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

Extrusion, calendaring…

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.

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.