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The research on normal temperature polycarboxylate superplasticizer production process and properties

Polycarboxylate superplasticizers (PCE) are the core admixture for high-performance concrete, playing a pivotal role in improving concrete workability, strength and durability. Traditional PCE synthesis relies on high-temperature free radical polymerization (60~130℃), which consumes large amounts of energy, causes environmental pollution and increases production costs. With the development of green building and low-carbon manufacturing, the normal temperature preparation technology of PCE has become a research hotspot in the concrete admixture industry.

This article describes a green, efficient, room-temperature synthesis of PCE using isopentenol polyoxyethylene ether (TPEG) as the core macromonomer, combined with a composite redox initiator system. It systematically analyzes the influence of key process parameters on PCE performance, and verifies that the PCE prepared by this normal temperature process has better dispersibility, slump retention and cement compatibility than high-temperature synthesized products, providing a feasible technical solution for industrial energy-saving and emission reduction.

Why Normal Temperature Preparation of PCE is a Green Trend?

The traditional high-temperature synthesis process of PCE has obvious drawbacks that restrict the sustainable development of the industry:

High energy consumption: Continuous heating is required during the polymerization reaction, which increases production costs and does not conform to low-carbon production requirements.
Environmental risks: High-temperature reactions may cause volatilization of raw materials, produce waste gas and waste water, and increase environmental treatment costs.
High investment cost: Special heating equipment (such as solar or electric heating) must be installed, increasing the production line’s initial investment.
Unstable product performance: Excessively high reaction temperature can easily cause local gelation and monomer self-polymerization, leading to uneven molecular weight distribution of PCE.

The normal temperature preparation technology of PCE realizes heat-free radical polymerization by optimizing the redox initiator system, which fundamentally solves the above problems. Its core advantages are:

Energy saving and emission reduction: No heating equipment is required, reducing energy consumption by more than 50% compared with the high-temperature process.
Green and environmental protection: The reaction is mild, no raw material volatilization and three wastes are produced, meeting the national environmental protection standards;
Low production cost: Simplified equipment configuration, reduced maintenance and operation costs, and improved economic benefits;
Stable product performance: The mild reaction condition effectively controls the polymerization process, resulting in uniform molecular weight distribution and excellent comprehensive performance of PCE.

Core Raw Materials and Synthesis Process of normal temperature polycarboxylate superplasticizer

The normal temperature synthesis of PCE is based on aqueous solution free radical copolymerization, with the key to selecting a suitable redox initiator system to reduce the activation energy of free radical generation and realize the reaction at 5~35℃ (room temperature).

Key Raw Materials

The raw material system is optimized for normal temperature reaction, with industrial-grade raw materials as the main components, which is suitable for large-scale industrial production:

Core macromonomer: Isopentenol polyoxyethylene ether (TPEG, molecular weight 2400), with high polymerization activity and good compatibility with other monomers.
Anionic monomers: Acrylic acid (AA) provides carboxyl groups, the core functional group for dispersion; Sodium p-styrenesulfonate (SSS) introduces sulfonic acid groups to improve cement compatibility and dispersion retention.
Composite initiator: Potassium persulfate (KPS) + L-ascorbic acid (Vc), a high-efficiency redox system that can generate free radicals at room temperature;
Neutralizer: Liquid caustic soda (NaOH), used to adjust the pH of the product to neutral and improve storage stability;
Solvent: Deionized water, green and pollution-free, in line with aqueous solution polymerization requirements.

Standard Normal Temperature Synthesis Process

The process is simple and easy to operate, with no special equipment required, and the solid content of the final product is 40%, which meets the industrial application standard:

Raw material dissolution: Add SSS, TPEG and an appropriate amount of deionized water into a four-necked flask equipped with a thermometer and stirrer, and stir until completely dissolved at room temperature.
Dropwise addition of monomers and initiator: Simultaneously, drop the aqueous solution of AA and the composite initiator (KPS+Vc) into the reaction system, and control the dropwise addition time to about 3.5h to ensure uniform polymerisation.
Heat preservation reaction: After dropwise addition is complete, maintain room temperature for 1h to allow the monomers to fully copolymerize and improve monomer conversion.
Neutralization adjustment: Add NaOH solution to the reaction system to adjust the pH value to neutral (6~7), and obtain the finished polycarboxylate superplasticizer (SPC) with a solid content of 40%.

Superior Performance of normal temperature polycarboxylate superplasticizer

The PCE (SPC) prepared by the optimal normal temperature process is compared with the high-temperature synthesized PCE (PC) in terms of molecular weight distribution, cement compatibility, concrete workability and mechanical strength. The results show that SPC offers comprehensive performance advantages and is better suited to the production of high-performance concrete.

More Uniform Molecular Weight Distribution and Higher Monomer Conversion

Characterized by gel permeation chromatography (GPC), the molecular structure of normal temperature-synthesised PCE is more optimized:

Index	Normal temperature PCE (SPC)	High-temperature PCE (PC)
Weight-average molecular weight (Mw)	28260	29060
Number-average molecular weight (Mn)	23280	20590
Molecular weight distribution index (DPI)	1.21	1.41
Monomer conversion rate	93.43%	89.29%

Core advantage: The mild, normal-temperature reaction effectively controls uniform copolymerization of monomers; the DPI is lower (closer to 1), the molecular weight distribution is more uniform, monomer residues are lower, and product performance is more stable.

Excellent Cement Compatibility

Tested with three common Portland cements (Huaxin P·O42.5, Yadong P·O42.5, Conch P·O42.5), the normal temperature PCE has good adaptability to different cements, with small slump loss over time:

The initial cement paste fluidity of SPC for all three cements is above 270mm, which is higher than that of PC.
The 60min fluidity retention rate of SPC is over 90%, which is significantly higher than that of PC, and the slump retention performance is excellent.
Mechanism: The uniform molecular weight distribution makes the adsorption rate of SPC on cement particles more moderate, avoiding rapid adsorption and large slump loss.

Excellent Concrete Workability and Mechanical Strength

Under the same concrete mix ratio and PCE dosage (0.14% solid content), the performance of concrete mixed with SPC is significantly better than that of PC:

(1) Superior slump retention

Initial slump/expansion of SPC concrete: 230mm/500mm, much higher than PC’s 200mm/430mm;
1h slump/expansion of SPC concrete: 215mm/485mm, the retention rate is over 93%, which is significantly higher than PC’s 87.5%;
No bleeding and segregation, good wrapping property of aggregate, and excellent construction workability.

(2) Higher mechanical strength at all ages

The compressive strength ratio of SPC concrete is significantly higher than that of PC and the blank group, with an obvious strength enhancement effect:

Age	3d Compressive Strength (MPa)	7d Compressive Strength (MPa)	28d Compressive Strength (MPa)
Blank group	16.13	26.98	29.45
PC concrete	25.02 (155% of blank)	31.82 (118% of blank)	34.31 (116% of blank)
SPC concrete	25.23 (156% of blank)	34.72 (129% of blank)	37.35 (127% of blank)

Core reason: The uniform dispersion of SPC makes the concrete structure more compact, the hydration of cement is more sufficient, and the mechanical strength at all ages is significantly improved.

Conclusion

he normal temperature preparation technology of polycarboxylate superplasticizer with TPEG as the core macromonomer and KPS+Vc as the composite redox initiator realizes the heat-free radical copolymerization of PCE at 5~35℃, which is a green and energy-saving synthesis process. The optimal process parameters are: Vc dosage 3.0% of total monomer mass, KPS dosage 1.5% of total monomer mass, acid-ether ratio 3.0∶1.0, n(SSS)∶n(AA) 0.3∶1.0, and reaction temperature 30℃.

The PCE prepared by this normal temperature process has a more uniform molecular weight distribution (DPI=1.21), higher monomer conversion rate (93.43%), and its dispersibility, cement compatibility and slump retention are significantly better than high-temperature synthesized products. The concrete mixed with this PCE has excellent workability and higher mechanical strength at all ages, with a 28-day compressive strength ratio up to 127% of the blank group.

This normal-temperature preparation technology has the advantages of energy saving, environmental protection, low cost, and stable product performance, which not only addresses the shortcomings of the traditional high-temperature process but also meets the development requirements of the low-carbon building industry. It is expected to become the standard process for industrial production of PCE, and provide strong technical support for the sustainable development of the concrete admixture industry and the construction of green high-performance concrete.