Technology and Applications of ALCOTEX Series Secondary Suspension Agents

Polyvinyl chloride (PVC) is one of the most widely used plastics, and its properties largely depend on the morphology, porosity, and bulk density of the PVC particles formed during suspension polymerization. The role of the suspending agent is crucial in the suspension polymerization process. ALCOTEX series polyvinyl alcohol products are specifically developed as secondary suspending agents (or pore enhancers) to synergize with conventional primary suspending agents, jointly optimizing the microstructure and macroscopic properties of PVC resin.

1. What is an auxiliary dispersant?

In complex dispersion systems, a single primary dispersant often struggles to simultaneously address multiple requirements such as wetting, depolymerization, and stabilization. This is where the role of auxiliary dispersants becomes prominent. They significantly improve the dispersion stability and flowability of the entire system by adjusting the surface tension of the system, improving the charge distribution between particles, and enhancing the adsorption capacity of the primary dispersant.

In pigment systems, it reduces the risk of flocculation and sedimentation;

In emulsion polymerization, it controls particle size distribution and polymerization rate;

In rubber latexes, it prevents particle agglomeration and improves emulsion storage stability.

2. Comparison of Technical Characteristics of ALCOTEX Series Products

High Hydrolysis Degree Products (approximately 55% mole %): 55-002H and 552P

• ALCOTEX 55-002H: A colloidal dispersion of polyvinyl alcohol (PVA) with a high degree of hydrolysis (54.0-57.0 mole %). Nuclear magnetic resonance (NMR) measurements show a random distribution of its acetate groups. For application, it is recommended to add a portion of the primary suspending agent before adding 55-002H to ensure good dispersion of the secondary additive. It is strictly forbidden to add it to the VCM feed line.
• ALCOTEX 552P: A 55% aqueous solution of hydrolyzed PVA, also with a high degree of hydrolysis. It has a low residual methanol content (<2% w/w) and a high cloud point (>45℃). It can be directly added to the reactor or pumped into a flowing water feed line. It is recommended to add 552P after adding at least a portion of the primary suspending agent.

Low degree of hydrolysis products (approximately 43%-45% mole %): WD100, 432P, and 45

• ALCOTEX WD100: A 43% aqueous solution of hydrolyzed polyvinyl alcohol, characterized by extremely low methanol content (<2% w/w). It can be infinitely diluted with water. Compared to conventional products, WD100 provides higher porosity for PVC resin and reduces gel or "fisheye" formation. Unlike traditional secondary additives, WD100 can be added before the primary suspending agent, or as a stable primary/secondary suspending agent co-solution. Adding via the water feed line is recommended.
• ALCOTEX 432P: A low-viscosity methanol-based solution of 43% hydrolyzed polyvinyl alcohol, with the lowest viscosity in the series (100-180 mPa·s). Due to its methanol solubility, its storage and transportation must strictly comply with local regulations regarding flammability and toxicity. It is typically pumped directly into the reactor after the addition of water and the primary stabilizer.
• ALCOTEX 45: A 45% hydrolyzed polyvinyl alcohol (PVC) water/isopropanol solution with moderate viscosity (300-600 mPa·s). Due to the presence of isopropanol, it is also subject to local flammability regulations. Its nuclear magnetic resonance (NMR) results also show a random distribution of acetate groups. It is typically pumped into the reactor after the addition of water and the main suspending agent.

All ALCOTEX products are designed to optimize the porosity/bulk density relationship, resulting in the following practical production advantages:

• Highly efficient VCM removal: Increased porosity allows for more thorough VCM release, permitting the use of gentler stripping conditions, potentially reducing stripping time, steam consumption, and stripping temperature.
• Optimized plasticizer absorption: Improves PVC's ability to absorb plasticizers, particularly beneficial for manufacturing flexible PVC products.
• Product consistency and design: ALCOTEX helps achieve a more uniform pore distribution and tends to make PVC particles more spherical, thus improving bulk density. This provides flexibility in polymer design, such as achieving higher conversion rates at a given porosity.

3. Conclusion 

The ALCOTEX series of secondary suspending agents are powerful tools for S-PVC manufacturers to optimize product structure and improve production efficiency. By precisely controlling the degree of hydrolysis, solution form, and addition method of polyvinyl alcohol, these products can significantly improve the porosity/bulk density relationship of PVC, simplify the stripping process, and ultimately enhance the thermal stability and processing performance of the product. Manufacturers can select the most suitable secondary suspending agent from this series based on their own equipment conditions, the required PVC molecular weight range, and sensitivity to methanol/isopropanol content.

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