Meaning
Controlled degradation of a polymer to increase its melt flow rate allows for the production of grades that are otherwise difficult to manufacture in a reactor. Performing visbreaking involves using heat or chemicals to break the long chains of a high molecular weight resin into shorter segments. This process is commonly used for polypropylene to create materials suitable for thin wall injection moulding or fiber production.
The process stops once the desired flow rate is achieved and the material is cooled.
Melt Flow
Measurement of the rate at which a polymer flows through a standard orifice reveals the effectiveness of the degradation. Since visbreaking increases the melt flow index, it makes the plastic much easier to push into a complex mould. This improvement allows for lower injection pressures and faster filling speeds.
These changes lead to a more efficient moulding process.
Chain Scission
Molecular mechanism behind the process involves the random breaking of the polymer backbone. Because visbreaking targets the longest chains most aggressively, it results in a narrower molecular weight distribution. This uniformity improves the predictability of the material during processing.
The shorter chains also change the physical properties of the solid part.
Production Consistency
Monitoring the visbreaking process is essential to ensure that every batch of resin has the same flow characteristics. While the process is efficient, it must be tightly controlled to prevent the creation of unwanted byproducts. Modern extrusion lines use real time sensors to adjust the amount of degradation.
Consistent resin ensures that the moulder does not have to constantly change their machine settings. Uniformity is the main requirement for high speed production.
