Tough and antibacterial poly(l-lactic acid) composites prepared via blending with the bifunctional macromolecular ionomer.

In order to expand the application of PLLA in the packaging field, improving its toughness and antibacterial activity has been widely concerned. However, seldom researches can simultaneously efficiently improve the toughness and antibacterial activity of PLLA by adding one kind of additions. To address above problems, the bifunctional branched poly(butylene adipate) ionomer additive (b-PBAUi) was synthesized. For b-PBAUi, its branched structure not only increased the plasticizing effect of additive, but also acted as reaction sites to introduce more antibacterial ionic salt. Due to the special structure of b-PBAUi, PLLA/b-PBAUi blends achieved excellent toughness and antibacterial efficiency. The elongation of blend reached 125 % even by adding 5 wt% b-PBAUi, which was 10 times higher than that of PLLA. From the analysis of phase morphology, it could be found that the microvoids promoting tensile yielding was the main tensile toughening mechanism for PLLA/b-PBAUi blends. In addition, the antibacterial activity of PLLA was significantly improved by adding b-PBAUi. For PLLA/b-PBAUi10 and PLLA/b-PBAUi15, the antibacterial efficiency against E. coli and S. aureus bacteria exceeded 99.0 %. By comprehensive consideration, the optimal blend ratio was achieved by PLLA/b-PBAUi10 due to its excellent toughness and antibacterial efficiency.

[Major Factors Influencing the Cd Content and Seasonal Dynamics in Different Land Cover Soils in a Typical Acid Rain Region].

Understanding the seasonal variations in active heavy metal components and sensitive impact factors is of importance for the ecological risk reduction during the agricultural production processes. Paddy fields, vegetable lands, and hilly forests were selected as three main land cover types to assess the seasonal characteristics of Cd bioavailability and reveal how or to what extent it was affected by the physiochemical parameters of soils, under different land-use types in a typical Cd-contaminated watershed in the middle and lower reaches of Xiangjiang River. One-year in situ monitoring results showed that natural rainfall pH in winter and spring was lower than in summer and autumn in the study region. The total Cd content of paddy soils was significantly higher than that of the vegetable soil, while the hilly forest soil showed the lowest total Cd value. Similar seasonal variations in total Cd content were found in three soil types with slightly lower summer and autumn concentrations than spring and winter values, but no obvious correlation was detected between the total and the available Cd components. The paddy soil available Cd concentration during the 5-9-month crop growth season was significantly lower than the other months of the year, while vegetable cultivation and hilly forest soils showed the opposite trend. Eh was the key factor that had a positive influence on the Cd activity in paddy soil. Soil TOC concentration was negatively correlated with soil activity in vegetable soil. TOC, water soluble organic carbon, showed a significant positive correlation with Cd effectiveness. The results provide scientific references for Cd contamination control and safe agricultural production.