Carlos Alfonso Cruz

The Sag Process in Modified Polypropylene

Infrared and isothermal heating of polypropylene and modified polypropylene sheets showed that the rate of sag was independent of the sample thickness and a power function of the blank, or opening, size. A temperature increase from 1900C to 2100C increased the steady sag rate by 10 to 25% for a 0.3 m diameter blank, the greater effect being observed with the modified resin; the sag rate increase was greater with a smaller blank size. The modified polypropylene has a lower sag rate and significantly extends the time before accelerated sagging or webbing occurs, especially at blank sizes below 0.4 m.

Acrylic-Modified Polypropylene for Thin-Gauge Thermoforming: Improved Processing Properties and Economics

Polyolefins are used extensively for thin-gauge, high speed, roll- fed thermoforming. However, polyolefins suffer from a variety of problems, in cluding slow processing speed, a narrow processing window and poor stretch ability. Trial results demonstrated that acrylic modified polypropylene has a broader processing window, improved stretchability and faster processing on conventional roll-fed thermoforming equipment. Trials on commercial equip ment, using sheet from 10-50 mils (.25-1.2 mm) are discussed, as well as the economics of the final parts.