KR101983882B1 - Rheology of cellulose nanofibrils in the presence of surfactants - Google Patents

Abstract

The present invention relates to the rheology of cellulose nanofibrils in the presence of surfactants, and more particularly to the CNF suspension in the presence of surfactants different from the rheological behavior of pure CNF suspensions.

Description

≪ Desc / Clms Page number 1 > Rheology of Cellulose Nanofibrils in the Presence of Surfactants in the Presence of Surfactants [

The present invention relates to the rheology of cellulose nanofibrils in the presence of surfactants, and more particularly to the CNF suspension in the presence of surfactants different from the rheological behavior of pure CNF suspensions.

Cellulose NanoFibrils (CNFs) can be used in a variety of applications, and interest in them has increased significantly over the past decade. Its usefulness comes from attractive properties such as biodegradability, low mass density, high tensile modulus, wide chemical modification potential, and sustainability of production. Cellulose nanofibrils have been proposed as low density rheology modifiers for high strength filler materials of nanocomposites and complex fluids.

CNFs are composed of long semi-flexible fibrils (or fibers) with a diameter as small as 4 nm and an aspect ratio of more than 100. Fibrils are usually obtained from the decomposition of cellulose from wood pulp through chemical and mechanical treatments. Fibrils are produced with surfaces that are generally negatively charged due to the carboxyl groups introduced into the cellulose during material production. Natural cellulose contains a wide distribution of crystalline and amorphous materials, but CNFs are very rich in crystal-line content, which effectively increases the mechanical properties along the long axis of the fibrils. Due to its large aspect ratio as a one-dimensional nanomaterial, at very low mass concentrations, the cellulose nanofibrils constitute a three-dimensional percolated network, resulting in a large viscosity increase of the aqueous medium (as is known by Iwamoto et al.). For this reason, the nanofibrils are of interest as rheology modifiers in complex fluids.

Other materials exhibiting thickening properties include clay nanoparticles, worm-like micelles, and microgels. Mechanisms for modifying rheology with these materials are well documented. For example, at low ionic strength, the gelation of the nanoclay suspension is due to the electrostatic repulsion between the edges of the clay plate at a distance greater than the physical size, resulting in the formation of a soft jammed material. The viscosification of microgels is the result of the large swelling properties of the gel particles and allows access to a soft jammed state at low mass concentrations. Finally, the viscosity enhancement (finally elasticity) of the worm-like micelles results from the network formation due to Michelle's entanglement, such as long threads.

A wide range of complex fluids related to the combination of properties ranging from well defined numerical parameter ranges such as optical clarity, recoverability, shear fluidization, yield stress and stability of complex fluids to properties of subjective sensations associated with consumer goods such as cosmetics It is clear that there is no single rheology modification method that can meet performance constraints.

To date there have been few studies on the rheology of CNF suspensions. Among other materials, the effect of salt and pH on the sol-gel transition of the CNF dispersion as well as the shear fluidization behavior of the suspension and the elastic properties of the CNF suspension have attracted great interest in recent years.

In particular, the present invention relates to rheology of nanofibrils in the presence of surfactants, and more particularly to the rheology of CNF suspensions in the presence of different surfactants, The purpose of the present invention is to provide a logistics service.

However, the problems to be solved by the present invention are not limited to the above-mentioned problems, and other problems not mentioned can be clearly understood by those skilled in the art from the following description.

One aspect of the present invention provides a solution comprising a cationic surfactant having a mass concentration of 0.08% or less and a cellulose nanofibril.

Another aspect of the present invention provides a solution comprising a nonionic surfactant having a mass concentration of 8% or less and a cellulose nanofibril.

Another aspect of the present application may include anionic surfactant and cellulosic nanofibrils having a mass concentration of 8% or less.

Another aspect of the present invention provides a method for controlling the viscosity of a solution comprising a step of mixing a cellulose nanofibril and a surfactant.

It is particularly useful to explore the properties of CNFs as rheology modifiers and to evaluate suspension stability in the presence of surface active agents often present in complex fluids.

The sustainability aspect of CNFs is also noteworthy. The resilience of the CNFs network (in the form of sodium carboxylate) predicted at high ionic strength and wide pH range can be an attractive alternative to conventional microgels in which CNFs rapidly lose their thickening properties under these conditions .

In addition, nonionic surfactants increase the storage of the CNF suspension while forming a transparent jammed material.

A single rheology modification method according to the present invention including the above effects can meet a wide range of performance constraints of a complex fluid applicable to various fields.

의 농도 의존성을 나타내는 그래프이다.
도 4는 순수한 CNF 현탁액의 탄성률 농도 의존성 그래프이다.
도 5(a)는 순수한 CNF 현탁액 및 0.6% 농도에서 비이온성 계면활성제로 개질된 CNF 현탁액의 저장 탄성률(G′) 및 손실 탄성률(G″)을 나타내는 그래프이고, 도 5(b)는 순수한 CNF 현탁액 및 1.2% 농도에서 비이온성 계면활성제로 개질된 CNF 현탁액의 저장 탄성률(G′) 및 손실 탄성률(G″)을 나타내는 그래프이다.
도 6(a)는 순수한 5% 농도의 TX100 용액과 비교한 5가지 상이한 농도의 TX100가 존재하는 0.1% 농도의 CNFs 현탁액의 전기장 자기 상관 함수 g(t)를 나타내는 그래프이고, 도 6(b)는 순수 TX100의 농도 함수로서 완화 시간(τ₁, τ₂)을 나타내며, 도 6(c)는 완화 시간(τ)에 해당하는 분포 p(τ)를 나타내는 그래프이다.
도 7은 계면활성제 미셸들과 브릿지 된 CNFs의 개략도이다.
도 8(a)는 8% 농도에서 상이한 계면활성제에 따른 0.6% CNFs의 사진이고, 도 8(b)는 SDS 및 DTAB를 함유한 0.6% CNFs의 사진이고, 도 8(c)는 순수한 0.6% CNF 현탁액 및 상이한 농도의 SLES가 함유된 0.6% 현탁액의 G′와 G″를 나타내는 그래프이다.
도 9(a)는 0.6% CNF 현탁액에서 겔 탄성률의 SLES 농도 의존성 그래프를 나타내며, 도 9(b)는 항복 응력 τ_y 및 항복 변형

의 SLES 농도 의존성을 나타내는 그래프이다.BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a graphical representation of the five surfactants (a) Pluronic F68 (PF68) used in embodiments of the present invention; (b) Triton-X 100 (TX100); (c) sodium dodecyl sulfate (SDS), (d) sodium lauryl ether sulfate (SLES); And (e) dodecyltrimethyl ammonium bromide (DTAB).
FIG. 2 (a) is a graph showing the viscosity as a function of the shear rate of a pure CNF suspension having a different mass concentration, and FIG. 2 (b) is a graph showing the frequency dependency of the storage elastic modulus (G ') and the loss elastic modulus to be.
Fig. 3 (a) is a graph showing the dynamic strain-dependent number of leaflets G 'and G''of pure CNF suspensions of different concentrations. Fig. 3 (b) is a graph showing the yield Stress τ _y and yield strain

Of FIG.
4 is a graph of the modulus dependency of the pure CNF suspension.
5 (a) is a graph showing storage elastic modulus (G ') and loss elastic modulus (G ") of a pure CNF suspension and a CNF suspension modified with a nonionic surfactant at a concentration of 0.6% (G ') and a loss elastic modulus (G'') of a suspension of CNF modified with a nonionic surfactant at a concentration of 1.2%.
6 (a) is a graph showing the electric field autocorrelation function g (t) of a 0.1% concentration CNFs suspension having five different concentrations of TX100 compared to a pure 5% TX100 solution, (Τ ₁ , τ ₂ ) as a concentration function of pure TX100 and FIG. 6 (c) is a graph showing a distribution p (τ) corresponding to the relaxation time (τ).
Figure 7 is a schematic view of bridged CNFs with surfactant micelles.
8 (b) is a photograph of 0.6% CNFs containing SDS and DTAB, and FIG. 8 (c) is a photograph of 0.6% CNFs according to different surfactants at 8% CNF suspension and G ' and G " of a 0.6% suspension containing different concentrations of SLES.
9 (a) shows a graph of the SLES concentration dependence of the gel modulus in a 0.6% CNF suspension, Fig. 9 (b) shows the yield stress τ _y and the yield strain

≪ / RTI >

Hereinafter, embodiments and examples of the present invention will be described in detail with reference to the accompanying drawings, which will be readily apparent to those skilled in the art to which the present invention pertains. It should be understood, however, that the present invention may be embodied in many different forms and is not limited to the embodiments and examples described herein. In order to clearly explain the present invention in the drawings, parts not related to the description are omitted.

Throughout this specification, when an element is referred to as " including " an element, it is understood that the element may include other elements as well, without departing from the other elements unless specifically stated otherwise.

Throughout this specification, the phrase " step " or " step " does not mean " step for.

Hereinafter, embodiments of the present invention are described in detail, but the present invention is not limited thereto.

One aspect of the present invention provides a solution comprising a cationic surfactant having a mass concentration of 0.08% or less and a cellulose nanofibril. Addition of a surfactant below the critical mass concentration Cc increases the gel reference with maintaining optical clarity and above a critical concentration results in significant fibril aggregates resulting in suspension stability and loss of optical clarity and sedimentation of aggregates.

In one embodiment of the invention, the cationic surfactant may be DTAB. Low concentration (0.02%) of surfactant leads to uniform and optically clear gel formation with CNFs (0.6%).

Another aspect of the present invention provides a solution comprising a nonionic surfactant having a mass concentration of 8% or less and a cellulose nanofibril. The addition of the nonionic surfactant at a concentration of 8% in the CNF suspension (1.2%) of the present invention does not significantly modify the rheology of the system.

In one embodiment of the invention, the nonionic surfactant may be Pluronic F68 or TX100. Nonionic suspensions (Pluronic F68 or TX100) maintain suspension stability at concentrations up to 8%.

Another aspect of the present application may include anionic surfactant and cellulosic nanofibrils having a mass concentration of 8% or less.

In one embodiment of the invention, the mass concentration may be 1.6% or less. The critical concentrations of the anionic surfactants DTAB and SDS in which the stability of the suspension is lost are ~ 0.08% and ~ 1.6%, respectively.

In one embodiment herein, the anionic surfactant may be SDS or SLES. In the present invention, the addition of SLES did not cause the destabilization of the CNF suspension at similar concentrations, and at 8% SLES exhibited syneresis and formed a clear, homogeneous gel.

Another aspect of the present invention provides a method for controlling the viscosity of a solution comprising the step of mixing a cellulosic nano-fibril and a surfactant .

In one embodiment of the present invention, the surfactant may be any one or more of a cationic surfactant, an anionic surfactant, or a nonionic surfactant, and may be a surfactant having an ethoxylated head group. The present invention suggests that micelles are weakly and reversibly related to fibrils, which occur via ethoxylated hydrophilic head groups of surfactants. It also suggests that ethoxylated head groups play an important role in alleviating the attraction strength between fibrils in suspensions containing surfactants.

In one embodiment of the invention, in the mixing step, micelle-bridging of the cellulose nanofibrils may be formed. Gelation occurs by micelle bridging of cellulose nano-fibrils, and viscosification occurs as a result of the large swelling of the gel particles.

[ Example ]

All concentrations in this example are percent by weight (wt%) unless otherwise noted.

CNF  Preparation of suspension

CNFs are obtained in a form functionalized with 0.96% sodium carboxylate in water (USDA Forest Products Laboratory (Madison, WI)). Was prepared using TEMPO-mediated oxidation in a manner similar to that reported previously. The fibrils have a diameter of ~ 5 nm, an aspect ratio of ~ 100, and a sodium carboxylate density of ~ 0.65 mmol g ^-1 . Dialysis was used to concentrate the suspension to 2%. 100 g of 0.96% CNFs stock were loaded into a 34 mm diameter dialysis bag with a molecular weight cut-off of 3500 (Spectra / Por) of a dialysis bag. The bag is immersed in a continuously stirred 10 kg mol ^-1 polyethylene oxide solution at 200 g ^{l -1} for about 6 hours.

The present invention relates to a nonionic surfactant F68 (Pluronic F68, PF68) and Triton-X100 (TX100), a cationic surfactant dodecyl trimethyl ammonium bromide (DTAB) Five different surfactants are used: active agent sodium dodecyl sulfate (SDS) and sodium lauryl ether sulfate (SLES). The formula of each surfactant is shown in FIG. All surfactants are Sigma Aldrich products except for SLES (Nature's Oil). Samples were prepared by adding a suitable amount of surfactant from a 20% stock solution to the CNF suspension. The sample was magnetically stirred for 2 hours, centrifuged at 1000 rpm for 1 minute, and bubbles were removed by sonication for 90 seconds. Thereafter, the samples were kept at rest for at least 2 hours before the experiment.

Rheology  analysis

= 10s^-1로 사전 전단 (pre-shearing)하고 10분간 휴지한 후에 수행되었다. 탄성률(G′) 및 손실 탄성률(G″)의 변형율 스윕(strain sweep) 측정은 ω = 10 rad s^-1에서 실시되었고, 선형 점탄성 영역에서 다음의 진동수 스윕(sub-sequent frequency sweep)를 측정을 위해 5%의 변형율 진폭(strain amplitude)을 설정하는데 사용되었다. 상승 및 하락 램프(60 rad s^-1 내지 0.1 rad s^-1 및 0.1 rad s^-1 내지 60 rad s^{- 1})의 두 가지 연속적인 동적 진동 주파수 스윕(dynamic oscillatory frequency sweep)은 결과의 재현성을 확인하기 위해 수행되었다. 전단속도

는 100 s^-1 내지 0.01 s^-1까지 범위의 동적 실험 후에 정상류(steady flow) 측정이 행해졌다.Rheological properties were analyzed using a rheometer (MCR301 rheometer (Anton Paar)) in cone-plate geometry (50 mm diameter, 1 degree angle) in strain-controlled mode. All measurements were carried out at 20 ° C. The instrument surface was roughened (with sandpaper) appropriately to eliminate slippage of the sample. A thin film of mineral oil applied around the sample was used to successfully inhibit water evaporation during the experiment. The rheology measurements were carried out on samples

= 10 s ^-1 before pre-shearing and 10 min resting. Strain sweep measurements of modulus of elasticity (G ') and loss modulus (G ") were carried out at ω = 10 rad s ^-1 and the following sub-sequent frequency sweep was measured in the linear viscoelastic region Was used to set the strain amplitude to 5%. Rising and falling ramp ^- two consecutive dynamic oscillation frequency sweep (dynamic oscillatory frequency sweep) of (60 rad s ^-1 to 0.1 s ^-1 rad and 0.1 rad s ^-1 to about 60 rad s ¹⁾ check the reproducibility of the results Lt; / RTI > Shear rate

This measurement was done steady flow (steady flow) after the dynamic test of the range up to 100 s ^-1 to 0.01 s ^-1.

dynamic Light scattering  analysis

Dynamic light scattering (DLS) was performed using a CGS-5000F goniometer (ALV GmbH) with wavelength λ = 532 nm (coherent) and angle θ = 65 °. The scattering vector q = (4πn ₀ / λ) sin (θ / 2) = 0.017 nm ^-1 where n ₀ is the refractive index of the continuous phase of the suspension (water) and θ is the scattering angle between the incident and scattering beams. Data were collected at a total of 30 times per sample, every 60 seconds. The autocorrelated intensity was analyzed using the CONTIN algorithm to obtain a relaxation time distribution.

Zeta potential measurements were obtained by electrophoresis light scattering using a Brookhaven NanoBrook Omni running at 658 nm wavelength. At least ten measurements were made on 0.01% CNFs suspensions and 0.01% CNFs containing surfactants (0.5%, 1%, 2%, and 5% concentration of Triton X-100, Pluronic F68, SDS, SLES and DTAB) . Zeta potentials were also obtained with 5% solutions of ionic surfactants SDS, SLES and DTAB. Several CNF suspensions were measured several times to confirm the reproducibility of the results between samples.

The chemical formulas of the surfactants used in the present invention are shown in FIG. 1 and are (a) Pluronic F68 (PF68) (x = 29, y = 76, z = 29); (b) Triton-X 100 (TX100) (n = 9-10); (c) sodium dodecyl sulfate (SDS); (d) sodium lauryl ether sulfate (SLES) (n = 3); And (e) dodecyltrimethyl ammonium bromide (DTAB).

= 10^-2s^-1)에서, 0.3% 내지 1.2% 샘플 사이에서 3 자릿수 크기로 증가하는 농도에 대한 강한 점도의 의존성이 있다. 상기 현탁액은 10^-2부터 10²s^-1까지의 전단속도에 걸쳐서 지속적인 전단 유동화(shear-thinning)를 보인다. 이러한 전단 속도 영역에서 점도는 멱법칙(power-law) 관계인 η =

(|n| ≤1, n은 전단 유동화 지수(shear thinning exponent)이고 K는 농도(1 s^-1의 전단 속도에서 점도에 상응하는))로 잘 표현된다. 근사(fit)는 실선으로 나타냈고, 삽도는 0.3%에서 n = 0.37부터 1.2%에서 n = 0.86까지 증가하는 전단 유동화 지수의 농도 의존도를 보여준다. 데이터로부터 고전단 속도 점도 평탄면 및 저전단 속도 점도 평탄면의 부재를 확인할 수 있다.Figure 2 (a) shows the viscosity as a function of the shear rate of the CNF suspension at three different mass concentrations (0.3% (●), 0.6% (■), 1.2% (▲)

= 10 < ^{-2 &} gt ^; s <" ¹ >), there is a strong viscosity dependence on the concentration increasing from 3% to 3% between 0.3% and 1.2% of the sample. The suspension exhibits continuous shear-thinning over shear rates from 10 < ^{-2 &} gt ^; to 10 < ^{2 >} s < ^{-1 &} gt ;. In this shear rate range, the viscosity is the power-law relationship η =

(where | n | ≤1, n is the shear thinning exponent and K is the concentration (corresponding to the viscosity at a shear rate of 1 s ^-1 )). The fit is represented by a solid line and the plot shows the concentration dependence of the shear fluidization index from 0.3% up to n = 0.86 from 1.2% to n = 0.37. From the data, it can be seen that there is no high shear rate viscosity flat surface and low shear rate viscosity flat surface.

The frequency dependence of the elasticity or storage elastic modulus (G ') and the viscosity or loss elastic modulus (G ") is shown in FIG. 2B (G' is a color symbol and G" is a solid line symbol). All three samples exhibit a weak power law dependence of dynamic moduli for frequency and loss tangent (tan δ = G "/ G '). It is substantially independent of frequency. The frequency dependence is G "~ ω ⁰ at 1.2% sample ^. Thus it is weakened as at ¹ and 0.3% Sample G '~ ω ^{0 .35} in concentration. Thus, the sample transitions from a state of fluid (G "> G ') at 0.3% to a state of solid (G'>G") at 1.2% G " and G " are equivalent in the considered frequency range, as reminiscent of " critical gel ".

(△)에 따른 변형율 스윕(Strain sweep) 데이터를 나타낸다. 도 3(a)는 순수 CNF 현탁액(0.3%(●), 0.6%(■), 및 1.2%(▲))의 동적 변형률 의존 전단지수 G′(채색기호) 및 G″(실선기호)를 나타내는 그래프이고, 도 3(b)는 응력-변형률 직선성으로부터 부분편차 ε(ε=0.05; 상향 삼각형, ε=0.10; 하향 삼각형)를 측정하여 얻은 항복 응력 τ_y(▲) 및 항복 변형

(△)의 농도 의존성을 나타내는 그래프이다.In the steady flow test, the shear rate range shows no dynamic yield stress, while in vibration measurements the suspension is virtually a yield stress fluid with a well defined static yield stress. Figure 3 shows the yield stress τ _y (▴) and the yield strain

(Strain sweep) data according to (?). 3 (a) shows dynamic strain dependent leaflets G '(color symbol) and G "(solid line symbol) of the pure CNF suspension (0.3% (●), 0.6% (■) and 1.2% Fig. 3 (b) shows the yield stress τ _y (▴) obtained by measuring the partial deviation ε (ε = 0.05; upward triangle, ε = 0.10; downward triangle) from the stress-

(?).

는 시스템이 ε=0.05 및 ε=0.10에서 측정된 응력-변형율 데이터(stress-strain data)의 응력값(stress value)의 직선성(linearity)으로부터 부분편차 ε을 나타내는 점으로서 결정되었다. 점성 소실(viscous dissipation)의 소폭 상승과 함께 가장 농축된 현탁액의 항복(yielding)이 일어난다. 이는

이상으로 변형율 증가시 G″가 증가하는 것으로 보아 명백하다. CNFs는 물리적 얽힘 때문에 피브릴러 네트워크(fibrillar network)를 형성하는 것으로 알려져 있다. 온도의 함수로 고분자 사슬이 피브릴을 형성하는 메틸셀룰로오스 용액에서 이러한 네트워크 형성이 최근 관찰되었다. 그러나, 필라멘트나 피브릴을 형성하는 생물학적 물질(액틴, 피브린, 콜라겐 등)에 형성된 네트워크 겔에서 보통 관찰되는 변형 강성도(strain stiffening)는 관찰되지 않았다.

가 0.3% 내지 1.2%로 농도가 변화할 때 100% 내지 10% 이하로 감소하는 반면에, σ_y는 0.5 Pa의 낮은 값에서부터 10 Pa까지 농도와 함께 증가한다. 피브릴러 겔(fibrillar gels)에서 τ_y와

사이의 역전관계는 종종 관찰되며, 탄성 계수(modulus)가 증가함에 따라서 시스템의 기계적 취성(fragility)의 증가가 예상하던 바와 같이 나타났다.G " rapidly increases from 0.3 Pa to 100 Pa in the concentration range considered. _y and τ

Was determined as a point representing the partial deviation epsilon from the linearity of the stress value of the stress-strain data measured at? = 0.05 and? = 0.10. Yielding of the most concentrated suspension occurs with a slight increase in viscous dissipation. this is

And the G "increases when the strain is increased. CNFs are known to form fibrillar networks due to physical entanglement. This network formation has recently been observed in methylcellulose solutions in which the polymer chains form fibrils as a function of temperature. However, strain stiffening usually observed in network gels formed in biological materials (actin, fibrin, collagen, etc.) forming filaments or fibrils was not observed.

Decreases from 100% to less than 10% when the concentration changes from 0.3% to 1.2%, while _y increases with the concentration from the low value of 0.5 Pa to 10 Pa. In fibrillar gels, τ _y and

Are often observed, and as the modulus increases, the increase in mechanical fragility of the system is as expected.

The yield strain is similar to or slightly greater than that observed in the biological gel discussed above. The concentration dependence of the elastic modulus is measured at ω = 10 rad s ^-1 at a mass concentration ranging from 0.2% to 2%, and is shown in FIG. Assuming that the elastic modulus of the sample is independent of the frequency, the storage modulus follows the power law with G '= c ^α (α = 2.1). By including samples with weak frequency dependence, the exponent increases to a = 4.1. In Fig. 4, the shaded portion is a density of elasticity independent of the frequency.

,

등에 의한 측정에 의하면 α = 3이었다. Gennes와 Doi-Edwards에 의해 제공된 얽힌 폴리머에 관한 표준 이론은, α를 2.25로 제시한다.Previous work on fibrillar gels has yielded another index of the power law relationship between the elastic modulus and the fibril concentration (nominal volume fraction) in the system. In a conventional study by Tatsumi and Matsumoto et al. On microcrystalline cellulose, bacterial cellulose, and fibrillated cellulose fibers from various sources, it was calculated as α = 2.25. According to Naderi and Pettersson et al., Carboxy-methylated nanofibrillated cellulose (α = 5.2)

,

, It was found that? = 3. The standard theory of entangled polymers provided by Gennes and Doi-Edwards presents α as 2.25.

The network's theoretical consideration of gel elasticity derived from the bending stiffness of the filament derived from the associated biopolymer yields an index of entangled solution diluted by 2.2 and an index of dense crosslinked gel of 2.5.

The theoretical presentation by Hill recently suggests a new scaling theory that suggests 11/3 of the exponent at low concentrations and a limiting exponent of 7 at high concentrations. Data from Jowkarderis and van de Ven on TEMPO-derived fibrils were analyzed using Hill's theory, but based on a simple power law approximation, we proposed α = 4.52.

There are considerable differences in the data known to date in the literature. This difference can be attributed to the inevitable deformation of the chemical composition and structure of the CNFs produced using different raw materials. In addition, the use of gel moduli is not independent of frequency, so it is not a plateau modulus in a strict sense.

It is clear that in the present state the scaling exponent is empirically accessible and that the modulus of elasticity can not be reliably determined at a given limited concentration range, but rather as a function of frequency. Therefore, no special significance can be given to the observed exponent value through measurement. G '~ ω ^3/4 days seomjil (filamentous) members of the high frequency region of the network that is commonly observed was observed due to contribution of a bending mode (bending modes) of the filaments in the network time. This can be attributed to the fact that the experimental conditions were not wide enough to capture the high frequency behavior of CNF. This is also useful to consider similarities between CNFs and filamentous networks that are inaccurately observed in other systems due to repulsion rather than associated binding interactions between the fibrils producing different binding dynamics.

Addition of a nonionic surfactant (Pluronic F68 or TX100) to the 0.6% CNF suspension caused the highest concentration, a slight increase in the gel modulus at 8%. As shown in Fig. 5 (a), the storage moduli of TX100 and Pluronic F68 increase sharply by two times and four times, respectively. In these samples, the storage elastic modulus exceeds the loss elastic modulus in the measured frequency range.

However, the presence of surfactant at concentrations lower than 4% did not result in an increase in the modulus of the CNF suspension. As shown in the data in Figure 5b, the addition of a nonionic surfactant at a concentration of 8% in a 1.2% CNF suspension does not significantly modify the rheology of the system (where TX100 (), 8% Pluronic F68 , Pure CNFs (●), G 'is a color symbol, and G "is a solid line symbol).

The suspension rheology was modified with nonionic surfactants and dynamic light scattering (DLS) was used to explain the micro-mechanics of the system and gain insight into the mechanism. The suspension was analyzed at a concentration of 0.1% ensuring that the low viscosity of the system was reasonably detectable in the experimental range of the measuring apparatus by the diffusive mode.

) 또한 사용된다. 도 6(b)에서 두 한계 지수(stretched exponential)의 합인 g(t) = A exp[-(t/τ₁]

+ B exp[-(t/τ₂)

] + C에 의한 자기 상관 함수를 근사함으로써 얻은 완화시간 값을 나타낸다. 도 6(c)에 완화 시간(τ)에 해당하는 분포 p를 표시하였고, g(t)는 g(t) = ∫p(τ)exp(-t/τ)dτ 형태의 지수 감소 분포에 의해 설명된다. 순수 CNFs 현탁액 및 순수 TX100 용액의 자기 상관 함수는 단일 지수 감쇠를 나타낸다.Figure 6 (a) shows the electric field autocorrelation function g (t) = g2 (t) -1 of a 0.1% concentration CNFs suspension with five different concentrations of TX100 compared to a pure 5% TX100 solution. Here, the concentrations of the different TX100s of the CNFs suspension are 0% (∘), 0.5% (◇), 1% (△), 2% (□), 5%

) Is also used. G (t) = A exp [- (t / τ ₁₎ ], which is the sum of two stretched exponents in FIG. 6 (b)

+ B exp [- (t / ₂ )

] + C, which represents the relaxation time value obtained by approximating the autocorrelation function. The distribution p corresponding to the relaxation time (τ) is shown in FIG. 6 (c) and g (t) is given by the exponential decay distribution in the form of g (t) = ∫p (τ) exp (-t / . The autocorrelation function of pure CNFs suspension and pure TX100 solution represents a single exponential decay.

8.8 nm로 추산하였다.Based on the scattering vector dependence of the relaxation time, the relaxation time is due to the mixed result of the diffusion mode of the TX100 micelles, the diffusion of CNFs and the diffusive and internal bending modes. The time scales were well distributed, consistent with the significant differences expected in the hydrodynamic radius of the TX100 Michel associated with CNFs. Michelle's hydrodynamic size is d _h

8.8 nm.

Considering the concentration of the surfactant used in the present invention, only the presence of spherical micelles in the suspension can be expected. Other forms of formation such as worm-like micelles or lamellar bilayers require the presence of very high concentration surfactant or second phase components. However, the possibility of forming lamellar morphologies at the CNF surface can not be ruled out, especially in the preferred linkage between a given CNFs and a surfactant head group.

Since samples containing both CNFs and surfactants exhibit two relaxations, there are two peaks in the relaxation time distribution. In particular, in short timescale mode, CNFs are significantly delayed when present. In the fibril mode, however, it is also shifted to a longer time (Fig. 6 (b)). The fast mode changes the concentration-dependent manner with the short time scale relaxation, which is steadily slower as the TX100 concentration decreases to 0.5%. In addition, the data strongly indicate the associated interactions between Michel and CNF.

The present invention suggests that micelles are weakly and reversibly related to fibrils. This association occurs via ethoxylated hydrophilic head groups of surfactants and has been previously observed in ethoxylated surfactants on cellulose. Ideally, the system exhibits a resolved peak corresponding to fibrils associated with free micelles, free fibrils and micelles.

However, the data is semantically intertwined with the time scale for connecting / separating Michel-fibrils, and these properties are expected to be erased or not easily dissociated except in the original mode of movement and expansion.

In this scenario, the effective diffusivity of the micelle is associated with the fibrils in a concentration-dependent manner that reflects the on / off time of the micelle-fibril relationship (ie, the micelle is adsorbed on the fibril). Relatively, the spread of micelles is substantially the slowest in low-concentration surfactants. The time scale of the fibrils increases similarly as the concentration of the surfactant increases. This is consistent with an increase in the effective size of the fibrils, which is caused by high surfactant concentrations causing an increase in micelle adsorption. Instead, Michelle's diffusion time-scale lag can represent a significant growth in michelle's size as the TX100 concentration decreases. However, this explanation contradicts the behavior of surfactants in solution (not even in the presence of nanomaterials), as the aggregation number and micelle size are not a function of concentration above CMC.

0.4 nm, d_미셀

10 nm, d_CNF

10 nm이고, CNFs의 길이는 1 ㎛이다. 자유 미셀은 녹색으로 표시되고, CNF 접합된 미셀은 삽도에 붉은색 코로나(corona)로 도시되어 있다. Based on the above observations, gelation appears to originate from the micelle bridging of fibrils, which is schematically shown in Fig. The composition size (diameter: d) of each gelation composition in Fig. 7 is d _{Na +}

0.4 nm, d _micelle

10 nm, d _CNF

10 nm, and the length of CNFs is 1 占 퐉. Free micelles are shown in green, and CNF-bonded micelles are shown as red corona in the illustration.

A small increase in elasticity in the presence of nonionic surfactant indicates that the association is not particularly active. It is interesting to consider DLS data of CNFs (pure solution, 0.6%) such as more concentrated gels. The autocorrelation function represents a significant expansion.

Approximating the autocorrelation function of the diluted gel-like sample to the limit indices (g (t) = exp [- (t / τ) ^β ] reflects a noticeably delayed relaxed relaxation time scale (0.01 and 0.6% , Respectively, tau is 1.45 and 50 and beta is 0.6 and 0.27).

1 mPa s이고 0.1% CNFs는

0.2 Pa s인 반면에, CNFs에서 TX100 미셸의 완화시간의 2 자릿수 크기 차이는 비율

2에 의해서만 변한다.As shown in FIG. 5B, the change in the rapid relaxation mode is not caused by the viscosity difference of the suspension. 5% The viscosity of TX100 is

1 mPa s and 0.1% CNFs

0.2 Pa s, while the two-digit magnitude difference of the relaxation time of TX 100 michel in CNFs is a ratio

2 only.

This is consistent with the idea that most michelles are just free to diffuse in the mesh space defined by the fibril crossing, where the local viscosity is the viscosity of the water.

In addition, the viscosity of a 0.1% CNF suspension containing TX100 can not be distinguished experimentally as a function of the TX100 content. Finally, the same gradual deceleration of the free michel mode can be observed in more diluted systems (0.01% CNFs). However, this is confounded by the experimental difficulties associated with finely scattered signals from CNFs associated with TX100 michelas that require the use of visualized logarithms.

In contrast to the case of nonionic surfactants, the presence of a 4% concentration of cation (DTAB) or anionic (SDS) surfactant in a 0.6% CNF suspension is deduced from the hazy appearance which indicates the formation of fibril aggregates Resulting in loss of suspension stability. Figure 8 (a) shows 0.6% CNFs with different surfactants at 8% concentration and the surfactants are shown as nonionic (0), cationic (+) and anionic (-). As shown in Fig. 8 (a), the sample in which DTAB exists has a cloudy appearance. However, low concentration surfactants of 0.02% (DTAB) and 0.16% (SDS) lead to uniform and optically clear gel formation with 0.6% CNFs (Fig. 8 (b)). The storage modulus for DTAB at 0.02% concentration in the CNF suspension is 2.2 Pa and increases from 0.08% DTAB to 15.2 Pa.

The critical concentrations at which the stability of the suspension is lost are ~ 0.08% and ~ 1.6% for DTAB and SDS, respectively. Surprisingly, however, the addition of SLES, which is widely used as anionic surfactant in detergent products, did not cause destabilization of the CNF suspension at similar concentrations. Even at 8%, SLES exhibited syneresis and formed a clear, homogeneous gel.

)은 도 9(b)에 나타낸 바와 같다. 응력-변형율 데이터의 응력 값의 직선성(linearity)으로부터 부분편차 ε를 나타내는 점으로 결정된, 항복응력 τ_y(▲) 및 항복변형

(▽)는 SLES 농도 의존성을 나타낸다(여기서, ε=0.05(상향 삼각형) 및 ε=0.10(하향 삼각형)).8 (c) is a graph showing the G 'and G''of a 0.6% suspension of pure 0.6% CNF and a 0.6% suspension of SLES containing 4% and 8%, wherein G' Symbol, G " is a solid line symbol). As shown in FIG. 8 (c), the addition of SLES increases the G 'and G "at almost frequency-independent storage modulus corresponding to a well-formed gel with a behavior similar to that of solid, ". The SLES concentration dependence of the gel modulus can be seen in Figure 9 (a), where the dashed line represents the modulus of the pure suspension. When SLES was added at a higher concentration (16%), there was destabilization of the CNF suspension. Yield stress (τ _y ) and yield strain

) Is as shown in Fig. 9 (b). The yield stress τ _y (▴) and the yield strain (ε) determined from the linearity of the stress values of the stress-strain data,

(∇) represents the SLES concentration dependence, where ε = 0.05 (upward triangle) and ε = 0.10 (downward triangle).

Increased yield stress due to the addition of SLES occurs in response to a reduction in yield strain as observed also in the pure suspension with increased CNF concentration. The difference in stability of the CNF suspension in which the five surfactants are present can be rationalized by considering the nature of the interaction between the surfactant head group and the cellulose nanofibrils.

Since cationic surfactants are expected to interact strongly with negatively charged fibrils, it is not only reasonable but also probable to induce a strong micelle-bridged association between the fibrils. CNFs were negatively charged at about -45 mV while the addition of 0.5% DTAB to a 0.01% CNFs suspension resulted in a positive charge of zeta potential comparable to DTAB Michel's zeta potential (nearly 40 mV) Charge causes.

Despite having the same negative charge, anionic surfactants are also seen to interact with the cellulose surface. This is characterized by the pH-dependent manner of NaDDBS on cellulose, which increases and decreases pH but increases the negative charge on the cellulose surface without excluding good interactions of cellulose with sodium dodecylbenzenesulfonate (NaDDBS).

A similar result also appears in the SDS for cellulose. The partial hydrophobic nature of cellulose plays a role in explaining the opposite connection to the intuition of nominally negatively charged surfaces and negatively charged species. Zeta potential measurements followed by an increase in zeta potential (ie, SDS and SLES zeta potentials of -60 mV and -70 mV, respectively) of a 5% pure surfactant solution were the first to decrease with the addition of anionic surfactant . Compared to SDS, a higher concentration of SLES is required to saturate the zeta potential of CNFs consistent with the threshold concentration profile.

The results show that the attraction induced by SDS is stronger than that induced by TX100 or Pluronic F68, despite the fact that both SDS and CNFs were negatively charged. Thus, ethoxylated head groups are preferred, but conclude that they have very weak interactions with CNFs.

Finally, a significant difference in the behavior between SDS and SLES is that the above results for the presence of ethylene oxide units, a hydrophilic head group, cause a sharp rise in the SLES concentration needed to induce fibril aggregates for SDS . In the present invention, the critical instability concentration is nominally uncorrelated with the CMCs of the surfactant.

The properties of the system are characterized by an increase in the modulus of elasticity with the addition of the surfactant and a final loss of stability of the suspension in the case of nonionic surfactants. Light scattering measurements indicate the michel-fibril linkage, indicating micelle-bridging of the fibrils resulting in gelation at low CNF concentrations and gel-based enhancement at higher CNF concentrations. The charged surfactant used in the present invention had a strong destabilizing effect on the gel network except for SLES. At low concentrations, the storage modulus of the CNF suspension increased similarly, but at high concentrations the suspension became unstable.

Significant differences between the critical SLES and SDS concentrations for the loss of stability of the suspension and the high stability in the presence of ethoxylated nonionic surfactants are due to the reduction of the attraction strength between the fibrils in the suspension containing the surfactant, Head group plays an important role.

0.08%), 비이온성 현탁액(Pluronic F68 또는 TX100)은 8%까지의 농도에서 현탁액 안정성이 유지된다. In summary, pure suspensions show a strong shear fluidization with a transparent yielding stress fluid and a power law dependence of the modulus of elasticity over the concentration expressed as G '~ c ^2.1 . The addition of surfactants below the critical mass concentration Cc increases the gel reference with maintaining optical clarity. Larger than the critical concentration results in significant fibril aggregates, resulting in suspension stability and loss of optical clarity and sedimentation of aggregates. The critical concentration is the lowest of the cationic suspension (DTAB), while (Cc

0.08%), nonionic suspensions (Pluronic F68 or TX100) maintain suspension stability at concentrations up to 8%.

1.6%에서 안정성 상실이 일어나는 반면에, 음이온성의 SLES는 8% 농도까지 현탁액 안정성이 유지된다. 동적 광 산란 데이터는 셀룰로오스 피브릴과 에톡시화된 계면활성제 헤드그룹의 결합 상호작용에 의해 매개되는 미셸-나노피브릴 브릿징에 의한 겔 형성 시나리오와 일치한다. 이는 SDS 및 SLES로 개질된 현탁액 특성 사이의 강력한 차이를 설명한다. 이러한 결과는 계면활성제를 함유한 시스템에서 레올로지 개질제로서 CNFs의 사용을 암시하고 있다.The anionic suspension, SDS,

While stability loss occurs at 1.6%, the anionic SLES maintains suspension stability to 8% concentration. Dynamic light scattering data is consistent with gel formation scenarios by Michel-nano fibril bridging mediated by the binding interactions of cellulose fibrils with ethoxylated surfactant head groups. This explains the strong differences between SDS and SLES modified suspension properties. These results imply the use of CNFs as rheology modifiers in systems containing surfactants.

Claims (15)

delete delete delete delete delete delete delete delete delete delete delete delete delete A solution containing a mass concentration of 8% Pluronic F68 nonionic surfactant and a mass concentration of 0.6% cellulose nanofibrils,
The solution is a frequency ω is 10 ^-1 rad.s ^-1 day time, the storage modulus G 'is 2 Pa, the loss modulus G''is 0.8 Pa, the frequency, the storage modulus when ω is 10 days rad.s ^-1 G '5 Pa, loss elastic modulus G''is 3 Pa. A mass concentration of 8% Pluronic F68 nonionic surfactant and a mass concentration of 0.6% cellulose nano-fibril, and the mixed solution has a viscosity at a frequency ω of 10 ^-1 rad.s ^-1 , A storage modulus G 'of 5 Pa and a loss modulus G "of 3 Pa when the storage modulus G' is 2 Pa, the loss modulus G" is 0.8 Pa, and the frequency ω is 10 rad.s ^-1 . Viscosity control method.

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