An advanced TekTuff SPA polyethylene (PE) lets Heritage Kayaks, Bristol, R.I., not only slim down its rotationally molded Featherlite kayaks without loss of structural toughness but also permits molding more boats per shift.
TekTuff SPA PE rotational-molding compound replaces conventional metallocene-based medium-density PEs. It is said to provide the same resin-saving economies as standard TekTuff PEs but requires an average of 12.5% less oven time to melt, fuse, and develop optimum physical properties in the mold. The SPA PE also sports a broader processing window, so there's greater latitude in molding conditions. This translates into fewer rejects without compromising the polymer's property development, reports Heritage kayaks.
TekTuff SPA from Teknor Color Co., Pawtucket, R.I., reportedly yields parts that are substantially stronger and stiffer than parts of similar thickness rotationally molded from conventional, medium-density PEs. This lets molders reduce part weight by 10 to 15%, says Teknor senior technical service engineer Gretchen Leighliter.
Standard TekTuff compounds process similarly to conventional medium-density PEs, says Leighliter. "But the 12.5% shorter oven time gleaned with the new SPA version drops overall molding cycles by roughly 10%. In addition, the SPA version is more forgiving than standard TekTuff compounds, so it's easier for molders to get target physical properties."
Heritage Kayaks rotomolds seamless hull-and-deck boats that weigh 37 to 73 lb (17 to 33 kg). "Because TekTuff SPA is so much stiffer than the conventional medium-density PEs previously used, we have reduced kayak weight up to 9% without degrading their toughness," says Carolyn Shea, Heritage Kayaks chief operating officer. "Dropping cycle times by as much as 10% also lets us produce roughly six to nine kayaks per shift instead of five to eight. We plan to shift completely to TekTuff SPA for all our products," says Shea.
In addition to watercraft, TekTuff SPA is a candidate for rugged-use applications including tanks and containers, playground toys, and transportation and agricultural items formerly produced from fiberglass. TekTuff SPA compounds come in natural form or as ready-to-mold custom-precolored formulations.
ROTATIONAL-MOLDING POLYETHYLENE COMPOUNDS
0.94 to 0.95
Melt index, gm/10 min
3.0 to 4.5
Tensile strength at yield, psi
2,800 to 3,700
Flexural modulus, 1,000 psi
110 to 130
Heat-distortion temperature at 66 psi, °C
60 to 70
Ultimate elongation, %
Falling dart impact strength at 40°C, ft-lb
55 to 65
Optimum oven time, min
* Medium-density linear polyethylene