By Elena Domínguez, Researcher at the AIMPLAS Sustainability and Industrial Recovery Department in
Paterna, Valencia, Spain.
In general, plastic mulch films help to increase yields, improve crop quality, enhance weed control and reduce water use for irrigation and pesticides. Biodegradable mulch films also have other advantages at the end of the crop cycle because they can be left in the soil and ploughed under. To harmonise European regulations on biodegradable mulch films, a new standard (EN 17033, for biodegradable plastic mulch films in agriculture) was developed last year by CEN Technical Committee 249 on Plastics (an EU standardisation organisation). It was developed for use in the agricultural and horticultural sectors.
Different certificates can be obtained for different conditions and environments, and biodegradable materials and products can be certified as degradable in soil, saltwater or fresh water. Suppliers that invest in adding this functionality to their products should be able to have this information verified according to international standards, obviously without encouraging consumers to litter.
Biodegradability in the soil offers huge benefits for agricultural and horticultural products that can be left to break down in situ after being used. Standard EN 17033 was introduced in the EU in 2018. Essentially, the standard is designed to be a clear reference for farmers, distributors, and stakeholders, and to be the basis for further certification and according labels for biodegradable mulch films. EN 17033 also aims to help maintain high environmental standards and reduce soil contamination.
Compostable polymers are increasingly found in applications such as packaging, disposable nonwoven and hygiene products, consumer goods products and agricultural products. A wide variety of compostable polymers, derived from both petrochemical and renewable sources, have been developed. But what do we know about how these materials behave in other environments and conditions outside industrial composting facilities such as the conditions established in Standard EN 17033?
This article will present the main findings of a study on the degree of disintegration of a compostable polymer and a visual analysis of material degradation in the environmental conditions established in standard EN 17033. Two of the main requirements evaluated by this standard (degree of disintegration and ecotoxicity) were evaluated, although other requirements were not evaluated such as the degree of biodegradation and the concentration of harmful substances and heavy metals. This article will present a test carried out under soil conditions (natural environment) at two different temperatures. Although the temperature set by the standard is 25°C, it is important to evaluate the effect of this factor. Furthermore, the ecotoxicological effects on the environment after the disintegration process were evaluated to obtain a full understanding of the behaviour of these polymers.
The present study revealed that the degree of disintegration of a compostable biopolymer (PLA and PBTA blend) was determined by two main aspects: the aggressiveness of the medium (microbial activity) and temperature.
The medium (normalised soil) thus reached disintegration degrees of 72.05% at a thermophilic temperature (58ºC). At a mesophilic temperature of 25ºC, the materials did not achieve degradation. It can be concluded that the percentage that reached a thermophilic temperature is due to thermal degradation of the polymer, but not to microbial action, given that the microorganisms present in the soil are predominately mesophilic (an organism that grows best in moderate temperature).
Furthermore, to evaluate the soil obtained from the disintegration of the polymeric material under thermophilic conditions, the ecotoxicological effects were evaluated in a fast-growing plant species (ray grass) using the medium where disintegration had occurred. The medium in which the polymeric material had disintegrated produced a toxic effect on the species in question and the vegetal biomass reached a germination and growth rate of more than 90% with respect to the reference substrate.
One limitation on the use of bioplastics is existing confusion about the behaviour of materials under different conditions. Industrially compostable material is not necessarily able to biodegrade under other temperature conditions or in other environmental conditions. There are now some international schemes for the certification of biodegradable materials in different environments that may cause confusion in this sector. These schemes guarantee customers that materials are biodegradable under certain conditions in accordance with international standards.
For proper communication of biodegradable polymers through product ecolabelling, different standards on biodegradation determination in different environments (e.g. compost, soil) have been used to create certification schemes that specify the requirements to be met in order to obtain the corresponding certificate and product labelling.
Spain-based AIMPLAS (@aimplas) is a plastics technology centre which was established in 1990. It provides solutions to companies throughout the value chain, from raw material manufacturers to plastic processors and end users.
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