Processing via the Solid State

In laminating or coating, a preformed solid film of plastic is bonded with glue or adhesive directly onto the material to be laminated. Composite films of cellulose and poly(ethylene), for example, are produced in this way. In these composite films, the cellulose protects from foreign odors and the poly(ethylene) assures water-tightness. Composite films of poly(isobutylene) and poly(ethylene) are used in the construction of chemical apparatus made of steel. Poly(ethylene) takes care of the protection against corrosion, and poly(isobutylene), with adhesives, the adhesion to steel. Steel sheet laminated with PVC can be processed as normal, but is noncorrosive in the absence of any further treatment. Metal aircraft parts are often coated with films of poly(tetrafluoroethylene). Poly(tetrafluoroethylene) is difficult to wet, and this decreases the tendency to ice over. 

Composites are often constructed by bonding two materials together as in the laminating technique. In the case of synthetic leathers, called poromers, layers of different plastics are bonded together. Corfam, the first product of this type, consists, for example, of an upper layer of vapor-permeable polyurethane and a central layer of a mixed fabric consisting of porous 95% poly(ethylene terephthalate) fleece held together by an elastomeric polyurethane cord. The fleece is produced from fibrils (see Section 12.3.1). 

Composites are particularly useful as construction materials. Car bodies, for example, can be manufactured according to the sandwich-construction technique A hard foam of polyurethane is sandwiched between 

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If substantial molecular displacements are involved in solid-state pol)niierization, the reaction has a type of nonuniqueness whose effect upon polymer crystal perfection depends upon the kinetics of reorganization processes in the solid state. For example, if the monomer-center to monomer-center separation in the reaction direction changes during polymerization, then the displacements in monomer centers can differ statistically within the pol3nnerizing monomer array. If reaction proceeds via formation of a random solid solution of polymer chains in the polymerizing phase, these shifts will be poorly correlated for essentially non-interacting (well separated) chains formed at low conversions. 

In order to establish die feasibility of alkaline hydrolysis with respect to recycling of nylon-4,6, it was necessary to determine whether die recovered oligomers could be repolymerized to form nylon-4,6. For diis purpose, solid-state polymerization was performed on nylon-4,6 oligomers formed via alkaline hydrolysis with 50 wt% NaOH at 165°C for 24 h. The solid-state polymerization process... 

The recently discovered Ugand precursor HOB[OSi(O Bu)3]2 was prepared by the hydrolysis of BuOB[OSi(O Bu)3]2 (in CeHe) with one equiv of H2O [64]. After stirring for 1 h, the solution is frozen and the solvent is removed via lyophiUzation under reduced pressure. Purification can be achieved via subUmation (ca. 50 °C) of the dry powder under reduced pressure to give yields in excess of 85%. Although not stable in solution for extended periods (due to condensation processes), HOB[OSi(O Bu)3]2 is stable indefinitely in the solid state imder an inert atmosphere. 

A unique characteristic of polyesters is their ability to undergo additional condensation reactions during processing or when in the solid state. These reactions redistribute the molecular weight of the polymer until a dynamic equilibrium is established. Water, when present at high temperatures in polyester melts, can depolymerize polyesters via a hydrolysis reaction. For this reason, manufacturers must carefully dry the polymer before processing. 

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