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Halloysite Filled Fluoropolymer Nanocomposites
Published in Soney C George, Sam John, Sreelakshmi Rajeevan, Polymer Nanocomposites in Supercapacitors, 2023
Deepalekshmi Ponnamma, Igor Krupa
Fluoropolymers are fluorocarbon-based polymers with multiple C-F bonds. They are stable chemically due to the presence of strong C-F bonds [17–18]. Such polymers can be homopolymers such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE or Teflon), and polychlorotrifluoroethylene (PCTFE), and copolymers such as fluorinated ethylene-propylene (FEP), polyethylene tetrafluoroethylene (ETFE), and polyethylene chlorotrifluoroethylene (ECTFE) [18]. PVDF-based copolymers are also notable for their high dielectric property and breakdown strength with low dielectric loss value [19]. The additional significance of fluoropolymer composites containing HNTs is that it achieves large polarized response under electric field, contributing to the high-energy capability for the final composite [1].
PFASs in Consumer Products
Published in David M. Kempisty, LeeAnn Racz, Forever Chemicals, 2021
Simona Andreea Ba˘lan, Qingyu Meng
Fluoropolymers are large molecules with fluorinated carbon atoms as part of the polymeric backbone. They are very durable materials that cannot degrade to PFAAs under typical environmental conditions, but certain PFAAs have been used as processing aids in their manufacturing and can occur as impurities. Moreover, fluoropolymers may release PFCAs, including PFOA, during combustion at temperatures between 180 and 800 °C (Feng et al. 2015, Schlummer et al. 2015). Examples of fluoropolymers include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), and polyvinyl fluoride (PVF). Some fluoropolymers, such as perfluoroalkoxy alkanes (PFAs) and fluoroelastomers, are made from a mix of perfluoroether monomers and tetrafluoroethylene (TFE) or hexafluoropropylene (HFP) (Nordic Council of Ministers et al. 2020). They are still classified as fluoropolymers rather than PFPEs because the ether linkages occur in the side chains, not in the polymer backbone.
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Published in Joseph C. Salamone, Polymeric Materials Encyclopedia, 2020
Poly(vinylidene fluoride) (PVDF) is one of the first discovered fluoropolymers and one of the most attractive in this class of materials for its very relevant industrial applications.1 Other important fluoropolymers are, in chronological order of their discovery, polychlorotrifluoroethylene (PCTFE) and polytetrafluoroethylene (PTFE).2,3 These polymers and some of their copolymers were used extensively during World War II in the Manhattan Project at Columbia University and the Oak Ridge National Laboratory in Tennessee, U.S.4 Their high degree of chemical and thermal stability filled a critical need in the gaseous diffusion process for separation of uranium isotopes, where the above polymers were exposed to rather severe conditions and to highly reactive fluorine derivatives.
Fabrication of fluoride-free water repellency cotton fabrics with water-borne polyurethane/acrylate dispersion
Published in The Journal of The Textile Institute, 2023
Yang Jiang, Yuqing Weng, Chuanli Wang, Zheng Zhang, Pengsheng Jing, Changhai Xu, Jinmei Du
Water repellent cotton fabrics possessing durable resistance to water have attracted considerable attention due to their wide applications in sportswear, medical, and protective textile (Busolo et al., 2021; Cao et al., 2016; Liu et al., 2012; Shen et al., 2018). It is generally recognized that the wettability of a solid surface lies in the combination of its chemical composition and its topographic structure (Hasan et al., 2008; Kolind et al., 2011). Modifying the surface of the fabric with finishing agents to get low surface free energy is an effective way to obtain the water repellent performance (Fürstner et al., 2005; Sun et al., 2017; Yu et al., 2016). Among various finishing agents, fluoropolymers have been proved to be a typical low surface energy coating that exhibits unique properties, including excellent chemical and thermal stability, hydrophobicity, and oleophobicity (Cai & Li, 2015; Tang et al., 2011). However, the fluorine compounds as water repellents would result in severe threats to the ecological environments and human health for their strong toxicity, bioaccumulation, and difficult biochemical degradation (T. Kim et al., 2017; Ma et al., 2018; W. Zhang et al., 2020). Compared with fluorinated water repellents, the environmentally friendly long-chain aliphatic hydrocarbon is one of the promising options in this regard (Fahmy et al., 2017; Kuo et al., 2021; Sheng et al., 2018; Q. Zhang et al., 2015).
Direct methanol fuel cells for automotive applications: a review
Published in International Journal of Ambient Energy, 2022
G. Amba Prasad Rao, K. Jayasimha Reddy, R. Meenakshi Reddy, K. Madhu Murthy, G. Naga Srinivasulu
Hwang et al. (2014) studied the DMFC unit performance for various compression ratios of a GDL on the cathode side. The performance of fuel cells is significantly influenced by the compression ratio of the GDL. The compression ratio of the GDL can be directly controlled by the concentration compression force at the central area of the cell and gasket thickness. The balancing of the compression ratio is an important factor to increase the unit cell performance of DMFCs. They studied the effect of the compression ratio on the cathode side and noticed that directly influences fuel cell performance. The GDL is a key element of the fuel cell. They used PTFE, a synthetic fluoropolymer of tetrafluoroethylene. They experimentally observed that varying the thickness of current collectors that reflected a very efficient way to decrease the ohmic loss by the concentration of the compression force at the central area of the unit cell. However, an over-compressed central area of the stack can affect an increasing mass transport loss. By over-compressing beyond a certain value for an optimum gasket thickness, the GDL is damaged. This is attributed to the rise in the ohmic loss for a gasket thickness below optimum thickness that decreased the porosity of the GDL, which affects the mass transport loss of the air.
Moisture evaluation of concrete pavement treated with hydrophobic surface impregnants
Published in International Journal of Pavement Engineering, 2020
Mazen J. Al-Kheetan, Mujib M. Rahman, Denis A. Chamberlain
In this research, three different protection materials were studied to evaluate their performance against water ingress. The materials were Fluoropolymer, Resin Silicate and Sodium Acetate Crystallising materials. Research on the use of Fluoropolymers in protecting concrete is limited (Zaggia et al. 2009, Krishnan et al. 2013). Fluorine is the primary element forming the Fluoropolymers, which provides them with low friction and improved resistance to aggressive chemicals (Morita et al. 1999, Zaggia et al. 2009). Also, studies on these materials showed high water and oil repellency, which drove researchers to apply them as surface hydrophobic impregnants to concrete (Zaggia et al. 2009). Silicate Resin has also been investigated a little in the field of concrete protection. Silicate Resins is a hydrophobic material that forms a coating in the pores of the concrete and works on repelling water (Dai et al. 2010). The Sodium Acetate Crystalline material is also gaining increasing popularity and has shown comparable performance to silane especially when applied on wet surfaces (Rahman et al. 2016).