Plasticizers polymeric, migration

Raw Materials. PVC is inherently a hard and brittle material and very sensitive to heat it thus must be modified with a variety of plasticizers, stabilizers, and other processing aids to form heat-stable flexible or semiflexible products or with lesser amounts of these processing aids for the manufacture of rigid products (see Vinyl polymers, vinyl chloride polymers). Plasticizer levels used to produce the desired softness and flexibihty in a finished product vary between 25 parts per hundred (pph) parts of PVC for flooring products to about 80—100 pph for apparel products (245). Numerous plasticizers (qv) are commercially available for PVC, although dioctyl phthalate (DOP) is by far the most widely used in industrial appHcations due to its excellent properties and low cost. For example, phosphates provide improved flame resistance, adipate esters enhance low temperature flexibihty, polymeric plasticizers such as glycol adipates and azelates improve the migration resistance, and phthalate esters provide compatibiUty and flexibihty (245). 

The Ts of methacryhc polymers may be regulated by the copolymerization of two or more monomers as illustrated in Figure 1. The approximate T value for the copolymer can be calculated from the weight fraction of each monomer type and the T (in K) of each homopolymer (15). Acrylates with low transition temperatures are frequently used as permanent plasticizers (qv) for methacrylates. Unlike plasticizer additives, once polymerized into the polymer chain, the acrylate cannot migrate, volatilize, or be extracted from the polymer. 

CPA. Copolymer alloy membranes (CPAs) are made by alloying high molecular weight polymeries, plasticizers, special stabilizers, biocides, and antioxidants with poly(vinyl chloride) (PVC). The membrane is typically reinforced with polyester and comes in finished thicknesses of 0.75—1.5 mm and widths of 1.5—1.8 m. The primary installation method is mechanically fastened, but some fully adhered systems are also possible. The CPA membranes can exhibit long-term flexibiHty by alleviating migration of the polymeric plasticizers, and are chemically resistant and compatible with many oils and greases, animal fats, asphalt, and coal-tar pitch. The physical characteristics of a CPA membrane have been described (15). 

It is desirable that the plasticizer compounded with a polymer be permanently retained. Loss of plasticizer changes the properties of a given formulation, and can be produced by volatilization, extraction or migration. The volatility of a plasticizer in a formulation can be related to the surface area, thickness of the polymeric material, and viscosity (e.g. molecular weight) of the plasticizer itself. 

These data show that the 566TPU/PVC polymeric blend has good mechanical properties, especially at low temperatures. Other tests showed very good oil resistance of this material. Also, the migration rate of plasticizer is only one-fourth of that of commercial medical grade flexible PVC material. 

About half of the styrene produced is polymerized to polystyrene, an easily molded, low-cost thermoplastic that is somewhat brittle. Foamed polystyrene can be made by polymerizing it in the presence of low-boiling hydrocarbons, which cause bubbles of gas in the solid polymer after which it migrates out and evaporates. Modification and property enhancement of polystyrene-based plastics can be readily accomplished by copolymerization with other substituted ethylenes (vinyl monomers) for example, copolymerization with butadiene produces a widely used synthetic rubber. 

Polymerization products with internal plasticization have the advantage that there is no migration or efflorescence of the plasticizer on storage. On the other hand, the mechanical properties—above all, flexibility at low temperatures—are decreased in comparison with the products with low molecular plasticizers. This is because mobility in the solvatized molecules is diminished. The same refers to tensile strength, which is often decreased with internally plasticized polymers. In this respect they are inferior to externally plasticized products, which also have an advantage in that type and quantity of plasticizer can be varied widely. Internally plasticized products must have a definite ratio of components. These are reasons why combinations of both types of plasticizers are preferred. 

Migration of ions through the plasticizer is frequently considered to be a function of the mobility of the plasticizer itself (2,5). In many electrical applications, where fugitive monomeric plasticizers like DOP can cause damage, they can be replaced by non-fugitive polymeric plasticizers such as viscous liquid polyesters. Comparison of DOP vs. a typical polymeric plasticizer, Rohm Haas Paraplex 0-25 poly (propylene sebacate), showed no significant improvement in volume resistivity (Table VI), particularly when its lower plasticizing efficiency was considered. Thus plasticizer mobilitv alone does not help us explain volume resistivity (5). 

Polymeric plasticizers are generally polyesters with a relatively low molecular weight. They rue used where resistance to high temperatures and freedom from migration and extraction are required. Polymeries are more difficult to incorporate, have poor low-temperature properties, and are expensive. 

Although MAA monomer possesses a larger reactivity ratio than MMA monomer, more MAA was found to exist in the outer side of the particle in the batch latex, as shown in Figures 5 and 6. This behavior could be explained if one can accept the fact that the MAA-rich polymers, which are formed early on during the polymerization, can migrate to the surface of the particle due to their higher hydrophilicity and plasticization of the polymer with the monomer. In the semi-continuous process, it could be expected that copolymer with the same composition as the comonomer feed is formed, and the particle contains a uniform distribution of carboxyl groups. 

Polymeric Types. When extreme resistance to volatility, marring, migration, and hydrocarbon extraction is required, polymeric plasticizers —the reaction product of aliphatic dicarboxylic acids and low molecular weight diols—are used. Performance varies directly as molecular weight. 

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