Mechanism of foaming on polymer‐paperboard composites

Abstract

in Wiley InterScience (www.interscience.wiley.com).Foamed paperboard is a composite material with applications in the consumer products industry. The composite is comprised of paperboard sandwiched between two layers of polymers. One layer foams upon heating while the other acts as a barrier layer. Foaming is caused by the vaporization of the small amount of moisture present in the board and the resulting increase in pressure. The mechanism of foaming was investigated with a combination of high-speed photography, scanning electron microscopy, and infrared thermography using foamed paperboard of different compositions prepared both in the laboratory and on a commercial machine. The surface uniformity of the paper was found to be the overriding paper-related property controlling bubble formation.

Effect of polymer properties on bubble growth in polymer–paperboard composites

“…We have previously shown that heating the paperboard–polymer composite initially leads to the formation of a large number of small bubbles 2. These then grow, collapse, or coalesce so that the bubble count decreases after an initial spike.…”

“…These then grow, collapse, or coalesce so that the bubble count decreases after an initial spike. The manner in which the board is constructed affects the pore structure of the sheet and, therefore, the number and geometry of the bubbles formed 2. The polymer is integral to the foaming process and must play a role in the growth of the foam.…”

“…Samples were prepared on a full‐scale commercial paper machine (machine‐made) and on a laboratory sheet former (handsheets). The samples were prepared at 250 g/m 2 from a 3:1 mixture of Southern hardwood and softwood pulps as described earlier 2. The polyethylene samples were obtained from Westlake Polymers (Houston, TX).…”

“…The development of bubbles on the surface of the board was imaged with a Phantom version 4.2 high‐speed camera from Vision Research (Wayne, NJ) at 100–2000 frames per second as described earlier 2. The onset of foaming was indicated by the light reflected from the bubble surface.…”

“…Upon heating, the moisture in the board vaporizes and foams the low‐density polymer face, thereby creating a surface that provides thermal insulation for hot liquids and foods 1. We have previously shown that the properties of the paperboard surface control the number of bubbles initially created in the foam 2. In this study, we examine the relationship between the paperboard and polymer properties and extrusion speed used to coat the polymer on the paper and the thickness of the foam.…”