PSI - Issue 40

Ivetta Varyan et al. / Procedia Structural Integrity 40 (2022) 445–449 Ivetta Varyan at al. / Structural Integrity Procedia 00 (2019) 000 – 000

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assessed according to two main criteria: 1) change in appearance and 2) weight loss of the samples. The measurements were carried out after holding the samples in soil for 6 and 18 months.

Fig. 1. Weight loss of composite PE/NR samples with natural rubber content in the range of 0-50% as a result of biodegradation after (a) 6 and (b) 18 months in synthetic soil.

Fig.1 shows a weight loss of PE/NR composite samples with different percentages of natural rubber. As can be seen in Figure 1a, the loss in weight is observed for all samples after 6 months in the soil. The greatest weight loss is observed for the composition with 50% NR content (PE/NR = 50/50). Here, the difference in weight compared to the initial sample is approximately 9-10%. A similar result can be observed for the sample with 40% NR content. At the same time, for all samples with a NR content of less than 40%, the weight loss is less than 2%. The smallest weight loss is observed for the pristine PE sample and is less than 0.5% over 6 months. As shown in Fig. 1b, a similar trend persisted after 18 months of exposure of the PE/NR composite samples to the soil. So, for samples with a polyethylene to rubber ratio of PE/NR = 50/50 and 60/40, the weight loss increased significantly and amounted to 40 and 26%, respectively. In addition, the value of weight loss increased slightly for the sample with 30% NR content. Note that all these composites are characterized by the highest water absorption, which probably contributes to the growth and development of microorganisms. For the rest of the samples (NR content ≤ 20%), the value of weight loss after 18 months in the soil did not practically differ from the results of similar measurements made after holding the sample in the soil for 6 months. It is interesting to note that despite the significantly increased biodegradability of polyethylene samples with the addition of natural rubber, their mechanical properties remained within the values that allow the use of these composites as packaging material. Fig. 2a shows the relationship between the elongation and tensile strength of PE/NR composites with different content of natural rubber. As you can see, both indicators undergo significant changes in the transition from pure polyethylene to PE/NR composite. Nevertheless, all the studied PE/NR compositions are characterized by satisfactory elastic properties in comparison with other composites based on polyethylene with dispersed fillers, which is due to the high elasticity and uniform distribution of rubber particles. It should also be noted that earlier studies of equilibrium water absorption showed a high degree of water absorption of the developed biopolymer, which made it vulnerable to soil microorganisms. At the same time, with an increase in the content of natural rubber in the PE/NR composite samples, the equilibrium water absorption values increased. The described properties of the developed biopolymers of the PE/NR composites allow us to conclude that they are highly efficient in the production of films for use in agriculture. In addition to weight loss, the effects of biodegradation of polymer films were observed by visual inspection of the PE/NR samples and were also clearly visible using an optical microscope. In particular, it was possible to observe the coloration of the surface of the samples with products of microbial activity, the formation of