Strength Properties of Water Resistant Papers Prepared from Carbamoylethylated Pulps and the Water-resistance Improving Mechanism

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Water-resistant paper derived from carbamoylethylated pulp was prepared, and some mechanical properties, repulping conditions and the water-resistance improving mechanism were investigated. Chemical modification of pulps was carried out by the following three steps :(1) P-OH+CH_2=CH-CN * P-O-CH_2-CH_2-CN (where P is pulp fiber)(2) P-O-CH_2-CH_2-CN+H_2O_2 * P-O-CH_2-CH_2-CONH_2(3) P-O-CH_2-CH_2-CONH_2+NaC1O * P-O-CH_2-CH_2-CON^-C1Wet-and dry-tensile strength of N-Chlorinated pulp (N-Cl-P) sheets was highly improved compared to that of untreated pulp sheets. Especially, wet tensile strength of N-Cl-P sheets with DS 0.04 was nearly equal to the dry tensile strength of corresponding untreated pulp sheets. Folding endurance, burst strength, brightness and dimentional stability were also improved by N-Chlorination of Carbamoylethylated pulp. The main mechanism of water-resistance improvement is considered to be the formation of interfiber urea bonding. The hypochlorite treatment in an alkaline medium was effective for reducing the wet strength to be able to repulp. Strength properties of the recycled sheets from the repulping pulp were fairly good when N-Cl-P sheets were treated with the lowest amount of hypochlorite within possible defibering without heating.