Effects of Foaming Agents and Calcium Carbonate on Thermo-Mechanical Properties of Natural Rubber Foams

Pjene od prirodnog kaučuka pripremljene su umreživanjem prirodnog kaučuka u sustavu sumpornog umreživanja pri 396 K s pomoću dvovaljčanog mlina s pjenilima: natrijev bikarbonatom (NaHCO3) ili N, N´-dinitrosopentametilen tetraminom (DNPT, C5H10N6O2), te s 0, 20, 40 i 60 phr kalcijeva karbonata (CaCO3) kao punilom. Dobivene pjene od prirodnog kaučuka su lagane, dobrih toplinskih i mehaničkih svojstava, prikladne za toplinsku izolaciju, apsorpciju energije i strukturne uporabe. Oba pjenila dodana u smjesu s prirodnim kaučukom, NaHCO3 i DNPT, razgradila su se i oslobodila plinove pri temperaturi umreživanja (umreživalištu) od 396 K, kako bi se stvorile otvorene i zatvorene stanične strukture. Dodavanje 60 phr CaCO3 čestica punila u pjene prirodnog kaučuka poboljšalo je mehanička i toplinska svojstva kako su ionski naboji Ca2+ i CO 3+ 2- proizveli veze među atomima unutar matrice pjene prirodnog kaučuka. Dobivena pjena od prirodnog kaučuka s punilom 60 phr CaCO3 i s NaHCO3 imala je nasipnu gustoću od 240,5 kg/m3, zaostalu pritisnu deformaciju od 32,60 % i toplinsku provodnost od 0,066 W/mK. Dobivena pjena od prirodnog kaučuka s punilom 60 phr CaCO3 i s DNPT imala je nasipnu gustoću od 219,0 kg/m3, zaostalu pritisnu deformaciju od 11,30 % i toplinsku provodnost od 0,070 W/mK, pri temperaturama iznad 800 °C.Natural rubber foams were prepared from the vulcanization of natural rubber in a sulfur curing system at 396 K by a two roll mill with foaming agents; sodium bicarbonate (NaHCO3) or N, N´-dinitrosopentamethylene tetramine (DNPT, C5H10N6O2), and with 0, 20, 40, and 60 phr calcium carbonate (CaCO3) as a fi ller. The obtained natural rubber foams are lightweight, with good thermal and mechanical properties, suitable for thermal insulation, energy absorption, and structural uses. Both foaming agents added in the natural rubber, namely NaHCO3 and DNPT, decomposed and released gases at the vulcanization temperature of 396 K to produce open and closed cell structures. Adding of 60 phr CaCO3 fi ller particles into the natural rubber foams enhanced the mechanical and thermal properties as the ionic charges Ca2+ and CO3+ 2- produced the interatomic bondings within the natural rubber foam matrix. The obtained natural rubber foam with the 60 phr CaCO3 fi ller and with NaHCO3 possessed the bulk density, compression set, and thermal conductivity of 240.5 kg/m3, 32.60%, and 0.066 W/mK, respectively. The obtained natural rubber foam with the 60 phr CaCO3 fi ller and with DNPT possessed the bulk density, compression set, and thermal conductivity of 219.0 kg/m3, 11.30%, and 0.070 W/mK, respectively, temperatures above 800°C

Urbanization and non-communicable disease mortality in Thailand: an ecological correlation study.

This study provides strong evidence from an LMIC that urbanization is associated with mortality from three lifestyle-associated diseases at an ecological level. Furthermore, our data suggest that both average household income and number of doctors per population are important factors to consider in ecological analyses of mortality

Lead zirconate (PbZrO3) embedded in natural rubber as electroactive elastomer composites

Perovskite lead zirconate (PbZrO3) was synthesized in an orthorhombic form at a temperature below the Curie temperature, TC. The orthorhombic form is a noncentrosymmetric structure which is capable of spontaneous polarization. Fourier transform infrared (FTIR) spectra and X-ray diffraction (XRD) patterns confirm the successful synthesis of the lead zirconate; and scanning electron microscopy (SEM) micrographs indicate that PbZrO3 particles are moderately dispersed in the natural rubber (NR) matrix. Without an electrical field, the particles merely act as a ferroelectric filler, which can absorb and store additional stress. Under an electrical field, particle-induced dipole moments are generated, leading to interparticle interaction and a substantial increase in the storage modulus. At a small amount of lead zirconate particulates present in the natural rubber matrix, at a volume fraction of 0.007306, the electrical conductivity increases dramatically by nearly two orders of magnitude at the electrical frequency of 500 kHz