Molecular Design of Functional Polyacrylamide and Its R&D and Practice in the Treatment of Complex Papermaking Wastewater

Wastewater treatment in the papermaking industry has always been a typical and common challenge in the field of industrial water treatment. Wastewater generated from multiple processes such as pulping, bleaching, and papermaking not only has complex and significantly varying pollutant compositions but is also often accompanied by severe operating conditions, including high temperatures, high suspended solids (SS), high chemical oxygen demand (COD), complex organic matter, and drastic fluctuations in water quality. These factors impose extremely high requirements on the stability and adaptability of water treatment flocculants. Traditional polyacrylamide (PAM), when facing such complex water quality, is prone to high-temperature degradation, molecular chain collapse in high-salt environments, a sharp decline in efficiency under acid-base fluctuations, and main chain scission under strong shear forces, making it difficult to guarantee long-term and stable treatment effects.

To address this industry bottleneck, the Shouxin R&D team started from the molecular structure source of polymer materials, focusing on the core goal of "performance stability under complex operating conditions in the pulp and paper industry." A series of functional modification studies were conducted, gradually breaking through multiple operating condition limitations and completing the entire chain from laboratory research to on-site application verification.

1. Technical Breakthroughs at the Molecular Level: Building the Ability to Cope with Water Quality Fluctuations with Stability as the Core

The complexity of papermaking wastewater conditions is essentially a multi-faceted challenge to the conformational stability of polymer flocculant molecules. The R&D team did not stop at adjusting the formulations of existing products but started from molecular design. Targeting three core pain points—high temperature and high salt, wide pH fluctuations, and strong hydraulic shear—corresponding modification mechanisms were established to endow the materials with the ability to actively adapt to complex environments.

1.1 Heat and Salt Resistance: Molecular-Level Protection and Anti-Salting-Out Capability

Specific Shouxin products introduce double-layer compression inhibition groups through molecular engineering and graft rigid groups to construct an intramolecular hydrogen bond network. This significantly increases the hydrolysis activation energy of amide groups and delays deamination degradation at high temperatures (60℃). Meanwhile, utilizing the anti-polyelectrolyte effect and steric hindrance supplementation mechanisms, the coiling and collapse of molecular chains in high-salt media (Na⁺, Ca²⁺) are inhibited, maintaining an expanded chain conformation. This design effectively avoids the attenuation of bridging ability of traditional PAM under high-temperature and high-salt conditions, ensuring the stability of flocculation efficiency.

 Figure 1 Schematic Diagram of the Flocculation Mechanism of Shouxin PAM Resistant to High Temperature and High Salinity

1.2 Wide pH Adaptability: Intelligent Responsive Charge Regulation System

A "pH-responsive zwitterionic copolymerization system" was developed. By precisely controlling the molar ratio and sequence distribution of cationic groups (quaternary ammonium salts) and anionic groups (carboxylates), adaptive charge matching over a wide pH range is achieved. Under acidic conditions, cationic groups dominate adsorption; in alkaline environments, anionic groups play a synergistic role to maintain efficient charge neutralization and bridging capabilities. A "dynamic protonation-deprotonation equilibrium mechanism" is adopted, where the segment conformation is regulated through an intramolecular hydrogen bond network, ensuring that the flocculation efficiency remains stable even when pH fluctuates drastically.

1.3 Shear Resistance: Topological Reinforcement and Dynamic Self-Repair Network

To address the strong shear environment in high-speed mixing and pipeline transportation, the Shouxin research team replaced traditional linear chains with chemically cross-linked molecular topological structures, constructing a three-dimensional network skeleton through multifunctional cross-linking agents. This structure is equivalent to "weaving" molecular chains into an elastic network, allowing mechanical forces to be dispersed and conducted along multiple branches, avoiding stress concentration at a single point that causes chain scission, and significantly increasing the fracture threshold.

At the same time, bulky protective groups are introduced at the ends of the molecular chains. Their physical barrier effect can effectively block the attack of oxidizing substances on the main chain and inhibit shear-induced oxidative degradation. This dual design of "structural reinforcement + terminal protection" enables the molecules to maintain their intact conformation under severe hydraulic conditions.

 Figure 2 Schematic diagram of the shear stability principle of Shouxin PAM

2. From Laboratory to Field: Establishing a Systematic Research Method for Operating Condition Adaptation

The wastewater characteristics of papermaking enterprises vary greatly; even materials with excellent performance do not equate to solutions suitable for all scenarios. To fully unleash the performance of modified PAM in real operating conditions, the R&D team established a three-level adaptation method of "water quality characteristic analysis and diagnosis—laboratory simulation experiments—pilot verification and engineering on-site optimization," forming a precise docking path between material R&D and on-site operating conditions.

First is the water quality diagnosis stage. Technical means such as GC-MS component analysis, Zeta potential detection, and laser diffraction particle size analysis are used to comprehensively analyze the pollutant composition, particle surface charge characteristics, and particle size distribution in the wastewater. This clarifies the impact mechanism of different water quality characteristics on the flocculation process, providing a basis for large-scale selection and parameter design.

On this basis, through dynamic simulation pilot equipment, the flocculation treatment process under different water temperatures, pH values, and chemical dosages is accurately simulated. The treatment efficiency and boundary conditions of the materials are verified one by one to determine the optimal process parameter range. Meanwhile, the synergistic effect between modified PAM and inorganic coagulants (PAC/PFS) is systematically explored. Through orthogonal experiments, the compounding ratio is optimized to enhance the treatment effect while further optimizing chemical input efficiency and reducing treatment costs.

Combined with actual operation data, the dosing scheme is continuously fine-tuned through full-process debugging. This achieves a deep match between material performance and on-site operating conditions, ensuring that the performance advantages developed in the laboratory can be fully implemented in engineering operations.

3. Engineering Application Verification: Dual Implementation of Stable Efficiency and Value Enhancement

Currently, this series of polyacrylamides has been applied in the wastewater treatment systems of multiple papermaking enterprises. Long-term operation data shows that its performance under complex operating conditions is significantly superior to traditional flocculation materials, mainly reflected in three aspects:

First, operational stability is significantly improved. Under continuous operating conditions with high temperatures and high pollutant loads, the flocculation effect of the material remains stable. The sludge settling rate is increased by 20%~30% compared to traditional chemicals. The formed floc structure is compact and has higher floc strength, effectively reducing the operating load of subsequent dewatering equipment and minimizing the risk of effluent exceeding standards caused by water quality fluctuations.

Second, the potential for resource recovery is released. High-efficiency solid-liquid separation achieves the effective recovery of fibers and fillers in the wastewater. In some customer application scenarios, the turbidity of reused water can be stably controlled within 5 NTU. The resource recycling rate is significantly improved, which aligns with the development direction of water conservation and energy reduction in the papermaking industry.

Third, operational material consumption and costs are optimized. Precise matching of operating conditions avoids excessive chemical dosing. Under the same treatment effect, chemical consumption is reduced by 15%~25% compared to traditional solutions. Meanwhile, the moisture content of the flocs decreases, and sludge production is reduced, correspondingly lowering the cost pressure of sludge transportation and disposal. The comprehensive treatment cost is reduced by 10%~20%.

This research not only breaks through the performance bottleneck of traditional polyacrylamide in the treatment of complex papermaking wastewater but also constructs a complete path of "molecular design—operating condition adaptation—engineering verification." Looking towards the long-term development direction of reducing energy consumption and improving resource recovery rates in industrial wastewater treatment, the Shouxin R&D Center will continue to advance related technology R&D and implementation practices.