Influence of Home Composting on Tensile Properties of Commercial Biodegradable Plastic Films

Abstract

In recent years biodegradable plastic films have been increasingly used for various purposes, most often as grocery bags and for collecting bio-waste. Typically, the biodegradation of these films should take place in industrial compost facilities where the biodegradation process occurs under controlled conditions. Nevertheless, many of these films are often disposed of in home composting bins, so the aim of this study was to examine the course of biodegradation of compostable plastic films under uncontrolled conditions in garden composting sites during a period of four months. Mechanical properties were tested on seven different commercially available biodegradable films and bags that were placed in a garden composting bin from February to May. Both tensile properties and tensile-impact strength showed some unexpected results in terms of increase of the properties after the first, second, and third month for some films and bags. The same unpredictability was seen in FTIR and TG analyses.

Keywords: FTIR; TGA; biodegradable bag; biodegradable film; biodegradable polymer; composting; garden composting site; poly(butylene adipate-co-butylene terephthalate) (PBAT); tensile impact strength; tensile strength.

Figure 1

Temperatures in the city of Zagreb from February to the end of May 2020 [16].

Figure 2

Test specimen for testing tensile properties [17].

Figure 3

Test specimen for testing tensile-impact strength [18].

Figure 4

Degradation of films after the third and fourth month: (a) B0 after 3 months, (b) B0 after 4 months, (c) SP after 3 months, (d) SP after 4 months, (e) SW after 3 months, (f) SW after 4 months, (g) B1 after 3 months, (h) B1 after 4 months, (i) B2 after 3 months, (j) B2 after 4 months, (k) Eco after 3 months, (l) Eco after 4 months, (m) K after 3 months, (n) K after 4 months. The figure shows all 7 films only after the third and the fourth month because in most cases after the first and even after the second month no change and decomposition was visually observed.

Figure 4

Degradation of films after the third and fourth month: (a) B0 after 3 months, (b) B0 after 4 months, (c) SP after 3 months, (d) SP after 4 months, (e) SW after 3 months, (f) SW after 4 months, (g) B1 after 3 months, (h) B1 after 4 months, (i) B2 after 3 months, (j) B2 after 4 months, (k) Eco after 3 months, (l) Eco after 4 months, (m) K after 3 months, (n) K after 4 months. The figure shows all 7 films only after the third and the fourth month because in most cases after the first and even after the second month no change and decomposition was visually observed.

Figure 5

Testing procedure and tensile stress-strain diagrams for groups of film samples in the period of 0, 1, 2, 3, and 4 months: (a) B0, (b) SP, (c) SW, (d) B1, (e) B2, (f) ECO, (g) K, (h) procedures of testing. The diagrams show that only after 3 or 4 months of decomposition a greater decrease in mechanical properties is observed.

Figure 6

Tensile-impact strength of the film samples in the period of 0, 1, 2, 3, and 4 months. The figure also shows the error bars through the standard deviation.

Figure 7

FT-IR spectra of tested samples before and after 3 months of decomposition.

Figure 8

TG curves of tested samples before and after 3 months of decomposition.