| In our daily life, the harmful microorganism can not only lead to human and animal diseases and death, but also cause decomposition, deterioration, and corruption of various materials. Textiles are excellen t habitats for these microorganisms and important sources for disease spreading. Development of antibacterial textiles can avoid damage due to microbial attack, prevent the spread of pathogenic bacteria, and thereby reduce the occurrence of diseases. One traditional method for preparation of antibacterial textiles is finishing. This method is very simple; however, the resultant textiles have poor antimicrobial durability. To gain fibers with long-lasting antimicrobial effects, the antimicrobial modification method is developed and gradually become the research focus.During this method, antibacterial agents are introduced into the surface and inside of fibers by physical or chemical methods. Because of the strong binding between the antibacterial agents and the fibers, the produced antibacterial fibers maintain long-lasting antibacterial effects. Currently, there are three categories of antibacterial agents namely inorganic, organic and natural agents. Generally speaking, natural agents have poor heat resistance and short-duration efficacy. Inorganic agents are restricted to use due to their expensive cost and antibacterial delayed action. Although organic agents have toxicity and poor heat resistance, they have the strongest antibacterial activity and broad a ntibacterial spectrum. In this study, a new organic bactericide named quaternary phosphonium salt with low toxicity was selected as the modifying agent, and PAN fibers which are widely used in the market were chosen as the matrix fibers. A series of novel antibacterial fibers were synthesized by modifying the PAN fibers with quaternary phosphonium salts having different alkyl chain lengths. By comparing their antimicrobial activities and anti-mold properties, a best modified fiber was screened. The underlying antibacterial mechanisms were discussed. The main results were as follows:1. Synthesis of quaternary phosphonium salts modified polyacrylonitrile fibers. Firstly, a chemical modification method was used to change the cyano(-CN) groups in the PAN fiber macromolecule chain to sodium carboxylate(-COONa) groups. Secondly, triphenyl quaternary phosphonium salts containing different carbon chain lengths were grafted onto the PAN fiber by cation exchange with Na+ in-COONa groups. Thereafter, a series of quaternary phosphonium salts modified antibacterial fibers namely MTBP-PANF(C1), ETBP-PANF(C2), HTBP-PANF(C6), OTBP-PANF(C8) and DTBP-PANF(C12) were synthesized. Results showed Na OH concentration was the key parameter controlling the transform of-CN to –COONa. The reaction time and temperature have little impact on the ion exchange reaction. In contrast, solution p H affected the ion exchange reaction significantly, and the best results occurred at neutral p H. Increase of the concentration of quaternary phosphonium salts and the length of their alkyl chain also facilitated the introduction of quaternary phosphonium cations.2. Characterization of quaternary phosphonium salts modified polyacrylonitrile fibers. The structure and physical morphology of fibers befor e and after modification with different alkyl chain lengths of quaternary phosphonium salts were characterized by Fourier transform infrared spectroscopy(FTIR), X-ray diffraction analysis(XRD), Scanning electron microscope(SEM), Energy spectrum analysis(EDS), Thermogravimetric analysis(TGA), Inductively coupled plasma atomic emission spectroscopy(ICP-AES), etc. Results showed that the functional quaternary phosphonium groups were successfully introduced into the macromolecular chain of PAN fibers. The as prepared antibacterial fibers kept their overall fibrous structure and showed good thermal stability before 230 oC. A negligible amount of phosphor was released during the pure water-immersion for 72 h, and the amount decreased obviously with the increment of the alkyl chain length.3. Study on the antimicrobial activities and anti-mold properties of quaternary phosphonium salts modified polyacrylonitrile fibers. The improved flask shake method was used to test the antimicrobial activities of modified fibers against Escherichia coli, Staphylococcus aureus, Canidia albicans and Pseudomonas aeruginosa. The results showed that all the quaternary phosphonium salts modified fibers had good antimicrobial properties, and they obtained their antimicrobial activities in different time. Generally, the longer the alkyl chain, the shorter the time. Moreover, the fiber DTBP- PANF(C12) with the longest alkyl chain killed all of the pathogens in 15 min, which was nearly unaffected by the environmental p H and had an excellent wash-resistant property even after 50 times washing. According to JLSZ 2911 standards, anti-mold performances of the modified fibers were tested against mixture of Aspergillus Niger, Aspergillus flavus, Trichoderma reesei, Trichoderma citrinoviride and Penicillium Chrysogenum. The results demonstrated that all of the modified fibers could inhibit the mold grow, and they belonged to zero grade mouldproof materials. Additionally, the mouldproof effect was proportional to the length of carbon chain. The above experiments showed that quaternary phosphonium salts modification greatly increased the antimicrobial and anti-mold ability of polyacrylonitrile fibers.4. Discussion on the antibacterial mechanism of quaternary phosphonium salts modified fibers. A series of methods including the hydrocarbons adsorption method(BATH), inductively coupled plasma atomic emission spectrometry( ICP-AES), coomassie brilliant blue method(Bradford), flow cytometry(FCM), electron microscopy(SEM and TEM) and polyacrylamide ge l electrophoresis(SDS-PAGE), were used to observe the change of bacterial cell wall, cell membrane, enzyme system and protein after cells exposure to modified fibers. On the basis of the experimental results, the following antibacterial mechanism was proposed. When the fibers were exposed to bacteria, the first step was to adsorb bacteria on the surface of fibers, and then the quaternary phosphonium groups began to execute the function of killing bacteria. They increased of cell surface hydrophobicity, damaged the cell membrane integrity, reduced the intracellular enzyme activities, and even inhibited the synthesis and expression of some specific structural proteins and functional proteins, leading to the outcomes that cell membrane cannot be synthesized, c atalytic activities were forced to stop, and at last bacteria were killed. The modified fibers were classified as the type of contact sterilization, the bacterial cell membrane was the main target, and the mechanism of action was similar to that of the "hole mechanism" of the antibacterial peptide. |
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