Long-Glass-Fiber Polyesters Sport Advanced Properties

Two major suppliers of long-glass-fiber-reinforced thermoplastics have introduced grades based on polyesters that provide significant performance enhancements over current polypropylene-based grades.

Ticona, with headquarters in Summit, nj, and Frankfurt, Germany, just announced polybutylene terephthalate (pbt) grades of its Celstran compounds. This follows the introduction by Saint-Gobain Vetrotex Reinforcement, in Chambéry, France, of new types of its glass/thermoplastic commingled composite based on polyethylene terephthalate.

Vetrotex’s Twintex composite is available as rovings, fabrics, and plates, as well as pellets, for processing with various techniques, including some that are based on those for thermoset polyester composites. Ticona’s Celstran pbt comes as pellets and is available with 30, 40, or 50% glass or 40% carbon-fiber reinforcement. They are said to provide nearly identical impact, tensile, and flexural strength as nylon-based compounds.

The Celstran pbt grades are stiffer than nylon types also offered by Ticona, yet have almost the same toughness. They have tensile and flexural strength 100 MPa greater than pp-based grades, as well as 10 kJ/m2 higher impact strength, which is three times greater than short-glass pbt. The fibers in Celstran, which run fully through the pellet, are around 11 mm long, compared to around 2 mm in conventional compounds.

The new grades use a formulation of pbt that improves the mechanical properties of long-fiber composites. Ticona says the resin, together with its proprietary compounding technology, ensures high adhesion between the matrix and the fiber, as well as molding ease. Warpage of critical parts is expected to be minimized while excellent surface finish is maintained.

Celstran grades are easier to color and provide a better substrate for painting and adhesive bonding than pp. The material comes in natural, black, and custom colors. Target applications are automotive underhood and industrial parts.

Vetrotex, which launched Twintex pet last year, and which is just beginning to market it in the U.S., has secured the first commercial application, a type of coextrusion with pvc for window profiles.

Vetrotex developed a process called “pulextrusion,” in which a profile pultruded from Twintex rovings immediately passes through an extruder crosshead, where it is coated with a thermoplastic. (The process can also be used with Twintex pp, and a wide range of materials can be coated onto the profile.)

The Twintex core replaces steel reinforcement, which normally has to be inserted into the pvc profile in a separate process after extrusion. Twintex costs much more than steel, but the overall cost of making the finished profile is similar, since the total production process is more efficient. In addition, the Twintex profile prevents thermal bridging.

Twintex pet has an impact behavior that’s equivalent to Twintex pp. But it also has stiffness and fatigue and temperature resistance that enable it to compete not only with long-fiber nylons, but thermoset polyester sheet molding compounds, aluminium, and steel.

The company envisages Twintex pet being used to make structural automotive components. Its temperature resistance allows parts to be painted with existing high-temperature processes, making them suitable for visible applications. Vetrotex also sees potential in sports and leisure equipment in which stiffness and fatigue resistance are essential, as well as electronics and windmills.

Currently, Twintex is only made in the U.S. European production is likely to begin in 2004, in the Czech Republic.