PAN Copolymer Research Articles

Effect of Bath Concentration on Coagulation Kinetics at the Early Stage during Wet Spinning of PAN Copolymer Nascent Fibers

A mathematical model was proposed to simulate the effect of bath concentration on coagulation kinetics at the early stage of wet spinning for the poly(acrylonitrile-co-vinyl acetate)/dimethylsulfoxide (DMSO)/water system. The dependence of critical precipitation time, components concentration distribution, and the radius of nascent fibers on the concentration of DMSO in the DMSO/water coagulation bath were estimated by solving the model equation numerically. The experimental results indicated the model was suitable to simulate the dynamic features of the early stage of the coagulation process. The critical precipitation time was found to increase with bath concentration. The mode of phase separation was changed from instantaneous demixing to delayed demixing as DMSO bath concentration increased. The simulation results showed that bath concentration influenced the phase separation path which determined the polymer concentration distribution in the spinning solution. As a result, nascent fibers with different structures would form in wet spinning and a radial homogeneous structure would be obtained when the DMSO bath concentration increased to some extent.

Morphology and thermal properties of PAN copolymer based electrospun nanofibers

Ultra-thin fibers are obtained from polyacrilonitrile co-polymer (PAN-CP)/N,N-dimethylformamide (DMF) solution by electro-spinning technique. The different wt. content of PAN-CP solution is electrospun with varying processing parameters to get nanofibers. The morphology of nanofibers is studied by scanning electron microscopy (SEM) and thermal properties are primarily investigated by DSC and TGA. The polymer nanofibers are stabilized and carbonized to get carbon nanofibers, after stabilization and carbonization nanofibers are characterized by FTIR, XRD, SEM and SPM. It is found that the diameter of nanofibers varies from 150 to 1300 nm, that increases with increasing polymer concentration and decreases with increasing the tip to collector distance and collector speed. The DSC studies show that the exothermic peak occurs at two different temperatures 275 and 320 °C in case of nanofibers. While in case of micron fiber single exothermic peak occurs at ∼275 °C. This might be due to the alignment of polymeric chain along the fiber direction. This is due to the stretching and whipping that occurs during the electrospinning process. As a consequence, increase in thermal stability and decrease in weight of nanofibers is confirmed by TGA. However, in the nanofibers of diameter >1000 nm, weight loss pattern is found to be similar as that of micron fibers. This could be due to the entrapping of solvent between polymeric chains. On stabilization and carbonization there is a decrease in fiber diameter in all the cases. The extent of decrease is higher in case of 10 wt.% electrospun fibers, from 350–400 nm to 100 nm. The SPM investigations reveal that the surface area and roughness changes due to the transverse shrinkage of nanofibers.

Smart Zwitterionic Membranes with On/Off Behavior for Protein Transport

Poly(acrylonitrile) (PAN)-based zwitterionic membranes, composed of PAN and poly( N, N-dimethyl- N-methacryloxyethyl- N-(3-sulfopropyl) copolymer, are electrolyte-sensitive smart membranes. The hydrophilicity was increased and protein adsorption was remarkably decreased for the membranes in response to environmental stimuli. FTIR spectroscopic analysis directly provided molecular-level observation of the enhanced dissociation and hydration of zwitterionic sulfobetaine dipoles at higher electrolyte concentrations. The smart PAN-based zwitterionic membranes can close or open channels for protein transport under different NaCl concentrations. The electrolyte-sensitive switch of on/off behavior for protein transport is reversible.

Mesoporous Carbons from Poly(acrylonitrile)-b-poly(ε-caprolactone) Block Copolymers

A series of degradable block copolymers, poly(acrylonitrile)-b-poly(ε-caprolactone) (PAN−PCL), have been synthesized by sequential living polymerization in this study. Well-defined, microphase-separated PAN−PCL microdomains can be efficiently achieved in the bulk by using appropriate solvents. The microphase-separated lamellar samples were then used as templates to produce mesoporous carbons at which large amounts of porous texture in carbonized PAN matrix were formed after degradation of PCL due to randomly oriented lamellar texture (namely, interconnection of PCL microdomains). The thermal profiles for efficient stabilization were examined by differential scanning calorimetry and thermogravimetric analyses as well as Fourier transform infrared spectroscopy. Consequently, mesoporous carbon materials might be prepared as evidenced by transmission electron microscopy, field emission scanning electron microscopy, and small-angle X-ray scattering. The formation of carbonized materials was identified in accordance with the presence of carbon diffractions by wide-angle X-ray diffraction. In contrast to the thermal stability of the carbonization of PAN homopolymers, it is noted that the carbonization procedure can be achieved in the PAN−PCL system regardless of the stretching process (that is an essential process to improve the thermal stability of PAN carbonization). We speculate that this unique feature for the carbonization of PAN copolymers might be attributed to the stretched chains of PAN under nanoscale confined environment.

Surface hydrolysis of polyacrylonitrile with nitrile hydrolysing enzymes from Micrococcus luteus BST20

A new Micrococcus luteus strain BST20 was isolated with ability to metabolize PAN polymers as sole carbon source. Out of seven synthetized PAN copolymers containing different moieties of acrylic acid and/or vinyl acetate the polymer with lowest crystallinity (PAN with 5% vinyl acetate) was most easily metabolized. (13)C labelled PAN was completely converted to the acrylic acid by this strain. M. luteus BST20 produced membrane-bound nitrile hydrolysing enzymes able to convert nitrile groups on PAN powder surface to the corresponding acids. Similarly, nitrile groups on PAN fabrics were transformed to the corresponding acid as indicated by an K/S increased after dying with Methylene blue and the released ammonia. On small soluble substrates the enzyme system showed a preference for aliphatic and aromatic substituted aliphatic nitriles.

Polyacrylonitrile-grafted Plantago psyllium mucilage for the removal of suspended and dissolved solids from tannery effluent

Grafted copolymer of Plantago psyllium mucilage and acrylonitrile (Psy–g–PAN) has been synthesized in the presence of nitrogen using a ceric ion–nitric acid redox system. The solid removal efficiency of this copolymer was tested with tannery effluent. The suitable pH, optimum dose of polymer and contact time for the maximum removal of suspended (SS) and dissolved solids (TDS) are reported. The optimum dose was found to be 1.2 mg l−1. The suitable pH values, at which a maximum SS removal of about 89% and TDS removal of about 27% occurred, were found to be 7.0 and 9.2 for SS and TDS, respectively. The optimum treatment duration was 3 h. The analysis of X-ray diffraction patterns of Psy–g–PAN and solid waste from effluent before and after treatment suggests the interaction of the solid waste with the Psy–g–PAN copolymer.

The Role of Different Factors in Creation of the Structure of Stabilized Acrylic Fibres

Chemical aspects of transformations of PAN fibres in the stage of thermooxidative stabilization are examined with methods of thermal analysis. The regions of cyclization and oxidation reactions are determined for three PAN copolymers of different composition. It is shown that the cyclization and oxidation reactions appearing on the DSC curves in the form of unseparated exothermic peaks can be separated by selecting the conditions of preliminary heat treatment of the fibres. It was found that preliminary heating of PAN fibres to a certain temperature causes the formation of a structure that does not undergo oxidation on repeated heating. An explanation of this phenomenon is proposed. Loading within certain limits does not affect the course of structural transformations of the fibres during thermooxidative stabilization.

IR Spectroscopic Characteristics of Polyacrylonitrile Copolymer Fibres

The 1500-1700 cm-1 frequency region in the spectrum of PAN copolymer fibre is structurally sensitive and can be used for the relative characterization of intra- and intermolecular interactions and level of supermolecular structural organization in fibres fabricated in different conditions, in particular, as a function of the nature of the solvent. In the systematic investigation of PAN copolymer fibres, the selectivity of absorption in the indicated frequency region could be analytically useful for further studies to solve both scientific and applied problems.

Electron-beam-induced cyclisation to obtain C-fibre precursors from polyacrylonitrile homopolymers

Alkyl radicals were produced and proved to be present (ESR) in polyacrylonitrile fibres which had been exposed to electron beams. By giving the irradiated fibres thermal treatment, it was possible to achieve a radical cyclisation of the PAN fibres. The mechanical textile characteristics of the fibres were determined; they were found to be suitable precursors for carbon fibres. In contrast to conventional cyclisation methods, the convenient high-energy method of irradiation does not need any external or internal catalysts (e.g. PAN copolymers), and it leads to reduced cyclisation times.

Poly(acrylonitrile-co-vinylcatecholborane): A new precursor for carbon containing B/C, B/N and B/O species

This paper describes a new PAN copolymer, poly(acrylonitrile-co-vinylcatecholborane), which is a precursor for carbon material containing B/C, B/N and B/O species in its molecular structures. Vinylcatecholborane, containing an appropriate protecting group in the borane moiety, can be copolymerized with acrylonitrile to high molecular weight copolymers under free radical polymerization conditions. The copolymers are processible by solution and melt methods. From 11B NMR studies, a clear B-N complex was formed in poly(acrylonitrile-co-vinylcatecholborane) copolymer. The carbonation and oxidative studies of poly(acrylnitrile-co-vinylcatecholborane) indicate effective interconversions of copolymers to various graphite-like structures containing B/C, B/N and B/O species, which show significantly higher oxidative stability than pure carbon material obtained from PAN under the same conditions.

Cyclization kinetics of poly(acrylonitrile)

Experimental studies of poly(acrylonitrile) (PAN) homopolymer and itaconic acid co-polymer stabilization examine the impact of polymer composition, temperature and reaction environment on the rate of cyclization. Stabilization of homopolymer PAN in nitrogen, 10.5 and 21% oxygen produces sigmoidally shaped curves when extent of cyclization is plotted as a function of reaction time. The length of the initial induction period in the sigmoidally shaped homopolymer curves decreases with increasing temperature and when oxygen is present in the reaction environment. Co-polymer cyclization curves also exhibit an induction period when reacted in nitrogen, but the period is less distinct than in the homopolymer case. The length of the induction period in the co-polymer data decreases with increasing temperature and increasing acid concentration. In the presence of oxygen, no induction period is present in any of the acidic co-polymer data. Reactions in 10.5 or 21% oxygen result in retardation of PAN homopolymer and co-polymer cyclization relative to reaction in a nitrogen environment. The retarding effect of oxygen is minimized as the acid concentration in the polymer is increased.

FT‐IR study of the stabilization reaction of polyacrylonitrile in the production of carbon fibers

AbstractThe stabilized fibers prepared by heating PAN and a PAN copolymer in air and under reduced pressure have been examined by FT‐IR spectroscopy in order to determine their chemical structures. Three kinds of reactions, cyclization, dehydrogenation, and oxygen uptake are found to occur almost simultaneously in the stabilization process in air by digital difference spectrum method. The effect of the comonomer is confirmed to accelate the dehydrogenation reaction and also the formation of acridone ring in the thermal stabilization in air by kinetic study.