Solvent properties, desirable environmental requirements

In the manufacturing process of most polymers, there is a need to separate and remove undesirable, residual volatile components such as solvents, monomers, and other low molecular weight components from the polymeric material. These volatiles are removed in one or more postreactor operations in order to recover the solvent and monomer, impart the polymer with the desired physical properties, meet environmental requirements, and eliminate residual odors and taste. In condensation polymerization, of course, the removal of volatiles is essential to drive the polymerization reaction and reach high molecular weights. Moreover, removal of volatiles, moisture and entrapped air is also essential for many types of down-stream compounding and processing equipment. 

Estimate key physical properties and review desirable solvent properties. Give careful consideration to safety, industrial hygiene, and environmental requirements. Use this preliminary information to trim the list of candidate solvents to a manageable size. (See Desirable Solvent Properties. )... 

A wealth of techniques exists for designing molecules with desired characteristics. Despite the plethora of approaches, most approaches focus on designing materials with the required processing properties without explicitly considering the plant-wide implications. In an attempt to address this limitation, Buxton (2002) proposed that only with an expanded process boundary, the selection of materials can lead to consistent cost optimal and environmentally benign improvements. Within this context, he developed a procedure for designing solvents using process and plant-wide environmental objectives. 

A wide variety of plasticizers are commercially available and novel types are replacing older compounds that were less stable or have higher environmental impact. Typical requirements for selection of a plasticizer include compatibility with the host polymer, low extractability by water and solvents, stability under heat and light exposure, good low-temperature properties, ease of processing, and low odor, taste, toxicity, and cost. Since no single plasticizer meets all of these requirements, and some are more appropriate than others for a specific polymer, blending of multiple plasticizers is often necessary to achieve the desired result in the final product. 

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