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Preparation of TPEG polycarboxylate superplasticizer at room temperature and its properties study

Polycarboxylate superplasticizers are essential components in modern concrete technology. They significantly improve workability, reduce water demand, and enhance durability while allowing lower cement content, which directly reduces the concrete production carbon footprint.

This article introduces a room-temperature synthesis method for a high-performance TPEG polycarboxylate superplasticizer.

What Makes TPEG polycarboxylate superplasticizer Different?

TPEG polycarboxylate superplasticizer is a TPEG‑based polycarboxylate superplasticizer. TPEG (isopentenyl polyoxyethylene ether) has a molecular weight of about 2400 and a high double‑bond retention (>97%). The synthesis uses three monomers:

TPEG 2400 (main macromonomer)
Acrylic acid (provides carboxyl groups for adsorption)
Unsaturated polyol ester (introduces ester groups that slowly hydrolyze to release additional carboxyl groups, extending slump retention)

The polymerization is initiated by a redox system composed of hydrogen peroxide (H₂O₂) and a binary complex of sodium formaldehyde sulfoxylate (SFS) with ascorbic acid (Vc). The chain transfer agent is β‑mercaptoethanol. The entire reaction is carried out at ambient temperature (25 ± 2 °C, with a gradient from 25 to 40 °C), eliminating the need for external heating.

Optimal Synthesis Parameters

Through single‑factor experiments and an L₉(3⁴) orthogonal design, the researchers determined the best formulation and process conditions. The key parameters (all relative to TPEG mass) are:

Parameter	Optimal value
Molar ratio (acrylic acid : TPEG)	3.6 : 1
Ester‑ether ratio (unsaturated polyol ester : TPEG)	0.6%
Oxidizer (H₂O₂) dosage	0.80%
Reducer (SFS : ascorbic acid = 9:1) dosage	0.12%
Chain transfer agent (β‑mercaptoethanol)	0.28%
Reaction dropwise addition time	150 min
Temperature range	25 °C → 40 °C (gradual rise)

The orthogonal analysis showed that the reducer dosage had the greatest influence on slump retention, followed by dropwise addition time, oxidizer dosage, and, finally, chain transfer agent dosage.

Molecular Structure and Polymerization Efficiency

Gel permeation chromatography (GPC) analysis compared TPEG polycarboxylate superplasticizer with two commercial high‑performance PCEs (SG‑PCE and BT‑PCE). Results are summarized below:

Sample	Weight‑average Mw (g/mol)	Number‑average Mn (g/mol)	Polydispersity (PDI)	Monomer conversion (%)
TG‑PCE	1.03 × 10⁵	4.34 × 10⁴	1.63	96.40
SG‑PCE	1.11 × 10⁵	4.43 × 10⁴	1.69	94.94
BT‑PCE	1.14 × 10⁵	4.61 × 10⁴	1.69	94.89

Key takeaways:

TPEG polycarboxylate superplasticizer achieves a higher monomer conversion (96.4% vs. ~94.9% for commercial products).
Its polydispersity index (1.63) is lower, meaning a more uniform molecular chain distribution.
The room‑temperature synthesis reduces side reactions (e.g., chain transfer agent self‑polymerization) and promotes even incorporation of functional groups (carboxyl, ester, hydroxyl).

Concrete Performance

All tests used a C30 concrete mix (cement 290 kg/m³, fly ash 30 kg/m³, sand 836 kg/m³, aggregates 1064 kg/m³, water 160 kg/m³) with a fixed PCE solid content of 0.25% by binder mass.

Workability and Slump Retention

Sample	Initial spread (mm)	60 min spread (mm)	120 min spread (mm)	120 min loss (%)
TG‑PCE	600 ±5	595 ±5	480 ±5	20.3
SG‑PCE	590 ±5	580 ±5	440 ±5	25.4
BT‑PCE	580 ±5	580 ±5	430 ±5	25.9

TPEG‑PCE shows better initial spread and significantly lower slump loss after 2 hours. This is due to the ester groups that slowly hydrolyze, continuously releasing new carboxyl groups to maintain adsorption as the PCE is consumed.

Mechanical Properties

Sample	Compressive strength (MPa)
Age	3d
TG‑PCE	23.6
SG‑PCE	23.2
BT‑PCE	22.9

TPEG polycarboxylate superplasticizer gave slightly higher 28‑day and 90‑day strengths. The uniform molecular structure and efficient dispersion lead to denser hydration products and fewer large pores.

Durability Indicators

Drying shrinkage (×10⁻⁶):

Age	3d	7d	28d	90d
TG‑PCE	117.9	239.4	332.1	435.4
SG‑PCE	121.5	233.3	330.6	429.9
BT‑PCE	115.6	255.8	325.3	426.5

Carbonation depth (mm):

Age	3d	7d	28d	90d
TG‑PCE	5.5	8.2	15.0	22.9
SG‑PCE	6.2	8.3	16.2	24.1
BT‑PCE	6.5	9.4	15.9	24.8

TPEG polycarboxylate superplasticizer shows slightly lower carbonation depth and comparable or lower drying shrinkage, indicating good durability.

Environmental Benefits

Conventional PCE production (like SG‑PCE) typically requires heating to ≥45 °C to initiate polymerization. TG‑PCE is synthesized at ambient temperature (starting at 25 °C, naturally rising to 40 °C during the exothermic reaction). The quantified savings per tonne of product:

Parameter	TG‑PCE	SG‑PCE (heated)	Difference
Energy consumption (kW·h/t)	66.70	185.93	−119.23
CO₂ emissions (kgCO₂eq/t)	17.44	48.54	−31.1

By eliminating the heating step, the new process reduces energy use by about 64% and CO₂ emissions by the same proportion. This aligns with the “dual carbon” goals of the construction materials industry.

Conclusion

The TPEG polycarboxylate superplasticizer (TG‑PCE) developed by Jia Bisheng et al. offers a compelling combination of performance and sustainability.

High monomer conversion (96.4%) and narrow molecular weight distribution (PDI 1.63) – results from room‑temperature redox polymerization.
Superior adsorption (3.2 mg/g on C‑S‑H) and higher zeta potential than commercial references, leading to better dispersion and slump retention (120 min loss only 20.3%).
Enhanced concrete durability – slightly higher 90‑day strength, lower carbonation depth, and comparable drying shrinkage.
Environmental advantage – room‑temperature synthesis cuts energy use by 119 kW·h/t and CO₂ emissions by 31 kgCO₂eq/t compared to conventional heating.

This innovation demonstrates that high‑performance PCEs can be produced without energy‑intensive heating, reducing both costs and the carbon footprint while maintaining, or even improving, concrete performance.