Extrusion foaming of thermoplastic cellulose acetate from renewable resources using a two-component physical blowing agent system

Abstract

Thermoplastic cellulose acetate (CA) is a bio-based polymer with optical, mechanical and thermal properties comparable to those of polystyrene (PS). The substitution of the predominant petrol-based PS in applications like foamed food trays can lead to a more sustainable economic practice. However, CA is also suitable for more durable applications as the biodegradability rate can be controlled by adjusting the degree of substitutions. The extrusion foaming of CA still has to overcome certain challenges. CA is highly hydrophilic and can suffer from hydrolytic degradation if not dried properly. Therefore, the influence of residual moisture on the melt viscosity is rather high. Beyond, the surface quality of foam CA sheets is below those of PS due to the particular foaming behaviour. This paper presents results of a recent study on extrusion foamed CA, using a two-component physical blowing agent system compromising HFO 1234ze as blowing agent and organic solvents as co-propellant. Samples with different co-propellants are processed on a laboratory single screw extruder at IKV. Morphology and surface topography are investigated with respect to the blowing agent composition and the die pressure. In addition, relationships between foam density, foam morphology and the propellants are analysed. The choice of the co-propellant has a significant influence on melt-strength, foaming behaviour and the possible blow-up ratio of the sheet. Furthermore, a positive influence of the co-propellant on the surface quality can be observed. In addition, the focus is laid on the effect of external contact cooling of the foamed sheets after the die exit

Surface roughness and foam morphology of cellulose acetate sheets foamed with 1,3,3,3‐tetrafluoropropene

“…) was attached to the die. Ethanol was used as coblowing agent to improve the cell structure and reduce decomposition of the compound, which can be caused by high shear forces . Table shows the constant parameters used in test series 3.…”

“…One application are food trays, produced by thermoforming of foamed sheets . In this context, the authors already studied the foam sheet extrusion of thermoplastic CA with different physical blowing agents (PBA) . The use of environmentally noncritical 1,3,3,3‐tetrafluoropropene (HFO‐1234ze) as PBA and 0.5 wt% talc as nucleating agent resulted in a 10‐fold expansion of the foam sheets .…”

Development and processing of flame retardant cellulose acetate compounds for foaming applications

“…Hence, potential applications for CA foams are, for example, food trays, which are produced by thermoforming of foamed sheets. In this context, investigations have already been done on the foam sheet extrusion of thermoplastic CA with different physical blowing agents (PBA) . The use of environmentally noncritical 1,3,3,3‐tetrafluoropropene (HFO‐1234ze) as PBA and 0.5 wt % talc as nucleating agent resulted in a 10‐fold expansion of the foam sheets.…”

Extrusion foaming of thermoplastic cellulose acetate sheets with HFO‐1234ze and co‐blowing agents

“…Hence, potential applications are for example food trays, which are produced by thermoforming of foamed sheets . In this context, the authors previously studied the foam sheet extrusion of thermoplastic CA with different physical BAs . The use of environmentally noncritical 1,3,3,3‐tetrafluoropropene (HFO‐1234ze) as BA and 0.5 wt% talc as nucleating agent resulted in foam sheets with a density of approximately 130 kg/m³ .…”

“…The use of environmentally noncritical 1,3,3,3‐tetrafluoropropene (HFO‐1234ze) as BA and 0.5 wt% talc as nucleating agent resulted in foam sheets with a density of approximately 130 kg/m³ . Another study focused on the effect of co‐BAs on the foaming behavior and morphology of strands . Depending on their solubility parameters, co‐BAs reduce the viscosity of the melt and increase the expansion rate at the die exit.…”