Houston-based Total Petrochemicals & Refining USA, Inc. has begun producing

high-melt-strength (HMS) PP for use in a gamut of applications, including

low-density foam extrusion, large-part blow molding and thermoforming, profile

extrusion, and extrusion coating.

Developmental HMS-PP, made by a proprietary technology, is available in commercial

quantities from Total’s LaPorte, Tex., site, an integrated 2.3-billion/lb PP facility producing

a wide range of homo- and copolymers. Total appears to be the first supplier to manufacture

HMS-PP resin in North America. HMS PP resin has been imported from

Austria’s Borealis (U.S. office in Port Murray, N.J.).

Polypropylene’s inherent chemical resistance and thermo-mechanical properties, plus

the higher melt strength of this version, suit it to producing high-performance technical

foams for specialty packaging, such as protective packaging for electronics and medical

devices, as well as automotive components and consumer products such as sports helmets.

Durable, low-density foams made with this HMS-PP offer superior recyclability, notes Musgrave,

making it a contender for foam applications currently dominated by crosslinked PE, PVC, and

PUR. Total’s high-melt-strength PP can produce closed-cell foams via direct gassing, for instance

with butane or CO2, having very low densities—0.05 to 0.250 g/cc, and superior mechanical and

aesthetic properties. Besides foams, Total sees the material as a challenger in other processes 

such as large-part blow molding, large-part thermoforming, extrusion coating and profile extrusion.

Durable, low-density foams made with HMS-PP are contenders for replacing crosslinked PE, PVC, and PUR foams.

Uses such as vessels or drums larger than 5 liters (1.32 gal), where HDPE is typically used, but

where both chemical and high-temperature resistance are required. Applications that traditionally

use ABS or HIPS, such as refrigerator liners, small boat hulls, and reusable materials-handling

bins, where use of PP was not possible due to low melt strength.

Extrude HMS-PP onto a woven fabric or paper, where it could replace PE because of its better

heat resistance, and potential for greater line speeds. Applications could include building and

construction, such as an alternative to PVC window profiles or HDPE pipe.

Foam extrusion evaluations comparing Total’s new HMS-PP to an existing commercial HMS-PP

show similar foam densities and closed-cell contents. However, the authors note that the two

products process differently and may not be interchangeable in any particular application. Therefore,

processors likely will need to optimize foam extrusion conditions and/or formulation for

specific HMS-PP materials.

Lab-scale evaluations with Total’s HMS-PP could achieve foam densities down to 0.1 g/cc with

a high level of closed cells, similar to the range achieved with the commercially available

HMS-PP. Most notably, Total’s research shows that foams produced with the new HMS-PP

have considerably higher stiffness, as well as a smoother and glossier surface, than foams

produced with the existing commercial competitor. The company sees these characteristics

opening opportunities for development of new foam applications that require excellent rigidity

and superior appearance.

Foam extrusion is of particular interest, as polyolefin foams are the fastest growing category

of foams globally. Extruded PP foams, in particular, are projected by industry studies to grow at

an annual 6.9% rate for the next five years.