Foaming behavior of water-soluble cellulose derivatives: hydroxypropyl methylcellulose and ethyl hydroxyethyl cellulose

Abstract

Hydroxypropyl methylcellulose and ethyl hydroxyethyl cellulose could be interesting candidates for production of lightweight, foamed packaging material originating from non-fossil, renewable resources. The foaming ability of nine different grades of the two cellulose derivatives, using water as the blowing agent, was investigated using a hot-mold process. The foaming process was studied by evaluating the water loss during the heating, both in a realtime experiment and by thermal gravimetric analysis. Further, the development of the rheological properties of the derivative-water mixtures during a simulated foaming process was assessed using dynamical mechanical thermal analysis and viscosity measurements. Five of the studied derivatives showed promising properties for hot-mold foaming and the final foams were characterized with regard to their apparent density. It was concluded that the foamability of these systems seems to require a rather careful tailoring of the viscoelastic properties in relation to the water content in order to ensure that a network structure is built up and expanded during the water evaporation.

Chain-Length Shortening of Methyl Ethyl Hydroxyethyl Cellulose: An Evaluation of the Material Properties and Effect on Foaming Ability

“…However, the foaming of aqueous HPMC solutions has been previously studied [7], and the foaming mechanism in case of the MEHEC system is believed to be of a similar kind. Like HPMC, MEHEC is clouding and exhibits a thermal gelation behaviour at temperatures below 100 °C.…”

“…If the sample had not expanded and filled the mould properly, a somewhat irregular shape was obtained. The volume of the sample was then estimated using a sand-displacement method [7,13] where the sample was immersed in sand in a measuring cylinder and the change in volume after tapping the cylinder was recorded. The weight was then divided by the volume to obtain the density.…”

“…The possibility of foaming cellulose derivatives using water (steam) as the blowing agent has previously been investigated and it was found that hydroxypropyl methylcellulose (HPMC) exhibited better foaming properties than MEHEC and EHEC when a hot-mould baking technique was used for the foaming [7]. One of the factors considered to be the reason for the poorer foamability of the EHEC samples was the difference in molecular chain length compared to the HPMCs.…”

“…The larger molecular chain length of the EHEC was believed to cause the sample to gel strongly in water solutions at low polymer concentrations, hindering the steam-assisted expansion of a growing bubble. Karlsson et al [7] noted that in case of HPMC, the storage modulus of the polymer solution was quite low at room temperature, allowing an expansion to take place as the water steam was formed as the temperature was increased. At the same time the storage modulus increased substantially with increasing temperature, stabilizing the final foam.…”

“…The treated derivatives were characterized with regard to their molecular chain lengths and rheological properties and furthermore their foamability was assessed by the same hotmould technique previously used [7].…”