Fully bio-based and intrinsically flame retardant unsaturated polyester cross-linked with isosorbide-based diluents.

Unsaturated polyester resins (UPR) are composed of prepolymers and styrene diluents, while the former are produced by co-polycondensation between diol, unsaturated diacid and saturated diacid. In this work, bio-based UPR prepolymers were synthesized from bio-based oxalic acid, itaconic acid, and ethylene glycol, which were then diluted with bio-based isosorbide methacrylate (MI). Meanwhile, the phenylphosphonate were introduced into the molecular chains of prepolymers to achieve intrinsic flame retardancy of bio-based UPR. The potential of the reactive MI diluents as substitutes of volatile styrene, was also assessed through the volatility test, curing kinetics and gel contents analysis. For UPR materials with styrene diluents, the UPR materials can achieve UL-94 V0 level and the 28% of limiting oxygen index (LOI) with 2.63 wt% of phosphorus contents. By contrast, the UPR materials with MI diluents can reach UL-94 V0 level with only 2.14 wt% of phosphorus contents. As the phosphorus contents were further increased to 2.63 wt%, UPR materials can achieve highest 29%, while the peak of heat release rate (PHRR) and total heat release (THR) were decreased by 68.01% and 48.62%, respectively. The Flame Retardancy Index (FRI) was also used to comprehensively evaluate the flame retardant performance of UPR composites. Compared with neat UPR, the composites with MI diluents and phosphorus containing structures increased from 1.00 to 6.46. The mechanism for improved flame retardancy was analyzed from gaseous and condensed phase. Additionally, the tensile strengths of bio-based UPR materials with styrene and MI diluents were studied. This work provides an effective method to prepared high-performance and fully bio-based UPR materials with improved flame retardant properties and safety application of reactive diluents.

Exploration on structural rules of highly efficient flame retardant unsaturated polyester resins.

Owing to the lack of research on structure-activity relationship and interaction mechanism between unsaturated polyester resins (UPR) and flame retardants, it has been a big challenge to prepare high-efficiency flame retardants for UPR in industry. In this research, to explore structural rules of high-efficiency flame retardants, several polymeric flame retardants were synthesized with varied main-chain, side-chain, phosphorus valence states and contents of flame retardant elements. The thermal stabilities of flame retardants and UPR composites were firstly assessed. It has been found the interaction existed between flame retardants and UPR, through transesterification reaction and ß scission pathway in polyester and polystyrene chains. With only 15 wt% of PCH3-S, UPR composites can reach V0 rating in UL-94. The PHRR and THR values can be maximumly decreased by 71.66 % and 77.67 %, with 20 wt% of PB-S. It has been found flame retardants with sulfone group and + 3 valence state of phosphorus in molecular backbone can release SO2 and phosphorus containing compounds in gaseous phase, which diluted fuel fragments and catalyzed H⋅ and HO⋅ radical removal. The mechanism for improved flame retardancy of UPR composites with various polymeric flame retardants were discussed in detail. Some general rules for highly efficient flame retardant UPR can be summarized: First, gaseous phase flame retardant mechanism plays the major role in improvement of flame retardant performance of UPR composites; Second, the combination of + 3 valence state of phosphorus structures, higher phosphorus contents and sulfone groups effectively improves the flame retardant efficiency of flame retardants.

Amentoflavone enhances osteogenesis of human mesenchymal stem cells through JNK and p38 MAPK pathways.

Amentoflavone is a bioflavonoid found in a variety of traditional Chinese medicines such as Gingko and Selaginella tamariscina. It has been reported that amentoflavone has anti-inflammatory, antioxidant, antiviral and anticancer effects. However, the effect of amentoflavone on osteogenic differentiation of human mesenchymal stem cells (hMSCs) has not been studied. In this study, we aim to explore the effect of amentoflavone on the proliferation and osteogenic differentiation of hMSCs. The results showed that amentoflavone significantly enhanced the proliferation, alkaline phosphatase (ALP) activity and mineralization in hMSCs. Western blot analysis revealed that the expression of runt-related transcription factor 2 and osterix proteins was upregulated in amentoflavone-treated hMSCs. Furthermore, we investigated the possible signaling pathways responsible for osteogenic differentiation of hMSCs by amentoflavone. We found that amentoflavone significantly increased the levels of phosphorylated JNK and p-p38. The amentoflavone-induced increases of ALP and mineralization were significantly diminished when the JNK and p38 MAPK pathways were blocked by selected inhibitors (SP600125, SB203580) in hMSCs. Furthermore, in vivo evidence indicated that amentoflavone protected against the dexamethasone-induced inhibition of osteoblast differentiation in tg(sp7:egfp) zebrafish larvae. Thus, we showed for the first time that amentoflavone improves the osteogenesis of hMSCs through the JNK and p38 MAPK pathway. Amentoflavone may be beneficial in treating bone-related disorders.