Biodegradability and Compostability of Biopolymers

The biodegradability of plastics is dependent on the chemical structure of the material and on the constitution of the final product, not just on the raw materials used for its production. Therefore, biodegradable plastics can be based on natural or synthetic resins. 

Bioplastics differ from conventional plastics in two important features  

For the first feature, no standardized measures for evaluation exist. It is subject to individual interpretation how big the proportion of renewable resources in a plastic product has to be in order for it to be called a bioplastic. No standard to approve this is available, although scientific methods to measure the renewable carbon in a given product exist 

European Bioplastics calls for plastic products to be approved according to EN 13432 [1] if the marketer advertises the product as compostable or biodegradable . Because these terms are not always used correctly, the association has published information on degradable or ox-degradable plastic products. Pro- 

Thermoplastic Starch. Edited by Leon P.B.M. Janssen and Leszek Moscicki 2009 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim ISBN 978-3-527-32528-3 

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Perhaps one of the biggest hurdles for the adoption of biodegradable and compostable materials has been the lack of kerb-side collection and municipal composting facilities, particularly in the USA and parts of Europe. Municipal composting would complete the circle for materials such as biopolymers, which start as natural renewable resources and degrade back to useable compost material. The wider development of a composting infrastructure would permit a realisation of the marketing benefits that seems to drive the adoption of sustainable materials. 

Poly(lactic acid) (PLA) is a thermoplastic polyester characterized by mechanical and optical properties similar to polystyrene (PS) and polyethylene terephthalate (PET). It is obtained from natural sources, completely biodegradable and compostable in controlled conditions as already stated in previous chapters. PLA offers some key points with respect to classic synthetic polymers, since it is a bioresource and renewable, while raw materials are cheap and abundant compared to oil. From a commercial point of view, a non-secondaiy approach, it can embellish with the word green so fashioned for the major stream consumers. Legislation can also help the commercial diffusion of biopolymers. As an example, a decisive leap has been made with the control of non-biodegradable shopping bags distribution in the European Commission and many of its member states. In addition, PLA has received some interest from the industrial sectors because of its relatively low price and commercial availability compared with other bioplastics. This is the veiy key point for any successful polymer application. In fact, the current price of commercial PLA falls between 1.5 and 2 kg , which is sufficiently close to other polymers like polyolefins, polyesters or poly(vinyl chloride) (PVC). Clearly, the PLA market is still in its infancy, but it is expected that the decrease in the production costs and the improvement in product performance will result in a clear acceleration in the industrial interest for PLA uses. It is estimated that PLA consumption should reach... 

Hybrid materials, containing biodegradable, but nonrenewable, petroleum-based polymers combined with renewable biopolymers (mainly starch), constitute an environmental compromise, but hybrids provide improved physical properties relative to the biopolymers alone they are biodegradable and, in many cases, they are compostable. Hybrids satisfy many of the growing environmental concerns of the major industrialized regions of North America, Europe, and Asia. 

For PLA, there are many advantages (1) Eco-friendly—Apart from being derived fix>m renewable resources, PLA is biodegradable, recyclable, and compostable. Its production also consumes carbon dioxide. These sustainability and eco-fiiendly characteristics make PLA an attractive biopolymer. (2) Biocompatibility—The most attractive aspect of PLA, especially witit respect to biomedical applications, is its biocompatibility. A biocompatible material should not produce toxic or carcinogenic effects in local tissues. Also, the degradation products should not interfere wifli tissue healing. PLA hydrolyzes to its constituent a-hydroxy acid... 

There are numerous national, European, and international standards defining compostability of biodegradable plastic materials and/or products manufactured using these materials (e.g., packaging). To provide an easier overview, the relevant standards for biopolymers are subdivided into two categories (see Table 2.20) ... 

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