Uniaxial and Biaxial Hot Pressing of PVDF Films: Advancing Solvent-Free Processing for High-Performance Piezoelectric Devices

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Poly(vinylidene fluoride) (PVDF) is among the most widely investigated piezoelectric polymers because of its flexibility, chemical resistance, mechanical durability, and suitability for lightweight sensing and energy harvesting applications. However, achieving a high fraction of the electroactive β-phase remains one of the primary challenges in PVDF processing, as conventional fabrication routes often require mechanical stretching, solvent-assisted processing, or high-voltage electrical poling. These methods may increase processing complexity, reduce thermal stability, or introduce environmental concerns associated with solvent use. This study investigates whether hot pressing under different stress distributions can provide a simpler and more sustainable alternative. By systematically comparing uniaxial and biaxial hot pressing, the research demonstrates how multidirectional compression influences crystalline phase transformation and piezoelectric performance, providing valuable insights for the development of next-generation flexible sensors and energy harvesting devices.

Bibliographic Information

Item Information
Article Title Uniaxial and biaxial hot pressing of PVDF films: A pathway toward high-performance piezoelectric sensors and energy harvesters
Authors Suprapto, Jubaidah, Selamat Triono, Hariyanto Gunawan, Lisyanto, Aditya Sukma Nugraha, and Yopan Rahmad Aldori
Journal Teknomekanik
Volume & Issue Volume 9, Issue 1
Publication Date February 2026
Pages 121–136
DOI https://doi.org/10.24036/teknomekanik.v9i1.44972
Publisher Universitas Negeri Padang
License Creative Commons Attribution 4.0 International (CC BY 4.0)
ISSN e-ISSN: 2621-8720
p-ISSN: 2621-9980
Keywords PVDF; uniaxial and biaxial; hot press; piezoelectric

Research Background

  • PVDF is an important electroactive polymer. Poly(vinylidene fluoride) possesses several crystalline phases (α, β, γ, δ, and ε), but the β-phase is the most desirable because of its superior polarization and piezoelectric characteristics. These properties make PVDF attractive for flexible sensors, actuators, wearable electronics, and energy harvesting technologies.
  • Producing a stable β-phase remains challenging. Conventional processing generally favors the thermodynamically stable α-phase, while obtaining the electroactive β-phase requires additional processing treatments that increase manufacturing complexity.
  • Current fabrication techniques have practical limitations. Mechanical stretching, high-pressure compression, electrical poling, and solvent-based processing have all been used to increase β-phase formation. However, these techniques often require careful process control, may reduce thermal stability, or depend on chemical solvents that present environmental and occupational health concerns.
  • Hot pressing offers a promising alternative. Simultaneous application of elevated temperature and pressure can improve structural uniformity, reduce porosity, and promote crystalline phase transformation without relying on solvent-assisted fabrication routes.
  • The influence of stress distribution remains insufficiently understood. Although previous studies have demonstrated the benefits of hot pressing, systematic comparisons between uniaxial and biaxial loading conditions have been limited, particularly regarding their effects on crystalline phase evolution and piezoelectric performance.
  • This study addresses an important research gap. The work evaluates how different hot-pressing stress distributions affect the crystalline structure, β-phase formation, crystallinity, piezoelectric coefficient, and electrical output of pure PVDF films, providing an additive-free processing strategy for advanced piezoelectric materials.

Research Objective

  • To systematically compare uniaxial and biaxial hot pressing as solvent-free processing techniques for fabricating PVDF films.
  • To investigate the influence of different stress distributions on crystalline phase transformation, particularly the formation of the electroactive β-phase.
  • To evaluate changes in crystallinity, crystal structure, and molecular orientation using X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR).
  • To assess the electromechanical performance of the processed PVDF films by measuring the piezoelectric coefficient (d33) and output voltage response.
  • To identify whether biaxial hot pressing provides superior piezoelectric performance compared with conventional uniaxial compression while maintaining a simpler and environmentally friendly manufacturing process.

Why This Research Matters

  • Supports greener manufacturing. The proposed hot-pressing approach minimizes dependence on solvent-based processing, reducing potential environmental and occupational risks during PVDF fabrication.
  • Improves piezoelectric material performance. Enhancing β-phase formation directly contributes to higher piezoelectric efficiency, enabling more sensitive sensors and more effective energy harvesting devices.
  • Simplifies PVDF processing. By relying on pressure-induced phase transformation instead of complex chemical modifications or additives, the proposed method offers a practical manufacturing alternative.
  • Advances flexible electronics. Improved PVDF films can benefit wearable sensors, biomedical monitoring systems, structural health monitoring, self-powered electronics, and other emerging smart-device applications.
  • Provides new understanding of multidirectional stress effects. The direct comparison between uniaxial and biaxial hot pressing offers valuable scientific insight into how stress distribution influences crystalline evolution and electromechanical behavior in PVDF.
  • Creates opportunities for scalable production. The demonstrated processing route combines competitive piezoelectric performance with manufacturing simplicity, making it attractive for future industrial implementation of flexible piezoelectric devices.

Research Methodology

  • Research Design

    This study employed an experimental materials engineering approach to evaluate the influence of stress distribution during hot pressing on the crystalline structure and piezoelectric performance of Poly(vinylidene fluoride) (PVDF) films. Two processing configurations—uniaxial hot pressing and biaxial hot pressing—were systematically compared under identical processing conditions to determine their effectiveness in promoting β-phase formation and enhancing electromechanical properties.

  • Raw Material

    Commercial PVDF pellets (Kynar PVDF®740, Arkema) with a molecular weight of approximately 180,000, melt flow rate of 1.1 g/10 min, specific gravity of 1.78 g/cm³, and an average pellet size of 0.5 × 4 mm were used as the starting material. Before fabrication, the pellets were dried at 50–75°C for 30 minutes to remove residual moisture and ensure consistent processing.

  • Fabrication of PVDF Films

    PVDF pellets were first melted and subsequently transferred into a stainless-steel mold for hot pressing. Both uniaxial and biaxial samples were processed at a pressure of 60 MPa and a temperature of 220°C. After pressing, the films were cooled inside the mold to preserve structural integrity. Each processing condition was repeated three times to improve experimental reproducibility.

    The primary experimental variable was the direction of compressive loading. Uniaxial hot pressing applied compression along a single axis, whereas biaxial hot pressing introduced multidirectional stress intended to promote more uniform molecular orientation and crystalline phase transformation.

  • Thickness Measurement

    Film thickness was measured using a digital micrometer at five different positions for every specimen to ensure dimensional consistency. The untreated PVDF film exhibited the greatest thickness, while both hot-pressed samples became considerably thinner because of pressure-induced densification during processing.

  • Crystalline Phase Characterization

    X-ray diffraction (XRD) analysis was performed to identify crystalline phases, evaluate crystal orientation, and determine the degree of crystallinity. Gaussian peak fitting was used to separate crystalline and amorphous contributions, allowing quantitative calculation of crystallinity for each processing condition.

    Fourier Transform Infrared Spectroscopy (FTIR) was conducted over the characteristic absorption range associated with α- and β-phase PVDF. The absorption peaks corresponding to each crystalline phase were used to calculate the fraction of electroactive β-phase generated during hot pressing.

  • Piezoelectric Performance Evaluation

    The electromechanical response of the fabricated PVDF films was evaluated using an impact-force testing system. Silver ink electrodes were applied to both surfaces of each film before testing. A steel ball was released from a controlled height to generate a constant mechanical impact, allowing measurement of the output voltage produced through the direct piezoelectric effect.

    The measured electrical response was subsequently used to determine the piezoelectric coefficient (d33), providing a quantitative assessment of piezoelectric performance for each processing method.

  • Comparative Analysis

    Experimental results obtained from untreated PVDF, uniaxially hot-pressed PVDF, and biaxially hot-pressed PVDF were compared in terms of crystal structure, β-phase fraction, crystallinity, piezoelectric coefficient, and electrical output. This comparison enabled the researchers to determine which stress distribution most effectively improved the functional properties of PVDF films.

Key Findings

Biaxial Hot Pressing Produced the Highest β-Phase Fraction

One of the most significant findings of the study is that biaxial hot pressing generated the greatest amount of electroactive β-phase among all investigated samples. The β-phase fraction increased from 47.80% in untreated PVDF to 49.30% after uniaxial hot pressing and reached 50.47% following biaxial hot pressing. This improvement indicates that multidirectional compressive loading is more effective in promoting the desirable molecular conformation required for piezoelectric applications.

Crystallinity Improved After Hot Pressing

Both hot-pressing techniques increased the overall crystallinity of PVDF compared with untreated material. The degree of crystallinity increased from 45% for untreated PVDF to 48% after uniaxial hot pressing and 49% after biaxial hot pressing. These results demonstrate that elevated temperature combined with mechanical pressure enhances molecular packing and promotes the development of more ordered crystalline structures.

Biaxial Stress Enhanced Molecular Orientation

XRD and FTIR analyses consistently showed that biaxial loading created more favorable conditions for molecular chain rearrangement than uniaxial compression. Multidirectional stress facilitated the transition from the non-polar α-phase to the electroactive β-phase by encouraging the alignment of polymer chains into the all-trans molecular conformation associated with superior piezoelectric behavior.

Piezoelectric Performance Increased Significantly

The improvement in crystalline structure directly translated into better electromechanical performance. The biaxially hot-pressed PVDF exhibited the highest piezoelectric coefficient, reaching 18.8 pC/N, indicating that enhanced β-phase formation resulted in greater electrical charge generation under mechanical loading.

Output Voltage Response Became More Stable

Impact-force testing demonstrated that PVDF films processed using biaxial hot pressing generated stronger and more consistent electrical responses than untreated and uniaxially processed films. The improved dipole orientation enabled more efficient conversion of mechanical energy into electrical energy, supporting the suitability of the material for sensing and energy harvesting applications.

Hot Pressing Eliminated the Need for Solvent-Based Processing

The proposed fabrication strategy successfully enhanced PVDF performance without requiring solvent-assisted processing or chemical additives. This finding highlights the potential of hot pressing as a cleaner manufacturing technique capable of simplifying production while maintaining competitive piezoelectric properties.

Multidirectional Compression Provides a Practical Processing Advantage

Beyond improving material properties, biaxial hot pressing offers practical manufacturing advantages by combining relatively simple processing with enhanced functional performance. The study demonstrates that controlling stress distribution during fabrication can be as important as modifying material composition for improving piezoelectric polymers.

Scientific Contribution

  • Provides one of the few systematic comparisons between uniaxial and biaxial hot pressing for pure PVDF films under identical processing conditions.
  • Demonstrates that stress distribution significantly influences crystalline phase transformation, molecular orientation, and piezoelectric behavior.
  • Establishes biaxial hot pressing as an effective solvent-free processing strategy capable of increasing β-phase formation without chemical additives.
  • Strengthens understanding of structure–property relationships by correlating XRD and FTIR observations with crystallinity, β-phase fraction, piezoelectric coefficient, and electrical output.
  • Contributes to sustainable materials processing by demonstrating an environmentally friendly fabrication route for electroactive polymer films.
  • Provides experimental evidence supporting the use of multidirectional mechanical stress as an effective processing parameter for enhancing PVDF performance.

Industrial Implications

  • Flexible sensor manufacturing. Improved PVDF films can enhance the sensitivity and reliability of pressure sensors, vibration sensors, tactile sensors, and wearable monitoring devices.
  • Energy harvesting systems. Higher piezoelectric efficiency enables more effective conversion of ambient mechanical energy into electrical power for self-powered electronic systems.
  • Biomedical engineering. The solvent-free processing technique offers potential advantages for producing flexible biomedical sensors where cleaner manufacturing processes are desirable.
  • Smart electronics. The improved electromechanical performance supports future applications in flexible electronics, Internet of Things (IoT) devices, and intelligent sensing platforms.
  • Sustainable polymer processing. Eliminating solvent-based fabrication reduces chemical handling requirements and may simplify industrial production while lowering environmental impacts.
  • Scalable manufacturing. Because hot pressing is already widely used in polymer processing, the demonstrated biaxial approach offers practical opportunities for scaling the production of high-performance PVDF films without introducing complex manufacturing steps.

Research Limitations

  • The investigation focused exclusively on pure PVDF films. The study did not evaluate composite formulations, polymer blends, or nanofiller-reinforced PVDF materials that may further improve piezoelectric performance.
  • Only two hot-pressing configurations were investigated. The comparison was limited to uniaxial and biaxial hot pressing under a single processing temperature and pressure. The influence of other processing parameters, such as pressure magnitude, pressing duration, cooling rate, and temperature variation, was not explored.
  • The experimental characterization emphasized structural and electromechanical properties. Although crystallinity, β-phase fraction, piezoelectric coefficient, and output voltage were comprehensively evaluated, long-term durability, fatigue resistance, thermal aging, and environmental stability were beyond the scope of the present work.
  • Performance evaluation was conducted under laboratory conditions. The piezoelectric response was measured using a controlled impact-force experiment. The behavior of the fabricated PVDF films under real operational environments, including continuous cyclic loading and varying environmental conditions, was not assessed.
  • The study concentrated on material fabrication rather than device integration. While the results demonstrate improved material performance, complete sensor fabrication, system integration, and application-specific validation were not included in this investigation.
  • Industrial manufacturing aspects remain to be evaluated. Production scalability, manufacturing cost, process repeatability under large-scale fabrication, and commercial feasibility require further investigation before widespread industrial adoption.

Future Research Opportunities

  • Investigate the influence of different hot-pressing temperatures, pressures, holding times, and cooling strategies to determine the optimum processing window for maximizing β-phase formation and piezoelectric performance.
  • Evaluate the combined effects of biaxial hot pressing with electrical poling, mechanical stretching, or thermal annealing to determine whether multiple processing techniques can further enhance the electromechanical response of PVDF.
  • Study composite PVDF materials incorporating nanoparticles, ceramic fillers, graphene, carbon nanotubes, or other functional reinforcements to examine potential synergistic improvements in piezoelectric properties.
  • Assess the long-term durability of hot-pressed PVDF films under cyclic mechanical loading, repeated electrical excitation, temperature fluctuations, and humid environments to determine their reliability for practical applications.
  • Develop complete prototype devices, including flexible sensors, wearable monitoring systems, tactile interfaces, and energy harvesting modules, to validate the material performance under realistic operating conditions.
  • Investigate numerical modeling and finite element simulations of stress distribution during hot pressing to better understand the mechanisms governing molecular orientation and β-phase development.
  • Examine industrial-scale manufacturing strategies capable of producing large-area PVDF films while maintaining consistent crystalline structure and piezoelectric performance.
  • Explore the applicability of biaxial hot pressing for other electroactive polymers and piezoelectric materials that require controlled crystalline phase transformation during fabrication.

Potential for Public Policy Citation (Overton)

Although this study primarily focuses on polymer processing and materials engineering, it has meaningful potential for citation within public policy documents related to advanced manufacturing, sustainable materials, clean production technologies, and industrial innovation. The proposed solvent-free fabrication approach aligns with growing international efforts to reduce hazardous chemical use during manufacturing while improving material performance through environmentally responsible processing techniques.

The research may also support policy initiatives promoting flexible electronics, smart sensing technologies, energy harvesting systems, and advanced functional materials for Industry 4.0 applications. Government agencies responsible for science, technology, manufacturing, and innovation may find the reported processing strategy relevant when developing roadmaps for sustainable advanced materials production and next-generation electronic devices.

Furthermore, the demonstrated improvement in piezoelectric performance without chemical additives supports broader sustainability objectives by encouraging cleaner manufacturing practices that reduce solvent consumption while maintaining high functional performance.

Who Should Read This Paper?

  • Researchers working in polymer science, functional materials, and piezoelectric materials.
  • Mechanical, materials, and manufacturing engineers interested in advanced polymer processing technologies.
  • Scientists developing flexible electronics, wearable sensors, tactile devices, and smart monitoring systems.
  • Researchers specializing in energy harvesting technologies and self-powered electronic systems.
  • Graduate students studying crystallography, polymer engineering, functional materials, and electromechanical systems.
  • Industrial researchers involved in sustainable manufacturing, polymer processing, and flexible device fabrication.
  • Engineers seeking environmentally friendly alternatives to conventional solvent-assisted fabrication methods for electroactive polymers.

Final Thoughts

This study demonstrates that the distribution of mechanical stress during hot pressing plays a decisive role in determining the structural and functional properties of PVDF films. By systematically comparing uniaxial and biaxial processing, the researchers show that multidirectional compression promotes greater β-phase formation, higher crystallinity, and superior piezoelectric performance than conventional uniaxial loading.

The results indicate that biaxial hot pressing represents an effective solvent-free processing strategy capable of improving PVDF performance while maintaining manufacturing simplicity. Rather than relying on chemical additives or complex post-processing treatments, the proposed approach exploits mechanical deformation to achieve favorable molecular orientation and enhanced electromechanical behavior.

Beyond its immediate contribution to PVDF processing, this research reinforces the broader principle that carefully controlled processing conditions can substantially influence the performance of electroactive polymers. The findings provide valuable guidance for future developments in flexible sensors, wearable electronics, biomedical devices, and mechanical energy harvesting technologies while supporting the transition toward cleaner and more sustainable manufacturing practices.

Suggested Citations

Teknomekanik (UNP) Style

Suprapto, Jubaidah, S. Triono, H. Gunawan, Lisyanto, A. S. Nugraha, and Y. R. Aldori, "Uniaxial and biaxial hot pressing of PVDF films: A pathway toward high-performance piezoelectric sensors and energy harvesters," Teknomekanik, vol. 9, no. 1, pp. 121–136, Feb. 2026. https://doi.org/10.24036/teknomekanik.v9i1.44972.

APA (7th Edition)

Suprapto, Jubaidah, Triono, S., Gunawan, H., Lisyanto, Nugraha, A. S., & Aldori, Y. R. (2026). Uniaxial and biaxial hot pressing of PVDF films: A pathway toward high-performance piezoelectric sensors and energy harvesters. Teknomekanik, 9(1), 121–136. https://doi.org/10.24036/teknomekanik.v9i1.44972

IEEE Style

S. Suprapto, Jubaidah, S. Triono, H. Gunawan, Lisyanto, A. S. Nugraha, and Y. R. Aldori, "Uniaxial and biaxial hot pressing of PVDF films: A pathway toward high-performance piezoelectric sensors and energy harvesters," Teknomekanik, vol. 9, no. 1, pp. 121–136, Feb. 2026, doi: 10.24036/teknomekanik.v9i1.44972.

Harvard Style

Suprapto, Jubaidah, Triono, S., Gunawan, H., Lisyanto, Nugraha, A.S. & Aldori, Y.R., 2026. Uniaxial and biaxial hot pressing of PVDF films: A pathway toward high-performance piezoelectric sensors and energy harvesters. Teknomekanik, 9(1), pp.121–136. Available at: https://doi.org/10.24036/teknomekanik.v9i1.44972.

Vancouver Style

Suprapto, Jubaidah, Triono S, Gunawan H, Lisyanto, Nugraha AS, Aldori YR. Uniaxial and biaxial hot pressing of PVDF films: A pathway toward high-performance piezoelectric sensors and energy harvesters. Teknomekanik. 2026;9(1):121-136. doi:10.24036/teknomekanik.v9i1.44972.

Chicago (Author–Date)

Suprapto, Jubaidah, Selamat Triono, Hariyanto Gunawan, Lisyanto, Aditya Sukma Nugraha, and Yopan Rahmad Aldori. 2026. "Uniaxial and Biaxial Hot Pressing of PVDF Films: A Pathway toward High-Performance Piezoelectric Sensors and Energy Harvesters." Teknomekanik 9 (1): 121–136. https://doi.org/10.24036/teknomekanik.v9i1.44972.

MLA (9th Edition)

Suprapto, et al. "Uniaxial and Biaxial Hot Pressing of PVDF Films: A Pathway toward High-Performance Piezoelectric Sensors and Energy Harvesters." Teknomekanik, vol. 9, no. 1, 2026, pp. 121–136. https://doi.org/10.24036/teknomekanik.v9i1.44972.

Editorial Note

This review has been prepared for Engineering Research Insights based exclusively on the published research article and its official bibliographic metadata. The scientific interpretation presented in this review reflects the objectives, methodology, experimental findings, and conclusions reported by the authors. It is intended to help researchers, students, engineers, and industry professionals quickly understand the significance of the work while encouraging readers to consult the original publication for complete experimental details, datasets, and technical discussions.

SEO Meta Description

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SEO Keywords

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Conclusion

This review highlights an important advancement in solvent-free processing of piezoelectric polymers through the systematic comparison of uniaxial and biaxial hot pressing. By demonstrating that biaxial compression promotes greater β-phase formation, higher crystallinity, and improved piezoelectric performance, the study offers a practical pathway toward manufacturing high-performance PVDF films without relying on chemical additives or solvent-assisted processing. These findings contribute not only to the understanding of PVDF phase transformation but also to the broader development of sustainable fabrication technologies for flexible sensors, wearable electronics, biomedical devices, and mechanical energy harvesting systems.

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