Polyvinyl chloride (PVC) requires specific additives to prevent degradation during high-temperature and shear-intensive processing. Among these, PVC lubricants play a critical role in ensuring smooth processing of rigid PVC by influencing flow behavior and viscosity within processing equipment. Below, TLD Vietnam explores some aspects of internal and external lubricants for PVC applications and their impact on processing efficiency.

The Role of PVC Lubricants

PVC lubricants serve to minimize friction within the polymer matrix before melting and reduce friction between the PVC melt and the machinery’s contact surfaces. This facilitates smoother processing, enhances material flow, and prevents issues such as sticking or burning. Let’s dive into the distinct functions of internal and external lubricants.

External Lubricants for PVC

External lubricants function by adhering to the surface of the processing equipment or the molten PVC, creating a thin molecular layer that acts as a lubricating interface. This layer reduces friction between the resin and the machine, with the lubricant’s efficiency depending on its melting point and processing temperature. Lubricants with longer carbon chains typically provide superior lubrication by increasing the distance between friction surfaces.

External lubricants ease the movement of PVC stock through machinery, preventing the formation of thick layers that could burn or stick to hot metal surfaces. They also delay gelation, extending fusion time and enhancing the thermal stability of PVC, resulting in a glossy finish on the final product.

Internal Lubricants for PVC

Internal lubricants work within the polymer matrix, acting as softeners or partial plasticizers. Unlike traditional plasticizers, they are less compatible with PVC due to their longer carbon chains and lower polarity, allowing only a limited number of lubricant molecules to penetrate the polymer chains. This reduces intermolecular attraction, lowers melt viscosity, and promotes chain slippage, enhancing flow.

In processes like injection molding, internal lubricants reduce shear-induced burning by minimizing friction between particles before the PVC melts. This leads to improved mold filling, reduced back pressure in extrusion, and better control over part dimensions. The result is a smoother surface finish, reduced sink marks, and enhanced mechanical properties. 

Consequences of Improper Lubricant Use

Using PVC lubricants incorrectly can lead to significant processing and product quality issues. A careful balance between internal and external lubrication, along with precise quantities, is crucial. Here’s what can happen if this balance is disrupted:

Over-lubrication

Excessive internal lubrication can lead to high extrusion volumes and poor plasticization, while too much external lubrication may increase extrusion speed but compromise plasticization, negatively affecting surface quality and internal performance.

Under-lubrication

Insufficient lubrication can cause excessive frictional heat, leading to poor fusion, material degradation, or loss of mechanical properties.

Excessive Lubricants

Overuse of lubricants, due to their partial incompatibility with PVC, can cause thermal stability issues, precipitation, or processing defects. Excessive internal lubricants may reduce plasticizing torque and time, leading to rough inner surfaces and reduced thermal stability. Excessive external lubricants can cause precipitation and diminish mechanical properties.

Exploring TLD Vietnam’s PVC Lubricants

Zinc Stearate

Zinc stearate is a highly effective lubricant that reduces friction between polymer chains, facilitating smoother processing and extrusion. As a zinc salt of stearic acid, it provides excellent lubricity, thermal stability, and hydrophobicity. It serves as both an internal and external lubricant, improving flow, reducing viscosity, and preventing adhesion to molds. Its non-toxic nature and mold-release properties make it ideal for plastics, rubber, cosmetics, and food-contact applications within regulatory limits.

Calcium Stearate

Calcium stearate is a versatile lubricant that minimizes friction between particles and surfaces, enhancing powder flow and preventing material adhesion during processing. In plastics, it supports smooth extrusion and molding, improving processing efficiency and product quality.

Stearic Acid

Stearic acid is an excellent lubricant used in plastics and polymer manufacturing. By reducing friction, it simplifies and accelerates processing, ensuring smoother production and high-quality finishes.

PE Wax

Polyethylene wax is a highly effective lubricant used across industries to reduce friction between polymer chains. As both an internal and external lubricant, it enhances molding and extrusion efficiency, leading to faster production and superior surface finishes.

G60

G60 is a specialized internal lubricant designed for rigid and semi-rigid PVC products, such as transparent sheets, bottles, low-foaming profiles, and wire/cable sheaths. It reduces melt viscosity, improves resin flow, and imparts transparency, making it ideal for specific PVC applications.

What sets TLD Vietnam apart is our strong technical expertise. With a highly skilled technical team, TLD Vietnam Chemicals can customize materials and provide consultation with a full package of materials to meet your specific requirements for optimizing your production.

Conclusion

Lubricants are vital for optimizing PVC formulations, but their selection and application require careful evaluation in the laboratory. Choosing the appropriate type and quantity of PVC lubricant is critical to achieving desired processing outcomes and product quality.