Controllable synthesis of high aspectratio Mg2B2O5 nanowires and their applications in reinforced PHA composites【推荐论文】.doc

精品论文Controllable synthesis of high aspect-ratio Mg2B2O5 nanowires and their applications in reinforced PHA composites5 MO Zhaojun, FAN Ying, LIN Jing, XU Xuewen, CHEN Jinpeng, TANG Chengchun(School of Materials Science and Engineering, Hebei University of Technology, Tianjin 300130)Abstract: Highly pure magnesium borate (Mg2B2O5) nanowires with an average diameter of ~30 nm,an average length of ~15 μm and a high aspect-ratio of ~500 have been synthesized in a large scale via10 a two-step method. MgBO2(OH) nanowires with high aspect-ratios were firstly prepared via aPVP-assisted hydrothermal technique. Then using the as-prepared MgBO2(OH) nanowires asprecursors, single crystalline Mg2B2O5 nanowires were synthesized by post-annealing treatment atrelatively low temperature of 700 °C. The important effect of conversion process on the morphology ofthe Mg2B2O5 nanowires was investigated, which indicated that the recrystallization process played an15 important role in protection of 1D nanostructure. Moreover, the rigid and the toughness of theMg2B2O5 nanowires reinforced PHA composites had been tremendously improved compared withpure PHA. The results demonstrate the effectiveness of Mg2B2O5 nanowires for reinforcementapplications in polymer composites.Key words: Nanowire; Magnesium borate; Recrystallization; Reinforcement20 0 IntroductionMetal borate is one of the most important technical ceramics owing to its interesting properties, such as high heat-resisting, corrosion-resisting, super-mechanical strength, super insulation and high coefficient of elasticity [1]. Among the various kinds of metal borates, magnesium borate (Mg2B2O5) whisker has been considered as a promising reinforcement in25 composite material applications due to its excellent mechanical properties, attractive thermal properties, thermo-luminescent properties[2] and good antiwear behavior [3]. In recent years, there has been a great deal of research in using Mg2B2O5 whiskers as reinforcement in Mg and Al matrix composites [4]. The significant mechanical reinforcement of Mg and/or Al matrix composites has been successfully achieved. It should be noted that the excellent mechanical30 properties of Mg2B2O5 whiskers also imply their promising applications as reinforcing additive for polymers. Polyhydroxyalkanoate (PHA) is a class of natural polyesters and has been currently under extensive investigations. This kind of polyester can be biologically synthesized from bio-renewable feedstocks and is generally biodegradable and biocompatible [5]. However, the brittle nature of the PHA polymers has hindered their development in practical applications.35 Reinforcing the PHA polymers by incorporation of Mg2B2O5 nanowires provides the possibility to obtain composite materials with high mechanical strength. However, the related study has not yet been initiated, and presents a challenge.Since reducing the size of whiskers into nanometer-scale can enhance their toughness and strength greatly [6, 7], one-dimensional (1D) Mg2B2O5 nanostructures are considered as more40 excellent candidate as a reinforcing element in composites compared with their micron-sized counterpart. It should be noted that the novel properties of 1D nanostructure greatly depend on their morphologies and aspect ratios (length vs diameter). Nanowires with high aspect-ratio couldFoundations: RFDP (NO. 20091317110005), the Key Project of Chinese Ministry of Education (NO. 209011) Brief author introduction:Mo Zhaojun (1984-), Mail, Master. He is currently involved in the investigations of nanofibers and nano-compositesCorrespondance author: Tang Chengchun (1968-), Mail, Professor, Nanomaterials. E-mail: tangcc@- 1 -be more beneficial to strengthen traditional materials. Therefore, the controlled synthesis of high aspect-ratio Mg2B2O5 nanostructures has become an important focus for their development in45 composite applications. So far, there has been great progress in the synthesis of 1D Mg2B2O5 nanostructures [8-10] based on various synthetic routes, such as high-temperature sintering technique, chemical vapor deposition (CVD) method etc. For example, using MgCl2×6H2O and NaBH4 as starting materials, Li et al. [11] synthesized single crystalline Mg2B2O5 nanorods with diameters of 200-400 nm and lengths up to 5 mm by a two-step process involving the50 mechanochemical technique and sintering method. Yi et al. [12] synthesized large quantities ofsingle crystalline Mg2B2O5 nanowires with typical diameters of 120-180 nm and lengths of 0.2mm through directly heating of the mixed tablet of Mg(BO2)2 and graphite in vacuum at 1200 °C for 1 h. Compared with the high-temperature sintering or CVD method, hydrothermal synthesis has shown some distinct a。