PASP-Na Dispersant for Herbicide SCs: Zeta & Stability
Zeta Potential Stabilization of PASP-Na in Hard Water Matrices for Herbicide SCs
In the formulation of herbicide suspension concentrates (SCs), maintaining colloidal stability under variable water hardness is a persistent challenge. Sodium Polyaspartate (PASP-Na), a biodegradable polyamino acid, functions as a highly effective dispersant by adsorbing onto active ingredient particles and imparting a strong negative zeta potential. Unlike conventional polyacrylate dispersants, PASP-Na exhibits remarkable tolerance to calcium and magnesium ions, which are prevalent in hard water sources used for spray dilution. Field observations indicate that in water with hardness exceeding 500 ppm CaCO₃, PASP-Na maintains zeta potentials below -30 mV, whereas many polyacrylates show significant charge neutralization leading to flocculation. This behavior is attributed to the chelating ability of the aspartic acid residues, which sequester divalent cations and prevent them from bridging between particles. For formulators seeking a drop-in replacement for traditional dispersants, PASP-Na offers a robust solution without the need for additional chelating agents. Our technical team has documented that a 1:1 substitution ratio by weight often yields equivalent or improved suspension stability, particularly with triazine and sulfonylurea herbicides. For a deeper understanding of how PASP-Na compares to polyacrylates in various applications, refer to our detailed analysis on Sodium Polyaspartate as a drop-in replacement for polyacrylate.
Polymer Chain Entanglement Effects on Microcapsule Wall Thickness in PASP-Na Dispersions
When formulating microencapsulated herbicide suspensions (CS or mixed SC/CS), the dispersant's molecular architecture directly influences the interfacial polymerization process. PASP-Na, with its linear polyamide backbone and pendant carboxylate groups, can participate in hydrogen bonding with polyurea or polyamide microcapsule walls. This interaction often results in a more uniform wall thickness and reduced porosity compared to dispersants that merely provide steric stabilization. In our laboratory, we have observed that PASP-Na concentrations between 2-5% w/w relative to the oil phase can reduce the coefficient of variation in wall thickness by up to 15%. However, an edge-case behavior worth noting: at high shear rates during emulsification, PASP-Na solutions exhibit a slight shear-thickening tendency at concentrations above 10% w/w, which can lead to localized viscosity spikes and inconsistent droplet breakup. This non-standard parameter is critical for scale-up; we recommend maintaining a maximum concentration of 8% w/w in the aqueous phase during emulsification to avoid processing issues. For formulators working on complex suspoemulsions, our Sodium Polyaspartate formulation guide for detergents provides additional insights into polymer-surfactant interactions that are transferable to agrochemical systems.
Phase Separation Risks and Compatibility of PASP-Na with Non-Ionic Surfactants
Non-ionic surfactants, particularly alcohol ethoxylates and alkyl polyglucosides, are commonly used as wetting agents in herbicide SCs. While PASP-Na is generally compatible with most non-ionics, certain combinations can induce phase separation via depletion flocculation or competitive adsorption. Our field experience shows that when the non-ionic surfactant has an HLB below 12 and is used at concentrations exceeding 5% w/w, the PASP-Na dispersant may be displaced from the particle surface, leading to rapid sedimentation. This is especially pronounced with active ingredients that have low water solubility and high lipophilicity, such as oxyfluorfen or pendimethalin. To mitigate this, we recommend a sequential addition protocol: first disperse the active ingredient with PASP-Na in water, allow equilibration for 30 minutes, then add the non-ionic surfactant under low shear. This ensures the dispersant anchors firmly before the surfactant competes for surface sites. Additionally, storage at elevated temperatures (54°C accelerated testing) has revealed that PASP-Na-based SCs may develop a slight yellow tint over time when formulated with certain amine salts, though this does not impact efficacy. This trace impurity effect is batch-specific and should be monitored via periodic COA review.
Technical Specifications, COA Parameters, and Bulk Packaging of PASP-Na Dispersant
NINGBO INNO PHARMCHEM CO.,LTD. supplies Sodium Polyaspartate (CAS 94525-01-6) as a high-purity, low-color dispersant specifically tailored for agrochemical suspension concentrates. The product is available as a 40% aqueous solution or as a spray-dried powder. Key parameters from a typical Certificate of Analysis (COA) are summarized below. Please refer to the batch-specific COA for exact values.
| Parameter | Specification (Typical) | Method |
|---|---|---|
| Appearance | Clear to pale yellow liquid / White powder | Visual |
| Solid Content (for liquid) | 40 ± 1% | Gravimetric |
| pH (1% solution) | 8.5 - 10.5 | pH Meter |
| Viscosity (25°C, liquid) | 50 - 200 mPa·s | Brookfield |
| Molecular Weight (Mw) | 3,000 - 5,000 Da | GPC |
| Heavy Metals (as Pb) | ≤ 10 ppm | ICP-MS |
| Chloride Content | ≤ 0.5% | Titration |
For bulk procurement, PASP-Na is packaged in 210L HDPE drums (250 kg net) or 1000L IBC totes. Custom packaging is available upon request. Our logistics team ensures secure, compliant shipping with a focus on physical packaging integrity. As a global manufacturer, we maintain consistent quality across batches, making PASP-Na a reliable drop-in replacement for conventional dispersants. For detailed performance benchmarks, request a sample and compare against your current formulation.
Frequently Asked Questions
How does PASP-Na control particle size distribution during milling?
PASP-Na adsorbs rapidly onto freshly created surfaces during wet milling, preventing re-agglomeration and enabling a narrow particle size distribution. Typical D90 values below 5 µm are achievable with standard bead milling. The dispersant's low molecular weight ensures fast diffusion to particle surfaces, which is critical for high-throughput manufacturing.
What is the shelf-life stability of PASP-Na-based SCs under tropical storage conditions?
Accelerated storage tests at 54°C for 14 days, simulating two years at ambient tropical conditions, show that PASP-Na formulations maintain viscosity, suspensibility, and re-dispersibility within acceptable limits. However, formulations containing high electrolyte loads may require a co-dispersant to prevent syneresis. Always validate with real-time storage at 30°C/75% RH.
What is the recommended substitution ratio when replacing polyacrylate dispersants with PASP-Na?
As a starting point, a 1:1 weight-for-weight substitution of active dispersant content is recommended. In many cases, PASP-Na provides equivalent or superior performance. However, optimization may be needed for highly hydrophobic actives; a slight increase of 10-20% in dispersant dosage can compensate for differences in adsorption affinity.
How to make suspension concentrate?
A typical SC is made by dispersing the solid active ingredient in water with a dispersant (like PASP-Na), wetting agent, thickener, and antifreeze, followed by wet milling to reduce particle size. The key is achieving a stable, pourable suspension with minimal sedimentation.
What is the best surfactant for herbicide?
There is no single best surfactant; it depends on the herbicide's properties and the formulation type. For SCs, a combination of an anionic dispersant (e.g., PASP-Na) and a non-ionic wetter often provides optimal stability and bioefficacy.
Which is better, EC or SC?
SC formulations are generally preferred over ECs due to lower VOC emissions, reduced phytotoxicity risk, and better safety profiles. However, ECs may offer better efficacy for certain lipophilic herbicides. The choice depends on the active ingredient and regulatory requirements.
What is an OD formulation?
An OD (oil dispersion) is a suspension of a solid active ingredient in a non-aqueous solvent or oil. It is used for water-sensitive actives or when enhanced penetration is desired. PASP-Na is not typically used in ODs due to its water solubility; instead, organo-modified clays or polymeric dispersants are common.
Sourcing and Technical Support
NINGBO INNO PHARMCHEM CO.,LTD. is a leading global manufacturer of Sodium Polyaspartate, offering consistent quality and competitive bulk pricing. Our technical team can assist with formulation optimization, compatibility testing, and scale-up support. To request a batch-specific COA, SDS, or secure a bulk pricing quote, please contact our technical sales team.