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Foaming temperature and grade of dry natural rubber were varied to evaluate their effects on the morphology and mechanical properties of natural rubber (NR) foams. Three different grades of NR were used; namely ENR-25, SMR-L, and SMR-10. NR foams from these grades were produced at three different foaming temperatures, i.e. 140, 150, and 1608C. The study was carried out using formulated compositions containing sodium bicarbonate as the chemical blowing agent and were expanded using conventional compression molding technique via a heat transfer foaming process. The NR foams were characterized with respect to their relative foam density, density of crosslinking, cell size, compression stress, and compression set. Increase in foaming temperature resulted in lower relative density and larger cell size.It was also discovered that the crosslink density slightly decrease with increasing foaming temperature. For mechanical properties, the highest foam density resulted in the highest compression stress. Compression stress at 50% strain increased with increasing foaming temperature and ENR-25 foam has the highest compression stress among the produced foams. The results showed that the morphology, physical, and mechanical properties of the rubber foams can be controlled closely by the foaming temperature and rubber grades.

Tensile and electrical properties of graphene nanopowder (GNP) and multiwalled carbon nanotubes (MWCNT) filled epoxy thin film nanocomposites were investigated. In addition, synergy effects of various mixture ratios of GNP–MWCNT hybrids on the properties of the epoxy thin film nanocomposites were evaluated. It was found that the addition of GNPs or MWCNTs decreased the tensile properties compared to that of unfilled epoxy. The electrical percolation threshold of MWCNT/epoxy was found to be 0.8 vol%. Addition of only 0.1 vol% GNPs results in significant improvement in the electrical properties of the composites. Enhanced tensile and electrical properties in the GNP–MWCNT/epoxy hybrid were achieved with GNP–MWCNT ratio of 0.1:0.4. Morphological analysis confirmed the uniform dispersion of both GNPs and MWCNTs within the epoxy matrix. For the hybrid GNP–MWCNT filler system (i.e., with the 0.1:0.4 ratio), MWCNTs were seen to align themselves on the GNPs surfaces creating an interconnected strong nanofiller network in the epoxy.

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Several parameters, such as crosslinking agent concentration, blowing agent concentration, and temperature, were varied to evaluate their effects on the structure and mechanical properties of low‐density polyethylene (LDPE) foams. Dicumyl peroxide (DCP) was used as crosslinking agent, while azodicarbonamide (ADC) was utilized as the blowing agent at different levels. The formulations were prepared by using a thermostatically controlled heated two‐roll mill and foamed by using a compression molding technique via a single‐stage foaming process at three foaming temperatures (165, 175, and 185°C). The resultant LDPE foams were characterized and found to have a closed cell structure. The density and gel content increased proportionally with crosslinking level, whereas density decreased when ADC level and foaming temperature were increased. Another characteristic evaluated was the foam cell size decreased when the crosslinking level and foaming temperature were increased. In contrast, increasing the ADC concentration only gave a maximum cell size increase up to 6 phr that decreased when 8 phr of ADC was used. Results also indicated that compression stress increased proportionally with DCP level and decreased when ADC concentration and foaming temperature were increased. Impact studies on the prepared foams showed that their ability to absorb impact energy decreased with increasing crosslinking level, foaming temperature, and blowing agent concentration. J. VINYL ADDIT. TECHNOL., 2009. © 2009 Society of Plastics Engineers

Abstract. The present study focuses on the development and characterization of epoxy syntactic foam filled with epoxy hollow spheres (ESF/EHoS). The epoxy syntactic foam (ESF) was produced by embedding epoxy hollow spheres (EHoS) into a mixture of epoxy-hardener and 3% KOH solution. An innovative approach and simple procedure was implemented in the preparation of the EHoS where expanded polystyrene (EPS) beads were used as initiation material. The EPS beads were coated with the epoxy resin and these coated EPS beads were later cured and post-cured at high temperature which will also shrink the EPS beads thus producing a hollow structure. The physical and compressive properties of the developed ESF were characterized. The progressive collapse of the syntactic foam was monitored in real-time with respect to percentage of strain during a compression test. Results also indicated that the (ESF/EHoS) showed similar deformation pattern with other types of syntactic foams which exhibited the common three regions of deformations.