Itasca, Ill. — Two officials of Dow Chemical Co. touted Dow's bimodal high density polyethylene at the Plastics Caps & Closures Conference.
The resins have a great balance of properties, including flow, resistance to environmental stress cracking and stiffness, said Yijian Lin, Dow associate research scientist, who works in packaging and specialty plastics.
Lin said consumer soft drink closures require those properties.
“It's a combination of properties that make the bimodal resin softer,” Lin said.
John Sugden, Dow application technology leader for rigid packaging, talked about bimodal HDPE for use in aseptic and hot-fill bottles.
In hot fill, the plastic bottle expands after filling. Cooling brings it back to the original shape. So the material needs to have a high level of flexural modulus to have good stiffness, he said.
Also, the material has to have high heat deflection, a high softening temperature and good resistance to stress cracking, he said.
Sugden presented results of a Dow study of hot fill caps from three resins, HDPE copolymer, HDPE homopolymer and bimodal HDPE.
Bimodal polyethylene gave the best performance, he said.
“Bimodal HDPE that we developed for this application shows improved heat deflection temperature, improved environmental stress crack, good processability and lower torque,” Sugden said.