Biopolymers composting

FIGURE 20 Factors affecting biopolymer composting (Pol. Char. - Polymer characteristics. Ext. cell. enz. - Extracellular enzymes,and Temp. - Temperature). 

Hence, with this background, there is an urgent need to develop renewable source-based environmentally benign polymeric materials (biopolymers [2]). Such materials would not involve the use of toxic or noxious components in their manufacture, and could be naturally degraded by composting. 

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. 

Many biopolymers are designed to be discarded in landfills, composts, or soil. The materials will be broken down, provided that the required microorganisms are present. Normal soil bacteria and water are generally all that is required, adding to the appeal of microbially reduced plastics. Polymers that are based on naturally... 

This was demonstrated by certificates of various PHA producers for industrial composting and also home composting, as well as in soil, fresh water, and marine seawater conditions. Furthermore, the complete biodegradation profile is often faster than for other biopolymers [11],... 

Poly(lactic acid) (PL A) is a renewable resource-based bioplastic with many advantages, compared to other synthetic polymers. PL A is eco-friendly, because, apart from being derived from renewable resources such as corn, wheat, or rice, it is recyclable and compostable [1, 2]. PLA is biocompatible, as it has been approved by the Food and Drug Administration (FDA) for direct contact with biological fluids [3] and has better thermal processability compared to other biopolymers such as poly(hydroxy alkanoate)s (PHAs), poly(ethylene glycol) (PEG), or poly(e-caprolactone) (PCL) [4]. Moreover, PLA requires 25-55% less energy to be produced than petroleum-based polymers, and estimations show that this can be further reduced by 10% [5]. 

Unlike xenobiotic substrates, biopolymers such as cellulose have been in the eco-system for a very long time, allowing the evolution of efficient enzymatic pathways specific for the breakdown of these substrates. Common biopolymers therefore readily undergo biodegradation in a wide variety of environmental conditions ranging from aerobic compost heaps to anoxic deep-sea marine sediments. 

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... 

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