Glass transition temperature, drying dispersion

Polymeric binder can be added to the network either as an aqueous latex dispersion or as a solution that should be dried prior to lamination in this process. In either case, the polymer should form a film and join adjacent fibers together and thus improve the stress transfer characteristics of the fibrous network. Provided that the proper film forming conditions are available, the property profile of the bonded network is determined to a significant degree by the properties of the polymeric binder at the temperature of use [20,22]. For example, if a softer type of product is desired, a binder with a relatively low glass transition temperature Tg) is often chosen. 

Series I Acrylic Latex Emulsions. A series of four acrylic latex emulsions varying in glass transition temperature (Tg) (3) were applied first. Tg is the temperature at which the resin changes from a relatively flexible to a relatively stiff material. The acrylic latexes are made from water-insoluble monomers such as acrylates and alkyl acrylates polymerized in emulsion form to produce an aqueous dispersion or latex of the polymer. Upon drying, the emulsion is irreversibly broken so that the applied material becomes wash-fast. The application requires no catalyst or high temperature heating. 

Poly(vinyl acetate) dispersions form lightfast, dry, hard, brittle films. Plasticizers therefore have to be used (external plasticization), which are, however, volatile and lead to embrittlement of the films after a relatively short time. Internally plasticized dispersions of copolymers of vinyl acetate with vinyl laurate, butyl maleate, Versatic Acid esters, or ethylene form permanently flexible, nonaging films that are not, however, always sufficiently resistant to hydrolysis. Terpolymer (vinyl acetate-ethylene-vinyl chloride) dispersions form films that are more resistant to hydrolysis than homopolymer and copolymer dispersions. The films also have a higher mechanical strength and lower flammability. The glass transition temperature of the terpolymer can be varied within wide limits and properties can be matched to requirements by using a suitable choice of comonomers. The same is true of vinyl propionate copolymer dispersions. 

Polystyrene Dispersions. On account of their glass transition temperature T of ca. lOO C, polystyrene dispersions do not form films at room temperature. These rigid polymers can only be applied with means of heat drying (e.g., to stiffen fabrics and nonwovens). Film formation is not required in agents used to protect floor coverings and paper coatings (plastic pigments) in this case polystyrene is therefore applied in the form of a dispersion at room temperature. 

Spray drying and hot melt extrusion are the two methods that are most commercially viable for the formation of ASDs. During the formation of ASDs, several considerations such as the relative glass transition temperature of the polymer and API and the miscibility of the API in the polymer must be evaluated. Other methods of note include Kinetisol Dispersing. 

Poly(vinyl acetate) is used for adhesives and as a wood glue (40% solution), as a raw material in lacquers and varnishes (dispersions), and as a concrete additive (in the form of a fine, dispersible powder obtained by spray drying). Poly(vinyl acetate) grades that are more resistant to hydrolysis are obtained by copolymerization with vinyl stearate or vinyl pivalate, since the saponification rate is reduced by the bulkier side groups. Pure poly(vinyl pivalate) has too high a glass transition temperature, 78 C, for most poly(vinyl ester) applications. Other copolymers of vinyl acetate are produced with ethylene (see Section 25.2.1) or vinyl chloride (see Section 25.7.5.3). 

The preparation of ZnO/ PS nanocomposites preceded as follows [112] First, 110 mg bare ZnO or 110 mg PMMA-grafted ZnO were added into a three-necked bottle. Then, 10 mL styrene was added into the reactor. The mixture was stirred with the aid of ultrasonic oscillation until a uniform dispersion of the ZnO particles in styrene was attained. Afterwards, 36 mg azobisisobutyronitrile (AIBN) was added into the reactor as initiator. The subsequent polymerization was conducted at 85°C for 2.5 h. Then, the obtained composites were dried under vacuum for 24 h. The differential scanning calorimetry (DSC) heating curves of neat PS, PS/ZnO (bare), and PS/ZnO (PMMA grafted) are shown in Fig. 10. DSC traces in Fig. 10a show that neat PS has a lower glass transition temperature (Tg = 87.7°C) than PS/ZnO (bare, 7 g = 97.9°C) and PS/ZnO (PMMA grafted, Tg = 95.3°C). This behavior can be explained by the restricting effect of the nanoparticles in polymer. ZnO... 

---