Biodegradability of Polyolefin-Based Compositions: Effect of Natural Rubber

Abstract

Recently, environmental problems caused by the overproduction and consumption of synthetic polymer materials led to an urgent need to develop efficient methods for processing plastics. The accumulation of polymer waste for their subsequent incineration does not solve the problem due to the limited areas of landfills for waste storage. In addition, the incineration of polymer waste can cause toxic air pollution, which, in turn, does not contribute to an improvement in the environmental situation. Recycling plastics, although a more environmentally friendly waste disposal method, requires significant labor and energy costs and can be performed a limited number of times. Thus, the most promising solution to this problem is the creation of biodegradable polymers capable of degradation with the formation of simpler chemical structures (water, carbon dioxide, biomass, etc.), which are easily included in the metabolic processes of natural biological systems. The article provides an overview of the main trends in the creation of biodegradable composites for the needs of agriculture. Also, the article proposes a new composition based on polyethylene with natural rubber that surpasses existing biodegradable materials in a number of physical and mechanical characteristics and has the ability to complete biodegradation in 60 months. It is shown that the studies carried out to date indicate that these composites are highly promising for the creation of biodegradable packaging materials with good performance characteristics. Thus, it was concluded that further research on composites based on polyethylene and natural rubber is important.

Keywords: biodegradation; life cycle; natural rubber; polyethylene.

Figure 1

(a) Stages of life cycle of polymeric materials. Cycle begins with extraction of fossil resources and ends with accumulation and, possibly, partial processing of polymer waste. (b) Expected life cycle of biodegradable polymer materials. At end of their service life, polymers decompose into simple chemical structures due to vital activity of bacteria. Further, decomposition products can be used to produce new materials.

Figure 2

Structural formulas of some biodegradable polymers.

Figure 3

Biodegradation of polymeric materials under aerobic and anaerobic conditions.

Figure 4

(a) Tensile strength and hardness; (b) percentage of water absorption of PE/corn husk fiber composites with different fiber percentages. Adapted from Ahmed Youssef et al. [40].

Figure 5

Scanning electron microscopy (SEM) micrographs of composites based on PE and corn husk fibers. Content of corn husk fibers in composites varies from 0–20%. Adapted from Ahmed Youssef et al. [40].

Figure 6

(a) Percentage weight loss of soy protein and PE/soy protein composite as a function of residence time in soil. SEM micrographs of a sample of the PE/soy protein composite (b) before and (c) after biodegradation in soil (magnification 2000×). Adapted from Inderjeet Kaur et al. [47].

Figure 7

Micrographs of composite PE/NR = 70/30: (a) original sample, (b) sample after aging in soil for 45 days, (c) sample after aging in soil for 90 days. All micrographs were taken in transmitted light at a magnification of 100×. Adapted from Mastalygina Elena et al. [52].

Figure 8

Photographs of composite samples of PE/NR = 70/30 25 days after inoculation with mold fungi (a) Trichoderma harzianum Rifai, (b) Penicillium chrysogenum Thorn, (c) Fiisarhim moniliforme Sheld, (d) Chaetomium globosum Kunze, (e) Trichoderma asperellum Samuels Lieckf and Nireberg. Adapted from Mastalygina Elena et al. [52].

Figure 9

(a) Micrographs of composite samples of PE/NR containing 10, 20 and 30 wt.% NR, made in transmitted light at a magnification of 200×. (b) Size distribution of NR domains in PE/NR composites containing 10, 20, and 30 wt.% NR. Adapted from Mastalygina Elena et al. [52].

Figure 10

Parameters of ultimate strength at break, elongation at break and modulus of elasticity in tension for pure PE and PE/NR composites with NR content at level of 10, 20, 30 wt.%. Adapted from Mastalygina Elena et al. [52].