SINVOCHEM: A special dispersant suitable for oil-based formulations and its application in OD

Date:11-11-2021

Oil dispersion (OD) is defined as “a stable suspension of active ingredient(s) in a water immiscible fluid, which may contain other dissolved active ingredient(s), intended for dilution with water before use” (FAO, 2002). Unlike suspension concentrate (SC), in oil dispersion, oily carrier replaces water to act as continuous phase. While there is a variety of dispersants to choose from for SC, there rarely are dispersants that can perform exceptional functions in OD.

The barrier mainly comes from:
A. Competitive adsorption: Within OD formulation, oil carrier competes with dispersants for the opportunity to be adsorbed on the surface of AI particles. A large part of dispersant molecules do not  function due to failure in adsorption.
B. Poor ionization: conventional surfactants, especially anionic dispersants, are difficult to ionize in an oil-based environment to form electric double layer.
C. Desorption: The existence of non-polar lipophilic end of conventional nonionic dispersants makes it hard for dispersants to be adsorbed on surface of AI particles in an orderly manner. This will lead to insufficient adsorption or desorption and finally aggregation of AI particles.

All above factors make it difficult to develop an excellent dispersant for OD. Physically unhomogeneous appearance, phase separation over time or formation of non-flowable cream, poor emulsion and dispersion upon dilution are commonly seen in OD formulations. Nevertheless, as an updated or optimized means of formulation technology, OD has advantages in other aspects such as:.A. The selected oil base on its own may be used as a herbicide and impart a synergistic effect. B Liquid film formed by OD may increase coverage of active(s) and improve rain fastness. When it is hard for actives that  do not dissolve in lipophilic materials to penetrate crop tissues,OD is able to assist in this respect.

Formulators in the industry have to come to a compromise: although heterogeneous appearance is not desirable and sediment layer inevitablely exists, it is still acceptable if we can control the sediment in a relatively loose and open structure. This means the separated concentrate, after slight shaking, can revert to the state when the formulation is freshly prepared.. Technically, formation of sediments of such nature is possible through selection and combined use of proper surfactants and rheological agents. Demand for high performance dispersants suitable for oil-based formulations is thus proposed. A desirable dispersant should have the ability to provide strong steric hindrance in oils and achieve electrostatic repulsion upon spray dilution. Sinvochem developed a dispersant called SP-3498D with amphiphilic character, with one part of molecule presenting high affinity to the particle surface and the other that is soluble in oil phase. In oil dispersion, oil moleculescompete with dispersant molecules to be adsorbed on AI particles, which may weaken particle-dispersant interaction. The comb-like molecule of SP-3498D provides multi-anchored groups which create an effective layer to adsorb particles. Side chains of molecule were also modified to be compatible with oil base, which further enhances steric interaction. This dispersant was demonstrated to be feasible to overcome above mentioned competition.

Below are some application cases:

CASE 1

Sometimes, off-grade active or impure oil base may destroy your formulation, making finished product highly viscous or even turn to a jelly cream. In Tabel 1, gradient addition of Dispersant SP-3498D was performed on  24% Nicosulfuron+Atrazine OD. Data of particle size D90 and photos of microscopy (Table 1, Fig 1) demostrate an improved control on crystal growth and prevention toward the risk of cream occurence. Performance elevationon single-active formulation or multi-active set-ups including mixture of Nicosulfuron, Mesotrine andAtrazine are also proven.  

Table 1. Viscosity and variation of paricle size using different dosage of SP-3498D in 24% Nicosulfuron+Atrazine OD

Figure 1. Microscopic observation on 24% Nicosulfuron+Atrazine OD with gradient addition of SP-3498D

CASE 2

5% SP-3498D was added in several oil dispersions to observe its impact on viscosity during milling process. A viscosity reduction was observed in all formulations added with SP-3498D.

Table 2. Viscosity of OD milling slurries with/without SP-3498D

Figure 2. Viscosity variation in OD milling slurry with/without SP-3498D

CASE 3

The major challenge to formulating 6% Mesotrine+35%Atrazine OD is the increasing viscosity and low milling efficiency in production process, thus giving rise to undesired particle size and unqualified finished product. Table 3.shows variation of particle size over milling time. We can find that by introducing 5% SP-3498D, a qualified particle size can be reached in short time. A similar level of elevation in milling efficiency was found in 3% Nicosulfuron+7% Mesotrine+20% Atrazine OD (Fig 3).

Table 3. Efficiency when milling 6% Mesotrine+35% Atrazine OD with/without SP-3498D

Figure 3. Particle size of 3% Nicosulfuron+7% Mesotrine+20% Atrazine OD after milling, with/without SP-3498D

CASE 4


When it comes to aging stability, the special structure of dispersant SP-3498D ensures the formation of above mentioned loose sediment (or named “soft” sediment). TURBISCAN was used to monitor and evaluate aging stability at 54℃ for48hrs. Turbulence arised less sharply in the recipe with 5% SP-3498D (Fig 4). This meant particle growth and agglomeration was successfully inhibited by the dispersant, which is beneficial to maintaining a stable concentrate over time. Visible performance elevation was also obtained in 25% Pymetrozine OD (Fig.5). Evidently, without adding SP-3498D, a sticky layer of non-dispersed matter formed at the bottom without possibility of reversion to a suspension while a soft sediment is formed by inclusion of dispersant SP-3498D in the recipe.

Figure 4. Turbiscan results of 6% Mesotrine+35% Atrazine OD with/without SP-3498D ( 54℃,48hrs)

Figure 5. 25% Pymetrozine OD during aging storage (after one year)

Features of SP-3498D in conclusion:

• Enables excellent dispersion in oil dispersion and effectively inhibits crystal growth
  

• Reduces OD viscosity and benefits producing high loading OD
  

• Makes milling process easy and highly efficient
  

• Improves OD long term stability

We warmly welcome your interest in cooperation with SINVOCHEM

Email: export@sinvochem.com

Tel: 86-514-89188900