Characteristics of experimental cis‐1,4‐polyisoprene latices

Abstract

Experimental latices of synthetic cis‐1,4‐polyisoprene and films and cellular objects produced from them are described. The latices of the synthetic polymers with molecular weights of about 2,000,000 are stabilized by anionic surfactants and have weight median particle diameters of about 0.9 μ and log normal particle size distribution. Tensile properties and flow characteristics of unvulcanized latex films could be regulated by introduction of controlled, small, amounts of crosslinking into the latex. Procedures used for crosslink density determination on cis‐polyisoprene latex at various stages of use are described. Vulcanized latex films having maximum tensile strengths (5500–6000 p.s.i. and 800–950% elongation) were obtained when the final crosslink density was in the range 1.0–1.6 × 10−4 moles of effective chains/cc. Use of the synthetic cis‐polyisoprene latex in production of foam is described. Gelation with sodium silicofluoride at room temperature occurs within 2–10 minutes. Production of a controlled level of crosslinking in the latex prior to frothing and gelling was found to improve the uniformity of cell structure of foams and to increase their resistance to compression. Excessive crosslinking in the latex during maturation was shown to cause a loss of tensile strength in cured products presumably because the coalescence of latex particles during gelation is adversely affected. The properties of synthetic cis‐1,4‐polyisoprene latices and the physical properties of films and foams derived from them are shown in general to be very similar to those of natural rubber latex and its products.

Contribution of hydrogen and/or covalent bonds on reinforcement of natural rubber latex films with surface modified silica

“…Presis et al have reported that excessive cross‐linking in the latex during maturation was shown to cause a loss of tensile strength in cured products. That was identified as the coalescence of latex particles during gelation which tend to get adversely affected by over curing . Manroshan and Baharin have explained the findings on tensile properties of nanosized CaCO 3 filled NR latex films supporting the hypothesis suggested by Presis et al The reduced tensile strength at higher loading of filler is attributed to filler‐filler interaction which goes beyond the enhanced filler–rubber interactions .…”

Physico-mechanical Effects of Surface-modified Sorgum Stalk Powder on Reinforced Rubber

“…It has been explained elsewhere that these sharp decreases indicate the loading at which the filler bears more of the stress, and in some way it also indicates the limiting levels of loading [13,27]. Preiss et al [28] while explaining the decrease in strength of an experimental cis-1,4 isoprene with increase in filler loading even as the crosslink density had increased, adduced it to the increasing inability of the rubber latex particles to coalesce and cooperate fully with increasing crosslink; other workers also gave the same explanation [29].…”

Effect of nanosized calcium carbonate on the mechanical properties of latex films

“…At 30 phr of filler loading, the tensile strength decreased but the crosslink density (in reference to swelling index), M 100 , and M 300 showed an increase, as seen in Figures 2, 3, and 4, respectively. In their study on the characteristics of experimental cis ‐1,4 polyisoprene latices, Preiss et al10 reported that the decrease in tensile properties with increasing crosslink density is a consequence of the decreasing ability of the latex particles to coalesce and integrate fully as the concentration of crosslinks in the particles increases. In this study, the decrease in tensile properties at 30 phr of filler loading is attributed to an increase of filler to filler interaction compared to the filler to rubber interaction, which is needed to reinforce the rubber network.…”