Charged Polypropylene Research Articles

Engineering nano-thin electrospun coatings for air filters with high filtration and breathability by nanofiber charge control

A modified electrospinning design was introduced to overcome the limitation in non-uniformity of the nanofibrous coating on the surface of non-conducting, statically charged polypropylene microfibers. By manipulating the charge distribution over the non-conducting surface via variations in the polarity of the Taylor cone and the electrospinning geometry, it was possible to obtain a uniformly adherent and thin nanofibrous coating over a large area to achieve a layer-by-layer simultaneous deposition of + ve and −ve fibers onto a non-conducting membrane. The uniformity and quality of this nanocoating was found to have a direct effect on particle filtration and breathability of air filters. The filter showed a high particle filtration efficiency of 96 % for 0.3 µm particles, with excellent breathability.

Quaternary ammonium salt coated air filter for bioaerosol removal from building indoor air

Developing air filters with biocidal ability is important to protect the public from infectious respiratory diseases. A simple spray-coating approach was devised to fabricate antimicrobial air filters to remove bioaerosols. The commercial antimicrobial agent Goldshield 75 was coated on the air filters through covalent immobilization, endowing the fabricated filter with long-lasting biocidal ability. All coated filters significantly inhibited both Gram-positive bacteria (Micrococcus luteus) and Gram-negative bacteria (Escherichia coli). The antibacterial ability of the coated filters is similar to the commercial AeraSafe antibacterial filter. The coated filter showed over 99.9 % antibacterial efficiency 3 months after the application of the coating. Both bacterial and virus filtration efficiencies of coated charged polypropylene filter were higher than 99.9 %. The coating did not have much effect on the NaCl aerosol filtration efficiency of the filters. This simple spray-coating strategy is a practical method for producing antimicrobial air filters for the prevention of infectious respiratory diseases.

Influence of the initial charge on the triboelectrification of millimeter size set of particles in an inclined tube

In this paper, the triboelectric charge buildup on a set of initially charged particles is investigated. During the study, 30 g of charged polypropylene particles of 2–3 mm size were repeatedly passed through a 1 m inclined copper or polyvinylchloride (PVC) tube. At the tube output, the charge is measured after each passage, allowing the cumulative charge evolution over time to be measured. The obtained curves are fitted to an exponential model to extract the time constant of the process. For each experience, particles are first charged at different levels and polarities relatively to the presumed saturation charge using both corona discharge and triboelectricity. The obtained results show that the initial charge value and polarity strongly affect the subsequent triboelectricity variations as well as the process speed. The triboelectric charge evolution is mainly related to the ratio between initial charge (Q0) and saturation charge value (Qs). Therefore, the particle's charge will increase if Q0 < Qs, decrease if Q0 > Qs, or be maintained at the same level when Q0 ≈ Qs. The particles can change polarity and be recharged with the opposite sign according to the tube and the initial charge level. This triboelectric charge behavior is explained based on the surface energy state in the electron transfer model. Furthermore, increasing the particles quantity from 5 g to 60 g reduces the saturation charge from 11 nC/g to 2.5 nC/g, which is approximately 77% less. Surface potential distribution measurements show an uneven distribution with less charge in large amounts compared to lower amounts.

Electrostatic charges and their distribution on the charged surfaces probed by sum-frequency generation spectroscopy

We examined the electrostatic charging states of insulating polymer surfaces using sum-frequency generation (SFG) spectroscopy. For the negatively charged polypropylene, the SFG peak amplitudes increased significantly with increasing surface potential, indicating that the electric-field formed by the electrostatic charges directly affects the SFG signal intensities. In the organic thin films stacked on top of PMMA, an increase in the SFG signal of buried PMMA is observed, indicating that the electrostatic field formed by the electrical charges is extended into the bulk direction. In addition, visualization of the location and distribution of the charges is demonstrated using the SFG intensity variations.

Recharging and rejuvenation of decontaminated N95 masks.

N95 respirators comprise a critical part of the personal protective equipment used by frontline health-care workers and are typically meant for one-time usage. However, the recent COVID-19 pandemic has resulted in a serious shortage of these masks leading to a worldwide effort to develop decontamination and re-use procedures. A major factor contributing to the filtration efficiency of N95 masks is the presence of an intermediate layer of charged polypropylene electret fibers that trap particles through electrostatic or electrophoretic effects. This charge can degrade when the mask is used. Moreover, simple decontamination procedures (e.g., use of alcohol) can degrade any remaining charge from the polypropylene, thus severely impacting the filtration efficiency post-decontamination. In this report, we summarize our results on the development of a simple laboratory setup allowing measurement of charge and filtration efficiency in N95 masks. In particular, we propose and show that it is possible to recharge the masks post-decontamination and recover filtration efficiency.

Optimization of the Active Neutralization of Polypropylene Film Using Response Surface Methodology

In roll-to-roll manufacturing of products, such as thin films, fibers, textiles, or membranes, the generation and accumulation of electric charges by the triboelectric effect represents a major source of electrostatic hazards. The best solution to this problem is to eliminate these charges. The aim of this article is to pave the way to the use of a triode-type corona electrode system at an industrial frequency (50 Hz) for active neutralization of electrically charged insulating films. The experimental study was carried out on dc corona charged polypropylene films that were neutralized by a sinusoidal corona discharge. The neutralization efficiency was evaluated by noncontact measurement of the electric potential at the surface of charged and neutralized polypropylene film samples. The response surface methodology was used for quantifying the effects of the various influential factors (i.e., voltage amplitude, duration of exposure to the discharge, and relative position of the neutralizer with respect to the sample) and optimizing the neutralization process.

Experimental study of controlled active neutralization of polypropylene films

AC corona discharge is widely employed for neutralizing the electric charges at the surface of insulating bodies: films, plates, granules, etc. If uncontrolled, this active neutralization process is accompanied by the persistence of a residual charge at the surface of the treated bodies. The aim of this present work is to demonstrate experimentally the efficiency of the controlled active neutralization using AC corona generated in a triode-type electrode configuration, with the grid connected to the ground. The experimental study was carried out on DC corona charged polypropylene films that were neutralized by a sinusoidal corona discharge at industrial frequency (50 Hz). The distribution of the electric potential at the surface of the charged and neutralized samples were measured by a non-contact electrostatic voltmeter. The factors under study were: the amplitude of the AC voltage applied to the corona electrode of the triode system, the duration of exposure to the corona discharge, the scanning speed, and the spacing between the grid and sample. The experimental results obtained show that the neutralization rate is close to 100%, i.e. the electric potential profiles obtained at the surface exposed to AC corona discharge show the absence of the residual charge. The results show that the efficiency of the controlled active neutralization depends on the energy that the AC corona discharge imparts to the charged samples, and that affects the trapped bulk charge.

Preparation of A. succinogenes immobilized microfiber membrane for repeated production of succinic acid.

A new applicability of cell-immobilized system for biological production of target chemical was reported in this work. A. succinogenes CCTCC M2012036 was immobilized on positively charged polypropylene microfiber membrane by physical interaction and were used for converting glucose into succinic acid. Glucose consumption and succinic acid production kinetics were investigated for optimizing the operational parameters. The cell-immobilized membrane presented good reuse stability, and six cycles of fermentation without activity loss were realized with an average succinic acid yield of 0.83g/g. Importantly, a biofilm was formed which favored the production of succinic acid. A microfiber membrane bioreactor was further constructed with the cell-immobilized membrane to perform fermentation in a larger scale, and the yield and productivity of succinic acid were 0.82g/g and 1.04gL-1h-1 using a fed-batch strategy. By combining mesoporous support with biotechnological techniques, this work offered a prospect of adopting reusable cells feasible for industry.

Magnetic memory effect in magnetite charged polypropylene composite

The behaviour of damping and dynamic shear modulus in polypropylene charged with either different volume fraction or size of magnetite (Fe3O4) particles, as a function of the applied magnetic field at 318, 353 and 403 K; has been studied. An increase of the alternating magnetic field oscillating with 50 Hz, leads to an increase of the damping. In addition, during the subsequently decreasing alternating magnetic field, the damping decreases, but a hysteretic behaviour appeared. The behaviour of the damping and the elastic modulus under the application of an alternating magnetic field was explained by the development of a magnetic fatigue damage occurring around the particle interface due to oscillation of magnetite particles. In contrast, during the increase of a direct magnetic field, the damping decreases and the elastic modulus increases. Measurements performed at 353 and 403 K allowed observing the interaction process among the particles of magnetite in the polymer matrix. After the decrease in the direct magnetic field, from the maximum reached value, damping and modulus remain smaller and higher, respectively; giving rise to a memory effect. In addition, a mesoscopic description of magnetite filled polymer composite materials has been performed in the continuous media by considering the interaction between magnetic and mechanical forces. Theoretical predictions of here developed model were qualitatively applied with good success for explaining the memory effect in magnetite filled polypropylene under the application of a direct magnetic field.

A novel bipolar electrostatic ionizer for charged polypropylene granules used in a pneumatic powder transport facility

As a method of preventing or mitigating explosion due to electrostatic discharges during the loading of polymer granules in a metal silo, we have developed a novel bipolar electrostatic ionizer. In this study, we investigated experimentally a practical version of the bipolar electrostatic ionizer with a modeling test device to measure the charge-neutralizing current, and a full-sized pneumatic powder transport facility. The electrostatic discharges generated inside a silo while loading polypropylene (PP) granules were also observed visually with/without the novel bipolar electrostatic ionizer. As a sample, 300 kg of polypropylene granules 2–3 mm in size was used in this study. The specific charge of the polypropylene granules was clearly decreased by approximately 85 percent with the novel bipolar electrostatic ionizer. The brush discharges, as well as the incendiary bulk surface discharges, completely died out inside the silo when the novel bipolar electrostatic ionizer used.

Measurement of the electric potential at the surface of nonuniformly charged polypropylene nonwoven media

The aim of this paper is to establish the conditions in which the vibrating capacitive probe of an electrostatic voltmeter could be employed for mapping the electric potential at the surface of non-uniformly charged insulating bodies. A first set of experiments are performed on polypropylene non-woven media (thickness: 0.4 mm; fiber diameter: 20 μm) in ambient air. In a second set of experiments the non-uniformity of charge is simulated using five copper strips (width: 2 mm or 3 mm; distance between strips: 2 mm). All the strips are connected to a high-voltage supply (Vs = 1000 V). The sample carrier is attached to a computer-controlled positioning system that transfers it under the capacitive probe (TREK, model 3451) of an electrostatic voltmeter (TREK, model 1341B). The measurements are performed at various relative speeds Vb between the sample and the probe, and for various sample rates Fe. A first set of experiments point out that the electric potential displayed by the electrostatic voltmeter depends on the spacing h between the sample and the probe. The diameter D of the spot “seen” by the probe is approximately D ≈ 8h/3. From the second set of experiments performed with the test plate, it can be concluded that the surface potential can be measured with the media in motion, but the accuracy is limited by the spatial resolution defined by k = Vb/Fe.

AC corona neutralization of positively and negatively charged polypropylene non-woven fabrics

The insulating materials can acquire high levels of electric charges, which are susceptible to generate electrostatic discharges. The present article aims at evaluating the efficiency of AC corona as neutralization mechanism for positively- and negativelycharged polypropylene non-woven fabrics. The samples were charged for 10 s, in ambient air, using a triode-type corona electrode system of positive polarity in the first set and negative polarity in the second set of experiments. In all experiments, the neutralization was performed 180 s after the charging process, with the samples moving at constant speed (3 cm/s) in the AC corona discharge zone generated by a dual-type corona electrode. The electric potential distribution at the surface of the samples was measured both before and after the neutralization. The experimental results show that the efficiency of neutralization depends on the amplitude and the frequency of the sinusoidal high-voltage that energizes the corona electrode. The negative charge proves to be more difficult to neutralize than the positive one.

The effective electromechanical properties of cellular piezoelectret film: finite element modeling

Cellular space-charge polymer film, also called cellular piezoelectret, has very large piezoelectric effect due to their unique microvoid structure. In this article, the cellular piezoelectret film is considered to be a periodic composite material with closed-cell microvoids aligned periodically. Three dimensional finite element modeling is carried out to obtain the effective elastic modulus and piezoelectric coefficients. Sensitivity analysis was presented by modeling the effective electromechanical properties with different individual variable, including material constants and void shape parameters. By assuming a relation between void shape and void volume fraction, the finite element model can simulate quite well the inflation experiments of the voided charged Polypropylene film published in literature. Finally, the finite element model is used to explore the voided charge polymer film with non-uniform distribution of the trapped charges on the internal surface of voids. It was found that the resultant overall piezoelectric coefficients will be more significant if charges are closely gathered in the central area, and sparse in the around area of the internal surface of voids.

MODELING THE PIEZOELECTRIC d33 COEFFICIENT OF THE CELLULAR PIEZOELECTRET FILM BY FINITE ELEMENT METHOD

The piezoelectric d33 coefficient of voided charged polypropylene film is much pronounced, which can be as large as that of PZT ceramics. The piezoelectric effect originates from the electric field of distributed charges that is coupled with elastic deformation of the host matrix. For modeling the piezoelectric effect of cellular piezoelectret, we present a finite element model for the electrostatic analysis and the solution of elastic deformation. Qualitative analysis of piezoelectric d33 coefficient is given with respect to various parameters including material constants, void geometry and charge density. Quantitative comparison shows that this finite element model can simulate the inflation experiments of cellular piezoelectret very well. This finite element model is believed to be conducive to the optimization design of cellular piezoelectret, where the analysis is generally encountered for the piezoelectret with complex microstructures.

Modeling the Piezoelectric D&lt;sub&gt;33&lt;/sub&gt; Coefficient of Voided Charged Polypropylene Film by Finite Element Method

Voided charged Polypropylene films have very large piezoelectric d33 coefficient and have emerged as a kind of novel electromechanical transducer materials. In this paper, we propose the analysis method of piezoelectric d33 coefficient of voided charged Polypropylene film by finite element model. The very flat voids are simulated by the hollow oblate tetrakaidecahedron and periodic boundary conditions are implied. The electrostatic analysis is conducted and elastic deformation is solved by using ANSYS FE software. Qualitative analysis is presented for the piezoelectric d33 coefficient, and several influencing parameters are discussed, including void geometry and charge density. This finite element model can provide help in the analysis and design of voided charged polymer film with complex microstructures.

Time dependence of piezoelectric d33 coefficient of cellular ferroelectret polypropylene film

Due to the inherent viscosity of polymer, piezoelectric response in the thickness direction (d33) of cellular ferroelectret films usually depends on the time of measurement. In this letter, the micromechanical theory of viscoelastic composite was extended to predict the time dependence of the overall piezoelectric d33 coefficient of voided charged polymer foam. Experiments were carried out to find the time spectra of piezoelectric d33 coefficient of voided charged polypropylene film. Theoretical simulation agrees well with experiment data.

Application of electrostatic force microscopy on characterizing an electret fiber: Effect of tip to specimen distance on phase shift

The application of Electrostatic Force Microscopy (EFM) on characterizing a corona charged polypropylene fiber by phase measurements was studied. Electrostatic force gradient images were obtained from the phase shifts with varied EFM tip bias voltages at a constant tip-to-sample distance, and with varied tip-to-sample distances at a constant tip bias voltage. Mathematical expressions were introduced to interpret the phase measurements in terms of the tip bias voltage and the tip-to-specimen distance. The phase measurements from EFM appeared feasible to provide the qualitative information of electrical properties of charged polymeric materials. The fit of mathematical expressions to the experimental measurements was discussed with regards to the effect of tip geometry on the interaction between the tip and the specimen.

Studies of Protein Absorption and Fouling Behavior on Amphoteric Charged Polypropylene Microfiltration Membrane

To improve the antifouling property of PP membrane, a series of amphoteric charged membranes was prepared by the introduction of cysteine on polypropylene membrane. The modified membrane presents higher water flux than original membrane due to the improved hydrophilicity. It was proved by zeta potential that modified membrane inherited the amphoteric characteristic from cysteine. The isoelectric point of modified membranes are at pH 7.2 and 6.5 for 7.6% and 16.1% grafted membranes respectively. Due to the amphoteric characteristic of both modified membrane and BSA, electrical repulsion exsists among grafting chains and BSA in acid and alkaline solution. As a result, modified membranes have much lower adsorption amount of BSA than original PP membrane. Moreover, modified membranes show obvious antifouling property to BSA, due to the improved hydrophilicity of membrane and the electrical repulsion between BSA and membrane. Therefore, the amphoteric charged membranes modified by cysteine show great potential to resist protein fouling in a wide range of pH.

Development of copper-charged polypropylene feedspacers for biofouling control

The productivity of membrane filtration is severely lowered by fouling, which is the accumulation of foreign substances on the surface and/or within pores of membranes. Microbial fouling, or biofouling, is the growth of microorganisms on the membrane surface and on the feedspacer as present between the envelopes. The fouling of membranes has demanded and continues to demand considerable attention from industry and research communities. The goal of this project was to develop and investigate the use of copper (Cu)-charged polypropylene (PP) feedspacers that target biofouling control. Cross-flow filtration experiments showed that membranes that used the Cu-charged feedspacers experienced a drastically lower rate of flux decline than the membranes that used unmodified feedspacers. After approximately 48 h of filtration, the flux of membranes that used unmodified feedspacers had declined to approximately 30% of the initial flux (or a 70% flux decline), while the flux of the membranes that used Cu-charged feedspacers had decreased to approximately 75% of the initial flux (or a 25% flux decline). Furthermore, it took membranes that used Cu-charged feedspacers approximately 12 days to reach 35% of the initial flux, a 65% flux decline. This decreased rate of flux decline was contended to be due to less extracellular polymeric substances (EPS) present on the membrane surface. Lastly, no significant amounts of copper leached from the Cu-charged PP during operation.

The effect of additives on charge decay in electron-beam charged polypropylene films

The charge decay in isotactic polypropylene (i-PP) films of 50 µm thickness, containing three kinds of additives, namely a trisamide, a bisamide and a fluorinated compound, with concentrations in the range 0.004–1 wt% was studied. Compression molding was used to produce the films. The samples were either surface-charged by a corona method or volume-charged by mono-energetic electron beams of different energies, having penetration depths up to 6 µm. In all cases, surface potentials of about 200 V were chosen. After charging the films, the decay of the surface potential was studied either by an isothermal discharge method at 90 °C or by thermally stimulated discharge measurements. The results show a dependence of the decay rate on the kind of additive used, on additive concentration and on the energy of the injected charges. In particular, for samples with fluorinated additives, the stability of the surface potential decreases markedly with increasing electron energy, while such a dependence is very weak for samples containing the bisamide additive and does not exist at all for samples with the trisamide additive. These observations are tentatively explained by the radiation-induced generation of relatively mobile negative ions originating from the bisamide and fluorinated additives.