LANXESS, one of the world's leading glass fiber manufacturers, is seeing a marked growth in demand for its milled short glass fibers (milled fiber). This is particularly true for the compounding of thermoplastics, polytetrafluoroethylene (PTFE) and polyurethane, which is processed using reinforced reaction injection molding, or R-RIM.

“Our milled short glass fibers are increasingly being used in R-RIM in place of natural mineral fiber fillers for producing bodywork parts in exclusive, small and medium-sized series. They are gaining popularity for PTFE compounding when light-colored components have to meet high optical requirements,” says Martin Wiemer, marketing expert for glass fibers at LANXESS.

Minimal distortion, isotropic shrinkage, stable manufacturing process

In the R-RIM process, a mixing head is used to mix the polyurethane raw materials polyol and diisocyanate with a reinforcing material such as LANXESS Milled Fiber. The mixture is discharged into a mold, where the reaction runs its course. Car parts such as rear wings and paneling/moldings for sills, bumpers and side members can be manufactured in this way. The requirements on gap dimensions for these large-scale components have increased hugely recently.

“More and more customers are telling us that they can meet these requirements more easily using our milled short glass fibers. This is due to their very narrow length distribution, which significantly improves the shrinkage behavior of the components. The gaps to neighboring assemblies therefore remain small and acceptable,” says Wiemer.

The narrow length distribution of the fibers also ensures that the viscosity of the polyurethane reaction mix can be adjusted precisely. As a result, the manufacturing process exhibits a high degree of reproducibility. For example, it is possible to fill the mold evenly and completely and achieve stable production.

No need for pretreatment

The very high purity of the milled short glass fibers from LANXESS really comes into its own for light-colored PTFE parts. “In most cases, time-consuming fiber pretreatments such as energy-intensive flaming are not necessary. The processor can therefore begin production directly and obtains products in a constant, reproducible quality,” says Wiemer. Typical PTFE components with milled short glass fibers include sealing rings for chemical reactors or other extremely heavy-duty applications, cable insulations and molded parts for use in bearings and sliding assemblies.

Uniform diameter, low moisture content

LANXESS has four basic grades of milled short glass fibers in its range (e-glass to DIN 1259). They differ in the formulation of their finishes (surface treatment) and the length of the fibers. Average fiber lengths range from 50 to 210 µm. They have a uniform fiber diameter of 14 µm and the residual moisture content is less than 0.05 percent by weight. “Our products are easy to dose and have a consistent white color. The range also includes product grades that meet the legal requirements for applications that come into contact with food,” says Wiemer.

New applications in sight

The milled short glass fibers also have attractive potential applications outside of “conventional” plastics compounding. For example, they could be used in coatings with fire-resistance additives, as they improve the effectiveness of the flame retardant. They can also be used when manufacturing fillers based on epoxy resins so as to optimize the viscosity of the chemical reaction partners and the strength of the filler.

Their small size also makes them ideal for use in reinforcing thermoplastics used by 3D printers to build up components layer by layer. “They also have good potential in ceramic catalysts for removing nitrogen oxides from wastewater and waste air, for example. They allow the catalyst honeycombs to be made very small, resulting in a large catalyst surface area and high effectiveness,” says Wiemer.