KR101391323B1 - Cotton fibers with conductivity and the fabrication method thereof - Google Patents

Abstract

The present invention relates to a cotton fiber having conductivity and a method for producing the same. More particularly, the present invention relates to a cotton fiber which is an insulator having no electrical characteristics and which is imparted with conductivity and electromagnetic wave shielding property by doping iodide in a natural cotton fiber, and a manufacturing method thereof.

Description

TECHNICAL FIELD [0001] The present invention relates to a cotton fiber having conductivity and a method of manufacturing the same,

The present invention relates to a cotton fiber having conductivity and a method for manufacturing the same, and more particularly, to a cotton fiber having conductivity and electromagnetic wave shielding property by doping a non-metallic material to a non-conductive cotton fiber.

In order to understand the charge transport properties in polymeric materials, the electrical conductivity properties in polymers have been extensively studied for the past 20 years. Identification of charge injection and charge transfer processes is also essential for future use of these materials. The conduction mechanism is characterized primarily by transport parameters such as charge carrier density and charge carrier mobility.

In the present invention, the doping effect on the transport properties of the polymer was noteworthy. Chemical, photochemical, or electrochemical doping has been used to introduce intrinsic charge carriers into organic semiconductors. In reaction with the macromolecular matrix, the doping materials differ in their degree of reducing the specific resistance of the polymer depending on their chemical structure and manner. These properties also provide various possibilities for natural cotton fibers.

,

및

과 같은 내부 수소 결합의 수는 셀룰로오스 섬유에 있어 정렬도(ordering)를 결정한다. (Abhishek S, Samir OM, Annadurai V, Gopalkrishne Urs R,Mahesh SS, Somashekar R (2005) Eur Polym J 41:2916)Cellulosic fibers (CFs) are smaller in particle size, and the boundaries of the particles can be regarded as relatively large polycrystalline materials. Moreover, the cellulose fibers can have various morphologies depending on the processing conditions. Also, even if they are composed of the same chemical unit,

,

And

The number of internal hydrogen bonds, such as < RTI ID = 0.0 > S, < / RTI > determines the ordering in the cellulose fibers. (Abhishek S, Samir OM, Annadurai V, Gopalkrishne Urs R, Mahesh SS, Somashekar R (2005) Eur Polym J 41: 2916)

Also, by applying different processing conditions, the shape of the resultant cellulose fibers may also vary. This also leads to a change in the physical properties of the resulting product. Many research groups have been studying these changes through various attempts, such as various chemical treatments between fibers and matrices, grafting, coupling, and physical range of fibers by polymeric sleeves. However, most studies have focused on in-situ polymerization, which does not require the destruction of materials and provides significant conductivity, in producing conductive cotton fibers. (Oh KW, Hong KH, Kim SH (1999) J Appl Polym Sci 74: 2094)

The conductivity and charge-storage capability of the cotton fiber are greatly affected by doping with appropriate impurities. These fibers are used in industrial applications such as filters as well as in home and commercial applications such as electrostatic discharge and electromagnetic interference shielding. The microwave absorption properties of these fibers are also highly desirable and can be used in military applications such as camouflage and stealth technology in stealth technology.

The present invention relates to a cotton fiber which is excellent in skin contact property, excellent in intimacy, excellent in adhesion to skin and excellent in thermal stability, and capable of washing at high temperature while maintaining conductivity, compared with synthetic fibers.

Another object of the present invention is to provide a cotton fiber which can be attached to various electronic products or parts that emit harmful electromagnetic waves to absorb or shield harmful electromagnetic waves.

In order to solve the above technical problem,

(1) immersing and washing the natural cotton fiber in a NaOH solution; (2) immersing the NaOH-treated cotton fiber in an iodine solution dissolved in alcohol; And (3) removing the cotton fiber from the iodine solution and drying the cotton fiber. The present invention also provides a method for producing an iodine-doped conductive cotton fiber.

According to an embodiment of the present invention, the concentration of the NaOH solution used is preferably 10-40 vol%, and the process of soaking the cotton fiber in the NaOH solution is preferably performed at a temperature of 15 ° C or lower.

According to another embodiment of the present invention, the concentration of the iodine solution may be 3-15 vol%, but it is not limited thereto and varies depending on the applied product. Also, the drying process of the cotton fiber can be performed at 60 - 90 캜.

Ultimately, the present invention provides a cotton fiber having conductivity and electromagnetic wave shielding property, characterized by iodine-doped natural cotton fiber.

In the present invention, iodine is doped in an electrically non-conductive natural cotton fiber to impart excellent conductivity. The photoconductivity of iodine-doped cellulosic fibers was first disclosed in the present invention and the conductivity of pure cellulosic fibers and doped cellulosic fibers was investigated to find that the i) , (Ii) the charge transport mechanism depending on both the temperature and the electric field, and (iii) the effect of doping on the photophysical properties. Through such iodine doping, various electrical conductivities can be imparted over a wide range from an insulating material to a metal-like material in a polymer material.

The cotton fiber according to the present invention is superior to synthetic fibers in skin contact, has excellent intimacy, is an environment-friendly material having excellent adhesion with skin, and has excellent thermal stability, so that it can be washed at high temperature and can have conductivity and electromagnetic wave shielding. In addition, since the existing synthetic fibers are manufactured by chemical bonding, not by coating or plating, they are not washed or peeled, so that the characteristics can be maintained for a long time. In addition, since it has the flexibility of fiber, it is excellent in stability in shape change, and is advantageous in mass production because the process is simple, and there is no problem of surface oxidation because metal material is not coated on the surface.

In addition, unlike conventional conductive fibers, the present invention can be used for military and civilian applications since an electric type can be used to manufacture a solar cell, and the fiber itself can be a solar cell .

Figure 1 is an Arrhenius graph of leakage current versus temperature for undoped cellulosic fibers and iodine doped cellulosic fibers.
2 is a log IV graph for undoped cellulosic fibers and iodine-doped cellulosic fibers, showing the voltage dependence of the leakage current.
Figure 3 shows the log I as a function of V ^1/2 for undoped cellulose fibers and iodine-doped cellulosic fibers.
4 is a graph showing IV characteristic curves for iodine-doped cellulosic fibers measured under dark conditions and under UV illumination, with the photoreaction graph of iodine-doped cellulosic fibers being inserted under different illumination.

Hereinafter, the present invention will be described in detail.

The present invention relates to a cotton fiber having a conductive and an electric type and a method for producing the same, wherein the conductive fiber is produced by adding iodine to the cotton fiber.

Specifically, the conductive cotton fiber according to the present invention comprises: (1) immersing and washing the natural cotton fiber in a NaOH solution; (2) immersing the NaOH-treated cotton fiber in an iodine solution dissolved in alcohol; And (3) removing the cotton fiber from the iodine solution and drying it.

The process of preparing a conductive cotton fiber according to the present invention includes a purification process through NaOH solution as a pretreatment process, which makes the cotton fiber more active in interaction.

According to an embodiment of the present invention, the concentration of the NaOH solution used is preferably 10-40 vol%, and the process of soaking the cotton fiber in the NaOH solution is preferably performed at a temperature of 15 ° C or lower.

According to another embodiment of the present invention, the concentration of the iodine solution may be 3-15 vol%, but it is not limited thereto and varies depending on the applied product. Also, the drying process of the cotton fiber can be performed at 60 - 90 캜.

The concentration of NaOH and iodine solution and the range of treatment temperature were obtained through several experiments. In this range, cotton fibers with excellent conductivity could be produced reproducibly.

Also, the present invention provides a cotton fiber having conductivity and electromagnetic wave shielding property, wherein iodine is doped in a natural cotton fiber.

It is a feature of the present invention that the conductive fiber is changed into covalent bond with iodine and cotton fiber. Conventionally, there are many restrictions in the secondary fabrication process by manufacturing the conductive fiber through the addition of the metal material, but this problem has been solved in the present invention.

In the present invention, experiments were conducted on the electrical transport and photoconductivity of pure cellulose fibers and iodine-doped cellulosic fibers. The experiments were carried out at 293-363 K with varying electric field in the range of 1-100 V cm ^-1 . Experimental results showed that the conductivity of iodine - doped cellulose fibers was significantly improved by four orders of magnitude over the undoped samples.

It has also been found, according to the present invention, that the electrical conductivity of iodine doped fibers follows Ohm's law, while undoped fibers are more likely to follow a bulk-limited Pool-Frenkel conduction mechanism. In particular, the clear-light-directing response in the UV and visible regions of the present invention demonstrates that photoconductivity is essential for the production of band-to-band electron-hole pairs and that the doped cellulose fibers are good conductors of the photogenerated carrier.

On the other hand, as a material for shielding electromagnetic waves, pure metals excellent in conductivity such as gold, silver, copper, nickel, and platinum have been known. These metals have been used for shielding electromagnetic waves. However, the excellent material for shielding electromagnetic waves is metal which is a conductive material. For example, in order to be applied to a material having a function of absorbing or shielding harmful electromagnetic waves that impart electrical characteristics to a flexible material having nonconductive properties, a method of covering a metal with a fiber, coating a conductive paint, plating or vacuum deposition However, the material produced by this method is used in a limited range of applications because of complicated procedures, high cost, low adhesion of metal to the surface of the fiber, and problems in electromagnetic shielding.

In addition, since the present invention has an electric type unlike conventional conductive fibers, it is possible to manufacture a solar cell to be worn. In other words, since the fiber itself becomes a solar cell, it can be widely used for defense and private sector.

Also, when iodine is added to a natural cotton fiber as in the present invention, an electrically n-type conductive cotton fiber can be produced. It is expected to be p-tpye when C is added. At this time, the amount of iodine added to the natural cotton fiber can be adjusted for each application. The present invention also provides a method for producing a p-n structure by adding iodine and C to a natural cotton fiber, or a synthetic fiber bonded with iodine and p-type to a natural cotton fiber. It can be applied to various types of solar cells.

The conductive natural cotton fibers according to the present invention can also be used for wearing solar cells or wearing thermal apparel.

Hereinafter, the structure and characteristics of the present invention will be described with reference to the following examples, which should be construed as illustrative only and not for the purpose of limiting the scope of the present invention.

Example

First, 1 g of cotton fiber was prepared to prepare pure fibers and doped fibers. Cotton fibers must be cleaned before starting the doping process. After washing, the cotton fibers were put into 20 vol% NaOH solution and kept in a water bath at a temperature of 15 DEG C or less for 2 minutes. Taken out of the water bath, washed several times with water, and dried under standard conditions of 20 ° C and 65% relative humidity. This work is beneficial for doping and conductive polymer processing because it can increase the stability of cotton fibers and absorption of reagents.

Isothermal immersion techniques were used to prepare the doped samples. Iodine was dissolved in ethanol at a concentration of 5%. The mercerized fiber was immersed in this solution for 15 minutes in a vertical manner, taken out and heat treated at 70 ° C for 6 hours in the atmosphere until equilibrium was reached.

Test Example

pure Cotton fiber Doped Cotton  Conductivity comparison

A silver electrode and sample (1.0 x 0.5 x 0.2 cm ³ ) were sandwiched between two tungsten electrodes in a specific temperature chamber. The low current level characteristics of the nanoamperes were measured by an electrometer of Keithley 617 under dark conditions and under UV illumination (254 nm). This measurement is carried out at a temperature of 293-363 K and an electric field of 1-100 V cm ^{-1 in the form} of current-voltage (IV) and current-time (I (t)) with metal-cotton and fiber- . The temperature was measured using a constantan thermocouple in complete contact with the specimen.

Current was measured as a function of voltage and temperature for pure cellulose fibers and iodine doped cellulosic fibers according to an embodiment of the present invention. First, when a voltage was applied to pure cellulose wax, a very small amount of current was obtained. The current did not exceed 10 ^-9 A up to a voltage of up to 100V.

Electrical conductivity is calculated as r = I (l / SV) by measuring the current flow through the sample. Where L (cm) is the length of the sample, S (cm ² ) is the area, V is the voltage across the material, and I is the normal observed normal current.

The electrical conductivity of the pure cellulose fiber is from about 7.8 x 10 ^-1 Ω ^-1 cm at ^room temperature and ^1. Other forms of electrical conductivity can be expressed as σ = Σ qi ni μi, where ni is the charge transport density and μi is the charge transport mobility. The values of conductivity (~ 8 x 10 ^-10 Ω ^-1 cm ^-1 ) and average mobility (~ 10 ^-3 cm ² V ^-1 s ^-1 ) are added to the above equation and the contribution to electrical conductivity in this bias range And the number of charge carriers is n ₀ to 10 ¹⁰ cm ^-3 .

On the other hand, steady state current values for the doped samples according to embodiments of the present invention were higher than those measured for pure cellulose fibers at the same operating temperature and electric field. Conductivity of the fiber was increased by four digits or more by iodine doping and was found to be 5.6 × 10 ^-6 Ω ^-1 cm ^-1 at room temperature. Therefore, the calculated charge carriers also ~ ¹⁰ 10 cm ^- was increased to ^{3 -} ~ 10 ¹⁴ cm ^3.

The increase in electric conductivity according to the present invention can be explained as follows. When impurity molecules are present, they connect two specific moieties and begin to lower the potential barrier between them. Thus promoting the movement of the charge carriers of the two specific portions. This phenomenon occurs because charge transfer complexes are formed in the polymer and they effectively reduce the trapping effect by "handing on" on the carrier. It can be inferred from the present invention that the increase in electric field and the improvement in conductivity are due to the gradual increase in bulk carrier density.

Temperature-current characteristics

To better understand the conduction mechanism of cellulose fibers, the present inventors conducted a two-point probe conductivity measurement experiment of a pure sample and a doped sample at room temperature and at 363 K during heating and cooling cycles. Figure 1 shows the current at 100 V obtained from a pure sample as a function of temperature. The current versus 10 < ³ > / T was plotted for the cellulose fiber samples to evaluate the activation energy. (Fig. 1)

At a given voltage the current increased with increasing temperature and appeared as two slopes. There was a slight change in the conductivity in the low temperature range of 323 K or less, and a drastic change in the conductivity in the high temperature range. The temperature coefficient of electrical conductivity in the two regions was positive, so that the samples have the characteristics of semiconductors. Cellulosic materials, when dry, are excellent electrical insulators, exhibiting structural deformations at certain transition temperatures, and containing a large number of traps. Thus, the complex morphology of the conductive polymer makes it difficult to determine the inherent conductivity characteristics.

As a result, the exponential relationship between conductivity and temperature associated with charge carrier generation is associated with not only inherent band transfer but also other thermal activation processes. The conduction properties of such fibers may be due to the nature of the amorphous region which raises the current state to a singulated state. The fact that the mercerized cellulose fibers are considered as mixed crystals (cellulose I or cellulose II) and / or amorphous cellulose may indicate that an increase in electrical conductivity at high temperatures may result in electrons or ions being liberated through the amorphous regions of the polymeric material have.

Molecular motion is initiated by the help of the charge carrier moving and exiting in a unified state, such as the surface, bulk dipole states, molecular ion states, impurities, ends and branches of the molecular chains and crystalline-amorphous boundaries, The conductivity of the substrate increases. The presence of both activation energies is thought to be associated with mixed crystals (cellulose I or cellulose II) and / or amorphous cellulose phase. Thus, electrical transport is likely to be influenced by potential barriers and homogeneities due to grain boundaries.

1, the general tendency of conductivity and temperature dependency was similar even when iodine was doped. That is, the graph curve shows that the temperature-activated behavior is positive as in the case of undoped cellulose fibers.

The room temperature conductivity of the doped sample before and after the temperature dependency measurement showed virtually no change, showing that the annealed sample showed air stability at elevated temperatures and was close to equilibrium. The activation energies obtained in this temperature range (50-100 ° C) were 0.68 eV for pure cellulose fibers and 1.03 eV for doped samples in the same temperature range, respectively. It has been found that at higher doping levels, additional iodine molecules are disordered and the concentration of the hopping center is increased.

The dopant molecules connect the polymer molecules in the amorphous region and serve as additional trapping centers to form the charge transport complex. Since there are many unidirectional parts, the release or excitation of the carrier in this state dominates the conduction process. The sample has low energy range shallow traps and high energy range deep traps. The deep trap lies between the conduction and the valence electron band, while the shallow trap lies below the continuous free level. At sufficiently low temperatures, the electrons are trapped deep. However, as the temperature rises, it is excited to let the deep trap enter the shallow trap or conduction band and participate in the conduction process.

A low value of activation energy for the irradiated sample (0.68 eV) indicates that electrical conduction is predominant. On the other hand, high values at low temperatures indicate the participation of ionic conduction.

Current-voltage characteristic

The current flowing through the undoped and doped samples is measured as a function of applied voltage while maintaining the sample at a constant temperature of room temperature. Leakage current - During the measurement of the voltage, it was observed that the leakage current was reduced by about 5-7% over time after the initial application of the voltage, and the leakage current was about ~ 10 ^-10 A. The higher electric field shortens the time to reach the steady state current. This change in time dependence shows that the first and latter currents are due to different conduction methods.

The temporary reduction in current is presumably due to the dipole direction, the electron trap in a large sample, and the absorption current due to charge accumulation near the electrode or ionic conduction, resulting from the internal charge transfer, the reduction of the substantial electric field in the bulk sample . Since the relaxation time is independent of the electric field, the reduction result is not due to the dipole direction. On the other hand, ionic conduction was not considered due to charge transport requiring bulk transport, the charge supply was reduced, and the current density rapidly decreased as a few coulons passed through the sample.

Log IV graphs of the isotherms at room temperature for the undoped and doped samples are shown in Figure 2 and in the inset, respectively. Two straight lines were observed for undoped samples. In this case, the slope in the low field is about 0.6, but about 0.85 in the high field. This indicates that the current-voltage relationship shows non-ohmic properties in all regions examined. After doping (FIG. 2 and inset), the log IV graph showed Ohmic behavior and increased in proportion to V. This is consistent with previous reports.

The results for the two samples are difficult to explain in the same manner as before. Other possible mechanisms include (a) injecting a charge carrier into the film from a contact through a field-assisted metal-insulator potential barrier, ie Schottky-Richardson (SR) emission reduction, (b) trap depth, ie, Poole-Frenkel (PF) effect, which can be used as a trap.

The current-voltage relationship for SR can be seen from the following equation.

는 Schottky-field 낮춤 상수이며, Φs는 금속 전극-절연체 포텐셜 장벽이고, T는 온도이며, K는 볼츠만(Boltzmann) 상수이고, ε0는 자유 공간의 투과율이며, ε는 물질의 고주파 유전체 상수이고, d는 샘플의 길이이며, V는 인가 전압이다. Where A * is a Richardson constant,

Is the Schottky-field lowering constant, Φs is the metal electrode-insulator potential barrier, T is the temperature, K is the Boltzmann constant, ε0 is the permeability of the free space, ε is the high frequency dielectric constant of the material, d Is the length of the sample, and V is the applied voltage.

The equation (1) predicts a linear relationship between the slope β _SR and log I ¹ and V ^{/ 2} at a constant temperature. Further PF bulk-limited process predicts a linear relationship between the similar I and V ^1/2 log I and Eq. In the above equation (1), the trap depth is replaced by? _SR is replaced by? _PF , and? S is replaced by? _PF . In theory, β _PF = 2 β _SR .

Log I vs. V ^{1 /} for the undoped and doped cellulosic fibers ² are shown respectively in Figures 3 and its insertion Fig. The result for the high field is almost straight, and the data for the low field is much off the straight line. Furthermore, the slope of the log I vs. V ^1/2 at the low voltage (i.e., linear release) for the doped sample is higher than that of non-doped samples.

The creation of a charge carrier is basically presented at the electrode representing the SR mechanism. At high voltage, a charge transfer electrode is reduced because the field of the electrode and injection in a direction to lower the potential barrier insulator, the slope of the log IV ^1/2 plot is comparable to the theoretical value. In the present invention, the linearity of the log IV ^1/2 in the plot shows the high voltage electrical type conduction mechanism.

To distinguish release SR and PF effect, β values were calculated from the slope of the log ^1, IV ^{/ 2} plots, as well as to the experimental value β theoretical values are shown in Table 1 below.

In undoped films, the experimental value of β _exp is close to the theoretical value of β _PF . Therefore, the charge conduction characteristics seem to follow the Poole-Frenkel mechanism. In this case, the emitted current is due to the thermally excited electrons trapped by the conduction band extended by the external field. Surface states, chain folding, molecular disorder, crystalline-amorphous boundaries, and chain ends can act as trapping sites in the polymer. Also, since many polymers contain polar groups, each dipole can act as an electron or hole trap. Charge carriers trapped at this site are excited to contribute to the overall conductivity.

On photoconductivity  Effect of charge separation

In dark and UV illumination, the I-V characteristic was measured in air using a 30 W halogen lamp as a light source. Figure 4 shows that the cellulose fibers measured under darkness (1) and UV illumination (2) at room temperature exhibit a completely ohmic IV characteristic curve. The average dark current of the measured cellulose fibers increased linearly to 0.1 μA with increasing bias from 0 to 10V. At UV illumination (254 nm), photocurrent (PC) exhibited photosensitivity and photocurrent at a dark current rate of 6 and ran at 0.62 μA at 10 V bias.

To stimulate the photoreaction in the doped cellulose fibers, LEDs with different energies in the visible range in ultraviolet light were used. As can be seen in FIG. 4, the photocurrent (PC) in white, yellow and green illumination increased to less than 5-7%, while the photoreactions of red and UV illumination were approximately 21 and 500%, respectively.

Band-to-band absorption occurs in UV. Photoconductivity is inherently caused by the generation of band-to-band electron-hole pairs. From a technical point of view, this result suggests that the doped cellulose fibers respond to UV photodetectors in the UV and visible regions. In the undoped sample, typical conductivity values were always 0.1 nS or less, and some photoreaction was observed after ultraviolet illumination.

The enhancement of photoconductivity in iodine-doped cellulosic fibers can be explained by the photo-induced charge transfer between the I ₂ molecule and the polymer network. This tendency is a unique characteristic of organic polymers and may be related to the charge separation process as well as the carrier formation and excitation process.

The electron transfer from cellulose fibers to iodine is consistent with the increase in electrical conductivity of the absorbing electrolyte and iodine-doped cellulosic fibers, suggesting that it is fairly good at the bottom. Thus, when illuminating with visible light, the generation of a free charge carrier takes place predominantly within the organic matrix. The doping effect of iodine can be explained by the emergence of the photoreaction in the red illumination region, followed by the hole tunneling from the bottom state of iodine to the photoexcitation of electrons and the cellulose fiber chain to the excited state. In particular, a clear photoconductive response at 2.0 eV was seen, indicating that the doped cellulose fibers are good conductors for the photogenerating carrier.

To summarize, in the present invention, the electric conduction currents of pure cellulosic fibers and doped cellulosic fibers were measured as a function of time, electric field and temperature. The experimental results are consistent with the theoretical curves for various conduction mechanisms. The conductivity of the fiber was doped with iodine and increased by more than four digits, and the Ohmic conduction mechanism seems to be well suited for steady-state currents. The significant improvement in conductivity observed in iodine-doped cellulosic fibers is due to the gradual increase in the number of electron carriers increased and the mass of free carrier density generated. The dopant molecules may act as additional trapping centers and are believed to link the polymer molecules in the amorphous region. Further, in the present invention is determined to be the Poole-Frenkel mechanism, the main conduction mechanisms, obvious photoconductive reaction shown in the UV and visible light is essentially a band-to-band electron-as being due to the generation of electron-hole pairs, I ₂ molecules and polymers This is explained by the photo-induced charge transfer between the networks.

Claims (6)

(1) immersing natural cotton fiber in NaOH solution and washing;
(2) immersing the NaOH-treated cotton fiber in an iodine solution dissolved in alcohol; And
(3) removing the cotton fiber from the iodine solution and drying it,
The concentration of the NaOH solution is 20 vol%
Wherein the immersion in the NaOH solution is performed at a temperature of 15 ° C or less. delete delete The method according to claim 1,
Wherein the concentration of the iodine solution is 3 to 15 vol.%. The method according to claim 1,
Wherein the drying of the cotton fiber is performed at 60-90 < 0 > C. delete

Images