The Impact of Abiotic and Biotic Conditions for Degradation Behaviors of Common Biodegradable Products in Stabilized Composts

Abstract

This work examines the influence of the degradation behaviors of biotic and abiotic conditions on three types of biodegradable products: cups from PLA and from cellulose, and plates from sugarcane. The main objective of this study was to evaluate if biodegradable products can be degraded in composts that were stabilized by backyard composting. Furthermore, the impact of crucial abiotic parameters (temperature and pH) for the degradation behaviors process was investigated. The changes in the biopolymers were analyzed by FTIR spectroscopy. This work confirmed that abiotic and biotic conditions are important for an effective disintegration of the investigated biodegradable products. Under abiotic conditions, the degradation behaviors of PLA were observable under both tested temperature (38 and 59 °C) conditions, but only at the higher temperature was complete disintegration observed after 6 weeks of incubation in mature compost. Moreover, our research shows that some biodegradable products made from cellulose also need additional attention, especially with respect to incorporated additives, as composting could be altered and optimal conditions in composting may not be achieved. This study shows that the disintegration of biodegradable products is a comprehensive process and requires detailed evaluation during composting. The results also showed that biodegradable products can also be degraded post composting and that microplastic pollution from biodegradable polymers in soil may be removed by simple physical treatments.

Keywords: FTIR—Fourier-transform infrared spectroscopy; PBAT—polybutylene adipate terephthalate; PBS—polybutylene succinate; PLA—polylactic acid.

Figure 1

Scheme of degradation behavior tests of biodegradable products. Each vessel contained six strips of polymer material and was prepared in triplicates.

Figure 2

Changes in basic properties of compost during the composting process at 38 °C (a) MC/% and (c) LOI/%; and at 59 °C (b) MC/% and(d) LOI/%. The results show the mean values and the error bars indicate the standard error.

Figure 3

FTIR results of composted PLA at 59 °C. (A) FTIR spectra of composted PLA biodegradable products before (0 weeks) and at 1, 2, 3, 4, and 5 weeks after composting. (B) Subtraction spectra of samples obtained after 1, 2, 3, 4, and 5 weeks, which were subtracted from the spectra of untreated PLA biodegradable products. The dashed lines indicate zero absorbance change for each subtraction spectrum. (C) Linear slopes of the subtraction spectra (B) at each wavenumber as the change in the absorbance per week. The horizontal line shows zero absorbance change per week. (D) The coefficient of determination (R²) of the linear slopes in (C). The horizontal line shows a threshold of 0.8. The gray areas that span over all four graphs indicate the wavenumbers of high linearity, with the assignment of the corresponding vibrations on top of the graph, with “str.” for stretching and “alk.” for alkane.

Figure 4

FTIR results of composted PLA at 38 °C. (A) FTIR spectra of composted PLA biodegradable products before (0 weeks) and at 1, 2, 3, 4, 5, and 6 weeks after composting. (B) Subtraction spectra of samples obtained after 1, 2, 3, 4, 5, and 6 weeks, which were subtracted from the spectra of untreated PLA biodegradable products. The dashed lines indicate zero absorbance change for each subtraction spectrum. (C) Linear slopes of the subtraction spectra (B) at each wavenumber as the change in the absorbance per week. The horizontal line shows zero absorbance change per week. (D) The coefficient of determination (R²) of the linear slopes in (C). The horizontal line shows a threshold of 0.8.

Figure 5

FTIR results of composted cellulose at 59 °C. (A) FTIR spectra of composted cellulose biodegradable products before (0 weeks) and at 1, 2, 3, 4, 5, and 6 weeks after composting. (B) Subtraction spectra of samples obtained after 1, 2, 3, 4, 5, and 6 weeks which were subtracted from the spectra of untreated cellulose biodegradable products. The dashed lines indicate zero absorbance change for each subtraction spectrum. (C) Linear slopes of the subtraction spectra (B) at each wavenumber as the change in the absorbance per week. The horizontal line shows zero absorbance change per week. (D) The coefficient of determination of the linear slopes in (C). The horizontal line shows a threshold of 0.8.

Figure 6

FTIR results of composted cellulose at 38 °C. (A) FTIR spectra of composted cellulose biodegradable products before (0 weeks) and at 1, 2, 3, 4, 5, and 6 weeks after composting. (B) Subtraction spectra of samples obtained after 1, 2, 3, 4, 5, and 6 weeks which were subtracted from the spectra of untreated cellulose biodegradable products. The dashed lines indicate zero absorbance change for each subtraction spectrum. (C) Linear slopes of the subtraction spectra (B) at each wavenumber as the change in the absorbance per week. The horizontal line shows zero absorbance change per week. (D) The coefficient of determination of the linear slopes in (C). The horizontal line shows a threshold of 0.8.

Figure 7

FTIR results of composted sugarcane at 38 °C. (A) FTIR spectra of composted biodegradable products made from sugarcane before (0 weeks) and at 1, 2, 3, 4, 5, and 6 weeks after composting. (B) Subtraction spectra of samples obtained after 1, 2, 3, 4, 5, and 6 weeks which were subtracted from the spectra of untreated PLA. The dashed lines indicate zero absorbance change for each subtraction spectrum. (C) Linear slopes of the subtraction spectra (B) at each wavenumber as the change in the absorbance per week. The horizontal line shows zero absorbance change per week. (D) The coefficient of determination of the linear slopes in (C). The horizontal line shows a threshold of 0.8.

Figure 8

FTIR results of composted sugarcane at 59 °C. (A) FTIR spectra of composted biodegradable products made from sugarcane before (0 weeks) and at 1, 2, 3, 4, 5, and 6 weeks after composting. (B) Subtraction spectra of samples obtained after 1, 2, 3, 4, 5, and 6 weeks which were subtracted from the spectra of untreated PLA. The dashed lines indicate zero absorbance change for each subtraction spectrum. (C) Linear slopes of the subtraction spectra (B) at each wavenumber as the change in the absorbance per week. The horizontal line shows zero absorbance change per week. (D) The coefficient of determination of the linear slopes in (C). The horizontal line shows a threshold of 0.8.

Figure 9

Visual identification of biodegradable products in 38 and 59 °C s: (A)—PLA, (B)—sugarcane, (C)—cellulose.