Compounding, masterbatch and dry blends: what’s the difference?
Nearly all plastic you come into contact with on a daily basis has undergone some form of ‘compounding. This is usually to enhance appearance with colour or to support processability and improve physical properties with specialist additives. This could be colour and antibacterial additives for consumer products, UV stabilising and flame retardant additives for automotive components, laser marking additives for medical devices, colours for wire and cable applications and much, much more.
There are different ways of creating a compound; this article will go into detail about the different options to help you find the most suitable one for your application.
Each project is different, and different applications require different methods and considerations. It's important to seek advice from compounding experts.
A plastic masterbatch is a highly concentrated mixture of pigments and/or additives that are encapsulated during a heat process (in a high shear mixing extruder) into a carrier resin (usually PE or PP). This is then cooled, extruded and cut into granular pellets. These pellets are then metered (‘let’) down into the natural base polymer, where it blends with the polymer. Addition ratios (otherwise known as let down ratios / LDR) are predetermined and are normally around 1-5%.
There are different types of masterbatch: white masterbatch, black masterbatch, colour masterbatch, additive masterbatch and special effect masterbatch.
There are advantages and disadvantages to using masterbatch as a colouring / additive blending method. Masterbatch can be more cost-effective than compounding, can be more flexible and require less stock holding. Additionally, a universal carrier can be used across generic material types such as LDPE, HIPS or ABS (although polymer specific carriers should be used for optimal results). Unfortunately, colour consistency throughout batches can be an issue. Accurate dosing of masterbatch to base is essential to avoid consistency issues, which can demand additional equipment and resource.
Fully Compounded Colour
Full compounding is the process of melt blending (blending in a molten state) plastic with colours and/ or additives. This process changes the physical, thermal, electrical or aesthetic properties of the base polymer. The final product is called a compound or composite.
While processes may differ between manufacturers, plastic compounding typically involves a basic set of steps. Additives and colours in the form of pellets, flakes or powders are conveyed through a screw feeder to a container of a molten plastic base material. Blending and dispersal processes ensure that the base material and added ingredients are well combined to create a homogenous final product. The compounded material is then cooled and extruded into pellets, which are then packaged and sold.
This method produces excellent distribution of colour and is very easy to use (no dosing equipment or additional measurements are required). It also provides consistent colour within a batch. However, fully compounded colours and additives can be costly, due to additional processing and stock holding requirements that may occur.
Dry blending involves mixing the polymer base with raw colour pigments and/or additives and processing thereafter (without further mixing steps). Dispersion aids and wetting agents are usually required to support the binding of the powders onto the base polymer. This is sometimes referred to as a ‘salt and pepper mix’ as the raw materials are simply blended together by hand / manually.
This method can provide low-quality products with varying colour consistency. Due to the lack of thorough mixing processes, there is a high chance of poor dispersion and distribution of colours and additives throughout the polymer. It can also be very messy and affect the drying process of the polymer compound. However, this process is very cost effective due to the low conversion cost and is very quick to prepare.
Matrix Plastics works with an incredibly versatile range of base polymers, including but not limited to: ABS / MABS, POM (acetal), ASA, PBT, Polycarbonate, PC/ABS, PMMA, PA (nylon), Polypropylene, Polystyrene, Styrene Copolymers and TPE.
To discuss which method is best suited to your polymer or application, or to take advantage of our 24-hour colour match service, contact us directly at firstname.lastname@example.org or call +44 (0) 1753 551177.