Technology

  2010 AUG 31 - (VerticalNews.com) -- "Exposure to natural weathering changes the mechanical properties of unsaturated polyester composites. These changes can negatively affect the mechanical properties of natural fibre composites, through UV radiation and relative humidity," scientists in Serdang, Malaysia report.

  "The idea of this study was to determine the durability of kenaf unsaturated polyester composites (KFUPC) in natural conditions, and in addition, to determine the effects of weathering on the performance of these composites and the biodegradability possessed by the composite when exposed to natural weather. KFUPC composites were exposed to the atmosphere for four months. Humidity up-take tests were performed on composite specimens containing (10%, 20% and 30%) weight percentage of fibre content. The tensile properties of exposed specimens were evaluated, and compared alongside dry composite specimens. A decrease in tensile properties of the weather exposed composites was demonstrated, compared with the dry samples," wrote A.A.A. Rashdi and colleagues ...read more

  2010 AUG 31 - (VerticalNews.com) -- According to recent research from Kuwait, "The isothermal crystallization kinetics of two different types of linear aromatic polyesters, namely poly(trimethylene terephthalate) (PTT), poly(butylene terephthalate) (PBT) and their blend with polycarbonate (PC) has been investigated using differential scanning calorimetry (DSC). The blend composed of PTT25/PBT25/PC50 (wt/wt.%) was synthesized using a twin screw extruder. ...read more

  2010 AUG 24 - (VerticalNews.com) -- "Polyimides exhibit outstanding thermal and thermo-oxidative stability, excellent solvent resistance, good mechanical and electrical properties and superior chemical resistance. However, their practical applications are frequently limited by their infusible and insoluble nature," investigators in Wuxi, People's Republic of China report.

  "Structural modifications of the polymer backbone have been utilized to modify polyimide properties, either by reducing the interaction or by reducing the stiffness of the polymer backbone. Novel organo-soluble polyimides containing spirobifluorene units were synthesized by the polycondensation of 2,7-bis-amino-2',7'-di-t-butyl-9,9'-spirobifluorene with three aromatic dianhydrides. The one-step polymerization procedure was conducted at 200 degrees C in m-cresol, and the structures of the resulting polyimides were confirmed using infrared and NMR spectroscopy. The weight-average molecular weights and polydispersities of the resulting polymers were in the ranges 20 600-341 000 and 1.02-1.30, respectively. The glass transition temperatures of the polyimides were in the range 289-322 degrees C, and the 10% weight loss in nitrogen appeared at a temperature higher than 435 degrees C and the residual weight at 800 degrees C was above 58%. The spiro segment has been introduced into polyimides, resulting in amorphous polyimides, conferring on them an enhanced solubility and leading to a significant increase in both glass transition temperature and thermal stability," wrote G.M. Jiang and colleagues ...read more