Influence of drying conditions on colour,betacyanin content and antioxidant capacities in dried red-fleshed dragon fruit (Hylocereus polyrhizus)

In this study, drying of red-fleshed dragon fruit at different temperatures (40, 50, 60, 70 and 80 °C) and air velocities (1.0 and 1.5 m s⁻¹) was conducted under the specific humidity of 25 g H₂O kg⁻¹ dry air. The results showed that drying at higher temperatures resulted in shorter drying times. However, temperature and air velocity did not significantly affect the total betacyanin contents and antioxidant capacities in dried products. Seven betacyanins identified by LC-MS were betanin, isobetanin, phyllocactin, isophyllocactin, betanidin 5 –O-(6′O-3-hydroxybutyryl)-β-glucoside, isobetanidin 5 –O-(6′O-3-hydroxybutyryl)-β-glucoside and decarboxylated phyllocactin. In addition, the temperature increased the isomerisation of betacyanins. The most preferable condition for preserving the colour and betacyanin contents of red-fleshed dragon fruit was the drying at a temperature of 80 °C and air velocity of 1.5 m s⁻¹ since it could shorten the drying time and give a bright red colour to the dried product as well as it had no significant impact on the betacyanins.     

Influence of magnesium carbonate loading on the compound properties of polychloroprene,natural rubber,and their blends

The effect of magnesium carbonate (MgCO₃) loading on the compound properties of polychloroprene (CR), natural rubber (NR), and their blends was investigated. The studied properties included Mooney viscosity, cure characteristics, and degree of filler–filler interaction. In addition to MgCO₃ loading, the effect of the blend ratio on such properties was simultaneously determined. The results reveal that, regardless of the rubber type and blend ratio, increasing MgCO₃ loading resulted in not only an increase in the compound viscosity, but also in the enhancements of the cure rate and state of cure. However, the effect of MgCO₃ loading on the overcured behavior was strongly dependent on the rubber type and blend ratio. For CR, the presence of MgCO₃ accelerated postcuring, whereas the opposite results were found for NR, in which the reversion rate was promoted. For CR/NR blends, a plateau behavior was obtained at a 50/50 blend ratio, where the degrees of postcuring and reversion were counterbalanced. The results also reveal that when MgCO₃ was loaded at low concentrations (≤20 phr), the degree of filler–filler interaction was very low and had no significant effect on the compound properties. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Rheological behavior of CPE/NR blends filled with precipitated silica

Blends of elastomeric chlorinated polyethylene (CPE) and natural rubber (NR) at the blend composition ratio of 80/20 CPE/NR with various precipitated silica loadings from 0 to 30 phr were prepared. Their rheological behaviors were determined using two rheometers with different shear modes, i.e., the oscillatory rheometer (Rubber Process Analyzer, RPA2000) and the rate‐controlled capillary rheometer (Goettfert Rheotester 2000). Results obtained reveal that the viscoelastic behavior of blends is influenced remarkably by loadings of silica. Within the oscillatory shear strains of 0.3–30%, the unfilled blend appears to be almost insensitive to shear strain that means the unfilled blend possesses a broad linear viscoelastic (LVE) region. As silica is incorporated, the elastic modulus (G′) of blends increases, particularly at silica loadings of 20 and 30 phr. The increase in G′ as a function of silica loading could be explained by a reinforcing effect via a hydrodynamic effect as well as a strong interaction between chlorine atoms on CPE molecules and silanol functional groups on silica surfaces associated with a formation of silica tridimensional transient network, usually known as a secondary filler network. Also, all blends with various loadings of precipitated silica reveal an increase in elasticity with increasing frequency, and those with high silica loadings (i.e., 20 and 30 phr) give a more time‐independent elastic response, which supports the presence of filler transient network in these blends. By applying the Cox and Merz concept to the rheological results, the superimposition of flow curves determined from of the oscillatory shear flow and steady shear flow in the highly silica filled blends is possible if the silica transient network effect is eliminated. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2565–2571, 2006