All plastics are polymers, but not all polymers are plastics. Polymer production is a multi-step process that transforms raw materials into products that we use in our day-to-day life with the help of polymer process equipment such as extruders, calenders and injection molding machines.
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What are polymers?
Polymers are natural or synthetic substances composed of macromolecules that are multiples of simpler chemical units called monomers. Natural polymers are found in living organisms, including proteins, cellulose, nucleic acids and starches. On the other hand, synthetic polymers are derived from petroleum oil, with examples of nylon, polyester, and Teflon.
Addition polymerization vs condensation polymerization
There are two types of polymerization: addition and condensation polymerization. In the former, a polymer is formed simply by linking monomers together without co-generating by-products. The addition polymerization has three steps: initiation, chain propagation and termination of the chain. During addition polymerization, the monomers rearrange and form a new structure without losing atoms or molecules. It results in homo-chain polymers such as polyethylene, polystyrene and methacrylates.
During the condensation polymerization, monomers are joined by releasing other small molecules as a byproduct, for example, water or methanol, resulting in hetero-chain polymers. For instance, cellulose, starch, nylon and polyester are the results of this process. These polymers tend to be more biodegradable due to weaker bonds.
Manufacturing processes and polymer process equipment
Transforming polymers into practical products starts by adding additives according to the desired specifications. Polymeric materials in the form of powder, granules or melts are transformed into end products by extrusion. It is a process in which plasticized material is forced through an orifice and cooled once it achieves the favored shape.
Polymer process equipment includes a variety of extruders, such as ram extruders for short product lengths, gear pump extruders for pre-plasticized and low-viscosity materials and a single screw extruder which produces the majority of extruded products, especially those with a constant profile such as window frames.
Another widely used method is calendaring – processing molten polymers, mostly rubber and thermoplastic, by squeezing them between a pair of heated counter-rotating rolls in a machine called calendar, which can easily be set up to produce preferred thickness and size. This process is used to manufacture floor tiles, shower curtains, signs, and displays.
…and injection molding
Injection molding is the leading process for producing complex shapes, for example, toys, some musical instruments, or automotive parts. The process in the injection molding machine consists of four phases: plasticization, which transforms thermoplastic powder or granules into a homogeneous melt state, injection of melt from the plasticization unit to all parts of the mold cavity, setting of the melt in the mold cavity and ejection of the finished product from the mold.
Technological Innovations: the versatility and future of polymers
Polymers can be used for various and unique products, some of them seemingly aiming to change our lives in the future. For instance, scientists from Defense Advanced Research Projects Agency developed a polymer foam that can be injected into an abdominal cavity and later easily removed to stop bleeding. Harvard University scientists found a way to inject polymers through needles, heal damaged tissue, and use polymers in robotics to add flexibility. Polymers can further be used to create artificial skin, ideal for prosthetics. Moreover, polymers might be an answer to cancer, as Duke University scientists tested a thermally responsive radioactive peptide polymer that is effective at controlling tumors. Other innovative applications are scratch repair, lotions against intense heat, and creating transparent soil.
Sustainable polymers as a solution
Sustainable polymers are materials that cater to consumers’ needs without damaging the environment. Namely, renewable sources, such as carbon dioxide, terpenes, vegetable oils and carbohydrates can be used to produce a variety of polymer end-products. Sustainable polymers can be made by fermenting the plant material to produce monomers, such as plant-derived sugar to lactic acid.
Another alternative is extracting chemicals from the plant like soybean oil or natural rubber. Finally, bioengineering and microbial pathways can convert plant molecules into monomers. Renewable polymers found their use in packaging, automotive parts and 3D printing. Sthereochemists strive to find a way to manufacture sustainable polymers while they keep the mechanical and physical properties of traditional plastics.
Economic and renewable – using CO2 to make polymers
The ability to use, and therefore reduce, CO2 emissions and convert them into usable products is the perfect example of renewability. Having significantly lower greenhouse gas emissions, CO2-based polymers are a striking sustainable alternative due to the source material being abundant, renewable, and inexpensive. As a very thermodynamically stable molecule, CO2 requires a significant amount of energy to be activated which is achieved with a specially-designed catalyst that reduces the energy barrier.
So far, there are two different approaches to introducing CO2 onto polymers. One is having CO2 participating directly in the polymerization process as a comonomer. The second approach uses CO2 for building blocks that are yet to undergo the polymerization process. This method could almost replace fossil raw materials as nearly all chemical products that use them can be produced from CO2.