Packaging‐related properties of alkyd‐coated,wax‐coated,and buffered chitosan and whey protein films

Packaging‐related properties of coated films of chitosan–acetic acid salt and whey protein concentrate (WPC) were studied. Chitosan (84.7% degree of deacetylation) and WPC (65–67% protein) were solution cast to films. These films are potential oxygen barriers for use in packaging. Coatings of wax or alkyds were used to enhance the water‐barrier properties. The packaging‐related properties of chitosan films treated in a buffering solution, with a pH of 7.8, were also investigated. The coated films were characterized with respect to Cobb absorbency, overall migration to water, water vapor transmission rate, and oxygen permeability. The creasability and bending toughness were determined. The wax was a more efficient barrier to liquid water and 90–95% relative humidity than the alkyd. However, the alkyd‐coated material had superior packaging‐converting properties. The alkyd‐coated WPC and chitosan–salt films were readily folded through 180° without any visible cracks or delamination. The overall migration from the alkyd‐coated materials was below the safety limit, provided the coat weight was higher than 7.5 mg/cm² on WPC and 2.1 mg/cm² on chitosan–salt. The barrier properties of chitosan film under moist conditions were improved by the buffer treatment. However, the buffering also resulted in shrinkage of the film. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 60–67, 2004     

Design and performance evaluation of multilayer packaging films for blister packaging applications

Five multilayer packaging film structures consisting of amorphous poly(ethylene terephthalate) (APET), low‐density polyethylene (LDPE), polypropylene (PP), and acrylonitrile/methyl acrylate copolymer (Barex) films [i.e., APET/polyethylene (PE), APET/PP, APET/PE + UV inhibitor, APET/PP/PE, and APET/Barex/PP] for blister packaging applications were designed and produced. Blister containers with APET/PE and APET/Barex/PP structures were prepared, and their optical, mechanical, barrier (O₂, CO₂, and H₂O), physical, and product/package compatibility performance properties were evaluated. Package/product compatibility with simulants (soy sauce and sunscreen skin cream) at 37.8°C was evaluated for 3, 7, 14, and 28 days in the multilayer films and the blister containers. APET/Barex/PP film showed significantly better O₂ and CO₂ barrier performance than the other four film structures. The UV inhibitor had no significant effect on the barrier properties in the APET/PE film structure. All of the film structures showed high enough elastic storage modulus values to be applied to blister packaging in a broad range of temperatures between ?45 and 80°C. The glass‐transition temperature of APET, which was responsible for the elastic modulus of the multilayer structure, decreased after the samples were exposed to the skin cream. This decrease may have been due to the sorption of the skin cream's active ingredients, such as ethylhexyl methoxycinnamate. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effect of chlorine dioxide gas on physical,thermal, mechanical,and barrier properties of polymeric packaging materials

The effects of gaseous chlorine dioxide (ClO₂) on properties and performance of 10 selected polymeric packaging materials, including polyethylene (PE), biaxially oriented poly(propylene), polystyrene, poly(vinyl chloride), poly(ethylene terephthalate) (PET), poly(lactic acid), nylon, and a multilayer structure of ethylene vinyl acetate (EVA)/ethylene vinyl alcohol (EVOH), were evaluated. Physical, mechanical, barrier, and color properties as well as infrared (IR) spectra were assessed before and after polymer samples were exposed to 3600 ppmV ClO₂ gas at 23°C for 24, 168, and 336 h. The IR spectra of the ClO₂‐treated samples revealed many changes in their chemical characteristics, such as the formation of polar groups in the polyolefin, changes in functional groups, main chain scission degradation, and possible chlorination of several materials. The ClO₂‐treated PE samples showed a decrease in tensile properties compared with the untreated (control) films. Decreases in moisture, oxygen, and/or carbon dioxide barrier properties were observed in the treated PE, PET, and multilayer EVA/EVOH/EVA samples. A significant increase (P < 0.05) in the barrier to O₂ was observed in the ClO₂‐treated nylon, possibly the result of molecular reordering, which was found through an increase in the crystallinity of the material. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

High oxygen barrier property of polyethylene composite films with bilayer polyvinyl alcohol coating for emergency foods in high-humidity environments

The limited oxygen barrier of polyethylene (PE) films has restricted their further application in food packaging, like emergency foods. Although its oxygen barrier property can be improved by applying a polyvinyl alcohol (PVA) coating, the application of PVA/PE composite films in high-humidity environments is still challenging. Hence, this study aimed to enhance the oxygen barrier properties of PVA/PE composite films in high-humidity environments. Specifically, PVA coatings were modified by the itaconic acid (IA) and magnesium-aluminum layered double hydroxides (LDH), and then applied to PE films as bilayer coating. Because of the unique bilayer coating on the PE surface, the oxygen barrier property of PVA/PE composite film (IA/LDH-p) in high-humidity environments has been further improved. The results confirmed that IA/LDH-p had an oxygen permeability coefficient of 1.92 ± 0.16 × 10⁻¹⁶ cm³ cm/(cm² s Pa) under a high-humidity environment test, 82.42% better than that of single-layer coating coated on PE surface. After being stored at RH 90% for 36 h, the tensile strength and elongation at break values of IA/LDH-p were 27.20 MPa and 919.63%, respectively. Overall, this obtained PVA/PE composite films showed great potential for application in emergency foods packaging, particularly in high-humidity environments.     

Hybrid multilayer thin-film fabrication by atmospheric deposition process for enhancing the barrier performance

In this paper, a multilayer barrier thin film, based on polyvinylidene difluoride (PVDF)–silicon dioxide (SiO₂), has been fabricated on a PET substrate through a novel method of joint fabrication techniques. The inorganic SiO₂ thin film was deposited using a roll-to-roll atmospheric atomic layer deposition system (R2R-AALD), while the organic PVDF layer was deposited on the surface of SiO₂ through the electrohydrodynamic atomization (EHDA) technique. The multilayer barrier thin films exhibited very good surface morphology, chemical composition, and optical properties. The obtained values for arithmetic surface roughness and water contact angle of the as-developed multilayer barrier thin film were 3.88 nm and 125°, respectively. The total thickness of the multilayer barrier thin film was 520 nm with a high optical transmittance value (85–90%). The water vapor transmission rate (WVTR) of the barrier thin film was ~?0.9?×?10^?2 g m^?2 day^?1. This combination of dual fabrication techniques (R2R-AALD and EHDA) for the development of multilayer barrier thin films is promising for gas barrier applications.     

Effect of TiO2 nanoparticles on the antibacterial and physical properties of polyethylene-based film

TiO₂ nanoparticles and their application in packaging systems have attracted a lot of attention because of its antimicrobial activity. In this work, effect of TiO₂ nanoparticles on the antibacterial and physical properties of polyethylene (PE)-based film was investigated. Results indicated that the antibacterial activity of TiO₂-incorporated PE films should be due to the killing effect property of TiO₂ nanoparticles against microorganisms. The TiO₂-incorporated PE film exhibited more effective antibacterial activity for Staphylococcus aureus. The antibacterial activity to inactivate Escherichia coli or S. aureus was improved by UV irradiation. The inhibition ratio of TiO₂-incorporated PE films sample irradiated for 60 min by UV light was improved significantly, which were 89.3% for E. coli and 95.2% for S. aureus, respectively, compared to that of TiO₂-PE film without UV irradiation. The analysis of physical properties revealed that TiO₂ nanoparticles increased the tensile strength and elongation at break of PE-based film. The climate resistance of nano-TiO₂ films is greatly enhanced, compared to that of the blank PE film. Water vapor transmission increased from 18.1 to 24.6 g/m²·24 h with the incorporation of TiO₂ nanoparticles. Results revealed that PE based film incorporating with TiO₂ nanoparticles have a good potential to be used as active food packaging system.     

聚乙烯醇/淀粉/凤仙透骨草提取物复合膜制备及性能

以聚乙烯醇(Polyvinyl alcohol,PVA)、淀粉(Starch,ST)为原料,凤仙透骨草提取物(Impatiens balsamina extract,IBE)为抗菌剂,通过共混法制备抗菌复合膜,通过FTIR、XRD、SEM和热重分析对复合膜的形貌和结构进行表征及对力学、光学、阻隔、抑菌等性能测试分析。结果表明,IBE与PVA/ST基膜复合良好,制备的PVA/ST/IBE抗菌复合膜对大肠杆菌、白色葡萄球菌和枯草杆菌具有良好的抑菌作用,抑菌性能随着IBE含量的增加而逐渐提高；同时具有良好的力学强度,IBE添加量为12.5 mL的复合膜拉伸强度达到22.97±0.68 MPa,断裂伸长率相比PVA/ST基膜提升了79.22%；透明度有所下降,透光率下降了11.90%；氧气阻隔性能良好,氧气透过系数为1.771±0.196×10_-12 ^cm₃^.cm/(cm₂^.s.Pa),在环保包装、食品保鲜等领域具有广阔的应用前景。     

Structure, dynamics and interactions of complex sol-gel hybrid materials through SSNMR and DSC: Part II, ternary systems based on PE-PEG block copolymer, PHS and silica

This work is the second part of a study aimed at understanding in more depth structure, dynamics, interactions and correlations between morphology and barrier properties against oxygen diffusion of complex PE-PEG/PHS/SiO₂ hybrids prepared through a sol-gel process. Using a combined DSC and solid-state NMR approach, including ¹³C and ²⁹Si experiments and ¹H ultra-fast MAS spectra, the structural, phase and interaction properties of three PE-PEG/PHS/SiO₂ samples with different compositions, exhibiting different barrier performances, have been investigated, also taking into account the results obtained for the simpler one- and two-component systems (Part I). While the structure of the silica domains has been found to be not affected by composition, many differences have been observed concerning the phase and dynamic properties of the organic components (PE and PEG crystallinity and mobility of their amorphous domains) and the inter-component interactions (strength of the hydrogen bonds between PHS and both silica and PEG and PHS/PEG miscibility). In particular peculiar phase and interaction properties of the sample exhibiting the best barrier properties have been identified and characterized.     

Suppression of radiation‐induced oxidation of polymers by sputtered silicon oxide coating

Oxygen barrier coating on polymers was attempted to obtain polymeric composite materials with improved radiation resistance. Silicon oxide (SiO_1.6) films ranging from 120 to 240 nm thick were formed on polypropylene (PP) and polyethylene (PE) by radio frequency (RF) magnetron sputtering. Oxygen permeability after SiO_1.6 deposition was reduced significantly in all samples studied, indicating that silicon oxide is a useful gas barrier. The oxygen permeability coefficient of deposited films for PP was 1.7–2.2 × 10^?14 cm³‐cm/cm²/s/cmHg and that for PE was 2.8–4.8 × 10^?13 cm³‐cm/cm²/s/cmHg. We studied the effect of such films on the radiation resistance of polymers in the presence of oxygen by microscopic infrared (IR) absorption spectroscopy. Silicon oxide films 180 nm thick were deposited on the surfaces of PP and PE, and the formation of carbonyl groups after irradiation in air was measured as a function of depth from the surface. Results compared with those for uncoated PE and PP showed that the radiation‐induced polymer oxidation is dramatically suppressed by silicon oxide coating. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 186–190, 2002     

Structure,gas-barrier properties and overall migration of poly(lactic acid) films coated with hydrogenated amorphous carbon layers

Hydrogenated amorphous carbon (a-C:H) films were grown on a poly(lactic acid) (PLA) substrate by means of a radiofrequency plasma-enhanced chemical vapour deposition (rf-PECVD) technique with different deposition times (5, 20 and 40 min). The main goal of this treatment was to increase the barrier properties of PLA, maintaining its original transparency and colour as well as controlling interactions with food simulants for packaging applications. Morphological, chemical, and mechanical properties of PLA/a-C:H systems were evaluated while permeability and overall migration tests were performed in order to determine the effect of the plasma treatment on the gas-barrier properties of PLA films and their application in food packaging. Morphological results suggested a good adhesion of the deposited layers onto the polymer surface and the samples treated for 5 and 20 min only slightly darkened the PLA film. X-ray photoelectron spectroscopy revealed that the structural properties of the carbon layer deposited onto the PLA film depend on the exposure time. PLA/a-C:H system treated for 5 min showed the highest barrier properties, while none of the studied samples exceeded the migration limit established by the current legislation, suggesting the suitability of these materials in packaging applications.     

Preparation of oxygen gas barrier polypropylene films by deposition of SiOx films plasma‐polymerized from mixture of tetramethoxysilane and oxygen

Silicon oxide (SiOx) film deposition on the surface of oriented poly(propylene) (OPP) films was done to form a new oxygen gas barrier material using plasma polymerization of the tetramethoxysilane (TMOS)/O₂ mixture. The SiOx film deposition on OPP films never improved oxygen gas barrier properties. The inefficacy of the SiOx deposition was due to poor adhesion at the interface between the deposited SiOx and OPP films and also to the formation of cracks in the deposited SiOx film. If prior to the SiOx film deposition surface modification of OPP films was done by a combination of the argon plasma treatment and TMOS coupling treatment, this contributed effectively to strong adhesion leading to success in the SiOx deposition on the OPP film surface, and then the oxygen gas barrier ability was improved. The oxygen permeation rate through the SiOx‐deposited OPP film was decreased from 2230 to 37–52 cm³/m²/day/atm, which was comparable to that of poly(vinylidene chloride), 55 cm³/m²/day/atm at a film thickness of 11 μm. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 2389–2397, 2000     

Formation of hydrophilic starch coatings on polyethylene films

Thin starch coatings were deposited onto polyethylene (PE) film surfaces when PE films were immersed in 1% jet cooked starch solutions and the hot solutions were allowed to cool. Normal cornstarch, waxy cornstarch, high amylose cornstarch, and solvent‐extracted normal cornstarch (to remove native lipid) were used in these experiments. Amounts of adsorbed starch varied from about 0.03–0.05 mg per cm² of PE, and these starch coatings imparted hydrophilic properties to film surfaces, as evidenced by contact angle measurements. Although starch could be removed by gently rubbing water‐wet PE surfaces, air‐dried coatings were more firmly attached, and did not separate from the PE surface when films were bent or flexed. SEM images of starch‐coated film surfaces showed that starch was deposited as particles less than 1 μm in diameter, and also as aggregates of these submicron particles. Despite the fact that some starch samples contained only very small amounts of amylose and native lipid, surface‐deposited starch in all experiments contained 90–100% amylose; and exhibited the same V_h X‐ray diffraction pattern, indicative of helical inclusion complex formation. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1781–1788, 2002; DOI 10.1002/app.10589     

Oxygen and water vapor gas barrier poly(ethylene naphthalate) films by deposition of SiOx plasma polymers from mixture of tetramethoxysilane and oxygen

SiO_x films were deposited from a mixture of tetramethoxysilane (TMOS) and oxygen on poly(ethylene 2,6‐naphthalate) film using ion‐assisted plasma polymerization technique (Method II) and conventional plasma polymerization technique (Method I), and were compared in chemical composition and gas barrier properties. Methods I and II were different in electrical circuit between electrodes (anode and cathode) and electric power supply. In Method I, the anode electrode was grounded, and the cathode electrode was coupled to the discharge power supply. In Method II, the anode electrode was connected with the discharge power supply, and the cathode electrode was grounded. There was not large difference in SiO_x deposition rate between the plasma polymerizations by Methods I and II. Plasma polymers deposited from TMOS/O₂ mixtures by Method II possessed smaller C/Si and O/Si atomic ratios than those deposited by Method I and showed advantage in gas barrier properties. The oxygen and water vapor permeation rates were 0.08–0.13 cm³ m^?2 day^?1 atm^?1 at 30°C at 90% RH and 0.244–0.276 g m^?2 day^?1 at 40°C at 90% RH, respectively. From these results, it can be concluded that the ion‐assisted plasma polymerization is a useful technique for deposition of gas barrier SiO_x thin films. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 915–925, 2007     

Grafting polythiophene on polyethylene surfaces

Polythiophene (PT) was grafted on PE film using three reaction steps. First, PE films were brominated in the gas phase, yielding PE–Br; second, a substitution reaction of PE–Br with 2‐thiophene thiolate anion gave the thiophene‐functionalized PE; finally PT was grafted on the PE surface using chemical oxidative polymerization to give PE–PT. The polymerization was carried out in a suspension solution of anhydrous FeCl₃ in CHCl₃, yielding a reddish PE–PT film after dedoping with ethanol. ATR‐FTIR shows that the PT was grafted on PE in the 2,5‐position. SEM imaging revealed islands of PT on the PE film. AFM analysis found the thickness of islands to be in the range of 120–145 nm. The conductivity of these thin films was in the range of 10^?6 S cm^?1, a significant increase from the value of ～10^?14 S cm^?1 measured for PE film. © 2003 Society of Chemical Industry     

Surface modification of atmospheric plasma activated BOPP by immobilizing chitosan

Summary Chitosan was immobilized onto plasma activated biaxially oriented polypropylene (BOPP) films aimed at producing antimicrobially active barrier film for food packaging applications. 1% chitosan dissolved into 0.1 M acetic acid was mixed with 0.1% glutaraldehyde (cross-linking agent) and applied onto N₂-plasma + NH₃ activated BOPP film. Amount of immobilized chitosan was 1.8 g/m². Films had strong antimicrobial activity against both Bacillus subtilis and Escherichia coli and they reduced the oxygen transmission rate (OTR) measured in dry conditions from 1500 down to 27 cm³/(m²·24 h). Migration tests for determining the total amounts of substances migrating into food simulants (3% acetic acid, 95% ethanol and iso-octane) indicated, that chitosan coating was permanently immobilized onto BOPP without any leaching (total migration < 2 mg/dm²), thus it met the requirements stipulated in Directive 2002/72/EC relating to plastic materials and articles intended to come into contact with foodstuffs. The results suggest that chitosan treated BOPP films may be exploited in various food packaging applications requiring high oxygen barrier and/or antimicrobially active packaging materials.     

Multiferroic properties of La/Er/Mn/Co multi-doped BiFeO3 thin films

Bi_0.9-xLa_xEr_0.1Fe_0.96Co_0.02Mn_0.02O₃ (BLa_xEFMCO) thin films were prepared by sol-gel method. The grain size, grain boundary resistance, oxygen vacancies and the amount of Fe²⁺ of the films were reduced by multi-ion doping to reduce the built-in electric field of the films. An applied voltage was adopted to regulate the effects of the directional alignment of the oxygen vacancies, defects, and defect pairs on the ferroelectric domains at the grain boundaries to control the ferroelectric polarization of the films. Meanwhile, the capacitance peak also reveals the effects of the ferroelectric domains switching, the migration of oxygen vacancies, and the directional alignment of defect pairs on the ferroelectric properties. In addition, the remnant polarization value of the BLa_0.01EFMCO thin film reaches 152?μC/cm², the squareness of the hysteresis loop (R_sq) is calculated to be 1.03, and the maximum switching current is 1.50?mA. The typical butterfly curves under positive and negative electric fields indicate the films with the enhanced ferroelectric properties. Moreover, the BLa_0.01EFMCO thin film exhibits the enhanced ferromagnetic properties, and its saturation magnetization (M_s) is 2.32 emu/cm³. Therefore, the ferroelectric properties of the BFO film can be enhanced by the multi-ion doped BFO film to reduce the grain boundary resistance (Rgb), the interface Schottky barrier formed by the asymmetric electrode material at the top and bottom of the film, and the built-in electric field formed by the film internal defect or defect pairs.     

Preparation and Performance of High-Barrier Low Density Polyethylene/Organic Montmorillonite Nanocomposite

Montmorillonite (MMT) was first modified with dodecyl dimethylbenzyl ammonium (DDA) salt and octadecyl trimethyl ammonium (OTA) salt. Then low density polyethylene (LDPE)/organic montmorillonite (OMMT) nanocomposites were prepared by twin-screw extruder and hot-press. Transmission electron microscopy (TEM) results showed that OMMT layers were homogeneously intercalated into the LDPE matrix. In terms of MMT, the modification effect of OTA is superior to that of DDA. CO₂ and O₂ barrier properties of nanocomposites were increased by 7 times and 4 times with 0.5 wt.% OTA-MMT loading, respectively. At 2 wt% OTA-MMT loading, water vapor permeability of LDPE has also decreased about 2.5 times. Compared with pure PE film, 49.5% and 178% improvement of tensile strength of nanocomposites films were obtained by addition of only 4 wt.% DDA-MMT and OTA-MMT, respectively. In addition, with only 0.5 wt.% OMMT loading, the onset degradation temperature of nanocomposites increases by 23°C and 26°C for LDPE/DDA-MMT and LDPE/OTA-MMT, respectively.     

Multifunctional MXene/CNT-based layered film for icing detection,anti-icing,and deicing application

Icing phenomenon usually happens in our daily life, especially in the cold winter or in high altitude areas, which makes us feel inconvenient and greatly threats some fields such as civil aviation or the manufacturing industry. In this study, a multifunctional film with properties of icing detection, anti-icing and deicing was fabricated. One-dimensional material carbon nanotube (CNT) and two-dimensional material Ti₃C₂T_x MXene were combined by two-step vacuum filtration. Polydimethylsiloxane (PDMS) as the flexible hydrophobic materials was then used to encapsulate layered film. Additionally, PDMS curing process on the sandpaper could make the surface of MXene/CNT layered film possess micro-structures. The low surface energy material PDMS and rough surface structures endow MXene/CNT layered film with good water-repellency. Compared with pure PDMS film (103°), the contact angle of MXene/CNT layered film surface reaches 128°. The result exhibits that a waterdrop(100uL) on the layered film surface takes 1425s to be frozen, which takes longer time than glass and pure PDMS. Additionally, excellent sensibility of the layered film could be used to detect icing phenomenon. The result manifests that gauge factor (GF) of MXene/CNT film reaches 15051 so that different icing stages could be identified by layered film clearly. MXene/CNT layered film possesses good electric heating and photo-thermal properties. The result shows that surface temperature can reach 89 °C with the 2.5 V voltage supply, and temperature reaches 95 °C through the radiation of near-infrared lamp as well. The dual-driven heating of MXene/CNT layered film shows the ability of deicing. 1000 mg ice just takes 223s to be melted entirely by 2.5 V input voltage, and 269s by radiation of 200 mW/cm², respectively. The multifunctional MXene/CNT based layered film prepared by a simple fabrication method that integrates hydrophobicity, dual-driven heating, and sensibility together, which shows potential application in icing detection, anti-icing, and deicing.     

A study on the growth mechanism and gas diffusion barrier property of homogeneously mixed silicon–tin oxide by atomic layer deposition

SiO₂ and SnO₂ films were deposited using plasma-enhanced atomic layer deposition (PEALD) at low temperature (100 °C), and homogeneously mixed structure (HMS) films consisting of Si, Sn, and O were deposited through a “1st precursor dose – 2nd precursor dose – oxidation”, a new ALD process method for mixing two elements. For a deep consideration of the growth mechanism during the HMS film deposition process, density functional theory (DFT) calculations of the adsorption reactions of the precursors on the surface were conducted. The properties of the thin films such as density, atomic composition, crystallinity, surface roughness, optical transmittance and the water vapor diffusion barrier property were analyzed by XRR, XPS, XRD, AFM, UV-VIS and the electrical Ca test.By changing the dose sequence of the two precursors in the HMS process, various physical/chemical characteristics of the films could be controlled. Also, by adjusting the appropriate amount of Sn in the HMS films, the shortcomings of SnO₂ were compensated by the mixed SiO₂; and through this process, excellent gas diffusion barrier properties of WVTR ∼ 1.33 × 10⁻⁴ g/m²day were secured.     

Structural and electrical properties of the sol-gel derived multiferroic BiFeO3 monolayer and NiTiO3-BiFeO3 bilayer thin films

In this paper, the multiferroic BeFiO₃ monolayer and NiTiO₃–BiFeO₃ bilayer thin films were fabricated by spin-coating method on the SrRuO₃/n⁺-Si substrate. The structural and ferroelectric properties of multiferroic BeFiO₃ monolayer and NiTiO₃–BiFeO₃ bilayer thin films were investigated. Both multiferroic films showed the typical XRD patterns of the perovskite structure without presence of the second phase. The electrical properties, such as leakage current and remnant polarization, of the NiTiO₃–BiFeO₃ bilayer film were superior to those of BeFiO₃ monolayer film, which those values were 1.94 × 10⁻⁴ A/cm² at electric field of 0.75 MV/cm and 14.05 μC/cm², respectively. This outcome is due to the NiTiO₃–BiFeO₃ bilayer film with a high Schottky barrier height as well as a top NiTiO₃ layer on the BiFeO₃ film inducing the strain-induced polarization rotation and forming the strong domain-wall pinning.