Ultrahigh molecular mass polyethylenes

Even polyethylene specially treated for medical implants has aluminum as a contaminant ultrahigh molecular mass polyethylene, considered of special quality, may present up to 40 ppm A1 [77]. 

Fu Y, Chen W, PydaM, Londono D, Annis B, Boiler A, Habenschuss A, Cheng J, Wnnderlich B. Strncture-property analysis for gel-spun, ultrahigh molecular mass polyethylene fibers. J Macromol Sci Phys 1996 35 37-87. 

Xie, X.L., Aloys, K., Zhou, X.P., Zeng, F.D. Ultrahigh molecular mass polyethylene/ carbon nanotube composites - crystallization and melting properties , J. Therm. Anal. Calorim. 74(1) (2003), 317-323... 

Figure 4 CP MAS NMR spectra of ultrahigh relative molecular mass polyethylene as a function of temperature. Reproduced with permission of John Wiley Sons from Akiyama (1990) Journal of Polymer Science, Part B Polymer Physics 28 587.

Polyethylene has been used in surgery since the 1950s. Experience shows that polyethylene cannot be used to replace soft tissue, but is a good substitute material for bone tissue (hip joint, pelvic bone). However, the first applications of PE-LD as bone tissue substitute resulted in high material wear. Subsequent developments in polymer synthesis led to a polyethylene with a higher molecular mass (PE-UHMW ultrahigh-molecular polyethylene (M, / = 4 10 g/mol)), that allowed wide application for pelvic prostheses. Table 5.129. 

Time-of-flight SIMS (Table 32.1) can be used in the determination of the chemical structure and the composition of a surface, and it detects all the elements from hydrogen to uranium (Holmbom and Stenius, 2000). The advantage of SIMS compared to XPS is that with SIMS precise molecular information of polymers can be obtained. Fingerprint spectra can also be found from literature for a series of polymers from low-density polyethylene to polyethyleneterephtalate (PET) (Vickerman, 1989). It is also possible to analyze the molar masses of polymer samples up to 10,000 g/mol (Belu et al., 2003). Several sample types can be analyzed (powders, liquids, and solids) and special pretreatment is not needed. However, the analysis is performed under ultrahigh vacuum, which means that to ensure stability under vacuum conditions membrane samples must be analyzed in their dry state (Belu et al., 2003 Hagenhoff, 1995). 

---