0.5-15 fim. 

Bouchard [161] developed a poly(vinyl acetate) adhesive formulation using hydrogen peroxide-zinc formaldehyde sulfoxylate as the initiator system, poly-(vinyl alcohol) and sodium decylbenzene sulfonate as the emulsification system, and lauryl peroxide dissolved in the seed monomer to reduce the viscosity of the final latex (see Table XVIII). To this, from separate streams, a hydrogen peroxide solution, a sodium bicarbonate solution, and vinyl acetate are added. The final latex had a pH of 4.5 and a viscosity of 7 cP at 25°C. 

The high melt viscosity of Larc-TPI at 350°C (10 Pas) prohibits its use as an adhesive for bonding metallic or laminate skins on core honeycombs to make high strength sandwich structures. The work of Chow et al. discussed in Section 4.3.2.2 demonstrates that the melt viscosity of the poly(isoimide) form 21 of Fare TPI is of the order of 10 Pas at 240-250°C, compared to 2 x 10 Pas for polyimide 22 [25]. A semi-crystalline form of Larc-TPI has been obtained by chemical imidisation of the polyamic acid with acetic anhydride and triethylamine [63]. The differential scanning calorimetric curve exhibits an endotherm at 274°C due to melting of the crystalline sites. The value of the initial inherent viscosity (0.22 dl g ) indicates, however, that the lower melt viscosity also results from lower molecular weight polymer. 

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