Eszter Kókai

57219178837

Publications - 11

Gas Barrier Properties of Organoclay-Reinforced Polyamide 6 Nanocomposite Liners for Type IV Hydrogen Storage Vessels

Attila Bata Eszter Kókai Dávid István Kis Péter Gerse Ferenc Tajti Pál Hansághy Nándor Nemestóthy

Publication Name: Nanomaterials

Publication Date: 2025-07-01

Volume: 15

Issue: 14

Page Range: Unknown

Description:

This study investigates the hydrogen permeability of injection-molded polyamide 6 (PA6) nanocomposites reinforced with organo-modified montmorillonite (OMMT) at varying concentrations (1, 2.5, 5, and 10 wt. %) for potential use as Type IV composite-overwrapped pressure vessel (COPV) liners. While previous work examined their mechanical properties, this study focuses on their crystallinity, morphology, and gas barrier performance. The precise inorganic content was determined using thermal gravimetry analysis (TGA), while differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), and scanning electron microscopy (SEM) were used to characterize the structural and morphological changes induced by varying filler content. The results showed that generally higher OMMT concentrations promoted γ-phase formation but also led to increased agglomeration and reduced crystallinity. The PA6/OMMT-1 wt. % sample stood out with higher crystallinity, well-dispersed clay, and low hydrogen permeability. In contrast, the PA6/OMMT-2.5 and -5 wt. % samples showed increased permeability, which corresponded to WAXD and SEM evidence of agglomeration and DSC results indicating a lower degree of crystallinity. PA6/OMMT-10 wt. % showed the most-reduced hydrogen permeability compared to all other samples. This improvement, however, is attributed to a tortuous path effect created by the high filler loading rather than optimal crystallinity or dispersion. SEM images revealed significant OMMT agglomeration, and DSC analysis confirmed reduced crystallinity, indicating that despite the excellent barrier performance, the compromised microstructure may negatively impact mechanical reliability, showing PA6/OMMT-1 wt. % to be the most balanced candidate combining both mechanical integrity and hydrogen impermeability for Type IV COPV liners.

Open Access: Yes

DOI: 10.3390/nano15141101

Mechanical Properties of Clay-Reinforced Polyamide 6 Nanocomposite Liner Materials of Type IV Hydrogen Storage Vessels

János Takács Attila Bata Eszter Kókai Dávid István Kis

Publication Name: Nanomaterials

Publication Date: 2024-09-01

Volume: 14

Issue: 17

Page Range: Unknown

Description:

This study focuses on polyamide 6/organo-modified montmorillonite (PA6/OMMT) nanocomposites as potential liner materials, given the growing interest in enhancing the performance of type IV composite overwrapped hydrogen storage pressure vessels. The mechanical properties of PA6/OMMT composites with varying filler concentrations were investigated across a temperature range relevant to hydrogen storage conditions (−40 °C to +85 °C). Liner collapse, a critical issue caused by rapid gas discharge, was analyzed using an Ishikawa diagram to identify external and internal factors. Mechanical testing revealed that higher OMMT content generally increased stiffness, especially at elevated temperatures. The Young’s modulus and first yield strength exhibited non-linear temperature dependencies, with 1 wt. per cent OMMT content enhancing yield strength at all tested temperatures. Dynamic mechanical analysis (DMA) indicated that OMMT improves the storage modulus, suggesting effective filler dispersion, but it also reduces the toughness and heat resistance, as evidenced by lower glass transition temperatures. This study underscores the importance of optimizing OMMT content to balance mechanical performance and thermal stability for the practical application of PA6/OMMT nanocomposites in hydrogen storage pressure vessels.

Open Access: Yes

DOI: 10.3390/nano14171385

A review on the factors of liner collapse in type IV hydrogen storage vessels

Eszter Kókai Dávid István Kis

Publication Name: International Journal of Hydrogen Energy

Publication Date: 2024-01-02

Volume: 50

Issue: Unknown

Page Range: 236-253

Description:

The on-board hydrogen storage of mobile applications is a key area of global industrial transformation to hydrogen technology. The research work provides an overview about the principle of hydrogen fuel cell vehicles, with a focus on the widespread on-board hydrogen storage technologies. In this work, type IV composite pressure vessels in particular are reviewed. The key challenges of polymeric liners are deeply investigated, and liner collapse was identified as a critical failure of type IV vessels. Different factors of liner collapse were categorized and relevant material properties - such as permeability, physical characteristics, and surface properties - were explained in more detail to lay the foundation for further research on high barrier, durable polymeric liner materials.

Open Access: Yes

DOI: 10.1016/j.ijhydene.2023.09.316

The Potential for Analyzing the Correlation Between the Compressive Stress Resistance of Red Clover Seeds and the Environmental Conditions during Seed Maturation Using FT-IR Spectroscopy

Eszter Kókai Gergely Zoltán Macher Dalma Bódizs Anett Bedő Marcell Lócsi Szilveszter Gergely

Publication Name: Chemical Engineering Transactions

Publication Date: 2024-01-01

Volume: 114

Issue: Unknown

Page Range: 715-720

Description:

The paper aims to examine the connection between environmental conditions during seed maturation and the ability of seeds to compressive stress, supported by statistically significant findings. The study involves using Fourier transform infrared (FT-IR) spectroscopic analysis on red clover seeds under varying pressure levels, specific tensions, and selected quality parameters. The methodology relies on a general FT-IR spectroscopic approach, with spectral comparisons made against results from pressure-induced rupture. Through this research, new methods for seed testing are intended to be informed by differential and correlation results across technical parameters and different measurement settings. The analyses indicated a noticeable difference of several 10 N in visible features between seed maturation stages and compressive tolerance. Given the novelty of the aspects being explored, one primary influencing factor is identified as the scarcity of available literature, which also serves as a limitation of this research. The obtained results have potential applications for analysts, agricultural specialists, consultants, and experts involved in seed management and distribution.

Open Access: Yes

DOI: 10.3303/CET24114120

Impact of process gases on wettability and adhesive bond strength of laser- treated DC01 steel and plasma-treated polypropylene surfaces

Eszter Kókai

Publication Name: Journal of Adhesion

Publication Date: 2025-01-01

Volume: Unknown

Issue: Unknown

Page Range: Unknown

Description:

This study investigates how different process gases (air, argon, and nitrogen) influence the wettability and adhesive bond strength of DC01 steel and polypropylene surfaces treated by laser and plasma methods. The aim was to clarify how gas composition and processing parameters affect surface activation and whether contact angle measurements alone can explain adhesive performance. On DC01 steel, laser treatment significantly reduced water contact angles, achieving full wetting at specific power and scanning speeds. However, lap shear testing showed that a 0° contact angle did not always result in the same bond strengths. Argon-treated samples consistently provided the highest shear strength. For polypropylene, plasma activation improved both wettability and bonding. Nitrogen plasma lowered contact angles from 63° on untreated surfaces to 14° at 200 mm/min and 9° at 400 mm/min, producing the strongest joints. This study is one of the first to systematically compare the effects of different gases on metals and polymers, linking wettability and mechanical testing to offer practical guidance for optimizing process parameters for strong and reliable adhesive joints.

Open Access: Yes

DOI: 10.1080/00218464.2025.2595302

Anthropogenic Waste Pollution of the Danube Shoreline between Komárom and Neszmély, with Special Emphasis on Mesoplastics

K. Kozma Eszter Kókai Boglárka Liszkai

Publication Name: Chemical Engineering Transactions

Publication Date: 2025-01-01

Volume: 121

Issue: Unknown

Page Range: 31-36

Description:

Research into microplastics is increasingly important, as these particles are widespread and their long-term effects remain unclear. Plastic waste enters rivers and breaks down into smaller fragments, prompting our focus on mesoplastics in rivers—an under-researched area. Based on litter collection efforts along the Danube, we selected sampling sites near Komárom, Almásfüzitő, Dunaalmás, and Neszmély. Data from these “clean-up” actions were used to assess anthropogenic inputs and to conduct both quantitative and qualitative analyses. During the river sampling methods, where the goal was to develop a method suitable for domestic conditions, custom-made nets were applied based on descriptions found in the literature. The size, quantity, and polymer type of the particles were determined through visual inspection and FTIR spectroscopy. According to our test results so far, most of the particles were identified as originating from packaging waste, mainly polyethylene and polypropylene. The highest contamination was measured 20 m from the shore of Almásfüzitő, close to the drift line, concentrated in the upper 20–50 cm layer of the river water, which correlates with the results found in the literature regarding water depth. Based on these findings, it can be concluded that our measurement method, which is still under development, is progressing in the right direction, but further measurements will be required to confirm this with greater certainty.

Open Access: Yes

DOI: 10.3303/CET25121006

The Role and Selection Criteria of Binder Materials for Sustainable Filaments Used in Additive Manufacturing

Eszter Kókai Norbert Simon

Publication Name: Chemical Engineering Transactions

Publication Date: 2025-01-01

Volume: 121

Issue: Unknown

Page Range: 73-78

Description:

The growing adoption of additive manufacturing increases the need for filament materials that satisfy both technical and environmental requirements. In Fused Filament Fabrication (FFF), the binder system in metal–polymer filaments plays a key role in determining environmental impact and processing quality. This review analyses potential binder materials for FFF-based metal additive manufacturing, focusing on how their properties influence printability, thermal stability, debinding behaviour, and the mechanical performance of green parts. Comparative data on thermal and mechanical characteristics are presented for conventional and bio-based polymers. The candidate binder materials show melting points between 60 °C and 200 °C and degradation onset from 240 °C to 340 °C, defining their usability range. PLA provides the highest strength, while PCL and TPS offer flexibility and low-temperature processing. PVB/PEG ensures rigidity and clean debinding, and HPMC enables easy water removal. PLA, TPS, and HPMC exhibit the best sustainability profile due to their bio-based origin. A similar comparative analysis has not been reported in the literature.

Open Access: Yes

DOI: 10.3303/CET25121013

Comparative Study of BASF Ultrafuse 316L and Markforged 17-4PH Stainless Steel Filaments Processed by Fused Filament Fabrication

Eszter Kókai Norbert Simon

Publication Name: International Journal of Automotive Science and Technology

Publication Date: 2025-12-17

Volume: 9

Issue: 1st Future of Vehicles Conf.

Page Range: 77-81

Description:

Metal additive manufacturing is receiving increased attention today, as major industries such as the automotive, aerospace, and medical sectors place a stronger emphasis on it. Among the numerous technologies, fused filament fabrication (FFF) is gaining more focus due to its relatively low equipment cost and ease of application. The production of a solid metal part begins with the extrusion of a metal powder-filled filament, followed by printing, debinding, and heat treatment, through which the final strength is achieved. Among the commercially available filaments, stainless steel–based composites are the most widespread, as they offer good printability, corrosion resistance, and mechanical stability. The two most used materials in this category are BASF Ultrafuse 316L and Markforged 17-4PH alloys. These two materials lend themselves well to comparison, as they are designed for the same manufacturing technology but exhibit different metallurgical behaviors and process requirements, thus providing a comprehensive view of the capabilities and limitations of metal FFF technology. In this study, we aim to demonstrate how these two materials differ in their processing requirements, microstructural evolution, and resulting mechanical performance, and to show what can be achieved when manufacturing metal composites using FFF technology. The main differences between the two filaments are presented in a comparative table to provide a clear and structured overview of their distinct characteristics.

Open Access: Yes

DOI: 10.30939/ijastech.1767208

Surface Activation of Polyamide 6 Nanocomposites by Atmospheric Plasma: Wettability and Chemical Changes for Type IV Pressure Vessel Liners

Eszter Kókai Dávid István Kis

Publication Name: International Journal of Automotive Science and Technology

Publication Date: 2025-01-01

Volume: 9

Issue: 1st Future of Vehicles Conf.

Page Range: 41-46

Description:

This study explores how atmospheric-pressure plasma treatments can modify the surface properties of polyamide 6 (PA6) and its nanocomposites reinforced with organomodified montmorillonite (OMMT), materials developed as potential liners for Type IV composite overwrapped pressure vessels (COPVs) designed for hydrogen storage. Four material compositions were examined: neat PA6 and composites containing 1, 2.5, 5, and 10 wt.% OMMT. Two different plasma systems—a piezoelectric plasma brush and a rotary plasma source—were used to activate the surfaces, and their effects were evaluated using water contact angle (WCA) measurements and Fourier transform infrared spectroscopy (FTIR). Both plasma treatments effectively increased the wettability of the tested materials, but the rotary plasma consistently produced the lowest WCA values across all compositions, reaching as low as 21° for neat PA6. These findings suggest that the rotary plasma’s higher power and dynamic exposure enhance the formation of polar functional groups and may increase micro-scale roughness, leading to improved surface activation. FTIR results confirmed the appearance and growth of oxidized functional groups, particularly carbonyl and hydroxyl species, which are linked to the increased surface polarity and hydrophilicity. Time-dependent contact angle tests revealed that the effects of plasma treatment were not permanent. Over several hours, the contact angles gradually increased, returning close to untreated values.

Open Access: Yes

DOI: 10.30939/ijastech..1753231

Comparative Study of BASF Ultrafuse 316L and Markforged 17-4PH Stainless Steel Filaments Processed by Fused Filament Fabrication

Eszter Kókai Norbert Simon

Publication Name: International Journal of Automotive Science and Technology

Publication Date: 2025-12-17

Volume: 9

Issue: 1st Future of Vehicles Conf.

Page Range: 77-81

Description:

Metal additive manufacturing is receiving increased attention today, as major industries such as the automotive, aerospace, and medical sectors place a stronger emphasis on it. Among the numerous technologies, fused filament fabrication (FFF) is gaining more focus due to its relatively low equipment cost and ease of application. The production of a solid metal part begins with the extrusion of a metal powder-filled filament, followed by printing, debinding, and heat treatment, through which the final strength is achieved. Among the commercially available filaments, stainless steel–based composites are the most widespread, as they offer good printability, corrosion resistance, and mechanical stability. The two most used materials in this category are BASF Ultrafuse 316L and Markforged 17-4PH alloys. These two materials lend themselves well to comparison, as they are designed for the same manufacturing technology but exhibit different metallurgical behaviors and process requirements, thus providing a comprehensive view of the capabilities and limitations of metal FFF technology. In this study, we aim to demonstrate how these two materials differ in their processing requirements, microstructural evolution, and resulting mechanical performance, and to show what can be achieved when manufacturing metal composites using FFF technology. The main differences between the two filaments are presented in a comparative table to provide a clear and structured overview of their distinct characteristics.

Open Access: Yes

DOI: 10.30939/IJASTECH..1767208

Microplastic pollution in the Szigetköz section of the Danube: sources, composition and FTIR-based quantification

K. Kozma András Torma A. Zseni Gábor Bordós Eszter Kókai Bence Prikler Gergely Zoltán Macher Anett Bedő

Publication Name: Environmental Systems Research

Publication Date: 2026-12-01

Volume: 15

Issue: 1

Page Range: Unknown

Description:

Microplastic (MP) pollution in river systems has become an increasing environmental concern, particularly in transboundary rivers such as the Danube. This study provides the first detailed assessment of microplastic contamination in the Szigetköz section of the Danube and its major tributary, the Mosoni-Danube. Depth-resolved pumped water samples were collected at three locations (Rajka, Mecsér and Gönyű) and analysed using Fourier Transform Infrared (FTIR) spectroscopy combined with automated spectral evaluation. MP concentrations showed a clear downstream increase, with average values of 83.8 particles/m³ at Rajka, 237.6 particles/m³ in the Mosoni-Danube at Mecsér, and 795.9 particles/m³ at Gönyű. Polyethylene (PE) was the dominant polymer in the tributary (70.6%), whereas both PE and alkyd resins were prevalent at the main Danube sites (Rajka: alkyd 37.7%, PE 31.8%; Gönyű: alkyd 39.9%, PE 37.3%). Particle size distribution also shifted downstream, with a higher proportion of smaller (50–100 μm) particles detected at Gönyű compared to upstream sites. The results suggest that the tributary may represent an important input to the main Danube channel in this section, while differences in polymer composition point to varying source characteristics within the study area. These findings provide an important baseline for future monitoring and support the development of targeted mitigation strategies in this transboundary river system.

Open Access: Yes

DOI: 10.1186/s40068-026-00473-3