PP Films Research Articles

Investigation and Comparison of Alternative Oxygen Barrier Coatings for Flexible PP Films as Food Packaging Material

One of the EU’s ambitious goals is to ensure all plastic packaging is reusable or recyclable by 2030. However, achieving higher recycling rates, particularly in flexible multilayer food packaging, is challenging due to the combination of diverse materials. This highlights the importance of designing for recyclability and exploring alternative barrier solutions. In this study, several types of coatings, such as ORMOCER® (Fraunhofer-ISC, Würzburg, Germany) Michem® Flex B3513 (Michelman International Belgium SRL, Aubange, Belgium), and PVOH (Kuraray Europe GmbH, Frankfurt am Main, Germany), are applied on different polypropylene substrates, including cast PP (CPP70), SiOx, and AlOx-coated PP films. The effect of double coating and optimized curing conditions of ORMOCER® on the oxygen permeability of CPP70 was also investigated. The results showed significant improvements in the barrier properties of PP/SiOx and OPP/AlOx films, and OTR values less than 0.1 cm3/m2·d·bar were achieved. It was also found that ORMOCER® and Michem® Flex B3513 could enhance the oxygen barrier property of CPP70 and the OTR value reduced by a factor of 88 and 551, respectively.

Analysis of Mechanical and Thermal Properties of Polymer Materials Derived from Recycled Overprinted Metallized PP Films.

Polymer materials and their composites are one of the most frequently used materials in the packaging and food industries. This applies to both disposable and reusable packaging, layered films with barrier properties, as well as densely overprinted polymer films and metallized food wrap films. According to statistical data from Plastics Europe, approximately 40% of processed thermoplastics are used to produce packaging, including single- and multi-layer film packaging. Growing requirements and new EU directives require the use of recycled materials in new products, which is not easy because the properties of recyclates may differ significantly from those of the primary materials with which the former are mixed. This work attempts to analyze the properties of the primary material used to produce a film using the casting method in comparison with the industrial recyclate obtained by the processing of film made of the primary material and then overprinted and metallized. The process of obtaining re-granulates and preparing test samples was presented, and the mechanical, structural, and thermal properties of the tested materials were compared. The conducted research and the obtained results demonstrated the advisability of conducting advanced mechanical recycling, which leads to obtaining re-granulates with repeatable processing properties and thermal and mechanical properties comparable to the original material despite the impurities they contain.

Effect of processing conditions on morphology and mechanical damage in glass‐reinforced polypropylene composite

AbstractThis study aims to analyze the effect of processing parameters, particularly the cooling rate, on the morphology and mechanical properties of reinforced glass fiber polypropylene (GF‐PP) films. To achieve the objective, a multi‐scale analysis was performed to study the different morphology of neat PP and reinforced PP films obtained by controlling the thermal condition during the fabrication process. Films of PP with a thickness of about 100 μm have been prepared to observe the crystalline microstructure's formation and follow its kinetics on the scale of the spherulites. The same procedure was followed using a single glass fiber to obtain the mono‐composite film of PP by controlling the interface/interphase between the fiber and the matrix. Moreover, the dependence of the damage mechanisms on the spherulite diameters and the mechanical test conditions was established. The deformation mechanisms (intra and inter‐spherulitic damage) were analyzed qualitatively and quantitatively according to the controlled morphologies produced for the polymer and the composite, especially at the level of the transcrystalline phase. The results confirm that the processing parameters affect not only the width of the transcrystalline phase but also the morphology of the fiber‐matrix interface. Furthermore, increasing the thickness of the transcrystalline phase exhibited remarkably higher interfacial shear strength, as demonstrated by the single fiber fragmentation test.Highlights Impact of cooling rate on morphology and mechanical properties of glass fiber polypropylene (GF‐PP). Multi‐scale analysis to investigate the distinct morphologies of PP and GF‐PP. Deformation mechanism particularly intra and inter‐spherulitic damage. Attention to the impact on the transcrystalline phase and the fiber‐matrix interface. Influence of transcrystalline phase thickness on interfacial strength.

The Influence of the Q-SUN and UV-B Irradiation on the Antiviral Properties of the PP Films Covered with the Coatings Based on ZnO Nanoparticles and TiO2

The purpose of this research was to analyze the antiviral activity of coatings based on ZnO nanoparticles and TiO2. The goal was also to investigate the influence of accelerated UV-B and Q-SUN irradiation on their effectiveness. The results of the performed analysis demonstrated that only one of four coatings containing nanoparticles demonstrated high antiviral activity. Q-SUN irradiation had a positive influence on the antiviral properties of the other three coatings. After 24 h of accelerated irradiation, these coatings demonstrated moderate antiviral effectiveness, confirming that Q-SUN irradiation improved the properties of the active layers (by activating ZnO nanoparticles and TiO2). Unfortunately, after 48 h of irradiation, the activity of the coatings decreased, confirming that the irradiation time should not be too long. Comparing the influence of the UV-B irradiation on the coating activity to the Q-SUN irradiation, it has to be mentioned that UV-B irradiation (24 h) also improved the antiviral properties of the three coatings, which were not active before irradiation. However, it decreased the activity of the coating that was active before UV aging. Unfortunately, none of those analyzed coatings were active after 48 h of UV-B irradiation, confirming that the irradiation time should be shorter.

Effect of UV Irradiation Time on Dielectric Performance of PP Film for HVDC Capacitor

Effect of UV Irradiation Time on Dielectric Performance of PP Film for HVDC Capacitor

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.

Improvement of Water Vapor Permeability in Polypropylene Composite Films by the Synergy of Carbon Nanotubes and β-Nucleating Agents.

A notable application of polymeric nanocomposites is the design of water vapor permeable (WVP) membranes. "Breathable" membranes can be created by the incorporation of micro/nanofillers, such as CaCO3, that interrupt the continuity of the polymeric phase and when subjected to additional uniaxial or biaxial stretching this process leads to the formation of micro/nanoporous structures. Among the candidate nanofillers, carbon nanotubes (CNTs) have demonstrated excellent intrinsic WVP properties. In this study, chemically modified MWCNTs with oligo olefin-type groups (MWCNT-g-PP) are incorporated by melt processes into a PP matrix; a β-nucleating agent (β-ΝA) is also added. The crystallization behavior of the nanocomposite films is evaluated by differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The WVP performance of the films is assessed via the "wet" cup method. The nanohybrid systems, incorporating both MWCNT-g-PP and β-NA, exhibit enhanced WVP compared to films containing only MWCNT-g-PP or β-NA. This improvement can be attributed to the significant increase in the growth of α-type crystals taking place at the edges of the CNTs. This increased crystal growth exerts a form of stress on the metastable β-phase, thereby expanding the initial microporosity. In parallel, the coexistence of the inherently water vapor-permeable CNTs, further enhances the water vapor permeability reaching a specific water vapor transmission rate (Sp.WVTR) of 5500 μm.g/m2.day in the hybrid composite compared to 1000 μm.g/m2.day in neat PP. Notably, the functionalized MWCNT-g-PP used as nanofiller in the preparation of the "breathable" PP films demonstrated no noteworthy cytotoxicity levels within the low concentration range used, an important factor in terms of sustainability.

Dual-layer composite solid polymer electrolytes with Janus properties for interface modification of solid state lithium metal batteries

Solid polymer electrolytes are widely applied in lithium metal batteries owing to good flexibility and machinability. However, monolayer polymer electrolyte are difficult to simultaneously satisfy the interfacial contact with the cathode and Li anode. Herein, the dual-layer composite solid polymer electrolyte with polypropylene film (CSPE@PP) are designed to promote the interfacial compatibility between the solid electrolytes and electrodes. The X-ray photoelectron spectroscopy (XPS) results confirm that poly (vinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) can react with Li metal to form LiF layer, restraining the Li dendrite growth. Meanwhile, the polyacrylonitrile (PAN) antioxidant layer strengthens the contact stability between the electrolytes and the cathodes. Moreover, the PP film serves as the electrolyte's skeleton and connecting layer, enhancing the ion diffusion and mechanical strength of the solid electrolytes. As a result, the Li||CSPE@PP||Li cell is able to stably cycle over 400 h at 0.1 mA cm−2. The LFP||CSPE@PP||Li solid-state batteries deliver 141.98 mAh g−1 discharge capacity and high retention rate (91.1%) after 100 cycles at 0.1C. This work provides a viable strategy for expanding the application of composite solid polymer electrolyte (CSPE) in lithium metal batteries.

Enhancing the Cycle Performance of Lithium-Sulfur Batteries by Coating the Separator with a Cation-Selective Polymer Layer.

Lithium-sulfur batteries are believed to possess the feasibility to power electric vehicles in the future ascribed to the competitive energy density. However, soluble polysulfides continuously shuttle between the sulfur electrode and lithium anode across the separator, which dramatically impairs the battery's capacity. Herein, the surface of a polypropylene separator (PP film) is successfully modified with a delicately designed cation-selective polymer layer to suppress the transport of polysulfides. In principle, since bis-sulfonimide anions groups on the backbone of the polymer are immobilized, only cations can pass through the polymer layer. Furthermore, plenty of ethoxy chains in the polymer can facilitate lithium-ion mobility. Consequently, in addition to obstructing the movement of negatively charged polysulfides by the electrostatic repulsive force of fixed anions, the coated multi-functional layer on the PP film also guarantees the smooth conduction of lithium ions. The investigations demonstrate that the battery with the pristine PP film only delivers 228.5 mAh g-1 after 300 cycles at 2 C with a high capacity fading rate of 60.9 %. By contrast, the polymer-coated sample can release 409.4 mAh g-1 under the identical test condition and the capacity fading rate sharply declines to 43.2 %, illustrating superior cycle performance.

From Independent to Related: Voltage Ramp Rate Effects on Self-Healing Scaling in Metallized Polypropylene Film Capacitors

Metallized polypropylene film capacitors (MPPFCs) are well-suited for high-frequency and high-electric-field applications, such as electric vehicles, aerospace, and pulsed power systems, due to their self-healing (SH) properties. However, the SH process is affected by operating conditions such as voltage level and ramp rate. It is not well understood whether the SH mechanism is consistent across various operating conditions, which may lead to inaccurate assessments of MPPFC reliability. This paper explores the effect of the DC voltage ramp rates on the SH performance of MPPFC. A more specific classification of SH processes under a high electrical field: independent SH (ISH) and related SH (RSH, composed of two or more sub-SHs). Additionally, the SH process of MPPFCs can be characterized using multiple Weibull subpopulation distributions for various voltage ramp rates. At slow ramp rates (<500 V/s), both ISH and RSH processes are present in the MPPFC, whereas at rapid ramp rates (≥500 V/s), the SH process is mainly dominated by ISH. Moreover, the cumulative SH energy of the MPPFC at the 30 V/s ramp rate is about 10 times that of the 900 V/s ramp rate. The ISH at the 900 V/s ramp rate causes several point-like damaged regions on the metalized PP film (~0.06% decrease in capacitance). In comparison, the RSH at the 30 V/s ramp rates induces clusters of holes across multiple layers in the MPPFC (~9.85% decrease in capacitance), implying that the MPPFC has overreached its expected lifetime.

Sustainable Solution for Plastic Pollution: Upcycling Waste Polypropylene Masks for Effective Oil-Spill Management.

The use of Polypropylene PP in disposable items such as face masks, gloves, and personal protective equipment has increased exponentially during and after the COVID-19 pandemic, contributing significantly to microplastics and nanoplastics in the environment. Upcycling of waste PP provides a useful alternative to traditional thermal and mechanical recycling techniques. It transforms waste PP into useful products, minimizing its impact on the environment. Herein, we synthesized an oil-sorbent pouch using waste PP, which comprises superposed microporous and fibrous thin films of PP using spin coating. The pouch exhibited super-fast uptake kinetics and reached its saturation in fewer than five minutes with a high oil uptake value of 85 g/g. Moreover, it displayed high reusability and was found to be effective in absorbing oil up to seven times when mechanically squeezed between each cycle, demonstrating robust oil-sorption capabilities. This approach offers a potential solution for managing plastic waste while promoting a circular economy.

Investigation of welding repair methods for thermoplastic composite joints

Repair is a common process to extend the service life of composite structures, and there is a need for techniques compatible with thermoplastic composites (TPCs). As the assembly of TPC joints through welding is gaining importance, evaluating their potential for repairability is essential. This work aims to develop novel techniques to repair welded TPC joints: 1) Successive repair (three cycles) of broken joints by ultrasonic-assisted method with neat and nanocomposite films, and 2) one-step repair using ultrasonic welding (USW) and resistance heating. It was found from tensile testing that multi-walled carbon nanotube/polypropylene (MWCNT/PP) films partially restored the lap shear strength (LSS), but pure PP films enabled significant recovery of the LSS as 94.5%, 89.4%, and 86.7% after the first, second, and third repair cycle, respectively. Nanocomposite films were however promising for monitoring the initiation and propagation of the damage occurring within the repaired joints, even after three repair cycles. Moreover, results from one-step repair using USW revealed that a stronger and more uniform repair interface was obtained, compared to resistance heating. Overall, the repair methods developed in this study exhibited promise for TPC joint repair, with strength recovery between 63.8% and 94.5%.

Structural and optical behaviours of methyl acrylate-vinyl acetate composite thin films synthesized under dynamic low-pressure plasma

Low-pressure (33.33 Pa) plasma polymerized methyl acrylate and vinyl acetate composite thin films with various monomer compositions were deposited onto glass substrates. Under the same plasma conditions, the homopolymer thin films were also prepared. The thickness of the composite films was observed to vary between 117 and 213 nm depending on the monomer ratio. The composite films exhibit a smooth, pinhole-free, and immaculate surface morphology, surpassing that of the homopolymers. The energy dispersive x-ray study shows that the films contain mainly carbon and oxygen with 26.09–37.20 at% and 35.03 − 40.10 at%, respectively. The composite films contain more carbon contents which enhance the film stability. The appearance of some broad absorption bands in the Fourier transform infrared spectroscopy indicates structural changes in the PP films caused by the restructuring or dilapidation of monomer molecules while forming the polymer. The UV–visible spectra analysis reveal that the composite films exhibited a tunable optical band gap by adjusting the monomer ratio. The decrease of methyl acrylate monomer reduces the direct and indirect optical band-gap values of composite films from 3.15 to 3.00 eV and 2.35 to 1.74 eV, respectively. While Urbach energy values increases from 0.33 eV to 0.90 eV. All the films showed good transmittance properties (86 − 96%) in the visible range wavelength (550 − 800 nm). Other optical parameters are also found better in composite films which indicates the aptness of the composite films in various optoelectronic or electronic applications.

Experimental Tests on Solvent Solutions for the Recycling of Coated Polypropylene in Food Packaging

The aim of this research is to analyze and develop technical methods that allow the recycling of food packaging coated in polypropylene films using solvents for the removal of the lacquer and/or aluminum layer without modifying their mechanical properties. Thus, this would allow the regranulation and re-extraction of the treated material for the creation of new polypropylene films. Water solutions of KOH 1M and methanol 99.9% were tested as solvents using the selective dissolution method. In order to rule out a significant effect of the mechanical stirring action on the removal of the surface layer, a deionized water solution was used as a control sample. By means of UV-VIS-NIR (ultraviolet, visible, near-infrared), LWIR (long-wave infrared), and ATR-IR spectrophotometers, spectrophotometric analyses were carried out on the samples before and after treatment. In order to investigate the efficiency of the solvents in removing the coating of polypropylene films, samples taken from the industry Jindal Films Europe Brindisi s.r.l., named BF (basic film, pp film not lacquered or metallized), AC (aluminum-coated pp film), and ACRC (acrylic-lacquer-coated pp film), were compared with samples treated with solvent solutions. The comparison was made by comparing the spectra obtained from the analyses carried out with the two different spectrophotometers. The absorbance values at the level of characteristic polypropylene spectrum peaks, detected with an ATR-IR, were also compared using the Pearson correlation coefficient. The results suggest that the optimal solvent for removing the aluminum and acrylic lacquer from pp films is the solution of KOH 1M. Future analyses will aim to investigate the maintenance of the mechanical characteristics of polypropylene treated with a selective dissolution using KOH. It is also planned to test the methodology of this study on an industrial scale.

Reactive Extrusion of Nonmigratory Active and Intelligent Packaging.

The environmental and economic burden of food waste demands new preservation technologies to reduce the degradative actions of spoilage such as moisture, oxygen, and microorganisms. Direct food additives can help maintain product quality; however, the limited life span of these additives combined with consumer desire for "clean label" products has motivated research into new food manufacturing technologies like active and intelligent packaging that can prevent and detect food spoilage. In this work, curcumin was grafted to polypropylene (PP-g-Cur) via reactive extrusion to produce nonmigratory active and intelligent packaging through a solvent-free, efficient, and continuous method. Immobilization of curcumin was confirmed by a standard migration assay exhibiting a maximum of 0.011 mg/cm2 migration, significantly below the EU migratory limit for food contact materials (0.1 mg/cm2). Compared to native PP films, PP-g-Cur films blocked 93% of UV light while retaining 64% transparency in the visible region, allowing for desirable product visibility while inhibiting UV degradation of packaged goods. While the ability of PP-g-Cur to inhibit growth of E.coli and L. monocytogenes was insignificant compared to control PP, free curcumin exhibited poor bacterial inhibition as well, suggesting that without hydrophilic modification, native curcumin has limited antimicrobial efficacy. PP-g-Cur films displayed significant radical scavenging in both organic (11.71 ± 3.02 TroloxEq (nmol/cm2)) and aqueous (3.18 ± 1.04 TroloxEq (nmol/cm2)) matrices, exhibiting potential for antioxidant behavior in both lipophilic and hydrophilic applications. Finally, when PP-g-Cur films were exposed to ammonia, an indicator of microbial growth, the color visually and quantitatively changed from yellow to red, demonstrating potential to indicate spoilage. These findings demonstrate the potential of a scalable technology to produce active and intelligent packaging to limit food waste and advance the capabilities of functional materials in a variety of applications.

Pectin/PVA and pectin-MgO/PVA films: Preparation, characterization and biodegradation studies

There is a great demand to replace non-renewable materials with eco-friendly renewable materials for many applications in recent times. In the present study, such an attempt was made to substitute synthetic polymer-based films used for food packaging applications with films prepared out of renewable materials derived from waste. The pectin/polyvinyl alcohol (PP) and pectin-MgO/polyvinyl alcohol (PMP) films were prepared and characterized to ascertain their suitability for packaging applications. To improve the mechanical strength and thermal stability of films, MgO nanoparticles were incorporated in situ into the polymer matrix. The pectin used in the study was extracted from citrus fruit peel. The prepared nanocomposite films were evaluated for physico-mechanical properties, water contact angle, thermal stability, crystallinity, morphology, compositional purity and biodegradability. The elongation at break for PP film was 42.24% and for PMP film it was 39.18%. Also, the ultimate modulus in terms of MPa for PP film was 6.8 and for PMP it was 7.9. So, it was found that PMP films have better ductility and modulus than PP films due to the presence of MgO nanoparticles. The spectral studies confirmed the compositional purity of the prepared films. The biodegradation studies revealed that both films could be degraded at ambient conditions at appreciable time span, suggesting them to be a better choice as an environmentally friendly food packaging material.

Novelty method based on thermal trigger mechanism for high energy density lithium-ion battery safety

Thermal runaway is the most serious issue for high energy density lithium-ion batteries. Adding flame retardants to electrolytes is a general way to improve safety of lithium-ion batteries. However, the addition of flame retardants will give rise to adverse effects on the electrochemical performance of batteries, especially phosphate ester flame retardants decompose on the surface of the negative electrode. This research innovatively outlines a heat-triggered addition method of flame retardants using the polypropylene film (PP film) package. Only under abusive circumstances can the flame retardants be released and have a profound effect. The feasibility of this addition method is verified by the battery thermal safety testing. This ingenious addition method not only avoids the negative effects of flame retardants on battery performance, but also provides a new way to prevent thermal runaway of batteries.

Dragon Fruit Peel Extract Enriched-Biocomposite Wrapping Film: Characterization and Application on Coconut Milk Candy.

Bio-based film is an eco-friendly alternative to petroleum-based packaging film. The effects of biocomposite wrapping film enhanced with dragon fruit peel extract (0, 2% w/v, respectively) and currently used commercial packaging film (polypropylene; PP) on coconut milk caramels during storage (30 °C, 75% RH, nine days) were studied. Both 0% and 2% DPE-enriched biocomposite films were thicker and had higher water vapor permeability and solubility than the PP film but poorer mechanical characteristics. In addition, the 2% film possessed antioxidants and antioxidant ability. A FESEM micrograph revealed the rough surface and porous path of the biocomposite films. Over the storage time, the moisture content, water activity, and springiness of the coconut milk caramel candy wrapped in the PP and all DPE-enriched biocomposite films were not significantly altered. However, the lipid oxidation as the thiobarbituric acid reactive substance (TBARS) and hardness of all coconut caramels were significantly (p < 0.05) increased during storage. Furthermore, the hardness of coconut candy covered in the control (0% DPE) biocomposite film was more pronounced on day nine of storage. However, the changes in quality characteristics of the coconut candy wrapped in each film type need to be better established. The investigating factors influencing the quality deterioration of coconut milk candy should be further identified to mitigate their effects and extend the shelf-life of the coconut candy.

Microplastic levels on sandy beaches: Are the effects of tourism and coastal recreation really important?

This study assessed the effect of tourism and other recreational activities on microplastic (MP) levels and their characteristics in the sand and surf zone of the seawater. Six sites were chosen belonging to three sandy beaches with similar geomorphologic and morphodynamic characteristics but with different tourism activities. On average, a concentration of 1133.3 ± 811.3 items/kg dry weight (d.w.) and 12.7 ± 14.9 items/m3 were found in the sand and seawater samples, respectively. Fibers and films predominated and were less than 1 mm in length. In the sand, the films mainly matched the PE polymer spectra and the fibers matched PET polymer, cotton, and indigo blue dye; in the seawater samples, PP films and PET fibers prevailed. At the Pehuén-Co – Monte Hermoso Coastal Marine MPA where the flow of tourists is low, the MP levels were the lowest and the largest particles were found, mainly blue or black fibers, with less polymer diversity, cotton and PET being the most prevalent suggesting a recent input of textile fibers to this site. Moreover, the highest concentration of MPs was found on the southern site of a beach considered to be more pristine due to negligible human activity, including the smallest size pattern, mostly composed of white films or fibers with a greater diversity of polymers, predominantly PE > PET > PP. A great occurrence of PVC white films was also found in the surf zone at this site. Proximity to the mouth of a river, littoral drift, and other point sources were identified as the main sources, indicating that, apart from the local tourism and recreational activities, other sources might play a major role in the input of MPs to sandy beaches, such as extensive/intensive agricultural land use and irrigation areas.

Revisiting the thermal ageing on the metallised polypropylene film capacitor: from device to dielectric film

AbstractMetallised polypropylene film capacitors (MPPFCs) are widely used in power electronics and are generally degraded by elevated temperatures. This work aims to determine the relationships between the structural changes of MPPFC and the microstructural variations of the PP film during the thermal ageing of MPPFC at 100°C for 38 days. The capacitance of MPPFC has a slight decrease during thermal ageing. However, the breakdown voltage of the MPPFC decreases by 39.4% by the ageing. The partial discharge (PD) number of MPPFC increases linearly with ageing time. The tear‐down analysis of the MPPFC reveals that the molecular structure of the PP film has not been altered but has led to molecular chain scission and the generation of some polar fragments/groups. Meanwhile, the relative permittivity of the PP films rises as the ageing time increases. Moreover, thermal ageing causes the conversion of aluminum to alumina in the metallised electrode, which is hydrophilic for polar groups and leads to an adhesion effect between the metallised electrodes and the PP film. Contact angle measurements prove that the surface hydrophilicity of the PP sample increased after thermal ageing. Therefore, the PD/breakdown voltage in the MPPFC increases/decreases due to the uneven adhesion of the metallised PP film.