Mechanically-induced dimensional extensibility of fibers towards tough fiber networks

The beneficial effect of materials with high aspect ratio as composite reinforcement has prompted continuous interest towards cellulosic fibers. Besides providing stiffness, fibers can potentially contribute to composite extensibility. While mechanical treatments are typically used to adjust the physical and surface properties of fibers, less is known about ensuing effects on their extensibility and that of associated networks. Fiber network dimensional extensibility of 16% was achieved by processing the precursor aqueous fiber dispersions following a simple mechanical treatment with a judicious combination of low (PFI refining) and high concentrations and temperatures (Wing defibrator). Consequently, deformation of fibers and increased inter-fiber bonding resulted in a three-fold increase in strength to rupture of the fiber network leading to the structures with unprecedented toughness.     

Improved surface properties of CTMP fibers with enzymatic pretreatment of wood chips prior to refining

Surface properties of chemithermomechanical pulp (CTMP) fibers produced from enzymatically pretreated eucalyptus wood chips prior to refining were investigated by Field Emission Scanning Electron Microscope (FE-SEM), Transmission Electron Microscope (TEM) and X-ray Photoelectron Spectroscopy (XPS). The results showed that in a traditional CTMP refining process most fiber disruptions occur in the middle lamella (ML) leaving behind a significant amount of hydrophobic materials on the resulting fiber surface. However, in a Bio-CTMP refining process, fiber fractures preferentially take place in the primary (P) and secondary 1 (S1) layers or the S1 and secondary 2 (S2) layers, which results in more fibrillation being generated in the subsequent refining thus improving inter-fiber bonding strength and paper strength. XPS chemical composition analysis together with pulp physical strength property showed that the surfaces of Bio-CTMP fibers become enriched with a greater proportion of carbohydrates in comparison with CTMP fiber surface, which supports FE-SEM and TEM observations.     

Diffusion of cationic polyelectrolytes into cellulosic fibers

The penetration of cationic polyelectrolytes into anionic cellulosic fibers was evaluated with fluorescent imaging techniques in order to clarify the mechanism and time scales for the diffusion process. The bulk charge of the cellulosic fibers indirectly creates a driving force for diffusion into the porous fiber wall, which is entropic in nature due to a release of counterions as the polyelectrolyte adsorbs. The individual bulk charges in the fiber cell wall also interact with the diffusing polyelectrolyte, such that the polyelectrolyte diffuses to the first available charge and consequently adsorbs and remains fixed. Thus, subsequent polyelectrolyte chains must first diffuse through the adsorbed polyelectrolyte layer before adsorbing to the next available bulk charges. This behavior differs from earlier suggested diffusion mechanisms, by which polyelectrolytes were assumed to first adsorb to the outermost surface and then reptate into the pore structure. The time scales for polyelectrolyte diffusion were highly dependent on the flexibility of the chain, which was estimated from calculations of the persistence length. The persistence length ultimately depended on the charge density and electrolyte concentration. The charge density of the polyelectrolyte had a greater influence on the time scales for diffusion. High charge density polyelectrolytes were observed to diffuse on a time scale of months, whereas the diffusion of low charge density polyelectrolytes was measured on the order of hours. An influence of the chain length, that is, steric interactions due the persistence length of the polyelectrolyte and to the tortuosity of the porous structure of the fiber wall, could only be noted for low charge density polyelectrolytes. Increasing the electrolyte concentration increased the chain flexibility by screening the electrostatic contribution to the persistence length, in turn inducing a faster diffusion process. However, a significant change in the diffusion behavior was observed at high electrolyte concentrations, at which the interaction between the polyelectrolyte charges and the fiber charges was almost completely screened.     

On the indirect polyelectrolyte titration of cellulosic fibers. Conditions for charge stoichiometry and comparison with ESCA

The effect of electrolyte (NaHCO3) concentration on the adsorption of poly-DADMAC (poly-diallyldimethylammonium chloride) onto cellulosic fibers with different charge profiles was investigated. Surface carboxymethylated fibers were obtained by grafting carboxymethyl cellulose (CMC) onto the fiber surface and bulk carboxymethylated fibers were obtained by reacting the fibers with monochloroacetic acid. It was shown that nonionic interactions do not exist between cellulose and poly-DADMAC, rather electrostatic interactions govern the adsorption. Charge stoichiometry prevails under electrolyte-free conditions, whereas surface charge overcompensation occurs at higher electrolyte concentrations. It was shown that charge stoichiometry prevails if the thickness of the electric double layer kappa(-1) was larger than the mean distance between the charges on the fiber surface, as predicted by polyelectrolyte adsorption theories, taking lateral correlation effects into account. In a second set of experiments the ESCA technique served to independently calibrate the polyelectrolyte titrations for determining the surface charge of cellulosic fibers. Various molecular masses of poly-DADMAC were adsorbed to carboxymethylated fibers having different charge profiles. The adsorption of low M(w) poly-DADMAC (7.0 x 10(3)), analyzed by polyelectrolyte titration, was about 10 times higher than that of the high M(w) poly-DADMAC (9.2 x 10(5)). Despite the difference in accessibility of these two polyelectrolytes to the fiber cell wall, ESCA surface analysis showed, as expected, only slight differences between the two polyelectrolytes. This gives strong credibility to the idea that surface charge content of cellulosic fibers can be analyzed by means of adsorption of a high-molecular-mass cationic polymer, i.e., by polyelectrolyte titration.     

Effect of tethered and free microfibrillated cellulose (MFC) on the properties of paper composites

High strength and low gas permeability cellulosic composites were produced using the papermaking technology with a commercial microfibrillated cellulose (MFC). The effect of blending MFC with hardwood fibers was compared to the direct refining of the fibers with and without polyamideamine-epichlorohydrin (PAE) addition. The addition of MFC, free or tethered, to pulp fibers combined with PAE can increase the dry strength and wet strength of cellulosic materials by an order of magnitude. Air permeability of the composites decreases by up to orders four of magnitude with MFC addition. The hypothesis that refining wood fibers can produce tethered MFC which provides equivalent strength properties but significant drainage benefits was proven. Furthermore, major benefits in paper formation uniformity (fiber distribution homogeneity) were achieved with refined fibers.     

Propionic Anhydride Modification of Cellulosic Kenaf Fibre Enhancement with Bionanocarbon in Nanobiocomposites

The use of chemical modification of cellulosic fibre is applied in order to increase the hydrophobicity, hence improving the compatibility between the fibre and matrix bonding. In this study, the effect of propionic anhydride modification of kenaf fibre was investigated to determine the role of bionanocarbon from oil palm shell agricultural wastes in the improvement of the functional properties of bionanocomposites. The vinyl esters reinforced with unmodified and propionic anhydride modified kenaf fibres bio nanocomposites were prepared using 0, 1, 3, 5 wt% of bio-nanocarbon. Characterisation of the fabricated bionanocomposite was carried out using FESEM, TEM, FT-IR and TGA to investigate the morphological analysis, surface properties, functional and thermal analyses, respectively. Mechanical performance of bionanocomposites was evaluated according to standard methods. The chemical modification of cellulosic fibre with the incorporation of bionanocarbon in the matrix exhibited high enhancement of the tensile, flexural, and impact strengths, for approximately 63.91%, 49.61% and 54.82%, respectively. The morphological, structural and functional analyses revealed that better compatibility of the modified fibre–matrix interaction was achieved at 3% bionanocarbon loading, which indicated improved properties of the bionanocomposite. The nanocomposites exhibited high degradation temperature which signified good thermal stability properties. The improved properties of the bionanocomposite were attributed to the effect of the surface modification and bionanocarbon enhancement of the fibre–matrix networks.     

Enhancing the effectiveness of a laccase–TEMPO treatment has a biorefining effect on sisal cellulose fibres

Enhancing the effectiveness of a laccase–TEMPO treatment on sisal pulp by increasing pulp consistency was for the first time found to increase the biorefining potential of this enzyme–mediator system. The operating conditions used were those previously found to maximize oxidative functionalization and paper strength. Prior to the enzyme treatment, the pulp was refined at a variable intensity (0, 3,000 and 4,500 revolutions) in order to ascertain whether the increased surface area would lead to enhanced functionalization and boost the refining effect as a result. Increasing pulp consistency increased the contents in aldehyde and carboxyl groups by 130% and 94%, respectively. Also, it resulted in more marked reduction of pulp viscosity during the enzyme treatment, especially at a high refining intensity; this had a detrimental effect on fibre strength and significantly reduced tear strength in the refined pulp. Oxidized pulp exhibited a considerably increased water retention value with respect to the initial pulp, particularly after refining. Dry tensile index was increased by 21, 18 and 12%, and burst index by 23, 16 and 13% at 0, 3,000 and 4,500 rev, respectively, by the laccase–TEMPO treatment as a result of increased inter-fibre hydrogen bonding offsetting the loss of fibre strength, an effect that can provide substantial savings in refining energy. Based on the results, a laccase–TEMPO treatment is an enzymatic booster of mechanical refining with the added advantages of providing unaltered drainability and increased air permeability. The most salient effect of the laccase–TEMPO treatment was an increase in wet tensile strength (by 160, 553 and 588% at 0, 3,000 and 4,500 rev, respectively) that can be ascribed to inter-fibre covalent bonding through hemiacetal linkages promoted by aldehyde groups. The improvement was much greater than that obtained at a lower consistency under identical conditions.     

Surface modification of cellulose fibers with layer-by-layer self-assembly of lignosulfonate and polyelectrolyte: effects on fibers wetting properties and paper strength

To convert the hydrophilic cellulose fiber into hydrophobic, multilayers composed of cationic polyacrylamide (CPAM) and lignosulfonate (LS) were constructed on cellulose fiber surface using layer-by-layer (LBL) self-assembly technique. The presence of CPAM/LS multilayers were validated by zeta potential, X-ray photoelectron spectroscopy and atomic force microscopy (AFM). It was found that potential of fiber surface inversed after deposition of each layer, the contents of characteristic elements (i.e. S and N) of CPAM/LS multilayers increased with increasing bilayer number, furthermore, the calculated surface LS content increased linearly as a function of bilayers. AFM phase images indicated that the cellulose microfibrils on fiber surface were gradually covered by LS granules, resulting in an increase in fiber surface roughness as self-assembly proceeded. The wetting properties of modified cellulose fibers were detected by dynamic contact angle measurement. The results showed that the initial water contact angle gradually increased and the attenuation rate of the contact angle gradually decreased with the number of bilayers, suggesting that the controllable hydrophobicity of cellulose fiber can be achieved depending on the number of bilayers. It also showed that the polyelectrolyte presented in the outermost layer significantly influenced the wetting properties of cellulose fibers, and a higher hydrophobicity was observed when LS was in the outermost layer. Moreover, tensile strength test was performed on the handsheet prepared from LBL modified fibers to evaluate the effect of CPAM/LS multilayers on strength property of cellulose fiber networks. The tensile index of handsheet prepared from fibers modified with a (CPAM/LS)₅ multilayer increased by 12.4% compared with that of handsheet prepared from original fibers. The print density of handsheet increased with the number of bilayers, suggesting that printability of the handsheet was improved by constructing CPAM/LS multilayers on cellulose fiber surface. This strategy will have a positive impact and potential application value in printing process control of cellulose fiber-based products.     

Effect of fiber length and composition on mechanical properties of carbon fiber‐reinforced polybenzoxazine

The mechanical strength and modulus of chopped carbon fiber (CF)‐reinforced polybenzoxazine composites were investigated by changing the length of CFs. Tensile, compressive, and flexural properties were investigated. The void content was found to be higher for the short fiber composites. With increase in fiber length, tensile strength increased and optimized at around 17 mm fiber length whereas compressive strength exhibited a continuous diminution. The flexural strength too increased with fiber length and optimized at around 17 mm fiber length. The increase in strength of composites with fiber length is attributed to the enhancement in effective contact area of fibers with the matrix. The experimental results showed that there was about 350% increase in flexural strength and 470% increase in tensile strength of the composites with respect to the neat polybenzoxazine, while, compressive properties were adversely affected. The composites exhibited an optimum increase of about 800% in flexural modulus and 200% in tensile modulus. Enhancing the fiber length, leads to fiber entanglement in the composites, resulted in increased plastic deformation at higher strain. Multiple branch matrix shear, debonded fibers and voids were the failures visualized in the microscopic analyses. Defibrillation has been exhibited by all composites irrespective of fiber length. Fiber debonding and breaking were associated with short fibers whereas clustering and defibrillation were the major failure modes in long fiber composites. Increasing fiber loading improved the tensile and flexural properties until 50–60 wt% of fiber whereas the compressive property consistently decreased on fiber loading. Copyright © 2008 John Wiley & Sons, Ltd.     

The fiber charge measurement depending on the poly-DADMAC accessibility to cellulose fibers

Cellulose fiber charge is a significant parameter for porous cellulose fibers, and strongly affects the swelling ability of cellulose fibers and the properties of cellulose-based materials as well. Actually, it includes surface charge and inner charge. The surface charge is mentioned often in papermaking wet-end chemistry, however, the inner charge or the total charge is paid less attention to. In this study, the cationic polydiallyldimethyl ammonium chloride (poly-DADMAC) with different molecular weight (Mw) was applied for the accessibility evaluation to the cellulose fiber charges by using polyelectrolyte adsorption technique. Results showed that higher fiber charge was detected by lower Mw poly-DADMAC (7.5–15 kDa) due to its highly efficient penetration into the fiber cell walls and neutralization with inner charges, while lower fiber charge was obtained by using higher Mw poly-DADMAC (higher than 100 kDa) because of its adsorption onto fiber surface. As a consequence, high-Mw poly-DADMAC was used to determine the surface charge of cellulose fibers, and low-Mw poly-DADMAC could be used to measure the total charge under the saturated adsorption and low ionic strength (or salts concentration). This was confirmed by SEM–EDS analysis. The low-Mw poly-DADMAC adsorption had a good agreement with conventional conductometric titration, and a linear regression equation with slope of 1.03 and regression coefficient of 0.99 was obtained.     

Characterization of poly(3,4-ethylenedioxythiophene)/poly(styrene sulfonate) (PEDOT:PSS) adsorption on cellulosic materials

The interaction between poly(3,4-ethylene dioxythiophene) doped with poly(styrene sulfonate) (PEDOT:PSS) and cellulosic fibers was characterized in order to obtain further understanding of the conductivity properties of the modified cellulosic fiber material. Microcrystalline cellulose (MCC) was used as a model surface to study the adsorption behavior at various pH and salt concentrations, while samples of low-conductivity paper, normally used for the production of electrical insulation papers, were dipped into PEDOT:PSS dispersion and air-dried for X-ray photoelectron spectroscopy (XPS) studies. The results showed a strong interaction between the MCC and PEDOT:PSS, which implied a broad molecular distribution of the conducting polymer. With increasing pH, less amount of the conducting polymer was adsorbed whereas the amount adsorbed passed through a maximum value with varying salt concentration. Zeta potential measurement and polyelectrolyte titration were used to determine the surface charge of both suspended MCC particles and dispersed PEDOT:PSS at various pH levels and salt concentrations. Dip-coated paper samples exhibited two peaks in the S(2p) XPS spectra at 168–169 and 164–165 eV which correspond to the sulfur signals of sulfonate (in PSS) and in thiophene (in PEDOT), respectively. It was found that the PEDOT:PSS with a ratio of 1:2.5 was adsorbed more in the base paper than that with a ratio of 1:6. The PEDOT:PSS ratio on the surface of the cellulosic material was higher than that in the bulk liquid for all samples. The results indicated that PEDOT was preferentially adsorbed rather than PSS. The degree of washing of the conducting polymer did not significantly affect the PEDOT enhancement on the surface.     

Adsorption and inactivation behavior of horseradish peroxidase on cellulosic fiber surfaces

The physical immobilization behavior of horseradish peroxidase (HRP) on cellulosic fiber surfaces was characterized using adsorption and inactivation isotherms measured by the depletion method followed by fitting of Langmuir’s and Freundlich’s models to the experimental data. The adsorption and inactivation behavior of simpler and relatively non-porous high and low crystalline cellulosic substrates (microcrystalline cellulose and regenerated cellulose) as well as more complex and porous cellulosic pulp fibers (bleached kraft softwood fibers) were investigated. The effect of the sorbent surface energy on HRP adsorption was demonstrated by increasing the hydrophobicity of the cellulosic fibers using an internal sizing agent. The influence of the fiber surface charge density on HRP adsorption was studied via modification of the cellulosic fibers using TEMPO (2,2,6,6-tetramethyl-1-piperidiniloxy radical)-mediated oxidation methods. Results showed that hydrophobic interactions had a much larger effect on HRP adsorption than electrostatic interactions. More hydrophobic fiber surfaces (lower polar surface energy) result in larger enzyme-fiber binding affinity constants and higher binding heterogeneity. It was also found that oxidation of the cellulosic fiber substrate reduces enzyme adsorption affinity but significantly increases the loading capacity per unit weight of the surface.     

A mechanically strong conductive hydrogel reinforced by diaminotriazine hydrogen bonding

Over the past decades,the urgent need for high strength conductive hydrogels in diverse applications has motivated an unremitting effort to combine the improved mechanical properties of hydrogels with conductive performances.In this work,high strength conductive hydrogels intensified with intermolecular hydrogen bonding are fabricated by in situ mixing poly(2-vinyl-4,6-diamino-1,3,5-triazine-co-polyethylene glycol diacrylates) (PVDT-PEGDA) hydrogels with poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT/PSS).The conductive hydrogels in deionized water exhibit high mechanical performances with compressive strength and tensile strength in the range of 7.58-9.52 MPa and 0.48-1.20 MPa respectively,which are ascribed to the intermolecular hydrogen bonding interactions of diaminotriazinediaminotriazine (DAT-DAT) in the network.Meanwhile,adding PEDOT/PSS can significantly increase both the specific conductivities and equilibrium water contents of the hydrogels.These cytocompatible conductive hydrogels may have a great potential to be used as electrical stimuli responsive soft biomaterials.     

Lignocellulosic fiber charge enhancement by catalytic oxidation during oxygen delignification

A series of one-stage oxygen delignification treatments with a softwood (SW) kraft pulp were studied employing 0.0-0.5% of a bismuth ruthenium pyrochlore oxide catalyst. The results demonstrated that a 0.09-0.18% charge of catalyst in an oxygen stage provided a 52.2-116.0% increase of carboxylic acid groups in the cellulosic component of kraft pulps without a significant decrease in fiber viscosity. A 3-factor at 3-level (L(9)3(3)) orthogonal experimental design was used to identify the main factors influencing acid group formation in pulp carbohydrates. The relative significance of experimental parameters for polysaccharide acid group formation was the molar equivalent NaOH, oxygen pressure, and finally, reaction temperature under the experimental conditions studied. The optimized reaction parameters for fiber charge development were shown to be 85-100 degrees C, 2.5% NaOH, and 800-960 kPa oxygen pressure. Pulps with higher fiber carboxylic acid content introduced by catalytic oxidation during oxygen delignification yielded a 10.9-33.7% increase in fiber charge after elemental chlorine free (ECF) pulp bleaching. The enhanced fiber charge resulted in 6.7-17.1% increase in paper sheet tensile index at comparable pulp viscosity.     

Electrospun PVA Nanofibrous Membranes Reinforced with Silver Nanoparticles Impregnated Cellulosic Fibers: Morphology and Antibacterial Property

To enhance the mechanical and antibacterial properties of silver nanoparticle impregnated cellulosic fibers, carboxy-cellulose nanocrystals(CCNs) were grafted with chitooligosaccharide(COS), which was used as a stabilizer for silver nanoparticles (AgNPs). Nanofibrous membranes reinforced with silver nanoparticle impregnated cellulosic fibers(CCN-COS-AgNP) were prepared via electrospinning using polyvinyl alcohol(PVA) as a matrix. The effects of CCN-COS-AgNP contents on the morphology, surface composition, mechanical properties, and antibacterial performances of the prepared CCN-COS-AgNP/PVA membranes were examined. The addition of CCN-COS-AgNP certainly improved the mechanical properties and antibacterial performances of the PVA nanofibers. The tensile strength was significantly increased from 4.40 MPa to 8.60 MPa when 8% CCN-COS-AgNP(mass ratio) was introduced. When 10%(mass ratio) CCN-COS-AgNP was added, the nanofibers showed an excellent antibacterial activity for S. aureus(Staphylococcus aureus) and E. coli(Escherichia coli), with the maximum inhibition zones of 2.30 and 1.60 cm, respectively. Moreover, the 2%(mass ratio) CCN-COS-AgNP/PVA fibrous membrane showed 126% cell viability for mg63 human osteoblasts. The electrospun PVA membrane has great potential application in biomedical field.     

聚氯乙烯/木纤维复合材料的研究Ⅰ.硬脂酸和ABS改性木纤维对复合材料力学性能的影响

为改善聚氯乙烯（PVC）和木纤维两者的界面亲合性，提高PVC／木纤维复合材料的机械力学性能，分别用硬脂酸和ABS来改性木纤维的表面，研究发现用硬脂酸处理木纤维可提高复合材料的拉伸强度，但对复合材料的冲击强度影响不大．ABS处理木纤维可同时提高复合材料的拉伸强度和冲击强度。本文也研究了改性剂用量和木纤维含量对复合材料力学性能的影响。     

芳纶纤维/SMPU-SiO2复合材料的界面性能研究

选用形状记忆聚氨酯(SMPU)和正硅酸乙酯(TEOS)为前驱体,固体酸对甲基苯磺酸(PTSA)为催化剂,利用空气中的水分为水解水源,通过溶胶-凝胶法原位制备了形状记忆聚氨酯与二氧化硅( SMPU-SiO2)杂化材料,并将杂化材料应用于芳纶纤维增强的柔性复合材料中,以期改善芳纶纤维与基体的界面性能.同时,针对芳纶纤维表面...     

Physicochemical properties of chemically and enzymatically modified cellulosic surfaces

Surface characteristics of modified cotton fibers have been studied using electrokinetic analysis (EKA), inverse gas chromatography (IGC) and dynamic contact angle (DCA) determinations. Modifications of cotton surfaces included mercerization, water-proofing, cross-linking, dyeing with a bifunctional reactive dye and cellulase biopolishing. Comparisons are made to linen as an example of a natural cellulosic fiber other than cotton and to rayon as a representative of a regenerated cellulosic fiber. Generally all cellulosic surfaces were bipolar with a slightly higher acidic contribution in the case of the cotton samples. EKA indicated ion dissociation as the predominant mechanism for surface charge in aqueous medium for all cellulosic samples, with the exception of greige cotton and the cotton sample with the hydrophobic finish. Results from EKA and IGC showed good correlation, while DCA yielded unreasonably high basic contributions most likely due to fiber swelling.     

Effect of on-line ultrasonic treatment on the properties of carbon fiber reinforced plastic composites

The strength, performance, and application of carbon fiber reinforced plastic (CFRP) composites are directly affected by the interfacial bonding between fiber and resin. Wet winding technology is a commonly used composite productive process, and improving interfacial bonding of composites by on-line treatment has always been the focus of attention. In this paper, an on-line ultrasonic treatment system is designed and realized, the resin content of prepregs is determined by the dissolution method; standard deviation and dispersion coefficient are also calculated. The surface morphology, internal structure of prepregs, and the component of resin are observed and analyzed using a Metallurgical Microscope, scanning electron microscope (SEM), and near infrared radiation spectra (NIRS). The strength and performance of prepregs [(tensile strength, bending strength, tensile modulus of elasticity, bending modulus of elasticity, and interlaminar shear strength (ILSS)] are also tested. The results show the on-line ultrasonic treatment system can effectively improve the interfacial bonding of CFRP composites and enhance the strength and performance of CFRP composites.     

Highly improved mechanical strength of aramid paper composite via a bridge of cellulose nanofiber

A novel aramid paper composite based on pretreated meta-aramid fiber via the addition of cellulose nanofiber (CNF) was fabricated, and the mechanical strength and interfacial strength of the aramid paper composite were investigated. The results indicated that modified fibers showed higher roughness and more available hydrophilic groups. Besides, compared with the pristine aramid paper, it turned out that the tensile index, tear index and interlayer bonding strength of the paper composites with CNF increased by 2.04 times, 2.36 times and 3 times, respectively. In addition, tensile energy absorption (TEA) was also improved by an increment of 99.7% with 20 wt% CNF. These apparent evidences can be accounted for the following mechanisms. On the one hand, enhanced mechanical properties of aramid paper composite were derived from the strong hydrogen bonding or dipole–dipole coupling interaction between aramid fiber and CNF. On the other hand, significant reinforcement of interlayer bonding strength can be attributed to the pivotal bonding bridge and filling agent between aramid chopped fibers (ACFs) and fibrid, which could improve interfacial adhesion of paper sheet. The thin film structure like “spider web” or “silk” from SEM images indicated the CNF was used as a bridge actually.