LG Chem Ltd.

In continuous superabsorbent polymer lines, LG Chem Ltd glacial acrylic acid is first diluted to 25–30 %(m/m) with deionized water and partially neutralized with 50 %(m/m) sodium hydroxide. The neutralization degree is held at 70–75 mol%. The exothermic neutralization step is carried out in a 316L stainless steel static mixer followed by an external loop cooler. Inlet coolant temperature is maintained at 35–40 °C. Adiabatic temperature rise in the neutralization loop reaches 85–95 °C under typical production rates. Trimethylolpropane triacrylate is added as internal crosslinker at 0.05–0.15 wt% relative to monomer. Redox initiation uses sodium persulfate at 0.15–0.30 wt% and sodium metabisulfite at 0.03–0.08 wt%. The feed is deposited on a moving belt under nitrogen at 90–105 °C. The gel is chopped to 2–10 mm granules, dried in a through-circulation belt dryer to 3–5 % moisture, milled, and sieved to 150–850 µm. Residual acrylic acid in the finished superabsorbent is controlled below 300 mg/kg by EDANA NWSP 210.0.R2. Centrifuge retention capacity measured under ISO 17190-3:2021 normally falls in the range of 28–33 g/g for hygiene grades. The terminal products are absorbent cores for infant diapers, adult incontinence pads, and sanitary napkins.

Polymer-grade acrylic acid used in this segment is supplied under a sales specification that references ASTM D4414-14 for assay and water content. Incoming assay is typically not less than 99.5 %(m/m). Water content is restricted to not more than 0.20 %(m/m). The monomethyl ether hydroquinone inhibitor level is controlled between 180 and 220 mg/kg to stabilize storage without scavenging the redox initiator. Dimer content above 1.0 %(m/m) reduces final crosslink density and shifts centrifuge retention capacity below the production target. Batch-to-batch variance in dimer content has been observed to produce a 2–4 g/g swing in retention capacity on the same belt line. The polymerization control system therefore includes near-infrared dimer monitoring on the acrylic acid feed tank.

What Limits Acrylic Acid Dosing in PCE Superplasticizer Synthesis?

The limiting factor in liquid-state polycarboxylate ether synthesis is not residual inhibitor but the acrylic acid-to-macromonomer molar ratio. For an isoprenyloxy polyethylene glycol macromonomer of 2400 g/mol number-average molecular weight, production formulations typically hold the acrylic acid-to-macromonomer ratio at 3.5–4.5:1. The acrylic acid and macromonomer are dissolved in deionized water to 55–60 %(m/m) total monomer concentration. Initiation is carried out with hydrogen peroxide at 0.5–1.0 wt% of total monomer and a reducing agent such as sodium formaldehyde sulfoxylate or L-ascorbic acid at 0.10–0.20 wt%. Reaction temperature is controlled at 55–65 °C for 3–4 hours. The acid value drop is monitored by potentiometric titration. Conversion above 95 % is considered stable for batching. After polymerization, the product is neutralized with 50 wt% sodium hydroxide to pH 5.0–6.5. The resulting copolymer is formulated into high-range water-reducing admixtures tested under ASTM C494/C494M-19 and EN 934-2. In a concrete mix with water-to-cement ratio of 0.35–0.40, a dosage of 0.10–0.30 wt% active polymer by cement weight yields water reduction between 25 % and 40 %. Workability retention beyond 120 minutes is achieved by matching acid-to-macromonomer ratio and backbone molecular weight.

The process boundaries are dictated by cement paste rheology rather than by acrylic acid purity alone. When the acrylic acid-to-macromonomer ratio exceeds 4.5:1, the admixture shifts toward higher charge density. Slump retention improves, but initial water reduction may decrease. Dosing above 0.35 wt% active polymer by cement weight can induce segregation, extended set time beyond 45 minutes, and surface retardation on formed concrete. In winter concreting below 5 °C, the dosage must be reduced 10–20 % to compensate for slower cement hydration. Terminal use is restricted to ready-mix concrete, precast elements, and self-consolidating concrete where the admixture is added at the batching plant or on-site under controlled shear.

Esterification of LG Chem Ltd acrylic acid with 2-ethylhexanol at an alcohol-to-acid molar feed of 1.1–1.3:1 proceeds in a continuous packed-bed reactor. p-Toluenesulfonic acid is used at 0.5–1.0 wt% of the organic phase. The reaction zone is held at 95–110 °C. Water is removed azeotropically with toluene or cyclohexane in a side-draw decanter. Air sparging is maintained at 0.5–1.5 volume percent oxygen in the overhead vapour to regenerate the monomethyl ether hydroquinone inhibitor. A thin-film evaporator downstream strips unreacted acrylic acid to below 50 mg/kg. The crude ester is washed with dilute sodium hydroxide and water. The finished 2-ethylhexyl acrylate is specified with acid number below 0.1 mg KOH/g and colour below 20 APHA. The ester is polymerized to pressure-sensitive adhesives, architectural coatings, and textile coatings. In adhesive production, residual acrylic acid in the ester is critical. Values above 50 mg/kg alter peel adhesion and shear strength. The acrylate ester is stored with 15–20 mg/kg MEHQ and blanketed with dry air.

Volatile content of formulated coatings derived from this ester is determined by ASTM D2369-20. EU coating formulations must comply with the volatile organic compound limits of Directive 2004/42/EC. For pressure-sensitive adhesives intended for skin contact, the absence of free acrylic acid above 50 mg/kg is required before migration testing. Dimer content in stored acrylic acid above 1.0 % produces higher colour in the ester and can slow conversion in continuous esterification. Field observations on structured-packing columns show that raising bottom temperature above 110 °C to force conversion also raises ester colour by 10–20 APHA units.

Polyacrylic Acid Scale Inhibition in Open Recirculating Cooling Systems

When scale inhibition is required in open recirculating cooling systems operating above 3 cycles of concentration, polyacrylic acid synthesized from LG Chem Ltd acrylic acid is produced by aqueous solution polymerization using hydrogen peroxide and sodium hypophosphite chain transfer agent. The hypophosphite is added at 2–6 wt% of monomer charge. Reaction temperature is held at 80–90 °C. The resulting polymer exhibits weight-average molecular weight between 2,000 and 5,000 Da by gel permeation chromatography and polydispersity between 2.0 and 2.5. In the cooling tower, the active polymer is dosed at 5–15 mg/L into the recirculating water at pH 7.5–8.5. The polymer disrupts calcium carbonate crystal growth and disperses suspended solids. Heat exchanger fouling rates are typically reduced below 0.15 m²·K/W per year under standard operating conditions.

Compliance for potable water contact is evaluated under NSF/ANSI/CAN 60-2022. Only certified grades are permitted in systems with drinking water makeup. The formulated product must also meet local discharge limits for residual acrylic acid and total organic carbon. The operational boundary is pH. Below pH 6.5, polyacrylic acid can form insoluble complexes with iron and aluminum coagulants. In systems dosed with cationic quaternary ammonium biocides, anionic polyacrylic acid above 10 mg/L can reduce biocide availability through polyelectrolyte complex formation. Dosing lines are therefore separated. Terminal products are cooling water treatment dispersants, antiscalants for reverse osmosis pretreatment, and boiler sludge conditioners.

When Acrylic Acid Binders Replace Melamine-Formaldehyde in Nonwoven Fabrics

If a carded nonwoven line must eliminate melamine-formaldehyde, a styrene-free emulsion copolymer of ethyl acrylate, butyl acrylate, acrylic acid, and N-methylolacrylamide is used. LG Chem Ltd acrylic acid is charged at 2–5 wt% of total monomer to provide colloidal stability, adhesion to cellulosic fibres, and reactivity with the crosslinker. The glass transition temperature of the copolymer is adjusted between -15 °C and +20 °C by varying the ethyl acrylate-to-butyl acrylate ratio according to the Fox equation. Emulsion polymerization is run with an anionic surfactant system and ammonium persulfate initiator at 75–85 °C. The latex is applied to a carded web by spray or foam padding at a binder pick-up of 8–20 g/m². Curing is carried out in a forced-air oven at 150–170 °C for 1–3 minutes. The crosslinking reaction via N-methylolacrylamide generates a solvent-resistant film. The finished fabric is tested for breaking strength under ASTM D5034-21 and for wet strength retention after soaking.

Formaldehyde release from the cured nonwoven is measured by ISO 14184-1:2011. When the binder is used in hygiene acquisition layers or medical nonwovens, the residual acrylic acid monomer in the latex is reduced below 100 mg/kg by post-polymerization oxidation with tert-butyl hydroperoxide and sodium metabisulfite. pH of the final latex is kept at 5.0–6.5 to avoid destabilization. The use of acrylic acid in this segment is not interchangeable with methacrylic acid. Methacrylic acid reduces the reactivity of the N-methylolacrylamide crosslinker and increases the minimum curing temperature by 5–10 °C. The terminal downstream products are wipes, medical drapes, air-laid absorbent cores, and disposable garment interlinings.

Hybrid UV-Curable Oligomers in Flexible Packaging Varnishes

In hybrid UV-curable varnish production, LG Chem Ltd acrylic acid is first reacted with bisphenol A diglycidyl ether through ring-opening esterification. Acrylic acid is fed at a stoichiometric ratio of 0.95–1.05:1 relative to epoxy groups. Triphenylphosphine catalyst is used at 0.5–1.0 wt% of the resin charge. Reaction temperature is held at 105–115 °C while dry air is sparged through the reactor. Acid number is monitored until it drops below 5 mg KOH/g. Viscosity of the resulting epoxy acrylate oligomer typically ranges from 3,000 to 8,000 mPa·s at 25 °C. The residual acrylic acid concentration is reduced to below 0.1 wt% by vacuum stripping at 5–10 kPa. The oligomer is then mixed with 20–35 wt% of a reactive diluent such as tripropylene glycol diacrylate. Photoinitiator systems are added at 2–5 wt% of the formulation. The varnish is applied by flexographic or offset coating and cured under UV-A at a peak irradiance of 1.0–1.5 W/cm².

Oxygen inhibition at the varnish surface is controlled by adding an amine synergist or by using a nitrogen inerting hood on the coating line. Without inerting, surface cure can be incomplete and the printed varnish may show tack at line speeds above 120 m/min. The flexible packaging varnish must comply with the European printing ink association exclusion list and REACH Article 3. Residual bisphenol A diglycidyl ether is kept below the specific migration limit for food contact under the European plastics regulation. Published data for this specific configuration is limited when coating thickness exceeds 12 µm; production-scale laminators therefore validate migration on the final printed structure rather than on cured film alone. Terminal products are overprint varnishes for folding cartons, flexible film labels, and retortable pouch lamination.