What suits these resins particularly to TP composites is their unusual ability to depolymerize in the melt phase, followed by very rapid rebuilding of molecular weight as the resin cools. The result is a melt viscosity at least an order of magnitude lower than those of other thermoplastics, which facilitates good glass wet-out. In addition, Isoplast has a natural affinity for glass.
As a result, Dow says it has pultruded unidirectional composites containing up to 70% by volume of glass at speeds to 10 meters/min with void contents below 2%. Glass volume fractions of 45-70% result in longitudinal tensile strength of 150-201 kpsi, flexural modulus of 4.6-7.3 Mpsi, and density of 1.74-2.02 g/cc.
These ETPU composites, which Dow has trade-named Fulcrum, can then be formed with heat and pressure to produce curved or angled parts for sports equipment, furniture or building profiles, or inserts for overmolding into a variety of engineered parts.
Forming requires preheating pultruded strips for 3 min at 435 F and then compressing them between matched molds. Fibers should be lightly tensioned by clamping the ends of the profile at around 150 psi, which allows the fibers to slip into the mold during pressing. Composite scrap can be granulated and reused by injection molding in a blend with unfilled Isoplast.
One of the first licensees for the Fulcrum process is Bemis Manufacturing Co., Sheboygan Falls, Wis. Executive v.p. Peter Bemis says the firm is setting up a line to pultrude approximately 1/4-in.-wide strips for use in office furniture and lawn-and-garden equipment.