With the progress and development of the times, human demands regarding paper quality have continued to rise; consequently, higher standards have been imposed on retention and drainage aids—agents that play a crucial role in the papermaking process. In recent years, researchers in the papermaking field have dedicated themselves to the development of novel, high-efficiency retention and drainage aids. Polyacrylamide, as a new type of highly efficient retention and drainage aid, has garnered increasing attention from researchers. Polyacrylamide (PAM) is a collective term encompassing both homopolymers and copolymers of acrylamide; it primarily comprises four categories: non-ionic polyacrylamide (NPAM), cationic polyacrylamide (CPAM), anionic polyacrylamide (APAM), and amphoteric polyacrylamide (AmPAM).
Due to the presence of a large number of amide groups within its structure, polyacrylamide readily forms hydrogen bonds, thereby exhibiting excellent stability and flocculation properties. Consequently, it finds extensive application across various industries, including wastewater treatment, petroleum extraction, and papermaking. Furthermore, polyacrylamide is amenable to chemical modification, allowing for the synthesis of functional polyacrylamide materials. For instance, introducing a small proportion of hydrophobic groups into the polyacrylamide structure yields hydrophobic associating polyacrylamide; this specific type of polymer exhibits unique properties in response to factors such as temperature and pH, enabling its utilization as a “smart polymer.” Additionally, cross-linked polyacrylamide demonstrates superior water absorption capabilities, facilitating the creation of hydrogels and superabsorbent resins—materials that hold significant potential for both research and practical application in fields such as biomedicine and plastic surgery. Driven by my country’s economic growth, the consumption of polyacrylamide products within the country has been on a steady upward trajectory. While the primary application of polyacrylamide products in my country has historically been in the petroleum extraction sector—in contrast to Western nations (Europe and the U.S.), where water treatment dominates consumption, and Japan, where the papermaking industry is the primary consumer—the increasing stringency of environmental protection regulations in my country has recently spurred substantial growth in the consumption of polyacrylamide within the water treatment sector as well.
Classification and Structure
Cationic Polyacrylamide (CPAM): CPAM constitutes a class of widely utilized agents—including dry-strength agents, retention aids, drainage aids, and flocculants—renowned for their superior performance characteristics. When used as a retention and drainage aid in the papermaking process, it helps reduce fiber loss and environmental pollution, while also enhancing the efficiency of processes such as filtration and sedimentation. Its chemical structure is illustrated below:
Anionic Polyacrylamide (APAM): Anionic polyacrylamide is a copolymer formed from acrylamide monomers and acrylic acid, or obtained through the hydrolytic modification of non-ionic polyacrylamide. Its structure contains functional groups such as -COOH, -SO3H, and -OSO3. Currently, APAM is widely utilized in fields such as oil extraction, papermaking, mineral processing, coal washing, metallurgy, construction materials, food processing, and soil remediation; it has found particularly extensive application in the realm of industrial water treatment. Its chemical structure is illustrated below:
Amphoteric Polyacrylamide (AmPAM): Amphoteric polyacrylamide generally refers to a water-soluble polymer whose macromolecular chains simultaneously bear both positively and negatively charged functional groups. It exhibits excellent water solubility, wherein the anionic groups serve a protective function relative to the cationic groups. Its chemical structure is illustrated below:
Non-ionic Polyacrylamide (NPAM): NPAM is a water-soluble polymer polyelectrolyte with a molecular weight ranging from 2 million to 12 million. Due to the presence of a certain number of polar groups within its molecular chains, it functions by adsorbing suspended solid particles in water—either by bridging the particles together or by neutralizing their surface charges—thereby inducing particle aggregation to form large flocs. Consequently, it accelerates the sedimentation of particles within suspensions and expedites the clarification of solutions. Its chemical structure is illustrated below:
Physicochemical Properties
Typically, it is a polymer formed by the head-to-tail linkage of acrylamide monomers; at room temperature, it exists as a hard, glassy solid. Depending on the specific manufacturing method employed, the product may take various forms, such as white powder, translucent beads, or flakes. It has a density of 1.302 g/cm³ (at 23°C) and a softening point of 210°C. It exhibits excellent thermal stability. It is soluble in water, yielding a clear and transparent aqueous solution. The viscosity of the solution increases markedly as the molecular weight of the polymer increases, and it demonstrates a logarithmic relationship with changes in the polymer’s concentration. With the exception of a few solvents—such as acetic acid, acrylic acid, chloroacetic acid, ethylene glycol, glycerol, and formamide—it is generally insoluble in organic solvents.
Production Processes
Currently, the primary synthesis methods for polyacrylamide include aqueous solution polymerization, inverse emulsion polymerization, inverse microemulsion polymerization, and aqueous dispersion polymerization. In recent years, researchers have combined emerging polymerization techniques—such as radiation technology and living/controlled free-radical polymerization—with the aforementioned methods, thereby advancing the development of polyacrylamide production technology.
Aqueous Solution Polymerization
The polymerization reaction of acrylamide monomers carried out in an aqueous solution is termed aqueous solution polymerization. Acrylamide monomers are readily soluble in water; consequently, both their polymerization rate and the relative molecular weight of the resulting polymer are higher in aqueous solutions than in organic solvents. Aqueous solution polymerization of acrylamide primarily employs redox initiation systems; however, the properties of the resulting product are susceptible to influence from factors such as the solvent, reactant concentrations, and temperature. Polyacrylamide products produced via aqueous solution polymerization typically exhibit a relatively low solids content; nevertheless, the process offers several advantages, including operational simplicity, minimal equipment requirements, high monomer conversion rates, and low environmental pollution. Consequently—despite being the earliest method adopted for polyacrylamide production—aqueous solution polymerization remains the most widely utilized production method to this day. Currently, polyacrylamide products manufactured via aqueous solution polymerization predominantly take the form of dry powder, typically produced through the polymerization of medium-concentration (20%–35%) acrylamide monomer solutions. The medium-concentration polymerization process primarily encompasses two variants: the belt-type sheet polymerization process and the kettle-type bulk polymerization process. In my country, the medium-concentration polymerization process is predominantly employed, utilizing a combination of stationary and mobile polymerization equipment, coupled with continuous hot-air drying systems.
Inverse Emulsion Polymerization and Inverse Microemulsion Polymerization
Inverse emulsion polymerization refers to a process in which water-soluble polymerization monomers are introduced into a non-polar organic solvent, wherein the polymerization reaction is initiated under the influence of a water-in-oil (W/O) type emulsifier. The underlying nucleation mechanisms involved in this process are micellar nucleation and homogeneous nucleation. Currently, the inverse emulsion production process for polyacrylamide is relatively complex and entails higher production costs; however, the resulting products feature a high solids content, low viscosity, and ease of use. As a result, polyacrylamide products manufactured via inverse emulsion polymerization have garnered significant favor among consumers. Inverse microemulsions typically appear transparent or semi-transparent and exhibit higher stability compared to conventional inverse emulsions; furthermore, microemulsions possess isotropic properties. Inverse microemulsion polymerization proceeds rapidly, lacking a distinct constant-rate period during the polymerization process. The primary nucleation mechanisms involved are continuous droplet nucleation and homogeneous nucleation; moreover, factors such as the emulsifier, monomer concentration, and temperature exert significant influence on the reaction.
Dispersion Polymerization
Dispersion polymerization is a type of precipitation polymerization wherein the reaction system consists of stabilizers, monomers, initiators, and other components. Once the polymer chains generated during the reaction reach a certain length, the polymer precipitates out of the solvent to form microspheres; subsequently, aided by the stabilizer, a stable dispersion system is established. For water-insoluble monomers, organic-phase dispersion polymerization is generally employed; conversely, water-soluble polymers are synthesized via aqueous-phase dispersion polymerization. Aqueous-phase dispersion polymerization utilizes water as the solvent, thereby significantly reducing the consumption of organic solvents and surfactants. This approach minimizes environmental pollution, representing a green and eco-friendly high-tech method that defines the future direction for polyacrylamide production technology.
Advancements in Polymerization Technology
Currently, building upon traditional polyacrylamide synthesis techniques, advanced methods—such as radiation polymerization, controlled/living polymerization, and seed polymerization—have been introduced. These techniques have emerged as focal points of research for scholars both domestically and internationally, driving the advancement of polyacrylamide synthesis technology. Among these methods, ultraviolet (UV) radiation polymerization and controlled/living free-radical polymerization have garnered particular attention and extensive study. UV-initiated polymerization is a simple and widely applied technique characterized by low reaction temperatures, short reaction times, and rapid reaction rates. Furthermore, under UV irradiation, the reaction can be triggered by adding only a minimal amount of initiator to the system, making it a green and environmentally friendly polymerization technology. Controlled/living polymerization techniques operate by utilizing reversible chain termination or chain transfer mechanisms to maintain a very low concentration of free radicals within the system, thereby suppressing termination via double-bond coupling. Moreover, this technology enables precise control over the product’s molecular weight and molecular weight distribution, allowing for the synthesis of polyacrylamide polymers with specific structures and targeted molecular weights.
Applications
As polymeric dispersants or polymeric flocculants, polyacrylamide products can either stabilize a system or induce the flocculation and precipitation of particles within it; consequently, they find significant application in fields such as water treatment, the petroleum extraction industry, and papermaking. Furthermore, polyacrylamide hydrogels—characterized by their excellent tissue compatibility and porous structure—also hold significant potential for research and application within the biomedical industry.
Applications in Water Treatment
With the growing global emphasis on environmental protection, the consumption of polyacrylamide products in the water treatment sector has been steadily increasing. Currently, polyacrylamide is primarily utilized in both potable water treatment and wastewater treatment processes as a coagulant aid and flocculant. Its advantages include reducing the required dosage of primary flocculants, enhancing the quality of wastewater treatment, boosting water treatment efficiency, minimizing scale formation, and protecting treatment equipment. The efficacy of polyacrylamide in treating water is primarily influenced by factors such as water temperature, pH value, stirring rate, and contact time. A novel porous cationic polyacrylamide/graphene oxide aerogel was successfully synthesized via freeze-drying and subsequently investigated for its adsorption capabilities regarding basic dyes in aqueous solutions. The study revealed that this adsorption process is endothermic in nature, and that the solution’s pH value, adsorbent dosage, contact time, and temperature exert a significant influence on adsorption efficiency. Specifically, as the solution pH increased from 2.6 to 8.9, the adsorption rate correspondingly rose from 90% to 99%, with a calculated maximum adsorption capacity reaching 1034.3 mg/g; furthermore, the adsorption system was found to conform to a pseudo-second-order kinetic model.
Applications in the Petroleum Extraction Industry
In China, the primary consumption of polyacrylamide products occurs within the field of oilfield chemical treatment. Polyacrylamide plays a vital role in various petroleum extraction processes—including drilling, acidizing, water shutoff, and enhanced oil recovery (tertiary recovery)—serving as a fluid loss reducer, flocculant, dispersant, and plugging agent. Consequently, the research and development of polyacrylamide have a profound impact on the overall growth and advancement of the petroleum industry. A ternary composite water-blocking agent for oilfields—comprising xanthan gum, 2-acrylamido-2-methylpropanesulfonic acid (AMPS), and bentonite—demonstrates a water absorption capacity of up to 1677 g/g at 20°C. Even after standing for 12 hours, its water absorption rate remains above 20%. Furthermore, at 20°C, it absorbs 165 g/g of a 0.9% sodium chloride solution, and the agent exhibits excellent thermal stability. By incorporating β-cyclodextrin structures into polyacrylamide, an anionic polyacrylamide and a cationic polyacrylamide were synthesized. Studies revealed that the introduction of the cyclodextrin structure enhanced the surface tension, salt tolerance, shear strength, thermal stability, and viscosity-increasing properties of the polyacrylamide. Among these variants, the cationic polyacrylamide is particularly well-suited for application in high-temperature and high-salinity oilfield recovery operations.
Applications in the Papermaking Industry
Polyacrylamide is one of the most widely utilized chemical auxiliaries in the papermaking industry. In the production of paper using long fibers, polyacrylamide facilitates superior fiber dispersion; when utilizing straw pulp, the application of polyacrylamide leads to significant improvements in paper quality. Depending on their relative molecular weight and electrical charge, polyacrylamide products serve various distinct purposes: anionic polyacrylamide functions as a pulp dispersant; low-relative-molecular-weight polyacrylamide acts as a paper strengthening agent; medium-relative-molecular-weight polyacrylamide is employed as a retention and drainage aid; and high-relative-molecular-weight polyacrylamide serves as a flocculant in the treatment of papermaking wastewater. Currently, anionic polyacrylamide sees the most extensive application within the papermaking industry; consequently, there is an urgent need for further research and development regarding the application of cationic and amphoteric polyacrylamides in this sector. When bagasse microfibrillated cellulose (MFC) was added to bagasse pulp—concurrently with the retention aid cationic polyacrylamide (C-PAM)—it was observed that the drainage performance of the resulting mixture remained essentially consistent with that of the reference sample when 1% MFC and 0.1% C-PAM were introduced; furthermore, properties such as paper tensile index and opacity demonstrated improvements to varying degrees.
Applications in the Biomedical Field
Polyacrylamide hydrogels possess characteristics similar to human tissues; moreover, their structural properties are controllable and tunable. Coupled with their excellent biocompatibility and inertness—as well as their non-toxicity to cells—these hydrogels are well-suited for *in vivo* implantation and for medical applications as viscoelastic materials. Currently, polyacrylamide hydrogels are primarily utilized in medical fields such as plastic surgery, embolization therapy, and sustained drug release systems. In a study investigating the treatment of bladder cancer, the anticancer drug Docetaxel (DTX) was loaded onto amino-functionalized, mucoadhesive polyacrylamide nanogels (PAm-NH2). The research revealed that the therapeutic efficacy of the drug-loaded PAm-NH2 nanogels was comparable to that of Docetaxel administered directly, yet without causing damage to normal bladder epithelial cells; this technology holds promise for development into a novel, highly effective therapeutic strategy for bladder cancer. Furthermore, using a polypropylene (PP) non-woven fabric as a substrate, fibronectin as a template molecule, and sodium alginate and acrylamide as functional monomers, a molecularly imprinted polymer film—specifically, polypropylene-grafted sodium alginate/polyacrylamide (PP-s-CA/PAM MIP)—was successfully synthesized via UV-radiation-induced polymerization. Compared to non-imprinted polymers, the imprinted PP-s-CA/PAM MIP demonstrated superior adsorption capabilities as well as excellent cell adhesion properties within cell culture environments.
Applications in Other Fields
Polyacrylamide polymers not only find extensive application in the aforementioned fields but are also frequently utilized in the mining and metallurgy industries as flocculants and filtration aids; in the textile dyeing and printing industries as sizing agents for spinning and finishing agents for fabrics; in the construction sector as decorative adhesives, cement additives, underwater grouting materials, and the like; and in agriculture and forestry to prevent soil erosion and serve as water-retention agents. Currently, research into the application of polyacrylamide polymers is also underway in emerging fields such as nanomaterials and composite materials.
