Separation Using Soluble Acrylic Polymers

The applications to recycling include use as an allowable material which would not hinder recycling (because it would be easily dissolved) and as a recyclable product. A PET beverage bottle which is affixed with such a soluble film plastic label, cup adhesive and ink, would allow for less contaminant in the PET recycle. Contamination of paper label residue and adhesives is a problem with PET bottle recycling. This also allows for recycle of the adhesive and film by precipitation ftrom the alkaline wash. - 

There has been little past nationwide activity in the recycle of polyurethanes (PUR) or phenolics even though these resins are among the largest produced. These two resins comprised 9.5% by weight of the resins produced in the U.S. in 1989 (refer to Table 1.2 in Part 1). An overview of some recent work is summariaed here. 

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Glass-ionomers have been used in various areas of restorative dentistry since the mid 1970s. They were invented and originally described by Wilson and Kent [208], and consist of a basic glass powder and a water-soluble acidic polymer. The most widely used polymer is poly(acrylic acid), but acrylic/maleic acid copolymer is also widely used [209]. The glass powder is a complex calcium (or strontium) aluminofluorosilicate [210] that is typically at least partially phase separated. 

PE would have a low solubility even in hot toluene. In the case of styrene-butadiene copolymer, the uncrosslinked polymer is soluble in aromatic solvents, whilst the highly crosslinked (gel) fraction is completely insoluble and, indeed, this can be used as the basis of a method for separating gel from uncrosslinked polymer. Copolymers usually dissolve in a greater number of solvents than homopolymers. Thus, whilst PVC is only slightly soluble in acetone or methylene chloride, its copolymers with vinyl acetate or acrylates dissolve easily. 

Some examples of acrylic polymers used in positive working photoresists are also shown in Table 2.2. The photoactive group can be incorporated into the polymer backbone or added to the resist as a separate component (section 2.4.5 in positive-working photoresists the areas irradiated with ultraviolet light become soluble in certain developers). Compounds 7 and 8 are examples of polymers that do not contain photoactive groups. 

Polyacrylates are an industrially important class of polymers. The name polyacrylate is variously used to refer to polymers of acrylate esters [e.g., poly(methyl methacrylate)] as well as polymers of acrylic acids [e.g., poly(meth-acrylic acid)]. Because the former is organic soluble while the latter is not, chromatographic analysis of these two requires quite different conditions. This chapter discusses both types of polymers, separating their consideration when necessary. We will refer to both types of polymers as polyacrylates, letting the context indicate whether we are referring to an ester or to an acid polymer. 

The conventional techniques for the purification of low-molecular-weight compounds, such as distillation, sublimation, and crystallization, are not applicable to polymers. In some cases, it is possible to remove the impurities by cold or hot extraction of the finely powdered polymer with suitable solvents or by steam distillation. Separation of low-molecular-weight components from water-soluble polymers (e.g., poly(acrylic acid), poly(vinyl alcohol), poly(acryl amide)) can be accomplished by dialysis or electrodialysis. However, the most widely used method of purification is by reprecipitation in which the solution of polymer (concentration less than 5-10 wt.%) is dropped into a 4- to 10-fold excess of precipitant, with stirring. If necessary, this operation is repeated with other solvent/precipitant pairs until the impurities are no longer detectable. 

Some polymers such as poly(acrylic acid) or polyacrylamide precipitate from aqueous solutions when cooled (normal solubility behavior) whereas others such as poly(ethylene oxide), poly(propylene oxide), or poly(methacrylic acid) phase separate when heated (inverse solubility behavior). Solution turbidimetiy is often used to obtain plots of phase-separation temperatures termed cloud point vs concentration for fixed solvent conditions. Changes in ionic strength, molecular weight, and addition of co-solvents or structure breakers affect the shapes of phase behavior curves. The important conclusion of such studies is that the total free energy of the polymer and water must be considered to predict phase behavior. The structin-e and dynamics of water surroimding polynucleotides, proteins, polysaccharides, and lipids are also major determinants of biological activity (8-10). 

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