• PDF / 953,629 Bytes
• 2 Pages / 612 x 792 pts (letter) Page_size
• 63 Downloads / 190 Views

DOWNLOAD

REPORT

---

structural concept for the polymer system because of their tailoring properties. Oligo(ε-caprolactone)diol (OCL), which is responsible for switching segments that determine both the temporary and permanent shape of the polymer, initiated a ring-opening polymerization of cyclic diesters or lactones to make macrodiols first, then two macrodiols were coupled with 2,2(4),4-trimethylhexanediisocyanate to form the multiblock copolymers. The crystallizable oligo(p-dioxanone)diol (ODX) was the hard segment in the polymer network. By varying the ratio of OCL and ODX, the cross-link density of the polymer can be adjusted. Thus, the mechanical strength and transition temperature of the polymers can be tailored over a wide range, which offered the materials “excellent” shape-memory properties. A series of tests confirmed that the materials can be programmed into permanent and temporary shapes in seconds with up to 400% deformation, while the maximum deformation for Nitinol is just 8%; the new materials can be adjusted at a lower transition temperature than metal alloys; and the introduced hydrolyzable ester bonds in the polymers will break under physio-

The International Union of Materials Research Societies Announces…

logical conditions, which provides an additional advantage (biodegradability) over Nitinol. The researchers said that the shapememory capability of the polymer materials enables bulky implants to be placed in the body through small incisions. These materials can also perform complex mechanical deformations automatically. Another possible application, the researchers said, is the design of a smart surgical suture that allows an optimized tightening process of the knot. YUE HU

Abrasive Jet Machining of Brittle Ceramics Yields Smoother Surfaces than Conventional Finishing Methods The most commonly used technique for surface finishing of ceramic components is grinding by a diamond wheel. However, this method is not ideal for brittle ceramics such as alumina and silicon carbide. A group of researchers at the Fine Ceramics Research Association and the National Institute of Advanced Industrial Science and Technology, Nagoya, have found that the use of abrasive jet machining (AJM) on alumina samples resulted in

a much smoother surface and a significant improvement in flexural strength as compared with the same samples processed by conventional methods. AJM is a specialized form of shot blasting, featuring the use of fine, hard, abrasive particles projected at an extremely high velocity. As described in the May issue of the Journal of the American Ceramics Society, Manabu Wakuda of the Association and co-workers prepared three sets of samples of the same dimensions by machining the alumina ceramic. One set was ground with a diamond wheel. Another set was subsequently finished by lapping with diamond pastes after grinding. The third set was finished by the AJM process, which uses a pressurized nitrogen stream containing silicon carbide particles in the 15–25-µm range. After the processes, the researchers evaluated mat