Preparation and mechanism analysis of morphology-controlled cellulose nanocrystals via compound enzymatic hydrolysis of eucalyptus pulp

First, making from eucalyptus cellulose fiber, the influences of different compound enzymolysis conditions on the morphology of cellulose nanocrystals (CNCs) were studied. Under the actions of the compound enzyme composed of cellulase and xylanase with the concentration ratio of 9:1, total enzyme concentrations of 10 and 500 U mL⁻¹ and the hydrolysis time of 12 and 5 h, the rod-like CNCs (length 600 nm, width 30 nm) and the spherical CNCs (40 nm) were obtained, respectively. Subsequently, the crystallinities, chemical structures, and thermal stabilities of the rod-like and spherical CNCs revealed that, the CNCs structures were still similar to those of the eucalyptus cellulose fiber, the thermal decomposition temperatures of the rod-like and spherical CNCs (345, 343 °C) were a little lower than that of the eucalyptus cellulose fiber (364 °C). Lastly, the control mechanism of CNC morphology by the compound enzymatic hydrolysis was also discussed. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48407.     

Mercerization of cellulose: 2. The morphology of Mercerized cotton cellulose

Mercerized cotton cellulose has been shown to consist of flexible microfibrils which are similar in dimension to the stiff microfibrils of native cotton. The Mercerized cotton microfibrils are smooth and completely different in appearance from the shish-kebab structures observed by Chanzy and Roche for Mercerized Valonia cellulose. Ultrasonic treatment shows that the Mercerized cotton microfibrils consist of an interconnected fibrous network. The fibrous units comprising this network have widths in the range 20 to 100 Å and appear to be very flexible, in contrast to the stiff 35 Å wide elementary fibrils found in native cotton. A possible mechanism for the Mercerization of cotton is discussed in terms of the rearrangement of sheets of cellulose chains, resulting in crystallites of extended antiparallel chains.     

Molecular Dynamics of Synthetic Flagelliform Silk Fiber Assembly

In order to better understand the relationship between flagelliform (Flag) spider silk molecular structural organization and the mechanisms of fiber assembly, the Nephilengys cruentata Flag spidroin analogue rNcFlag2222 is designed and produced. The recombinant proteins are composed by the elastic repetitive glycine-rich motifs (GPGGX/GGX) and the spacer region, rich in hydrophilic charged amino acids, present at the native silk spidroin. Using different approaches for nanomolecular protein analysis, the structural data of rNcFlag2222 recombinant proteins are compared in their fibrillar and fully solvated states. Based on the results, it is possible to identify the molecular structural dynamics of NcFlag2222 prior to and after fiber formation. Overall rNcFlag2222 shows a mixture of semiflexible and rigid conformations, characterized mostly by the presence of polyproline type II helix (PPII), β-turn, and β-sheet. These results agree with previous studies and bring insights about the molecular mechanisms that might drive Flag silk fibers assembly and elastomeric behavior.     

NMMO溶剂法纤维素海绵的制备及性能研究——成孔剂用量的影响

以N-甲基吗啉-N-氧化物(NMMO)为溶剂、以棉浆粕为原料、以无水硫酸钠为成孔剂制备了纤维素海绵,探讨了成孔剂用量对纤维素海绵形态结构、孔隙率、吸水性、保湿性和拉伸强度的影响。结果表明,随着成孔剂用量的提高,所制得的纤维素海绵平均孔径变大,孔壁变薄,通孔增多,但成孔剂用量过多时,海绵孔壁会产生轻微断裂。此外,随着成孔剂用量的提高,海绵的孔隙率及吸水保湿性提高,拉伸强度则有所下降,综合考虑海绵的性能及成型过程的难易程度等因素,当成孔剂用量为纤维素溶液的3倍为宜,所得纤维素海绵的孔隙结构均匀饱满、综合性能较高。     

离子液体法纤维素海绵的制备——成孔剂种类的影响

以离子液体1-丁基-3-甲基咪唑氯盐([BMIM]Cl)为溶剂、棉浆粕为原料、脱脂棉为增强纤维素,并分别以氯化钠、无水碳酸钠和无水硫酸钠为成孔剂制备了纤维素海绵,探讨了相同条件下不同成孔剂对纤维素海绵形态结构、吸水保湿性能和力学性能的影响。研究发现,以无水硫酸钠为成孔剂制备的纤维素海绵的孔隙结构较为均匀饱满,吸水保湿性能和力学性能也相对较好。     

Simultaneous SAXS and WAXS investigations of changes in native cellulose fiber microstructure on swelling in aqueous sodium hydroxide

Simultaneous small‐ and wide‐angle X‐ray scattering was used to follow changes in the microstructure of native cellulose (cellulose I) fibers during conversion to sodium cellulose I (Na‐cellulose I) by aqueous sodium hydroxide. Wide‐angle X‐ray scattering was used to monitor the extent of conversion, while small‐angle X‐ray scattering was used to explore what occurs at the higher structural levels of the elementary fibrils, microfibrils, and interfibrillar voids. Native cellulose fibers, swollen in either water or aqueous sodium hydroxide, exhibited an increase in the void volume fraction and a decrease in the void cross‐section size, as the swelling agent separated elementary fibrils, opening up the structure, and creating many small voids. After conversion of swollen native cellulose to sodium cellulose I, the void volume fraction and average void cross‐section dimensions both increased. During conversion from dry cellulose I fibers to swollen Na‐cellulose I fibers, the void cross‐section dimensions went through a minimum, suggesting that the void structure may go via an intermediate similar to the water swollen structure of cellulose I. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1209–1218, 2002     

过硫酸铵氧化速生杨木残渣制备纤维素纳米晶体及其表征

以去除半纤维素的速生杨木残渣为原料,在70℃下按固液比1：100（g：mL）加入1.5 mol/L过硫酸铵溶液,处理16 h制备纤维素纳米晶体。所得样品为白色粉末状固体,得率（以原料中纤维素质量计）为57%,氧化度为0.156,表面电荷为-42.15 mV。采用透射电子显微镜、傅里叶变换红外光谱、X射线衍射、核磁共振等技术对得到的纳米纤维素进行表征。结果表明：过硫酸铵去除了原料中的木质素和残余的少量半纤维素,并有选择地将纤维素C6位置上的伯醇羟基氧化成羧基,纤维素纳米晶体保留了原纤维素的结构特征,结晶度为77%,晶体结构以I_β晶型为主,88.4%的纤维素纳米晶体宽度在10~24 nm之间。     

Office waste paper as cellulose nanocrystal source

Cellulose nanocrystals (CNC) are isolated from office waste paper using an alkali solution and a subsequent acid hydrolysis process. The Fourier transform infrared spectroscopy and X‐ray diffraction (XRD) results demonstrate that ink and fillers used in the papermaking industry are almost totally removed after alkali treatments. The XRD results show that CNCs obtained after 2 wt % NaOH solution treatment and a subsequent hydrolysis process exhibit only a cellulose I crystalline structure, and the crystallinity index value increases around 42% with respect to initial office waste paper. Nevertheless, CNCs obtained after 7.5 wt % NaOH solution treatment and a subsequent acid hydrolysis process show a mixture of cellulose I and cellulose II polymorphs. The thermal analysis shows that the CNCs obtained after 7.5 wt % NaOH solution treatment and a subsequent acid hydrolysis process are thermally less stable than other samples, suggesting that the cellulose chains could depolymerize into low molecular weight sugar compounds. Even though the atomic force microscopy images confirm the presence of CNCs, the optical images show that some cellulose microfibers still maintain their structure. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45257.     

HEC与SA复合海绵的制备及性能表征

制备不同比例的羟乙基纤维素/海藻酸钠复合海绵,根据医用敷料海绵的国家标准要求,对其进行表面密度、吸水、保湿、孔隙率等测试,并利用红外光谱仪测试其复合前后的结构变化以及利用万能试验机及热重分析仪测试复合海绵的力学性能及热稳定性等特征。结果表明：羟乙基纤维素与海藻酸钠溶液可以以一定比例共混并冷冻干燥制备成复合海绵,两者之间只是物理共混,没有发生化学变化,其相容性良好,无明显相分离现象出现;共混比例对混合海绵的物理性能产生一定的影响。综合考虑各项性能参数,羟乙基纤维素与海藻酸钠两种组分的比例为3：1时,此时所制备形成的海绵为最佳。     

磷酸锆辅助催化水解菌糠制备纳米纤维素晶体的性能

以食用菌产业的副产品菌糠为原料,采用磷酸锆催化剂辅助稀硫酸水解制备纳米纤维素晶体(cellulose nanocrystals,CNCs).与传统酸水解方法相比,该方法简化了工艺流程,制备过程环境友好。考察了超声时间、超声温度以及稀硫酸浓度等因素对CNCs得率的影响。结果表明当超声时间为5h、超声温度为75℃及稀硫酸浓度为12.3%时,CNCs得率为42.80%.采用透射电子显微镜(TEM)、扫描电子显微镜(SEM)、傅里叶变换红外光谱(FTIR)以及X射线衍射仪(XRD)对样品的微观形貌、谱学性能和晶体结构进行了研究分析,结果表明所制得的CNCs呈棒状,直径介于10～30nm之间;CNCs属于纤维素I型,与原料菌糠相比,结晶度由63.79%增大到81.04%;且CNCs仍具有天然纤维素的基本化学结构。论文研究为菌糠的资源化高效利用开辟了新途径。     

Cellulose Nanocrystals/ZnO as a Bifunctional Reinforcing Nanocomposite for Poly(vinyl alcohol)/Chitosan Blend Films: Fabrication,Characterization and Properties

In this study, cellulose nanocrystals/zinc oxide (CNCs/ZnO) nanocomposites were dispersed as bifunctional nano-sized fillers into poly(vinyl alcohol) (PVA) and chitosan (Cs) blend by a solvent casting method to prepare PVA/Cs/CNCs/ZnO bio-nanocomposites films. The morphology, thermal, mechanical and UV-vis absorption properties, as well antimicrobial effects of the bio-nanocomposite films were investigated. It demonstrated that CNCs/ZnO were compatible with PVA/Cs and dispersed homogeneously in the polymer blend matrix. CNCs/ZnO improved tensile strength and modulus of PVA/Cs significantly. Tensile strength and modulus of bio-nanocomposite films increased from 55.0 to 153.2 MPa and from 395 to 932 MPa, respectively with increasing nano-sized filler amount from 0 to 5.0 wt %. The thermal stability of PVA/Cs was also enhanced at 1.0 wt % CNCs/ZnO loading. UV light can be efficiently absorbed by incorporating ZnO nanoparticles into a PVA/Cs matrix, signifying that these bio-nanocomposite films show good UV-shielding effects. Moreover, the biocomposites films showed antibacterial activity toward the bacterial species Salmonella choleraesuis and Staphylococcus aureus. The improved physical properties obtained by incorporating CNCs/ZnO can be useful in variety uses.     

Polymer-Decorated Cellulose Nanocrystals as Environmentally Friendly Additives for Olefin-Based Drilling Fluids

In this study, we intended to evaluate the performance of olefin-based drilling fluids after addition of cellulose nanocrystal (CNC) derivatives. For this purpose, firstly, cellulose nanocrystals, produced from sulfuric acid hydrolysis of cotton fibers, were functionalized with poly(N-isopropylacrylamide) (PNIPAM) chains via free radicals. The samples were then characterized via Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), confocal microscopy, dynamic light scattering (DLS), and zeta potential measurements in water. The FTIR and NMR spectra exhibited the characteristic signals of CNC and PNIPAM groups, indicating successful grafting. As expected, X-ray diffractograms showed that the crystallinity of CNCs reduces after chemical modification. TGA revealed that the surface-functionalized CNCs present higher thermal stability than pure CNCs. The confocal microscopy, zeta potential, and DLS results were consistent with the behavior of cellulose nanocrystals decorated by a shell of PNIPAM chains. The fluids with a small amount of modified CNCs presented a much lower volume of filtrate after high-temperature and high-pressure (HTHP) filtration tests than the corresponding standard fluid, indicating the applicability of the environmentally friendly particles for olefin-based drilling fluids.     

Extraction and characterization of cellulose nanocrystals from cotton fiber by enzymatic hydrolysis-assisted high-pressure homogenization

Cellulose nanocrystals (CNCs) have attracted increasing attention in the field of nanomaterials because of its high aspect ratio, good structure, and high thermal stability. In this study, enzymatic hydrolysis-assisted high-pressure homogenization was applied as an environmentally friendly technique to extract CNCs from cotton-derived microcrystalline cellulose (MCC). The overall optimization of enzymatic pretreatment was conducted by response surface methodology, and the maximum CNCs yield was 40.09% under the optimized experimental conditions. The extracted CNCs under the optimal conditions showed needle-like shape with a length of 100–250 nm and a width of 5–10 nm and exhibited an overall particle size range of 3–80 nm. The basic chemical structure of cellulose was not changed after enzymatic hydrolysis and high-pressure homogenization. The CNCs exhibited slightly lower crystallinity and higher thermal stability than MCC. High aspect ratio CNCs extracted in this present study have great potential as a reinforcing agent in biodegradable packaging materials.     

纤维素氨基甲酸酯法制备纤维素海绵

海绵因具有蓬松度好、质地柔软、吸水性好等优点而得以广泛应用。但目前市面上的聚氨酯海绵,不仅原料紧缺,制备过程有污染物产生,而且废弃后难降解,会产生二次污染。为开发可自然降解的纤维素海绵无污染制备工艺,研究了采用纤维素氨基甲酸酯法制备纤维素海绵的工艺。结果表明：由纤维素氨基甲酸酯的氢氧化钠溶液捏合而成的海绵混合体经蒸煮,纤维素再生,成孔剂溶于水中而留下空隙,所得纤维素海绵孔径均一,表面光滑平整,具有较好的柔韧性和黏弹性,完全具有普通聚氨酯海绵的基本特征。     

基于互穿网络技术构筑的氧化海藻酸钠/纤维素纳米晶/聚丙烯酰胺-明胶复合水凝胶与性能

为了提高海藻酸盐水凝胶的生物应用性,采用互穿网络技术、纤维素纳米晶(CNCs)补强和明胶表面覆积相结合的方法构建了氧化海藻酸盐/纤维素纳米晶/聚丙烯酰胺-明胶 (OSA/CNCs/PAM-GT) 复合水凝胶。通过FT-IR、TGA、 XRD、溶胀性和降解性实验以及细胞相容性测试考察了CNCs含量对OSA/CNCs/PAM-GT复合水凝胶结构和性能的影响。实验结果表明,CNCs能够与基体中的聚合物产生相互作用力。并且随着CNCs含量的增加,OSA/CNCs/PAM-GT 复合水凝胶的孔隙率下降,力学性能提高。而且它们的溶胀性和生物降解性虽然受CNCs含量增加而呈现下降的趋势,但是幅度较小,说明CNCs能够在一定程度上调控复合水凝胶的物化性能。同时,OSA/CNCs/PAM-GT 复合水凝胶展现出较好的细胞粘附、增殖和分化性能。当CNCs的含量在0.5%时,细胞增殖的效果最佳,而CNCs的含量为1.5%时,细胞分化效果最显著。因此,将CNCs掺杂到OSA/PAM互穿网络基体中能够有效地调控其生物性能,使其适用于生物医学领域。     

Microstructural,Thermal, Crystallization,and Water Absorption Properties of Films Prepared from Never-Dried and Freeze-Dried Cellulose Nanocrystals

In this paper, the microstructural, optical, thermal, crystallization, and water absorption properties of films prepared from never-dried (ND) and freeze-dried (FD) cellulose nanocrystals (CNCs) are reported. Morphology of the ND CNCs reveals a needle-like structure, while after freeze-drying, they show a flake-like morphology. Microstructural analysis of ND and FD CNCs are further studied via small angle X-ray scattering to probe interactions. ND CNCs yield a transparent film with a low surface roughness (14 ± 4 nm), while the FD CNC film evidence a significant reduction of their transparency due to their higher surface roughness (134 ± 20 nm). Although Fourier transform infrared spectroscopy and energy-dispersive X-ray spectroscopy analyses reveal no chemical change occurs during the freeze-drying process, yet a more intense thermal degradation profile is observed for FD CNC film, probably due to the higher oxygen ingress within the gaps created between the stacked flakes. This, in turn, results in a greater loss of crystallinity at a higher temperature (300 °C) compared to the ND CNC film. A rapid decrease in water contact angle of the FD CNC film proves that the morphology of flakes and their orientation within the film has a strong influence in increasing water absorption capacity.     

Development and characterization of bionanocomposites based on poly(3‐hydroxybutyrate) and cellulose nanocrystals for packaging applications

Poly(3‐hydroxybutyrate) (PHB)‐based bionanocomposites were prepared using various percentages of cellulose nanocrystals (CNCs) by a solution casting method. CNCs were prepared from microcrystalline cellulose using sulfuric acid hydrolysis. The influence of CNCs on PHB properties was evaluated using differential scanning calorimetry, Fourier transform infrared spectroscopy, X‐ray diffraction, thermogravimetry and tensile testing. Vapor permeation and light transmission of the materials were also measured. Differential scanning calorimetric tests demonstrated that CNCs were effective PHB nucleation agents. Tensile strength and Young's modulus of PHB increased with increasing CNC concentration. Moreover, the PHB/CNC bionanocomposites exhibited reduced water vapor permeation compared to neat PHB and had better UV barrier properties than commodity polymers such as polypropylene. It was found that nanocomposites with 6 wt% of CNCs had the optimum balance among thermal, mechanical and barrier properties. © 2016 Society of Chemical Industry     

Thermoplastic Starch Nanocomposites Reinforced with Cellulose Nanocrystal Suspensions Containing Residual Salt from Neutralization

Sulfuric acid-catalyzed hydrolysis of cellulose commonly isolates cellulose nanocrystals (CNCs). Neutralizing the reactant solution with sodium hydroxide facilitates efficient downstream processing, but residual salt remains in the product. This study examines the reinforcing effects of CNCs from suspensions that contain residual salt on the mechanical properties of thermoplastic starch nanocomposites. By reinforcing starch films with up to 5 wt% CNCs, stiffness and strength are improved by 118% and 79%, respectively, indicating a good dispersion of CNCs in the starch matrix. Compared to nanocomposites incorporating salt-free CNCs, the remaining salt has no significant impact on the material's mechanical performance. The results indicate great potential of CNCs containing residual salt as biobased, low-cost nanofiller in hydrophilic polymer matrices.     

A facile approach for fabricating fluorescent cellulose

Fluorescent cellulose nanocrystals (CNCs) were prepared through a two‐step approach. Reactive amino groups were first introduced onto the CNCs through a silanization reaction with 3‐aminopropyltrimethoxysilane. The fluorescent moieties were then attached onto the cellulose by covalent grafting between the amino groups and 1‐pyrenebutyric acid N‐hydroxy succinimide ester or fluorescein isothiocyanate. The synthesized fluorescent CNCs were investigated and characterized with attenuated total reflectance Fourier transform infrared spectroscopy, ultraviolet–visible absorbance and fluorescence spectroscopy, confocal microscopy, and dynamic light scattering. The same fluorescent functionalization strategy could also be applied to other cellulose materials, such as microcrystalline cellulose and bulky paper sheets. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Thermally activated shape memory behavior of melt‐mixed polyurethane/cellulose nanocrystal composites

Building blocks made from renewable sources attract increasing attention for the design of new polymer systems. Recently, in this particular context, cellulose nanocrystals (CNCs) have gained great interest in both academic research and industry, mainly on account of their ability to reinforce range of polymer matrices and afford nanocomposites with attractive mechanical properties. The limited thermal stability of conventionally produced cellulose nanocrystals (CNCs) has, however, so far limited the range of polymers that could be used as basis for melt‐processed CNC nanocomposites. We herein show that a commercially accessible nanocrystal source, a particular grade of microcrystalline cellulose (MCC), can easily be converted into thermally stable CNCs by ultrasonication in phosphoric acid. A scalable melt‐mixing process was used to produce nanocomposites of these CNCs with a thermoplastic polyurethane (TPU) elastomer. A significant improvement of the room temperature storage modulus from 40 MPa (neat polymer) to 120 MPa (10% w/w CNC) was observed. The introduction of CNCs not only increased the stiffness of the polymer matrix, but also improved the shape memory properties of the nanocomposite. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45033.