Search

Low-resilience flexible polyurethane foams (FPUFs) with varying crosslinking densities, were synthesized from polyols, 4, 4'-diphenyl methane diisocyanate (MDI-100), and water. The effects of crosslinking agent content, the molecular weight ([M.sub.w]) of polyether diol, and the ratio of (polyether triol)/(polyether diol) on the resilience performance of FPUFs were investigated. Results indicate that higher crosslinking density was beneficial to the increasing of recovery time. The recovery time of the FPUF using polyether diol with [M.sub.w] of 400 was 24.3 s. It was 3.2 times longer compared with FPUF using polyether diol with [M.sub.w] of 3000. Dynamic mechanical analysis (DMA) results showed that, FPUFs with high crosslinking density displayed viscoelasticity in a wider range of temperature. However, when molecular chains were longer enough, FPUFs with low crosslinking density also demonstrated significant viscoelasticity, which is owing to the excess of physical crosslinking points. The results in stress-strain cycling and recovery time experiments were consistent with the results of DMA. POLYM. ENG. SCI., 55:308-315, 2015., INTRODUCTION Flexible polyurethane foam (FPUF) as a type of versatile plastic material has been applied in mattresses, packaging, furniture cushioning, and automotive seating [1-3]. Different from rigid polyurethane (PU) foams, [...]

The objective of this work was to elucidate the influence of shear rates on the properties of polyamide 6/multiwalled carbon nanotube (PA6/CNT) composites which was realized by adopting different types of processing methods that feature different orders of magnitude in shear rates, such as compression molding (CM, ~0 s−1), conventional injection molding (CIM, ~102 s−1) and microinjection molding (μIM, ~105 s−1). Electrical conductivity (σ) results indicated that the prevailing high shearing conditions in injection molding was unfavorable for the formation of intact filler network, thereby resulting in a much lower σ than CM counterparts. Moreover, the σ of PA6/CNT microparts was higher than that of CIM macroparts when the filler content was less than 5 wt%, otherwise the σ of CIM macroparts prevailed over that of μIM counterparts. A better filler distribution was observed when PA6/CNT composites were processed under higher shearing conditions, as corroborated by SEM. In addition, CNTs were preferentially aligned along flow direction and a higher degree of CNT orientation was expected with increasing shear rates, as confirmed by Raman spectral analysis. The tensile strength of injection molded PA6/CNT samples increased with increasing filler concentrations, and the more preferential orientation and better distribution of CNT were considered to be the contributing factors. The comparative study of the properties of PA6/CNT composites that processed using different methods was important for their practical applications in industrial sectors. [ABSTRACT FROM AUTHOR]

Through the redistribution reaction of PPO, the hydroxyl‐terminated low molecular weight PPO (PPO‐OH) was prepared. Furthermore, after the reacting of PPO‐OH with methacrylic anhydride, the double‐bond‐terminated low‐molecular weight PPO (R‐PPO) were synthesized, its Mn was 2631 g/mol. The R‐PPO were co‐cured with epoxidized polybutadiene (JP‐100) to prepare JP‐100/R‐PPO cured systems. The JP‐100/R‐PPO cured systems showed single‐phase morphology. The co‐curing reaction with R‐PPO could effectively improve the thermal performance of JP‐100, the glass transition temperature (Tg) of cured JP‐100/R‐PPO systems raised greatly. For the cured JP‐100/R‐PPO (100/30) system, its Tg was 192°C. The dielectric constant and dissipation factor of cured JP‐100/R‐PPO systems were both decreased and showed good frequency stability. The dielectric constant and dissipation factor at 1 MHz of cured JP‐100/R‐PPO (100/30) system were 2.61 and 0.0038, respectively, were obviously lower than those of cured JP‐100 system (which were 3.10 and 0.0099, respectively). The JP‐100/R‐PPO systems exhibited an excellent thermal stability. The 5% weight loss temperature (T5%) of cured JP‐100/R‐PPO system was around 340°C. [ABSTRACT FROM AUTHOR]

In this work, a comparative study on the electrical, morphological, and thermal properties of polypropylene/multiwalled carbon nanotubes (PP/CNT) composites which were prepared by three different processing methods, such as compression molding (CM, shear rate: ~0 s−1), conventional injection molding (CIM, shear rate: ~102 s−1), and microinjection molding (μIM, shear rate: ~105 s−1), was reported. The difference in shear rates among these processing methods and matrix viscosity would significantly affect the state of filler distribution, thereby determining the properties of subsequent moldings. Electrical conductivity results showed that the percolation threshold of PP/CNT moldings followed a trend of μIM > CIM > CM. A higher degree of CNT orientation and a better filler distribution were achieved under the influence of higher shearing conditions, as corroborated by scanning electron microscope observations and Raman spectral analysis. Moreover, increasing filler concentrations played a positive role in improving the thermal stability of PP/CNT composites and the formation of CNT network was believed to be a contributing factor. [ABSTRACT FROM AUTHOR]