Shandong Qilu Dioctyl Phthalate (DOP)

Shandong Qilu Dioctyl Phthalate (DOP), bis(2-ethylhexyl) benzene-1,2-dicarboxylate, CAS 117-81-7, EC 204-211-0, is supplied as standard industrial-grade DOP and low-color DOP. The product is obtained by continuous esterification of phthalic anhydride with 2-ethylhexanol over titanium alkoxide catalysis, followed by catalyst deactivation, neutralization, water washing, vacuum steam stripping, and filtration. Process control targets residual monoester below 0.20% and residual 2-ethylhexanol below 50 mg/kg to limit odor and volatility. Lot-release parameters under GB/T 11406-2001 and ASTM D1045-19 include ester content ≥99.5%, acid value ≤0.07 mg KOH/g, moisture ≤0.10%, density at 20 °C of 0.983–0.987 g/cm³, refractive index at 20 °C of 1.485–1.487, and platinum-cobalt color ≤30 Hazen for standard grade or ≤20 Hazen for low-color grade. The molecular weight is 390.56 g/mol, the dynamic viscosity at 20 °C is typically 77–82 mPa·s, and the flash point determined by Cleveland open cup is ≥196 °C.

Trace phthalic anhydride and 2-ethylhexanol quality influence the color and acid value of Qilu DOP. Phthalic anhydride with maleic anhydride content above 0.05% promotes color bodies during esterification; therefore Qilu-grade raw material purity is typically controlled at ≥99.8%. 2-Ethylhexanol acidity below 0.01 mg KOH/g prevents excess catalyst demand and reduces post-neutralization salt loading. The neutralization step uses aqueous sodium carbonate, and residual sodium is controlled to ≤5 mg/kg to avoid haze in transparent films. Vacuum steam stripping at 200–240 °C under absolute pressure 1–5 kPa removes unreacted alcohol and low-boiling byproducts, while activated carbon filtration can reduce color to ≤20 Hazen for the low-color grade.

What Differentiates Qilu DOP from Lower and Higher Molecular Weight Phthalate Alternatives?

Plasticizer selection in flexible PVC often reduces to a trade-off among solvation strength, volatility, and viscosity. DBP has lower molecular weight and lower viscosity, enabling faster dry blend absorption and lower fusion temperatures, but its boiling point of 340 °C restricts continuous processing at temperatures above 160 °C and permits higher evaporation loss from finished articles. Qilu DOP with molecular weight 390.56 g/mol and boiling point 386 °C provides a lower-volatility alternative while retaining adequate solvation for plastisol and dry-blend operations. DINP, made from mixed branched C9 alcohols, has a molecular weight of 418.61 g/mol and a boiling point near 400 °C, resulting in lower volatility and fuming, but its solvation rate is slower and fusion can shift upward by 5–10 °C compared with DOP at equivalent phr. DOTP has the same molecular weight as DOP but a para-terephthalate geometry; it is not subject to the same EU CLP reproductive toxicity classification, making it a preferred drop-in replacement where regulatory constraints dominate. However, DOTP often exhibits higher gelation temperature and lower plastisol viscosity stability compared with DOP.

Plasticizing efficiency differences are expressed in phr for equal Shore A 80 hardness at 23 °C. DBP may achieve Shore A 80 at 40 phr, DOP at 50 phr, DINP at 52 phr, and DOTP at 50 phr in a standard suspension PVC K-value 70. These values are indicative because stabilizer, filler, and processing history shift the plasticizer demand by ±3 phr. DOP’s solvation strength is sufficient for low-temperature flex at −20 °C to −10 °C compound glass transition temperature, whereas DBP moves the glass transition lower but suffers higher evaporation loss.

Dry blending and twin-screw compounding constitute the highest-volume processing routes for Qilu DOP. Production-scale dry blending commonly uses a heated high-speed mixer paired with a water-cooled cooling mixer; the heating mixer operates at tip speeds of 25–35 m/s and discharge temperatures between 105 °C and 115 °C. DOP is metered through a heated flow meter and injected through a top-mounted nozzle to maximize contact with the resin surface; DOP temperature at the nozzle should be 35–45 °C. Dry blend bulk density of 0.55–0.62 g/cm³, free-flowing behavior, and residual plasticizer absorption confirmed by a 30-mesh screen retention test are standard release criteria. If DOP temperature falls below 20 °C, viscosity rises above 80 mPa·s and spray droplet size increases, producing wet spots that cause feed throat bridging on twin-screw extruders with L/D 28:1–36:1. Extrusion barrel temperatures of 150–175 °C and screw speeds of 250–400 rpm are typical for pelletizing; screw back pressure is kept below 1.0 MPa to limit local shear heating. Tensile and hardness verification should follow ASTM D638-14 and ASTM D2240-15, respectively.

Rheology and Thermal Limits in Plastisol Dip-Coating Lines

In plastisol dip coating and slush molding, Qilu DOP is compounded with PVC paste resin at 60–80 phr. Brookfield viscosity at 20 °C and 20 rpm typically falls between 2,000 and 5,000 mPa·s; values above 5,000 mPa·s reduce drainage and produce uneven film thickness. Severs extrusion rheometry at 90 psi can be used to distinguish high-shear response; Qilu DOP plastisols display pseudoplastic flow with Severs efflux of 20–80 g/100 s depending on paste resin type. Solvation at 25 °C is moderate, with viscosity build over 24 h usually 500–1,500 mPa·s for medium-viscosity paste resin, but storage at 35 °C can double the rate of viscosity rise. After 7 days at 25 °C, plastisol viscosity should remain below 8,000 mPa·s to avoid pumping problems. Gelation begins near 150 °C and tensile strength plateaus at 180–190 °C; under-fused coatings retain surface tack and show low tear strength. Industrial gelation ovens for Qilu DOP plastisols are typically set at 180–210 °C for 5–10 min, depending on part mass and line speed. Degassing under vacuum at 20–40 kPa is commonly used to remove entrained air before coating.

Calendering and injection molding impose different thermal profiles. For calendered sheet at 40–60 phr Qilu DOP, roll temperatures are maintained at 160–180 °C with friction ratios of 1.05:1–1.30:1 to control the rolling bank. If DOP concentration is too high or roll temperature exceeds 180 °C, plate-out forms on chrome-plated rolls. Plate-out composition typically includes metal soaps from stabilizers, free phthalic acid from DOP hydrolysis, and low-molecular-weight PVC fractions; cleaning intervals are shortened when DOP moisture or acid value is above specification. In injection molding, melt temperatures of 180–195 °C, injection pressures of 80–120 MPa, and screw back pressure below 1.0 MPa are typical; molds are water-cooled to 15–30 °C because DOP compounds have low melt viscosity and may flash when clamp force is below 0.4 t/cm² of projected area.

When DOP Is Replaced by DOTP in High-Heat Cable Jacketing

High-temperature PVC cable jacketing with service ratings of 90–105 °C often requires replacement of Qilu DOP by DOTP or a trimellitate plasticizer such as TOTM. At 50 phr DOP in PVC K-value 70, the compound displays useful low-temperature flexibility, but volatile loss under thermal aging reduces elongation retention. Replacement with DOTP at equivalent phr may require a 5–10 °C increase in barrel set temperature because DOTP solvation is slower. In accelerated aging under ISO 188:2019 at 100 °C for 168 h, DOP-plasticized cable compounds can lose 5–10% tensile elongation depending on stabilizer type, whereas DOTP typically retains higher elongation. Published lot-specific data for Qilu DOP in 105 °C cable jacketing is limited; the comparison is therefore drawn from general DEHP and DOTP plasticizer literature. Qilu DOP therefore remains suitable for standard 70 °C PVC cable insulating and sheathing compounds, but not for extended high-temperature exposure without additional stabilizer or a higher molecular weight plasticizer.

Compliance screening is required before export. Qilu DOP is DEHP, classified as Repr. 1B, H360FD under Regulation (EC) No 1272/2008 and listed as an SVHC under REACH. Under EU RoHS Directive 2011/65/EU Annex II as amended by Delegated Directive (EU) 2015/863, DEHP is restricted to 0.1% by mass in homogeneous materials of electrical and electronic equipment. REACH Annex XVII entries 51 and 52 restrict DEHP in toys and childcare articles at 0.1% by mass of plasticized material. For permitted industrial applications, Qilu DOP should be stored in closed carbon steel or stainless steel tanks under nitrogen or dry air at 20–30 °C. Avoid strong oxidizers and prolonged heating above 180 °C to limit ester decomposition and color development.