Solvent cracking

In addition to orientation in one direction (mono-axial orientation), biaxial orientation is possible. This is achieved when sheet is stretched in two directions resulting in layering of the molecules. This can increase the impact strength, tensile strength and solvent cracking resistance of polymers and with crystalline plastics the polymer clarity may also be improved. 

Of the instances of so-called solvent cracking of amorphous polymers known to the author, the liquid involved is not usually a true solvent of the polymer but instead has a solubility parameter on the borderline of the solubility range. Examples are polystyrene and white spirit, polycarbonate and methanol and ethyl acetate with polysulphone. The propensity to solvent stress cracking is however far from predictable and intending users of a polymer would have to check on this before use. 

Methylnaphthalene was then used as a vehicle, but even in this case very poor results were obtained, i.e.y conversion to methyl ethyl ketone (MEK) solubles and distillate products was very low. Results of this run are not reported since they are obscured by extensive solvent cracking. 

This effluent then goes to a condenser where aldehydes and by-products drop out this mixture is removed in a separator. The liquid stream from the separator contains appreciable amounts of dissolved gases, mainly propylene and propane. A product stripping column distills these out. The liquid stream from this stripper goes through two distillation columns in series that remove iso- and n-butyraldehyde as overhead products, respectively. A small stream that contains heavy by-products formed in the reactor leaves the bottom of the second column. This stream can be combined with the heavy ends stream from the n-butanol column and valuable aldehydes and alcohols recovered for recycle. The iso-butyraldehyde overhead product from the first aldehyde column may be hydrogenated and sold as a low cost solvent, cracked to synthesis gas and recycled to the oxo reactors, or burned as fuel. 

The foregoing considerations about the mechanism of solvent cracking and solvent crazing suggest that the solubility parameter difference, as a quantitative measure of the interaction between polymer and solvent, will play an important part in these phenomena. 

So attempts to correlate solvent cracking and solvent crazing with solvent properties lead to the same conclusion as was drawn in Chap. 7 for the solubility of polymers, viz. that besides the solubility parameter at least one other solvent property must be taken into account. The method proposed by Vincent and Raha is one of several possible two-dimensional correlation methods. 

CSPE have excellent combinations of properties that include total resistance to ozone excellent resistance to abrasion, weather resistance even in light colors, heat, flame, oxidizing chemical, solvents, crack growth, and dielectric properties. Also provide low moisture absorption, resistance to oil similar to neoprene, low temperature flexibility is fair at -40C (-40F), low gas permeability for an elastomer and good adhesion to substrates. Can be made into a wide range of colors. Use includes hoses, roll covers, tank liners, wire and cable covers, footware, and building products (flash, sealing, etc.). 

Selection of a suitable barrier material for plastics raises identical challenges to selection of an adhesive or cleaning product Solvent in the lacquer must neither dissolve the plastic substrate nor induce solvent cracking, while the lacquer must wet the plastic sufficiently well to produce a cohesive film. Both rigid and flexible plastics can be damaged by use of inappropriate barrier materials, causing either ESC, sweUing or distortion. 

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