If your business processes thermoplastic films, foams or moulded parts, static charge and surface friction are two issues that tend to show up at the worst possible moments.
Dust contamination on film surfaces and parts sticking in the mould can lead to slower cycle times and create handling problems on your converting line.
Glycerol Monostearate (GMS) is one of the most widely used additives for tackling both problems at once. It’s been a staple of thermoplastic processing for decades, and for good reason. It delivers rapid antistatic performance and reduces surface adhesion from a single, well-understood ingredient.
This article looks at how GMS works, where it performs best, and what to think about when you’re incorporating it in your formulation.
What is GMS, and how does it work?
GMS is a non-ionic fatty acid ester, produced from glycerol and stearic acid, typically derived from vegetable sources.
It behaves in a way that will be familiar if you’ve ever worked with slip additives. After processing, it migrates from within the polymer matrix to the surface, where it does its work. Once there, it absorbs moisture from the surrounding atmosphere, forming a thin, conductive layer across the polymer surface. That layer provides a pathway for static charge to dissipate rather than accumulate.
It’s a straightforward principle, but it’s incredibly effective. It also kicks in quickly, which is why GMS is classified as a short-term antistat.
The same behaviour also helps reduce friction on the polymer surface, which is what makes GMS a useful additive in thermoplastic injecting moulding processes.
It’s a dual-function additive, and in many applications, you get both benefits from a single inclusion.
Antistatic performance
GMS’s antistatic effect develops quickly after processing, making it well-suited to applications where you need to control static build-up during production, converting or early end-use, rather than sustained long-term performance out in the field.
However, GMS’s antistatic properties are dependent on humidity. Because it works by drawing moisture from the atmosphere, its performance can vary in ambient conditions. If you’re formulating for controlled-environment applications or low-humidity climates, that’s a variable worth factoring in.
In those situations, pairing GMS with a longer-acting antistat, such as a fatty acid amide-based additive, can give you a more complete performance profile, delivering fast-acting static control from the GMS before the second additive takes over as the GMS’s effect fades.
Mould release and other uses
In thermoplastic injection moulding, GMS’s surface activity makes moulded parts easier to eject. The lubricating layer it forms at the polymer surface reduces adhesion between the part and the mould wall, which means less resistance during ejection. It can significantly reduce cycle times, which is a meaningful productivity gain when you’re running high volumes.
And in PE and PP foam applications, GMS helps stabilise cell structure and provides antistatic properties during production. Uniform cell structure has a direct bearing on the foam’s density and mechanical properties. Irregular cells can introduce weak points and inconsistency into the finished product.
Formulation considerations
You can introduce GMS during the additivation or compounding stages, or via a masterbatch, which gives you reasonable flexibility depending on how your process is set up.
When it comes to interaction with other additives, GMS is commonly used alongside longer-acting antistats to deliver a combined short- and long-term performance profile. If you’re working with BOPP or PP film and need both immediate and sustained antistatic protection, a blended formulation is usually the more reliable route.
However, it’s worth noting that when GMS migrates to the surface, it can create a haze effect in film applications. So, if clear film is a requirement for your end-product, it’s worth evaluating the effect at your intended loading.
GMS also has a relatively low melting point, so you’ll want to confirm it’s suitable across your full processing window before committing to a formulation.
Typical use levels run from 0.5% to 1.0% for films, EVA compounds and most moulding applications, rising to 1.0–1.5% for PE and PP foams, but these are starting points. Your actual loading will depend on your polymer system, processing conditions and end-use requirements, so finding the right balance for your specific application is worth spending time on.
Get it right, and you’ll see the mould release and antistatic performance you’re looking for. Use too little and the effect may be insufficient for your application. Push it too high, and you risk surface bloom, increased haze or adhesion problems downstream, especially if your process includes printing, laminating or coating.
What to look for when sourcing GMS
Beyond the technical specifications, there are a few things worth paying attention to when you’re evaluating a GMS supplier.
Batch-to-batch consistency is essential. GMS’s antistatic and mould release performance are both sensitive to variability in quality. If your supplier can’t demonstrate reliable adherence to spec, it introduces risk into your process.
If your application involves any contact with food, make sure the specific grade you use is approved for that. Your supplier should be able to provide up-to-date safety data sheets, regulatory compliance information, and storage and handling advice without you having to chase for them.
On the technical side, selecting the right grade isn’t always straightforward, especially if you’re looking at combining it with other antistats. A supplier who knows your application and can help you think through the options will save you a lot of time.
That’s where MegaChem UK can help. We supply GMS and a broader range of antistatic additives for polyolefin film, foam and thermoplastic moulding applications.
Whether you’re evaluating GMS on its own or looking at how it fits into your antistat system alongside longer-acting additives, our team can help you work through the right approach for your application. Get in touch to discuss your requirements, or request a sample to evaluate its performance in your processes.
