Polystyrene Ionomer Extrudes More Easily

Total Petrochemicals in Houston has invented what it calls a “breakthrough resin technology,” believed to be the first commercial styrenic ionomer. Previous commercial thermoplastic ionomers have all been based on ethylene, though styrene-based ionomers are known in academic literature. Ionomers are thermoplastics with reversible crosslinks, created by ionic bonds that link polymer chains together as the melt cools, but unlink again when remelted.

These “extra” ionic bonds confer enhanced properties.
Total’s new material (U.S. Patent Application 20060167149, July 27, 2006) is described as a branched ionomer based on styrene monomer. The patent application suggests that it’s a copolymer of styrene and an unsaturated alkyl monomer like sodium methacrylate or zinc dimethacrylate (among numerous other possibilities), plus 1 pph or less of a branched ionic monomer.

The first commercial product is a new high-heat crystal PS, CX5229, with enhanced flow at lower processing temperatures and pressures. Total says its main benefit is 10% to 15% higher throughput in PS foam and OPS sheet for clamshells and other food packaging. CX5229 also has about 9% higher melt strength, useful in blown film and foams. The latter now can be blown with more CO2 in place of organic chemical foaming agents, resulting in lower VOC emissions.

The new material was developed in a pilot plant at Total’s LaPorte, Texas, technical center. Total has made two successful full-scale production runs at a slightly modified PS plant in Carville, La., to produce material for sampling to customers. Some modifications at Carville would be required before the plant could go into continuous production.

New CX5229 has an MFR of 3 g/10 min. vs 1.6 for standard high-heat crystal PS. Its molecular weight is slightly higher than standard PS, and it has a much broader molecular-weight distribution.