Impact of Chemical Pretreatment on Cellulose Nanofibrillation of Agricultural Byproducts

ZAHRA AUDREY 충북대학교 일반대학원 2026 국내박사

Agricultural byproducts represent a sustainable source of cellulose nanofibrils (CNF), yet their complex composition rich in pectin and cellulose poses challenges for efficient nanofibrillation. Carboxylates from pectin (galacturonic acid) and cellulose (glucuronic acid) coexist, but only cellulose-derived carboxylates significantly influence fibril formation. Understanding this distinction is critical for optimizing pretreatment strategies and producing high-quality CNF for advanced applications. Three substrates with varying pectin levels were bleached kraft pulp (no pectin), bleached corn cob (low pectin), and bleached banana peel *A thesis for the degree of Doctor in February 2026 (high pectin) were subjected to TEMPO-mediated oxidation followed by high-pressure homogenization. Carboxylate content and oxidation degree were analyzed using conductometric titration, FT-IR and proton nuclear magnetic resonance (¹H-NMR). Among these, ¹H-NMR provided precise quantification of monosaccharides and accurate calculation of the degree of oxidation (DO), distinguishing glucuronic acid and galacturonic acid. The characterization included fibril size, water retention value (WRV), and rheological properties to evaluate nanofibrillation efficiency. TEMPO-oxidation selectively converted glucose to glucuronic acid and galactose to galacturonic acid, but only glucuronic acid attached to cellulose improved nanofibrillation not galacturonic acid from pectin. Higher DO correlated with smaller fibril size, increased WRV, and enhanced gel strength. Kraft pulp achieves optimal fibrillation because oxidation focuses entirely on glucose, while pectin-containing substrates such as BC and BB fragment oxidation by converting galactose to galacturonic acid, thus yielding less optimal results. Application to red ginseng residue (RGR) validates these findings: 1H-NMR confirms an increase in uronic acid, FT-IR verifies the conversion of hydroxyls to carboxylates, and physical tests demonstrate WRVs of up to thousands of%, nanometer-scale fibrils, and stable viscoelastic gels, as well as a decrease in zeta potential. Successful nanofibrillation relies on carboxylates generated by cellulose oxidation, not natural pectin. TEMPO-mediated oxidation is crucial for producing high-quality CNF from agricultural byproducts, including red ginseng residue, which offer significant potential for cosmetics, hydrogels, and sustainable material applications.

셀룰로오스 나노섬유를 이용한 첨단 소재로의 기본특성 규명

전상진 서울시립대학교 일반대학원 2012 국내박사

셀룰로오스 나노섬유(CNF)는 고압균질기에의해 여러 번 통과되어 셀룰로오스 분말로부터 얻어진다. 본 연구에서는 매우 높은 인장 강도의 나노종이를 구현하고자 셀룰로오스 나노섬유를 사용하였다. 화학적 개질과 균질기 통과 횟수의 증가로 인해 나노종이의 인장탄성율과 강도가 증가하게 된다. 셀룰로오스 나노종이의 높은 인장물성은 표면적 증가, 결정성 향상, 균질기에 의한 수소결합 사이트, 셀룰로오스의 나노섬유간의 3차원적 네트워크 구조 그리고 인장시험 동안의 응력 분포의 향상에 기인한다. 매우 강한 인장성능을 갖는 셀룰로오스 나노필름은 감압여과장치를 이용하여 제조한다음, 1H, 1H, 2H, 2H-perfluoroctyltriethoxysilane (PFOTES)를 사용하여 용액 함침법에 의해 화학적으로 표면을 개질하여 제조한다. 나노필름의 인장 물성은 필름 표면에 자기조립단분자막 형성을 통해 향상되었다. PFOTES 농도의 증가와 함께 나노필름의 수분 접촉각(WCA)이 130.1° 까지 증가하는 소수성 특성을 보였다. 고착된 물방울 접촉각에서는 함침시간과 PFOTES 농도가 클수록 소수성 특성이 향상되어 줄어드는 WCA값의 기울기가 감소하는 것을 알 수 있다. 미결정 셀룰로오스(MCC)를 고압균질기 20000 psi 에서 0,1,2,5,10,15, 20회를 통과시켜 CNF를 얻는다. CNF가 강화된 hydroxypropyl cellulose (HPC)필름은 다양한 CNF의 함량에 따라 제조된다. 주사전자현미경을 통해서 균질화 공정에 의해 셀룰로오스 섬유가 나노크기와 높은 종횡비값을 갖는 나노섬유가 된 것을 알 수 있다. 균질기를 5에서 10회 통과하여 만들어진 CNF로 HPC 필름에 보강하여 HPC 필름의 인장 강도와 인장 탄성율을 보다 향상시켰다. HPC 필름의 열안정성에서는 MCC가 HPC보다 열적인 안정성이 우수하나 셀룰로오스 나노섬유의 첨가로 인한 영향은 없었다. 그러나 CNF와 높은 인장물성의 복합체를 균질화 공정의 적용을 통해 얻을 수 있었다. 본 연구에서는 아이소프로필 알코올과 물을 다양한 부피 비로 혼합하여 셀룰로오스 물질로부터 얻은 CNF를 이용한 나노구조의 분리막을 연구하였다. CNF 분리막의 다공성 구조와 기공 크기의 조절은 리튬이온 배터리에 적용되도록 하였다. 용매의 처리 효과를 통한 CNF 분리막과 상용화된 PE/PP/PE 분리막과의 cell 성능을 비교 실험하였다. CNF 분리막의 공기 투과도는 상용화된 분리막보다 낮은 성능을 보이고, 저항은 높았으며, 이온전도도 또한 낮았다. 전기적인 화학 안정성 면에서는 CNF 분리막이 상용화된 분리막보다 우수하였다. 저전압 특성평가에서는 CNF 분리막이 약간 높았다. 게다가 다양한 전류밀도에서의 방전 용량은 상용화된 분리막 보다 낮은 값을 보였다. 율방전율의 성능에서 CNF 분리막이 상용화된 분리막 보다 낮은 이온 전도도를 보임을 알 수있다. Cellulose nanofibrils (CNFs) were manufactured from cellulose powder (45 mm particle size) using a high pressure homogenizer with various pass numbers. In the present study, the CNFs were used to prepare nanopapers of extremely high tensile performance. Chemical modifications with the increased pass number through the homogenizer provided the dramatically increased tensile modulus and strength of the nanopapers. The high tensile properties are related to the increased surface area, improved crystallinity, hydrogen bonding sites by the homogenization, 3-dimension network structure between the cellulose nanofibrils, and improved stress distribution during the tensile test. Cellulose nanofilms with extremely high tensile performance were fabricated by a vacuum filtration method, and then chemically-modified with 1H, 1H, 2H, 2H-perfluoroctyltriethoxysilane (PFOTES) by a solution-immersion method. The tensile properties of the treated nanofilms were significantly increased by the self-assembled monolayer (SAM) formation on the surface. With the increase of the PFOTES concentration, the water contact angle (WCA) value of the nanofilms increased up to 130.1o, showing an excellent hydrophobic characteristic. From a sessile water droplet method, the slope of the decaying WCA values of the treated nanofilms decreased with increasing the immersion time and PFOTES concentration, indicating the improved hydrophobicity. CNFs were prepared from starting material microcrystalline cellulose (MCC) by an application of high pressure homogenizer at 20,000 psi and treatment consisting of 0, 1, 2, 5, 10, 15 and 20 passes. Hydroxypropyl cellulose (HPC) films reinforced with those cellulose nanofibrils were prepared at different filler loading levels. According to the morphology study by scanning electron microscope (SEM), the complete filbrillation of the bulk cellulose fibrils to nano scale and high aspect ratio was accomplished by the homogenization process. The HPC film reinforced with cellulose fibrils after the 5 to 10 passes through homogenizer improved significantly the tensile modulus and strength values for the HPC films. The thermal stability of HPC films is not affected by the addition of the cellulose nanofibrils, although MCC has the lower thermal stability than neat HPC. Therefore, the development of novel CNFs and composites with high strength can be achieved by an application of the homogenization process. In the present study, the nanostructured separators using CNFs (with diameter of 20-50 nm and lengths of hundreds of nanometer) were developed from cellulose materials by introducing isopropyl alcohol/water systems as a solvent at different volume ratios. A control of the porous structure and pore size of the CNF separators was conducted for an application in lithium ion batteries. The effects of the solvent treatment for the CNF films on the cell performance were investigated in comparison with a commercialized PP/PE/PP separator. The air permeability of the CNF separators is considerably lower than that of the PP/PE/PP separator, providing the higher resistance and lower conductivity of the CNF separators. The electrochemical stability of the separator from the CNFs was highly comparable to that of a commercialized PP/PE/PP separator. From the open circuit voltage drop of the CNF separator were slightly higher than that of PP/PE/PP separator. In addition, the discharge capacities of the CNF separators at various discharge current densities are slighly lower than those of the commercialized PP/PE/PP separator.

Fundamental properties of nanofibrillated cellulose in suspension and mat states

류재호 서울대학교 대학원 2013 국내박사

Nanofibrillated cellulose has great potential as a new material in cosmetics, automobiles, pharmaceutical and medical science, electrical devices, papermaking industry, and other applications. Nanofibrillated cellulose has a high aspect ratio and hydrophilic characteristics that leads to unique rheological properties and network forming ability from even low consistency. Nanofibrillated cellulose suspension may have several processes such as transferring, dewatering and drying to use as the shape of sheet or foam. Therefore, the network properties and mechanical properties of nanofibrillated cellulose need investigation and better understanding. To achieve these objectives, the effect of nanofibrillation process, solidification of nanofibrillated cellulose, and the addition of polyelectrolyte on network properties are investigated. Nanofibrillated cellulose is prepared by mechanical treatment using a grinder. The morphological change of the pulp fiber with mechanical treatment, water retention value, sedimentation concentration, and viscosity are evaluated through a number of passes. In this study, nanofibrillated cellulose can be prepared through 15 - 20 passes. However, it is important that the number of passes could be improved by changing the method of pretreatment or operation condition in the grinding process. Network properties are evaluated as the state of suspension and mat through dynamic and tensile measurements. The network strength of nanofibrillated cellulose increased rapidly as a function of solids content, and showed a power law relationship. This result is similar to pulp fiber suspension. Thus, the network forming phenomenon is similar, even though the aspect ratio of nanofibrillated cellulose is much higher and the dimension is much smaller than pulp fiber. However, network formation of nanofibrillated cellulose occurred at a lower consistency of 0.2%, and the network strength is 5 - 20 times higher than pulp fiber with solids content. Previous studies on network properties of nanofibrillated cellulose are limited to a low consistency. However, nanofibrillated cellulose of high solids content can be prepared using pressurized dewatering equipment, which is developed in this study. The yield stress had a power law relationship with the solids content over a wide range from 0.5% to 99% independent of the measurement method. Elastic modulus, tensile breaking stress and strain at break are evaluated. The elastic modulus and tensile breaking stress increased exponentially as a function of solids content. The wet strain at break of pulp fiber decreased gradually. However, the nanofibrillated cellulose increased until 50% of the solids content. When the degree of nanofibrillation is high, the strain at break increased more rapidly. Over 50% of the solids content, and strain at break decreased greatly. Therefore, the increase in the ability of maintaining the network structure even at higher deformation of nanofibrillated cellulose mat may be the reason. However, the solids content affected the ability of standing from deformation. Above 50% of the solids content, the rigidity increased significantly, which may be due the increase of hydrogen bonded areas. The network properties of nanofibrillated cellulose can be changed by the addition of polyelectrolytes. Different types of polyelectrolytes are applied in this study. In particular, polyethyleneimine with a branched structure showed an increase in yield stress with increasing addition amount. However, the yield stress of nanofibrillated celullose suspension with a linear structure polyelectrolyte such as poly-diallyldimethyl ammonium chloride and cationic polyacrylamide decreased above a certain addition amount. The structure type and molecular weight of polyelectrolyte influenced the viscosity and the reformation of the network structure of nanofibrillated cellulose. Furthermore, polyelectrolytes affected the dewatering ability even though nanofibrillated cellulose is highly associated with each other. The results indicate that polyelectrolyte can change the network structure of nanofibrillated cellulose. The tensile properties of nanofibrillated cellulose are evaluated through a wet and dry state. In particular, the tensile breaking stress increased more than three times in the case of wet mat as to the type of polyelectrolyte and the addition amount. In the case of branched polyelectrolyte, the rapid change of tensile breaking stress is observed at the isoelectric point. From this result, it was found that the modification of surface charge of nanofibrillated cellulose is an important factor that determines the network or mechanical properties of the nanofibrillated cellulose mat. In the case of dry mat, the effect of the polyelectrolyte is not shown. For this reason, the effect of the hydrogen bond may be much higher than the polyelectrolyte. This study provides a foundation for utilizing nanofibrillated cellulose. The network properties of nanofibrillated cellulose with solids content are traced and the possibility of controlling network properties by adding polyelectrolyte is investigated. It was expected that utilization of nanofibrillated cellulose for various fields of applications can increased. 나노피브릴화 셀룰로오스는 제지 산업을 포함하여 화장품, 자동차, 의/약학, 디스플레이용 필름, 전자 소재 등 다양한 분야에서 잠재적 신소재로서 인정 받고 있다. 종횡비가 크고 친수성을 가지는 표면 특성으로 인하여 독특한 유변학적 성질을 나타내며 저농도에서부터 네트워크를 형성한다. 현탁액상으로 제조되는 나노피브릴화 셀룰로오스를 시트 및 폼 형태로 활용하기 위해서는 이송, 탈수, 건조 등의 공정을 거쳐야 한다. 따라서 나노피브릴화 셀룰로오스의 탈수 특성, 네트워크 특성 및 기계적 물성에 대한 이해가 반드시 필요하다. 이를 위하여 본 연구에서는 나노피브릴화의 과정과 고형분 함량에 따른 네트워크 특성을 구명하고, 고분자전해질이 네트워크 특성에 미치는 영향을 구명하고자 하였다. 그라인더를 이용한 기계적 처리를 통하여 나노피브릴화 셀룰로오스를 제조하였다. 형태적 특성, 보수도, 침전 농도, 점도 분석을 통해 처리 횟수에 따른 나노피브릴화 정도를 평가하였다. 이를 통해 펄프 섬유로부터 나노피브릴화가 진행되는 정도를 판단할 수 있는 근거를 마련하였다. 본 연구에서는 15회-20회 처리로 나노피브릴화 셀룰로오스를 제조할 수 있는 것으로 나타났으나, 이는 전처리 조건 및 그라인더의 운전조건 변화 다양한 요인에 의해 더욱 개선될 수 있을 것으로 판단된다. 고형분 함량에 따른 나노피브릴화 셀룰로오스의 네트워크 특성은 현탁액상과 매트상으로 구분하여 평가하였다. 저농도 현탁액 수준에서의 유변특성 평가에 머무른 기존 연구의 한계를 벗어나 고농도 및 건조되기까지의 고형분 함량에 따른 네트워크 특성을 구명하기 위해 가압 탈수 장치를 이용한 압착 및 건조를 통해 고형분 함량을 조절하였다. 나노피브릴화 셀룰로오스는 현탁액 상태(0.5%-10%)로부터 매트 상태(10%-99%)에 이르기까지 네트워크 강도는 농도에 대한 하나의 멱함수 관계를 나타냈다. 이는 나노피브릴화 셀룰로오스가 펄프 섬유에 비해 매우 큰 종횡비를 가지고 그 크기가 매우 작은 수준임에도 불구하고 고형분 함량 증가에 따른 네트워크의 형성은 유사하게 진행됨을 의미하였다. 그러나 나노피브릴화 셀룰로오스는 펄프 섬유에 비해 2배 이상 더 낮은 농도인 0.2%에서부터 네트워크가 형성되었으며 형성된 네트워크 강도는 펄프 섬유에 비해 5-20배 더 크게 나타났다. 매트상의 나노피브릴화 셀룰로오스의 인장 특성을 평가한 결과, 탄성계수는 고형분 함량의 증가에 대해 지수 함수적인 경향을 따랐다. 인장 응력은 네트워크 강도와 마찬가지로 고형분 함량에 따라 멱함수적인 관계를 따르는 것으로 나타났다. 그러나 변형률은 고형분 함량 약 50%까지 증가하였다. 이는 나노피브릴화 셀룰로오스 매트의 경우 변형에 의해 파괴되는 시점까지 네트워크 구조가 유지되었기 때문으로 판단된다. 고형분 함량 약 50% 이상에서 변형률의 급격한 감소는 나노피브릴간의 수소 결합이 형성되면서 가소성이 감소했기 때문으로 판단된다. 또한 나노피브릴화가 많이 진행된 섬유일수록 변형률은 크게 나타났다. 펄프 섬유 매트의 변형률은 고형분 함량의 증가에 따라 지속적으로 감소하였다. 다양한 고분자전해질을 이용하여 나노피브릴화 셀룰로오스 현탁액의 네트워크 특성을 변화시킬 수 있었다. 특히 양이온성 분지상 고분자전해질인 polyethyleneimine은 양이온성 선형 고분자전해질 (polydiallyldimethyl ammonium chloride, cationic polyacrylamide)과는 다르게 투입량의 증가에 따라 현탁액의 네트워크 강도를 지속적으로 증가시켰다. 또한 고분자전해질의 전하 특성, 구조 및 분자량에 따라 점도와 이력 현상을 변화시킬 수 있었다. 고도로 네트워크를 이루고 있는 나노피브릴화 셀룰로오스 현탁액은 탈수성이 매우 낮지만, 고분자전해질의 투입에 의해 탈수성이 조절될 수 있었고 최대 3배까지 증가시킬 수 있었다. 매트의 인장 특성을 고분자전해질의 종류 및 투입량에 따라 습윤 매트와 건조 매트로 구분하여 평가하였다. 특히 습윤 매트의 경우 고분자전해질의 종류 및 투입량에 따라 인장 응력이 최대 325%까지 증가하였다. 특히 분지상 고분자전해질의 경우 등전점을 나타내는 투입량에서 인장 응력의 급격한 변화가 나타났고 이를 통해 표면 전하 특성을 변화시키는 것이 고고형분 함량에서의 네트워크 특성 및 기계적 물성을 좌우하는 중요한 요소로 판단되었다. 그러나 완전히 건조된 매트의 인장 응력은 건조 과정에서 수소 결합에 의한 영향이 고분자전해질에 비하여 훨씬 더 컸기 때문에 그 영향은 미미하였다. 본 연구를 통해 향후 나노피브릴화 셀룰로오스의 활용성을 높일 수 있는 기초를 마련하였다. 특히 물의 제거 과정에서 네트워크 특성이 변화하는 바를 연속적으로 추적하였고, 고분자전해질을 이용해 네트워크 특성 변화의 가능성을 살펴보았다. 본 연구는 향후 나노피브릴화 셀룰로오스의 활용성을 높일 수 있을 것으로 기대된다.

Cellulose Nanofibril-Based Functional Hydrogels for Drug Release Application : 셀룰로오스 나노피브릴을 이용한 약물방출용 기능성 수화젤

Masruchin, Nanang 경북대학교 대학원 2017 국내박사

셀룰로오스는 자연에서 가장 풍부한 천연고분자로 재생가능성, 친환경성 및 인체 친화성으로 인해 다양한 기능성재료를 만드는 많은 관심을 받고 있다. 더욱이 최근 나노기술과 나노재료의 발달은 다양한 나노세룰로오스를 이용에 많은 관심을 일으켰다. 본 연구의 목적은 셀룰로오스 C6의 수산기를 카르복실기로 전환시키는 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO) 산화반응으로 단리한 셀룰로오스 나노 피브릴(CNF: cellulose nanofibril)을 이용하여 약물 방출용 기능성 수화젤(hydrogel)을 개발하고자 하는 것이다. 본 연구의 목적을 달성하고자 본 연구는 네 부분, 즉 CNF의 단리, CNF 특성분석, CNF기반 수화젤 제조 및 특성분석, 그리고 기능성 CNF/고분자 복합수화젤 제조를 중점적으로 연구하였다. 첫 번째 부분의 연구는 셀룰로오스 원료종류, 초음파처리 시간, 및 산화제인 NaCl의 첨가량에 따라TEMO산화반응 후CNF 또는 셀룰로오스 마이크로 피브릴(CMF: cellulose micro fibril) 표면의 카르복실기 특성을 분석하였다. 전도도 적정(conduct metric titration)과 적외선 분광기(FT-IR)를 이용하여 cellulose의 표면 carboxylate 함량을 측정하였다. 산화반응 후 초음파 처리는 표면 carboxylate 함량을 증가시켰다. 또한 셀룰로오스의 원료 종류에 따라 표면 carboxylate 함량이 다르게 나타났다. 또 산화제 첨가량을 조절하면 CNF와CMF의 표면 carboxylate 함량을 조절할 수 있는 것으로 나타났다. 따라서 적절한 원료 선택과 산화제 투입량으로 CNF 또는 CMF의 표면 carboxylate 함량을 제어 할 수 있었다. 두 번째 부분의 연구는 CNF 또는 CMF의 현탁액에 양이온 즉 Al3+, Ca2+ 및H+을 첨가하여 셀룰로오스표면의 음이온성 표면 carboxylate와 이온성 가교결합을 유도하여 수화젤인 nanogel과 microgel을 제조하고자 하였다. 먼저 본 연구는 Al3+를 이용하여 microgel를 제조하는데 초음파 처리시간이 미치는 영향을 연구하였다. 초음파 처리 시간은 CMF 현탁액의CNF 함량에 영향을 미쳤으며 이는 수화젤의 내부 구조를 영향을 미쳤다. 긴 초음파 처리시간은 수화젤의 저장탄성계수(G’), 압축강도, 표면적을 증가시켰다. 이 같은 결과는 수화젤의 내부구조는 수화제의 팽윤 및 약물방출 거동에 큰 영향을 미치며 초음파 처리로 내부구조를 제어 할 수 있다는 것을 보여주었다. 또한 삼가(tri-valent) 양이온으로 만든 수화젤이 이가(di-valent) 및 수소이온(H+)으로 제조한 수화제로 보다 더 강한 피브릴간 또는 피브릴 내 상호작용을 나타냈다. 두 종류의 수화젤의 기계적 물성과 팽윤거동은 약물방출 과 반대의 상관관계를 나타내었다. 단단하고 기공이 많은 모든 수화젤은 낮은 약물방출을 나타내었다. Microgel과 nanogel의 약물방출 거동은 Higuchi model에 가장 잘 적합하였다. 이들 연구결과는 수화젤의 구조-물성 간의 밀접한 관련이 있다는 것을 나타내었다. 즉 수화젤의 내부구조는 약물방출에 많은 영향을 주었으며 내부구조 제어를 통한 약물방출 거동을 제어할 수 있음을 시사하였다. 세 번째 부분의 연구는 다른 수준의 표면전하를 갖는 CNF와 저임계용액온도(LCST: low critical solution temperature)에서 온도반응성 고분자인 poly(N-isoproylacrylamide) (PNIPAAm)를 이용하여 온도에 반응하는 수화젤를 개발하기 위한 실험을 실시하였다. 순수한 PNIPAAm와 CNF/PNIAAm 복합수화젤은 CNF와 단량체를 혼합하여 용기 내에서 합성하였다. Carboxylate 함량이 증가할수록, CNF 현탁액의 전단점도와 전단응력이 감소하는 반면, 저장탄성계수 및 손실탄성계수는 유동학적 측정에서 각 주파수에 더 의존하게 된다. 결과적으로, CNF/PNIPAAm 복합수화젤의 압축강도는 보다 낮은 CNF 표면전하 수준에서 더 커지며, 이것은 그들의 긴밀한 상호 가교결합에 기인할 수 있다. CNF 표면전하 수준은 CNF/PNIPAAm 수화젤의 특성에 큰 영향을 미치며, 이는 CNF 표면 전하의 적절한 수준의 선택이 온도반응성 수화젤에 중요하다는 것을 나타낸다. 이 연구의 마지막 부분에서는 pH와 온도에 반응하는 CNF/PNIPAAm 복합수화젤을 제조하고자 PNIPAAm의 2가지 다른 중합온도 즉, -20℃ 및 11℃와 CNF농도의 영향을 연구하였다. CNF/PNIPAAm 복합수화젤은 11℃와 낮은 CNF농도(8% 이하)에서 제조되었으며, CNF의 첨가 최소량이 10% 일 떄 나타나는 표면층(skin layer) 형성효과에 의해 기포가 형성되었다. CNF/PNIPAAm 복합수화젤은 순수한 PNIPAAm 수화젤보다 더 큰 팽윤을 나타내었고, -20℃에서 제조된 복합수화젤의 팽윤비율이 11℃에서 제조된 것보다 우수했다. CNF 첨가와 동결 중합 온도 사이의 상승 효과는 빠른 수분보유(water retention)값으로 높은 압축강도를 나타냈다. CNF/PNIPAAm 복합수화젤의 팽창거동 및 박동 온도거동은 pH와 온도에 대해 이중 반응성을 보였다. 그러나 11℃에서 제조된 수화젤은 박동 pH에 대하여 매우 낮은 반응성을 보였다. 예상한 바와 같이 보다 높은 표면 전하의 레벨의 CNF로 제조된 복합수화젤은 낮은 표면 전하를 사용하여 제조된 것보다 더 큰 pH반응성을 나타냈다. -20℃에서 준비된 복합수화젤에서 미세 기공 구조로 인하여 온도에 따른 약물모델로서의 methylene blue 의 더 큰 방출이 발견되었다. 그러나 pH에 대한 반응에서는 반대였다. 전반적으로, 이 연구는 TEMPO-산화반응에 의해 분리된 carboxylated CNF가 순수 CNF기반 수화젤 및 CNF/PNIPAAm 복합수화젤을 포함하여 CNF 기반 기능성 수화젤을 약물 방출 용도로 성공적으로 개발한다는 것을 밝혀냈다. 그리고 이 연구는 CNF의 특성과 수화젤의 제조방법이 수화젤 네트워크 매개 변수, 즉 내부 구조의 소형화, 상호 작용의 정도, 기공 크기 및 생성된 수화젤의 특성, 약물 방출 거동, 압축 강도에 큰 영향을 준다는 것을 발견했다. Cellulose is the most abundant natural polymer, and attracting a great amount of attention in developing numerous cellulose-based functional materials because it is renewable, biodegradable, environmentally friendly and biocompatible in a broad range of applications. Furthermore, recent advances in nanotechnologies and nanomaterials also increasingly brought a lot of attention on the utilization of a variety of nanocellulose materials. Thus, the goal of this study was to develop functional hydrogels for drug release application, using cellulose nanofibril (CNF) isolated by 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated oxidation which had converted the primary hydroxyl groups at C6 to carboxylate groups. In order to achieve the goal, this study focused on four main parts, including the isolation and characterization of CNFs, CNF-based hydrogels, and functional CNF/polymer composite hydrogels. In the first part of this research, different carboxyl group contents on the surface of CNFs or cellulose microfibrils (CMFs) after TEMPO-oxidation were characterized, depending on the source of cellulose raw materials, sonication treatments, and the addition level of NaClO as an oxidant. Both conductometric titration and infrared spectroscopy were employed to quantify the amount of carboxyl content. It was found that a post sonication treatment of the oxidized cellulose had no influence on the level of the surface carboxylate content of CMFs. However, the carboxylate content of CNF increased after the sonication treatment. The results also showed that the carboxyl content of CNFs was different from those of their corresponding bulk oxidized cellulose. The carboxyl content of CNFs or CMFs could be optimized by controlling the addition level of NaClO for the oxidation and by selecting the source of cellulose raw materials. These findings revealed ways of controlling the level of carboxylate groups on CNFs for further functionalization of CNFs. The second part of this study emphasized on the development of CNF- or CMF-based hydrogels by inducing ionic cross-linking with cationic ions such as Al3+, Ca2+ and H+. Both CNFs and CMFs were used to prepare nanogels and microgels, respectively. In particular, this study investigated the effect of sonication time to characteristics of microgels that were prepared by combing CMFs with the addition of Al3+. Sonication treatment time influenced the proportion of CNFs in the CMF suspension, which in turn influenced the internal structure of the obtained cation rendered-hydrogels. A longer sonication time resulted in an increase of the storage modulus, compression strength, and surface area of the microgels. This result suggests that the internal structure of the hydrogel has a significant impact on the swelling and drug release behavior of the hydrogels, and the internal structure of the microgels be controlled by the sonication time to manipulate the release of drugs from the microgels. It was found that the tri-valent ion showed stronger intra- and inter-fibrillar interactions than those of di-valent or mono-valent ions. Freeze-dried hydrogels were composed of interconnected porous networks. Mechanical properties and swelling ratios of both hydrogels were inversely proportional to their cumulative drug release profiles. All hydrogels with compact and highly porous structures resulted in slow and low drug release. Drug release kinetics of microgels and nanogels were best fitted to the Higuchi model. These results of this study demonstrate that there is close structure-property relationships for all hydrogels, and suggest that characteristics and internal structure of hydrogel had a great impact on its properties and drug-release behavior. The third part of this study was conducted to develop thermally responsive hydrogels using CNF with different levels of the surface charge and poly (N-isoproylacrylamide) (PNIPAAm), a thermally responsive polymer at the low critical solution temperature (LCST). Pure PNIPAAm and CNF/PNIAAm composite hydrogels were prepared in situ polymerization and by incorporating CNF into the polymer. As the carboxyl content increased, the shear viscosity and shear stress of the CNF suspension decreased, while the storage and loss modulus become more dependent on the angular frequency in the rheological measurements. Consequently, the compression strength of the CNF/PNIPAAm composite hydrogels was greater at lower CNF surface charge level, which could be ascribed to their tight interconnections structure. It was found that the CNF surface charge level had a great impact on the characteristics of the CNF/PNIPAAm hydrogels, indicating that the selection of a proper level of CNF surface charge was important for temperature responsive hydrogels. In the last part of this study, CNF/PNIPAAm composite hydrogels responsive to pH and temperature were developed by combining CNFs with thermal responsive PNIPAAm at two different temperatures for in situ polymerization, i.e., -20 oC and 11 oC as well as at different CNF addition levels. The CNF/PNIPAAm composite hydrogels prepared at 11 oC and lower CNF levels (below 8%) showed the formation of bubbles by a skin layer effect, indicating that the minimum amount of CNF loading was 10% w/w. CNF/PNIPAAm composite hydrogels displayed greater swelling than those of pure PNIPAAm hydrogels, and the swelling ratio for the composite hydrogels prepared at 11 oC was superior compared to those prepared at -20 oC. Synergistic effect between CNF loading and freezing polymerization temperature resulted in high compression strength with a fast water retention value. Swelling behavior and pulsatile temperature behavior of CNF/PNIPAAm composite hydrogels showed dual responsiveness to pH and temperature. However, those hydrogels prepared at 11 oC had a very low responsiveness to the pulsatile pH. As expected, the composite hydrogels prepared with CNFs of higher surface charge level resulted in greater pH responsiveness than those prepared with low surface charge. A greater release of methylene blue as a model drug in the response to temperature was found at the composite hydrogels prepared at -20 oC, owing to their micro porous structures. However, it was opposite in the response to pH. Overall, this study revealed that the carboxylated CNFs isolated by TEMPO-mediated oxidation were successfully used to develop CNF-based functional hydrogels, including pure CNF-based hydrogels and CNF/PNIPAAm composite hydrogels for drug release application. And this study also found that characteristics of CNFs and preparation methods of hydrogels had a great impact to properties and drug release behavior of the resultant hydrogels in term of the hydrogel network parameters such as compact internal structure, the degree of interaction, pore size, and compression strength

Streamlined Synthesis of Sulfated Cellulose Nanofibrils Using Chlorosulfonic Acid and Their Applications in Conducting Materials

Pingrey, Benjamin Earl University of California, Davis ProQuest Dissertat 2023 해외박사(DDOD)

Cellulose nanofibrils (CNF) are one-dimensional semicrystalline nanomaterials liberated from native cellulose through chemical or mechanical processes, or some combination thereof. Individually, they possess high mechanical strength, with estimated tensile strength and Young's modulus as high as 7.5 GPa and 150 GPa, respectively. They also serve as a diverse platform for further chemical modification due to their abundant surface hydroxyl groups, which can be functionalized through a wide array of chemical reactions. Isolating CNF from cellulose can be an energy intensive process and chemical pretreatments are often utilized to reduce the required energy expenditure.Herein a streamlined scheme for producing sulfated cellulose nanofibrils (SCNF) is proposed and optimized, utilizing chlorosulfonic acid to simultaneously functionalize cellulose while also acting as a pretreatment to facilitate defibrillation into nanofibrils. Through careful manipulation of reaction conditions, SCNF are produced with a wide range of sulfation levels without destroying the underlying cellulose 1β crystalline structure. Utilizing wet-spinning, SCNF was spun into fibers with a tensile strength and Young's modulus of 675 MPa and 26 GPa, respectively. It was also demonstrated that SCNF could serve as host polyelectrolytes for the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) to create dispersible polyelectrolyte complexes, with shear-mediated alignment of nanofibrils allowing for the creation of fibers with a conductivity of more than 6000 S/cm. Additionally, SCNF were able to aid in aqueous exfoliation of graphite flakes and dispersion of graphene, producing exclusively monolayers and bilayers.

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.

(The) role of cellulose nanofibrils in structure formation and drying stress development of pigment coating layer

오규덕 서울대학교 대학원 2017 국내박사

Coating structure is one of the important factors determining pigment coated paper quality including printability. The structure is influenced by the type or composition of pigment, binder, and additives. Even though the pigment and binder determine the structure of the coating layer most significantly, a small amount of additives can also influence the structure. In this study, cellulose nanofibrils (CNF) were used as an additive of the coating color. CNF was selected as an additive because it is a potential material to thicken the coating color. The effect of CNF on the coating color and coating layer was suggested compared to carboxymethyl cellulose (CMC) that has been used as a traditional thickener. Initially, the rheological properties of the coating color were investigated to understand the effect of CNF on the microstructure of the coating color. Drying kinetics was evaluated using the multispeckle-diffusing wave spectroscopy (MS-DWS) technique to suggest structure formation in the coating layer. Stress development was evaluated to investigate the effect of CNF on shrinkage of the coating layer. In addition, surface characteristics of the coating containing CNF were evaluated. Finally, CNF was applied to coated paper to investigate the change of in the optical, structural, and absorption properties of the coated paper. CNF coating showed lower elastic behavior than CMC coating because there was no interaction between the particles in the coating color containing CNF. The microstructure of the coating color influenced the drying process. The particles in the CNF coating color moved freely because CNF did not form a structural network and increase the viscosity of the aqueous phase. The movement of the coating components, however, was greatly restricted by CMC because it created a network structure and increased the viscosity of the aqueous phase. CNF made the coating layer porous in a different manner than CMC. The voluminous characteristics of CNF made the coating layer porous. CNF coating showed different stress development behavior compared to CMC. The drying stress of the coating layer increased with the addition of CMC because of the loosely packed structure of CMC coating, which increased the total shrinkage of the coating layer after the solidification point and the shrinkage of the precipitated CMC during drying. The stress of the CNF coating, however, was lower than that of the CMC coating because of the less structured CNF coating and the low shrinkage characteristics of cellulose. The CNF coating showed much lower gloss than the CMC coating due to its water absorbing characteristics. The swollen CNF caused a rough surface because the shrinkage of CNF proceeded until the end of the drying process. The CNF coating gave lower coated paper gloss than that of the CMC coating due to non-uniform shrinkage, which came from the gel-like structure of CNF. To improve the gloss of the coated paper, the coated paper was made with a low coat weight and under high shear rate. The gloss and roughness of the coated paper were similar for the CNF and CMC coatings. In addition, the surface defects in the coated paper diminished. The CNF coating greatly improved ink absorption compared to CMC coating in the ink absorption test and the modified Vandercook press test by forming a porous coating layer due to its low shrinkage characteristics. The small amount of CNF addition can promote the absorption rate and uniformity of coated paper without changing the material properties.

전자선 전처리를 이용한 셀룰로오스 나노섬유 제조기술 개발

김은혜 경상대학교 대학원 2017 국내석사

Cellulose exists the most abundant renewable polymer resource available. The production of nano-scale cellulose fibers has gained high strength, high surface area and modulus. Nanocellulose be isolated from nature through chemical or mechanical treatments, as cellulose nanofibril, cellulose nanocrystal or bacterial cellulose. In recent years the nanocellulose has become an important topic. Thus, it can be used nanocomposite materials, bio composite, paper filler. Many studies have reported that cellulose nanofibril show high potential for use in many industries, but this material has been considered too costly for commercialization. An effective treatment is therefore needed to reduce the production costs of CNFs. In this study, we attempted to evaluate the possibilities of energy savings by applying electron beam irradiation. Electron beam irradiation is also an eco-friendly treatment compared to other physical and chemical treatments. Softwood–Bleached Kraft Pulp and Hardwood-Bleached Kraft Pulp were irradiated with electron beams at 50 and 100 kGy, it was beaten in a laboratory beater and then refining properties were analyzed. Also the physical properties of their fiber handsheet were measured. Increased in the irradiation dose of the electron beam and in the beating time decreased the freeness and fiber length of the pulps. The strength of the handsheets decreased at 50 kGy. So the irradiation dose must be controlled under 50 kGy to minimize the loss of paper strength. After Sw-BKP and Hw-BKP were irradiated with electron beam at 50 kGy, refining and subsequent grinding. The physical properties as the viscosity, particle size and crystallinity of the cellulose nanofibril were measured. Physical properties with EB-CNFs and CNFs were no significant difference. So we confirmed the possibility of electron beam irradiation as a new pretreatment for the manufacture of CNFs.

Surface-engineered Nanofiber with Bioactive substance for Biomedical application

jiunshin 강원대학교 대학원 2019 국내석사

생체 환경 모방 구조를 가진 나노구조물은 표면적 대비 부피비가 높은 특징을 가지고 있으며 다양한 형태로 바이오 의료 분야에서 사용되고 있다. 나노 디바이스의 표면 개질은 재료의 특성 및 세포 친화성에 영향을 미치며, 세포는 나노 디바이스의 표면 개질과 형태에 의해 세포의 성장률, 분화률에 영향을 미친다. 여기에, 나노 디바이스의 다양한 표면 개질은 물리적, 화학적 방법을 통해 이루어진다. Silver-nanoparticle을 표면에 부착한 셀룰로오스 나노섬유 (CNFs)와 알지네이트를 사용하여 항균성 하이드로겔을 제조했습니다. CNF의 표면 수산기는 (2,2,6,6-tetramethylpiperidin-1-yl) oxidanyl (TEMPO)를 사용하여 카르복실기 그룹으로 산화되었고 (TCNF), 은이온의 표면흡착을 위해 질산은 용액으로 처리하였다. CNF에 흡착된 은이온을 은나노입자로 환원하기 위해 포름알데하이드를 처리하였다. 전자 현미경, X-선 회절 및 분광 분석을 통해 CNF 표면보다 TCNF 표면에 더 많은 은나노입자가 고정화되었음을 확인할 수 있었다. 알지네이트에 은나노입자 고정된 TCNF를 섞어 하이드로겔로 만들어 (AL/AgNP@TCNF), 겔로부터 은 이온을 천천히 7 일 동안 방출된 것을 확인하였다. Ag/AgNP@TCNF 은 AL/Ag+@TCNF와 비교할만한 항균 활성을 보였으나, 동물 세포에 대한 세포 독성이 유의하게 낮았다. 따라서 항균성 하이드로겔은 피부 손상을 최소화하면서 세균 감염을 방지하기 위해 다양한 피부 표면에 잠재적으로 적용될 수 있다. 두 번째로, 줄기 세포와 나노섬유의 자발적인 조립은 젤라틴으로 레이어링 코팅된 nanofibrils과 조립된 세포시트의 피부회복을 확인하였다. 분쇄 및 가수 분해에 의해 전기 방사 된 나노섬유를 단편화 한 후, 양이온, 음이온 젤라틴 코팅을 교대로 5 번 반복하여 표면을 개질하여 나노섬유 상에 젤라틴을 층별로 코팅 하였다. 코팅의 안정성은 water swelling ratio, surface-charge analysis, X-ray photoelectron spectroscopy으로 확인되었다. 지방-유래 줄기세포 (ADSC)와 젤라틴이 코팅된 나노섬유는 4일 만에 세포 시트가 자기 조립되었고 세포확산은 높은 젤라틴 함량을 가진 그룹이 더 두드러지게 나타났으며 생존력은 모든 그룹에서 유사했다. 생쥐의 등쪽 상처에 대한 연구에서 젤라틴 함량이 높은 세포 시트는 낮은 젤라틴 함량 및 무 세포 나노섬유가있는 동물 시트에 비해 우수한 피부 재생 효능을 보였다. Nanoscale structures with mimicking the bio-environments have features including high surface area-to-volume ratio, it is apply to bio-medical device in various forms. The surface modification of nanodevice affects the material property and cellular affinity. The interaction between cells and nanodevice are depended by the surface decoration and surface morphology of the nanodevice, changing the nanodevice is modified to promote or inhibit of cell growth. Here, the variously surface-decoration of the nanodevies is modified by physical or chemical modification to develop various biomedical application. A free-standing, antibacterial hydrogel was fabricated using silver-nanoparticle-immobilized cellulose nanofibers (CNFs) and alginate. Surface hydroxyl groups of CNFs were oxidized to carboxylate groups using (2,2,6,6-tetramethylpiperidin-1-yl)oxidanyl (TCNF), followed by the treatment with silver nitrate solution for surface adsorption of silver ions. In situ reduction of silver ions to produce silver nanoparticles was performed for the silver adsorbed CNFs. Electron microscopy, X-ray diffraction, and spectroscopic analysis revealed that higher amounts of silver nanoparticles were immobilized on the surface of TCNF than on the surface of native CNF. Silver-nanoparticle immobilized TCNF was embedded in alginate gels and silver ions from the matrix were slowly released for 7 days. Silver-nanoparticle-loaded alginate gels showed comparable antibacterial activity to silver-ions-loaded alginate gels, although the former showed a significantly lower cytotoxicity against animal cells. Thus, the antibacterial gels can potentially be applied to various skin surfaces to prevent bacterial infection while minimizing skin damage. Secondly, Spontaneous assembly of stem cells and nanofibrils was accomplished with surface-engineered nanofibrils with layer-by-layer coating of gelatin and skin recovery with the cell sheets was confirmed. After fragmenting electrospun nanofibers by milling and hydrolysis, the surface was engineered with five alternating cycles of cationic and anionic gelatin coating to obtain optimized layer-by-layer assembly of gelatin on nanofibrils. Stable layering on nanofibrils were confirmed by water swelling ratio, surface-charge analysis, and X-ray photoelectron spectroscopy. Adipose-derived stem cell (ADSC) and gelatin-layered nanofibrils were self-assembled to cell sheets in 4 days and cell spreading showed more prominent in those with higher gelatin contents while the viabilities were similar in all groups. In vivo study on mouse dorsal wounds revealed that cell sheets with high gelatin contents showed excellent skin recovery efficacy in comparison to those with low gelatin contents and acellular nanofibrils. As a result, the surface-engineered of the nanofibers can potentially be applied to wound healing patch.

Preparation and Application of Precipitated Calcium Carbonate-Cellulose Nanofibril Composite Filler in Papermaking

He, Ming Kangwon National University 2017 국내박사

Nanotechnology is an emerging area of science and technology that will revolutionize materials use in the 21st century. Recently, as a cellulosic nanomaterial, cellulose nanofibril (CNF) have attracted much attention and shown enormous potential in the field of pulp and paper technology. Mechanical treatment has been the primary disintegration technique used to produce CNFs. The decreased size of fibers from micro-scale to nano-scale in width by mechanical force offers a new potential with unique properties such as high mechanical strength, large specific surface area, high aspect ratio, barrier properties, biodegradability and biocompatibility. Moreover, CNFs form a network already in very dilute aqueous suspensions. Therefore, it seems that they can flocculate small particles such as fines and fillers effectively. In this study, the effect of CNFs on the flocculation of precipitated calcium carbonate (PCC) was elucidated. The PCC aggregation was analyzed using particle size measurement, photometric dispersion analysis (PDA), and scanning electron microscopy (SEM). The result showed that CNFs can be used to flocculate particles such as calcium carbonate fillers and the CNFs functioned as bridges between the two PCC particles. Although the synthetic polymers are much more effective than the CNFs because of their versatile tailorability, a noticeable reflocculation capability was observed in one- and two-component systems that consisted of CNFs. The presence of cationic starch could strengthen and induce formation of CNF/starch bridges between filler particles. A noticeable reflocculation capability was also observed in one- and two-component systems that consisted of CNFs. Many researchers have reported to use CNFs as strength additives in paper and paperboard products. With the ability to flocculate filler of CNFs, a concept of composite filler was developed by using CNF, PCC and cationic starch (C-starch) in this work. Moreover, cellulose nanofibrils were utilized in two different ways: a PCC-CNF composite filler and a papermaking additive in sheet forming. Almost 90% filler retention was achieved with the use of PCC-CNF composite fillers. The paper filled with the composite fillers had much higher bursting and tensile strengths than conventional PCC loading. It was also found that the paper prepared with PCC-CNF composite fillers became denser with increasing the filler content of paper. Even with increased density, composite fillers containing handsheet showed better light scattering than conventional PCC loaded handsheet. However, CNFs can form a cross-linked network with a pseudoplastic behavior, even in very dilute aqueous suspensions duo to their large specific surface area and high aspect ratio. They are expected to affect sheet dewatering properties negatively due to high water retention capacity. The effect of CNF on the drainage properties of pulp furnish and on the strength properties of paper sheets were also studied. An undesirable increase in drainage time was observed which might be due to that the pre-flocculated PCC-CNF composite filler get a higher retention of CNF in fiber web than CNF used as a papermaking additive. But a favorable effect on solid content after press was observed. This may be considered as that the water holding ability of the CNF was outweighed by the non-swelling PCC at proper dosage of CNF. Although CNFs will cause dewatering difficulties in papermaking applications, it is expected that these difficulties will be overcome by optimal selection of CNF adding method and filler content which will not influence the pressability of the sheet in the wet end.