Shrinkage behaviour of polyacrylonitrile during thermal treatment

Abstract

A detailed study of the shrinkage behaviour of homopolymers and copolymers of acrylonitrile has been made. Apart from chemical shrinkage, a physical shrinkage, which is independent of temperature and oxidizing gas was observed. This shrinkage occurs even at temperatures below 180°C. The effect of temperature and oxidizing gas on the chemical shrinkage is reported. The shrinkage is faster in the presence of O 2 than in presence of air and N,, This chemical shrinkage can be checked with smaller loads in case of oxygen as compared to the loads required in case of air and nitrogen. The effect of load on shrinkage in presence of oxygen is reported. By use of oxygen, a maximum elongation of 65% can be achieved as compared to 40% maximum elongation reported in the literature. An empirical method has been described which can be used for the estimation of optimum peroxidation time at any temperature. ZUSAMMENFASSUNG:Das Schrumpfverhalten von Homo-und Copolymeren aus Acrylnitril wurde untersucht. Neben chemischer Schrumpfung wurde auch die physikalische Schrumpfung beobachtet, die von Temperatur und oxidierender Atmosphare unabhangig ist. Diese Schrumpfung tritt auch noch bei Temperaturen unter 180°C ein. Der EinfluD von Temperatur und oxidierender Atrnosphare auf die chemische Schrumpfung wird beschrieben. Die Schrumpfung lauft in Gegenwart von Sauerstoff schneller ab als unter Luft oder Stickstoff. Sie kann in Gegenwart von Sauerstoff mit geringerer Zugbelastung untersucht werden als unter Luft und Stickstoff. Der EinfluI3 der Zugbelastung auf die Schrumpfung in Gegenwart von Sauerstoff wird beschrieben. Hierbei wird eine maximale Dehnung von 65% beobachtet; die Literaturwerte liegen bei 40%. Eine empirische Methode wird beschrieben, die zur Bestimmung der optimalen Voroxidationszeit bei gegebener Temperatur herangezogen werden kann. 145 0. P. Bahl and L. M. Manocha

Studies of reaction mechanisms during stabilization of electrospun polyacrylonitrile carbon nanofibers

“…As seen from the figure, shrinkage in the yarn was observed beyond 237°C. Similar behavior was also observed by other researchers where the shrinkage was discussed as chemical shrinkage and attributed to the 120° rotation of the molecular chain due to the intermolecular cyclization (Fig. a‐II) of the neighboring polymer chains.…”

“…Although cyclization can occur in inert environment, oxygen can also affect the cyclization reaction. According to literature, the oxidative groups formed during stabilization in air can also initiate cyclization reaction through ionic mechanism . While radical cyclization is fast, ionic cyclization progresses slowly as it depends on oxygen diffusion and occurs over a broader temperature range.…”

Effect of the aggregation structure on the thermal shrinkage of polyacrylonitrile fibers during the heat‐treatment process

“…Warner and coworkers1–3 found that the overall shrinkage of PAN fibers could be classified into two stages: initial shrinkage and secondary shrinkage. The initial shrinkage is a totally physical process and is also called entropic shrinkage; it is caused by the relaxation of molecular chains in the amorphous phase 4–6. The secondary shrinkage (chemical shrinkage) is mainly due to the crosslinking of molecular chains via chemical reactions.…”

Investigation the jet stretch in PAN fiber dry‐jet wet spinning for PAN‐DMSO‐H2O system

“…[1][2][3][4] Polyacrylonitrile (PAN) fibers are the most widely used precursors for producing carbon fibers, owing to a variety of reasons. [5][6][7][8][9] Generally, optimum PAN precursors have many features, such as homogeneous structure, fine denier, high crystallinity, high orientation, and so on.…”