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ISSN : 1226-0088(Print)
ISSN : 2288-7253(Online)
Membrane Journal Vol.34 No.3 pp.192-203
DOI : https://doi.org/10.14579/MEMBRANE_JOURNAL.2024.34.3.192

Polymeric Additive Influence on the Structure and Gas Separation Performance of High-Molecular-Weight PEO Blend Membranes

Hyo Jun Min, Young Jae Son, Jong Hak Kim†
Department of Chemical and Biomolecular Engineering, Yonsei University, Seoul 03722, Korea

1 The authors equally contributed to this work.


†Corresponding author(e-mail: jonghak@yonsei.ac.kr; http://orcid.org/0000-0002-5858-1747)
May 1, 2024 ; June 7, 2024 ; June 7, 2024

Abstract


The advancement of commercially viable gas separation membranes plays a pivotal role in improving CO2 separation efficiency. High-molecular-weight poly(ethylene oxide) (high-Mw PEO) emerges as a promising option due to its high CO2 solubility, affordability, and robust mechanical attributes. However, the crystalline nature of high-Mw PEO hinders its application in gas separation membranes. This study proposes a straightforward blending approach by incorporating various polymeric additives into high-Mw PEO to address this challenge. Four commercially available, water-soluble polymers, i.e. poly(ethylene glycol) (PEG), poly(propylene glycol) (PPG), poly(acrylic acid) (PAA), and poly(vinyl pyrrolidone) (PVP) are examined as additives to enhance membrane performance by improving miscibility and reducing PEO crystallinity. Contrary to expectations, PEG and PPG fail to inhibit the crystalline structure of PEO and result in membrane flaws. Conversely, PAA and PVP demonstrate greater success in altering the crystal structure of PEO, yielding defect-free membranes. A thorough investigation delves into the correlation between changes in the crystalline structure of high-Mw PEO blend membranes and their gas separation performance. Drawing from our findings and previously documented outcomes, we offer insights into designing and selecting additive polymers for high-Mw PEO, aiming at the creation of cost-effective, commercially viable CO2 separation membranes.


poly(ethylene oxide) , polymer blend , CO2 , gas separation , membrane

고분자량 PEO 기반 분리막에 대한 다양한 고분자 첨가제의 영향 분석

민 효 준, 손 영 재, 김 종 학†
연세대학교 화공생명공학과

초록


기체 분리막의 상업적 발전은 CO2 분리 효율을 향상시키는 데 중요한 역할을 한다. 고분자량 PEO (high-Mw PEO)는 높은 CO2 용해도, 가격 경쟁성 및 견고한 기계적 특성을 가져 분리막 제조용 고분자로 유력하지만 그 특유의 결정성 으로 인해 기체 분리막에 응용이 어렵다. 본 연구에서는 결정성 감소를 위해 다양한 고분자 첨가제를 고분자량 PEO에 혼합 하는 방법을 제시하였다. 폴리에틸렌글리콜(PEG), 폴리프로필렌글리콜(PPG), 폴리아크릴산(PAA) 및 폴리비닐피롤리돈(PVP) 과 같은 상업적으로 이용 가능하고 섞임성이 좋은 수용성 고분자를 첨가제로 사용하여 PEO 결정성을 감소시킴으로써 가스 분리 성능을 향상시키고자 하였다. PEG 및 PPG의 경우 PEO의 결정 구조를 억제하지 못하고 분리막의 결함을 초래하였으나, PAA 및 PVP는 PEO의 결정 구조를 바꿔 결함이 없는 분리막을 제조하는 데 성공하였다. 고분자량 PEO 혼합막의 결정 구조 변화와 기체 분리 성능의 상관관계를 조사하여 본 연구의 결과와 이전에 기록된 결과를 바탕으로 고분자량 PEO에 대한 첨가 제 고분자의 설계 및 선택에 대한 통찰력을 제공하며, 이를 통해 비용 효율적이고 상업적으로 실용적인 CO2 분리막을 제조하 고자 하였다.


    1. Introduction

    Elevated atmospheric levels of carbon dioxide (CO2), primarily attributed to human activities like industrial processes and the burning of fossil fuels, have sparked urgent concerns regarding global warming and climate change[1,2]. Addressing these challenges requires innovative solutions to mitigate CO2 emissions and steer toward a more sustainable trajectory. A promising avenue for CO2 capture is through membrane separation processes, offering advantages such as energy efficiency, scalability, and reduced environmental impact compared to conventional methods such as absorption or cryogenic distillation[3,4].

    Poly(ethylene oxide) (PEO) has emerged as a notable contender among various membrane materials for CO2 separation, garnering attention for its favorable properties[5,6]. PEO-based membranes demonstrate high selectivity for CO2 due to the quadrupole-dipole interaction between CO2 molecules and ether groups within the polymer structure[7]. Various strategies have been investigated to utilize PEO in gas separation membranes. These include synthesizing PEO-based copolymers, blending PEO with other polymers, creating mixed-matrix membranes (MMMs) with fillers, and preparing crosslinked poly(ethylene glycol diacrylate) (XLPEGDA)[8-13]. Commercial block copolymers such as Pebax and Polyactive, derived from PEO, have been developed to advance gas separation membrane technology[8,14]. Among these approaches, polymer blending stands out as one of the most effective methods for preparing gas separation membranes, owing to its cost-effectiveness, simplicity, and scalability[5].

    High-molecular-weight PEO (high-Mw PEO) emerges as a highly promising material for CO2 separation membranes, offering robust mechanical strength and affordability, rendering it suitable for industrial applications[15]. The good solubility in mild solvents such as water and ethanol, and cost-effectiveness of high-Mw PEO membranes position them as an appealing choice for industries seeking sustainable and economical CO2 capture solutions. However, despite its potential, the crystalline structure of high-Mw PEO presents challenges for membrane usage[6,16]. The presence of densely packed polymer chains within crystalline domains impedes gas transport properties, resulting in inadequate membrane permeability[17]. Additionally, defects arising from the growth of PEO crystals limit the overall performance of high-Mw PEO membranes[18]. Overcoming these limitations necessitates enhancing the amorphous regions within the PEO matrix while minimizing defects.

    To address these challenges, we introduced four distinct types of amorphous and polar polymer—poly(ethylene glycol) (PEG), poly(propylene glycol) (PPG), poly(acrylic acid) (PAA), and poly(vinyl pyrrolidone) (PVP)—to investigate the effect polymer additives on the high-Mw PEO-based blend membranes. These polymers feature functional groups capable of interacting strongly with PEO through hydrogen bonding or dipole- dipole interactions. By modulating the interactions between polymer chains, we aimed to restrain PEO chain packing and suppress the formation of defects between PEO spherulites, thereby facilitating the diffusion of gas molecules through the membrane with enhanced selectivity. We systematically investigated the effects of these polymers on the crystalline structures and gas separation performances of the PEO-based membranes using a straightforward blending approach. The crystallinity of PEO in the membranes was assessed through various analyses, including X-ray diffraction (XRD), differential scanning calorimetry (DSC), and small-angle X-ray scattering (SAXS). Gas separation performances were evaluated under conditions of 1 atm and 35°C. By correlating the crystalline structure of the PEO-blend membranes with their gas separation performances, we propose guidelines for selecting additive polymers in high-Mw PEO to prepare gas separation membranes using simple, cost-effective methods.

    2. Experimental

    2.1. Materials

    Poly(ethylene oxide) (PEO, average molecular weight: 1,000,000 g mol-1), poly(ethylene glycol) (PEG, Mv ~400 g mol-1), poly(propylene glycol) (PPG, Mv ~425 g mol-1), poly(acrylic acid) (PAA, Mw ~1,800 g mol-1) and poly(vinyl pyrrolidone) (PVP, Mw ~40,000 g mol-1) was purchased from Sigma–Aldrich. Deionized water and ethanol (99% purity) were obtained from Duksan Reagent & Chemicals. All the materials were used without further purification.

    2.2. Preparation of PEO blend membranes

    High-Mw PEO was dissolved in a solvent comprising 95% ethanol and 5% water at a concentration of 2 w/v%, followed by vigorous stirring at 50°C for 24 hours. An appropriate amount of the selected polymer additive (PEG, PPG, PAA, or PVP) was introduced into the solution to achieve a 30 wt% blend membrane. The mixture underwent overnight stirring to ensure uniformity. Subsequently, the solution was poured into a Teflon dish covered with aluminum foil punctured with pinholes to regulate evaporation rate. The dish was then placed in a drying oven at 50°C for two days and completely dried in a vacuum oven. The resulting membranes were denoted as PEO/PEG, PEO/PPG, PEO/PAA, and PEO/PVP based on the incorporated polymers.

    2.3. Gas separation measurements

    The gas permeabilities and diffusivity of the dense polymeric membranes were evaluated at a temperature of 35°C using a time lag technique with a constant volume/variable pressure apparatus provided by Airrane Co., Ltd., Korea. The membranes had an active area of 15.2 cm2. Gas permeability was determined using the time-lag method, which involved monitoring the increase in downstream pressure within a fixed volume at an upstream pressure of 760 torr. The results for gas permeability were reported in units of barrer, where 1 barrer equals 1 × 10-10 cm3 (STP) cm/cm2 × s × cmHg. CO2/N2 selectivity was calculated by dividing the permeability values for each pure gas.

    2.4. Characterizations

    The interactions between high-Mw PEO and the polymer additives were examined using an FT-IR spectrometer (Spectrum Two, Perkin Elmer, USA). X-ray diffraction (XRD) analysis (D8 Advance, Bruker, Germany) was conducted with a scanning speed of 2° min-1 across the 2θ range of 5~50° to investigate the crystalline structure of PEO in the PEO blend membranes. Thermal properties and the degree of crystallinity of PEO within the membranes were analyzed via differential scanning calorimetry (DSC; Discovery DSC, TA Instrument) at a heating rate of 20°C min-1 under a N2 atmosphere. Small-angle X-ray scattering (SAXS) patterns were obtained for characterizing the lamellar crystallites of PEO using the 4C SAXS beamline at the Pohang Light Source, Korea.

    3. Result and Discussion

    3.1. Preparation of PEO blend membranes

    Four distinct polymers—PEG, PPG, PVP, and PAA— were selected as additives to modulate the crystalline structure of PEO due to their shared hydrophilicity and compatibility with benign solvents such as water or alcohol, owing to the presence of strong polar groups such as ether, carbonyl, or hydroxyl groups. These groups are anticipated to interact strongly with the ether groups of PEO, promoting excellent miscibility. Moreover, being amorphous at room temperature, these polymers are expected to diminish the crystallinity of PEO. The flexible chain structures of these polymers facilitate intermolecular entanglement, disrupting the regular packing of crystalline chains and impeding the formation of crystalline domains. Consequently, the overall degree of crystallinity in the blend membrane is reduced, akin to a plasticizer effect. This results in a more disordered chain arrangement and lower crystallinity compared to pure crystalline polymer, thereby increasing the free volume and gas diffusivity of the membranes.

    PEO and PEG share similar repeating units of ethylene oxide, with PEG typically referring to lower molecular weight polymers. Despite the propensity for crystallization based on ethylene oxide groups, PEG with a molecular weight below 1,000 g mol-1 is known to exist in an amorphous state. While it exhibits high CO2 permeability and selectivity, its liquid state at room temperature poses challenges for its application in gas separation membranes. Consequently, considerable research has focused on using it as an additive polymer in polymeric membranes to enhance its performance[19,20]. However, despite its high potential, PEO/PEG blend membranes have not been extensively analyzed. Due to their chemical structural similarity, PEG and PEO are expected to exhibit good miscibility, with PEO compensating for the poor mechanical properties of PEG, rendering them suitable for gas separation membrane applications.

    PPG shares very similar chemical structures with PEO but possesses more hydrophobic properties due to the additional methyl group in its repeating units. The presence of the methylene group disrupts the dense chain packing of PEO, thereby reducing its crystallinity upon the addition of PPG[21,22]. Block copolymers composed of PEG and PPG blocks are commonly used in gas separation applications for this reason[23,24]. We anticipate PPG playing a similar role in high-Mw PEO membranes. PAA can form robust hydrogen bonding interactions with PEO owing to the presence of the carboxylic acid group[25]. This interaction involves the donation of a hydrogen bond from the carboxyl group of PAA to the ether linkages or hydroxyl groups of PEO[26], facilitating the formation of hydrogen- bonded networks that enhance miscibility and intermolecular interactions between the polymers. PVP is another additive polymer utilized in polymer blend composites, known for its high polarity and miscibility [27]. It exhibits strong compatibility with PEO based on robust dipole-dipole interactions. The carbonyl oxygen atom in PVP carries a partial negative charge, while the carbon atom bears a partial positive charge. This polarity enables strong dipole-dipole interactions between the oxygen atoms of PEO and the carbonyl groups of PVP, promoting the miscibility and compatibility of the polymer blend[28]. PVP aids in mitigating defects and enhancing the overall gas permeability of the membrane while preserving selectivity.

    We conducted an investigation into the impact of these polymers on PEO, particularly focusing on the crystalline structure of PEO, which is crucial for the application of gas separation membranes. We anticipated the intrusion of amorphous polymer chains into crystalline PEO domains, thereby characterizing their effect on the crystalline structure. The membranes were prepared using simple blending and solution-casting techniques. PEO was dissolved in an ethanol/water mixture, and the additive polymer was introduced into the solution. The solution exhibited a slightly opaque appearance due to the presence of crystalline PEO. Subsequently, the solution was cast onto a Teflon dish to fabricate free-standing membranes, as depicted in Fig. 1b. The high-Mw PEO membrane appeared translucent due to its semi-crystalline nature. Additionally, the surface of the high-Mw PEO membrane displayed roughness and unevenness, attributed to the formation of crystalline spherulites. In the case of PEO/PEG and PEO/PPG membranes, the surface roughness remained unchanged, and the color of the PEO/PPG membrane even intensified. However, PEO/PVP and PEO/PAA membranes exhibited smoother surfaces, potentially indicating a reduction or elimination of spherulite sizes. Moreover, these membranes appeared clearer and more transparent compared to others.

    3.2. Characterization of PEO blend membranes

    The interaction between the polymers was assessed using FT-IR analysis, as shown in Fig. 2. We examined the band shifts of both PEO and additive polymers post-blending. In the case of high-Mw PEO, particular attention was given to two prominent bands at around 2880 and 1097 cm-1, corresponding to methylene stretching and ether bond group stretching, respectively. The stretching vibration peak of C–O–C manifested as three peaks at 1060, 1097, and 1145 cm-1, indicative of the strong crystallinity of PEO[29]. PEG, lacking the triplet observed in high-Mw PEO spectra, indicated an amorphous state due to its lower molecular weight. The -OH group bands of PEG around 3446 cm-1 exhibited a slight shift to 3449 cm-1, suggesting weak interaction with the PEO membrane. However, discerning changes in the ether bond of PEG proved challenging due to overlap with that of PEO. Similar observations were made following the addition of PPG, with only minor shifts observed in methylene and hydroxyl group stretching. Despite the potential for strong hydrogen bonding between the hydroxyl groups of PEG and PPG with PEO, their limited presence impedes significant interchain interactions. In contrast, a substantial shift in the carboxyl group bands of PAA from 1699 cm-1 to 1729 cm-1 was observed in the PEO/PAA membrane, indicating strong interaction between PAA and PEO via hydrogen bonding. This interchain interaction between PAA and PEO, driven by hydrogen bonding, resulted in a blue shift of the carboxyl group. Intriguingly, no observable band shift was noted for the ether bond of PEO. Similarly, in the PEO/PVP membrane, a notable shift in the carbonyl group bands of PVP from 1651 cm-1 to 1668 cm-1 indicated strong interaction with PEO. Additionally, the ether bond of PEO shifted from 1097 cm-1 to 1101 cm-1, suggesting alterations in the chain packing of high-Mw PEO. The FT-IR analysis revealed that polymers with polar groups interacted with the ether bonds of PEO, influencing the crystalline structure of the membrane.

    The crystalline structures of the membranes were further analyzed using XRD and DSC techniques. Firstly, XRD patterns of the membranes were examined, as shown in Fig. 3. The two prominent peaks of high-Mw PEO observed around 19.1° and 23.3° correspond to the (120) and (112) planes, respectively[30]. Interestingly, PEO/PEG and PEO/PPG membranes also exhibited strong peaks despite the reduction in the overall PEO content in the membrane. This suggests that the crystallinity of PEO within the membrane was not significantly affected by the incorporation of PEG or PPG. Conversely, PEO/PAA and PEO/PVP membranes displayed much lower intensity peaks, indicating a decrease in the crystallinity of PEO.

    The degree of crystallinity of PEO in the membrane was quantified using DSC data. Initially, the melting temperature (Tm) of PEO crystals was observed at 64.0°C for the pristine high-Mw PEO membrane. Upon the addition of amorphous polymers, the Tm decreased due to polymer-polymer interactions[31]. The crystallinity of PEO was determined by measuring the heat of fusion during PEO melting.

    X c , t o t a l ( % ) = Δ H m Δ H m , P E O o × 100
    (1)

    X c , P E O ( % ) = Δ H m × w P E O Δ H m , P E O o × 100
    (2)

    where ΔHm is the calculated fusion enthalpy per gram of the membrane which is measured from the melting peak in DSC. Δ H m , P E O o is the heat of melting per gram of 100% crystalline PEO with the molecular weight of 106 g mol-1, reported as 205 J g-1[32]. wPEO is the weight fraction of PEO in the PEO blend membrane, which is 0.3 in this study. In the PEO/PEG blend, the degree of crystallinity of PEO experienced a slight increase from 66.4% to 66.9%. This suggests that PEG might have struggled to penetrate through the densely packed PEO chains. Conversely, in the case of PEO/PPG, the degree of crystallinity of PEO exhibited a more notable increase, rising to 69.4%. The hydrophobic methylene group of PPG likely induced denser chain packing of PEO, consistent with both XRD results and the observed opaque, bumpy surfaces of the membranes. Despite expectations, the high crystallinity of high-Mw PEO, combined with the influence of the -CH3 group in PPG, contributed to an increase in crystallinity rather than disrupting chain packing.

    While both PEG and PPG are commonly employed as plasticizers in other polymers due to their amorphous nature, they proved ineffective in reducing crystallinity within the PEO matrix. Conversely, a significant decrease in crystallinity was observed in PEO/PAA and PEO/PVP blends. In these cases, the crystallinity of PEO dropped to 47.7% and 58.6% for PEO/PAA and PEO/PVP, respectively. The strong interaction between PAA and PEO led to a sharp decrease in PEO crystallinity. However, it is important to note that the degree of crystallinity alone does not fully describe the overall crystalline structure of the membranes. Further detailed characterization is necessary to investigate the microstructure of PEO crystals within the membranes.

    For semi-crystalline polymers such as PEO, the formation of lamellar crystals progresses into crystalline fibrils or spherulites. High-Mw PEO is known to develop crystalline spherulites originating from lamellar crystals[33]. Interspherulitic defects, occurring between the spherulites, are often the primary cause of defects in PEO membranes used for gas separation. Therefore, it is crucial to prevent the formation of these defects to enable the application of high-Mw PEO in gas separation membranes. While thermal treatment near the melting temperature of PEO can reduce these defects, it necessitates additional processes and costs and may potentially harm the membranes. In crystalline/amorphous polymer blends, the segregation of the amorphous phase influences crystallization[34]. Hence, it's essential to characterize which type of phase morphologies (such as interlamellar, interfibrillar, interspherulitic segregation, and intralamellar) of the additive amorphous polymer predominates in the blend membranes[35,36].

    SAXS analysis serves as a potent tool for investigating the lamellar microstructure of membranes. In the SAXS graph of pristine high-Mw PEO, a distinct lamellar structure was evident, with peaks appearing at a ratio of 1:2:3, indicative of a well-defined lamellar structure comprising the continuous crystalline region and the amorphous region of PEO. Utilizing Bragg’s law, the d-spacing from the peak was calculated as 66.7 nm, representing the sum of the crystalline and amorphous thicknesses of PEO. However, in the case of PEO/PEG and PEO/PPG membranes, the peak ratio deviated from the lamellar structure, appearing around 1:2.3. This deviation can be attributed to the disorder in the lamellar structure caused by the interference of the additive polymer. It is speculated that the amorphous PEG or PPG polymer randomly penetrated within the amorphous phase of PEO, as evidenced by the unchanged crystallinity of PEO upon incorporation of PEG or PPG. The substantially increased d-spacing of PEO indicates segregation of PEG or PPG within the interlamellar amorphous region of PEO crystals. This random increase in amorphous thickness led to structural irregularity in the lamellar structure of PEO crystals. The PEO/PAA membrane displayed two peaks with a ratio of 1:2, suggesting the presence of a lamellar structure. However, a peak shift was observed, indicating a decrease in lamellar thickness from 66.7 nm to 61.0 nm. This decrease is attributed to the reduced crystalline thickness of PEO crystals, corroborating the significantly decreased crystallinity observed in the DSC results. Additionally, PAA was inferred to be present not only in the interlamellar region but also in the interspherulitic region of PEO, potentially preventing the formation of interspherulitic defects in the membrane. In contrast, no strong peaks were observed in the SAXS graph of the PEO/PVP membrane, suggesting the destruction of the lamellar structure by the incorporation of PVP. Thus, PVP was found to be effective in decreasing the crystallinity of PEO and preventing the formation of lamellar crystals, potentially attributed to segregation at the intralamellar phase of PEO.

    3.3. Gas separation performance of PEO blend membranes

    The pure gas permeability of CO2 and N2 of the PEO-based membranes was measured at 1 atm and 35°C using the time-lag method. The pure PEO membrane exhibited defects due to the presence of defects between the crystalline spherulites, leading to gas leakage. Similarly, both PEG and PPG-based blend membranes showed defects. Interestingly, we observed an increase in the crystallinity of PEO in the membrane upon addition of the amorphous polymer. This increase in crystallinity can be attributed to the segregation of PEG or PPG within the amorphous layer of the lamellar crystals of PEO, failing to reduce the crystallinity and prevent defect formation. One significant reason for this result is the short chain length of PEG or PPG polymers, hindering their effective entanglement among the PEO chains and crystals. Research on PEG blend membranes with varying molecular weights has shown similar findings. Additionally, increasing the molecular weight of PEG or PPG may not be effective in improving gas separation performance, as it may further increase the crystallinity of the polymer. To address this issue, previous studies have suggested the use of poly(oxyethylene methacrylate) (POEM)-based copolymers as additives for PEO-based membranes. POEM, despite its high molecular weight, maintains amorphous properties and can effectively entangle with high-Mw PEO crystals, potentially preventing crystalline defects.

    In contrast, the gas separation performance of the PAA-based membrane indicated no defects between the PEO crystalline spherulites, likely due to strong hydrogen bonding between PAA and PEO. However, the gas permeability of the PEO/PAA membrane was extremely low, attributed to the inferior gas separation performance of PAA. The PEO/PVP membrane exhibited the best gas separation performance among the prepared membranes. PVP, with a molecular weight long enough to entangle with PEO chains, effectively eliminated lamellar crystals, resulting in a defect-free membrane. However, the gas separation performance was not optimal compared to reported PEO-based membranes, likely due to the inferior CO2 separation performance of PVP.

    In conclusion, while the selected commercially-available, amorphous, water-soluble polymers showed promise in enhancing gas separation performances, the results were not sufficient for practical application as gas separation membranes. Guidelines for designing additive polymers include considerations for strong interactions with PEO, sufficient molecular weight for entanglement with PEO crystals, and high gas separation performance. Other approaches such as branched polymers or crosslinking could also be explored to prevent PEO chain packing and induce segregation of additive polymers in interspherulitic defects. Further research in this area holds promise for the development of highperformance gas separation membranes based on high- Mw PEO using low-cost, simple blending methods.

    4. Conclusion

    In this study, we assessed commercially-available, water-soluble amorphous polymers (PEG, PPG, PAA, and PVP) as additives in high-Mw PEO to fabricate high-performance gas separation membranes. These polymers were chosen for their polar and hydrophilic properties, anticipating good compatibility with PEO in solution. Membranes were then produced using a simple blending technique. However, despite initial hopes for enhanced compatibility and interaction with PEO, both PEG and PPG failed to reduce the crystallinity of PEO. Their short chain lengths led to segregation within the amorphous regions of PEO rather than within the crystalline domain during PEO crystal growth. Consequently, the membranes exhibited defects, allowing gases to diffuse through the gaps between the crystalline spherulites. In contrast, PAA and PVP effectively disrupted the chain packing of PEO, lowering its crystallinity. Our SAXS results suggest that PAA segregated not only along the crystalline chains of PEO but also within the interspherulitic region, preventing interspherulitic defects. The lamellar crystalline structure of PEO was notably diminished in the PEO/PVP membrane, indicating the efficacy of PVP in reducing the crystallinity of high-Mw PEO. Consequently, membranes with added PAA and PVP were defect-free. However, their overall impact on gas separation performance was adverse. Given the economic and commercial feasibility of using high-Mw PEO in gas separation membrane production, a thorough design of the additive polymer is essential.

    Acknowledgements

    This work was supported by the National Research Foundation (NRF) of Korea, funded by the Ministry of Science and ICT (RS-2024-00333678) and the Korea Institute of Energy Technology Evaluation and Planning (KETEP) grant funded by the Korea government (MOTIE) (20214000000090, Fostering human resources training in advanced hydrogen energy industry).

    Figures

    MEMBRANE_JOURNAL-34-3-192_F1.gif

    (a) Chemical structure of high-Mw PEO, PEG, PPG, PAA, and PVP, (b) schematic illustration of the process to fabricate PEO blend membranes, (c) photo of high-Mw PEO and PEO blend membranes.

    MEMBRANE_JOURNAL-34-3-192_F2.gif

    FT-IR spectra of high-Mw PEO and polymer additive; (a) PEG, (b) PPG, (c) PAA, and (d) PVP and their blend membranes.

    MEMBRANE_JOURNAL-34-3-192_F3.gif

    XRD patterns of high-Mw PEO and the PEO blend membranes with different additive polymers.

    MEMBRANE_JOURNAL-34-3-192_F4.gif

    (a) DSC curves of high-Mw PEO and PEO/blend membranes and (b-f) their magnified curves with the calculated heat of enthalpy per gram of membrane.

    MEMBRANE_JOURNAL-34-3-192_F5.gif

    SAXS spectra of high-Mw PEO and PEO blend membranes with different additive polymers.

    Tables

    Melting Temperature (Tm, PEO), Heat of Fusion (△Hm, PEO), Glass Transition Temperature[12], and Degree of Crystallinity (Xc) of Blend Membranes Obtained from DSC

    SAXS Profiles of High-Mw PEO and PEO Blend Membranes

    CO2 Permeance and CO2/N2 Selectivity of PEO Blend Membranes and Previously Reported PEO-Based Blend Membranes

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