Biaxially Oriented Polypropylene Research Articles

Improved Energy Storage Performance of Composite Films Based on Linear/Ferroelectric Polarization Characteristics.

The development and integration of high-performance electronic devices are critical in advancing energy storage with dielectric capacitors. Poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) (PVTC), as an energy storage polymer, exhibits high-intensity polarization in low electric strength fields. However, a hysteresis effect can result in significant residual polarization, leading to a severe energy loss, which impacts the resultant energy storage density and charge/discharge efficiency. In order to modify the polarization properties of the polymer, a biaxially oriented polypropylene (BOPP) film with linear characteristics has been selected as an insulating layer and combined with the PVTC ferroelectric polarization layer to construct PVTC/BOPP bilayer films. The hetero-structure and polarization characteristics of the bilayer film have been systematically studied. Adjusting the BOPP volume content to 67% resulted in a discharge energy density of 10.1 J/cm3 and an energy storage efficiency of 80.9%. The results of this study have established the mechanism for a composite structure regulation of macroscopic energy storage performance. These findings can provide a basis for the effective application of ferroelectric polymer-based composites in dielectric energy storage.

Polyphenylene Oxide Film Sandwiched between SiO2 Layers for High-Temperature Dielectric Energy Storage.

The commercial capacitor using dielectric biaxially oriented polypropylene (BOPP) can work effectively only at low temperatures (less than 105 °C). Polyphenylene oxide (PPO), with better heat resistance and a higher dielectric constant, is promising for capacitors operating at elevated temperatures, but its charge-discharge efficiency (η) degrades greatly under high fields at 125 °C. Here, SiO2 layers are magnetron sputtered on both sides of the PPO film, forming a composite material of SiO2/PPO/SiO2. Due to the wide bandgap and high Young's modulus of SiO2, the breakdown strength (Eb) of this composite material reaches 552 MV/m at 125 °C (PPO: 534 MV/m), and the discharged energy density (Ue) under Eb improves to 3.5 J/cm3 (PPO: 2.5 J/cm3), with a significantly enhanced η of 89% (PPO: 70%). Furthermore, SiO2/PPO/SiO2 can discharge a Ue of 0.45 J/cm3 with an η of 97% at 125 °C under 200 MV/m (working condition in hybrid electric vehicles) for 20,000 cycles, and this value is higher than the energy density (∼0.39 J/cm3 under 200 MV/m) of BOPP at room temperature. Interestingly, the metalized SiO2/PPO/SiO2 film exhibits valuable self-healing behavior. These results make PPO-based dielectrics promising for high-temperature capacitor applications.

Using disposable food packaging materials as printing, embedding, and sectioning media in the plant anatomy lab.

During the COVID-19 pandemic lockdown, all laboratory work was suspended, and we were obliged to work from home, causing delays in our research. As the disruption to supply chains made it difficult to obtain our regular lab supplies, we were obliged to search for substitutes. We became familiar with a plastic material known as biaxially oriented polypropylene (BOPP) that is widely used in the food industry for wrapping or storing fruits, vegetables, and meat. BOPP is easily dissolved in organic solvents such as xylenes, acetone, or thinner, but these reagents are very toxic, flammable, and can cause nausea in some users. After testing several alternatives, we found a polyurethane remover that proved to be an effective and relatively harmless BOPP solvent. By dissolving thin slices of BOPP in a polyurethane solvent, we obtained a clean fluid that we used to obtain leaf surface prints that could be mounted on microscope slides with a coverslip. This fluid produced excellent bark and wood sections and can be used to obtain wood or charcoal surface prints. Our attempts to use it as a mounting medium were unsuccessful. BOPP dissolved in a polyurethane remover is a handy, versatile resource for plant microtechniques. In addition to its economic advantages, it is useful in terms of reducing plastic pollution.

Improving Charge Storage of Biaxially-Oriented Polypropylene Under Extreme Electric Fields by Excimer Uv Irradiation.

Biaxially-oriented polypropylene (BOPP) is one of the most commonly used materials for film-based capacitors for power electronics and pulsed power systems. To address the pressing issue of performance-limiting loss under extreme electric-fields, here we demonstrate a one-step, high-throughput, and environment-friendly process based on very low-dose ultra-violet irradiation from KrCl (222nm) and Xe2 (172nm) excimer. The performance of commercial BOPP is boosted in terms of withstanding electric-field extremes (Weibull breakdown strength 694 to 811V μm-1 by 17% at 25°C and 428 to 651V μm-1 by 52% at 120°C), discharged energy density, and conduction losses. Importantly, the depth profile of space charge is precisely measured in-situ with a high resolution of 500nm by laser induced pressure pulse. Consequently, the space charge effect and electric-field distortion are reduced and related to the improved polymer films. It is demonstrated that energetic UV photons act as scissors for BOPP chains and dissociate oxygen molecules leading to the more thermally stable oxygen-containing structures, as deep traps to impede charge migration. This work provides a promising approach to produce polymers with customized microscopic characteristics that is compatible with the assembly lines of polymer-based capacitors. This article is protected by copyright. All rights reserved.

γ-Ray Irradiation Significantly Enhances Capacitive Energy Storage Performance of Polymer Dielectric Films.

Polymer dielectric capacitors are fundamental in advanced electronics and power grids but suffer from low energy density, hindering miniaturization of compact electrical systems. It is shown that high-energy and strong penetrating γ-irradiation significantly enhances capacitive energy storage performance of polymer dielectrics. γ-irradiated biaxially oriented polypropylene (BOPP) films exhibit an extraordinarily high energy density of 10.4 J cm-3 at 968 MV m-1 with an efficiency of 97.3%. In particular, an energy density of 4.06 J cm-3 with an ultrahigh efficiency of 98% is reliably maintained through 20000 charge-discharge cycles under 600 MV m-1. At 125°C, the γ-irradiated BOPP film still delivers a high discharged energy density of 5.88 J cm-3 with an efficiency of 90% at 770 MV m-1. Substantial improvements are also achieved for γ-irradiated cycloolefin copolymers at a high temperature of 150°C, verifying the strategy generalizability. Experimental and theoretical analyses reveal that the excellent performance should be related to the γ-irradiation induced polar functional groups with high electron affinity in the molecular chain, which offer deep energy traps to impede charge transport. This work provides a simple and generally applicable strategy for developing high-performance polymer dielectrics.

Improving the performance of polyacrylate latex binders for water-based inks through the application of reactive emulsifiers and nanosized zinc oxide

The poor redissolution and low ethanol resistance stability of room temperature self-cross-linking polyacrylate latexes (RTSPLs) made from conventional emulsifiers are the main obstacles for their industrial application in water-based inks. To address these issues, in this study, anionic SR-10 (allyloxy polyoxyethylene ammonium sulfate) /nonionic ER-10 (allyloxy fatty alcohol polyoxyethylene ether) dual-reactive composite emulsifier is developed to replace the conventional 2A1 (sodium dodecyl diphenyl ether disulfonate) /TX-30 (alkyl phenol polyoxyethylene ether) non-reactive composite emulsifier for the synthesis of polyacrylate latexes, and a certain mass of nanosized zinc oxide (ZnO) was added into as-prepared latexes as an ionic cross-linking agent to partially replace the cross-linking monomer of diacetone acrylamide (DAAM). Properties of the latexes and the latex films, with emphasis on redissolution, stability against ethanol, and adhesion on biaxially oriented polypropylene (BOPP) and polyethylene (PE) substrates, were evaluated to study the effect of the reactive emulsifiers and the nanosized ZnO. The application of the reactive composite emulsifier eliminates the disadvantages associated with the desorption from the latex particles and migration during film formation of the non-reactive emulsifier, thus improving the ethanol resistance stability of latexes and adhesion of their inks on BOPP substrate. The introduction of a certain amount of nanosized ZnO to replace DAAM in equimass amounts improves the redissolution but reduces the cross-linking density and water resistance of the latex film. Surprisingly, the addition of nanosized ZnO substantially improves the ethanol stability of latexes. When ZnO replaces DAAM, accounting for approximately 1 wt% of the total monomers, not only the prepared latex exhibits excellent alcohol dilution stability, but also the latex film has a relatively high cross-linking density, good redissolution, and good comprehensive properties. These findings provide an effective, yet simple way to balance the redissolution and high cross-linking degree of latex films while ensuring that the latexes have good ethanol resistance stability.

Nonpolar sub-10 nm TiO2 nanocrystal for high energy density polypropylene nanocomposites

Film capacitors have shown great potential in high-power energy storage devices due to their high breakdown strength and low dielectric loss. However, the state-of-the-art commercial capacitor dielectric, biaxially oriented polypropylene (BOPP), exhibits limited energy storage density below 2 J cm−3 because of its low dielectric constant (approximately 2.2 at 103 Hz). In this work, we present a novel PP-based nanocomposites by incorporating nonpolar sub-10 nm sized TiO2 nanoparticles into the PP matrix for the first time. The nonpolar TiO2 nanoparticles are functionalized with Trioctylphosphine oxide (TOPO) ligands, ensuring excellent compatibility and dispersion of the TiO2 fillers in the PP matrix, resulting in a homogeneous dielectric PP nanocomposite. Moreover, the TOPO ligand, with lower LUMO energy level and higher HOMO level than that of PP matrix, serves as an energy trap to capture carriers upon their occurrence. Furthermore, the well-dispersed sub-10 nm sized TiO2 nanoparticles enlarges the interfacial area, thereby increasing the interfacial polarization and the dielectric constant. The resultant PP nanocomposites exhibit a high discharged energy density of 4.19 J cm−3 at 600 MV m−1, representing a remarkable 74.9% increase compared to that of the pure PP films. This work provides a brand-new strategy for constructing homogeneous PP nanocomposite dielectrics by incorporating nonpolar sub-10 nm sized TiO2 nanoparticles as fillers. And this approach is critical for the design of high energy density PP-based nanocomposites.

Significantly improved high-temperature capacitive performance in polypropylene based on molecular semiconductor grafting

The high-temperature dielectric properties and energy storage performance of capacitive materials are of great significance for the sustainable development of new energy-related fields. However, the most widely used commercial capacitor dielectric biaxially oriented polypropylene (BOPP) films fail to satisfy the requirements of continuous operation above 105 °C at high electric fields. Here we demonstrate a molecular semiconductor-grafted polypropylene (PP) composite that possesses substantially enhanced dielectric and capacitive performance up to 120 °C by virtue of the modulated carrier transport behavior. The organic molecular semiconductor [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) is chemically grafted onto PP chains (PCBM-g-PP) to achieve strong interaction and decent compatibility between the PCBM and the polymer matrix. Based on computational simulation and experimental verification, it is confirmed that the grafted molecular semiconductor introduces deep traps to inhibit the migration of high-energy charge carriers excited by heat. In the meantime, the grafting also helps to intensify the regulation effect by exerting positive influences on the microstructure of the polymer. The PCBM-g-PP/PP composite films possess reduced leakage current and dielectric loss, as well as suppressed electric field distortion and elevated breakdown strength. At 120 °C, the energy storage density of the composite with an efficiency above 90% reaches 1.59 J/cm3, which is 683.62% that of the original PP film. The reported molecular semiconductor-grafting strategy is expected to promote the capacitive performance of polypropylene under hash-temperature conditions, facilitating the development of lightweight and compact-size dielectric capacitors.

Dynamic Cross-Linked Polyethylene Networks with High Energy Storage and Electrical Damage Self-Healability.

Dielectric polymers that exhibit high energy density Ue, low dielectric loss, and thermal resistance are ideal materials for next-generation electrical equipment. The most widely utilized approach to improving Ue involves augmenting the polarization through increasing the dielectric constant εr or the breakdown strength Eb. However, as a conflicting parameter, the dielectric loss also increases inevitably at the same time. In addition, due to the long-term work under a strong electric field or high potential, dielectric materials often produce electrical damage (electrical tree), which is one of the main factors affecting the reliability and service life of electrical equipment. To address these problems, we herein develop dynamic cross-linked polyethylene materials (PE-MA-Epo) by polyethylene-graft-maleic anhydride (PE-MA) and polar epoxy monomers, which showed high εr (>7), low dielectric loss (<0.02), high Ue (5.16 J/cm3 at 425 MV/m), and outstanding discharge efficiency (97%). The performances of the materials are adequate to rival biaxially oriented polypropylene (BOPP) films. Moreover, the excellent self-healing capability of PE-MA-Epo enables the total recovery of εr and tan δ after electrical tree healing. After two cycles of electrical breakdown healing, Eb remained at 80%, which improves the durability and reliability of dielectric polymers. Therefore, PE-MA-Epo shows great potential for applications in advanced electronic power devices.

Nanoscale thinning of metal-coated polypropylene films by Helium-ion irradiation

Polypropylene (PP) films have a wide range of applications, e.g. as dielectric materials for metallized film capacitors. In this article, we present a method for thickness reduction of PP films by ion irradiation, which has a direct effect on device capacitance. We show that the thickness of PP layers can be reduced by irradiation with He+ ions and controlled on the nanometer scale by the irradiation dose. The effect of different thin metal film coatings on PP surface was also investigated. The metal coatings were used for two reasons: they function as one of the metal electrodes in the capacitor structure, and they minimize sample charging during ion irradiation. Three different metallization materials were investigated: 5 nm Pt60Pd40, 5 nm Au, and 15 nm Al. We studied two technologically relevant PP films: the thinnest commercially available biaxially oriented polypropylene (BOPP) and spin-coated polypropylene (SC-PP) thin films. The irradiation was done with a focused Helium-ion beam (He-FIB) in a Zeiss Orion NanoFab Microscope at a landing energy of 30 keV with doses in a range of 5.4 × 10–5 nC/μm2 to 8.1 × 10–3 nC/μm2. An atomic force microscope (AFM) was used to analyze the details of surface modification: the surface height of the irradiated regions and surface morphology changes caused by the irradiation. For all applied doses, the Al-coated samples demonstrated smaller surface-height reduction compared to the Pt60Pd40 and Au-coated samples. We speculate that the possible factors responsible for this effect include differences in the thickness and the crystalline-grain orientation (texture) of the metallization films. Both BOPP and spin-coated PP presented surface ridges at the borders between the irradiated and non-irradiated regions. It can be attributed to the mechanical strain induced by the material modification.

Mechanically robust and functional anisotropic conductive polymer composites with alternating microlayers

Anisotropic conductive polymer composites (ACPCs) are of great significance in electrical interconnection, miniaturized sensing devices and thermal management. The conductivity of ACPCs and conductivity ratio in different directions are the key to realize their applications. Actually, electrical properties are of significance, furthermore the mechanical properties of materials should attract more concern because conductive networks in ACPCs are commonly constructed by high volume of fillers with sacrificing mechanical properties of the final composites. Therefore, this study aims to improve significantly electrical properties of ACPCs while breaking limitation of the conductive fillers to damage the mechanical properties. In this work, ACPCs with alternative microlayers of biaxially oriented polypropylene (BOPP) and polypropylene (PP) filled carbon nanotubes (CNTs) are fabricated by low-temperature welding strategy. The electrical conductivity in X-direction reaches up to 10.1 S/m exhibiting a value 9.5 orders of magnitude higher than the value in Z-direction, while the products show super-high impact toughness of 12.3 kJ/m2 and tensile strength of 62.5 MPa, which is by far the most remarkable mechanical properties compared with the reported conductive PP-based composites. The integration of excellent electrical properties and high mechanical properties enables the materials to be applied to complex intelligent electronic device showing great applications value. Moreover, this ACPCs fabricating strategy is able to be scaled up due to simple, environmentally-friendly preparation process and low-cost raw materials, promoting ACPCs to be implemented in a variety of applications.

UV-Induced Thiol-Ene "Click" Surface Grafting Polymerization on BOPP Substrate and Its Postmodifying for Hydrophilic and Antibacterial Applications.

This paper proposed a novel and versatile surface modification route by integrating UV light-mediated thiol-ene "click" surface grafting polymerization and postmodification via the reactions of the surface thiol groups. At first, poly(thiol ether) layers with tunable thiol group density, up to 8.2 × 102 ea/nm3 for cross-linked grafting layers, were grafted from biaxially oriented polypropylene (BOPP) film. Then, the surface -SH groups reacted with epoxy compounds to introduce quaternary ammonium salt. With the immobilized quaternary ammonium salt and coordinated Zn2+ ions, the modified film demonstrated 99.98% antibacterial rate against Staphylococcus aureusafter soaking in DI water for 21 days and in a highly alkaline environment (0.1 M NaOH aqueous solution) for 3 days, and the surface water contact angle decreased to 39°. At last, the polymethacrylate chains were also successfully grafted from the surface thiol groups of the cross-linked poly(thiol ether) under visible light irradiation. With 2-(dimethyldodecylammonium) ethyl methacrylate as the grafting monomer, the modified BOPP film had shown a 99.99% antibacterial rate against both Escherichia coliand S. aureus. Meanwhile, with 2-methacryloxyethyl phosphoryl choline as grafting monomer, the modified surface showed an excellent antibioadhesion of living S. aureus, and the surface water contact angle was as low as 48°.

Improving the High-Temperature Energy Storage Performance of Epoxy Films: Moderately Reducing Unsaturation for Extremely High Efficiency.

The rapid development of renewable energy systems, electric vehicles, and pulsed equipment requires energy storage media to have a high energy storage density and efficiency in a wide temperature range. The state-of-the-art biaxially oriented polypropylene (BOPP) film is insufficient to meet the growing demand for energy storage devices due to its low energy storage density and working temperature, which make it a research hotspot for developing dielectric energy storage materials. In this manuscript, based on the epoxy materials that have been shown as a potential energy storage medium, we aim to reduce the influence of the benzene ring delocalization structure on the energy storage losses and enhance the efficiency by gradually replacing them with cyclohexane structures to adjust the segment unsaturation of epoxy materials. The results show that by partially reducing the unsaturation of the curing agent, the epoxy material achieves an excellent high-temperature energy storage density of 2.21 J/cm3 at 150 °C and 300 MV/m while maintaining an extremely high energy storage efficiency of 99.2%. Leakage current density and high-voltage dielectric spectroscopy tests confirm that a moderate reduction of the segment unsaturation of epoxy materials can greatly inhibit polarization loss at high temperatures, which may explain their high energy storage efficiency.

Microfabrication of Thermoplastic Polypropylene Surface Structures via Thermal Imprinting for Controlling the Adhesion of Easy Peel Package.

Micropatterns were fabricated on polypropylene (PP) surfaces using the hot embossing technique with various temperatures ranging from 160 to 175 °C and applying force conditions from 100 to 300 N. To evaluate the replication quality, an effective filling ratio of 1 indicates that the volume of the formed pattern is similar to the mold cavity volume. From the results, the filling ratio increased with increasing the embossing temperature. For instance, under a constant force of 100 N, the filling ratio of polypropylene (PP) with small square arrays (pattern SS) increased from 0.08 to 0.41 when the embossing temperature was raised from 160 to 175 °C, respectively. With the increase of applied force, the filling ratio also increased. At an imprinting temperature of 175 °C and an applied force of 300 N, the highest effective filling ratio that was achieved was approximately 0.99. Furthermore, the effect of PP with different melt flow indexes (MFIs) on the filling ratio was investigated. For food packaging applications, a micropatterned PP sheet was heat-sealed with a biaxially oriented polypropylene (BOPP) film. The micropatterned PP sheet demonstrated easy-opening properties by varying sealing contact areas and micropattern geometries between the sheet and the BOPP film. All micropatterned PP sheets with an MFI of 25 g/10 min exhibited an easy peel property with adhesive failure characteristics at a heat-sealing temperature of 150 °C and a dwell time of 3 s. There was no residue on the PP substrate surface. The overall findings are beneficial in understanding the hot embossing technology for fabricating micropatterns on polymer surfaces, and it can be applied in an easy peel property for packaging applications.

Influence of sustainable packaging material and packaging conditions on physicochemical, microbiological, and sensorial properties of cheeses

The aim of this study was to evaluate the influence of different packaging materials [standard foil: BOPP (biaxially oriented polypropylene)/PET (polyester)/PE (polyethylene) for upper layer, and APET (polyethylene terephthalate)/PE for bottom layer; foil 1: PP (polypropylene)/PET/PE/EVOH (ethylene-vinyl alcohol copolymer)/PE upper layer, and PP/PE/EVOH/PE bottom layer; foil 2: PP/PET/PE/EVOH/PE upper layer, and PA (polyamide)/EVOH/PE bottom layer; foil 3: PP/PET/PE upper layer, and PA/EVOH/PE bottom layer; foil 4: PP/PET/PE upper layer, and PA/PE bottom layer; foil 5: PP upper layer, and PP/PP bottom layer] on the quality of 3 different ripening rennet cheeses packed under different modified atmosphere (MAP) conditions as reflected in particular physicochemical, microbiological, and sensorial changes. The changes were monitored during a period of 90 d of storage at 2°C or 8°C. For Gouda cheese, CO2 content of the headspace of the packages was in the range 35% to 45%, whereas for Maasdamer and Sielski Klasyczny cheeses it was 55% to 65%. Three-way ANOVA showed that the foil type influenced the moisture content of Gouda cheese stored for 90 d at 2°C and for Sielski Klasyczny cheese at 8°C, whereas the moisture content was not dependent on MAP conditions during storage. Moreover, the foil type had a significant effect on free fatty acid changes for Gouda and Sielski Klasyczny cheeses stored at 2°C for 90 d. Sensory attributes changed significantly over storage time at 2°C for all studied cheeses as affected by foil type, whereas there was no effect of MAP conditions. In general, the cheeses packed in standard foil and foil 4 were characterized by the highest values of mean sensory attributes. Time was the most significant factor influencing most changes in physicochemical and sensory attributes of cheeses stored at 2°C and 8°C. The storage temperature did not affect the moisture of the samples during storage. In general, we found an increase in the pH value during storage regardless of storage temperature. It was possible to decrease the thickness of the packaging material from initial 103 and 250 µm (standard foil; lid and bottom, respectively) to 98 and 100 µm (foil 4) without affecting sensory attributes of the product.

Low-Temperature Assembling Strategy of a Nacre-Inspired Lamellar Configuration to Upcycling Biaxially Oriented Polypropylene Film Waste.

The efficient recycling and utilization of plastic waste have become a hot topic of global concern, but conventional mechanical recycling not only deteriorates the performance of recycled plastic but also loses the intrinsic structure and properties of the original product. Herein, an upcycling strategy of a biaxially oriented polypropylene (BOPP) film was proposed by duplicating the lamellar configuration established in nature nacre. Especially the suspension of PP wax was deposited on the surface of the BOPP film by spray-coating, followed by layer-by-layer assembling and hot-pressing at 160 °C above the melting temperature of PP wax but below the initial melting temperature of the BOPP film. In this case, PP wax not only functioned as a binder to enable strong interfacial adhesion between the BOPP films via interfacial diffusion but also acted as a soft phase to insert between the rigid BOPP films, constructing a soft-hard alternatively aligned configuration similar to brick-and-mortar architecture in nature nacre. As a result, the mechanical properties of the lamellar sample markedly outperformed those of the conventional mechanically recycling sample, evidenced by 113 and 1141% increases in tensile strength and impact strength, respectively. This simple and effective method provides a new strategy for efficient upcycling of oriented packaging films, which is important to realize the sustainable recycling of plastic waste.

Influence of frequency on the partial discharge characteristics of biaxially oriented polypropylene film under nanosecond pulse voltage

Partial discharge (PD) is one of the key factors leading to premature insulation failure of film capacitors used in pulse power devices. To study the effect of frequency on the PD characteristics of biaxially oriented polypropylene (BOPP) film, a sphere-plate electrode was used to simulate defects of the air gap between the film layers. PD experiments of the BOPP film were carried out under 1, 10, 100, 500 Hz, and 1 kHz with a rising edge of 65 ns and a pulse width of 300 ns. The results show that the repetitive partial discharge inception voltage (RPDIV), the number of discharges, the rising stage discharge (RSD) amplitude, and the falling stage discharge (FSD) time-lag, all show an increase and then decrease with increasing pulse frequencies and reach a maximum value at a pulse frequency of 100 Hz. Moreover, the FSD discharge amplitude and the RSD discharge time-lag increase with an increasing pulse frequency. From the perspective of initial electron generation, the quantitative mathematical relationship between PD characteristics (RPDIV, PD amplitude, PD number, and PD time-lag) and frequency was established based on the Fowler–Nordheim field emission effect for the first time, which can reflect the influence of frequency on the memory effect and the development process of PD. The results can provide an experimental basis and a mechanistic explanation for the evaluation of PD characteristics for film capacitors under nanosecond pulse voltage.

A novel dual-purpose thermal runaway propagation mitigation system using a liquid cooling pipe with aperture sealed by films

Preventing thermal runaway (TR) propagation in lithium-ion battery (LIB) modules is essential for the safe application of LIBs. The current study proposes a novel dual-purpose system using a liquid cooling pipe with aperture sealed by films (LCPASF). The system can maintain the module within the desired temperature by the rapid heat dissipation of the liquid cooling during the normal operation. Once TR occurs, the film on the aperture of the pipe melts and the coolant in the pipe correspondingly releases to cool the cells to prevent the TR propagation. Induced by heater, all of the cells in the module get involved in TR without preventing measures. Systems using polyethylene (PE), biaxially oriented polypropylene (BOPP), polyimide (PI) and polytetrafluoroethylene (PTFE) films limit the TR within 0, 1, 1 and 3 cells, respectively. The melting temperature of PE is much lower than the TR onset temperature, thus the PE film melts before the TR occurrence and no cells get TR. For the film with melting temperature much higher than the TR onset temperature, increasing the aperture diameter can improve the cooling effect. This study provides critical insights for the design of thermal management and TR propagation mitigation system for LIB modules.

Alternative flexible plastic packaging for instant coffees

Instant coffees are consumed worldwide and their packages must protect them mainly from moisture gain. Flexible packaging stand-up pouches made by PET/Al foil/LDPE are currently used but, the look for alternative materials is interesting to replace the aluminum foil with reducing costs and focusing on sustainability. Therefore, the aim of this study was to evaluate the quality loss of freeze-dried and spray-dried (agglomerated and powder) instant coffees during 365 days at 25 °C/75% RH, packaged in five plastic structures: PET (polyethylene terephthalate)/Al (aluminum) foil/LDPE (low density polyethylene), LDPE/HDPE (high density polyethylene)/LDPE, BOPP (biaxially oriented polypropylene)/BOPP met (metallized)/PP, PET/PET met/LDPE and PET/BOPP met/LDPE. The results were compared with the shelf-life estimated by modeling the moisture sorption isotherms of the products by mathematical models. Results indicated that the lower the barrier to water vapor of the packaging material, the greater the gains in moisture and water activity of the instant coffees and in addition to being thermally less stable. After 365 days of storage, the three soluble coffees still had acceptable characteristics in the five packaging structures, indicating that it is possible to replace the currently used laminate, which contains aluminum foil, with recyclable structures. However, the greatest stability for the coffees was obtained using the alternative structures: BOPP/BOPP met/PP and LDPE/HDPE/LDPE, a result that was in concordance with that obtained by mathematical modeling.

Evolution Characteristics of DC Breakdown for Biaxially Oriented Polypropylene Films

Biaxially oriented polypropylene (BOPP) films are the preferred storage dielectric for dry-type film capacitors due to excellent dielectric properties. However, the evolution characteristics of DC Breakdown of BOPP film in air remain unclear. This study focuses on the influence of curvature, contact area and material of electrode on the DC breakdown in BOPP films. The on-line/off-line measurements of surface potential and characterizations of trap distribution are achieved. And the simulations of surface charge, electric field and energy injection are accomplished. The breakdown path and degradation traces in BOPP films are also analyzed. The experimental results show that the effective insulation distance is the key to determine the actual performance of the film, affected by the trap distribution and density. This paper has a reference for the optimization of insulation structure for dry-type film capacitors in the field of high-voltage direct current (HVDC).