Improving performance of plastic products using glass microspheres sustainably

Driven by increasing demands to reduce greenhouse gas emissions, automakers worldwide are in a race to find new ways for improving the fuel efficiency of passenger cars and trucks. Along with more aerodynamic designs and incremental improvements to internal combustion engines, one of the key strategies automakers are employing to meet efficiency targets is weight reduction. This has led to extensive research into new materials that are lighter in weight without compromising performance.
 
For example, automotive plastics have been extensively used for years to replace metal parts, shaving hundreds of pounds of weight. This represents a significant improvement: according to the US Department of Energy, “...for every 10% of weight eliminated from a vehicle’s total weight, fuel economy improves by 7%.”
 
Today, research is focusing on new, low-density plastics compounds that reduce part weight even further, while maintaining an acceptable balance of performance and processing characteristics. Glass microspheres are inert spherical fillers, compatible with most polymers. They have long been relied upon as density reducing additives in a wide range of thermoplastics, composites and elastomers.
 
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For example, glass microspheres are strong enough to survive harsh injection moulding and compounding processes, yet have a specific density of only 0.46 g/cc – enabling weight reductions of 10% or more in many polypropylene-filled systems, and 15% or more in nylon glass fiber-filled parts. Because of their ultra-low density, using smaller fractions of glass microspheres in conjunction with heavier fillers can help achieve significant weight reductions while maintaining the compound’s critical mechanical properties.
 
Producers of sheet moulding (SMC) and bulk moulding (BMC) compounds have reported even greater weight reductions using glass microspheres - as much as 30%, in some applications, while maintaining a desirable balance of properties, including the ability to deliver Class A paintable surfaces.
 
Glass microspheres vs other fillers
Compared to other heavy fillers such as talc, calcium carbonate, glass fiber, and clay (from 2.5 to 2.8 g/cc), glass microspheres for plastics and rubber applications have densities ranging from 0.1 to 0.6 g/cc.
 
Glass microspheres are excellent strength/weight optimisers. Replacing a certain percentage of conventional high density fillers with glass microspheres results in weight reduction while maintaining the original mechanical properties. As an example, this is shown in the following case study with glass fiber filled nylon 66:

• Materials: Commercially available, high strength (18000 psi isostatic crush strength), low density (0.46g/cc) glass microspheres were selected for these experiments. A commercially available, injection moulding grade of polyamide 66 and polypropylene. All samples were compounded on a twin screw equipped with top feeders for microspheres and glass fibers (GF), and pelletiser.
• Results and discussion: The results indicate that the presence of glass microspheres significantly reduced the density of the injection moulded parts. Glass microspheres allow the end product properties to be retained to a large extent while decreasing the density.

 There are several other benefits of adding glass microspheres into thermoplastics compounding formulations.
 
Increasing productivity
The same combination of high strength and low density that enables glass microspheres to produce lighter weight finished parts can also help manufacturers improve productivity - ie, to ‘do more with less’. The lower mass of glass microspheres-filled plastics requires less torque to process. That means reduced energy consumption and lower costs. It can also potentially reduce cycle time as much as 25%, allowing the production of more parts per hour. Productivity does not stop there.
 
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High strength glass microspheres allow improved dimensional stability and less warpage, even on large and complex parts, helping to reduce rejects and reprocessing.
 
Contributing to environmental sustainability
Today, businesses in every industrial sector understand the need to ‘do more’ to reduce their carbon footprint and improve the sustainability of their products throughout their life cycles.
 
While their relationship to light weighting and reduced fuel consumption is readily apparent, the use of glass microspheres in plastics can make other important contributions to sustainability. In a single-site carbon footprint study conducted, in which polymers commonly used in transportation applications were evaluated, the addition of glass microspheres had a neutral impact on the carbon footprint of finished plastic parts made with these polymers. In addition, they may be recyclable, and can be re-ground as many as five times with minimal change in properties.
 
As plastics manufacturers become more and more familiar with the capabilities of glass microspheres, demand for these versatile materials continues to grow. Compounding glass microspheres with polymers offers a ‘plug-and-play’ weight reduction solution. The method is rapid, cost effective, and does not require any complex material or process modification. 
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The author is the General Manager in 3M Advanced Materials Division