Plasticizer adsorption

Adsorption, where the preservative attaches itself to the surface of a plastic, tends to vary according to the type of plastic, constituents in the plastic, surface treatment, surface area of the plastic. Adsorption has been found with most mercurials, including Thiomersal, benzalkonium chloride and bromide, etc. Small amounts of chlorhexidine, benzoic acid and hydroxybenzoates have also had losses reported for certain plastics. 

Step 2 A temperature is reached (70-90°C), at which interactions between PVC particles and plasticizer begin, prodncing an increase in modnlns and viscosity dne to the plasticizer adsorption in PVC particles and the snbseqnent PVC dissolntion. This step, known as gelation, can be observed as more than one process. This depends on concentrations of the plasticizer and PVC resin and its type, as shown in Figures 10.26. In this case, different partiele sizes or molecular weight distributions of PVC can be responsible for different interactions or dissolution rates in plasticizers. 

The retention volumes on poly(vinyl chloride) powders were correlated with their capacity for incorporating the plasticizer [153]. The diffusion of plasticizer in the polymer powder being controlled by the external smface, by the plasticizer diffusion coefficient and by a shape factor, some connection with gas chromatographic measurements is to be expected. The plasticizer adsorption was found to take place only at a temperature slightly above T,. 

The world s most popular method of PVC polymerization is the suspension method. Around 80% of PVC is produced this way. The difference in this method is that it uses initiators soluble in the monomer. They are dialkyl and diacyl peroxides, ketone peroxides, peroxo-dicarbonates, peroxo-ketals, alkyl peresters or azo compoimds. Seldom is the role of emulsifiers played by alkalies or buffers in order to improve the plasticizer adsorption in PVC. In this process, in order to obtain proper porosity and particle granulation, so-called suspension stabilizers are used, which are derivatives of meth-ylhydroxypropyl cellulose, karboxymethyl cellulose and poly(vinyl alcohols). PVC obtained this way is of high purity. Its molecular mass depends on the temperature of polymerization. Other parameters depend on the interfacial tension at the water-monomer interface. 

Adsorption of t-PA to process equipment surfaces consisting of either stainless steel or glass was minimized by adding the detergent polyoxyethylene sorbitan monooleate (Tween 80) to the semm-free culture conditioned media at 0.01% (vol/vol). The equipment was also rinsed, before use, with phosphate buffered saline (PBS) containing 0.01% Tween 80. Hydrophilic, plastic equipment was used whenever possible. AH buffers were sterile filtered. Sterile filtration of Hquids and gases is usually carried out using 0.2 or 0.45 p.m filters. 

The mixed monocyclic aromatics are called BTX as an abbreviation for ben2ene, toluene, and xylene (see Btxprocessing). The benzene and toluene are isolated by distillation, and the isomers of the xylene are separated by superfractionation, fractional crystallisation, or adsorption (see Xylenes and ethylbenzene). Bensene is the starting material for styrene (qv), phenol (qv), and a number of fibers and plastics. Toluene (qv) is used to make a number of... 

Physical and ionic adsorption may be either monolayer or multilayer (12). Capillary stmctures in which the diameters of the capillaries are small, ie, one to two molecular diameters, exhibit a marked hysteresis effect on desorption. Sorbed surfactant solutes do not necessarily cover ah. of a sohd iaterface and their presence does not preclude adsorption of solvent molecules. The strength of surfactant sorption generally foUows the order cationic > anionic > nonionic. Surfaces to which this rule apphes include metals, glass, plastics, textiles (13), paper, and many minerals. The pH is an important modifying factor in the adsorption of all ionic surfactants but especially for amphoteric surfactants which are least soluble at their isoelectric point. The speed and degree of adsorption are increased by the presence of dissolved inorganic salts in surfactant solutions (14). 

The main characteristic properties of asbestos fibers that can be exploited in industrial appHcations (8) are their thermal, electrical, and sound insulation nonflammabiUty matrix reinforcement (cement, plastic, and resins) adsorption capacity (filtration, Hquid sterilization) wear and friction properties (friction materials) and chemical inertia (except in acids). These properties have led to several main classes of industrial products or appHcations... 

The situation becomes most complicated in multicomponent systems, for example, if we speak about filling of plasticized polymers and solutions. The viscosity of a dispersion medium may vary here due to different reasons, namely a change in the nature of the solvent, concentration of the solution, molecular weight of the polymer. Naturally, here the interaction between the liquid and the filler changes, for one, a distinct adsorption layer, which modifies the surface and hence the activity (net-formation ability) of the filler, arises. Therefore in such multicomponent systems in the general case we can hardly expect universal values of yield stress, depending only on the concentration of the filler. Experimental data also confirm this conclusion [13],... 

Preservative availability may be appreciably reduced by interaction with packaging materials. Examples include the permeation of phenolic preservatives into the rubber wads and teats of multi-dose injection or eye-drop containers and by their interaction with flexible nylon tubes for creams. Quaternary ammonium preservative levels in formulations have been significantly reduced by adsorption onto the surfaces of plastic and glass containers. Volatile preservatives such as chloroform are so readily lost by the routine opening and closing of containers that their usefulness is somewhat restricted to preservation of medicines in sealed, impervious containers during storage, with quite short use lives once opened. 

The sample water container should be made of appropriate materials to avoid adsorption of the chemical of interest on the vessel surfaces. In most cases, a glass bottle may be better than a plastic bottle. The bottle is washed with an organic solvent in advance and also washed with sample water just before sampling. The bottle should be tilled to the limit with water and capped tightly with a Teflon seal to prevent contamination. The top 1-cm of water is not taken to prevent the mixing of floating materials such as oil. 

FIG. 10 SEM photographs for sol-gel-derived (a) and plasticized-PVC (b) membranes encapsulating bis(12-crown-4) after protein adsorption test. (From Ref 27.)... 

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