Polyvinyl chloride suspension polymerization

In the suspension polymerization of PVC, droplets of monomer 30—150 p.m in diameter are dispersed in water by agitation. A thin membrane is formed at the water—monomer interface by dispersants such as poly(vinyl alcohol) or methyl cellulose. This membrane, isolated by dissolving the PVC in tetrahydrofuran and measured at 0.01—0.02-p.m thick, has been found to be a graft copolymer of polyvinyl chloride and poly(vinyl alcohol) (4,5). Early in the polymerization, particles of PVC deposit onto the membrane from both the monomer and the water sides, forming a skin 0.5—5-p.m thick that can be observed on grains sectioned after polymerization (4,6). Primary particles, 1 p.m in diameter, deposit onto the membrane from the monomer side (Pig. 1), whereas water-phase polymer, 0.1 p.m in diameter, deposits onto the skin from the water side of the membrane (Pig. 2) (4). These domain-sized water-phase particles may be one source of the observed domain stmcture (7). 

Figure 12-4. The European Vinyls Corp. process for producing polyvinyl chloride using suspension polymerization (1) reactor, (2) blow-down vessels (to separate unreacted monomer), (3) stripping column, (4) reacted monomer recovery, (5) slurry centrifuge, (6) slurry drier.

In suspension polymerization, the monomer is agitated in a solvent to form droplets, and then stabilized through the use of surfactants to form micelles. The added initiator is soluble in the solvent such that the reaction is initiated at the skin of the micelle. Polymerization starts at the interface and proceeds towards the center of the droplet. Polystyrene and polyvinyl chloride are often produced via suspension polymerization processes. 

Why are suspension and emulsion polymerization processes the primary methods by which polyvinyl chloride is manufactured How are these processes carried out ... 

Suspension polymerization. In this process, monomers and initiator are suspended as droplets in water or a similar medium. The droplets are maintained in suspension by agitation (active mixing). Sometimes a water-soluble polymer like methylcellulose or a finely divided clay is added to help stabilize or maintain the droplets. After formation, the polymer, is separated and dried. This route is used commercially for vinyl-type polymers such as polyvinyl chloride and polystyrene. 

Polyvinyl chloride is produced by the free-radical polymerization of vinyl chloride. Bulk, emulsion, solution, and suspension polymerization processes have been used. 

Application A process to produce polyvinyl chloride (PVC) from vinyl chloride monomer (VCM) using suspension polymerization. Many types of PVC grades are produced including commodity, high K-value, low K-value, matted type and co-polymer PVC. The PVC possesses excellent product qualities such as easy processability and good heat stability. 

Vinnolit A process for making polyvinyl chloride by suspension polymerization. Developed by Vinnolit, Germany, and engineered by Uhde. Widely licensed worldwide. 

Application A process producing polyvinyl chloride (PVC) from vinyl chloride monomer (VCM) using suspension polymerization. 

Emulsion Polymerization Emulsions have particles of 0.05- to 5.0-pm diameter. The product is a stable latex, rather than a filterable suspension. Some latexes are usable directly, as in paints, or they may be coagulated by various means to produce very nigh-molecular-weight polymers. Examples are polyvinyl chloride and butadiene-styrene rubber. 

Thus, to modify compositions with finely dispersed suspensions it is necessary for the latter to be active enough that should be controlled with IR speetroseopy. A number of results of material modification with finely dispersed suspensions of metal/carbon nanocomposites are given, as well as the examples of changes in the properties of modified materials based on concrete compositions, epoxy and phenol resins, polyvinyl chloride, polycarbonate, and current-conducting polymeric materials. 

Suspension polymerization occurs in water with the liquid monomer dispersed by agitaliorL The polymer is produced as a dispersed solid phase fiom polymerization of initiator-containing, 10 to 500 pm droplets under kinetics that match those of the bulk reaction of the monomer (7). The suspension is stabilized by insoluble organic or inorganic solids, electrolytes to increase monomer-water interfacial tension, and water soluble polymers that increase aqueous viscosity. Suspension polymerization is commonly used to synthesize two polymers covered in this book, polystyrene and polyvinyl chloride. 

When solid polymer precipitates fiom bulk, solution, suspension, or emulsion polymerizations by a chain mechanism, the kinetics of the reaction and properties of the product may change sharply. If the solid phase is not swollen by the reaction mixture, the active site of the polymerization is isolated from possible termination reactions and may produce pronounced auto acceleration and increases in molecular weight of polymer formed. This behavior was quantified for one chain reaction polymer, polyvinyl chloride, covered in this book. Micldey (9) showed that polyvinyl chloride synthesis in bulk followed a two term kinetics equation with the second term representing incremental increases in polymerization rate due to accelerated polymerization in precipitated particles of polymer. 

Some peculiarities of the thermal and thermooxidative decomposition of polyvinyl chloride depend on the conditions of its production. Thus, it is known that samples of the polymer produced by initiating the polymerization of vinyl chloride with ultraviolet irradiation possess higher stability in comparison with samples produced in polymerization under the action of chemical agents [26, 27]. Reversibility of the process of dehydrochlorination in the decomposition of samples of polyvinyl chloride produced by the latex method is noted, while in the process of decomposition of suspension polymer, the phenomenon of reversibilily is not observed [21]. It has been shown that the rate of dehydrochlorination of the latex polymer is significantly higher than that of the suspension polymer under the same conditions [21]. It has been established that the polymerization of vinyl chloride in the presence of oxygen leads to the formation of unstable peroxide groups, which can initiate decomposition of the polymer [28, 29]. It is noted that an extremely substantial influence on the stability of polyvinyl chloride is exerted by the purity of the monomer, as well as the presence of impurities of metals of variable valence [28]. 

Polyvinyl chloride is one of the cheapest plastics in use today. It is prepared by the polymerization of vinyl chloride (VCM) (CH2=CHC1, B.P.—14°C) as a suspension or emulsion in a pressure reactor. The polymer is unstable at high temperamres and liberates HCl at T > 200°C. It can be injection molded or formed into a hard and brittle material. It can be readily softened by the addition of plasticizers such as diethylhexylphthalate to the extent of 30%. Plasticized PVC is used as an upholstery substitute for leather. Since the plasticizer is volatile to a small extent, it slowly leaves the vinyl which eventually becomes hard, brittle, and then cracks. This can be restored by replacing the plasticizer by repeated conditioning of the vinyl surface. 

The term "suspension polymerization" is used traditionally for polymerization in a dispersed monomer phase. Occasionally the term is also u for the type of process described in the preceeding section, but for that the term "precipitation polymerization" is more appropiate. The polymerization in a dispersed monomer phase might also be called "dispersion polymerization", but this term is used for polymerizations where the monomer is originally dissolved, and the polymer is separated as a second liquid phase, usually absorbing some monomer. Suspension polymerization is used on a large scale for the manufacture of polyvinyl chloride (PVC), and for specific grades of polystyrene. 

Polyvinyl chloride (PVC) is a homopolymer of vinyl chloride. Eighty percent of commercial PVC in packaging is produced by chain-reaction polymerization using a suspension method. Other methods are emulsion and solution polymerization. Chain-reaction polymerization requires initiators to produce free radicals, then the reaction proceeds until the chain is terminated. The predominant configuration of the monomer in the polymer chain follows a head-to-tail alignment to yield a syndiotactic polymer. 

Polyvinyl chloride resin is made from suspension polymerization of vinyl chloride monomer (Figure 4.21). 

---