Nanoscale Res Lett (2009) 4:420–430 as-prepared crosslinked gels has been carried out by measuring various physical properties including cross- link density and the optimum level of gel loading has been determined from the rheological properties of the gel ﬁlled systems [17, 19]. However, the extent of property enhancement upon the addition of chemically crosslinked gels varies with the nature of matrix and gels. In the present work, our aim was to improve the deﬁciency in virgin NR property by using SBR nanogels and vice versa. For example, we have attempted to improve the thermal sta- bility of NR using SBR gels which have inherently better thermal stability, without sacriﬁcing any other properties. Similarly, green strength of SBR can be improved greatly by using the relatively high strength NR gels. For this purpose, NR and SBR latex nanogels having gradient of crosslink density and different particle sizes were prepared by sulfur prevulcanization technique and thoroughly char- acterized. These latex gels were then intermixed with neat NR and SBR lattices at different loadings. Finally, inﬂu- ence of these chemically crosslinked gels on mechanical, dynamic mechanical, and thermal behavior of virgin elas- tomers was studied in detail along with an extensive morphological study, for the ﬁrst time. Experimental Materials High ammonia centrifuged natural rubber (NR) latex hav- ing 60% dry rubber content (DRC) was provided as free sample by the Rubber Board, Kottayam, India. Sulfur, zinc oxide (ZnO), and zinc diethyl dithiocarbamate (ZDC), all in 50% aqueous dispersion, were also obtained from the same source and used as received. Styrene butadiene rub- ber (SBR) latex having 30% total solid content (T.S C) and 30% bound styrene content, with a pH of 10.5 was gen- erously received as gift sample from the Apar Industries, Ankeleswar, India. Toluene (LR-grade), potassium hydroxide (KOH), and potassium laurate (KC12H23O2) were procured from s.d. Fine Chemicals, Mumbai, India. Table 1 Formulations for sulfur prevulcanization 421 Doubly distilled water was obtained from indigenous source. Preparation of Sulfur Prevulcanized Latex Gel and Gel Filled Rubber Chemically crosslinked NR latex and SBR latex gels were prepared by employing sulfur prevulcanization technique. The virgin lattices were compounded with S, ZDC, and ZnO dispersions and subsequently prevulcanized. The formulations of different mixes for sulfur prevulcanization are given in Table 1. Sulfur to accelerator ratio was varied from 0.5 to 3 in the crosslinking recipes. Vulcanization reaction of the compounded latex was carried out at 80 C for 2 h; the detailed procedure was described in our earlier communications [17, 19]. Films of crosslinked gel were obtained from prevulcanized latex by casting on a level glass plate and subsequent drying at ambient temperature (25 ± 2 C) to constant weight. Finally, the ﬁlms were vacuum dried at 50 C for 12 h. These ﬁlms were used for characterization of gelled rubber. Intermixing of gel ﬁlled raw rubber samples was carried out by adding a given amount of a particular type of NR latex gel to virgin SBR latex and vice versa, followed by gentle stirring (200–300 rpm) for 1 h at 25 ± 2 C. Then, these were cast and dried following the above-mentioned procedure. These gel ﬁlled raw rubber ﬁlms were used for further testing. Sample Designations Control natural rubber latex and styrene butadiene rubber latex were designated as NR and SBR, respectively. Indi- vidual NR and SBR gels were expressed as NSa and SBSa, respectively, where ‘a’ represents the ratio of sulfur to accelerator used in the prevulcanization recipe. NR gel mixed SBR systems were denoted as SBNSa/b, where ‘a’ has the same notation as stated above and ‘b’ is the amount (phr) of prevulcanized NR gel added into the SBR latex. Similarly, SBR gel ﬁlled NR latex systems were noted as NRSBSa/c, where ‘a’ has the same meaning as stated above Ingredients (dry wt basis) NR latex (60%) SBR latex (30%) 10% KOH 10% potassium laurate 50% sulfur dispersion 50% ZDC dispersion 50% ZnO dispersion NS0.5 100.00 0.0 0.25 0.25 0.60 1.20 0.20 NS1 100.00 0.0 0.25 0.25 1.20 1.20 0.20 NS2 100.00 0.0 0.25 0.25 1.20 0.60 0.20 NS3 100.00 0.0 0.25 0.25 1.80 0.60 0.20 SBS0.5 0.0 100.00 0.0 0.0 0.60 1.20 0.20 SBS1 0.0 100.00 0.0 0.0 1.20 1.20 0.20 SBS2 0.0 100.00 0.0 0.0 2.40 1.20 0.20 SBS3 0.0 100.00 0.0 0.0 3.60 1.20 0.20 123