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Polyoxyethylene 35 Castor Oil, often called El35, stands out as a non-ionic surfactant built from natural castor oil and ethylene oxide. In the world of pharmaceuticals, this material does more than blend oils and water; it holds together complex mixtures that support drug delivery, injection solutions, and infusion therapies. The received grades BP, EP, and USP confirm its relevance globally, meeting the heavy demands of British Pharmacopoeia, European Pharmacopoeia, and United States Pharmacopeia standards. Through decades of laboratory and industry use, I have watched how its broad compliance helps pharmaceutical teams work across borders. The unique blend of castor oil backbone and around 35 ethylene oxide units creates a distinct molecular architecture, giving this product an impressive solubilizing and emulsifying ability.
Looking through portfolios of raw materials used in pharmaceutical manufacturing, El35’s significant role as a solubilizer comes into view. Many injectable drugs exist in oily forms that will not dissolve in water on their own. Polyoxyethylene 35 Castor Oil transforms these challenges, helping produce clear solutions for intravenous use. Common examples include chemotherapy medicines and immunosuppressive drugs. Beyond pharmaceuticals, El35 sees use in cosmetics and personal care products, thanks to its emulsifying power and mildness to skin. Over the years on factory floors and formulation labs, I’ve observed how technicians rely on this product not only for its technical performance, but also its consistent results and contaminant-free batches. Consistency supports patient safety and regulatory acceptance—critical concerns in health-focused industries.
The structural core of Polyoxyethylene 35 Castor Oil brings together a triglyceride skeleton from castor oil, grafted with about 35 moles of ethylene oxide for every mole of oil. This results in a molecular weight around 2680 g/mol to 3390 g/mol, though exact weights shift with the number of polyoxyethylene units. Such a configuration leads to a long, chain-like molecule studded with ether groups. Visually, it often appears as a thick, yellowish, clear or slightly hazy liquid, resisting crystallization or solidification under normal storage conditions. Chemists appreciate the hydrophilic-lipophilic balance (HLB) value, typically around 13–14, which makes it suitable for making oil-in-water emulsions. The density usually falls in the 1.06 – 1.12 g/cm3 range at room temperature. I’ve handled El35 in both ambient and refrigerated rooms, noticing how it resists thickening or breaking down across a wide range of temperatures. The substance remains unreactive with stainless steel processing equipment and glassware, reducing maintenance downtime during clean-up.
In industrial supply chains, El35 comes mostly as a viscous liquid, packaged in drums and intermediate bulk containers. Storage as a liquid eases transportation, batching, and blending. Rarely does one find it in solid, powder, flakes, or pearl forms at a commercial scale, because high ethoxylation prevents solidification even during winter shipping in temperate zones. Should the temperature drop sharply, El35 can turn hazy or become more viscous but regains transparency and flow upon gentle warming. The liquid remains both stable and free-flowing under a range of humidity conditions. I can recall working through cold storage checks, where drums of El35 remained unfazed by power outages, providing peace of mind during complex campaigns.
El35’s look at specifications reveals a high degree of purity: water content typically below 1%, acid value below 2 mg KOH/g, saponification value close to 45–55 mg KOH/g, and hydroxyl value in the 28–33 mg KOH/g range. The chemical formula is represented as C57H104O21 (approximate), though degree of polymerization introduces some variability. Color, odor, and clarity tests form part of each batch release. The HS Code used for customs and international trade purposes usually falls under 3402.13.0000 under the tariff schedule for organic surface-active agents and preparations. Across regulatory audits I’ve participated in, I have seen these specifications make all the difference in confirming that every batch received matches the intended pharmaceutical purpose.
Polyoxyethylene 35 Castor Oil rates as relatively safe for direct pharmaceutical use, but every chemical comes with precautions. Manufacturing documentation and safety assessments identify it as non-irritant at standard doses for most administration routes, yet cases of hypersensitivity, like allergic reactions, do exist—most famously in connection with certain IV chemotherapy drugs. I’ve had colleagues work through these adverse event reports and participate in risk reduction efforts, like running allergy tests for high-risk patient groups. In handling and blending, spills bring a slippery hazard, so strict housekeeping practices are essential for worker safety. Transporters and warehouse teams treat El35 as non-hazardous under most shipping regulations, but Material Safety Data Sheets emphasize wearing eye and hand protection. In wastewater treatment, the high ethylene oxide content could affect aquatic ecosystems if discharged in bulk, so strict environmental controls remain in place throughout the supply chain.
The two core raw materials in producing El35 are castor oil and ethylene oxide. Castor oil originates from the pressed seeds of Ricinus communis, a crop widely grown in India, Brazil, and China—places with climates suited for tall, leafy castor plants. Ethylene oxide comes from petrochemical processes, and its handling requires secure closed systems due to its flammability and toxicity. Industrial producers blend these two in specialized reactors under controlled temperature and pressure, usually with basic catalysts on hand. Upon reaction completion, purification steps remove residual unreacted ethoxylating agents, unused base, and byproducts. Quality control labs run spectral analyses—NMR, FTIR, and chromatography—on every lot. Working in such facilities has taught me the value of vigilance in raw material contracts, as diversion or adulteration can lead to off-specification surfactants, loss of efficacy, or product recalls.
For the future, manufacturers are probing alternate ethoxylation agents from plant-based sources to lower dependence on fossil fuels, and developing advanced filtration for further allergen removal. Continuous monitoring of adverse events in hospital pharmacy practice may spark more rigorous patient screening or dosing adjustments for products containing El35. Technical upskilling of manufacturing staff along with better vendor qualification can help keep contamination and safety risks low. To keep supply chains open and products available, diverse sourcing of castor oil and rigorous audit of ethylene oxide handlers should remain a top management priority, especially during times of global tension or crop disruption. By sharing experiences as chemists, pharmacists, or quality professionals, industry veterans help push the field toward greater transparency, patient safety, and sustainable use of resources all along the road from castor field to pharmacy shelf.
Chengguan District, Lanzhou, Gansu, China
