New fluorinated polymer- based nanocomposites via combination of sol -gel chemistry and reactive extrusion for polymer electrolyte membranes fuel cells (PEMFCs)

Abstract

Proton exchange membranes designed via reactive extrusion from the in situ generation of functional silica-like particles in a new poly(vinylidene fluoride-co-hexafluoropropylene (poly(VDF-co-HFP)) copolymer are presented. These sulfonic acid-functionalized polysiloxane-based fillers were synthesized via sol-gel chemistry from 3mercaptopropyltri(ethoxy)silane and polydimethoxysiloxane in the molten PVDF-co-HFP polymer. To process such nanocomposites materials, the reactive extrusion parameters were selected to (i) reach silanol condensation extents in the processing conditions of a conventional poly(VDF-co-HFP) copolymer and (ii) obtain a surface functionalization high enough with respect to reach a suitable protonic conductivity value of the nanocomposites films. Nevertheless, the enhancement of the proton conductivity being deeply associated with the morphologies of the nanocomposites materials (i.e. the dispersed functional silica phase need to display the larger interface area with the polymer matrix), an interfacial agent was synthesized. This compatibilizer was either poly(VDF-co-α-trifluoromethacrylic acid) or poly(VDF-co-MAF) copolymers or a poly(VDF-co-HFP) copolymer grafted with maleic anhydride, denoted poly(VDF-co-HFP)-g-MA. In a second step, to obtain the required sulfonic acid-functionalized silica dispersed phase from the presence of the mercaptan functions, the resulting films were oxidized. Electrochemical properties were evaluated: for a theoretical ionic exchange capacity (IEC) of 2 meq.g-1 , while experimental IEC ranged between 1.0 and 1.3 meq.g-1. The proton conductivity was found to reach 78 mS.cm-1 at room temperature for 100% of relative humidity. Interestingly, these values are higher than those of the same membranes processed without any compatibilizer (54 mS.cm-1) and to that of Nafion ® NR112 (52 mS.cm-1). This approach also allows limiting the swelling (or water uptake) of proton conductive membranes below 15wt% while it reachs 30 wt% for Nafion ® NR112 in similar conditions.

Copolymers of vinylidene fluoride with functional comonomers and applications therefrom: Recent developments, challenges and future trends

“…The conductivity reached 54 mS.cm -1 when poly(VDF-co-HFP)-g-MA-0.75 was used (Fig. 30) which is comparable to that of Nafion ® NR112 (52 mS.cm -1 in similar conditions of temperature and RH) highlighting the crucial role of the interface and its impact on the accessibility to the sulfonic acid functions [205,206] of such hybrid membranes produced in a clean process. Table 4: Physical properties of poly(VDF-co-HFP)-g-MA/ SiO 2 composites depending of the MA concentration [205,206].…”

“…In addition, the RAFT copolymerization of VDF with tert-butyl α-trifluoromethacrylate (MAF-TBE) controlled by a linear [202][203] or cyclic [204] xanthate was achieved with the goal to design original emulsifiers between nanosilicates and commercially available poly(VDF-co-HFP) copolymers for polymer exchange fuel cell membranes (PEMFCs) by reactive extrusion ( [205][206], section 7.6.1).…”

“…A recent study used reactive extrusion of commercially available poly(VDF-co-HFP) copolymer or grafted with maleic anhydride (MA) [poly(VDF-co-HFP)-g-MA] (Fig. 30) with functional sulfur-containing silanes in presence of a few percents (up to 5%) of poly(VDF-co-MAF) copolymers [205][206]. The process was first optimized on a bis screw Lab and then further scaled up on extruder (with 400 g batch).…”

Experimental methods in chemical engineering: Reactive extrusion

“…REX processes mainly focus on standard polymer synthesis, such as TPU, modifying existing polymers, and upcycling. Future directions include flame‐retardant polymers materials development, [ 93 ] green and solvent‐free production of regular polymers (like LDPE and polyimides), [ 94,95 ] REX intensified polymerization mechanisms, [ 96 ] proton exchange membranes for fuel cells, [ 97 ] compatibility blending of immiscible or partially miscible polymers, bio‐based polymer production, [ 98 ] food packaging films processing, [ 99 ] polymer controlled degradation and depolymerization, and process intensification coupled REX. Alternative energy sources applied to REX include ultrasound, [ 83 ] microwave, and laser.…”