Extrusion foaming of PHBV

Abstract

This paper reports work on extrusion foaming of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) with a chemical blowing agent based on sodium bicarbonate and citric acid and calcium carbonate nucleation agent. It includes investigations in the effects of rheological behaviour of the polymer, blowing agent, nucleation agent and processing conditions on the foam density and morphology. The poly(3-hydroxybutyrate-co-3-hydroxyvalerate) is a natural biodegradable polyester with high crystallinity, low melt viscosity and slow crystallisation rate and high sensitivity to the thermal degradation at temperatures above its melting point, making it particularly difficult to control the foaming process. Use of negative gradient temperature profile was found beneficial to minimise the thermal degradation and achieve necessary melt strength to stabilise the cell structure. Solidification of the super-cooled polymer melt occurring at the die was discussed in relation to the selection of the temperature profile and rheological behaviour and solidification of the poly(3-hydroxybutyrate-co-3-hydroxyvalerate) characterised by rotational rheometry. In addition to extrusion foaming conditions, effect of the blowing and nucleation agents on rheology of the polymer, the cell refinement on foam density and morphology were discussed. The poly(3-hydroxybutyrate-co-3-hydroxyvalerate) was extruded with a twin screw extruder fitted with a strand die yielding up to 60% density reduction with uniform fine cell structure.

Foamability and Special Applications of Microcellular Thermoplastic Polymers: A Review on Recent Advances and Future Direction

“…Thus, foams produced at higher screw speeds were found to possess higher cell densities and lower cell sizes. Szegda et al., [ 239,240 ] in their investigations on the extrusion foaming of poly(3‐hydroxybutyrate‐ co ‐3‐hydroxyvalerate) with a CBA (sodium bicarbonate and citric acid) and calcium carbonate nucleation agent, reported a lowering of VE with an increase in screw speed. They attributed this observation to the lowering of residence time of increase because of in screw speed, which reduced the decomposition of the blowing agent.…”

Cellulose Nanostructure-Based Biodegradable Nanocomposite Foams: A Brief Overview on the Recent Advancements and Perspectives

“…In particular, the melt strength and melt viscosity are the most important properties because they control the cell morphology in stabilising the nucleated bubbles during processing. Biodegradable polymers, including PLA and PHBV, have low melt strength and viscosity, which inhibits their foaming [13,14]. Poor melt strength and viscosity result in cell clustering and cell rupture.…”

“…Low melt strength results in cell coalescence and cell rupture during cell growth. To mitigate this shortcoming, enhanced crystallisation rates are required to compensate for the low melt strength and melt viscosity [13,14,15] and can be achieved by blending with other polymers that crystallise much faster. The incorporation of nanofiller materials in biopolymers is another alternative to improve the low melt strength and viscosity and, thus, enhance foaming [1,14,15,16,17].…”

“…To mitigate this shortcoming, enhanced crystallisation rates are required to compensate for the low melt strength and melt viscosity [13,14,15] and can be achieved by blending with other polymers that crystallise much faster. The incorporation of nanofiller materials in biopolymers is another alternative to improve the low melt strength and viscosity and, thus, enhance foaming [1,14,15,16,17]. Nanofiller materials derived from biomass, such as cellulose nanostructure (CN) materials, are suitable for the development of biopolymer-based nanocomposites and foams because of their low density, high aspect ratio, large surface area, non-toxicity, and, most importantly, biodegradability and environmental friendliness [18,19,20].…”

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

“…Szegda et al also studied PHBV but with a masterbatch blowing agent consisting of sodium bicarbonate (SB) and citric acid. It is expected that the decomposition products of SB—carbon dioxide and water—will have higher solubility in PHBV owing to a slight polarity compared to the nonpolar nitrogen produced by AZ.…”