Mica to Replace Glass Fiber in Plastics

Glass fiber is a popular reinforcement for plastics and has been for decades. Recently however, price increases and supply shortages, have driven customers to look for alternatives. As a leading supplier of minerals and reinforcements, Arctic Minerals have been asked for recommendations. So, what can replace glass fiber with equivalent or superior properties but with lower cost and plentiful supply?

Many additives are used in plastics and Arctic Minerals sells several of them. However, only one is proven to compete with, and in some cases exceed, the performance of glass fiber – and best of all, it costs less than half as much.

If you like the sound of fewer supply headaches, great performance and substantial savings, then read on…

What makes a good reinforcement?

The principal property that creates reinforcement is the aspect ratio of the particles meaning their largest dimension divided by their narrowest dimension. Glass fibers work because they have a large ratio of length to width whereas typical fillers like calcium carbonate, silica, dolomite and so on, are not effective reinforcements because they are essentially round or blocky with very low aspect ratio. Talc, clays and wollastonite have intermediate aspect ratio and provide a modest level of reinforcement.

ThermaFlex™ Mica – the ultimate reinforcement

Of all the multitudinous particulate additives available for plastics, only one competes with and even exceeds the performance of chopped glass fiber. Specially milled very high aspect ratio mica gives exceptional properties in plastics including PE, PP, nylons, PBT and more. First generation micas had good aspect ratio and competed with talc, but the latest generation of mica, made using advanced milling techniques has even higher aspect ratio and that explains the leap in performance. The mills are designed to separate mica sheets without damaging them, so they become thinner, which increases the aspect ratio substantially.

Figure 1 The importance of aspect ratio
Figure 1 The importance of aspect ratio (length : width)

Wollastonite is only a weakly reinforcing fibrous filler because of limited aspect ratio, whereas glass is also available in fiber form but performs much better due to increased length to width ratio, as shown in Figure 1. Similarly, many of you are familiar with talc as a filler that gives some benefits to strength and stiffness. In recent years, new higher aspect ratio talcs have gained traction for the increased reinforcement attributable to the increase in aspect ratio. However, talc has reached its limits. Mica is the reinforcement of choice if you need even better strength, stiffness and HDT.

Table 1 Aspect ratio and properties of polymer composites
Table 1 Aspect ratio and properties of polymer composites

ThermaFlex™ Mica vs Chopped Glass Fiber Performance Comparison

The general influence of aspect ratio of properties is well-established. So, here are some specific examples to illustrate the exceptional performance of the latest generation of high aspect ratio mica.

Table 2 Minerals & reinforcements compared in nylon 6
Table 2 Minerals & reinforcements compared in nylon 6

It is clear that mica and glass fiber are the best performers. What is not immediately apparent is that mica reinforces in all three directions, namely x, y and z whereas glass fiber reinforces only in one direction. It is well-known that glass fiber composites suffer from warpage and the difference in properties in the different planes is the reason. Glass fiber gives marginally better stiffness than mica in one direction, but performs like calcium carbonate, meaning that it gives no reinforcement, in the other two directions. In contrast, mica offers excellent reinforcement in all directions. Not only that but low Mohs hardness means that pure ThermaFlex mica does not cause the abrasion issues seen with chopped glass fiber. From the data in Table 2 we can calculate that the average tensile modulus across all three directions, x, y and z would be over 11000 MPa but the average for glass fiber filled nylon would be ~7000 MPa.

Mica is also frequently used as a partial glass fiber replacement. This gives excellent mechanical properties while substantially reducing warpage seen when glass fiber is used alone.

Table 3 Glass fiber at 25 % loading plus 15 % mica to replace 40% GF in PA6
Table 3 Glass fiber at 25 % loading plus 15 % mica to replace 40% GF in PA6


The latest generation of very high aspect ratio mica to replace chopped glass fiber:

  • Proven reinforcement for over a decade with major OEMS
  • Equivalent stiffness and strength
  • Lower warpage
  • Lower CTE
  • Lower machine wear (means less downtime and maintenance)
  • Safe
  • Less than half the cost and with ready availability (no supply constraints)

Like any very high aspect ratio reinforcement, mica is fragile and must be added into the polymer melt to avoid damage. Anyone used to dosing glass fiber will already be equipped to dose mica into the melt rather than the main hopper.

Available in a range of grades and silane surface treatment options, contact Arctic Minerals to get samples from your local sales representative. We keep stock in our 20 warehouses so that our customers get reliable deliveries.

Contact Arctic Minerals

If you would like to hear more about our mica product line, then feel free to contact us today. We have experts to help you select the best grade for your application and to supply samples for evaluations.