Sizing hysteresis is one of the main disadvantages of AKD sizing. The sizing and maturation rate of ordinary AKD emulsion is generally less than 40%. The fast-curing AKD can improve the sizing degree of the paper sheet, reduce the moisture absorption rate of the paper, thereby improving the dimensional stability of the paper, ensuring that the quality of the paper is not affected by the climate environment, and meeting the sizing needs of high-end cultural paper. Rapid maturation AKD mainly improves its rapid maturation performance through high charge density and low molecular weight polymers, which can be polydiallyldimethylammonium chloride (PDMDAAC), polyethylenimine (PEI) and polyamine (PA). ), etc., among which PDMDAAC is the most commonly used due to its good cost performance. PDMDAAC used as AKD curing agent is mainly a product with low molecular weight and high charge density, while more products with high molecular weight and low charge density are used in oil extraction and water treatment. This topic mainly discusses the factors affecting the synthesis of DMDAAC aqueous solution, examines the viscosity and charge density of the synthesized products, evaluates the application performance of the synthesized products for AKD, and provides a theoretical basis for the technological progress of PDMDAAC synthesis.
1． Synthesis of PDMDAAC
Weigh 100g of absolute dry monomer DMDAAC solution into a four-neck bottle, add EDTA·4Na, ammonium persulfate/NaHSO3 and chain transfer agent in sequence, and then add a certain amount of The ionized water adjusts the monomer mass fraction to 40%. After the temperature is raised to initiate polymerization for a certain period of time, the heating is stopped and the material is cooled and discharged.
2. Effect of initiator dosage
As can be seen from Figure 1, as the amount of initiator increases, the intrinsic viscosity of PDMDAAC first increases and then decreases, that is, the molecular weight of PDMDAAC first increases and then decreases, while the charge density continues to increase and tends to be stable. When the initiator dosage is 0.3%, the molecular weight of PDMDAAC is the highest. However, when the amount of initiator is too high, more free radicals will be generated per unit time, and along with a higher probability of chain termination, the molecular weight of PDMDAAC will decrease, but there will be no adverse effect on its charge density.
3. Effect of polymerization temperature
When the polymerization temperature increases from 50°C to 70°C, the intrinsic viscosity and charge density of PDMDAAC gradually increase, but the increase in the later period tends to slow down. However, the reaction temperature cannot be too high, otherwise it will easily cause the decomposition rate of the initiator and the polymerization rate to increase significantly, and the heat release of the reaction system will increase, which will have an adverse effect on the polymerization.
4. Response time
As can be seen in Figure 3, as the reaction time increases, the intrinsic viscosity of PDMDAAC gradually increases.
5． Application effect of PDADMAC
5.1 Effect of intrinsic viscosity on AKD sizing effect
The increase in the intrinsic viscosity of PDMDAAC, that is, the increase in the molecular weight of PDMDAAC, can improve the retention of AKD and cover the paper surface more completely, and the sizing effect of the paper is improved. However, when the intrinsic viscosity of PDADMAC is too large, the flocculation formed by AKD and paper components may be too strong, which will adversely affect its sizing effect (Figure 5).
5.2 Effect of charge density on AKD sizing effect
As can be seen from Figure 6, within a certain charge density range, an increase in charge density is conducive to an increase in the electropositivity of AKD, an improvement in the stability of AKD, and an improvement in the rapid curing performance of its sizing. However, when the charge density of PDMDAAC exceeds 6.4mmol/l, it has a negative impact on the curing rate of AKD sizing.
5.3 Effect of AKD dosage on the sizing degree of the paper after the machine is finished
As the amount of AKD gradually increases, the Cobb value of the paper sheet gradually decreases, that is, the sizing degree gradually increases (Figure 7).
6. Conclusion
6.1 The initiator can effectively increase the charge density of PDMDAAC, while its intrinsic viscosity first increases and then decreases. When the initiator dosage is 0.3%, the intrinsic viscosity of PDMDAAC is the highest.
6.2 Polymerization temperature and reaction time both contribute to the improvement of the intrinsic viscosity and charge density of PDMDAAC. 65~70°C is a more suitable temperature range, and 7h is a more suitable reaction time.
6.3 The synthesized PDMDAAC can effectively improve the curing performance of AKD. Increasing the dosage of AKD is conducive to improving the curing effect, and a maximum off-machine curing rate of 85% can be obtained.
