44 Figure 2.12 SEM images of surface of control PAN, in-situ PAN/CNC and ex-situ PAN/CNC. 50 Figure 2.15 The behavior of (a) tensile strength, (b) tensile modulus, and (c) toughness of drawn fibers of control PAN, in-situ PAN/CNC, and ex-situ PAN/CNC on various TDR. 58 Figure 2.19 The 2D WAXD integrated, equatorial and meridional scans of (a) control PAN, (b) in-situ PAN/CNC and (c) ex-situ PAN/CNC at various TDR.
Deconvolution of 2D WAXD azimuthal scans of CNC(200) planes (a) in situ. b) Crystalline size of PAN(100) planes of control PAN, in-situ PAN/CNC and ex-situ PAN/CNC fibers. 65 Figure 2.25 Raman spectra of stabilized fibers of control PAN, in-situ PAN/CNC and ex-situ.
Polyacrylonitrile (PAN)
The synthesis of PAN
PAN polymer is synthesized not only as homopolymer but also as a copolymer with comonomers such as methyl acrylate (MA), methyl methacrylate (MMA), methacrylic acid (MAA) and itaconic acid (IA), etc. First, emulsion polymerization is a synthetic method that uses a monomer that is insoluble in a solvent and an initiator that is soluble in solvent 13. Ammonium persulfate (APS) 14, potassium persulfate (PPS) 13, 2-2' Azobis(2-methylpropionitrile) (AIBN) are mainly used as initiators, alkyl -surfate and sulfonate sulfate are used as surfactants, and water is mainly used as a solvent.
AIBN is mainly used as an initiator, and organic solvents such as dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) are often used as a solvent 16. The PAN synthesized by solution polymerization has a slightly lower conversion of 20-40 % as the polymer synthesized by emulsion polymerization and has a relatively linear chain structure.
Polyacrylonitrile (PAN)/Cellulose Nanocrystal (CNC) nanocomposites
Therefore, research is being conducted on PAN/CNC nanocomposite using PAN fibers with high mechanical properties and the strengthening effect of CNC, a renewable source. 20 reported that PAN/CNC nanocomposite fibers containing the weight percentage of CNCs were fabricated by a gel spinning process. They found that rheological properties such as storage modulus and complex viscosity of PAN/CNC solutions were affected by the CNC content.
23 also reported on the fabrication of carbon fibers using PAN/CNC nanocomposite fibers as a precursor. PAN/CNC-based carbon fibers exhibit approximately 2.3 GPa of tensile strength and 265 GPa of tensile modulus and this is comparable to control PAN-based carbon fibers.
Poly (Arylene Ether Sulfone) (PAES)
To maximize the strengthening effect of CNC, the degree of orientation of CNC in the polymer matrix is very important. In particular, the greatest strengthening effect can be obtained when the CNC is aligned in the axial direction instead of in the transverse direction. This is due to the well-aligned PAN chain and the high crystallinity of PAN due to the integration of CNCs.
In general, PAES have a structure in which flexible ether linkage groups are added to the poly(phenylene sulfone) backbone (Figure 1.3). Environmentally friendly PAES synthesized on the basis of ISB was also used for the research carried out in this work, and the chemical structure of PAES is shown in Figure 1.4.
Cellulose nanocrystal (CNC)
Preparation of cellulose nanocrystals
When the number of negatively charged sulfate groups on the CNC surface increases, the functionalized CNC particles are easily dispersed in water due to the repulsive forces between CNCs 31 .
Mechanical properties of cellulose nanocrystals
The synthesis of polyacrylonitrile (PAN)/cellulose nanocrystal
Introduction
- In-situ polymerization including nanofillers
Experimental
- Materials
- Synthesis of polyacrylonitrile
- In-situ polymerization of PAN/CNC (In-situ PAN/CNC) nanocomposite
- Control PAN, ex-situ PAN/CNC spinning dope preparation
- Fiber spinning and post-drawing
- Heat treatment of control PAN and PAN/CNC nanocomposite fibers
- Characterization
Control PAN, in-situ PAN/CNC and ex-situ PAN/CNC fibers were spun by dry-jet wet spinning as shown in Figure 2.2. The control PAN, in-situ PAN/CNC and ex-situ PAN/CNC fibers were stabilized at 260 ℃ for 3 h at a heating rate of 3 ℃/min and flow rate of 2 L/min using aluminum (Al) tube furnace (Nasiltech , Korea). Only in-situ PAN/CNC fibers were carbonized using the iso-strain method (in-situ_iso_PAN/CNC).
The homo-PAN powders used for control PAN and ex-situ PAN were washed using the same method above. The fiber as spun was used for in-situ PAN/CNC (before filtration) sample and in situ PAN/CNC (after filtration) and control PAN, ex-situ PAN/CNC sample was powder after processing process.
Results and Discussion
- Proton Nuclear Magnetic Resonance (1H-NMR) and Fourier-Transform Infrared
- Molecular weight and Elemental analysis studies
- Rheological properties of dope solution
- Thermal analysis of Control PAN and PAN/CNC nanocomposite fibers
- Morphology of nanocomposite and carbonized fibers
- Tensile properties of nanocomposite fibers
- Wide Angle x-ray Diffraction (WAXD) analysis of fibers
- Structural characterization of carbon fibers
The viscosity average molecular weights of in-situ PAN/CNC after filtration (Mv,after) and control PAN/ex-situ PAN/CNC (Mv,PAN) were 370,000 and 360,000, respectively. As shown in Table 2.2, the O content of in-situ PAN/CNC fibers was comparable to that of ex-situ PAN/CNC fibers. The number average molecular weights of in situ PAN/CNC after filtration (Mn,after) and control PAN (Mn,PAN) were 347,000 and 345,000, respectively.
On the other hand, the number average molecular weight of PAN/CNC in situ before filtration (Mn, before) was 310,000. First, the Tg of in-situ PAN/CNC and ex-situ PAN/CNC containing CNC is greater than that of control PAN fibers. Conversely, the Tg of in-situ PAN/CNC was higher than ex-situ PAN/CNC.
The tensile fracture cross-sectional fiber surface of PAN, in-situ PAN/CNC and ex-situ PAN/CNC is shown in Figure 2.11. The tensile properties of control PAN, in-situ PAN/CNC and ex-situ PAN/CNC fibers, dependent on the tensile ratio, are listed in Table 2.7. First, the mechanical properties of in-situ PAN/CNC used as the precursor fibers were the greatest than the.
In Figure 2.17, there are 2D WAXD pattern images of control PAN, in-situ PAN/CNC, and ex-situ PAN/CNC fibers. The 2D WAXD integrated, equatorial and meridional scans of control PAN, in-situ PAN/CNC and ex-situ PAN/CNC fibers are shown in Figure 2.19. The interaction between the PAN chain and CNC in the in-situ PAN/CNC fiber was confirmed.
Deconvolution of 2D WAXD azimuthal scans of CNC(200) planes of (a) in-situ PAN/CNC and (b) ex-situ PAN/CNC with TDR 18. Raman spectra of control PAN, in-situ PAN/CNC and ex -situ PAN/ CNC fibers after the stabilization and carbonization process are shown in Figure 2.25 and Figure 2.26.
Conclusion
Amorphous Poly(Arylene Ether Sulfone) (PAES)/cellulose
Introduction
- Current study of Poly(Arylene Ether Sulfone) (PAES) nanocomposites
Experimental
- Materials
- PAES Filtration
- Solution Preparation
- Fiber spinning and post-drawing
- Characterization
To prepare the PAES/CNC solution, PAES is first dissolved in DMAc according to the corresponding concentration, and then CNC/DMAc/DI water dispersion solution was added to the prepared PAES/DMAc solution. CNC/DMAc/DI water solution was added until the desired CNC concentration was obtained, and the DI water and excess DMAc were evaporated using vacuum distillation at 90 °C. Through the above solution preparation process, spin dopes with CNC concentrations of 1, 5, and 10 wt% compared to the total solid weight were prepared.
The control PAES and PAES/CNC nanocomposite fibers were produced by dry-jet wet spinning as shown in Figure 3.1(a). The temperature of spinning agent was 60 ℃ and spinning agent was passed through the spinneret (4 holes, 200 μm diameter/hole) in a coagulation bath filled with DI water at 10 ℃ to make fiber form. As-spun fibers were immersed in DI water for 24 h at room temperature to remove residual solvent.
Images of the fiber surface and cross-section were observed with a scanning electron microscope (FE-SEM, Nanonova 230, FEI Co.) at an accelerating voltage of 10 kV. The tensile properties of control PAES and PAES/CNC fibers were measured using a single filament tensile tester (FAVIMAT+, Textechno, GmbH). The linear density was measured with a vibroscope, which obtains the value by measuring the resonance frequency.
The effective diameter was calculated using linear density measured with vibroscope and bulk density of polymer.
Result and Discussion
- Fiber Morphology of control PAES and PAES/CNC nanocomposite fibers
- Tensile properties of control PAES and PAES/CNC nanocomposite fibers
- Chain orientation and CNC alignment of PAES and PAES/CNC nanocomposite fibers
The tensile properties of control PAES, PAESCNC1, PAESCNC5 and PAESCNC10 depending on the content of CNC and tensile ratio are displayed in Table 3.1. However, when the CNC content increased to 5 or 10 wt%, the tensile strength tended to decrease to 146.3 MPa. They analyzed that polymer chains along the CNC could not be aligned as the CNC content increased, regardless of the interaction between the CNC and the amorphous polymer chain.
In addition, as the CNC content increases, the probability of occurrence of CNC agglomeration is due to many hydroxyl groups. The CNC(110) and (200) planes are formed in the transverse direction of CNC, and the CNC(004) is a plane formed in the CNC axial direction. It can be seen that the intensity of the azimuthal scan increases as the CNC content increases at the same TDR.
However, the orientation of the PAES chain shows the opposite trend to that of CNC. CNC-adjacent PAES chains having a solid crystalline form are difficult to link due to the anisotropic properties of PAES. From this orientation trend of the CNC chain and PAES, it can be seen that the effect of increasing the modulus is due to the stretch of the CNC and the high modulus of the CNC itself, not due to the stretch of the PAES chain.
The tensile property trends of the nanocomposite fibers prepared in this study were analyzed depending on the CNC content and tensile ratio. However, in the case of tensile strength, although it increases with the draw ratio, it tends to decrease when the CNC content increases from 1 wt% to 10 wt%. The increase in tensile modulus according to the tensile ratio and CNC content is due to the high tensile modulus (150 GPa) of the CNC itself and the increase in the alignment of the CNC.
On the other hand, the tendency of strength to decrease with respect to CNC content is due to the fact that CNC acts as a factor that hinders the alignment of the amorphous polymer chains of PAES and the agglomeration of CNC due to the many functional groups on the CNC surface. This phenomenon increases as the CNC content increases, resulting in a decrease in tensile strength.
