Liquid rubber bonding

Vulcanization by the traditional curing methods utilized in the rubber industry is based on sulfur or sulphur-containing compounds and is also the most widely applied technique for curing liquid rubbers containing macromolecules with double bonds. Chinons, peroxides, phenol formaldehyde resins, and other compounds are often used for curing liquid rubbers as an alternative sulfur vulcanization. 

We believe that the Hycar 1312 is not cured. In these systems there exist only the van der Waals attractive and/or hydrogen bonding type forces between the epoxy matrix and the liquid rubber particles. In such two-phase systems the liquid rubber merely acts as a diluent and will show physical properties analogous to mechanical mixtures of two different polymers. 

High temperature epoxy resins are brittle materials, and one method of improving their fracture properties is to incorporate reactive liquid rubbers in the formulations In situ phase separation occurs during cure the cured rubber-modified epoxy resins consist of finely dispersed rubber-rich domains ( 0.1-S pm) bonded to the epoxy matrix. TTT diagrams can be used to compare different rubber-modified systems. 

Figure 5. Influence of type of liquid rubber and weight fraction on the lap shear strength of bonded aluminum sheets. Key A, ETBN , PPU , PPU/ETBN (50/50) calculated and , PPU/ETBN (50/50) found.

Leir, C. M. Galkiewicz, R. K. Kantner, S. S. Mazurek, M., Telechelic SUoxanes with Hydrogen-Bonded Polymerizable End Groups. I. Liquid Rubbers and Elastomers. J. Appl. Polym. Sci. 2010,117,756-766. 

The reason why I take up these polymers in this review is that (1) CB-BR is a cure type solid rubber carrying OH groups and Cl atoms as active species besides double bonds, (2) viologen elastomers are thermoplastic elastomers (TPE) derived from liquid rubber, indicating some characteristic behaviors, i.e., high tensile properties and special functions, and (3) ABA type liquid crystalline elastomers are also new TPE at room temperature, but behave as liquid rubber at high temperature. 

Engine/suspension mounting metal to rubber bonding Badge and trim fixing pressure sensitive, hot melt and liquid forms... 

All polymers, if really solid, should have moduli above the lowest level we have calculated - about 2 GN m - since they are held together partly by Van der Waals and partly by covalent bonds. If you take ordinary rubber tubing (a polymer) and cool it down in liquid nitrogen, it becomes stiff - its modulus rises rather suddenly from around lO GNm" to a proper value of 4GNm . But if you warm it up again, its modulus drops back to 10 GNm . ... 

Many of the most floppy polymers have half-melted in this way at room temperature. The temperature at which this happens is called the glass temperature, Tq, for the polymer. Some polymers, which have no cross-links, melt completely at temperatures above T, becoming viscous liquids. Others, containing cross-links, become leathery (like PVC) or rubbery (as polystyrene butadiene does). Some typical values for Tg are polymethylmethacrylate (PMMA, or perspex), 100°C polystyrene (PS), 90°C polyethylene (low-density form), -20°C natural rubber, -40°C. To summarise, above Tc. the polymer is leathery, rubbery or molten below, it is a true solid with a modulus of at least 2GNm . This behaviour is shown in Fig. 6.2 which also shows how the stiffness of polymers increases as the covalent cross-link density increases, towards the value for diamond (which is simply a polymer with 100% of its bonds cross-linked. Fig. 4.7). Stiff polymers, then, are possible the stiffest now available have moduli comparable with that of aluminium. 

The moduli of metals, ceramics and glassy polymers below Tq reflect the stiffness of the bonds which link the atoms. Glasses and glassy polymers above are leathers, rubbers or viscous liquids, and have much lower moduli. Composites have moduli which are a weighted average of those of their components. 

A somewhat similar thing happens in many polymers at the glass-rubber transition that we mentioned in Chapter 6. Below the transition these polymers are much more brittle than above it, as you can easily demonstrate by cooling a piece of rubber or polyethylene in liquid nitrogen. (Many other polymers, like epoxy resins, have low Gc values at all temperatures simply because they are heavily cross-linked at all temperatures by covalent bonds and the material does not flow at the crack tip to cause blunting.)... 

Creep of polymers is a major design problem. The glass temperature Tq, for a polymer, is a criterion of creep-resistance, in much the way that is for a metal or a ceramic. For most polymers, is close to room temperature. Well below Tq, the polymer is a glass (often containing crystalline regions - Chapter 5) and is a brittle, elastic solid -rubber, cooled in liquid nitrogen, is an example. Above Tq the Van der Waals bonds within the polymer melt, and it becomes a rubber (if the polymer chains are cross-linked) or a viscous liquid (if they are not). Thermoplastics, which can be moulded when hot, are a simple example well below Tq they are elastic well above, they are viscous liquids, and flow like treacle. 

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