Degradation of Polylactic Acid/Polypropylene Carbonate Films in Soil and Phosphate Buffer and Their Potential Usefulness in Agriculture and Agrochemistry

Abstract

Blends of poly(lactic acid) (PLA) with poly(propylene carbonate) (PPC) are currently in the phase of intensive study due to their promising properties and environmentally friendly features. Intensive study and further commercialization of PPC-based polymers or their blends, as usual, will soon face the problem of their waste occurring in the environment, including soil. For this reason, it is worth comprehensively studying the degradation rate of these polymers over a long period of time in soil and, for comparison, in phosphate buffer to understand the difference in this process and evaluate the potential application of such materials toward agrochemical and agricultural purposes. The degradation rate of the samples was generally accompanied by weight loss and a decrease in molecular weight, which was facilitated by the presence of PPC. The incubation of the samples in the aqueous media yielded greater surface erosions compared to the degradation in soil, which was attributed to the leaching of the low molecular degradation species out of the foils. The phytotoxicity study confirmed the no toxic impact of the PPC on tested plants, indicating it as a "green" material, which is crucial information for further, more comprehensive study of this polymer toward any type of sustainable application.

Keywords: agrochemistry; biodegradable polymers; polylactide; polymer ecotoxicity; polypropylene carbonate.

Figure 1

Weight loss of polymers and blends during incubation in soil and phosphate buffer. (A,B)—incubation in soil, (C,D)—incubation in buffer.

Figure 2

GPC elugrams of examined polymers incubated in soil.

Figure 3

¹H NMR spectrum of PLA/PPC blends with signals assigned to the appropriate protons: a, b correspond to proton signals assigned to -CH- and -CH₃ groups of PLA, respectively, and c–e correspond to proton signals assigned to -CH₂-, -CH- and -CH₃ groups of PPC, respectively.

Figure 4

The selected SEM micrographs of the surfaces of incubated foils before and during incubation.

Figure 5

Oat seedlings (Avena sativa): (A) control sample (without PPC), (B) 250 mg, (C) 500 mg, (D) 750 mg, and (E) 1000 mg of PPC/kg soil dry matter.

Figure 6

Radish seedlings (Raphanus sativus): (A) control sample (without PPC), (B) 250 mg, (C) 500 mg, (D) 750 mg, and (E) 1000 mg of PPC/kg soil dry matter.

Figure 7

Root systems of oat seedlings (A. sativa): (A) control sample (without PPC), (B) 250 mg, (C) 500 mg, (D) 750 mg, and (E) 1000 mg of PPC/kg soil dry matter.

Figure 8

Root systems of radish seedlings (R. sativus): (A) control sample (without PPC), (B) 250 mg, (C) 500 mg, (D) 750 mg, and (E) 1000 mg of PPC/kg soil dry matter.

Figure 9

(A,B)—Chlorophyll content in oat and radish seedlings, respectively. (C,D)—carotenoids content in oat and radish seedlings, respectively [mg/g of dry weight]. Error bars represent standard deviation of three replicates.