The Polymer Development Process

When material scientists look to develop new lightweight, flexible, cost-effective, or otherwise better solutions, they frequently look to polymers. For food packaging, automotive components, construction materials, electronics, healthcare and medical applications, textiles and apparel, aerospace and defense,  clean energy, and a variety of other products, researchers often turn to the polymer analysis and development process. Processes such as extrusion and compounding can help in the development of novel polymer materials with specific desired properties.

The Making of Polymers

Polymers are large molecules made up of repeating subunits called monomers. They are macromolecules composed of thousands or even millions of monomer units covalently bonded together in a chain-like structure. The process of joining these monomers together to form a polymer is known as polymerization. There are two types of polymers: synthetic polymers, which are man-made polymers that are produced through chemical reactions, and natural polymers, which are produced by living organisms through biological processes.

The formulation of modern polymer compounds can be quite complex and include many ingredients. Equipment that streamlines the polymer development process enables researchers to experiment with different materials while also ensuring consistent quality of products. The proper instrumentation can also help scientists transition from lab-scale compounding to large-scale production and help ensure that polymer materials comply with applicable standards and regulations. Advanced extrusion equipment can optimize compounding, facilitating the production of these complex polymer materials.

Whether the aim is to optimize material usage, develop environmentally friendly new polymers, or guarantee consistent quality, material scientists look to overcome these challenges with leading technologies to conduct R&D more efficiently.

Types of Polymers

Polymers can have diverse properties depending on their chemical structure and the arrangement of monomer units. Some common properties of polymers include flexibility, toughness, elasticity, thermal stability, electrical insulation, chemical resistance, and biocompatibility.

Synthetic polymers are created by polymerizing monomers derived from petroleum and other raw materials. Examples of synthetic polymers include polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS), and polyethylene terephthalate (PET). Synthetic polymers offer a wide range of properties and can be tailored to specific applications through modifications in their chemical structure.

Natural polymers, as the name implies, are found in nature and are derived from renewable sources. They are produced by living organisms through biological processes. Examples of natural polymers include proteins (such as collagen and silk), nucleic acids (such as DNA and RNA), carbohydrates (such as cellulose and starch), and natural rubber. Natural polymers often exhibit unique properties and biocompatibility, making them suitable for various applications, including food, medicine, textiles, and cosmetics.

The Process

The virgin polymer development process involves several steps that are essential for creating a new polymer material. Here are the general steps involved:

1. Monomer Selection: Monomers are small molecules that can react together to form long chains, which are the building blocks of polymers. Which monomers are selected for use as starting materials depends on the preferred properties and characteristics of the final polymer.
2. Polymerization: Polymerization is the process of chemically bonding the monomers together to form a polymer chain. There are different methods of polymerization, including addition polymerization, condensation polymerization, and ring-opening polymerization. The choice of polymerization method depends on the monomers being used and the desired properties of the polymer.
3. Catalysts and Initiators: Catalysts or initiators may be used to facilitate the polymerization reaction. Catalysts help increase the reaction rate, while initiators start the polymerization reaction by initiating the formation of free radicals or other reactive species.
4. Reaction Conditions: The reaction conditions, such as temperature, pressure and solvent, play a crucial role in the polymer development process. These conditions can influence the reaction rate, molecular weight, polymer structure, and overall properties of the final polymer.
5. Purification: After the polymerization reaction, the polymer material is usually purified to remove any impurities or unreacted monomers. This purification process can involve techniques such as filtration, precipitation, or extraction.
6. Characterization: The next step is to characterize the properties of the polymer. This involves analyzing its molecular weight, thermal stability, mechanical properties, chemical resistance, and other relevant characteristics. Various techniques such as spectroscopy, chromatography, and microscopy are used to assess the polymer’s properties.
7. Testing and Optimization: Once the polymer is characterized, it undergoes testing to evaluate its performance in specific applications. This may involve testing for factors like strength, flexibility, durability, or chemical resistance. Based on the test results, adjustments or modifications to the polymer formulation may be made to optimize its properties.
8. Scale-up and Production: After successful testing and optimization, the polymer development process moves towards scale-up and production. This involves producing the polymer on a larger scale, optimizing manufacturing processes, and ensuring consistent quality control.

It’s important to note that the specific steps and processes involved in polymer development can vary depending on the intended properties, applications, and types of polymer being developed.

Polymer Compounding

The diversity of plastics needed to meet the requirements of the broad range of potential applications is brought about through polymer compounding.  Compounding is the process of formulating resins into customized materials by using one or more polymer resins with corresponding additives to meet the exact requirements of an application. For instance, in terms of physical requirements, it could mean developing a material with better heat resistance, greater strength, or more flexibility, or it could just mean ensuring the right coloring.

A masterbatch is also a compound, consisting of at least two components that are mixed together using the extrusion process. The term “masterbatch” refers to plastic additives in the form of granules with a higher content of colorants or additives than in the end application. They are added to the polymer to color it or to change its properties. Compared to powder additives, masterbatches increase technical process reliability and are easy to process.

The main compounding steps are feeding, melting, conveying, mixing, venting, and extrusion of the homogenized product. In the feed zone, solid material is fed by the volumetric or gravimetric feeder. Air is removed and low-density material is compacted. In the next step, the material is moved forward and heated up in a partially-filled, non-pressurized conveying section. In the first mixing zone, the material is melted and plasticized. The mixing zones are filled completely with material. Another conveying zone follows and can be used for venting, split feeding of fillers, or liquid feeding. Alternating mixing and conveying sections then follow to achieve a homogeneous product. The conveying screw elements within venting zones are used for venting volatiles and air, either at ambient pressure or by vacuum. Lastly, an extrusion section is used to build up pressure and shape the material. In most of the applications, a strand is extruded, which is then cooled in a water bath and cut into pellets.

Scientists in research and industry have been working on material development so they can modify compounds for better properties, for better re-usability or enhanced sustainability. A systematic development approach is needed to identify the best suited compound composition for a given application as well as to investigate the processability for production of novel materials. In early stages of development, novel materials used for such new compounds may only be available in small quantities. To address this issue, researchers can use small-scale extrusion or micro-compounders to assess the compounding behavior and to subsequently characterize polymer properties. A micro-compounder with the capability of detecting the relative viscosity while compounding delivers additional information about structural changes caused by the compounding process.

Summary

Overall, polymers are essential materials that have revolutionized various aspects of modern life due to their unique properties and versatility in meeting the demands of different industries and applications. Research and development in polymer science are continuously evolving, leading to the discovery of new methods and techniques for polymer development. Extrusion helps enable material scientists to perform numerous trials efficiently and cost effectively, which could lead to developing new materials at a faster pace.

Additional Resources

• Extrusion Technologies
• Compounding and Extrusion Online Resources
• Application note: Incorporating sensitive or low bulk density fillers in a polymer compound
• Polymer sustainability application compendium
• Application note: Why use a twin screw extruder for reactive organic reactions?
• Application note: Benefits of solvent-reduced twin-screw compounding for cost-efficient, eco-friendly, and high-performing lithium-ion batteries