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The viscosity of freshly prepared poly(vinyl chloride) (PVC) plastisol increases with time, and this phenomenon is called viscosity aging. The increase is rapid in the beginning and slows down to a quasistable value, but a very slow increase continues. The phenomenon may be a result of either the deagglomeration of agglomerated particles or the dissolution of low‐molecular‐weight PVC into the plasticizer. In this work, two typical commercial resins were used, one containing friable agglomerates and the other containing nonfriable agglomerates. With the friable‐agglomerate resin, about 40% of the initially present agglomerates deagglomerated, whereas the viscosity increased in a week to twice the initial value. With the nonfriable‐agglomerate resin, very fine and very low molecular weight particles, about 3% of all the particles, dissolved into the plasticizer in 2 days. The effect of the plasticizer type on the viscosity aging through deagglomeration was investigated with four plasticizers and three plasticizer blends. The emulsifiers used for polymerization, and retained through drying, affected the aging in the beginning. On the other hand, the viscosity after 1 week was free from the effect of the emulsifier and was affected only by the plasticizer type. With the exception of two blends, the 1‐week viscosity was quantitatively related to the dielectric constant divided by the molecular weight of the plasticizer. For the plasticizer blends, one of the plasticizers could have a dominant effect on the promotion of deagglomeration. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 448–464, 2005

Mill behavior was examined with gum rubbers and carbon black-filled compounds of different types of cis-1,4-polybutadiene. The rubbers were Ti-, Nd-, and Co-polymerized polymers. The Co-polymerized rubber contained crystalline particles of 1,2-polybutadiene. The carbon black was 50 phr N330. Photographs of the samples on the mill were taken after milling for 2 min. The mill behaviors were classified according to the four regions of Tokita and White. Behavior at loading, stickiness, and mill shrinkage were evaluated qualitatively to interpret mill behavior with aid of the deformational data of previous publications. The Ti-rubber, containing relatively short branches and exhibiting a strain-softening, was in Region III. The Nd-rubbers, containing relatively long branches and exhibiting a strain-hardening, tended to go to Region IV, because the degree of branching was low. The Co-rubbers containing crystalline particles were in Region II, even though they gave strain-softening since they had a high modulus because of the presence of the particles. An overriding effect on the mill behavior appeared to come from how high the modulus of the gum rubber was at the milling condition. Both the gum rubber and the corresponding compound were in the same region of the mill processability. The strain-induced crystallization occurred only when the compounds were under tension on the mill, i.e., Region II. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 1995–2001, 1997

The effect of fillers and the structure of matrix rubbers on the tensile stress—strain behavior were examined with unvulcanized compounds of cis-1,4-polybutadiene. The matrix rubbers were CB11, CB22, and VCR412, which had been studied previously. The fillers were two different carbon blacks (N110 and N330) and silica. The tensile modulus was found to be separable into the time-dependent and strain-dependent functions. The time dependence was represented with a universal form, the observed time being reduced with the extension ratio. The strain-dependent function was affected by material variables. The function indicated a strain-softening tendency. The extent of softening is related to the softening or hardening observed with the unfilled matrix rubbers, which are in turn related to the length and degree of branching and to the presence of crystalline particles of 1,2-polybutadiene. However, carbon black evidently accentuates the softening tendency. Also, poorer dispersion results in higher softening. The silica-filled compound had a poor dispersion. With the addition of a coupling agent, the dispersion improved but the compound behaved like it was crosslinked. The strain-induced crystallization previously observed with CB11 and VCR412 gum rubbers (but not with CB22) appears as significant differences of the moduli of the compounds. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1445–1453, 1997