Mosaic tile model

NOTE In the mosaic tile model, please note that the particle-particle ties provided by the binder not only hold the particles together but also hold them apart. This particle separation function of the binder is a steric hindrance or steric stabilization mechanism that aids and sometimes overshadows the dispersing property of the dispersant. It was mentioned in the Surfactants section that the binder is sometimes a more powerful dispersant than the dispersant itself. The mosaic tile model provides a good picture of the dispersing power of some binders. 

Two distinctly different mechanisms can be used to plasticize a green tape. Confusion arises quickly, however, since the end result of these different mechanisms looks very similar in most tests. The mosaic tile model will be useful in displaying the two different mechanisms. As we left the model, we have a 12" wide, 24" long, and 24" high block of 1" X 1" ceramic tiles bound together with metal wires. Bending this stack around a pipe would require not only a fair amount of force, but it would also require the outer layer of wires to stretch, since the ceramic tiles need to move farther apart. The first type of plasticizer... 

It can be seen using the mosaic tile model that relative changes in Type I and Type II plasticizer additions will cause logical and predictable changes in tape flexibility and plasticity that can be charted by or even read from a standard stress-strain diagram. 

Referring back to the mosaic tile model in Section 2.5, over time some of the rubber bands from particle to particle wrap around the particles instead. This action displaces the menhaden fish oil which then acts like a Type II plasticizer to lubricate the system. The end result of this interaction follows logically out of the mosaic tile model. Fewer rubber band ties between particles result in a weaker tape. More olive oil, or in this case fish oil, in the matrix results in greater deformation under its own weight and higher plastic deformation. As aging time increases with both PVB and MFO in proximity to the particle surface, the tape becomes weaker and floppier and can even discolor the drying surface of the tape. 

Mosaic tile model A metaphorical tool to help visualize a green cast tape. Mosaic tiles and some other small tiles sold for bathrooms, kitchens, etc., are sold in sheets. Each tile in these sheets is bound to the others by plastic or metal wire. Seeing the tape-cast sheet as ceramic particles held together by binder wires is useful in understanding and consequently designing the cast tape to suit individual applications. This is covered in depth in Chapter 2. 

---