Method and apparatus for reducing impurities in cellulose fibers for manufacture of fiber reinforced cement composite materials

A method of making a fiber reinforced composite building material comprising:

• preparing delignified cellulose fibers to have a COD content of less than about 4.5 kg/ton of oven dried pulp by pretreating through an elevated temperature washing process that includes chemicals which react with COD compounds causing the COD compounds to be more soluble and to reduce COD content of the cellulose fibers to less than 4.5 kg/ton using an elevated temperature between about 65 degrees Centigrade to about 120 degrees Centigrade, wherein COD content is measurable from a filtrate obtained from prepared cellulose fibers alone in a solution in the absence of cement and prior to forming the fiber reinforced composite building material;
• incorporating the prepared and delignified cellulose fibers with a cementitious mixture;
• forming the fiber cement mixture into a fiber cement article using a process selected from the group consisting of Hatschek, Mazza pipe, Magnani, injection molding, extrusion, hand lay-up, multi-wire forming, gap blade forming and bel-roll forming, the fiber cement article of a pre-selected shape and size;
• and
• curing the fiber cement article so as to form the fiber reinforced composite building material, wherein preparing the delignified cellulose fibers increases strength reinforcement to the fiber reinforced composite building material when formed by increasing the ultimate strain by more than about 10% as-compared with a fiber reinforced composite building material made with a same formulation containing cellulose fibers with COD content greater than 5 kg/ton of oven dried pulp measurable from a filtrate.

A fiber cement composite building material comprising

• a cementitious matrix and
• pretreated and delignified cellulose fibers with a reduced COD content,
• wherein the delignified cellulose fibers are pretreated before incorporating into the cementitious matrix using an elevated temperature washing process to reduce COD content of the delignified cellulose fibers to less than 4.5 kg/ton of oven dried pulp and the elevated temperature is between about 65 degrees Centigrade to about 120 degrees Centigrade,
• wherein COD content of the pretreated and delignified cellulose fibers is measurable from a filtrate prior to being incorporated into the cementitious matrix, and the filtrate is obtainable from dispensing the pretreated and delignified cellulose fibers into a solution without cement, and
• wherein the cellulose fibers with reduced COD improve one or more of the modulus of rupture (MOR) of the fiber cement composite building material by more than about 10% or the ultimate strain of the fiber cement composite building material by more than about 10% as compared with a fiber cement composite building material made with a same formulation containing cellulose fibers with a COD content greater than 5 kg/ton of oven dried pulp measurable from a filtrate.