SYNOPSISPolyurethanes were synthesized from polyester and butanediol with three different diisocyanates, i.e., 4,4'-diphenylmethane diisocyanate (MDI), m-xylene diisocyanate (XDI), and 2,4-toluene diisocyanate (TDI). The effect of chemical structures of diisocyanate compounds on the degree of crystallinity and the thermal stability were observed. Differential scanning calorimetry (DSC) and small-angle X-ray scattering (SAXS) were used to determine the degree of crystallinity of the hard segment. The thermal degradation of polyurethanes was studied by the thermogravimetric method. It has been shown that the polyurethane hardsegment crystallinity decreases in the following order: MDI > XDI > TDI. The experimental results also indicated that polyurethanes with aralkyl diisocyanates, i.e., XDI, had the best thermal stability. The polyurethanes synthesized from aromatic diisocyanates, i.e., MDI and TDI, had worse thermal stability than from XDI. However, owing to the higher degree of hard-segment crystallinity for polyurethanes from MDI, these polyurethanes had a better thermal stability than those based on TDI. 0 1996 John Wiley & Sons, Inc. I NTRO DUCT10 NProperties of segmented polyurethanes depend on the structure of hard and soft segments, their length, and concentration, as well as the interaction of both phases. Usually the soft segment is based on polytetramethylene oxide or aliphatic polyester and the hard segment on butanediol (BD) and diisocyanate compounds such as diphenylmethane diisocyanate (MDI), xylene diisocyanate (XDI), and toluene diisocyanate (TDI). Being of different chemical nature from the soft segments, the hard segment tend to separate in the matrix due to immiscibility of both phases and tend to associate into "domains" forming physical crosslinks.'-6 While hard segment is glassy or semicrystalline at room temperature, the soft segment phase is in the rubbery state. Polyesters synthesized from adipic acid and low molecular weight glycols are crystalline homopolymers having melting points around 50°C. However, polyester soft segments in polyurethanes lose the ability to crystallize for short segment length, due to steric hindrances. Because crystallization of the soft segments is an undesirable property, it can be avoided by copolymerization or, as in some commercial prepolymers, by inserting TDI or other irregularities into the soft segments. Generally speaking, polyurethanes are thermally very stable polymers. The onset degradation temperature of the urethane bond depends on the type of isocyanate and glycol used. It is a general rule that the more easily formed urethanes are less stable, i.e., more easily dissociated than are the more difficult ones. Thus, the highest degradation temperature, above 250°C, is observed for a urethane formed from alkyl isocyanate and alkyl alcohol, followed by aryl isocyanate-alkyl alcohol, alkyl isocyanate-aryl alcohol, and an aryl isocyanate-aryl alcohol corn bin at ion^.^,^ In this work, crystallinity and thermal stability of segmented polyurethanes based o...
In this paper, we propose an adaptive radio frequency identification (RFID) indoor positioning system technology for wheelchair home health care robot with wireless communication. The proposed RFID positioning system uses one reader and four tags which is low cost when applying in a large space of the indoor environment. It reduces the measured calculation by using multiple RFID tags instead of multiple RFID readers. While the measured experimental RFID data found with error leading to signal changes in different environmental parameters, we developed the adaptive fuzzy neural network technology to adjust the measurement data. Through the compensation of the measurement error, the actual wheelchair robot location-based application could be performed to overcome the uncertain environmental parameters. The positioning system provides very good accuracy and make home health care wheelchair robot positioning system available for navigation and guidance.
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