High branch cationic starch for papermaking wet end and preparation method thereof

The invention provides high branch cationic starch for a papermaking wet end and a preparation method thereof. The high branch cationic starch comprises the following raw materials in parts by weight: 30-60 parts of arrow root starch and 40-70 parts of water, and is prepared through a cationic etherification step, a cross-linking reaction step and a drying step. The high branch cationic starch isadded into paper to improve the paper force strength of the paper or to maintain the paper force strength under the condition of improving the primary retention rate and the ash content of the paper.The preparation method provided by the invention benefits the control of the influence of cross-linking degree for starch molecular weight in the synthesis technology of the high branch cationic starch, and the diminishment of the increased scope of the cross-linking degree so as to improve the starch molecular weight to the most extent. The result of combinedly using phosphorus oxychloride, sodium trimetaphosphate and epoxy chloropropane as a cross-linking agent is better than the result of singly using the phosphorus oxychloride as the cross-linking agent. The high branch cationic starch isapplicable to papermaking enterprises which produce cultural paper and are equipped with continuous digesters.