Retained solvents plasticizers

Retained solvents may act as plasticizers (i.e., unless the solvent evaporates completely, the deposited resin may not have the same properties as the original solid in its pure state). Retained solvent lowers the glass-transition temperature. If the Tg of the mixture is at or below room temperature, rubbery behavior will result, and consolidant effectiveness will be reduced. Acryloid B72 seemed to retain solvent in films cast from acetone and toluene solutions and then air-dried (12). Further study showed that Acryloid B72 may retain measurable amounts of solvent even after 30 days at room temperature (16, 17). Results are shown in Table II. 

Absorption and even adsorption of a solvent of a similar solubility parameter to the plastics material. This can be a very serious problem, since retained solvent within the bond line could well act as a release agent. 

Solutions of Polymeric Substances and Resins in Organic Solvents. A distinction is be drawn between adhesives that set by evaporation of the solvent and form an adhesive joint by adhesion of the dissolved polymer to the substrate surfaces, and adhesives for plastics, the solvent of which dissolves and swells the plastics surfaces and joins them by means of migration processes. This allows bonding of plastics that are otherwise difficult to join. The polymer solutes in solution adhesives act primarily as thickeners for establishing certain flow properties and retaining the solvent for the duration of the dissolution process. These solid components also may perform a limited gap-filling function. 

The largest market for g. as such is for pharmaceuticals and especially cosmetics (together 33% of the total consumption). It functions as moisture retainer, solvent, substance carrier and plasticizer for hydrophilic polymers. It is easy to perfume, nontoxic and has good skin care properties. It is used in many formulations, such as ointments, shaving creams, creams and lotions, toothpastes, ear and nose drops, and many more. 

Other polymers used in the PSA industry include synthetic polyisoprenes and polybutadienes, styrene-butadiene rubbers, butadiene-acrylonitrile rubbers, polychloroprenes, and some polyisobutylenes. With the exception of pure polyisobutylenes, these polymer backbones retain some unsaturation, which makes them susceptible to oxidation and UV degradation. The rubbers require compounding with tackifiers and, if desired, plasticizers or oils to make them tacky. To improve performance and to make them more processible, diene-based polymers are typically compounded with additional stabilizers, chemical crosslinkers, and solvents for coating. Emulsion polymerized styrene butadiene rubbers (SBRs) are a common basis for PSA formulation [121]. The tackified SBR PSAs show improved cohesive strength as the Mooney viscosity and percent bound styrene in the rubber increases. The peel performance typically is best with 24—40% bound styrene in the rubber. To increase adhesion to polar surfaces, carboxylated SBRs have been used for PSA formulation. Blends of SBR and natural rubber are commonly used to improve long-term stability of the adhesives. 

Phase separation of the saturated solution from the excess solid solute is a critical process. If a filter is employed, it must be inert to the solvent, it must not release plasticizers, and its pore size must be small enough to retain the smallest particles of the solid solute. Furthermore, steps must be taken to monitor, minimize, and preferably avoid losses of the dissolved solute by adsorption onto the filter material [27-30] and/or onto the vessels, pipettes, and syringes. Typically, the first small volume of filtrate is discarded until the surfaces of the filter and/or vessels are saturated with the adsorbed solute, to ensure that the filtrate analyzed has not suffered significant adsorption losses. Adsorption can be a serious problem for hydrophobic solutes, for which filtration would not be recommended. 

Union Carbide (34) and in particular Dow adopted the continuous mass polymerization process. Credit goes to Dow (35) for improving the old BASF process in such a way that good quality impact-resistant polystyrenes became accessible. The result was that impact-resistant polystyrene outstripped unmodified crystal polystyrene. Today, some 60% of polystyrene is of the impact-resistant type. The technical improvement involved numerous details it was necessary to learn how to handle highly viscous polymer melts, how to construct reactors for optimum removal of the reaction heat, how to remove residual monomer and solvents, and how to convey and meter melts and mix them with auxiliaries (antioxidants, antistatics, mold-release agents and colorants). All this was necessary to obtain not only an efficiently operating process but also uniform quality products differentiated to meet the requirements of various fields of application. In the meantime this process has attained technical maturity over the years it has been modified a number of times (Shell in 1966 (36), BASF in 1968 (37), Granada Plastics in 1970 (38) and Monsanto in 1975 (39)) but the basic concept has been retained. 

Since the discovery of Teflon by Roy Plunkett in 1937 a number of fluorinated plastics have reached commercial status. These plastics, exemplified by polytetrafluoroethylene (PIPE), have outstanding electrical, chemical, and thermal properties. AU these commercial materials are either crystaUine or semicrystalline. Teflon AF is a family of amorphous copolymers that retain the desirable electrical, chemical, and thermal properties of semicrystalline fluorinated plastics and also have such properties associated with amorphous materials as optical clarity, improved physical properties, and solubility in selected fluorinated solvents. 

From the viewpoint of retention in the plastic (i.e. more likely to have residual solvent problems) ethyl acetate is the least desireable solvent to use in the printing ink. However, from the viewpoint of migration into the beverage it may be the best solvent to use since it is the least soluble in the beverage. Based on this the KP// for ethyl acetate will be the largest of the three solvents thus favoring it to be retained by the plastic. One can estimate relative KP/L for the different solvents between LDPE and water by combining Eqs. (4-35) and (4-58) ... 

For practical applications, fulgides must retain their excellent photochromic properties in solvent and in a polymer matrix, because the ultimate photomemoiy media will certainly be provided as a plastic layer containing photochromic... 

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