| The recycled fibers and non-wood fibers are short. They have weaker strength and poorer drainage. The content of their non-fiber cells is high. All these shortages make them unfit the challenge of the highspeed paper machine. Also, to reduce the effluent load and the consumption of resource, the fines and fillers retention should be improved.Considering the situation and problem of paper industry and research on paper aids in our country, a new constructional amphoteric polyacrylamide was prepared as strength, retention and drainage aids. This product had been come into service under different conditions. The mechanisms of NPAM modification and application of modified product as strength, retention and drainage aids were studied. In order to provide the theoretical foundation for practical production and application, the feasible technical conditions were probed through mill trails.In the first part of this paper, the synthesis of NPAM was studied. A series of NPAM with different molecular weight were prepared as water solution by oxidation and reduction initiating system. In order to get the best technical conditions, the effects of some factors on molecular weight are studied such as the amount of initiator, consistency of the reactant and the temperature and time of reaction.In the second part, amphoteric polyacrylamide was prepared by modification of NPAM. The effects of some factors on modification reaction of NPAM were studied such as temperature, purity and dosage of the reactant, and reaction time through testing product performance as strength, retention and drainage aids.In the third part, the mechanism of modification of NPAM was studied. Cationic agent for modified PAM was chosen followed the principle. The result showed that it was the intermediate (isocyanate) of Hoffman reaction that reacted with cationic agent. According to it, the cationic agent should have functional group ?hydroxyl group and quaternary ammonium group.In the fourth part, the performances of the strength improvement, retention and drainage of modified PAM were studied. The results showed that modified PAM had good effects on the recycled fibers andnon-wood fibers. Modified PAM could be used in acidic papermaking together with A12(SO4)3, also in neutral papermaking alone. Contrast experiments were carried out between modified PAM with various commercial strength aids. Modified PAM is the same as the other aids in retention, but better in strength improvement compared with commercial amphoteric PAM. Compared with cationic and amphoteric starches, modified PAM has obvious advantages in strength improvement, especially in the folding strength of paper.In the fifth part, the strength improvement, retention and drainage mechanism of modified PAM was studied. Experiments showed that modified PAM is a kind of amphoteric PAM with low molecular weight and higher density of electric charge. Its retention and drainage effects are obtained mainly depending on itself anionic and cationic charge through the way of "patch mechanism ". As for strength improvement, modified PAM had little effects on fiber strength, but it can increase the bonding area and bonding strength. The reasons were mainly because of increasing number of hydrogen bond, partly may be because that the primary amide groups in modified PAM molecule form ionic and covalent bond with little carboxyl or aldehyde groups in pulp.In the sixth part, mill trials were conducted according to the synthesis process in the laboratory. The performance of the product made by trial were determined and compared with that of laboratorial product and commercial amphoteric starches of made in China and abroad. All the aids have almost the same drainage, but both of modified PAM have better retention than amphoteric starch. Modified PAM is somewhat less in strength improvement compared with overseas amphoteric starch, but compared with in-country amphoteric starch, modified PAM made by trial has obvious advantages in strength improvement, retention and drainage.
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