Systematic Investigation on the Swelling Response and Oil Resistance of NBR Using the Prediction Models Determined by the Modified Flory-Huggins Interaction Parameter.

The equilibrium swelling test was employed to determine the swelling response of Nitrile Butadiene Rubber (NBR) with various acrylonitrile (ACN) contents, and the three-dimensional solubility parameter (HSP) and modified Flory-Huggins interaction parameter (χHSP) were used to establish the prediction model of the oil-resistant property. The results indicate that the energy difference (Ra) between NBR and solvents calculated by HSP values can be correlated with the swelling response qualitatively with an inversed "S-shape", and high swelling response occurs at Ra < 8 MPa1/2 for NBR. For the purpose of establishing the prediction model, the new modified χHSP value has been calculated and fitted with the swelling response using exponential and logarithmic fittings, respectively. Two prediction models considering all the possible influencing factors have been obtained to determine the swelling response and oil resistance of NBR-based rubber products in bio-fuels, represented by the bio-diesel and IRM 903 test oil in this work. The swelling response of NBR can be evaluated precisely, and high swelling regions can be predicted and avoided in the new emerging fuels through the prediction models. Thus, the oil resistance of NBR-based rubber products, such as seals, holes and gaskets can be well predicted now.

A Systematic Investigation of the Kinetic Models Applied to the Transport Behaviors of Aromatic Solvents in Unfilled Hydrogenated Nitrile Rubber/Ethylene Propylene Diene Monomer Composites.

Kinetic models of solvent transport behaviors are widely used in rubber-solvent systems, and some key points are still worthy of attention. In this work, the Korsmeyer-Peppas and Peppas-Sahlin models were chosen to fit the transport behaviors of three aromatic solvents, benzene, toluene and p-xylene, in the hydrogenated nitrile rubber (HNBR)/ethylene propylene diene monomer (EPDM)-based vulcanizates. The different effects of the various selected transport times (ti) used for fitting on the results of the mathematical models were compared. Moreover, a method to obtain the n parameter for the Korsmeyer-Peppas model and the m parameter for the Peppas-Sahlin model at ti = 0 was discussed. It was found that the differences in values of ti greatly influenced the impact on the fitting results of all the parameters for the two models. In addition, the n parameter for the Korsmeyer-Peppas model along with the m parameter for the Peppas-Sahlin model, which can characterize the transport mechanism, showed differing applicability. But the n and m parameters at ti = 0 obtained by linear fitting showed similar rules with some differences in values. These discussions give important guidance for the application of kinetic transport models in rubber-solvent systems.

Responses of species abundance distribution patterns to spatial scaling in subtropical secondary forests.

To quantify and assess the processes underlying community assembly and driving tree species abundance distributions(SADs) with spatial scale variation in two typical subtropical secondary forests in Dashanchong state-owned forest farm, two 1-ha permanent study plots (100-m × 100-m) were established. We selected four diversity indices including species richness, Shannon-Wiener, Simpson and Pielou, and relative importance values to quantify community assembly and biodiversity. Empirical cumulative distribution and species accumulation curves were utilized to describe the SADs of two forests communities trees. Three types of models, including statistic model (lognormal and logseries model), niche model (broken-stick, niche preemption, and Zipf-Mandelbrodt model), and neutral theory model, were estimated by the fitted SADs. Simulation effects were tested by Akaike's information criterion (AIC) and Kolmogorov-Smirnov test. Results found that the Fagaceae and Anacardiaceae families were their respective dominance family in the evergreen broad-leaved and deciduous mixed communities. According to original data and random sampling predictions, the SADs were hump-shaped for intermediate abundance classes, peaking between 8 and 32 in the evergreen broad-leaved community, but this maximum increased with size of total sampled area size in the deciduous mixed community. All niche models could only explain SADs patterns at smaller spatial scales. However, both the neutral theory and purely statistical models were suitable for explaining the SADs for secondary forest communities when the sampling plot exceeded 40 m. The results showed the SADs indicated a clear directional trend toward convergence and similar predominating ecological processes in two typical subtropical secondary forests. The neutral process gradually replaced the niche process in importance and become the main mechanism for determining SADs of forest trees as the sampling scale expanded. Thus, we can preliminarily conclude that neutral processes had a major effect on biodiversity patterns in these two subtropical secondary forests but exclude possible contributions of other processes.