Newest Barrier Resin Is Thermoplastic Epoxy.

"Blox" is the trade name of a new series of clear, tough, highly adhesive barrier polymers from Dow Plastics, Midland, Mich. They are described as polyamino ethers and are made by polymerizing liquid epoxy resins with an amine to create solid, low-melting thermoplastics. They can be extruded into films, injection molded, or blow molded. One series of Blox resins shows promise as barrier layers in coextruded or coinjected packaging such as multi-layer bottles for juices, beer, or carbonated soft drinks. Oxygen and [CO.sub.2] barrier is about 10 times higher than that of PEN--i.e., in the range of EVOH or MXD6 nylon, depending on humidity level. Clarity and toughness of Blox are both higher than those of EVOH or MXD6.

Blox is also said to have better adhesion to PET, thus permitting design of more complex bottle shapes without risk of unsightly delamination. No tie layer is required. On the other hand, Blox facilitates recycling by separating readily from PET during regrinding, Dow sources say. Tetra Pak, based in Geneva, Switzerland, is conducting European trials of multi-layer bottles of PET and Blox. They are expected to be commercial in the next three months.

A second series of Blox resins is aimed at adhesive applications, including extrusion coating, tie layers, and resin modification. They reportedly adhere well to metal, glass, paper, cotton, and wood, as well as polar polymers like PET and nylon. The resin is already commercially used as a binder in foamed loose-fill packing ("peanuts") filled with more than 90% starch. American Excelsior, Arlington, Texas, and StarchTech, Golden Valley, Minn., are making such loose-fill packing.

Blox resins have a density of 1.20-1.23 g/cc and melt indexes of 1-50 g/10 min. These amorphous resins are processed at 375-445 F. Typical properties include ultimate elongation of 45-52%, flexural modulus of 427-593 kpsi, tensile yield strength of 8900-11,600 psi, notched Izod impact of 0.5-2.0 ft-lb/in., Tg of 142-172 F, and HDT of 129-157 F at 66 psi (124-141 F at 264 psi). Experimental grades include food-contact and biodegradable types, Dow has a commercial plant capable of producing 8 million lb/yr in Freeport, Texas. Price range is $1.50-3.00/lb.