Radiation grafting of vinyl monomers onto poly(tetrafluoroethylene) powder produced by gamma irradiation and properties of grafted poly(tetrafluoroethylene) filled low density polyethylene

Scrap poly(tetrafluoroethylene) (PTFE) was gamma irradiated under an ambient atmosphere in order to produce extensive chain scission and oxidative degradation. After irradiation the PTFE was ground into a fine powder (2 degrees -PTFE) and graft;ed with styrene (St), vinyl acetate (VAc), and 4-vinylpyridine (4-VP) by using the direct irradiation technique. The grafted PTFE were then blended with low density polyethylene (LDPE). The study covered the characterization of irradiated PTFE and grafted 2 degrees -PTFE powder with various methods. Mechanical grinding was found to reduce trapped radicals formed during the irradiation process faster than the annealing process. Grafting on 2 degrees -PTFE was followed by gravimetric analysis, TGA, and the change in the particle size of the samples. Although we reached almost 20% grafting by weight in the St and 4-VP monomers, VAc grafting was found to be maximum at around 8% by weight at the maximum absorbed dose. The addition of VAc grafted 2 degrees -PTFE into LDPE produced better final mechanical properties with a fine dispersion. However, as may be expected, the incorporation of the other two 2 degrees -PTFEs into LDPE showed low film quality and poor mechanical properties. (C) 2000 John Wiley & Sons, Inc

Stealth technology: Methods and composite materials—A review

Composites have revolutionized the field of aeronautics with its intriguing properties including high strength to weight ratio, low weight, chemical and weather resistance, flexible design and low cost of installation. Also, composites are used as radar absorbing materials (RAMs) in the manufacturing of stealth aircraft. Stealth technology (ST) uses a combination of RAMs and geometry to minimize the reflection of electromagnetic waves back to a radar system. In this review article, working principle and basic constituents of ST are examined along with RAMs types in the light of composites. Moreover, recently developed carbonaceous-based polymer composites are critically discussed in terms of RAMs for stealth applications. A carbonaceous-based composite provides a high flexibility for the design and properties control. Carbon black particles, carbon fibers, carbon nanotubes (CNTs), and graphene are used in composites to tailor the wave's absorption properties of a composite. Multilayered structures are also recommended by researchers to extend the absorption band for better stealth application. Optimized absorption properties were achieved from composites containing carbon fiber as filler. Also, CNTs are preferred due to its smaller loading (0.35%) to get conductivity equal to higher concentration of carbon black (20%), which consequently improves the ST. Enhanced electromagnetic absorption properties can be achieved form the graphene-based RAMs along with incorporating the magnetic particles of different microstructures, particle size, and electromagnetic characteristics. This review will intensively cover the methodology of ST and different composites including carbon-based composites as RAMs for the use in stealth technology