Degradation of a poly(3-hydroxybutyrate- co-3-hydroxyvalerate) (PHBV) compound in different environments

Abstract

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) is a promising biodegradable bio-based material, which is designed for a vast range of applications, depending on its composite. This study aims to assess the degradability of a PHBV-based compound under different conditions. The research group followed different methodological approaches and assessed visual and mass changes, mechanical and morphological properties, spectroscopic and structural characterisation, along with thermal behaviour. The Ph-Stat (enzymatic degradation) test and total dry solids (TDS)/total volatile solids (TVS) measurements were carried out. Finally, the team experimentally evaluated the amount of methane and carbon dioxide produced, i.e., the degree of biodegradation under aerobic conditions. According to the results, different types of tests have shown differing effects of environmental conditions on material degradation. In conclusion, this paper provides a summary of the investigations regarding the degradation behaviour of the PHBV-based compound under varying environmental factors. The main strengths of the study lie in its multi-faceted approach, combining assessments of PHBV-based compound degradability under different conditions using various analytical tools, such as visual and mass changes, mechanical and morphological properties, spectroscopic and structural characterization, and thermal behavior. These methods collectively contribute to the robustness and reliability of the undertaken work.

Keywords: Degradation; Laboratory scale testing; Morphological properties; Natural environment; PHBV; Polymer blends.

Fig. 1

Set up for field exposure of T-PHBV (a) Dumbbell bars immersed in tanks with circulating Mediterranean Sea water and (b) sheets submerged at 10–20 cm depth in coastal, surface seawater in the North Sea. Bars (c, d) and sheets (e) visual aspect after 12-months of exposure.

Fig. 2

T-PHBV sheets (a) before and after field exposure in coastal, surface seawater in the North Sea. Samples submerged for 3 (b), 6 (c) and 12 (d) months show gradually increasing biofouling of marine species.

Fig. 3

PHBV film after eight weeks degradation in home-compost (a) and after 12 weeks in river Elbe (b): dark-coloured edges with cracks and fractures were observed after degradation experiments.

Fig. 4

Samples 1 (a) and 2 (b) after 60 days in anaerobic conditions.

Fig. 5

Optical pictures of the dumbbell-shaped T-PHBV samples (a) before and (b–f) during the burial test in soil for (b) 0.5 week, (c) 1 week, (d) 2 weeks, (e) 4 weeks and (f) 7 weeks.

Fig. 6

Mechanical relative ε_b, E_t, and σ_b values of T-PHBV samples aged in soil (a) and climate chamber (b).

Fig. 7

ATR-FTIR spectra recorded for T-PHBV at various times of exposure in Mediterranean seawater.

Fig. 8

FTIR spectrums of T-PHBV before (black) and after (red) methane production potential test.

Fig. 9

FTIR-ATR spectra during degradation in climatic chamber. Changes in FTIR-ATR spectra due to UV irradiation were followed. Characteristics spectral groups were present in the spectra without variation during the experiment.

Fig. 10

Changes in low molecular weight (Mw) of T-PHBV samples during accelerated photo-degradation in the climatic chamber and soil biodegradation.

Fig. 11

TGA curves for T-PHBV at various times of exposure in Mediterranean seawater.

Fig. 12

DSC 1st heating curves for T-PHBV at various times of exposure in Mediterranean seawater.

Fig. 13

SEM pictures of the surfaces of untreated T-PHBV material (a, d, f, h, k) and after exposure to different conditions. b: Six months of exposure to seawater under controlled conditions. c: Six months exposure in estuarine mud under controlled conditions. e: Twelve months in Mediterranean seawater. g: Six months in compost. i: Eight weeks in home compost. j: Twelve weeks in a flow-through chamber in a river. l: Seven weeks in soil.

Fig. 13

SEM pictures of the surfaces of untreated T-PHBV material (a, d, f, h, k) and after exposure to different conditions. b: Six months of exposure to seawater under controlled conditions. c: Six months exposure in estuarine mud under controlled conditions. e: Twelve months in Mediterranean seawater. g: Six months in compost. i: Eight weeks in home compost. j: Twelve weeks in a flow-through chamber in a river. l: Seven weeks in soil.

Fig. 14

Hydrolytic degradation of T-PHBV by PHBV depolymerase measured by pH Stat titration at 5 °C, 15 °C, and 25 °C (means ± SD, n = 3).

Fig. 15

Carbon dioxide production monitored from compost only and compost mixed with T-PHBV monitored for 6 months.

Fig. 16

T-PHBV degree of biodegradation of the maximum degradation of TLC grade cellulose. Biodegradations were performed under controlled composting conditions from the beginning of the experiment until the end as described in Materials and Methods. The calculation was performed based on ISO 13432.

Fig. 17

T-PHBV methane production potential test results for 60 days exposure.