Complex fibers of cellulose fibers with inorganic particles and processes for preparing them

A process for preparing a complex fiber of a cellulose fiber with inorganic particles, wherein the inorganic particles comprise BaSO4, CaCO3 or hydrotalcite and the complex fiber has a ratio (B/A or C/A) of 0.3 or more;

• wherein said process comprises:
• synthesizing the inorganic particles in a suspension containing 0.5% to 4.0% of a cellulose fiber to obtain the complex fiber, and analyzing the complex fiber to determine the B/A or the C/A of the complex fiber, wherein:
• (1) B/A is determined by:
• filtering an aqueous suspension of the complex fiber having a solids content of 0.1% through a 60-mesh sieve (having an opening of 250 μm);
• and calculating B/A in which A is an inorganic content of the complex fiber before the filtration, and B is an inorganic content of the complex fiber obtained after the filtration as the residue remaining on the sieve;
• and
• (2) C/A is determined by:
• treating an aqueous suspension of the complex fiber having a solids content of 0.3% using a fiber classification analyzer under the conditions of a flow rate of 5.7 L/min, a water temperature of 25±1° C., and a total elution volume of 22 L;
• and calculating C/A in which A is an inorganic content of the complex fiber before the classification, and C is an the weight ratio C/A between the inorganic content of the complex fiber in fractions corresponding to an elution volume (L) of 16.00 to 18.50 and an elution time (sec) of 10.6 to 37.3.