Can grease damage plastic?

Thicker lubricants like grease are mostly used when oil is an impractical choice.

More viscous, they provide a stay-in-place seal for machinery with high load, low-speed and intermittent operations.

Grease is also ideal for equipment with hard-to-access innerworkings like electric motors, bearings and other sealed-for-life components. Quality products from brands like Fuchs and Total can offer protection against corrosion, contaminants and high temperatures.

While grease is renowned for protecting metal, some machinery includes plastic parts like gears, sprockets and wear strips. Unfortunately, some greases can harm plastic, making it important to understand equipment applications before buying a lubricating grease.

Here, we explore the impact of different greases on plastic components and discuss points to consider regarding grease and plastic compatibility.

Mineral and petroleum-based grease

The reputation of grease being damaging to plastic comes from products that have a mineral- or petroleum-derived base oil. Grease typically contains a base oil (between 80 and 90 per cent), a thickening agent (5 to 20 per cent) and additives (0 to 10 percent). As such, the properties of the base oil have substantial impact.

This category includes polystyrene (PS), acrylonitrile butadiene styrene (ABS) and polycarbonate (PC) greases, but also common off-the-shelf solutions like petroleum jelly and WD-40, and each can harm plastic, making it crack, swell and degrade. Base oils in the greases break down the structural integrity of plastic, making it softer and weaker, eventually leading to total part failure.

Damage is not always instantaneous and can take hours of exposure to appear, especially at high temperatures.

Lithium grease

Although some nylon plastics can stand-up to it, lithium grease has an oil-base. As a result, it can degrade most plastic components as well as elastomers such as rubber, a material often used for seals.

Silicone grease

Along with specialised synthetic solutions like perfluoropolyether (PFPE) grease and polyalphaolefin (PAO) grease, silicone-based greases are usually safe for plastic. Non-reactive with metal-on-plastic and plastic-on-plastic machine operations, silicone grease is considered the go-to choice for application involving plastic gears and components in consumer electronics.

Grease resistance

Different plastics have varying resistance to grease. For instance, polypropylene (PP) and polyethylene (PE) are typically inert and can resist damage, but polycarbonate (PC) is exceptionally sensitive and at risk from non-silicone-based greases.

Always ensure greases ordered are completely compatible with machinery by reviewing original equipment manufacturer (OEM) recommendations.

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