Increasing cell homogeneity of semicrystalline, biodegradable polymer foams with a narrow processing window via rapid quenching

Abstract

Biodegradable polymer foams have the potential to lessen environmental burdens caused by traditional petroleum-based plastics. One such family of alternatives, poly(hydroxyalkanoates), have tremendous potential in this regard, but have poor foamability owing to a narrow thermal processing window. Of particular interest for this study is poly(hydroxybutyrate-co-valerate) (PHBV). Two chemical blowing agents were tested for their ability to create low density, closed-cell PHBV foams, and it is shown here that sodium bicarbonate decreases the bulk density compared to azodicarbonamide blowing agents but with the loss of a closed-cell structure. To counter this, PHBV foams were quenched with water, leading to faster crystalline formation in the polymer matrix. As a result of faster solidification, a more uniform, closed-cell bubble morphology was entrapped in the final foam product, leading to high-expansion ratio foam. Thus, PHBV, a material with poor melt strength, has enhanced melt properties for foaming applications when crystallization is induced on the same time scale as cell coalescence.

Assisted heterogeneous multinucleation and bubble growth in semicrystalline ethylene-vinyl acetate copolymer/expanded graphite nanocomposite foams: Control of morphology and viscoelastic properties

“…By rapid pressure quenching [17], melt blending using polymers with high glass tran-sition temperature (T g ) [4] and incorporating nanoclay into polymers [7], micron or submicron size cellular structures have been successfully obtained. Most polymers investigated in the previous researches have been amorphous, though there are several papers discussing microcellular foams of semicrystalline polymers [15,16,[18][19][20][21][22][23]. The influences of nanofiller characteristics such as aspect ratio and surface chemistry on the properties of solid polymer nanocomposites have been extensively studied [24][25][26][27].…”

Extrusion Parameters for Foaming of a β-Glucan Concentrate

“…The lowest obtained density was around 0.55 g/ cm 3 , whereas the more dense samples had values around 1.2 cm 3 they investigated the effect of different blowing agents on poly(hydroxybutyrate-co-valerate) (PHBV) foaming. Citric acid was eliminated early in the experimental phase due to its lack of gas production and due to a thermal degradation of the PHBV at 160 °C [25]. One explanation for the lack of expansion when adding the citric acid could therefore be that the decomposition temperature of the substance is above where thermal degradation of the β-glucan concentrate starts.…”

Effect of chain extender and water-quenching on the properties of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) foams for its production by extrusion foaming

“…A possible strategy to reduce the amount of polymer required for a certain application, and therefore, the cost of the final good, is the weight reduction obtained from foaming the solid material leading to a foam with improved specific mechanical properties [4]. Nonetheless, the foaming of PHAs has some difficulties, since most PHAs are intrinsically difficult to foam because of a narrow processing window and a low melt strength, which leads to a tendency towards cell coalescence and collapse at high expansion [5].…”

“…With this technique, blowing agents can be physical (PBAs) or chemical (CBAs). PHAs have already been foamed with super critical CO 2 gas as PBA [6], with exothermic CBAs such as azodicarbonamide (ADA) [5,7], or with more eco-friendly endothermic CBAs mainly based on sodium bicarbonate (SB) and citric acid [5,8,9]. The use of PBAs requires extruders with PBA-pumping systems and, in some cases, screws with special profiles, thus meaning that special processing machinery is necessary.…”

“…The aforementioned endothermic CBAs, which release CO 2 gas, have been shown to achieve lower density-PHA foams than exothermic CBAs such as ADA, which release N 2 gas [5].…”