The first stage of the modification targets the fundamental chemistry of the membrane itself. The researchers synthesized poly(sodium p-styrene sulfonate), or PSS, a polymer densely decorated with negatively charged sulfonate groups, and wove it into the PVDF matrix during membrane fabrication. Rather than simply blending the two polymers, which risks the hydrophilic component washing away over time, the team used a one-pot approach combining free-radical polymerization with non-solvent induced phase separation, the standard industrial casting technique. The result is a semi-interpenetrating polymer network, in which linear PVDF chains are physically entangled with a crosslinked PSS network at the molecular level. This interlocking creates what polymer scientists call a forced compatibility effect: the two dissimilar phases cannot easily separate, component leaching is suppressed, and the sulfonate groups remain permanently anchored where they can attract water molecules.

The consequences of this structural change ripple through the entire architecture of the membrane. During phase inversion, the sulfonate groups draw water into the casting film, accelerating the exchange between solvent and non-solvent and promoting the formation of finger-like pores in the supporting layer, which replaced the sponge-like structure of the unmodified PVDF membrane. Scanning electron microscopy revealed fewer large surface defects and a far more efficient pore network for water transport. The water contact angle, a measure of surface wettability, dropped from 81.3 degrees for the pristine membrane to 63.3 degrees after the first modification. Pure water flux surged more than fivefold, from 141.54 to 737.20 liters per square meter per hour, though the protein rejection rate of 86.83 percent still fell short of the 90 percent benchmark demanded of practical ultrafiltration membranes. That shortfall set the stage for the second modification.

The team explored two distinct routes to grow a polyaniline layer on the membrane surface. In the first, the membrane was soaked in an aniline solution so that protonated monomers adsorbed electrostatically onto the negatively charged sulfonate sites, then transferred to an oxidizing solution to trigger polymerization. In the second, a custom reactor delivered monomer and oxidant simultaneously across a liquid-liquid interface at the membrane surface, enabling polymerization to proceed directly where it was wanted. Both routes exploit the same anchoring chemistry: the protonated imine nitrogen atoms of the growing polyaniline chains form ionic bonds with the sulfonate groups of PSS, reinforced by hydrogen bonding, effectively locking the functional layer in place. The films announced their presence visually, turning one membrane dark brown and the other green depending on the oxidation state of the polyaniline.

The choice between the two polymerization methods proved decisive. With adsorption followed by polymerization, aniline monomers penetrated into the membrane pores before reacting, and the polyaniline formed inside partially blocked the channels, throttling flux to 265.39 liters per square meter per hour. Synchronous polymerization, by contrast, confined the reaction largely to the surface, producing a thin, uniform and dense sieving layer that left the transport channels open. The resulting membrane, designated M3, achieved a pure water flux of 401.03 liters per square meter per hour while rejecting 99.02 percent of bovine serum albumin, a standard protein foulant. Its water contact angle fell to 42.9 degrees, and its surface carried a stronger negative charge at neutral pH than either precursor membrane, sharpening the electrostatic repulsion that keeps negatively charged proteins at bay.

Antifouling performance, the metric that ultimately determines whether a membrane survives real-world service, improved dramatically. After a cycle of protein filtration and a simple water rinse, the pristine PVDF membrane recovered only 54.30 percent of its original flux, while the dual-modified M3 membrane recovered 95.59 percent. Its irreversible fouling ratio, the portion of fouling that physical cleaning cannot remove, dropped to just 4.41 percent, compared with 45.69 percent for the unmodified control. Static adsorption experiments told the same story: the M3 membrane bound the least protein of all four samples tested. The researchers attribute this resilience to a stable hydration layer, in which hydrophilic PSS and PANI chains hold water molecules at the surface as a sacrificial barrier, combined with steric hindrance from the anchored polymer layer that physically blocks proteins from entering the pores.

The membrane also showed unexpected muscle against biological fouling, one of the most expensive problems in water treatment. In plate-counting assays, the M3 membrane inhibited 88.00 percent of Escherichia coli and 87.38 percent of Staphylococcus aureus colonies, far outperforming the modest effects of the PSS-only membrane. The mechanism, according to the study, hinges on the positively charged imino sites of polyaniline, which bind to the negatively charged bacterial cell membranes and disrupt the potential gradient across bacterial ion channels, destroying the cells. Because the polyaniline is anchored ionically rather than merely coated onto the surface, this antibacterial activity should persist through cleaning cycles rather than being lost, addressing a common failure mode of antimicrobial membrane coatings.

Chemical robustness tests reinforced the picture of a membrane built for harsh duty. After 28 days of immersion in acidic solution at pH 2, the dual-modified membrane still rejected 86.83 percent of albumin, and after 28 days in alkaline solution at pH 10, it retained 84.67 percent rejection, with flux increases far smaller than those of the unmodified control. The semi-interpenetrating network raises the thermal degradation temperature of the matrix as well, limiting the motion of PVDF chains under heat. Stability against component loss is equally important: unlike conventional blended membranes, in which hydrophilic additives gradually leach into the treated water, the interlocked PSS network and ionically bonded polyaniline layer resist dissolution, a property the authors link directly to the high and repeatable flux recovery observed across filtration cycles.

Perhaps most striking is the membrane’s performance against dye pollution. Treating simulated wastewater containing Methylene Blue and Congo Red at 10 milligrams per liter, the M3 membrane rejected 99.99 percent of both dyes, relying on a combination of surface adsorption, size exclusion, electrostatic repulsion or attraction, and steric hindrance from the PANI layer. Cationic Methylene Blue was initially captured by the negatively charged surface, forming a concentration-polarization layer that then repelled further deposition, while anionic Congo Red was largely deflected electrostatically and blocked by the aggregation of its molecules in solution. After extended filtration and cleaning, dye fluxes remained stable above 200 liters per square meter per hour, with recovery rates near 97 percent. An economic analysis estimated production costs at roughly 3 to 3.5 dollars per square meter, far below typical commercial PVDF membrane costs, suggesting that this laboratory-scale dual-modification strategy could, if it survives scale-up, offer an affordable route to treating protein-rich and dye-laden industrial wastewater.

Subject of Research: Dual hydrophilic and antibacterial modification of PVDF ultrafiltration membranes for wastewater treatment

Article Title: Dual-modified PVDF ultrafiltration membranes via semi-interpenetrating polymer network construction and PANI surface polymerization

Article References: Zhang, J., Han, Y., Wu, M., Zhang, D., Zhao, W., Shi, C., Xu, J., & Cui, H. (2026). Dual-modified PVDF ultrafiltration membranes via semi-interpenetrating polymer network construction and PANI surface polymerization. Journal of Saudi Chemical Society, 30(4), Article 48. https://doi.org/10.1007/s44442-026-00099-1

Image Credits: AI Generated

DOI: 10.1007/s44442-026-00099-1

Keywords: PVDF, ultrafiltration membrane, semi-interpenetrating polymer network, polyaniline, poly(sodium p-styrene sulfonate), antifouling, antibacterial, dye removal, wastewater treatment, NIPS, membrane fouling, BSA rejection

The research, led by Chloé Melin of the École de Technologie Supérieure in Montreal and INSA-Lyon, together with Jean-Fabien Capsal, Ricardo Zednik, Angelo Pommella, Nicole Demarquette, and Jean-Marc Chenal, set out to answer a question that has lingered in the literature for years: does PLA actually help PVDF become a better piezoelectric material, or does it merely look like it does on a spectroscopy plot? The team attacked the problem from two processing directions at once. They melt-blended PVDF with PLA at weight ratios of 95/05 and 60/40 using a twin-screw extruder at 210 degrees Celsius, then compression-molded films and stretched them uniaxially at draw ratio 3 across a range of temperatures. In parallel, they prepared the same blend compositions as electrospun fibrous membranes using a semi-industrial twenty-needle unit, with both polymers dissolved together in a dimethyl sulfoxide and acetone mixture.

The central character in this story is the crystal structure of PVDF. The polymer can solidify into several distinct lattice forms, and they are not equal partners. The alpha phase, which forms readily when PVDF cools from the melt, is non-polar and piezoelectrically useless. The beta phase, in which polymer chains adopt an all-trans conformation, is highly polar and delivers the strongest piezoelectric response when the molecular dipoles are aligned by a high-voltage poling treatment. Converting alpha to beta is therefore the name of the game, and the two classic routes are uniaxial stretching of solid films and electrospinning, in which a jet of polymer solution is whipped by intense electric fields into nanometer- and micrometer-scale fibers, combining extreme elongational deformation with rapid solvent evaporation.

Morphology turned out to be the first fork in the road. In the melt-processed blends, scanning electron microscopy revealed that the 95/05 formulation produced a beaded, droplet-in-matrix structure, with discrete PLA domains dispersed in the PVDF, while the 60/40 blend formed a co-continuous architecture in which both polymers formed interpenetrating networks. Differential scanning calorimetry showed that adding PLA left the overall crystallinity of PVDF essentially unchanged at roughly 42 percent, before and after stretching, a consequence of the micrometric PLA domain size and the fact that PVDF crystallizes at a higher temperature than PLA. But the phase composition told a very different story. In the stretched 95/05 blend, the beta-phase fraction matched that of pure PVDF, whereas in the co-continuous 60/40 blend the beta fraction collapsed to 36 percent from the 86 percent achievable in well-processed samples, leaving the material dominated by the inert alpha phase.

The reason for that collapse is a lesson in mechanics. In a co-continuous blend, the macroscopic deformation applied during stretching is shared between the two continuous polymer networks, so the PVDF phase simply never sees enough local stress to drive the alpha-to-beta conformational transformation. Meanwhile, in the beaded 95/05 blend, the team observed cavitation, tiny voids opening at the PVDF-PLA interfaces during stretching, which relaxed local stresses and prevented the hoped-for enhancement of stress transfer to PVDF crystals. Earlier hypotheses in the literature had suggested that PLA could act as a stress concentrator, boosting beta formation through cavitation and heterogeneous deformation. This study’s data call that idea sharply into question: the beta fraction in the stretched blend was no better than in neat PVDF, and in some conditions worse.

Then came the electrical measurements, and the results were even more striking. After poling at 100 volts per micrometer for one hour in dielectric oil, the stretched 95/05 blend showed a piezoelectric coefficient d33 that was 34 to 45 percent lower than pure PVDF stretched under equivalent conditions, despite having a nearly identical beta-phase fraction. The culprit, the researchers showed, is dielectric mismatch. PVDF has a relative permittivity of about 10.8, while PLA’s is only 2.7. During poling, electric field lines preferentially route through the low-permittivity PLA inclusions and through the air-filled cavities left by stretching-induced voids, starving the surrounding PVDF matrix of the field it needs to rotate its dipoles. Finite element simulations in COMSOL Multiphysics, built on a representative volume element containing a PLA inclusion surrounded by an air ellipse, reproduced exactly this field concentration. When the team measured the piezoelectric response of pure PVDF poled at the reduced effective field of roughly 65 volts per micrometer, they obtained a d33 of about 6 piconewtons per coulomb, in close agreement with the blend’s measured value. The physics, in other words, checks out.

The co-continuous 60/40 blend, being overwhelmingly alpha phase, registered no measurable piezoelectric response at all, a d33 of zero. But the electrospinning results added their own twist. Pure electrospun PVDF membranes outperformed their stretched-film counterparts, delivering a d33 roughly 30 percent higher, thanks to about 29 percent greater overall beta-phase content and the superior chain alignment imparted by the enormous elongational forces inside the spinning jet. Interestingly, electrospinning also introduced a significant gamma-phase fraction, an intermediate polar conformation rarely seen in the stretched films, which the authors attribute to the rapid solvent evaporation and extreme deformation rates preserving the initially beta-nucleated chains only partially, letting them relax toward the gamma conformation rather than all the way to alpha.

Yet even electrospinning could not rescue the blend. The electrospun PVDF/PLA 95/05 membranes, despite achieving an electroactive phase fraction of about 86 percent, essentially identical to neat electrospun PVDF, showed a d33 of exactly zero after poling. The team points to a convergence of factors: the finely dispersed, highly elongated PLA domains formed during fiber formation disrupt the local electric field and hinder chain and lamellar orientation; the vastly increased interfacial area places PLA, which is stiffer than amorphous PVDF at the poling temperature, immediately adjacent to the crystal-amorphous interfaces where dipole switching initiates; and interfacial interactions locally stiffen the material, impeding the conformational kinks that must propagate through PVDF chains during poling. Raising the poling temperature triggered electrical breakdown, and lowering the field produced no effective dipole alignment, leaving the membranes piezoelectrically mute.

The study also challenges another widespread assumption. None of the electrospun membranes in this work showed measurable piezoelectric activity before an external poling step, even though the poling field used was nearly twice that of most previous studies reporting self-poled electrospun PVDF. The through-thickness dipole orientation required for a d33 response, the authors note, evidently does not emerge from the electrospinning process alone under these conditions, contradicting a body of literature that has treated self-poling as an intrinsic benefit of the technique.

The broader takeaway is a warning against a seductive shortcut. In the drive toward sustainable, flexible sensors and energy harvesters, blending PVDF with biobased PLA seems like an obvious win: PLA is renewable, biodegradable, stiff, and easy to process. But this work demonstrates that a high beta-phase fraction alone does not guarantee functional piezoelectricity. Electric field distribution, interfacial cavitation, domain size, chain mobility, and processing route all conspire to determine whether a material that looks piezoelectric under an infrared spectrometer actually produces a measurable voltage under stress. For engineers designing the next generation of self-powered wearables and structural health monitors, the message is clear: composition, morphology, and processing must be engineered together, and the role of PLA in enhancing the beta phase of PVDF, once considered promising, is now very much in doubt.

Subject of Research: Piezoelectric performance of PVDF/PLA polymer blends prepared by melt processing and electrospinning

Article Title: Piezoelectric properties of PVDF/PLA blends prepared by melt processing and electrospinning

Article References: Melin, C., Capsal, J.-F., Zednik, R., Pommella, A., Demarquette, N., & Chenal, J.-M. (2026). Piezoelectric properties of PVDF/PLA blends prepared by melt processing and electrospinning. Journal of Materials Science: Polymers, 1(1), Article 13. https://doi.org/10.1007/s44493-026-00010-9

Image Credits: AI Generated

DOI: 10.1007/s44493-026-00010-9

Keywords: PVDF, PLA, piezoelectricity, polymer blends, electrospinning, melt processing, beta phase, energy harvesting, flexible sensors, poling, crystallinity, dielectric permittivity

The research addresses a persistent challenge in modern food supply chains. Even with advances in processing and logistics, food products remain vulnerable to spoilage through oxidation and the proliferation of pathogenic microorganisms, leading to quality deterioration, shortened shelf life, and potential safety risks. Packaging materials that can actively scavenge destructive free radicals and suppress bacterial growth have therefore become a major focus of food science. Electrospun nanofiber membranes are particularly attractive candidates because their high surface-to-volume ratio, breathability, and capacity for controlled release of active substances make them ideal platforms for functional additives.

The choice of materials reflects a deliberate balancing act. Zein is abundant, renewable, and biodegradable, with excellent film-forming ability and biocompatibility, but films made from it alone are brittle and mechanically weak. PVDF, by contrast, is a semi-crystalline fluoropolymer offering excellent barrier properties, thermal stability, and mechanical strength, and it improves the chain entanglement of spinning solutions, making electrospinning easier. Combining the two polymers mitigates the brittleness of protein-based films while retaining a substantial bio-based component. The missing ingredient was a functional filler that could add antioxidant and antibacterial activity without compromising the composite structure, and that is where the coffee grounds came in.

To make the carbon dots, the researchers dried waste coffee residue from a franchise café, dispersed two grams of the powder in water, and sealed it in an autoclave at 200 degrees Celsius for six hours in a hydrothermal reaction. The resulting dark brown dispersion was filtered through microporous membranes, dialyzed for 24 hours to remove low-molecular-weight impurities, and freeze-dried into a solid powder. Transmission electron microscopy revealed quasi-spherical particles ranging from 0.91 to 3.00 nanometers in diameter, with an average of 1.88 nanometers, well dispersed without aggregation. Lattice fringes with an interplanar spacing of about 0.21 nanometers indicated locally ordered carbon domains embedded in a largely disordered framework, a structure typical of carbon dots.

Spectroscopic analysis painted a detailed picture of the nanoparticles’ chemistry. X-ray photoelectron spectroscopy showed the dots were composed of roughly 70 percent carbon, 6 percent nitrogen, and 24 percent oxygen, with the carbon core containing sp2 and sp3 hybridization and the surface decorated with hydroxyl, carbonyl, and carboxyl groups. Nitrogen was present in pyridinic, pyrrolic, and graphitic forms, making these nitrogen-doped carbon dots with good water solubility. Optically, the dots absorbed strongly in the ultraviolet and emitted blue fluorescence at 430 nanometers when excited at 350 nanometers, with emission that shifted depending on the excitation wavelength, a hallmark of carbon dots with multiple surface defect states serving as emissive sites.

The functional performance of the dots proved impressive. In radical-scavenging assays, the DPPH inhibition rate climbed from less than 1 percent to 93.41 percent as the concentration rose to 128 micrograms per milliliter, accompanied by a visible color change from dark purple to yellow. Similar concentration-dependent activity was recorded against ABTS radicals. The mechanism, the authors suggest, involves hydrogen atom transfer, electron transfer, or both, driven by the abundant surface functional groups. More striking was the antibacterial behavior: under illumination from a full-spectrum LED lamp, the dots inhibited Staphylococcus aureus and Escherichia coli in a concentration-dependent manner, while activity in the dark remained limited. Electron spin resonance spectroscopy confirmed that light exposure triggered the generation of superoxide and hydroxyl radicals, but no detectable singlet oxygen, pointing to a Type I radical-mediated photodynamic pathway rather than the singlet-oxygen-dominated Type II route.

With the dots characterized, the team electrospun composite membranes containing 0, 1, 3, 5, and 7 percent CG-CDs by weight relative to the total polymer mass, using a solution of 15 percent total polymer at a 1:1 zein-to-PVDF ratio in a dimethylformamide and acetone solvent mixture. Scanning electron microscopy showed smooth, continuous, bead-free fibers at all loadings, though average fiber diameter increased gradually with higher dot content. The researchers attribute this to molecular associations between the dots’ surface groups and the polymer matrix, which raised solution viscosity and chain entanglement while charge shielding effects weakened the electric-field stretching of the jet, allowing fibers to solidify before they could be drawn thinner.

The structural and physical consequences of doping were systematic and, in places, surprising. Fourier transform infrared spectroscopy confirmed that the primary chemical structures of both polymers were preserved, while X-ray diffraction showed that the characteristic alpha-phase crystal structure of PVDF remained intact at all loadings, with crystalline ordering actually sharpening up to 5 percent before broadening at 7 percent, likely due to local aggregation of the dots. Thermogravimetric analysis revealed slightly improved thermal stability at moderate loadings, as interfacial interactions restricted polymer segment mobility. Water contact angles fell from about 118 degrees for the undoped membrane to roughly 85 degrees at 7 percent, shifting the surface from hydrophobic to hydrophilic thanks to the dots’ oxygen-containing groups. Mechanical testing exposed a clear trade-off: tensile strength dropped from about 12 megapascals to 6, while elongation at break rose from roughly 45 percent to 72 percent, meaning the membranes became more flexible and extensible at the cost of strength, possibly because thicker fibers slip more easily within the network during deformation.

The functional payoff was substantial. DPPH scavenging by the membranes rose from negligible levels to more than 90 percent at the highest loading, and ABTS radical reduction followed the same trend, confirming that the antioxidant capacity of the dots survived the electrospinning process. Under light irradiation, the composite membranes showed substantially enhanced antibacterial activity against both bacterial strains compared with dark conditions, consistent with the ROS-generating capability confirmed by electron spin resonance. Gram-positive S. aureus proved more susceptible than Gram-negative E. coli, likely because the outer membrane of E. coli provides an additional protective barrier against oxidative attack. Notably, Caco-2 intestinal cell viability exceeded 90 percent when exposed to extracts of even the highest-loaded membrane, offering preliminary evidence that the materials are cytocompatible and plausible candidates for food-contact use.

The study’s broader significance lies in its demonstration of a circular-economy pathway for active packaging: a waste product that cafés discard daily becomes the functional heart of a multifunctional material. By systematically mapping how loading level controls fiber diameter, crystallinity, wettability, thermal behavior, mechanics, and light-responsive antibacterial performance, the researchers have provided a design framework for tuning such membranes to specific applications. The authors caution that practical packaging performance and food-contact safety still require further evaluation, and a possible photothermal contribution to the antibacterial effect remains to be investigated. But the core result stands: coffee grounds, carbon dots, and electrospun proteins can be combined into smart packaging that fights oxidation and bacteria with nothing more than light.

Subject of Research: Coffee ground-derived carbon dots incorporated into zein/PVDF electrospun nanofiber membranes for antioxidant and photodynamic antibacterial food packaging

Article Title: Coffee ground-derived carbon dots reinforced zein/PVDF electrospun nanofiber membranes with antioxidant and photodynamic antibacterial activities

Article References: Coffee ground-derived carbon dots reinforced zein/PVDF electrospun nanofiber membranes with antioxidant and photodynamic antibacterial activities. (n.d.). https://doi.org/10.1016/j.fochx.2026.104414

Image Credits: AI Generated

DOI: 10.1016/j.fochx.2026.104414

Keywords: carbon dots, coffee grounds, electrospinning, zein, PVDF, nanofibers, antioxidant, photodynamic antibacterial, food packaging, biomass waste, reactive oxygen species, food safety

The metals in question are among the most frequently detected pollutants in industrial wastewater. Lead and copper ions originate from mining, electroplating, battery manufacturing, and metallurgical processing, and even at trace concentrations they can trigger neurological, renal, and cardiovascular disorders in humans while accumulating in aquatic food chains. Conventional remediation techniques such as chemical precipitation, ion exchange, coagulation–flocculation, and activated carbon adsorption all carry drawbacks, including high operational costs, the generation of contaminated sludge, and poor performance at low metal concentrations. Membrane-based separation has emerged as an appealing alternative because of its operational simplicity, compact footprint, and potential for continuous treatment, but the performance of any membrane depends heavily on how it is made.

That is where the Brazilian team’s choice of fabrication method becomes significant. Most nanofiber membranes described in the literature are produced by electrospinning, a technique that draws fibers from a polymer solution using high voltage. Electrospinning produces excellent fibers but suffers from low production rates and high energy consumption, which have limited its industrial adoption. The researchers instead used solution blow spinning, or SBS, a technique that replaces the electric field with a stream of compressed air. In SBS, the polymer solution is fed through a concentric nozzle while pressurized air simultaneously stretches the emerging jet into fine fibers, which are collected on a rotating drum. The method requires no high-voltage equipment, offers higher throughput, and still yields highly porous micro- and nanofibrous mats, making it an attractive route to membranes that could one day be manufactured at scale.

To give the inherently hydrophobic PVDF an affinity for metal ions, the team dispersed montmorillonite clay into the polymer solution at loadings ranging from 3 to 30 percent by weight relative to the polymer. Montmorillonite is a layered silicate with a high specific surface area and a substantial cation exchange capacity. Its negatively charged interlayer spaces and surface hydroxyl groups attract divalent metal cations such as Pb²⁺ and Cu²⁺ through electrostatic interactions and ion exchange, effectively turning the clay particles scattered through the fibrous network into a dense population of active adsorption sites. The researchers fabricated two families of membranes: pristine PVDF nanofiber mats and PVDF–clay composites, keeping the solution volume constant at five milliliters for every production run so that thickness differences could be attributed to the clay content itself.

Scanning electron microscopy confirmed that the process worked as intended. The membranes displayed uniform, smooth, cylindrical fibers with only occasional bead-like imperfections, a sign that the spinning parameters—30 percent polymer concentration, a solution flow rate of 76 microliters per hour, air pressure of 140 kilopascals, a working distance of 21 centimeters, and a collector speed of 80 revolutions per minute—were well chosen. X-ray diffraction revealed the characteristic crystalline phases of PVDF alongside clay-derived peaks corresponding to quartz and aluminum oxide, confirming that the filler was genuinely incorporated into the fibers. At the highest loading of 30 percent, however, clay agglomerates began to appear, producing structural defects, thinner and more fragile films, and, above that threshold, outright clogging and failure of fiber formation.

Before testing adsorption, the team determined the point of zero charge of the membranes, the pH at which the surface carries equal numbers of positive and negative charges. This value came out at 6.9 in pure water and 6.4 in a water–ethanol mixture, and the adsorption experiments were conducted near these values to minimize interference from the liquid medium. Batch tests, in which membrane pieces of roughly 50 milligrams were stirred with 20 milliliters of metal solution at 5 milligrams per liter, showed a familiar pattern: rapid uptake in the first hours as abundant adsorption sites were available, followed by a gradual slowdown as those sites filled. Adsorption was consistently higher in the water–ethanol mixture, which the authors attribute to ethanol acting like a surfactant, lowering the surface tension of water and helping the solution wet the hydrophobic polymer and penetrate the spaces between fibers to reach buried clay sites.

The kinetic and equilibrium analysis told a coherent mechanistic story. A pseudo-first-order model fit the data poorly, with correlation coefficients as low as 0.674, whereas the pseudo-second-order model tracked the experiments closely in both media, indicating that the rate-limiting step involves chemical interaction—chemisorption—between the metal ions and functional sites on the clay surface. Equilibrium data were best described by the Langmuir isotherm, which assumes monolayer adsorption on a finite number of identical sites, and the calculated maximum adsorption capacities matched the experimental values well. The dimensionless separation factor derived from the Langmuir constant was below one in every test, confirming that adsorption of both metals is thermodynamically favorable. Still, the Langmuir constants were low, between 0.044 and 0.298, and more than half of the dissolved metal remained in solution at equilibrium in the static tests—a limitation the researchers trace directly to the hydrophobic PVDF matrix, which impedes ion access to clay sites in stagnant water.

The picture changed dramatically when the membranes were operated as filters. In dead-end filtration experiments, in which the metal solution was forced through a 12.5 square centimeter membrane area under roughly one bar of pressure from a vacuum pump, removal efficiencies soared above 90 percent, with the membrane containing 10 percent clay achieving 92 percent copper removal in aqueous medium. The lead removal performance matched that of comparable electrospun membranes reported in the literature, but with the advantage of a faster, cheaper production process. Even pure PVDF removed a meaningful fraction of the metals, demonstrating that the porous fibrous architecture itself contributes to capture. The combined mechanism—physical retention by the dense fiber network working in tandem with adsorption at clay sites under pressure-driven flow—proved far more effective than batch adsorption alone, because the applied pressure overcomes the wetting resistance that limits ion penetration in static conditions.

Intriguingly, more clay was not always better. At 30 percent loading, filtration performance deteriorated: aggregates identified by energy-dispersive X-ray analysis acted as bypass routes that let water, and the metals it carried, slip through without contacting adsorbent sites, while the weakened mechanical properties of the highly loaded membranes allowed pores to widen under pressure. The study also revealed a classic trade-off between selectivity and permeability, with thicker, less permeable membranes delivering the highest selectivity. The authors are candid about the work’s limits: no regeneration or reuse studies were performed, long-term stability remains untested, and performance in multicomponent, real-world wastewater has yet to be assessed. Future work, they note, should address membrane reuse, metal leaching, permeability–selectivity trade-offs, and continuous-flow operation. Even so, the message is clear: solution blow spinning can rapidly produce PVDF–clay nanofiber membranes that excel as filtration materials, and with moderate clay loadings of around 10 percent, they offer a promising, scalable route to stripping toxic lead and copper from contaminated water.

Subject of Research: PVDF–montmorillonite clay nanofibrous membranes produced by solution blow spinning for the removal of lead and copper ions from contaminated water

Article Title: Removal of Pb and Cu metals by PVDF/clay membranes obtained through solution blow spinning technique

Article References: da Cruz Dias, G., Zadorosny, L., Sanches, A. O., dos Santos, M. C., & Malmonge, L. F. (2026). Removal of Pb and Cu metals by PVDF/clay membranes obtained through solution blow spinning technique. Journal of Materials Science: Polymers, 1(1), Article 18. https://doi.org/10.1007/s44493-026-00020-7

Image Credits: AI Generated

DOI: 10.1007/s44493-026-00020-7

Keywords: solution blow spinning, PVDF, montmorillonite clay, nanofibrous membranes, heavy metal removal, lead, copper, water treatment, adsorption kinetics, Langmuir isotherm, membrane filtration, wastewater remediation

PVDF is a semicrystalline fluoropolymer prized for its chemical resistance, thermal robustness, mechanical durability, and innate hydrophobicity. It is also polymorphic, crystallizing in phases that include the nonpolar alpha form and the piezoelectric beta phase, a combination that makes it attractive for filtration membranes, sensors, energy harvesters, and water-oil separation systems. The Brazilian group, led by Gabriel da Cruz Dias of the Universidade Estadual de Maringá together with colleagues at UNESP and UNIFUNEC, asked a question that most prior studies had avoided: what happens when clay content climbs far beyond the low loadings, typically at or below 10 percent by weight, that researchers usually dare to use?

The answer required an unconventional fabrication route. Electrospinning, the dominant method for producing polymer nanofibers, relies on high electric fields, delivers modest production rates, and is difficult to scale. Solution Blow Spinning instead uses a pressurized gas jet to draw fibers from a polymer solution, offering higher throughput, simpler equipment, and lower cost. In the experiments, PVDF was dissolved in N,N-dimethylformamide at a concentration of 30 percent weight per volume, and montmorillonite K10 clay was dispersed in the solvent beforehand at levels of 3, 5, 10, 20, and 30 percent relative to the polymer mass. The mixture was fed through the nozzle at 76 microliters per minute under an air pressure of 140 kilopascals, with a working distance of 21 centimeters, yielding self-supported fibrous mats whose average fiber diameters stayed below 200 nanometers.

Scanning electron microscopy revealed that pure PVDF fibers were uniform, smooth, and cylindrical, with only occasional bead defects caused by jet instability and incomplete solvent evaporation. As clay content rose, imperfections multiplied. At 30 percent loading, clay clusters became prominent, hanging from the fibers like stones tied to a string and, according to the authors’ vivid analogy, pulling the loaded jets toward the collector faster than the polymer threads could follow. The consequence was measurable: with a constant 5 milliliters of solution for every production run, composite thickness fell only slightly up to 10 percent clay but dropped considerably at 20 and 30 percent, signaling that the process was losing efficiency as aggregates sabotaged fiber deposition.

Perhaps counterintuitively, the viscosity of the spinning solutions decreased as more clay was added. The explanation lies in sample preparation: because the clay was first dispersed in DMF, higher clay concentrations demanded additional solvent, and this dilution effect outweighed the thickening expected from suspended solid particles. Thinner solutions allowed polymer chains to disentangle and stretch more easily under the constant air pressure, producing finer fibers at high clay contents. Up to 10 percent clay, where solvent content remained constant, the trend reversed, with diameters rising slightly as viscosity increased—behavior consistent with earlier electrospinning and blow-spinning studies of clay-laden polymer solutions.

Elemental mapping by energy-dispersive X-ray spectroscopy confirmed that silicon, oxygen, and aluminum from the clay were distributed fairly homogeneously through the fibrous networks, with localized clustering at the two highest loadings. X-ray diffraction showed that both the alpha and beta crystalline phases of PVDF coexisted in every mat and, crucially, that clay addition did not alter this balance. The researchers attribute the phase formation to the blow-spinning process itself, in which rapid solvent evaporation favors the alpha phase while simultaneous fiber stretching promotes the beta phase, and they note that room-temperature processing may explain why clay did not act as the beta-phase nucleation catalyst reported in studies using heated routes. Differential scanning calorimetry reinforced the structural picture, showing a single melting peak near 176 degrees Celsius for all compositions, with a shoulder attributed to melting of the interfacial region between crystalline and amorphous lamellae.

Thermogravimetric analysis, however, delivered a caution. Pure PVDF remained stable to roughly 420 degrees Celsius before losing about 75 percent of its mass through dehydrofluorination, the reaction that releases hydrogen fluoride and leaves behind unsaturated carbon species. The composites degraded in two steps, and an initial degradation peak intensified with clay content, evidence that dispersed rather than exfoliated clay particles, and particularly the metal ions within them, catalyzed chain scission. Without the barrier effect that well-exfoliated clay layers would provide, higher filler contents reduced the composite’s thermal stability rather than enhancing it.

Mechanical testing traced a clear arc from reinforcement to collapse. Pure PVDF membranes were highly ductile, stretching about 58 percent before breaking with an elastic modulus near 13 megapascals, behavior typical of fibrous mats in which fibers align and reorient under load. Adding up to 5 percent clay increased both stiffness and tensile strength, because rigid particles acted as bridging points that transferred stress between neighboring fibers. Beyond roughly 5 to 10 percent, however, performance deteriorated sharply: elongation at break fell steadily with filler content, and at 30 percent clay the tensile strength had dropped by about 54 percent relative to pure PVDF. The culprit, visible in both electron micrographs and elemental maps, was agglomeration—defects that concentrate stress and sever efficient load transfer through the network.

Wettability measurements added an unexpected twist. All composites remained hydrophobic, with static water contact angles of 114 degrees for pure PVDF and, apart from a slight dip at 3 percent clay, rising values of 115, 119, 122, and 123 degrees as clay content climbed to 5, 10, 20, and 30 percent. Because montmorillonite is inherently hydrophilic, the trend runs against intuition, but the authors attribute it to increased surface roughness imparted by clay particles, which amplifies the low surface energy conferred by PVDF’s strongly bonded carbon-fluorine groups. A water-ethanol mixture reduced the contact angles, offering a simple lever for tuning wettability in applications such as filtration and separation without changing the material’s composition.

The study’s broader message is twofold. First, Solution Blow Spinning is a genuinely viable and scalable route to PVDF-based fibrous nanocomposites, producing sub-200-nanometer fibers at productivity levels electrospinning cannot match—here, 5 milliliters of a 30 percent solution yielded mats roughly 500 micrometers thick. Second, the technique’s tolerance for inorganic fillers has hard limits. The 30 percent formulation, with its thin, fragile mats, abundant aggregates, and depressed mechanical performance, marks a boundary that future work should not cross without improved dispersion strategies. For now, the sweet spot sits at low clay contents, where composites combine hydrophobic surfaces, controllable porosity, and enhanced stiffness, positioning them for filtration, environmental remediation, and membrane applications. The authors suggest that next steps should focus on refining filler dispersion, optimizing processing parameters, and evaluating functional metrics such as permeability, selective adsorption, and long-term stability under realistic operating conditions.

Beyond the specific findings, the study offers a useful methodological template for anyone probing the limits of high-throughput fiber fabrication. Rather than presenting a single optimized formulation, the authors deliberately swept a wide compositional range and documented where each characterization technique registered a change in behavior. This threshold-mapping approach—tracking solution viscosity, fiber diameter, mat thickness, crystalline phase content, degradation onset, tensile response, and contact angle as a function of filler loading—makes the results directly comparable across laboratories and provides benchmarks against which future dispersion strategies can be judged.

The work also situates itself within a broader shift in fibrous membrane research. Electrospinning remains the reference technique for producing submicron polymer fibers, but its dependence on high voltages and modest throughput has long constrained industrial adoption. Solution Blow Spinning, by contrast, requires only a pressurized gas supply, a syringe pump, and a rotating collector, all of which are inexpensive and straightforward to operate. The demonstration that this setup can accommodate inorganic loadings up to 30 percent by weight—while still yielding self-supported mats with sub-200-nanometer fibers—suggests that the technique’s real bottleneck is not fiber formation itself but the rheology and homogeneity of the precursor solutions.

For applications, the combination of hydrophobic surfaces, interconnected porosity, and tunable stiffness is particularly relevant to membrane-based separations, where water-repellent fibrous mats are sought for treatments involving oily wastewater or for supporting catalytic and adsorptive phases. The observation that a simple water-ethanol test liquid lowers contact angles hints at how wetting behavior could be tuned in practice, either through liquid choice or through post-processing that modifies surface texture. The authors’ open-access publication, released in the first volume of the Journal of Materials Science: Polymers, makes the full dataset available to groups working on scalable nanocomposite fibers, and the identification of agglomeration as the dominant failure mode above roughly 10 percent clay gives a clear target for subsequent studies employing surface-modified or organophilic clays, alternative solvents, or in-line dispersion methods.

Subject of Research: Fabrication of hydrophobic PVDF/clay fibrous nanocomposites via solution blow spinning with tunable mechanical properties

Article Title: Hydrophobic PVDF/clay fibrous nanocomposites prepared by solution blow spinning with tunable mechanical properties

Article References: Dias, G. D. C., Zadorosny, L., Sanches, A. O., de Paula, F. R., dos Santos, M. C., & Malmonge, L. F. (2026). Hydrophobic PVDF/clay fibrous nanocomposites prepared by solution blow spinning with tunable mechanical properties. Journal of Materials Science: Polymers, 1(1), Article 19. https://doi.org/10.1007/s44493-026-00018-1

Image Credits: AI Generated

DOI: 10.1007/s44493-026-00018-1

Keywords: PVDF, montmorillonite clay, solution blow spinning, nanocomposites, nanofibers, hydrophobicity, contact angle, tensile properties, thermal stability, crystalline phases, fibrous membranes, morphology