Understanding the Role of Lubricants in Polymer Processing

The processing of polymers, particularly in manufacturing applications, often involves the use of lubricants to enhance efficiency and product quality. These lubricants can be broadly categorized into two types: internal and external. Internal lubricants work by reducing intermolecular friction within the polymer matrix, leading to a decrease in melt viscosity and improved rheological characteristics. This modification is particularly beneficial during processes such as extrusion or injection molding, where smooth flow is crucial for optimal performance.

In contrast, external lubricants function differently. They tend to be insoluble in the polymer and migrate to the surface during processing. This action creates a slippery layer between the polymer melt and the machinery, effectively reducing friction between these two surfaces. However, the weak bond strength between external lubricants and the polymer can lead to reduced efficiency under high shear conditions, as the lubricants may be squeezed out during processing.

To ensure the stability of the boundary layer between the polymer and processing equipment, it is important for lubricants to have polar groups that can chemically bond with metal surfaces. Such interactions can enhance the lubricant’s effectiveness, maintaining a consistent performance even under stress. The identification of whether a substance acts as an internal or external lubricant is not straightforward, but it can be assessed by examining its impact on various properties such as fusion, millstick times, and melt viscosity.

The classification of lubricants based on their chemical composition offers valuable insights. Common types include amides, hydrocarbon waxes, fatty acids, esters, and metallic soaps. The distinction between surface and bulk properties in polyurethanes (PUs) is also notable, as research by Ratner and Paynter revealed that low molecular weight lubricant molecules often aggregate at the surface, contributing to differences in composition.

Additionally, studies using techniques such as Fourier Transform Infrared (FT-IR) spectroscopy and X-ray Photoelectron Spectroscopy (XPS) have highlighted the complex interactions between lubricants and PUs. For instance, findings showed that while the surface of extruded PU tubing may be enriched with amide materials from lubricants, the bulk composition remains distinct, illustrating the nuanced role of lubricants throughout the polymer processing continuum.