Molecular and thermal studies of carbon fiber precursor polymers with low thermal‐oxidative stabilization characteristics

Abstract

In this investigation, terpolymers, copolymers, and homopolymer of acrylonitrile with dimethylaminopropyl acrylamide (DMAPA), itaconic acid (IA) viz., poly(acrylonitrile‐ran‐3‐dimethylaminopropyl acrylamide‐ran‐itaconic acid) [P(AN‐DMAPP‐IA)], poly(acrylonitrile‐co‐3, dimethylaminopropyl acrylamide) [P(AN‐DMAPP)] were synthesized with varying amounts of comonomers using solution polymerization process. The chemical structure, composition, bonding network were determined employing infrared, 1H and, 13‐carbon nuclear magnetic resonance spectroscopic techniques. Molecular characteristics of as‐synthesized polymers such as different kinds of average molecular weights, molecular weight distribution were estimated applying solution viscometry and size exclusion chromatography. The influence of comonomers (DMPAA, IA) on the thermal stabilization characteristics of acrylonitrile terpolymers in comparison with copolymers and homopolymers of acrylonitrile were studied using differential scanning calorimetry (DSC), hyphenated thermal techniques (thermal gravimetry coupled with differential thermal analyzer).The DSC curves of P(AN‐DMAPP‐IA) exhibit a distinct broader bimodal peaks with thermal exotherm initiating at as low as 165 °C, and followed by two peaks with temperature difference of 42 °C, releasing the evolved heat at a release rate of 0.7–0.11 J g−1s−1over 10 min as compared to 1.2, 7.5 J g−1s−1 in 4.5, 2 min as observed in P(AN‐DMAPP), polyacrylonitrile, respectively. The thermal stability of P(AN‐DMAPP‐IA) and P(AN‐DMAPP), as evidenced by TGA‐DTA was found to be higher than PAN homopolymers. Specific heat capacity measurements confirmed the DSC results. Bulk densities of P(AN‐DMAPP‐IA) were in the range 0.31–0.35 g/cc. These results confirm the low‐temperature stabilization characteristics and suitability of P(AN‐DMAPP‐IA) as low cost carbon fiber precursor polymers. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46381.

Introduction of a Methodology to Enhance the Stabilization Process of PAN Fibers by Modeling and Advanced Characterization

“…Cyclization index (CI) and nitrile to methylene ratio (rnm) are used: It can be seen that, by increasing intensity of treatment (either the temperature or the duration), the peaks at 2940 and 2240 cm −1 are decreased (attributed to methylene and nitrile groups, respectively), due to dehydrogenation and cyclization reactions, respectively. Peaks approximately at 1740 and 1600 cm −1 are attributed to the carbonyl and the conjugated double bonds are progressively formed as expected, with simultaneous decrease of the methylene groups (which can be better observed from the peak at 1446 cm −1 rather than 2924 cm −1 ) [7,8,11,13,16,22,24,29,57,58]. By comparing the spectra at 150 • C and 200 • C, a higher reduction of methylene groups than of the -C≡N groups is observed, indicating that in the latter case dehydrogenation progressed to higher degree.…”

“…Polyacrylonitrile (PAN)-based CFs are more efficiently manufactured (due to their high carbon yield) and demonstrate a structure with less defects and voids, affording CF with high tensile strength in comparison to CFs derived from pitch, Rayon, or renewable precursors [1,[10][11][12][13][14][15]. Given that PAN-based CFs represent about 80-90% of the world production, there is a strong incentive for improving the process design, so that it might be further optimized [9,14,16].…”

Introduction of a Methodology to Enhance the Stabilization Process of PAN Fibers by Modeling and Advanced Characterization

“…It can be seen that, by increasing intensity of treatment (either the temperature or the duration), the intensity of peaks at 2940 cm -1 and 2240 cm -1 (attributed to the methylene and nitrile groups, respectively) decrease, due to dehydrogenation and cyclization reactions, respectively. Peaks at around 1740 cm -1 and 1600 cm -1 attributed to the carbonyl and the conjugated double bonds are progressively formed as expected, with simultaneous decrease of the methylene groups (which can be better observed from the peak at 1446 cm -1 rather than 2924 cm -1 ) [7,8,11,13,16,21,23,28,51,52]. By comparing the spectra at 150 o C and 200 o C, a higher reduction of methylene groups than of the -C≡N groups is observed, indicating that in the latter case dehydrogenation progressed to higher degree.…”

“…PAN-based CFs are more efficiently manufactured (due to their high carbon yield) and demonstrate a structure with less defects and voids, affording CF with high tensile strength in comparison to CFs derived from pitch, Rayon, or renewable precursors [1,[10][11][12][13][14][15]. Given that PAN-based CFs represent about 80-90 % of the world production, there is a strong incentive for improving the process design, so that it might be further optimized [9,14,16].…”

Brief overview of electrospun polyacrylonitrile carbon nanofibers: Preparation process with applications and recent trends

“…Simple mixing of another polymeric precursor with PAN can give very different CNFs than the use of a block copolymer of PAN with the same polymer. Some recent reports in this trend include the synthesis and use of polymers such as polyacrylic acid‐b‐PAN‐b‐polyacrylic acid, poly(acrylonitrile‐block‐methylmethacrylate), poly(acrylonitrile‐co‐β‐methylhydrogen itaconate) [P(AN‐co‐MHI)], poly(acrylonitrile‐ran‐3‐dimethylaminopropyl acrylamide‐ran‐itaconic acid) [P(AN‐DMAPP‐IA)], and poly(acrylonitrile‐co‐3, dimethylaminopropyl acrylamide) [P(AN‐DMAPP)] as precursors for the synthesis of CNFs.…”