Processing polyfvinyl chloride

Akutin (52) performed an exhaustive study on the influence of processing conditions and the nitrile rubber/poly(vinyl chloride) ratio on the mechanical characteristic of the product. The experiments were carried out in a Brabender Plastograph at 160-180° C and rotor speed of 10-50 rpm. The polyfvinyl chloride) molecular weight was 83500. A resin with an epoxy group content of 20.75% was added to the blend as plasticizer and stabilizer. Figure 29 shows that the... 

Approximately 10 million tons of 1,2-dichloroethane are manufactured each year in the United States by the reaction of ethylene with chlorine. The process is the first step in making PVC [polyfvinyl chloride)] plastics. 

Polyfvinyl chloride) (PVC) is produced by mass, suspension, and emulsion processes. Mass polymerization is an exatiiple of a heterogeneous bulk system. PVC is virtually insoluble in vinyl chloride because the polymer is about 35% more dense than the monomer under normal polymerization conditions. Vinyl chloride, however, is quite soluble in polymer. The two phases in PVC polymerizations are pure monomer and monomer-swollen polymer. Polymerization proceeds in both phases, but it is very much faster in the polymer-rich phase because the mobility of macro radicals and mutual termination reactions are. severely restricted (cf. Section 6.13.2). 

Highly polar polymers like polyfvinyl chloride) and some cellulose derivatives require polar liquids as solvents, in which dipole interactions or hydrogen bonding between polymer and solvent molecules occur. However, solvation does not necessarily lead to solution because the liquid, if it is to act as a solvent, must dissolve the solvated polymer. This process may be very slow because of the high viscosity of the partially solvated system. 

A similar process takes place during the formation of CH3CI in the pyrolysis of polyfvinyl chloride-co-methyl methacrylate) ... 

In addition, the surface should be free of contaminating particles and occlusions that would interfere with the information retrieval process. A typical ablative-mode optical disk has the structure shown in Figme 16.14. The substrate is an optically transparent material such as polycarbonate, PMMA, polyfethylene terephthalate), or polyfvinyl chloride) topped by a subbing layer to provide an optically smooth surface for the recording layer. A metal reflector (typically aluminum) is then incorporated next to a transparent dielectric medium such as poly(a-methyl styrene) and, finally, the absorbing layer where the information pits are created is added. The latter can be a metal-polymer composite (silver particles in a gel) or a dye molecule dispersed in a polymer matrix such as squaryllium dyes, which act as infrared absorbers for GaAs lasers, typically... 

Although for most analytical pyrolysis techniques it is advisable to heat the sample to its final temperature as rapidly as possible, there are times when just the opposite is required. To simulate thermal processes, such as TGA on a small scale, or to analyze the degradation products produced from a sample as they are generated, slower, controlled heating is required. These slow-rate experiments demonstrate, for example, that polyfvinyl chloride) degrades in a two-step process, producing HCl at a relatively low temperature and aromatics at elevated temperatures. 

Gaseous monomers may also be trapped within the processing equipment and accidents have occurred as a consequence of the resulting pressure buildup. In the case of the polyacetals and polyfvinyl chloride) it is reported that at elevated temperatures these materials form a more or less explosive combination so that it is important to separate these materials rigorously at the processing stage. 

It is observed that the initial reaction with amines is accompanied by formation of colour ranging from yellow to a dark red-brown. This is consistent with the formation of a sequence of conjugated double bonds along the chain somewhat reminiscent of the dehydrochlorination process that occurs during the degradation of polyfvinyl chloride). 

Recently, Wills et al. [16,17] proposed a novel agglomeration method. Core/shell impact modifiers, useful in toughening polyfvinyl chloride) and other thermoplastics, are prepared at small particle size by an emulsion polymerization process, agglomerated by the novel technique which has little effect on emulsion solid, are further encapsulated by a final shell, and are isolated by spray drying or coagulation. The isolated particles are readily redispersed to their original particle size in the matrix polymer. 

A plasticizer is a material that enhances the processibility or flexibility of the polymer with which it is mixed. The plasticizer may be a liquid or solid or another polymer. For example, rigid polyfvinyl chloride) is a hard solid material used to make credit cards, pipe, house siding, and other articles. Mixing with about 50-100 parts by weight of phthalate ester plasticizers converts the polymer into leathery products useful for the manufacture of upholstery, electrical insulation, and other items. Plasticizers in surface coatings enhance the flow and leveling properties of the material during application and reduce the brittleness of the dried film. 

Bromine and chlorine add rapidly to alkenes to yield 1,2-dihalides, a process called halogenation. For example, more than 18 million tons 1,2-dichloroethane (ethylene dichloride) is synthesized worldwide each year, much of it by addition of GI2 to ethylene. The product is used both as a solvent and as starting material for the manufacture of polyfvinyl chloride), PVG. Fluorine is too reactive and difficult to control for most laboratory applications, and iodine does not react with most alkenes. 

Over the past years considerable attention has been paid to the dispersing system since this controls the porosity of the particle. This is important both to ensure quick removal of vinyl chloride monomer after polymerisation and also to achieve easy processing and dry blendable polymers. Amongst materials quoted as protective colloids are vinyl acetate-maleic anhydride copolymers, fatty acid esters of glycerol, ethylene glycol and pentaerythritol, and, more recently, mixed cellulose ethers and partially hydrolysed polyfvinyl acetate). Much recent emphasis has been on mixed systems. 

As with poly(vinyl alcohol), polyfvinyl cinnamate) is prepared by chemical modification of another polymer rather than from monomer . One process is to treat poly(vinyl alcohol) with cinnamoyl chloride and pyridine but this is rather slow. Use of the Schotten Baumann reaction will, however, allow esterification to proceed at a reasonable rate. In one example s poly(vinyl alcohol) of degree of polymerisation 1400 and degree of saponification of 95% was dissolved in water. To this was added a concentrated potassium hydroxide solution and then cinnamoyl chloride in methyl ethyl ketone. The product was, in effect a vinyl alcohol-vinyl cinnamate copolymer Figure 14.8)... 

Emulsion polymerization is an important technological process widely used to prepare acrylic polymers, poly(vinyl chloride), polyfvinyl acetate), and a large nnm-ber of copolymers. The technique differs from the suspension method in that the particles in the system are much smaller, 0.05 to 5 pm diameter, and the initiator is soluble in the aqueous phase rather than in the monomer droplets. The proeess oITcts the uniqne opportunity of being able to increase the polyma- ehain laigth withont altering the reaction rate. This can be achieved by changing dther the tempraature or the initiator coneentration, and the reasons for this will become more obvions when we examine the teehniqne more closely. 

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