Surface modification of cellulose nanocrystals

In order to improve the dispersibility of cellulose nanocrystal (CNC) particles, three different grafted reactions of acetylation, hydroxyethylation and hydroxypropylation were introduced to modify the CNC surface. The main advantages of these methods were the simple and easily controlled reaction conditions, and the dispersibility of the resulting products was distinctly improved. The properties of the modified CNC were characterized by means of Fourier transform infrared spectroscopy (FT-IR), ¹³C nuclear magnetic resonance (NMR), transmission electron microscopy (TEM) and thermogravimetric analyses (TGA). The results indicated that after desiccation, the modification products could be dispersed again in the proper solvents by ultrasonic treatments, and the diameter of their particles had no obvious changes. However, their thermal degradation behaviors were quite different. The initial decomposition temperature of the modified products via hydroxyethylation or hydroxypropylation was lower than that of modified products via acetylation. Translated from Acta Polymerica Sinica, 2006, (8): 982–987 [译自: 高分子学报]     

Coupling onto surface carboxylated cellulose nanocrystals

Non-flocculating aqueous suspensions of cellulose nanocrystals with different sizes were prepared by the combination of acid hydrolysis and surface TEMPO oxidative carboxylation of cotton linter and microfibrils of parenchyma cell cellulose (PCC). A decrease of the crystal size occurred and the introduction of negative charges at the interface of the crystalline domains induced a better individualization of the crystallites. These suspensions were further amidated by interaction with 4-amino TEMPO; a nitroxide radical containing a terminal amino group. The products were characterized by elemental analysis, conductimetry, solid-state ¹³C NMR, FTIR and EPR spectroscopies, together with X-ray diffraction analysis and the coupling performance was deduced with a high correlation. The results indicated that the amidation was effective with yield roughly of 30%, the reaction yield being somewhat more important on samples from cotton origin. In all samples, the amidation was realized at the surface of the samples from carboxylated functions, which kept their intrinsic crystallinity, integrity and perfection throughout the preparation protocol. Their hydrophobic character was evaluated by observing their behavior in polar and non-polar solvents.     

Enhancement effect of acylated cellulose nanocrystals on waterborne polyurethane

Journal of Polymer Research - Tissue engineering aims to exploit the regenerative capacity of cells and connect the inherent ability of the body to repair and regenerate. Cells are seeded onto a...     

Comparison of cellulose and chitin nanocrystals for reinforcing regenerated cellulose fibers

In this study, regenerated cellulose fibers reinforced by cellulose nanocrystals (CENC) and chitin nanocrystals (CHNC) were prepared by blending the nanocrystals suspensions with the cellulose solution in NaOH/urea/water solvent at room temperature. The effect of nanocrystals' addition on the properties of spinning dopes and regenerated fibers were investigated and compared. Results showed that the obtained CENC and CHNC had different dimensions, and both of them increased the viscosity and decreased the transparency of the spinning dopes. However, the dissolution state of cellulose was not changed. CHNC had a greater influence on the properties of spinning dopes, while CENC had more obvious effect on the performance of regenerated fibers. The CENC reinforced fibers showed a higher crystallinity index as compared to the CHNC reinforced fibers. The tensile strength of the regenerated fibers was evidently improved when 3 wt % CENC or 2 wt % CHNC were added, while the elongation at break of the fibers was slightly decreased with the increase of nanocrystals content. The morphology and thermal stability of the regenerated fibers was not affected by the addition of nanocrystals. This study suggested that the dimension, group and content of nanocrystals were important factors for the reinforcement of regenerated cellulose fibers. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44880.     

High-concentrated zirconia suspensions stabilized by cellulose nanocrystals

In this work, cellulose nano crystals (CNC) as a biodegradable and non-toxic dispersant were used in water-based suspensions of zirconia to examine their stabilization in ceramic processing. The zirconia suspensions for solid content, pH and CNC concentration were studied and the optimum pH value and minimum CNC concentration to produce stable highly concentrated water-based suspensions were determined. The achieved stability was found to be due to the adsorption of CNC nanofibers around the zirconia particles revealed by scanning electron microscopy (SEM). Suspensions with the lowest viscosity and highest stability over 24 h achieved at pH 4 i.e., 30 wt% zirconia particles stabilized with the addition of 1 wt% CNC.     

Surface modification and antimicrobial properties of cellulose nanocrystals

A novel and simple surface modification of cellulose nanocrystals (CNC) was performed by chloroacetylation and subsequent reaction with tertiary amines to form quaternary ammonium modified CNCs. The acetylation of CNC and quaternary ammonium modified CNCs was confirmed using IR spectroscopy and solid state NMR spectroscopy. The ¹³C NMR spectrum of quaternary ammonium modified CNC showed several additional resonances ranging from 14.5 ppm to 58.0 ppm compared to ¹³C NMR spectrum of pure CNC, suggesting that alkyl chains have been added to the pure CNC. The disc diffusion method was used to evaluate the antimicrobial properties of quaternary ammonium modified CNCs. It was found that modified CNCs with alkyl chain longer than ten carbons are effective antimicrobial agents against Staphylococcus aureus and E. coli bacteria. These CNCs can be chemically modified to tailor the properties to improve dispersion in the polymer matrix. This will expand the application of CNC as a reinforcing material. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44789.     

基于机械力化学作用制备荧光纳米纤维素

采用机械力化学法,以磷钨酸-柠檬酸为复合水解剂处理竹浆纤维,再进一步加入半胱氨酸,使降解的纤维素发生接枝反应,从而在水相中一锅法制备高荧光、高量子产率荧光纳米纤维素（fluorescent cellulose nanocrystals, F-CNC）。研究考察了半胱氨酸溶液浓度、反应时间、反应温度等因素对F-CNC的得率和荧光强度的影响。采用紫外分光光度计（UV-vis）、荧光分光光度计、透射电子显微镜（TEM）、傅里叶红外光谱仪（FTIR）、核磁共振光谱仪（NMR）、X-ray光电子能谱（XPS）、X射线衍射仪（XRD）以及热分析仪（TGA）等对F-CNC的光学性质、形貌结构、化学结构、晶体结构以及热稳定性等进行了表征分析。结果表明,半胱氨酸溶液浓度为1mol/L,反应时间为8h,反应温度为140℃,F-CNC的得率为56.8%,荧光量子产率达到34.24%,荧光寿命达到3.44ns,且F-CNC的直径在20~40nm,长度为150~300nm。基于机械力化学法制备F-CNC工艺简便、绿色环保且所制备的F-CNC在水中具有良好的分散性,在防伪和生物传感器中具有潜在的应用前景。     

Biobased nanocomposites based on collagen,cellulose nanocrystals,and plasticizers

Collagen (Col) is extensively used in various applications, including pharmaceutical, agricultural, and food applications. The materials based in Col may exhibit properties of biomedical interest because of their low toxicity, high structural capacity support, controlled biodegradability, and biocompatibility. However, Col has poor thermal and mechanical properties. The addition of plasticizers (Plas's) and fillers is an established strategy for enhancing the properties of the resulting nanocomposites. In this study, nanocomposites based on Col and cellulose nanocrystals were developed in two different ways and with three different Plas's. These materials were subjected to structural, thermal, mechanical, and morphological analysis. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44954.     

Some observations on food allergy

Conclusions Some fundamenally important concepts of allergy and the methods of identification of the extrinsic causative factors in allergic disease have been reviewed. Clinical evidence beasung upon the occurrence of allergic sisturbances attributed to allergens othe cottonseed has been assembled and examined to illustrate the fact that effective discrimination against, a single class of food products may result from faulty interpretation of valid clinical data.     

基于纤维素纳米晶稳定的亚微米Pickering乳液制备

与传统表面活性剂稳定的乳液相比,固体纳米颗粒稳定的Pickering乳液具有较强的界面稳定性、多功能性、低毒性等优势,在生物医药领域具有较大的应用潜力。而相较于尺寸较大的微米级Pickering乳液,亚微米Pickering乳液具有更大的比表面积、更有效的递送效率,有望进一步拓展Pickering乳液在生物医药领域的应用。但由于Pickering乳液的制备影响因素众多,且相互制约,刚性的固体颗粒难以在较小的有限油水界面排布,增加了亚微米Pickering乳液的制备难度。本工作以制备稳定的亚微米Pickering乳液为研究目标,采用具有良好生物相容性的天然多糖–纤维素纳米晶(CNCs)为颗粒乳化剂,角鲨烯作为油相,考察了颗粒浓度、油水比例、水相成分、超声时间及频率对Pickering乳液粒径分布及稳定性的影响,最终得到了具有良好的储存稳定性和抗离心稳定性的粒径为638.7?8.40 nm的亚微米Pickering乳液(CNCs-PE)。通过激光共聚焦显微镜证实了CNCs吸附在油水界面,形成了Pickering乳液结构。利用CCK-8法评价了CNCs和CNCs-PE的细胞毒性,结果表明,两者都具有良好的细胞安全性。此外,将其用于吸附模型抗原OVA,吸附率达到约80%,且肌肉注射部位的切片结果也表明其注射安全性良好。此结果为亚微米Pickering乳液进一步研究提供了参考,并有望拓展CNCs稳定的亚微米Pickering乳液在生物医药领域的应用。     

Nanocomposites made from cellulose nanocrystals and tailored segmented polyurethanes

The effect of the addition of microcrystalline cellulose nanofibers into linear segmented polyurethanes (SPU) was investigated. The polymers were synthesized with 4,4‐methylene‐bisphenyldiisocyanate (MDI) and poly(tetramethyleneglycol) (PTMG) with 1,4‐butanediol (BD) as chain extender. The nanocrystals were introduced during the PU polymerization, which resulted in cellulose nanofibrils covalently linked to the polymer. The interactions between the cellulose nanofibrils and the matrix lead to interesting changes in the behavior of the PU, with the hard segment (HS) phase being more affected by these interactions. SPUs with different contents of HS were synthesized to better understand these effects (23 to 45 wt %). Thermal, thermo‐mechanical and mechanical characterization of the nanocomposites were performed. In general, the nanocellulose favored the phase separation between the soft and hard domains generating an upward shift in the melting temperatures of the crystalline phases, an increase in the Young's modulus and a decrease in deformation at break. Comparison of the unfilled polymer responses and that of the nanocomposites showed that by increasing cellulose content, increased dynamic storage and tensile modulus as well as melting temperatures and enthalpy of melting of the soft domains can be achieved. Addition of cellulose during the polymerization essentially erased the potential shape memory behavior originally displayed by some of the SPU. However, a sample prepared by adding the cellulose nanocrystals after the reaction showed that the mechanical properties were still improved, while the shape memory behavior of the polymer was preserved. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Castor oil‐based polyurethanes containing cellulose nanocrystals

Partially foamed and nanocellulose‐reinforced polyurethanes (PU) based on castor oil (CO) were prepared and their different properties were measured and related to their structures. A castor oil‐based polyol (COPO) was obtained by alcoholysis of CO with triethanolamine. The COPO was used in the preparation of partially foamed and solid PU. Cellulose nanofibrils (NC) in the range of the rheological percolation content were incorporated to the materials and the final mechanical properties of these nanocomposites were analyzed. The incorporated NC considerably affected the rheology of the suspensions, which presented solid‐like behavior under frequency sweep tests with the addition of only 0.5 wt% of NC. By increasing the NC concentration the dispersion becomes increasingly difficult. The properties of the solid PU were also affected by the incorporation of NC and a significant increase of the tensile modulus was observed for the 0.5 wt% NC composite, compared to the unfilled solid PU. This behavior was associated to the incorporation of the rigid particle reinforcement and the interfacial bonding. As expected, the partially foamed PU showed lower modulus than the corresponding solid PU. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Aramid nanofiber reinforced nitrile rubber assisted by cellulose nanocrystals

A fiber-reinforced rubber composite was prepared by mixing aramid nanofibers (ANF) suspension and nitrile rubber (NBR) latex. The effects of ANF content and corresponding surface modification on the microstructure, vulcanization performance, processing and mechanical properties of composite materials, were systematically investigated. We found that, compared with commonly used short-cut aramid fibers, ANF fillers tend to form a stronger filling network within NBR matrix, resulting in a pronounced Payne effect. By improving the interfacial adhesion via dopamine (DA) coating onto ANF surface, the tensile strength can be further enhanced as expected. Besides, to eliminate the detriment of mechanical performance due to residual sodium polyacrylate in the course of flocculation, cellulose nanocrystal (CNC) was adopted to serve as a thickener during solution mixing. The incorporation of CNC can significantly improve the mechanical properties, which identifies a synergistic reinforcement effect arising from the cooperation of two types of fillers.     

Mechanical properties of UV-waterborne varnishes reinforced by cellulose nanocrystals

There are many instances in the literature of nanocellulose-thermoplastic composites, but there are few studies on coatings reinforced by cellulose nanocrystals (CNCs). The overall objective of this research was to develop organic nanoparticles-reinforced UV-water-based coatings for wood applications and to study the effect, mainly on wear properties, of the final composite coatings. CNC was mixed in the varnishes to improve the mechanical properties of the coatings. One of the key aspects in the technology of nanocomposites remains the dispersion of the nanoparticles within the matrix as well as its affinity with the matrix. To quantify the dispersion, efficient methods of characterization are needed in order to reveal the nanosized particles. In this article, a novel characterization method based on atomic force microscopy was employed to characterize such nanocomposite coatings, by measuring surface nanoroughness, which is clearly correlated with quality of dispersion and mechanical properties. CNC was modified by either alkyl quaternary ammonium bromides or acryloyl chloride. The mechanical properties (abrasion and scratch resistances, hardness and adhesion) were analyzed and compared to the reference varnish without nanoparticles. The modified CNC addition in UV-water-based coatings results in an approximately 30–40% increase in wear resistance (abrasion and scratch), without any loss of appearance.     

Melt processing of polyamide 12 and cellulose nanocrystals nanocomposites

The fabrication of nanocomposites of polyamide 12 (PA12) and cellulose nanocrystals (CNCs) isolated from cotton and tunicates is reported. Through a comparative study that involved solution‐cast (SC) and melt‐processed materials, it was shown that PA12/CNC nanocomposites can be prepared in a process that appears to be readily scalable to an industrial level. The results demonstrate that CNCs isolated from the biomass by phosphoric acid hydrolysis display both a sufficiently high thermal stability to permit melt processing with PA12, and a high compatibility with this polymer to allow the formation of nanocomposites in which the CNCs are well dispersed. Thus, PA12/CNC nanocomposites prepared by melt‐mixing the two components in a co‐rotating roller blade mixer and subsequent compression molding display mechanical properties that are comparable to those of SC reference materials. Young's modulus and maximum stress could be doubled in comparison to the neat PA12 by introduction of 10% (CNCs from tunicates) or 15% w/w (CNCs from cotton) CNCs. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42752.     

Surface modification of cellulose nanocrystals towards new materials development

Cellulose nanocrystals (CNCs) are a kind of sustainable nanoparticle from biomass, which are widely used as reinforcing filler and assembly building block for high-performance composites and function materials including biomaterial, optics, and so forth. Here, their unique advantages in material applications were reviewed based on their rod-like morphology, crystalline structure, dimension-related effects, and multi-level order structure. Then, we focused on the molecular engineering of CNCs, including the structure and physicochemical properties of their surface, along with surface modification methods and steric effects. We further discussed the performance-improvement and functionalization methods based on multi-component complex systems, together with the effects of surface molecular engineering on the performance and functions. Meanwhile, methods of optimizing orientation in uniaxial arrays were discussed along with those of enhancing photoluminescence efficiency via surface chemical modification and substance coordination. In the end, we prospected the design, development, and construction methods of new CNCs materials.     

Some observations on the concept of the degree of crystallinity in cellulose fibers with reference to moisture effects

A conceptual effort has been made here to reconcile two approaches of defining the degree of crystallinity by the x-ray diffraction method, (a) one as proportion of x-ray diffracting matter in the entire fibrous material, and (b) another as the extent of qualitative perfection of the crystalline region only, since these two approaches often lead to opposite conclusions from the same set of observations.     

Modification of cellulose nanocrystals as reinforcement derivatives for wood coatings

Cellulose nanocrystal (CNC), an emerging renewable nanomaterial, was subjected to carbon chains grafting in order to improve its dispersion and its ability to transfer its rigidity properties into less polar matrixes, especially acrylic wood coatings. Chemical modifications used to this purpose are required to be simple, not affecting the CNC main structure and compatible or synergistic to oligomer reticulation inside the targeted UV-waterborne formulation. Those modifications were carried out using either alkyl quaternary ammonium bromides or acryloyl chloride. These new chemical functionalities, not inducing deep structural changes in modified CNCs, were highlighted through nuclear magnetic resonance, infrared and nitrogen content analyses. CNC derivatives were better dispersed in aqueous acrylic coating as suggested by atomic force microscopy, with a mean surface roughness falling from 9 to 6 nm on the coatings containing unmodified and treated CNCs, respectively. For mechanical evaluations, the coatings including various CNC derivatives were applied on sugar maple wood, a much appreciated material as indoor timber or wooden furniture which requires an efficient surface protection. The abrasion tests indicated that the modified CNCs confer a higher scratch resistance, with an improvement from 24% to 38% for coatings containing CNC derivatives over those with unmodified CNC.