Plastisols, Commercial

Random copolymers of vinyl chloride and other monomers are important commercially. Most of these materials are produced by suspension or emulsion polymerization using free-radical initiators. Important producers for vinyl chloride—vinyUdene chloride copolymers include Borden, Inc. and Dow. These copolymers are used in specialized coatings appHcations because of their enhanced solubiUty and as extender resins in plastisols where rapid fusion is required (72). Another important class of materials are the vinyl chloride—vinyl acetate copolymers. Principal producers include Borden Chemicals Plastics, B. F. Goodrich Chemical, and Union Carbide. The copolymerization of vinyl chloride with vinyl acetate yields a material with improved processabihty compared with vinyl chloride homopolymer. However, the physical and chemical properties of the copolymers are different from those of the homopolymer PVC. Generally, as the vinyl acetate content increases, the resin solubiUty in ketone and ester solvents and its susceptibiUty to chemical attack increase, the resin viscosity and heat distortion temperature decrease, and the tensile strength and flexibiUty increase slightly. 

The first four types are most conveniently distinguished by reference to formulations A to D in Table 12.5. Formulation A is a conventional plastisol. The viscosity of the paste is largely controlled by the choice of type and amount of polymer and plasticiser. In order to achieve a sufficiently low viscosity for processing, large quantities of plasticiser must be added, thereby giving a product of lower hardness, modulus, tensile strength and other mechanical properties than would be the case if less plasticiser could be used. In many applications this is not a serious problem and plastisols are of some considerable importance commercially. 

The first successful static firing of plastisol propellant took place late in 1950 as part of a broad program conducted by Atlantic Research Corp. to investigate and evaluate plastisol propellants and methods for their manufacture (16). Major attention was directed to poly (vinyl chloride), cellulose acetate, and nitrocellulose, although other polymers were tested for their suitability (17). Patent applications were filed for plastisol propellant compositions and manufacturing processes, based on poly(vinyl chloride) (PVC) (19) and on nitrocellulose (18). The commercial availability of dispersion grade PVC enabled work with this resin to advance rapidly. The balance of this paper is devoted to a discussion of PVC plastisol propellants and their manufacture. 

The 20-minute dwell time used is considerably greater than that used in commercial practice. For example, in the spreading of PVC plastisols on cloth, depending on the thickness of film applied and the method of heating, such as infrared or more recently hot air jets, the dwell time can be as low as 30 seconds. The temperature attained by the plastisol in these commercial processes can be as high as 190°C. In the study reported here, however, we had to choose a dwell time which would allow the attainment of an equilibrium over the whole temperature range being studied. 

The carbon black plastic concentrates are often not prepared by the plastics processor. They may be purchased, from the pigment-black manufacturer in the form of chips, pellets, or powders. Black-plasticizer pastes (e.g., black/DOP pastes for tinting plastisols) and water- and solvent-based dispersions (e.g., for fiber manufacture) are also commercially available. 

Commercial Plastisols, Accdg to definition given in Ref 2, a plastisol is a liquid dispersion of finely divided resin in a plasticizer. It is usually 100% solid with no volatiles when volatile content exceeds 5% of the total wt it is called organosol. When the plastisol is heated, the plasticizer solvates the resin particles, and the mass gels. With continued application of heat the mass fuses to become a conventional thermoplastic material... 

Nine commercial plastisols were investigated at PicArsn in order to determine their possible use in Ordnance items. Results of invistigation are given in Ref 1 Refs 1)R.J.Samuels, "Evaluation of Commercial Plastisols A Comparison of Their Physical Properties , PATR 2023, (1954)... 

As the shear rate increases, the viscosity of some dispersions actually increases. This is called dilatancy, or shear-thickening. Dilatancy can be due to the dense packing of particles in very concentrated dispersions for which at low shear, the particles can just move past each other but at high shear they become wedged together such that the fluid cannot fill (lubricate) the increased void volume, and the viscosity increases. An example of this effect is the apparent drying of wet beach sand when walked on, the sand in the footprint initially appears very dry and then moistens a few seconds later. Other examples include concentrated suspensions (plastisols) of polyvinyl chloride (PVC) particles in plasticizer liquid and the commercial novelty product Silly Putty (which is a silicone material). 

During the early forties flexible PVC use was mainly limited to military applications, including wire and cable, and various film and sheeting applications, etc. With the conclusion of World War II, new markets for PVC developed rapidly. Aside from DOP, which was commercialized in 1940(4), dicapryl phthalate (DCP) was introduced by Rohm and Haas C5), also in the early forties. With the development of plastisols(6), DCP became a plasticizer of choice because of the favorable balance of properties it imparted — especially low viscosity. However, DCP s subsequent growth has been limited since capryl alcohol (octanol-2), a monohydric secondary alcohol, is a by-product of limited volume sebacic acid manufacture. 

The possible interaction between PVC and several commercial plasticizers has also been investigated by Marcilla and Beltran.86,87 Figures 4.17(A), (B) and (C) show the TGA and DTG curves corresponding to plastisols formed by PVC and three commercial plasticizers (DBP, DOP and DIDP). The first weight loss... 

Figure 4.17 TG and DTG curves of plastisols formed by PVC and three commercial plasticizers (dotted line experimental, continuous line theoretical) 6 (A) PVC + DBP, (B) PVC + DOP, (C) PVC + DIDP.

Plastisols are of considerable importance commercially. Tbey are converted into tougb, rubbery products by heating at about 160°C (gelation). Organosols are cbaracterized by the presence of a volatile organic diluent whose sole function is to reduce the paste viscosity. The diluent is removed after application and before gelling the paste. 

More recent efforts have focused on developments that create true hybrids. For example, blocked isocyanate prepolymers have been mixed with epoxy resins and cured with amines [68-70]. These blocked prepolymers will react initially with the amines to form amine-terminated prepolymers that cross-link the epoxy resin. Several blocked isocyanates are commercially available. The DESMOCAP (Bayer) llA and 12A products are isocyanates (believed to be blocked with nonylphenol) used as flexibilizing agents for epoxy resins. ANCAREZ (trademark. Pacific Anchor, Inc.) 2150 is a blocked isocyanate epoxy blend used as an adhesion promoter for vinyl plastisols. A one-package, heat-cured hybrid adhesive was reported consisting of isophorone diisocyanate, epoxy resin, and a dispersed solid curative based on the salt of ethylenediamine and bisphenol A [71]. Urethane amines are offered commercially that can be used with epoxy resins to develop hybrid adhesive systems [72]. 

Sealant applications are major commercial products, which fall into two categories PVC plastisols whieh do not have reactive components and PVC plastisols combined with blocked isoeyanates or isocyanurates. The first category of sealants is the most popular as an underbody sealant, whereas the seeond category includes construction and general purpose sealants. PVC gels are used occasionally as electrolytes, vibration reducing materials, and the like. 

The development of hollow thermoplastic microspheres has offered the prospect of lower density plastisols with superior physical properties and appearance than have been attainable by other known techniques. Such microspheres have become available, having, for example, diameters on the order of 10 to 200 im, most often 20 to 100 pm, and densities of 0.06 to 0.02 g/cm, or even as low as 0.015 g/cm. The thermoplastic material of which the microspheres are formed is typically a polyvinylidene chloride or a copolymer of polyvinylidene chloride with other vinyl or acrylic monomers, such as acrylonitrile, butylene, and the like. The hollow microspheres contain a physical blowing agent, typically a lower alkane, most often a butane or pentane, or their mixtures. A variety of such materials are commercially available. 

Plastisols are the result of a special class of fine-particle PVC resin (dispersion grade) being dispersed in liquid plasticizers. Organosols are the product of a plastisol and a volatile diluent or a solvent. Commercial PVC copolymers include grades copolymerized with vinyl acetate, vinylidene chloride, and maleate and fiimarate esters. 

Figure 9.3. Behavior of the elastic and viscous moduli of a commercial PVC plastisol containing DIDP. [Reprinted from Polymer, Vol. 39, Garcia J.C., Marcilla A., Rheological Study of the Influence of the Plasticizer Concentration in the Gelation and Fusion Processes of PVC Plastisols, p. 3507-3514, 1998, with permission from Elsevier Science].

Table 14.4. Deviation in part waii thickness for moldings obtained with a commercial plastisols containing 70 phr of DOP, 2 phr of thermal stabilizer, and 0.1 phr of pigment, processed at 230°C for 8 min at different rotation speeds...

Typical Particle Size Distribution Information of a Commercial PVC Plastisol Resin. 

Change of Viscosity with Time for Selected Commercial PVC Plastisol Resins. 

The polymer can be made by suspension, emulsion, solution, or bulk polymerization methods. Most of the PVC used in calendering, extrusion, and molding is prepared by suspension polymerization. Emulsion polymerized vinyl resins are used in plastisols and organisols. ° Only a small amount of commercial PVC is prepared by solution polymerization. The microstructure of PVC is mostly atactic, but a sufficient quantity of syndio-tactic portions of the chain allow for a low fraction of crystallinity (about 5 percent). The polymers are essentially linear, but a low number of short-chain branches may exist. The monomers are predominantly arranged head to tail along the backbone of the chain. Due to the presence of the chlorine group, PVC polymers are more polar than polyethylene. The molecular weights of commercial polymers are M = 100,000 to 200,000 ... 

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