Polymers recovery

Aqueous media, such as emulsion, suspension, and dispersion polymerization, are by far the most widely used in the acryUc fiber industry. Water acts as a convenient heat-transfer and cooling medium and the polymer is easily recovered by filtration or centrifugation. Fiber producers that use aqueous solutions of thiocyanate or zinc chloride as the solvent for the polymer have an additional benefit. In such cases the reaction medium can be converted directiy to dope to save the costs of polymer recovery. Aqueous emulsions are less common. This type of process is used primarily for modacryUc compositions, such as Dynel. Even in such processes the emulsifier is used at very low levels, giving a polymerization medium with characteristics of both a suspension and a tme emulsion. 

Eig. 1. The key steps for the Phillips PPS process are (/) production of aqueous sodium sulfide from aqueous sodium hydrogen sulfide (or hydrogen sulfide) and aqueous sodium hydroxide 2) dehydration of the aqueous sodium sulfide and NMP feedstocks 5) polymerization of the dehydrated sulfur source with -dichlorobenzene to yield a slurry of PPS and by-product sodium chloride in the solvent (4) polymer recovery (5) polymer washing for the removal of by-product salt and residual solvent (6) polymer drying (7) optional curing, depending on the appHcation and (< ) packaging. 

Fig. 3. The key steps of the Kureha process, as disclosed in the patent Hterature (48), are (/) dehydration of aqueous feedstocks (sodium sulfide or its functional equivalent) in the presence of A/-methyl-2-pyrrohdinone (2) polymerization of the dehydrated sodium sulfide with -dichlorobenzene at alow temperature to form a prepolymer (J) addition of water to the prepolymer (4) a second, higher temperature polymerization step and (5) polymer recovery.

Reaction and Heat-Transfer Solvents. Many industrial production processes use solvents as reaction media. Ethylene and propylene are polymerized in hydrocarbon solvents, which dissolves the gaseous reactant and also removes the heat of reaction. Because the polymer is not soluble in the hydrocarbon solvent, polymer recovery is a simple physical operation. Ethylene oxide production is exothermic and the catalyst-filled reaction tubes are surrounded by hydrocarbon heat-transfer duid. 

Oringer, K. Current Practice in Polymer Recovery Operations, Chemical Engineering, Mar. 20, 1972, p. 

The method of pure polymer recovery from the biomass prior to characterization can influence the molecular weight of the polymer significantly. Extraction of PHB-bacterial cells with organic solvents yields polymers with higher molecular weight compared to sodium hypochorite treatment [44-46]. Pretreatment of the biomass with a surfactant prior to hypochlorite digestion... 

When Zotefoam HDPE materials of density 98 kg m" were subjected to a single major compressive impact (419), after recovery at 50 °C for 1 hour, the performance, defined as the energy density absorbed before the compressive stress reached 2.5 MPa was back to 75% of the initial value. Further severe impacts caused a further deterioration of the performance of the recovered foam. Peak compressive strains of 80 to 90% caused some permanent buckling of the cell walls of HDPE foams. The recovery is much slower than the 0.1 second impact time, so is not a conventional linear viscoelastic response. It must be driven by the compressed air in internal cells in the gas, with some contribution from viscoelasticity of the polymer. Recovery of dimensions had slowed to a very low rate after 10 seconds at 20 °C or after 10 seconds at 50 °C. 

Simplest of the techniques requiring only monomer and monomer-soluble initiator, and perhaps a chain-transfer agent for molecular weight control. Characterized, on the positive side, by high polymer yield per volume of reaction, easy polymer recovery. Difficulty of removing unreacted monomer and heat control are negative features. Examples of polymers produced by bulk polymerization include poly(methyl methacrylate), polystyrene, and low-density (high pressure) polyethylene. 

The quality of the results from SEC-FTIR strongly depend on the surface quality of the deposited sample fractions. Cheung et al. demonstrated that the surface wetting properties of the substrate dominate the deposit morphology [145]. The spectra fidelity, film quality, resolution and polymer recovery were considered by Balke et al. [ 146]. For different interface designs it was found that the morphology of the deposited polymer film was a key parameter for quantitative measurements. 

Delgado, C., Barmetabena, F., et al. (2007) Assessment of the environmental advantages and drawbacks of existing and emerging polymers recovery processes. Luxembourg, European Commission, Joint Research Centre, Institute for Prospective Technological Studies. 

Polymer recovery is done by stripping of the diluent, washing to remove residual catalyst, and extraction of undesirable polymer components, if necessary. 

Filter wash water approx. 1 kg/1 kg polymer Recovery column yield 98% (percentage recovered) Dryer feed 5% water, product specification 0.5% H2O Polymer losses in filter and dryer 1%... 

By localizing reagents in polymers, recovery of valuable reagents is eased. Often a convenient filtration removes the polymers and facilitates work-up. Frequently... 

Based on the generation of each stream, polymer recovery program trends, and expansion of recycling programs, it is estimated that close to 15 billion pounds of polymer streams will be available for recycling or recovery (Table 5) These... 

Silicone Polymers. - The photolysis of an alternating copolymer of 2,6-diethylene-acetophenone/disiloxane in the absence of oxygen resulted in complete polymer recovery with no change in molecular weight, whereas in the presence of oxygen significant chain scission was observed. In this case, hexa-methyldisiloxane and 1,2-diacetylbenzene were formed as products. 

DCE and AIBN (2.0 wt%) were combined and sealed (Neoprene stopper) under nitrogen in 50ml glass serum bottles. The polymerizations were run in a shaker bath for 5 hr. at 70°C. Polymer recovery and purification was the same as previously described. 

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