Cellulose Microbeads with Tunable Physicochemical–Structural Properties: Preparation, Characterization, and Functionalization

Feng Xu 강원대학교 대학원 2024 국내박사

Microbeads offer a high specific surface area, abundant pores, low density, good dispersion, and controllability, and therefore have excellent application prospects in water treatment, chromatographic separation, drug delivery, and personal care products. Traditional microbeads are mainly derived from fossil resources, causing resource depletion and environmental pollution. Cellulose is one of the most abundant natural biopolymers on Earth and has various advantages including renewability, degradability, and environmental friendliness. Therefore, synthesizing microbeads from cellulose is an ideal method for replacing fossil-fuel-based microbeads and promoting green and sustainable development. Generally, the dissolution of cellulose is a critical step in the production of regenerated cellulose microbeads. However, the homogeneous dissolution of cellulose at room temperature is challenging because of its strong inter- and intramolecular hydrogen bonds. Furthermore, the structure-property relationship of cellulose microbeads remains unclear, which restricts their wide application in functional materials. In view of this background, commercial pulp was used as the raw material to prepare cellulose microbeads. A tetraethylammonium hydroxide (TEAH)/urea/H2O system was first employed to dissolve the cellulose at 25 ℃, followed by shaping and regeneration. The formation mechanism, structure, and physicochemical properties of cellulose microbeads were systematically investigated. Furthermore, the application potential of the cellulose microbeads as absorbents was evaluated. First, to prepare the cellulose solution (CS–T/Ux:y), hardwood bleached kraft pulp (HwBKP) and the TEAH/urea/H2O system with various mole ratios of TEAH and urea (T:U = 1:0–1:5) were chosen as raw materials and solvents, respectively. It was found that the TEAH/urea/H2O system could effectively dissolve HwBKP in 1 h under ambient conditions (25 ℃). When the T:U ratio was 1:2, HwBKP showed that a high proportion of 99 wt% had dissolved, and the resultant CS–T/U1:2 exhibited excellent long-term stability with a high cellulose regeneration yield (98 wt%). Second, porous regenerated cellulose microbeads (RCMs) were fabricated using CS–T/U1:2 via a simple emulsion–coagulation–oven-drying process. It was found that RCMs were synthesized via continuous agglomeration of micro/nanospheres formed in the early stages of the coagulation process. The mean diameter of the RCMs increased by altering the stirring time and speed. RCMs possess high porosity and low density, endowing them with an excellent methylene blue (MB) adsorption capacity. Third, porous cellulose aerogel beads (CABs) with tunable core-shell structures were successfully synthesized via a sequential process involving dropping and regeneration in an acetic acid bath, dilute ethanol substitution, and freeze-drying. It was found that the difference in regeneration speeds between the central and peripheral areas of the cellulose droplet enabled the formation of the core-shell structure. Ethanol molecules can induce the growth of small and uniform ice crystals during the freeze-drying of hydrogel beads, endowing CABs with non-obvious structural shrinkage, large particle size, uniform pores, and high porosity. Finally, porous quaternized cellulose beads (QCBs) were developed by the in situ grafting of glycidyl trimethylammonium chloride (GTAC) onto cellulose chains in a TEAH/urea/H2O system, followed by dropping and regeneration in an acetic acid bath, dilute ethanol substitution, and freeze-drying. It was found that with increasing GTAC dosage, the mean particle size increased owing to the enhanced positive charge, resulting in high porosity and pore volume in the QCBs. In particular, QCBs-1.5 exhibited a high water absorption efficiency as a superabsorbent.

지속 가능 광학 소자 응용을 위한 계층적 셀룰로오스 기반 하이브리드 구조체 연구

김지연 인하대학교 대학원 2026 국내박사

Synthesis of cellulose based hybrid and functional materials and its applications

고재옥 성균관대학교 일반대학원 2018 국내석사

Cellulose is a raw material for paper and a bio-polymer obtained from wood. It is environment-friendly, has low cost, has excellent mechanical strength and high specific surface area. As a result, interest in cellulose and hybrid materials based thereon has rapidly increased in recent years to become a leading-edge research field. Key applications include armor, filters, bio materials, membranes, nanohybrid reinforcements, aerogels, lithium ion batteries, supercapacitors, electronic paper, and sensors. However, due to the insulator properties of cellulose, there is a drawback that it is difficult to apply a single material base. In this study, we developed fabrication of CNT/Cellulose hybrid materials which is a cellulose based hybrid materials with carbon nanotubes for the foldable electrode to complement electrically insulating property of cellulose and utilize the high mechanical properties of cellulose. And also, we developed synthesis of cellulose based funtional materials using chemical funtionalization which is a sulfonation to cellulose in order to give the property of proton conduction for application to eco-friendly solid state electrolyte. In the case of carbon nanotube / cellulose hybrid material, carbon nanotube / cellulose hybrid conducting paper excellent in both electrical characteristics and mechanical properties is produced by hybridization cellulose and carbon nanotubes having excellent electrical characteristics, which are reported to have excellent mechanical strength and Such a hybrid conducting paper is manufactured through an incomparably simple and low-cost drop casting and subsequent drying process, and is capable of changing the shape and size of the electrode freely. The structural characteristics, surface hydrophobicity and chemical interactions between the carbon nanotubes and the cellulose of the hybrid conducting paper were analyzed according to the concentration of the carbon nanotubes. As a result, it was found that the hybrid conducting conducting paper of 50 wt% Electrical conductivity, and showed excellent flexibility to preserve electrical characteristics even when crumpled state. Also, it showed excellent bending durability due to less than 10% change in electrical resistance even in the test of bending at a bending. In addition, due to the excellent hydrophobicity of carbon nanotubes, the disadvantage of cellulose, which is vulnerable to water, is complemented. In the water, the electrical properties of carbon nanotube / cellulose hybrid conducting paper are well preserved. In addition, because of the paper, the hybrid conducting paper has excellent foldability that can be folded into a desired shape like an actual paper, and since it can be produced with ink, it can be directly applied to cloth or cloth, so that it can be applied to wearable devices. In the case of cellulose functional materials through chemical functionalization, we synthesized a paper having proton conductive properties using chemical functionalization which is forming a sulfonated group in the hydroxyl group of cellulose for eco-friendly solid state electrolyte. This proton conducting paper, that is, the sulfuric acid solid electrolyte in paper form, has a proton conductivity of 0.172 S / cm in a 100% relative humidity atmosphere, which is nearly twice as high as that of nepion, which has the highest proton conductivity as a proton conductive material Showed proton conductivity. It was also combined with metal organic structures to improve proton conductivity in low relative humidity atmospheres. Due to the water trapping properties of the metal organic structure, it showed improved proton conductivity up to 10 times higher in low relative humidity atmospheres. The paper type solid electrolyte showed excellent properties as an electrolyte because it measured the supercapacitor characteristics by using the solid electrolyte of paper type and showed the non-electric capacity of 135.14 F / g at 75% relative humidity respectively. 셀룰로오스는 종이의 원료가 되며 나무로부터 얻어지는 바이오 폴리머로써 친환경적이며 값이 싸고 기계적 강도와 비표면적이 높다는 특징을 가지고 있는 소재이다. 이러한 특성을 이용하여 셀룰로오스는 현재 필터, 분리막, 방탄복, 약물 전달 물질로써 많이 사용하고 있다. 최근 셀룰로오스는 탄소 기반 물질과 복합화하여 고강도 복합소재와 전도성 유연소재로써 연구되고 있디. 또한, 셀룰로오스의 고분자 단량체에는 수산화기가 풍부하게 있어 이종의 기능기와 화학적 결합을 유도하여 새로운 특성 나타내는 화학적 기능화가 용이하기 때문에 술폰화기를 셀룰로오스의 수산화기에 반응시켜 고체 전해질 등과 같은 에너지 소재로써 연구가 진행중이다. 셀룰로오스 기반의 필름 같은 경우, 높은 기계적 특성과 유연성으로 인해 벤더블 배터리의 핵심요소 중 하나인 전극이나 전해질과 플렉서블 디스플레이의 전극 등과 같은 플렉서블 일렉트로닉스에도 활발히 연구가 진행 중이다. 하지만 셀룰로오스를 활용하여 전극이나 전해질에 사용하기 위해서는 전기적으로 절연체라는 특성이 한계점을 작용해 이종의 전도성 물질과 복합화와 기능화를 통해 전도성 소재 및 기능성 소재 합성이 요구된다. 본 연구에서는 셀룰로오스 기반의 유연 전극과 고체 전해질 합성을 하기 위하여 전극과 전해질에 적용하기에 한계점으로 작용하는 셀룰로오스의 절연체 특성을 보완하고 셀룰로오스의 우수한 기계적 특성을 활용하여 폴더블 전극으로의 응용을 위한 탄소 나노튜브/셀룰로오스 복합소재 연구와 친환경 고체 전해질으로의 응용을 위하여 셀룰로오스에 황산화계 물질을 화학적 기능화하여 양성자 전도성 특징을 보이는 셀룰로오스 기반 기능성 소재 합성을 진행하였다. 먼저 탄소 나노튜브/셀룰로오스 복합소재의 경우, 기계적 강도가 매우 우수하다고 보고된 셀룰로오스와 전도성 특성이 매우 우수한 탄소 나노튜브를 복합화 하여 전도성 특성과 기계적 특성이 모두 우수한 탄소 나노튜브/셀룰로오스 복합소재를 제작하였고 이러한 복합소재는 간단하고 용액공정을 이용하여 혼합 용액의 드롭 캐스팅 및 후속 건조 과정을 거쳐 제조되었으며, 전극의 모양과 크기는 제한이 없다는 특징을 가지고 있다. 복합소재의 탄소 나노튜브와 셀룰로오스 사이의 구조적 특징, 표면 소수성 및 화학적 상호 작용을 탄소 나노튜브의 농도를 5, 10, 20, 30, 50 질량비에 따라 분석을 실시하였다. 50 질량 비의 경우 15.87 S/Cm의 높은 전기전도도를 보였으며 접히는 수준의 구부림 반경이 2mm에서의 구부림 10만번 반복 실험에서도 전기적 저항 변화율이 10, 20, 30, 50 질량비에 각각 0.4%, 5%, 8%, 6%를 나타내며 탄소 나노튜브의 농도가 증가할수록 저항변화율이 높게 나타나는 경향을 보였으며 저항 변화율이 최대 10% 미만을 보임으로서 우수한 구부림 내구성을 나타내었다. 또한 소수성 특징이 뛰어난 탄소 나노튜브의 영향으로 물에 잘 용해된다는 셀룰로오스의 특성이 보완되어 물속에서도 탄소 나노튜브/셀룰로오스 복합소재는 전도성 특성을 잘 보존하였으며, 용액공정으로 이루어 지기 때문에 대면적으로도 제작 가능하다. 또한 종이이기 때문에 복합소재는 실제 종이처럼 원하는 모양대로 접을 수 있는 우수한 접힘성을 보였으며 잉크로도 제작이 가능하여 옷이나 천에 직접 프린팅 할 수 있어 웨어러블 디바이스에도 적용이 가능하리라 판단된다. 화학적 기능화를 통한 셀룰로오스 기능성 소재의 경우, 친환경 소재인 셀룰로오스를 활용하여 술폰화 그룹을 셀룰로오스의 수산화기에 직접 합성하는 화학적 기능화를 통하여 양성자 전도성 특성을 보이는 종이를 합성하였다. 이러한 양성자 전도성 종이, 즉 종이 형태의 황산화계 고체전해질은 양성자 전도도가 100% 상대 습도 분위기에서 0.172 S/Cm로 기존의 양성자 전도성 물질로 가장 높은 양성자 전도도를 나타내는 네피온과 비교하여도 2배 가까이 더욱 높은 양성자 전도도를 나타내었다. 이러한 양성자 전도체는 시료 내부의 물을 활용하여 양성자를 수송시키는 메커니즘을 가지고 있기 때문에 낮은 상대 습도 분위기에서 양성자 전도도가 급격히 감소되는 특징을 가지고 있다. 양성자 전도체를 실질적으로 활용하기 위해선 낮은 상대습도에서도 높은 양성자 전도도를 보이는 것이 매우 중요한 이유이다. 이러한 문제점을 보완하여 낮은 상대습도에서 양성자 전도도를 향상시키기 위해 금속유기구조체의 한 종류인 알루미나 퓨마레이트와 복합화 하였다. 금속유기구조체는 금속과 유기물로 이루어진 3차원 다공성 구조체로써 기공안에 물을 흡수하고 물과 금속유기구체간에 반데르발스 힘, 수소결합 등과 같은 물리적 화학적 결합력으로 물을 가두는 특성을 가지고 있다. 이러한 특성을 활용하여 낮은 상대 습도 분위기에서도 물을 잘 가둘 수 있어 최대 10배 이상의 향상된 양성자 전도도를 보였다. 이러한 종이 형태의 황산화계 고체전해질을 활용하여 슈퍼커패시터 특성을 측정하였고 75%의 상대 습도 분위기에서 비 전기용량이 135.14 F/g을 나타내는 등 합성된 종이형태의 고체 전해질은 전해질로써 우수한 특성을 보이는 것을 확인하였다.

온·습도 및 방사선에 의한 셀룰로오스 열화 평가 및 예측

황유진 전북대학교 대학원 2025 국내박사

Cellulose, the primary component of paper, is an organic material that can undergo degradation through hydrolysis and oxidation. These degradation are influenced by environmental factors such as temperature, relative humidity, light, and air pollutants. In addition to natural aging, exposure to radiation for paper sterilization or cellulose modification can also lead to degradation of cellulose. Therefore, the purpose of this study is to assess and compare the degradation behavior of cellulose under major degradation factors, specifically temperature, relative humidity, and radiation, including electron beams, gamma rays, and X-rays. Chapter 2 presents a predictive model to estimate the degradation rate and expected lifespan of paper under various temperature and humidity conditions. To enhance prediction accuracy, the model takes into account moisture loss during long-term aging. In addition, moisture content, rather than relative humidity, was used to more precisely reflect the hydrolytic behavior of cellulose. By establishing a quantitative relationship between moisture content and the cellulose chain scission rate, the model enables accurate estimation of the paper degradation rate. Chapter 3 investigates the chemical, physical, and optical properties of cellulose paper irradiated by an electron beam. Radiation-induced cellulose chain scission and oxidation increased considerably at a dose of 25 kGy, whereas folding endurance, morphology, and crystallinity remained largely unchanged. The cellulose chain scission rate irradiated under air-dried (23℃, 50 % RH) and wet conditions showed no significant difference; however, cellulose oxidation was more pronounced under wet conditions. Electron beam irradiation did not significantly affect paper discoloration, which is known to be associated with oxidation. However, when the irradiated papers were aged, the color difference increased with irradiation dose, as oxidized functional groups in cellulose can act as triggers for color change. In the low-dose range, electron beam irradiation did not adversely affect the physical properties of paper, although notable changes were observed in both chemical and optical properties. Chapter 4 investigates the effects of gamma and X-ray irradiation on cellulose degradation and long-term preservation stability. The molecular weight of cellulose decreased with increasing doses of gamma rays and X-rays. The most pronounced reduction in molar mass was observed under oven-dried conditions. This is likely because radical interactions were restricted within the cellulose matrix in the absence of moisture, thereby promoting chain scission. In contrast, cellulose oxidation was most prominent under wet conditions, which is the opposite trend observed for molar mass. This oxidation is presumed to result from the extensive formation of hydroxyl radicals generated through radiolysis of water molecules during irradiation. Electron spin resonance (ESR) analysis confirmed the long-term persistence of radicals generated by irradiation. These radicals are presumed to be primarily trapped within the crystalline regions of cellulose, thereby contributing to continued degradation. The results highlight the importance of evaluating not only the immediate effects of irradiation but also long-term degradation behavior in cellulose-based materials following radiation exposure. Chapter 5 compares the degradation behavior of cellulose induced by temperature and humidity conditions and radiation. For this comparison, the relationships between the degree of polymerization (DP) and two parameters were evaluated: zero-span tensile strength and the leveling-off degree of polymerization (LODP), which reflects the crystalline integrity of cellulose. Despite having similar DP values, irradiated samples retained higher zero-span tensile strength than thermally aged ones. In terms of LODP, thermally aged samples exhibited a stable value of approximately 133, whereas irradiated samples showed a marked decrease in LODP as the DP declined. The observed differences in degradation behavior can be attributed to whether chain scission occurs within the crystalline or amorphous regions of cellulose. Under elevated temperature conditions, acid hydrolysis predominantly occurs in the amorphous regions, leading to a rapid decrease in mechanical strength. In contrast, radiation is capable of inducing chain scission not only in the amorphous regions but also within the crystalline regions. In irradiated samples, partial chain cleavage in the crystalline regions does not lead to an immediate loss of mechanical strength, likely due to intermolecular hydrogen bonding between adjacent cellulose chains in the crystalline regions. However, as radiation progressively shortens the chain length in the crystalline regions, the LODP, which represents the minimum structural unit of the crystalline domain, correspondingly decreases. The results highlight fundamental differences in the degradation mechanisms of cellulose under the two conditions. Finally, Chapter 6 presents the predictive assessment of paper degradation under thermal-humidity, and radiation conditions, based on the results presented in Chapter 2 through 4. For thermal-humidity conditions, the degradation rate and life expectancy of paper were estimated under various environmental scenarios. Specifically, a passive preservation strategy reflecting seasonal climate variations was proposed as a means to reduce energy demands. Under the passive environment, the cellulose degradation rate decreased by approximately 34 % compared to that in the constant environment (20 ℃, 50 % RH). In the case of radiation, the DP of cellulose was predicted as a function of irradiation dose for three radiation types: electron beams, gamma rays, and X-rays. Although a dose of 10 kGy has been proposed by the International Atomic Energy Agency (IAEA) as safe for paper-based cultural heritage, the DP of cellulose was found to decrease by up to approximately 55 % at a dose of 10 kGy, depending on the type of radiation. These findings indicate that irradiation should not be considered a routine preservation treatment, but rather applied with caution and only in exceptional cases where microbial damage is expected to outweigh the physical and chemical degradation caused by irradiation.

Preparation and characterization of cellulose nanofibril aerogel cross-linked with maleic acid and sodium hypophosphite

김채훈 서울대학교 대학원 2015 국내박사

Cellulose nanofibril (CNF) is defined as a nano-scale fibrous material which can be obtained from cellulose fiber by means of a mechanical shearing action. Its diameter is in the range of 5 – 50 nm and its length is typically several micrometers. CNF is being studied by academia and industry for various applications; however, the most promising of these is considered to be as a starting material for the preparation of cellulose aerogel. An aqueous suspension of CNF produces a homogeneous hydrogel structure at a concentration of 1 wt % due to mechanical entanglement and interfibrillar hydrogen bonding. This unique capability of CNF to build up a self-assembled hydrogel structure allows for the preparation of a highly porous aerogel through direct water removal by means of freeze-drying. However, the network structure of CNF aerogels is built by interfibrillar hydrogen bonds between adjacent individual fibers. As a result, the network structure of CNF aerogel is easily destroyed by absorbed water. This weakness of the wet strength limits the wider application of the CNF aerogel. In this research, a cross-linked CNF aerogel was prepared. As cross-linking agents, maleic acid and hypophosphite were used. The cross-linking reaction was composed of esterification between maleic acid and cellulose in a suspension state and the formation of cross-linking by means of chemical bonds between cellulose-grafted maleic acid and hypophosphite in an aerogel state. Through this cross-linking reaction, the network stability of the CNF aerogel in a wet state was reinforced. Unlike typical CNF aerogels, the cross-linked CNF aerogel maintained its original shape after immersion in water under a mild shear condition. Moreover, the cross-linked CNF aerogel was rapidly able to absorb considerable amounts of water. The cross-linked CNF aerogel exhibited shape-recovery characteristics as well in a wet state. The shape-recovery characteristics of the wet cross-linked CNF aerogel were explained in terms of the interaction between the absorbed water and the amorphous region of the CNF. As potential applications, carrying media or a supporting matrix for precious materials are feasible. In order to evaluate the potential applicability of these suggestions, the ion-adsorption performance of the cross-linked CNF aerogel was investigated. The surface charge of CNF was made positive by means of a surface modification with glycidyltrimethylammonium chloride (GTMAC). Through an etherification process, GTMAC was grafted onto the surface of the CNF and the zeta potential of the cationic CNF was then increased to +39.5 mV. From the cationically modified CNF, a positively charged cross-linked CNF aerogel was prepared. The functional groups generating the surface charge of the positively charged cross-linked CNF aerogels were quaternary ammonium and carboxylic groups. For the negatively charged cross-linked CNF aerogel, only carboxyl groups contributed to the surface charge. As a result, the zeta potential of both cross-linked CNF aerogels was affected by the pH of the aqueous media. The pH also affected the ion-adsorption performance of the cross-linked CNF aerogels. An adsorption isotherm was carried out and the theoretical maximum adsorption performances of the cross-linked CNF aerogels were calculated using the Langmuir adsorption model. The ns value, representing the maximum ion-absorption capacity of the negatively charged cross-linked CNF aerogel, was 0.79 mmol/g for nickel ion, while the ns value of the positively charged aerogel was 0.62 mmol/g for permanganate ions. These values are low relative to previously reported performance levels of chemically modified micro-particular cellulose absorbent materials, but they are higher than those of commercially available strong acid ion-exchange resins.

Study on Control of Dynamic Properties of Cellulose-Ionic Liquid Solution for Fabrication of Nanostructures

안용준 서울대학교 대학원 2019 국내박사

지구상에서 가장 풍부한 고분자 중 하나인 셀룰로오스는 고강도, 생분해성, 생체적합성 등과 같은 우수한 성질을 지니고 있다. 그러나 셀룰로오스는 용융이 되지 않으며 용해할 수 있는 용매가 매우 제한적이기 때문에 공정적으로 불합리한 조건을 가지고 있다. 최근, 상온에서 쉽게 셀룰로오스를 용해할 수 있는 이온성 액체가 개발된 이후, 관련 연구는 막대히 증가하고 있다. 이온성 액체는 거대 양이온 분자와 상대적으로 작은 음이온이 이온결합을 하고 있는 염으로 구성되어 있다. 셀룰로오스 용해 원리는 수소결합이 가능한 음이온이 셀룰로오스 수소결합 네트워크를 붕괴시키고 이 공간을 양이온이 채워서 셀룰로오스의 견고한 구조를 해리시키는 것으로 알려져 있다. 많은 연구에도 불구하고, 이온성 액체 내에서 셀룰로오스의 분자량이 감소되는 현상과, 재생 후 결정성이 회복되지 않아 강도가 저하되는 문제점이 발생한다. 따라서 본 연구에서는 이온성 액체내에서 셀룰로오스의 해중합에 대한 근본적 고찰과 동시에 미세구조를 제어하여 균일한 나노구조를 갖는 셀룰로오스 소재를 개발하는 것을 주요 목표로 한다. 첫째로, 서로 다른 음이온을 갖는 이온성 액체를 사용하여 셀룰로오스를 용해 후, 해중합되는 속도와 원인을 관찰하였다. 셀룰로오스의 해중합은 이온성 액체에서 발생하는 산에 의한 가수분해 현상으로 밝혀졌다. 이온성 액체에서 발생한 산은 음이온의 염기도가 클수록 많이 생성되는 것을 확인하였다. 산 가수분해에 의해 분자량의 낮아진 셀룰로오스를 이용하여 점도평균분자량 상수를 구할 수 있었다. 또한 기존에 보고되지 않았던 셀룰로오스의 유방성 액정현상을 관찰하였다. 둘째로, 이온성 액체 내에서 가수분해된 셀룰로오스 분자의 운동성을 평가하고 결정화 거동과의 상관관계를 조사하였다. 분자량이 낮아진 셀룰로오스는 운동성이 점차 향상되며, 특히 얽힘 분자량 이하에서 급격히 증가하였다. 이를 증명하기 위해 분자 확산 계수와 점도의 상관관계를 분석하여 운동 상수를 계산하였다. 셋째로, 가수분해 거동과 운동성 데이터를 바탕으로 리그노셀룰로오스 바이오매스 전처리 공정에 이온성 액체를 적용하였다. 리그노셀룰로오스 전처리는 구조의 이완과 분자량의 감소를 목적으로 한다. 이온성 액체의 용해도가 증가할수록 비 셀룰로오스계 성분의 제거 효율은 증가하였나 재결정화도가 크게 증가하였다. 이 연구를 통해 각 리그노셀룰로오스의 구조에 최적화된 이온성 액체 선정에 대한 레퍼런스를 제시하였다. 넷째로, 분자 운동성이 조절된 셀룰로오스 분자를 이용하여 균일한 크기와 우수한 분산성을 갖는 셀룰로오스 나노입자를 제조하였다. 가수분해 도중 이온성 액체의 양이온이 셀룰로오스 환원성 말단에 치환되는 반응을 유도하여 마이셀과 유사한 셀룰로오스 나노입자를 형성시켰다. 표면의 양이온에 의해 셀룰로오스 나노입자는 높은 분산성을 나타내었다. 다섯째로, 나노기공을 갖는 셀룰로오스 분리막을 제조하고 표면에 아민기 도입을 통해 엑스트라 버진 올리브유의 산패성분을 분리하는 공정을 제시하였다. 앞서 나노입자 제조의 원리와 마찬가지로, 운동성이 향상된 셀룰로오스 분자 사슬은 높은 기공성을 나타내었다. 제조된 셀룰로오스 나노분리막에 토실기와 에틸렌디아민을 차례대로 치환하여 아민기를 도입하였다. 엑스트라 버진 올리브유의 산패성분으로 알려진 유리지방산과 엽록소는 각각 분리막 표면의 아민기와 기공크기에 의해 분리되었다. 또한 엑스트라 버진 올리브유의 성분 변화없이 산패성분만 선택적으로 제거 가능함을 확인하였다. 본 연구에서는 다양한 조건에서 셀룰로오스를 이온성 액체에 용해하고 분자의 특성 변화를 규명하였다. 이를 기반으로 셀룰로오스의 나노화에 대한 기술을 확립하였다. 특히, 이온성 액체에서 재생된 기존 셀룰로오스의 한계로 여겨지는 분자량의 감소와 낮은 결정성을 극복하고 분산성과 크기 균일성을 확보하는 방법을 개발하여 셀룰로오스/이온성 액체 공정의 새로운 지평을 열 수 있을 것으로 기대된다. Cellulose, one of the most abundant polymers on the planet, has excellent properties such as high strength, biodegradability and biocompatibility. However, cellulose does not melt, and because of the limited solubility of the solvent, it is fairly unreasonable for use in relative industries. Recently, since the development of ionic liquids, which can easily dissolve cellulose at room temperature, related research has been increasing enormously. Ionic liquids is one of the type of salts consisting of large cation molecules and relatively small anions. The principle of cellulose dissolution is that the anion capable of hydrogen bonding disrupts the cellulosic hydrogen bonding network and the cation penetrates into the relaxed network, thereby dissociating the structure of the cellulose. Despite a number of studies, there is a problem that the molar mass of the cellulose is decreased in the ionic liquid and the crystallinity after regeneration is not recovered, resulting in a decrease in strength. Therefore, this study aims to develop a cellulosic material having uniform nanostructure with fundamental understanding for depolymerization and recrystallization of cellulose in ionic liquid. First, the depolymerization and its rate were investigated after dissolving the cellulose using an ionic liquid having different anions. The depolymerization of cellulose in ionic liquid was found to be acidic the hydrolysis. The acid generated from the ionic liquid was found to be produced more as the basicity of the anion was larger. The constant of viscosity average molar mass was obtained by using cellulose having molar mass distribution by hydrolysis in ionic liquid. In addition, it was observed for the lyotropic liquid crystalline of cellulose which was not previously reported. Second, the mobility of hydrolyzed cellulose molecules in ionic liquids was determined and correlated with the recrystallization behavior. Cellulose has increased mobility when the molar mass was decreased, especially below the entanglement molar mass. The kinetic constants were calculated by analyzing the correlation between the molecular diffusion coefficient and recrystallization for investigation of improving crystallinity. Third, based on the hydrolysis behavior and mobility data, an ionic liquid was applied to the lignocellulosic biomass pretreatment process. Lignocellulose pretreatment aims to relax the structure and reduce the molar mass. As the solubility of the ionic liquid for cellulose increased, the crystallinity and removal efficiency of the non-cellulosic component increased significantly. This study has provided a reference for the selection of ionic liquids optimized for the structure of each lignocellulose. Fourth, cellulose nanoparticles with uniform size and high dispersity were prepared using cellulose molecules to be controlled molecular motility in ionic liquid. During the hydrolysis, the reaction of the cation of the ionic liquid to the reducing end of the cellulose was induced to form cellulose nanoparticles similar to micelle structure. Cellulose nanoparticles showed high dispersity due to surface cation. Fifth, process for separating rancid ingredients, such as free fatty acid and chlorophyll, of extra virgin olive oil is proposed using cellulose nanofiltration membrane functionalized by amine groups onto the surface. Similar to the principle of nanoparticle preparation, the cellulose moleculars with improved motility showed high porosity. The amine group was induced by substituting the tosyl group and ethylenediamine in turn. The free fatty acids and chlorophyll, known as the rancid ingredients of extra virgin olive oil, were separated by the amine groups and pore size of the membrane, respectively. Moreover, it was confirmed that only the acid component can be selectively removed without changing the composition of the extra virgin olive oil. In this study, celluloses were dissolved in ionic liquids under various conditions and their molecular properties were investigated. Based on the database, the technology for the preparation of nano-cellulose materials was established. Particularly, it is possible to open a new horizon for the cellulose process by developing a method to overcome the reduced molar mass and low crystallinity considered as be the limitation of conventional cellulose regenerated from ionic liquid.

The removal of anionic micropollutants by chemically modified biomass-based adsorbents

진세라 전남대학교 2024 국내석사

It is necessary to remove anionic micropollutants since they harm the aquatic environments. An adsorption technique may be utilized to remove these pollutants, however, to remove anionic adsorbents effectively, an adsorbent must be developed. The ability to remove micropollutants rapidly and extensively is crucial for the development of an adsorbent. Here, biomass-the most prevalent polymer materials in nature-such as cellulose and chitin were used to develop adsorbents that could eliminate anionic micropollutants. The biomass’s surface was chemically altered to increase the removal rate of anion micropollutants from the biomass. After the biomass rings open, amination of the biomass by applying aminoguanidine to the amine group was performed (Part I), and in Part II, polyethyleneimine (PEI) coating on biomass. The modification steps are as follow: In Part I, an adsorbent using amination was developed. For this purpose, cellulose and chitin were treated with sodium periodate (NaIO4) to produce dialdehyde groups by opening the ring structure, and subsequently, aminoguanidine was treated to address an amine group on the surface of biomass. Here, an experiment based on the ratio of NaIO4 to cellulose quantities was conducted to find the optimal treatment quantity of NaIO4. Then, to enhance the stability of the chemically prepared adsorbent, they were cross-linked with each non-treated biomass. Here, also to find a good mixing ratio between treated and untreated cellulose, a one-point experiment was evaluated by ratio. In Part II, a biomass-based adsorbent coated with PEI was developed. For this purpose, PEI polymer was coated on the biomass by using cross-linker, which are ethylene glycol diglycidyl ether (EGDE) for cellulose and epichlorohydrin (ECH) for chitin. To examine the adsorption properties of all four types of adsorbents, instrumental analyses (i.e., FT-IR and zeta potential analysis) were performed, and then kinetic and isotherm experiments were performed. In this adsorption study, twelve pharmaceutical-based micropollutants were tested. The results are summarized as follows: In Part I, the chemical reactions of the surface-modified cellulose (SMC) were confirmed by checking the FT-IR results. Dialdehyde groups generated by the biomass ring opening were checked at the peak of 1760 cm-1, but the peak is very weak. The amine group generated by combining aminoguanidine was confirmed by the generation of the peak C-N peak at 1059 cm-1. Moreover, it was found that the optimal amount of NaIO4 was 8.2 g per 10 g of cellulose, and the treated cellulose has the highest adsorption when mixed with untreated cellulose in a ratio of 1:4. In kinetic and isotherm studies of the SMC, it was shown that the adsorbent had very rapid adsorption and reached equilibrium within 10 mins. The adsorption capacities of the surface-modified cross-linked cellulose varied depending on the types of anions. Its adsorption capacity ranges from 53.42 to 853.63 μmol/g. In the meanwhile, there were no appreciable alterations in the FT-IR data of the adsorbent treated with chitin, and the adsorption capacity did not differ much from that of raw chitin. This could be because the acetyl group in chitin might prevent IO4- from accessing the two hydroxyl groups in chitin, which would prevent the reaction process from working as intended. In Part II, after the PEI coating on cellulose and chitin, FT-IR analysis was performed and confirmed that the coating reaction occurred successfully by checking the peaks of N-H and C-N. Kinetic results revealed that PEI-based adsorbents have rather slower adsorption rates. PEI-cellulose and PEI-chitin reached adsorption equilibrium 1 h and 30mins, respectively. Not surprisingly, isotherm results showed that the adsorption capacities were different depending on the types of anionic pollutants. PEI-cellulose showed from 20.37 to 1973.33 μmol/g, and PEI-chitin showed from 46.52 to 267.06 μmol/g.

Sustainable Fabrication of Bioderived and Biodegradable Cellulose Membranes for Organic Solvent Nanofiltration

HAIYEN 인천대학교 대학원 2024 국내박사

Membrane technology has become a dominant and indispensable tool in chemical engineering processes. Although it is popularly considered as a green process, the fabrication of the membrane itself needs to be significantly improved to be green and sustainable. So far, commercially available membranes have been prepared from fossil-based polymers and toxic solvents while generating enormous amounts of wastewater. Hence, there is an urgent requirement to come up with a protocol for sustainable membranes both bioderived and biodegradable. Meanwhile, biodegradable polymers have been developed to be used as an alternative for non- biodegradable polymer materials in a variety of applications, under this tendency, cellulose is a promising option as it is the most abundant biopolymer that is biodegradable upon disposal. However, it is technically challenging to process cellulose into membranes, as it is only soluble in unconventional solvents and extreme conditions. Under this work, we have developed an innovative methodology to fabricate solvent-resistant cellulose membranes, starting from a soluble precursor with a sacrificial acetate group. After successfully fabricated cellulose membrane with outstanding solvent resistance, the research will be extended to tackling the nanofiltration of cellulose membrane. The cellulose membrane on PET was use as the porous support to form thin film composite (TFC) membrane in order to improve it PPG rejection in organic solvent, in addition to traditional technique, a new protocol namely support-free interfacial polymerization (SFIP) was employed at the same time for preparing the TFC membrane with target to overcome some potential difficulty that may be caused by the conventional path. And finally, the PET support was replaced by Hanji support – Korean traditional paper that made of cellulosic material, the membrane was also used as a base support for TFC membrane using SFIP technique. Eventually, every component involved in the fabrication process, including the solvents and nonwoven supports, was bioderived and bio-recyclable (i.e., closed life-cycle), In summary, the cellulose membranes developed in this work show higher sustainability and competitive membrane performance compared to non-biodegradable conventional polymeric membrane such as fossil-based polyimide (PI) and polybenzimidazole (PBI).

Spinning and Properties of Cellulose Fibers using 1-Allyl-3-methylimidazolium chloride as a Solvent

Kim, Su-jin 금오공과대학교 대학원 2012 국내석사

Computational study to understand cellulose dissolution in Alkali/Urea aqueous solution

허유진 Graduate School, Yonsei University 2022 국내박사

Cellulose is of interest for use in various fields such as industry. However, due to the structural properties of cellulose, it is difficult to dissolve in general solvents. To overcome this limitation, many researchers have investigated several methods and solvents to better dissolve cellulose. Recently, it has become known that an alkali/urea aqueous solution can dissolve cellulose with a higher degree of polymerization than NaOH solution. Many experiments have been conducted to elucidate the mechanisms of cellulose dissolution in alkali/urea aqueous solution, but the precise understanding is still lacking, and further studies are needed for commercialization. The purpose of this thesis is to analyze the relationship between solvent molecules and cellulose and to provide theoretical insight into cellulose dissolution in an alkali/urea aqueous solution through computational chemistry based on previously reported experimental results. The three-dimensional reference interaction site model theory with the Kovalenko–Hirata closure (3D-RISM–KH) was used to study the interaction between cellulose and solvents in cellulose solvation in an alkali/urea aqueous solutions. First, the distribution of NaOH, urea, and water molecules around a cellulose chain was determined when a single cellulose chain was dissolved. This distribution indicated that water molecules approach cellulose in aqueous NaOH/urea solution, which suggests that the solvated structure is composed of cellulose as an inclusion in helical clusters of Na+, OH−, urea, and water and that these clusters are comprised of a repeated arrangement of OH− hydrate, water molecules, urea hydrate, and water molecules. Second, by adding Li+ and K+ as well as Na+ ions, the interaction between cellulose and alkali ions was calculated according to ion hydrate size. The most stable Li+ hydrate, which was the most stable due to Li+ having the highest charge density was the closest to the cellulose resulting in the most electrostatic interaction and possibly hydrogen bonding with the cellulose. Since Li+ hydrate is located close to cellulose and has the highest probability of existence, the solvent reorganization energy, which arises from the solvent clustering around cellulose, was the most negative in the LiOH/urea solution. Therefore, the calculation results obtained using 3D-RISM–KH and KBI explained the difference among the cellulose solubilities in the LiOH/urea, NaOH/urea, and KOH/urea aqueous solutions. Third, the process of dissolving a cellulose bundle chain by chain in NaOH/urea aqueous solution was briefly described using two or three cellulose chains. The dissolution free energy when dissolved as a single cellulose chain was calculated by selecting two types of dimer (offset stacked and parallel side by side) and trimer structures in the cellulose bundle, and the distribution of the solvent around the cellulose was confirmed. It was found that the dissolution free energy was lowest and a single chain from an offset stacked structure dissolved most easily because urea and NaOH molecules were more accessible together and interacted more strongly with the cellulose. In addition, as the number of chains increases, the interaction between the cellulose chains increases, and the solvent does not easily penetrate the cellulose, making it difficult to dissolve into a single cellulose chain. Research on the mechanism of cellulose dissolution with computational chemistry supports the experimental results, and an understanding of cellulose dissolution was presented by studying the interaction and energy between cellulose and solvents that were not seen in the experiment. Furthermore, it is to be hoped that this approach will contribute to the development of new and more diverse methods for cellulose dissolution. 셀룰로오스는 산업과 같은 다양한 분야에서 사용가능성이 크기 때문에 관심이 높다. 그러나 셀룰로오스의 구조적 특성으로 인해 일반적인 용매에서 용해되기 어렵다는 한계가 있다. 이러한 한계를 극복하기 위해 많은 연구자들이 여러 가지 방법으로 시도하고 셀룰로오스 용해에 도움이 되는 용매를 제안했다. 최근에 알칼리/요소 수용액이 수산화나트륨(NaOH) 수용액보다 높은 중합도로 셀룰로오스를 용해시킬 수 있다는 사실을 실험을 통해 밝혀냈다. 알칼리/요소 수용액에서 셀룰로오스가 용해되는 메커니즘을 밝히기 위해 많은 실험이 수행되었지만 아직 정확한 이해가 부족하고 상용화를 위해서는 추가적인 연구가 필요하다. 이 논문의 목적은 이전에 보고된 실험 결과를 기반으로 전산화학을 통해 알칼리/요소 수용액의 용매 분자와 셀룰로오스 사이의 관계를 분석하고 용해에 대한 이론적 통찰력을 알아보고자 한다. 용질 주변에 존재하는 용매 위치 분포를 3차원으로 얻기위해 통계 역학에 기반한 3차원 기준 상호작용 사이트 모델이론 (3D-RISM-KH)를 사용하여 용매화 에너지와 용매의 분포에 대한 계산을 하였다. 첫째, 단일 셀룰로오스 사슬이 용매화 될 때 셀룰로오스 사슬 주변에 존재하는 수산화나트륨 (NaOH), 요소 그리고 물 분자의 분포도를 확인하였으며, 수산화나트륨/요소 수용액에서 물 분자가 셀룰로오스에 가까이 접근한다는 결과를 토대로 나트륨이온 (Na+), 수산화이온(OH–), 요소 그리고 물이 나선형 클러스터를 형성하여 셀룰로오스를 용해함을 제안하였다. 둘째, 나트륨 이온 이외에 알칼리 금속 이온 인 리튬 이온, 칼륨 이온으로 확대함으로 이온 크기 및 수화물에 따른 셀룰로오스와의 상호작용을 계산하였다. 리튬 이온은 높은 전하 밀도 덕분에 가장 안정적인 리튬 수화물을 형성하고 셀룰로오스와 큰 정전기적 상호작용과 수소결합을 형성한다. 뿐만 아니라 수산화리튬/요소 용액에서 리튬 수산화물이 셀룰로오스와 가장 가까운 곳에서 존재하는 확률이 높으므로 용매 분자 사이에 발생하는 용매 재구성 에너지가 가장 낮아졌고, 이를 통해 수산화리튬/요소, 수산화나트륨/요소 그리고 수산화칼륨/요소 수용액에서 셀룰로오스의 용해도 차이를 계산하였다. 셋째, 수산화나트륨/요소 용매에 셀룰로오스 다발이 존재할 때 다발 내 사슬이 하나씩 빠져 나가면서 용해되는 과정을 셀룰로오스 두개 또는 세개의 사슬을 통해 간략하게 묘사하였다. 셀룰로오스 다발에서 존재 할 수 있는 이량체 구조 두가지와 삼량체 구조 한가지를 선택하여 단일 사슬로 용해 될 때 에너지를 계산함으로 셀룰로오스 구조에 따른 용해 관계성을 확인하였다. 셀룰로오스가 적층형으로 존재할 때 수산화나트륨/요소 용매 분자가 셀룰로오스에 쉽게 접근하게 되므로 단일 사슬로 용해되기에 용이하며, 셀룰로오스 사슬의 수가 늘어날수록 용해되기 어려움을 확인하였다. 전산 화학으로 셀룰로오스 용매화에 대한 메커니즘 연구는 실험 결과를 뒷받침할 수 있었으며, 실험에서 볼 수 없었던 용매와 셀룰로오스 사이의 상호작용과 에너지를 연구함으로 폭 넓은 셀룰로오스 용매화에 대한 이해를 제시하였다. 더 나아가서 이러한 접근은 셀룰로오스의 용매화에 새롭고 더 다양한 방법을 제시할 수 있을것으로 보여진다.