Abstract: A carbon fiber chopped strands suitable for use in production of a composite with a matrix material, which have a circular or elliptical cross-section, wherein carbon fiber filaments are bundled by a sizing agent in an amount of from 1 to 10% by weight based on the chopped strand, and which have denseness of from 0.4 to 0.9 according to the formula below: ##EQU1## where D denotes the average diameter of the chopped strands, d denotes the average diameter of filaments constituting the chopped strand and N denotes the number of the filaments, and a method for production thereof by impregnating a carbon fiber strand with a sizing agent in an amount of from 1 to 10% by weight based on the total weight of the chopped strand to form a sized strand, and then cutting the sized strand, thereby giving the denseness of from 0.4 to 0.9 according to the formula (1).

Abstract: A process for producing preoxidized fibers, which comprises preoxidizing acrylic fibers having a fluorine-containing surface active agent and at least one phosphoric surface active agent selected from the group consisting of compounds represented by the following formulae (I), (II) and (III), and preoxidizing the acrylic fibers thus-obtained: ##STR1## wherein R.sub.1 represents an aliphatic hydrocarbon group having 1 to 17 carbon atoms, R.sub.2, R.sub.3 and R.sub.4, which may be the same or different, and each represents a hydrogen atom, a lower alkyl group, a hydroxyethyl group or a hydroxyisopropyl group, ##STR2## wherein R.sub.5, R.sub.6 and R.sub.7, which may be the same or different, each represents a hydrogen atom or a hydroxyethyl group.

Abstract: Acrylic fibers suitable for producing preoxidized fibers free from coalescence which have a fluorine-containing surface active agent or further have at least one phosphoric surface active agent selected from the group consisting of compounds represented by the following formulae (I), (II) and (III): ##STR1## (wherein all the symbols are defined in the appended claims).

Abstract: High-performance carbon fiber or graphite fiber can be produced by treating the preoxidized fiber or carbon fiber strand with an aqueous solution containing at least one member of polyethylene oxide having a molecular weight greater than 100,000, methyl cellulose, ethyl cellulose, and hydroxyethyl cellulose, and drying the treated fiber strand at a temperature lower than 250.degree. C. prior to carbonization or graphitization.