Investigation of the Photosensitized Mechanisms of PCBs in the Presence of Natural Organic Matter

The structures of 26 different congeners of polychlorinated biphenyls（PCBs, including monothrough deca-chlorinated） were optimized using density functional theory（DFT） calculations with the 6-31＋G（d,p） basis set. The activation energies for the dechlorination of these systems were calculated for direct photodegradation and photosensitized degradation reaction pathways in the presence of natural organic matter（NOM）. The dechlorination mechanism of these PCBs and the ring-opening reaction mechanisms（using QST3 method） of the photosensitive degradation products were analyzed. The results showed that（i） the activation energy for the photosensitized degradation of PCBs was much lower than that of direct photodegradation;（ii） the degradation activities（i.e., C–Cl bond cleavage energies） were the same for both degradation pathways and followed the order ortho 〉 meta 〉 para;（iii） the degradation activities of asymmetric PCBs were higher than those of the corresponding symmetrical PCBs for the direct photodegradation and it was completely opposite in the photosensitive degradation;（iv） there was no correlation between the dissociation energy and the number of C–Cl bonds for the direct photodegradation and dechlorination products were all biphenyl;（v） the degradation activity of PCBs decreased as the number of C–Cl bonds increased in the presence of NOM; and（vi） even when the dechlorination reaction was incomplete, it produced chlorophenol. Furthermore, the free radicals of NOM led to the ring-opening reactions of PCBs via an initial addition step. The main site of these ring-opening reactions was the ortho position. Notably, the likelihood of ring-opening reactions occurring involving the degradation products increased as the degradation degree of PCBs increased.

A Municipal Management Plan for Urban Groundwater Investigation and Remediation

The project MAGPIan, funded by the European Commission under the program LIFE＋2008, aims to develop and implement an optimal strategy for integral groundwater investigation and efficient remediation of key sources of pollution for the whole inner city area. The first investigations included descriptions of the complex hydro-geological system of the eight aquifers, drilling of monitoring wells and set up of the conceptual contaminant model. A conceptual contaminant model was developed to describe the status quo of the present contaminant distribution, as well as the basic processes controlling contaminant migration within the observed aquifers. This included the characterization of redox conditions and natural chlorinated hydrocarbons degradation processes, as well as age dating, forensic interpretations with respect to the contaminant origin, and determination of radioactive and stable isotopes. Further on, a numerical unsteady groundwater flow and contaminant transport model were developed, which enabled a quantitative description of the mass balance within the project area. The unsteady numerical model provided detection of migration paths in the valley of Stuttgart and identification of key sources of pollution.

Relative humidity and temperature dependence of mechanical degradation of natural fiber composites^(?)

In this paper,the mechanical degradation of natural fiber composites is studied with the consideration of the relative humidity and the temperature.A nonlinear constitutive model is established,which employs an internal variable to describe the mechanical degradation related to the energy dissipation during moisture absorption.The existing experimental researches demonstrated that the mechanical degradation is an irreversible thermodynamic process induced by the degradation of fibers and the damages of interfaces between fiber and matrix,both of which depend on the variation of the relative humidity or the temperature.The evolution of the mechanical degradation is obtained through the determination of dissipation rates as a function of the relative humidity and the temperature.The theoretically predicted mechanical degradations are compared with experimental results of sisal fiber reinforced composites subject to different relative humidity and temperatures,and a good agreement is found.

Development and Performance Study of CaCO_3 Modified PP Spun-Bonded Nonwovens

The manufacturing process of CaCO3 modified Polypropylene (PP) spun-bonded nonwovens was studied. Then the effect of the additive amount of CaCO3 on mechanical properties of the product was analyzed, and a compatible mechanism between CaCO3 particles and the main component of PP was established. In the end, the mechanical performance of the products was studied when the natural light degradation was changed. The experiment results show that after adding CaCO3 to the PP spun-bonded nonwovens and through the application of complex coupling agent and organic modification, hardcore of rigid particles and polymer composite elastomers can be combined together tightly and disperse rapidly and evenly in the main part of PP. In addition, CaCO3 can catalyze the light degradation of PP spun-bonded nonwovens. The larger the content of CaCO3 is, the faster the light degradation will be.