No abstract

No abstract

Green biopolymer alloys based on the bacterial polyester poly­(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and softwood Kraft lignin were successfully prepared via dicumyl peroxide (DCP) initiated free radical grafting during melt extrusion to improve interfacial adhesion. It is postulated that lignin was grafted onto PHBV to form a cross-linked copolymer gel. The gel fraction of the biopolymer alloy grafted at four different loading levels of DCP was determined. At an optimal total concentration of 2 wt % DCP, tensile strength, Young’s modulus, and storage modulus, by dynamic mechanical analysis (DMA), of the biopolymer alloy showed a maximum, coinciding with the highest gel yield. The presence of both lignin and PHBV characteristic bands by Fourier transform infrared spectroscopy (FTIR) in the extracted biopolymer alloy gel confirmed lignin was successfully grafted onto PHBV. Adhesion factor calculated from DMA data also indicated improved interfacial interaction. The crystallinity degree in the grafted alloy was reduced while crystallization temperature was increased as determined by FTIR, X-ray diffraction (XRD) and differential scanning calorimetry (DSC) analyses. Hot stage polarized optical microscopy observation confirmed that DCP induced grafting significantly reduced the spherulite size and increased nucleation density of PHBV. Glass transition temperature, thermal stability, and melt strength of the biopolymer alloy were all enhanced as a result of better molecular interaction by grafting. This study opens up a pathway to utilize effectively the low-cost and renewable lignin as a component in a biopolymer alloy based on sustainable materials.

The pattern of carbon (C) allocation across different stages of stand development of Chinese pine (Pinus tabulaeformis) forests is poorly documented. In order to understand the effects of stand age on the C pool of the Chinese pine forest ecosystem, we have examined the above‐ and belowground C pools in three differently aged stands of Chinese pine in the northern mountains of Beijing, China, by plot‐level inventories and destructive sampling. Our results suggest that tree branch and foliage biomass should be estimated by age‐specific equations. Reasonably accurate estimates of tree stem, tree root, aboveground, and total tree biomass in a Chinese pine forest at different development stages were obtained using age‐independent allometric equations from tree diameter only. The ratio of belowground to aboveground tree biomass was relatively constant with stand aging, remaining around 21 %. The contribution of aboveground tree biomass C increased from 21 % of the total ecosystem C in a 25‐year‐old stand to 44 % in a 65‐year‐old stand, subsequently falling to 41 % in a 105‐year‐old stand, while the contribution of mineral soil C decreased from 64 % of the total ecosystem C in 25‐year‐old stand to 38 % in a 65‐year‐old stand, subsequently increasing to 41 % in a 105‐year‐old stand. The C stock of the total ecosystem and its aboveground tree, tree root, forest floor, and mineral soil components continuously increased with stand ageing, whereas the C stock of the understory showed a declining trend and contributed little to the total site C pool.