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EO Addition (ring‑opening addition of the oxirane/oxyethylene chain)

The ethylene oxide (EO) molecule is a highly strained three‑membered ring with high reactivity that readily undergoes ring‑opening reactions under acidic or basic catalysis to form polyoxyethylene chains via ring‑opening polymerisation. Industrially, by controlling the feed of ethylene oxide during the addition polymerisation process, the length of the polyoxyethylene chain can be precisely regulated (including block or graft structures). As the molecular chain grows, a polyoxyethylene segment comprising repeating —CH₂CH₂O— units is formed. This process is also referred to as EO addition. The ultimate chain length determines product properties such as cloud point, calcium soap dispersing power, emulsifying capacity, HLB value (hydrophile–lipophile balance), foaming, and wetting characteristics.

Materials prepared by EO addition are commonly used as non‑ionic surfactants, detergents, and pigment dispersants in formulated products. This is because the length of the polyoxyethylene chain can be tailored to the application, adjusting the HLB to meet different end uses. For example, when rosin derivatives (gum rosin derivatives) are chosen as the starting substrates, the hydrophilic polyoxyethylene segment is covalently linked to the hydrophobic groups of the rosin derivative. When hydrophobic and hydrophilic groups are incorporated within the same molecule, an amphiphilic molecule results.

Such molecules spontaneously arrange into micelles in aqueous solution, with the hydrophobic ends oriented towards air or water‑insoluble substances (such as oily soils), and the hydrophilic ends oriented towards the water phase. This specific interfacial arrangement lowers the surface tension of water and forms stable emulsions or dispersions at the oil–water interface. This is the core function of surfactants

Selecting Rosin Derivatives as Starting Substrates

Different rosin derivatives contain diverse reactive functional groups whose “active hydrogens” can initiate ring‑opening addition reactions. For example, rosin acid bears carboxyl groups, rosin amine bears amino groups, and rosin pentaerythritol ester contains ester linkages and hydroxyl groups. These functionalities act as “hooks” that, upon initiating ring‑opening addition, graft strongly hydrophilic polyoxyethylene chains onto the hydrophobic moieties of the rosin derivatives.

Concurrently, the backbone of rosin derivatives is a rigid carbon framework based on a tricyclic rosin hydrocarbon (abietane/pimarane-type, dihydrophenanthrene-like), conferring hydrophobicity and resistance to heat, light, and corrosion. By grafting polyoxyethylene chains at terminal groups (such as carboxyl, hydroxyl, or amino), amphiphilic molecules are formed with excellent surface activity.

EO adducts using rosin derivatives as starters include: rosin polyoxyethylene glycerol esters (RPGC), polyoxyethylene rosin ethers (PORE), polyoxyethylene rosin esters (ROE), rosin amine polyoxyethylene ethers (RAEO), and rosin pentaerythritol ester polyoxyethylene ethers (RPEO). At present, EO adducts derived from rosin are regarded as low‑toxicity, safe surfactants. Related studies indicate that the toxicity of polyoxyethylene rosin esters is significantly lower than that of AEO‑9 (fatty alcohol polyoxyethylene ether) and TX‑10 (nonylphenol polyoxyethylene ether), at roughly one‑tenth of their level.

Applications of EO Adducts Based on Rosin Derivatives

Application in papermaking sizing

Papermaking sizing is employed to enhance the water‑resistance of paper, enabling effective resistance to liquid penetration. The role of a sizing agent is to render the paper fibre surface hydrophobic, preventing liquid spread, which is especially important for printing and writing performance. Polyoxyethylene rosin esters can serve as amphiphilic non‑ionic surfactants.

During the sizing process, polyoxyethylene rosin esters can act as dispersants or emulsifiers, uniformly dispersing other sizing components in water and ensuring that the sizing agent is evenly taken up by pulp fibres. According to related papers, polyoxyethylene rosin esters exhibit good surface activity at relatively low CMC, and show a calcium‑soap dispersing power of about 10%, effectively inhibiting reactions between dissolved calcium ions and sizing agents in the wet end, thus maintaining sizing efficiency. Their emulsifying capacity is comparable to commonly used non‑ionic surfactants such as Tween‑60 and AEO‑9.

Application in pesticide adjuvants

Many pesticide actives are oil‑soluble and must be formulated as emulsifiable concentrates (EC) or oil‑in‑water emulsions (EW) to enable dilution and use in water. Dispersants stabilise immiscible liquid phases, preventing phase separation, sedimentation, or flocculation, while lowering interfacial tension between the two phases. By adsorbing at the oil–water interface, dispersants reduce interfacial tension, allowing the active’s oil droplets or water droplets to disperse more finely and uniformly, thereby forming a stable emulsion. A stable emulsion ensures homogeneous distribution of the active in the spray liquor, enabling more effective biological performance.

Rosin polyoxyethylene glycerol esters can be employed in pesticide adjuvants to provide emulsifying, wetting, dispersing, and synergistic effects. This arises from the amphiphilic molecular architecture produced by EO addition. In pesticide formulations, this amphiphilicity is crucial to uniformly dispersing water‑insoluble actives within aqueous spray systems. Related research indicates that when the EO degree of polymerisation of rosin polyoxyethylene glycerol esters is around 10, properties such as surface tension, critical micelle concentration, calcium‑soap dispersing power, and cloud point are near‑optimal.

On the other hand, improved wetting and spreading increase contact between the active ingredient and target pests or plant surfaces, thereby promoting uptake and enhancing application efficiency. Selecting non‑ionic surfactants with appropriate polarity can further align with the active’s solvation characteristics, improving deposition and, in some cases, penetration into the leaf cuticle.

Application as pigment dispersants

Paint and ink products require dispersants to achieve uniform and stable dispersions in liquid media. The wetting capability of a dispersant rapidly and effectively wets pigment particle surfaces, displacing air at pigment–pigment interfaces and thereby lowering interparticle cohesive forces. A good dispersant can deagglomerate pigment clusters into individual fine particles and form a stable protective layer on their surfaces to prevent reagglomeration. For example, there are studies reporting reporting the use of hydrogenated rosin alcohol polyoxyethylene ether and rosin amine polyoxyethylene ether as dispersants for Pigment Violet 23.

When hydrogenated rosin alcohol polyoxyethylene ether is used as a dispersant, dispersion stability decreases as the polyoxyethylene chain length is reduced. Conversely, increasing the EO chain length enhances hydrophilicity and strengthens steric stabilisation, helping to prevent pigment particles from reaggregating.

In contrast, rosin amine polyoxyethylene ether shows a trend opposite to that of the hydrogenated rosin alcohol derivative. This is attributed to rosin amine acting as the hydrophobic anchoring group, with a structure and interfacial adsorption mode that differ from those of hydrogenated rosin alcohol. Taken together, tuning the functional group nature across different rosin derivatives allows targeted adjustment of dispersion performance, underscoring the development potential of rosin‑based EO adducts.

Application as surfactants in detergents

Soil removal is a key function of surfactants in detergent and laundry‑liquid formulations. First, surfactants wet fabric and soil surfaces, lowering the surface tension of water to increase the efficiency of detersive action. Second, the emulsifying action of surfactants breaks oily soils into fine droplets and forms micelles around them to prevent recoalescence, thereby achieving oil‑soil removal. By the same logic, the dispersing action of surfactants acts on solid particulate stains such as dust and clay, detaching them from fabric surfaces and dispersing them in the wash liquor. In addition, surfactants form micelles that can solubilise water‑insoluble materials (such as fragrances) within micellar cores, allowing uniform dispersion in the liquid phase.

Studies show that when polyoxyethylene rosin esters are used as detergent surfactants, the CMC is relatively low. Laundry liquids formulated in combination with such surfactants can exhibit surface activity at lower in‑use concentrations, helping to reduce detergent dosage and cost. Consistent with the papermaking sizing application, the emulsifying power of polyoxyethylene rosin esters is comparable to common non‑ionic surfactants such as Tween‑60 and AEO‑9, which supports enhanced detergency.

Furthermore, research also indicates that detergent formulations containing polyoxyethylene rosin esters show notable anti‑redeposition effects. Benefiting from the amphiphilic structure, a stable protective layer can form; after soil particles are detached, surfactant molecules provide a micellar protective environment that inhibits resticking or reagglomeration of soil. Polyoxyethylene rosin esters can also exhibit good synergy with common anionic surfactants such as LAS and builder/auxiliaries such as STPP.

Rosin‑based EO Adducts are an Excellent Choice for Bio‑based Product Formulations

Rosin‑based ethylene oxide (EO) adducts represent a highly promising class of bio‑based chemicals whose development artfully integrates the unique structural advantages of natural rosin and its derivatives with the precise, directional controllability of polyoxyethylene chains, jointly conferring diverse functional attributes and wide‑ranging application prospects. These products are founded on abundant and renewable rosin, inherently aligning with contemporary green chemistry and sustainability trends while markedly reducing dependence on conventional petrochemical feedstocks. Their environmental credentials are reflected not only in renewable sourcing but also in the typically low toxicity and favourable biodegradability of the products themselves, enabling compliance with high biobased‑content labelling schemes such as the USDA BioPreferred programme and the EU bio‑based product standard EN 16785‑1, thereby offering independently verified, more environmentally considerate options for consumers and industrial users.

At the molecular level, rosin derivatives (e.g., rosin acids, rosin alcohols, rosin amines, or rosin pentaerythritol esters) act as robust hydrophobic cores that provide the lipophilic scaffold essential for surfactant design, whilst controllably introduced hydrophilic chains via ethoxylation elegantly couple hydrophilic and hydrophobic termini within a single molecule to yield highly efficient amphiphiles. This distinctive architecture imparts excellent wetting, emulsifying, dispersing, and detergency capabilities, enabling performance optimisation for disparate use cases (such as detergents, pigment dispersants, paper sizing agents, and even emergent medical carriers).

Notably, multiple studies have substantiated that, relative to many traditional petrochemical‑based surfactants, rosin‑based EO adducts generally display lower toxicity and often good biodegradability; this not only enhances product safety but also meets escalating demands for environmentally benign chemicals. In summary, rosin‑based EO adducts exemplify high‑value utilisation of natural resources and offer an innovative solution balancing performance, cost, and environmental benefits, providing more sustainable, efficient, and safe alternatives across industrial sectors.