Latex fractional coagulation

Coagulation of natural rubber latex by stages with the object of removing the yellow colouring matter in the first fraction. The latex in the second fraction produces a white crepe rubber. See Bleaching Agent. 

Figure 6.16 Plot of yield stress versus concentration for a coagulated latex, perhaps indicating a transition between low and high volume fraction behaviour...

Economical soy products including SPI, DSF, SPC, and SSF can be mixed and coagulated with polymer latex in the aqueous phase to form dry composites with significantly enhanced modulus. These dry soy products have a shear elastic modulus of 1-5 GPa within the temperature range of -40 to 140 C. The carboxylated styrene-butadiene composites filled with these soy products show a significant increase of shear modulus compared to that of the polymer matrix alone. The different compositions of these soy products generate a different reinforcement effect and approximately follow the order SPC > DSF > SSF SPI. The dehydration of these soy reinforcement fractions causes the... 

Alternatively, an oligomeric polymerase enzyme formed in the cytoplasm precipitates or adsorbs onto the granule surface. At a volume fraction of PHA in the bacterium of approximately 0.58 the latex particles reach a close-packing density and coagulation between latex particles occurs, which is accompanied by a decrease in both the rate of polymerization and molar mass of the polymer formed [41,42,46]. 

Continuous stirred-tank reactors (CSTRs) are used for large productions of a reduced number of polymer grades. Coordination catalysts are used in the production of LLDPE by solution polymerization (Dowlex, DSM Compact process [29]), of HDPE in slurry (Mitsui CX-process [30]) and of polypropylene in stirred bed gas phase reactors (BP process [22], Novolen process [31]). LDPE and ethylene-vinyl acetate copolymers (EVA) are produced by free-radical polymerization in bulk in a continuous autoclave reactor [30]. A substantial fraction of the SBR used for tires is produced by coagulating the SBR latex produced by emulsion polymerization in a battery of about 10 CSTRs in series [32]. The CSTRs are characterized by a broad residence time distribution, which affects to product properties. For example, latexes with narrow particle size distribution cannot be produced in CSTRs. 

In previons work (Allen et al., 1963 Tangpakdee et al., 1997), NR coagulated from fresh NR latex, just after tapping from Hevea brasiliensis, was found to be soluble in tolnene, cyclohexane, and tetrahydrofuran. In contrast, the mbber from latex preserved in the presence of ammonia contained about 30-70% gel fraction, which was insolnble in the solvents. The formation of the insoluble fraction would be concerned with the interactions of mbber and proteins, because the gel fractions are reported to be soluble in the solvents after the enzymatic deproteinization (Eng et al., 1994 Tangpakdee et al., 1997). If the interactions are physical but not chemical, it is possible to remove the proteins from the mbber after denaturation of the proteins with urea. Here, the removal of the proteins from fresh NR latex and preserved high-ammonia latex was investigated with mea in the presence of surfactant. 

Further studies also deal with the use of the dodecyl moiety of the allylic compound SAAS (already studied by Urquiola [36] in the semibatch polymerization of butyl acrylate. Such surfactant was reported to behave like SDS, with the fraction of chemically incorporated surfactant hurried inside the particles increasing with the size of the particles [60]. A study of the stability of these latexes was recently reported, showing the influence of the shear rate during the polymerization, as well as the critical coagulation concentration (CCC) in the presence of electrolytes [61],... 

---