Polyethylene terephthalate (PETE) fibers are used as a reinforcing agent to enhance concrete strength as well as to shield against thermal neutrons. This study increased the stability of PETE fibers in a strong alkali solution characteristic of concrete (pH = 12) using low-dose gamma radiation to induce crosslinking of the polymer chains. Results indicated that gamma ray dose of only 30 kGy resulted in the highest molecular weight, tensile strength and degree of crystallinity of PETE fibers with size 1.3 D. The surface topology using SEM micrography were also evaluated. An accelerated age testing revealed that these radiation-treated fibers will maintain their mechanical strength in concrete for up to at least 60 months. Thermal neutron attenuation test of fiber-reinforced concrete (FRC) indicated that the degree of thermal neutron shielding increased with increasing PETE fiber content, and that at 0.3% fiber content, FRC exhibited the highest thermal neutron attenuation of about 60% compared to unreinforced concrete. Therefore, these FRCs can readily be utilized as an effective neutron shielding material for nuclear and radiation applications to enhance radiation safety.

Abstract. A 13.56 MHz RF plasma discharge was successfully utilized to activate and coat Thai silk fabrics with chitosan for durable antibacterial property. Uncolored and untreated Thai silk fabrics were activated in Ar plasma for 5 minutes with an optimized RF power of 120 W under Ar pressure of 0.8 Torr. After plasma activation, specimens were submerged and stirred in a 1% (w/v) chitosan solution. FTIR analysis confirmed the presence of chitosan on the silk fabrics. From SEM analysis, chitosan was observed to coat silk fibers almost everywhere. RF plasma treated fabrics were able to absorb the chitosan solution substantially faster than those without the treatment. Another benefit of increased hydrophilicity is the ability of the treated fabrics to allow human perspiration to flow through more effectively, providing additional comfort when worn in tropical-zone countries. Antibacterial properties against E. coli and S. aureus reduced with increasing washing cycles dropping to approximately 95% after 5 rounds of washing. Extrapolation of linear trend lines revealed that for the case of E. coli, it will take approximately 16 washing cycles to reduce the antibacterial ability to 90%. For the case of S. aureus, it will take approximately 10 washing cycles to reduce the antibacterial ability to 90%. Fabrics without RF plasma treatment prior to chitosan solution submersion will have their antibacterial ability for E. coli and S. aureus reduced to 90% after only about 5 washing cycles. Thus, RF plasma treatment can effectively induce chitosan to provide a strong and durable coating for Thai silk fabrics, thus, offering a new, very environmentally-friendly coating technique for Thai silk with chitosan for potential use in the textile industry.

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