Unexpected Stress Overshoot in Extensional Flow of Star Polymer Melts.

Previous studies have shown that the nonlinear rheological behavior of 3-arm star polymer melts in fast extensional flow is identical to that of linear polymers with the same span molecular weight, because the star polymers are highly aligned and have a similar conformation as the corresponding linear polymers. However, with more arms, it would be more difficult for the stars to be aligned like linear chains, and the nonlinear extensional rheology of star polymers with more arms under large deformations has not been investigated yet. Here we show that the star polystyrene (8-10 arms) melts behave differently from the linear polystyrenes. A transient stress overshoot is observed in the fast extensional flow, probably due to the difference in entanglement density near and far away from the branch point.

Occurrence and risk assessment of PAHs from athletic fields under typical rainfall events.

Six polycyclic aromatic hydrocarbons (PAHs) including naphthalene (Nap), fluorene (Flu), phenanthrene (Phe), fluoranthene (Fla), pyrene (Pyr), and chrysene (Chr) were detected in runoff from five athletic fields during three rainfall events. The event mean concentration (EMC) of ∑6PAHs ranged from 3.96 to 23.23 µg/L, which was much higher than the EMC in urban traffic area runoff. Except for Nap, the PAH concentrations followed in the order of artificial turf > badminton court > basketball court > plastic runway > optennis court. The surface characteristics of the athletic fields, such as the composition of materials and roughness, played an essential role in the release of PAHs. ∑6PAHs concentration during the 2nd rainfall event (July 22nd) was the highest among the three rainfall events, indicating that high rainfall intensity facilitated the PAHs release. PAHs during three rainfall events showed little first flush effect except for the artificial turf during the 2nd (22nd July) and 3rd (29th July) rainfall events. The first flush effect could be affected by rainfall characters, PAH properties, and surface characteristics of athletic fields. Ecological risk assessment showed that PAHs in runoff corresponded to moderate-to-high risk, while health risk assessment showed that PAHs could pose a potential carcinogenic danger to human health via dermal contact.

Evaluation of modified permeable pavement systems with coal gangue to remove typical runoff pollutants under simulated rainfall.

Coal gangue (CG) as mineral waste was properly treated and applied as the filter media in permeable pavement systems due to its good sorption ability and mechanical strength. Batch experiments show the maximum adsorption capacity of calcined CG to phosphorus could reach 2.63 mg/g. To evaluate the removal effect of typical runoff pollutants including chemical oxygen demand (COD), total nitrogen (TN), total phosphorus (TP) and ammonia (NH4+-N), the gravel and sand in a traditional pavement system were replaced by CG respectively. The leaching behavior of the four pollutants in CG modified systems is limited and comparable with traditional system, indicating pretreated CG as filler would not cause environmental risk. CG-based pavement systems improved the removal efficiency of the four pollutants especially for TP. The removal mechanisms including interception, adsorption and microorganism degradation. The removal rates of COD, NH4+-N and TN by CG modified and traditional systems decreased with rainfall duration, while it is not obviously changed with rainfall recurrence period and drying period. Overall, the permeable pavement with CG layers that replaced both sand and gravel layers show best removal efficiency of all pollutants investigated especially for TP (>95%). This study provides a new way for CG utilization and gives the reference for the process design of permeable pavement.